[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 3949

INTERNET-DRAFT                                               R. Buckley
Fax Working Group                                     Xerox Corporation
June 12, 2003                                                D. Venable
draft-ietf-fax-tiff-fx-13.txt                         Xerox Corporation
                                                            L. McIntyre
                                                             G. Parsons
                                                        Nortel Networks
                                                            J. Rafferty
                                                             Brooktrout
                                                              June 2003


                     File Format for Internet Fax


Status of this Memo:

    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026.

    Internet-Drafts are working documents of the Internet Engineering
    Task Force (IETF), its areas, and its working groups.  Note that
    other groups may also distribute working documents as
    Internet-Drafts.

    Internet-Drafts are draft documents valid for a maximum of six
    months and may be updated, replaced, or obsoleted by other documents
    at any time.  It is inappropriate to use Internet- Drafts as
    reference material or to cite them other than as "work in progress."

    The list of current Internet-Drafts can be accessed at
    <http://www.ietf.org/ietf/1id-abstracts.txt>

    The list of Internet-Draft Shadow Directories can be accessed at
    <http://www.ietf.org/shadow.html>.

    A version of this draft document is intended for submission to the
    RFC editor as a Proposed Standard for the Internet Community.
    Discussion and suggestions for improvement are requested.


Copyright Notice

    Copyright (C) The Internet Society 2003.  All Rights Reserved.










Buckley et al.             Expires December 2003                [Page 0]

Internet Draft        File Format for Internet Fax             June 2003





Abstract

   This document is a revised version of RFC 2301.
   The revisions, summarized in the list attached as Annex C to this
   document, are based on the discussions and suggestions for
   improvements that have been made since RFC 2301 was issued in March
   1998, and on the results of independent implementations and
   interoperability testing.

   This RFC 2301 revision describes the TIFF (Tag Image File Format)
   representation of image data specified by the ITU-T Recommendations
   for black-and-white and color facsimile. This file format
   specification is commonly known as TIFF-FX. It formally defines
   minimal, extended and lossless JBIG profiles (Profiles S, F, J) for
   black-and-white fax, and base JPEG, lossless JBIG and Mixed Raster
   Content profiles (Profiles C, L, M) for color and grayscale fax.
   These profiles correspond to the content of the applicable ITU-T
   Recommendations.






























Buckley et al.             Expires December 2003                [Page 1]

Internet Draft        File Format for Internet Fax             June 2003


Table of Contents

1. INTRODUCTION........................................................4
   1.1. Scope..........................................................5
   1.2. Approach.......................................................5
   1.3. Overview of this draft.........................................5
   1.4. IPR Notification...............................................7
2. TIFF and Fax........................................................7
   2.1. TIFF Overview..................................................7
     2.1.1. File Structure.............................................7
     2.1.2. Image Structure............................................9
     2.1.3. TIFF File Structure for Fax Applications..................10
   2.2 TIFF Fields for All Fax Applications...........................11
     2.2.1. TIFF Fields required for all fax profiles.................12
     2.2.2. Additional TIFF Fields required for all fax profiles......13
     2.2.3. TIFF Fields recommended for all fax profiles..............15
     2.2.4. New TIFF Fields recommended for fax profiles..............16
3. Profile S - Minimal Black-and-White Fax Profile....................18
   3.1. Overview......................................................18
   3.2. Required TIFF Fields..........................................18
     3.2.1 Baseline Fields............................................18
     3.2.2 Extension Fields...........................................20
     3.2.3 New Fields.................................................20
   3.3. Recommended TIFF Fields.......................................20
   3.4. End of Line (EOL) and Return to Control (RTC).................20
     3.4.1 RTC Exclusion..............................................21
   3.5. File Structure................................................22
   3.6. Profile S - Minimal Black-and-White Profile Summary...........23
4. Profile F- Extended Black-and-White Fax Profile....................24
   4.1. TIFF-F Overview...............................................25
   4.2. Required TIFF Fields..........................................26
     4.2.1. Baseline Fields...........................................26
     4.2.2. Extension Fields..........................................28
     4.2.3. New Fields................................................29
   4.3. Recommended TIFF Fields.......................................29
     4.3.1. Baseline Fields...........................................29
     4.3.2. Extension Fields..........................................29
     4.3.3. New Fields................................................29
   4.4. Technical Implementation Issues...............................30
     4.4.1. Strips....................................................30
     4.4.2. Bit Order.................................................31
     4.4.3. Multi-Page................................................31
     4.4.4. Compression...............................................31
     4.4.5. Example Use of Page-quality Fields........................32
     4.4.6. Practical Guidelines for Writing and Reading Multi-Page
            TIFF-F Files..............................................33
     4.4.7. Use of TIFF-F for Streaming Applications..................34
   4.5. Implementation Warnings.......................................34
     4.5.1. Uncompressed Data.........................................34



Buckley et al.             Expires December 2003                [Page 2]

Internet Draft        File Format for Internet Fax             June 2003


     4.5.2. Encoding and Resolution...................................35
     4.5.3. EOL byte-aligned..........................................35
     4.5.4. EOL.......................................................36
     4.5.5. RTC Exclusion.............................................36
     4.5.6. Use of EOFB for T.6 Compressed Images.....................37
   4.6. Example Use of TIFF-F.........................................37
   4.7. Profile F - Extended Black-and-white Fax Profile Summary......37
5. Profile J - Lossless JBIG Black-and-White Fax Profile..............39
   5.1. Overview......................................................40
   5.2. Required TIFF Fields..........................................40
     5.2.1. Baseline Fields...........................................40
     5.2.2. Extension Fields..........................................40
     5.2.3. New Fields................................................40
   5.3. Recommended TIFF Fields.......................................41
   5.4. Profile J - Lossless JBIG Black-and-White Profile Summary.....41
6. Profile C - Base Color Fax Profile.................................43
   6.1. Overview......................................................43
   6.2. Required TIFF Fields..........................................43
     6.2.1. Baseline Fields...........................................43
     6.2.2. Extension Fields..........................................45
     6.2.3. New Fields................................................46
   6.3. Recommended TIFF Fields.......................................47
   6.4. Profile C - Base Color Fax Profile Summary....................47
7. Profile L - Lossless Color Profile.................................49
   7.1. Overview......................................................50
     7.1.1. Color Encoding............................................50
     7.1.2. JBIG Compression..........................................50
   7.2. Required TIFF Fields..........................................51
     7.2.1. Baseline Fields...........................................51
     7.2.2. Extension Fields..........................................52
     7.2.3. New Fields................................................53
   7.3. Recommended TIFF Fields.......................................53
   7.4. Profile L - Lossless Color Fax Profile Summary................53
8. Profile M - Mixed Raster Content Profile...........................55
   8.1 Overview.......................................................55
     8.1.1. MRC 3-layer model.........................................55
     8.1.2. A TIFF Representation for the MRC 3-layer model...........57
   8.2. Required TIFF Fields..........................................59
     8.2.1. Baseline Fields...........................................59
     8.2.2. Extension Fields..........................................60
     8.2.3. New Fields................................................61
   8.3. Recommended TIFF Fields.......................................63
   8.4. Rules and Requirements for Images.............................64
   8.5. Profile M - MRC Fax Profile Summary...........................65
9. MIME content-types image/tiff and image/tiff-fx....................68
10. Security Considerations...........................................69




Buckley et al.             Expires December 2003                [Page 3]

Internet Draft        File Format for Internet Fax             June 2003


11. References........................................................69
12. Authors' Addresses................................................71
Annex A: Summary of TIFF Fields for Internet Fax .....................72
Annex B. List of technical edits to RFC2301...........................77
Full Copyright Statement..............................................78

1. Introduction

   This document describes the use of TIFF (Tag Image File Format) to
   represent the data content and structure generated by the current
   suite of ITU-T Recommendations for Group 3 facsimile. These
   Recommendations and the TIFF fields described here support the
   following facsimile profiles:

      S:  minimal black-and-white profile, using binary MH compression
             [T.4]
      F:  extended black-and-white profile, using binary MH, MR and MMR
             compression [T.4, T.6]
      J:  lossless JBIG black-and-white profile, with JBIG compression
             [T.85, T.82]
      C:  lossy color and grayscale profile, using JPEG compression
             [T.42, T.81]
      L:  lossless color and grayscale profile, using JBIG compression
             [T.43, T.82]
      M:  mixed raster content profile [T.44], using a combination of
             existing compression methods

   Each profile corresponds to the content of ITU-T Recommendations
   shown and is a subset of the full TIFF for facsimile specification.

   Profile S describes a minimal interchange set of fields, which will
   guarantee that, at least, binary black-and-white images will be
   supported. Implementations are required to support this minimal
   interchange set of fields.

   With the intent of specifying a file format for Internet Fax, this
   draft:

       1.  specifies the structure of TIFF files for facsimile data,
       2.  defines ITU fax-compatible values for existing TIFF fields,
       3.  defines new TIFF fields and values required for compatibility
           with ITU color fax.

   This specification of TIFF for facsimile is known as TIFF-FX (TIFF
   for Fax eXtended). References to the format described by this
   specification should always use the term "TIFF-FX", and some profiles
   in this specification may not be interpreted correctly by other TIFF
   applications.



Buckley et al.             Expires December 2003                [Page 4]

Internet Draft        File Format for Internet Fax             June 2003

1.1 Scope

   This document defines a TIFF-based file format specification for
   enabling standardized messaging-based fax over the Internet. It
   specifies the TIFF fields and field values required for compatibility
   with the existing ITU-T Recommendations for Group 3 black-and-white,
   grayscale and color facsimile. TIFF has historically been used for
   handling fax image files in applications such as store-and-forward
   messaging.  Implementations that support this file format
   specification for import/export may elect to support it as a native
   format. This document recommends a TIFF file structure that is
   compatible with low-memory and page-level streaming implementations.

   Unless otherwise noted, the current TIFF specification [TIFF] and
   selected TIFF Technical Notes [TTN1, TTN2] are the primary references
   for describing TIFF and defining TIFF fields. This document is the
   primary reference for defining TIFF field values for fax
   applications.

1.2 Approach

   The basic approach to using TIFF for facsimile data is to insert the
   compressed fax image data in a TIFF file and use TIFF fields to
   encode the parameters that describe the image data. These fields will
   have values that comply with the ITU-T Recommendations.

   This approach takes advantage of TIFF features and structures that
   bridge the data formats and performance requirements of both legacy
   fax machines and host-based fax applications. TIFF constructs for
   pages, images, and strips allow a TIFF file to preserve the fax data
   stream structure and the performance advantages that come with it. A
   TIFF-based approach also builds on an established base of users and
   implementors and ensures backward compatibility with existing TIFF-
   based IETF proposals and work in progress for Internet fax.

1.3 Overview of this draft

   Section 2 gives an overview of TIFF. Section 2.1 describes the
   structure of TIFF files, including general guidelines for structuring
   multi-page TIFF files. Section 2.2 lists the TIFF fields that are
   required or recommended for all fax profiles. The TIFF fields used
   only by specific fax profiles are described in Sections 3-8, which
   describe the individual fax profiles. These sections also specify the
   ITU-compatible field values (image parameters) for each profile.

   The full set of permitted fields of TIFF for facsimile are included
   in the current TIFF specification, Section 2 of this document and the
   sections on specific profiles of facsimile operation. This document
   defines profiles of TIFF for facsimile, where a profile is a subset



Buckley et al.             Expires December 2003                [Page 5]

Internet Draft        File Format for Internet Fax             June 2003


   of the full set of permitted fields and field values of TIFF for
   facsimile.

   Section 3 defines the minimal black-and-white facsimile profile
   (Profile S), which is required in all implementations. Section 4
   defines the extended black-and-white fax profile (Profile F), which
   provides a standard definition of TIFF-F. Section 5 describes the
   lossless black-and-white profile using JBIG compression (Profile J).
   Section 6defines the base color profile, required in all color
   implementations, for the lossy JPEG representation of color and
   grayscale facsimile data (Profile C). Section 7 defines the lossless
   JBIG color and grayscale facsimile profile(Profile L) and Section 8
   defines the Mixed Raster Content facsimile profile(Profile M). Each
   of these sections concludes with a table summarizing the required and
   recommended fields for each profile and the values they can have.

   Section 9 refers to the MIME content types used in connection
   with TIFF for facsimile. Sections 10, 11, 12 and 13 give Security
   Considerations, the ISOC Copyright Notice, References and Authors'
   Addresses. Annex A gives a summary of the TIFF fields used or defined
   in this document and provides a convenient reference for implementors.

   To implement only the minimal interchange black-and-white set of
   fields and values (Profile S), one need read only Sections 1, 2, 3, 9
   and 10.

   The following tree diagram shows the relationship among profiles and
   between profiles and coding methods.

                                S (MH)
                               / \
                       B&W    /   \   Color
                  ------------     ----------
                 /      \                    \
                /        F (MH, MR, MMR)      C (JPEG)
               /                             / \
              J (JBIG)                   ----   \
                                        /        \
                                       L (JBIG)   \
                                                   \
                                                    M (MRC)

   A profile is based on a collection of ITU-T facsimile coding methods.
   For example, Profile S, the minimal profile, is based on Modified
   Huffman (MH) compression, which is defined in ITU-T Rec. T.4.
   Profile F specifies Modified Huffman (MH), Modified Read (MR) and
   Modified Modified Read (MMR) compressions, which are defined in ITU-T
   Rec. T.4 and T.6.



Buckley et al.             Expires December 2003                [Page 6]

Internet Draft        File Format for Internet Fax             June 2003


   All implementations of TIFF for facsimile MUST implement Profile S,
   which is the root node of the tree. All color implementations of TIFF
   for facsimile MUST implement Profile C. The implementation of a
   particular profile MUST also implement those profiles on the path
   that connect it to the root node, and MAY optionally implement
   profiles not on the path connecting it to the root node. For example,
   an implementation of Profile M must also implement Profiles C and S,
   and may optionally implement Profile F, J or L. For another example,
   an implementation of Profile C must also implement Profile S, and may
   optionally implement Profile F or J.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", " NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [REQ].

1.4 IPR Notification

   The IETF has been notified of intellectual property rights claimed in
   regard to some or all of the specification contained in this
   document.  For more information consult the online list of claimed
   rights in <http://www.ietf.org/ipr.html>.


2. TIFF and Fax

2.1. TIFF Overview

   TIFF provides a means for describing, storing and interchanging
   raster image data. A primary goal of TIFF is to provide a rich
   environment within which applications can exchange image data. The
   current TIFF specification [TIFF] defines a commonly used, core set
   of TIFF fields known as Baseline TIFF. The current specification,
   the set of Pagemaker TIFF Technical Notes [TTN1], and TIFF Technical
   Note 2 [TTN2] define several TIFF extensions. The TIFF- based
   specification for fax applications uses a subset of Baseline TIFF
   fields, with selected extensions, as described in this document. In
   a few cases, this document defines new TIFF fields specifically for
   fax applications.

2.1.1. File Structure

   TIFF is designed for raster images, which makes it a good match for
   facsimile documents, which are multi-page raster images. Each raster
   image consists of a number of rows or scanlines, each of which has
   the same number of pixels, the unit of sampling. Each pixel has at
   least one sample or component (exactly one for black-and-white
   images).




Buckley et al.             Expires December 2003                [Page 7]

Internet Draft        File Format for Internet Fax             June 2003

   A TIFF file begins with an 8-byte image file header. The first two
   bytes describe the byte order used within the file. Legal values are
   "II" (0x4949) when bytes are ordered from least to most significant
   (little- endian), and "MM" (0x4D4D), when bytes are ordered from most
   to least significant (big-endian) within a 16- or 32-bit integer.
   Either byte order can be used, except in the case of the minimal
   black-and-white profile, which SHALL use value "II". The next two
   bytes contain the value 42 that identifies the file as a TIFF file
   and is ordered according to the value in the first two bytes of the
   header. The last four bytes give the offset that points to the first
   image file directory (IFD). This and all other offsets in a TIFF file
   are with respect to the beginning of the TIFF file. An IFD can be at
   any location in the file after the header but must begin on a word
   boundary.

   An IFD is a sequence of tagged fields, sorted in ascending order by
   tag value. An IFD consists of a 2-byte count of the number of fields,
   a sequence of field entries and a 4-byte offset to the next IFD. The
   fields contain information about the image and pointers to the image
   data. Each separate raster image in the file is represented by an
   IFD.

   Each field entry in an IFD has 12 bytes and consists of a 2-byte Tag,
   2 bytes identifying the field type (e.g. short, long, rational,
   ASCII), 4 bytes giving the count (number of values or offsets), and 4
   bytes that either contain the offset to a field value stored outside
   the IFD, or, based on the type and count, the field value itself.
   Resolution and metadata such as dates, names and descriptions are
   examples of "long" field values that do not fit in 4 bytes and
   therefore use offsets in the field entry. Details are given in the
   TIFF specification [TIFF].

   A TIFF file can contain more than one IFD, where each IFD is a
   subfile whose type is given in the NewSubfileType field. Multiple
   IFDs can be organized either as a linked list, with the last entry in
   each IFD pointing to the next IFD (the pointer in the last IFD is 0),
   or as a tree, using the SubIFDs field in the primary IFD [TTN1]. The
   SubIFDs field contains an array of pointers to child IFDs of the
   primary IFD.

   Child IFDs describe related images, such as reduced resolution
   versions of the primary IFD image. The same IFD can point both to a
   next IFD and to child IFDs, and child IFDs can themselves point to
   other IFDs.

   All fax profiles represent a multi-page fax image as a linked list of
   IFDs, with a NewSubfileType field containing a bit that identifies
   the IFD as one page of a multi-page document. Each IFD has a
   PageNumber field, identifying the page number in ascending order,
   starting at 0 for the first page. While a Baseline TIFF reader is not


Buckley et al.             Expires December 2003                [Page 8]

Internet Draft        File Format for Internet Fax             June 2003


   required to read any IFDs beyond the first, an implementation that
   reads the files that comply with this specification SHALL read
   multiple IFDs. Only the Mixed Raster Content fax profile, described
   in Section 8, requires the use of child IFDs.

   The following figure illustrates the structure of a multi-page TIFF
   file.

                   +-----------------------+
                   |         Header        |------------+
                   +-----------------------+            | First IFD
                   |      IFD (page 0)     |<-----------+ Offset
               +---|                       |------------+
         Value |   +-----------------------+            |
        Offset +-->|      Long Values      |--+         |
                   +-----------------------|  | Strip   |
                   |       Image Data      |<-+ Offset  |
                   |     strip 1 page 0    |  |         |
                   +-----------------------+  |         |
                   |           :           |  :         |
                                                        |
                   +-----------------------+            | Next IFD
                   |      IFD (page 1)     |<-----------+ Offset
               +---|                       |------------+
         Value |   +-----------------------+            |
        Offset +-->|      Long Values      |--+         |
                   +-----------------------|  | Strip   |
                   |       Image Data      |<-+ Offset  |
                   |     strip 1 page 1    |  |         |
                   +-----------------------+  |         |
                   |     strip 2 page 1    |<-+         |
                   +-----------------------+  |         |
                   |          :            |  :         |
                                                        |
                   +-----------------------+            | Next IFD
                   |      IFD (page 2)     |<-----------+ Offset
                   |          :            |

2.1.2 Image Structure

   An IFD stores an image as one or more strips, as shown in the
   preceding figure. A strip consists of 1 or more scanlines (rows) of
   raster image data in compressed form. An image may be stored in a
   single strip or may be divided into several strips, which would
   require less memory to buffer. (Baseline TIFF recommends about 8k
   bytes per strip, but existing fax usage is typically one strip per
   image.)




Buckley et al.             Expires December 2003                [Page 9]

Internet Draft        File Format for Internet Fax             June 2003

   Each IFD requires three strip-related fields: StripOffsets,
   RowsPerStrip and StripByteCounts. The StripOffsets field is an array
   of pointers to the strip or strips that contain the actual image
   data. The StripByteCounts field gives the number of bytes in each
   strip after compression. TIFF requires that each strip, except the
   last, contain the same number of scanlines, which is given in the
   RowsPerStrip field. This document introduces the new StripRowCounts
   field that allows a variable number of scanlines per strip, which is
   required by the Mixed Raster Content fax profile (Section 8).

   Image data is stored as uninterpreted, compressed image data streams
   within a strip. The formats of these streams follow the ITU-T
   Recommendations. The Compression field in the IFD indicates the type
   of compression, and other TIFF fields in the IFD describe image
   attributes, such as color encoding and spatial resolution.
   Compression parameters are stored in the compressed data stream,
   rather than in TIFF fields. This makes the TIFF representation and
   compressed data format specification independent of each another.
   This approach, modeled on [TTN2], allows TIFF to gracefully add new
   compression schemes as they become available.

   Some attributes can be specified both in the compressed data stream
   and within a TIFF field. It is possible that the two values will
   differ. When this happens for values required to interpret the data
   stream, then the values in the data stream take precedence. For
   informational values that are not required to interpret the data
   stream, such as author name, then the TIFF field value takes
   precedence.

2.1.3 TIFF File Structure for Fax Applications

   The TIFF specification has a very flexible file structure, which does
   not specify the ordering of IFDs, field values and image data in a
   file. Individual applications may require or recommend an ordering.

   This specification recommends that when using a TIFF file for
   facsimile, a multi-page fax document SHOULD be represented as a
   linked list of IFDs. It also recommends that a TIFF file for
   facsimile SHOULD order pages in a TIFF file in the same way that they
   are ordered in a fax data stream. In a TIFF file, a page consists of
   several elements: one or more IFDs (including subIFDs), long field
   values that are stored outside the IFDs, and image data (in one or
   more strips).

   The minimal black-and-white profile (Profile S) specifies a required
   ordering of pages and elements within a page (Section 3.5). The
   extended black-and-white profile (Profile F) provides guidelines for
   ordering pages and page elements (Section 4.4.6). Other profiles




Buckley et al.              Expires December 2003              [Page 10]

Internet Draft        File Format for Internet Fax             June 2003


   SHOULD follow these guidelines. This recommendation is intended to
   simplify the implementation of TIFF writers and readers in fax
   applications and the conversion between TIFF file and fax data stream
   representations. However, for interchange robustness, readers SHOULD
   be prepared to read TIFF files whose structure is consistent with
   [TIFF], which supports a more flexible file structure than is
   recommended here.

   This specification introduces an optional new GlobalParametersIFD
   field, defined in Section 2.2.4. This field has type IFD and
   indicates parameters describing the fax session. While it is often
   possible to obtain these parameters by scanning the file, it is
   convenient to make them available together in one place for fast and
   easy access. If the GlobalParametersIFD occurs in a TIFF file, it
   SHOULD be located in the first IFD, immediately following the 8-byte
   image file header.

2.2 TIFF Fields for All Fax Applications

   The TIFF specification [TIFF] is organized as a baseline set and
   several extensions, including technical notes [TTN1, TTN2] that will
   be incorporated in the next release of TIFF. The baseline and
   extensions have required and optional fields.

   Facsimile applications require (and recommend) a mixture of baseline
   and extensions fields, as well as some new fields that are not part
   of the TIFF specification and that are defined in this document. This
   sub- section lists the fields that are required or recommended for
   all profiles. In particular, Section 2.2.1 lists the fields that are
   required by all profiles and that have values that do not depend on
   the profile. Section 2.2.2 lists the fields that are required by all
   profiles and that have values which do depend on the profile. Section
   2.2.3 lists the fields that are recommended for all profiles. Fields
   that are required or recommended by some but not all profiles are
   given in the section (Section 3-8) that describes that profile. The
   sections for each fax profile have sub-sections for required and
   recommended fields; each sub-section organizes the fields according
   to whether they are baseline, extension or new.

   The fields required for facsimile have only a few legal values,
   specified in the ITU-T Recommendations. Of these legal values, some
   are required and some are optional, just as they are required
   (mandatory) or optional in fax implementations that conform to the
   ITU-T Recommendations. The required and optional values are noted in
   the sections on the different fax profiles.






Buckley et al.              Expires December 2003              [Page 11]

Internet Draft        File Format for Internet Fax             June 2003


   This section describes the fields required or recommended by all fax
   profiles. The pattern for the description of TIFF fields in this
   draft is:

FieldName(TagValueInDecimal) = allowable values.                    TYPE
    WhetherRequiredByTIFForTIFFforFAX
    Count = (omitted if =1) = (if not in current spec but available)
    Explanation of the field, how it's used, and the values it can have.
    Default value, if any, as specified in [TIFF]

   When a field's default value is the desired value, that field may be
   omitted from the relevant IFD unless specifically required by the
   text of this specification.

2.2.1.  TIFF fields required for all fax profiles

   The TIFF fields listed in this section SHALL be used by all fax
   profiles, but have field values that are not specified by the ITU
   standards, i.e. the fields do not depend on the profile. The next
   sub-section lists the fields that SHALL be used by all fax profiles,
   but which do have values specified by the ITU-specified or profile-
   specific values. Fields that SHALL be used by some but not all
   profiles are given in the sections (3-8) which describe the profiles
   that uses them.

ImageLength(257)                                           SHORT or LONG
    RequiredByTIFFBaseline
    Total number of scanlines in image.
    No default, must be specified.

PageNumber(297)                                                    SHORT
    RequiredByTIFFforFAX, TIFFExtension
    Count = 2
    The first number represents the page number (0 for the first page);
    the second number is the total number of pages in the document. If
    the second value is 0, then the total page count is not available.
    No default, must be specified

RowsPerStrip(278)                                          SHORT or LONG
    RequiredByTIFFBaseline
    The number of scanlines per TIFF strip, except for the last strip.
    For a single strip image, this is the same as the value of the
    ImageLength field.
    Default = 2**32 - 1 (meaning all scanlines in one strip)

StripByteCounts(279)                                       SHORT or LONG
    RequiredByTIFFBaseline
    Count = number of strips
    For each strip, the number of bytes in that strip after compression.


Buckley et al.              Expires December 2003              [Page 12]

Internet Draft        File Format for Internet Fax             June 2003


    No default, must be specified.

StripOffsets(273)                                          SHORT or LONG
    RequiredByTIFFBaseline
    Count = number of strips
    For each strip, the byte offset from the beginning of the file to
    the start of that strip.
    No default, must be specified.

2.2.2 Additional TIFF fields required for all fax profiles

   The TIFF fields listed in this section SHALL be used by all fax
   profiles, but the values associated with them depend on the profile
   being described and the associated ITU Recommendations. Therefore,
   only the fields are defined here; the values applicable to a
   particular fax profile are described in Sections 3-8. Fields that
   SHALL be used by some but not all profiles are given in the section
   (3-8) describing the profile that uses them.

BitsPerSample(258)                                                 SHORT
    RequiredByTIFFBaseline
    Number of bits per image sample
    Default = 1 (field may be omitted if this is the value)

Compression(259)                                                   SHORT
    RequiredByTIFFBaseline
    Compression method used for image data
    Default = 1 (no compression, so may not be omitted for FAX)

FillOrder(266)                                                     SHORT
    RequiredByTIFFforFax
    The default bit order in Baseline TIFF per [TIFF] is indicated by
    FillOrder=1, where bits are not reversed before being stored.
    However, TIFF for Fax typically utilizes the setting of FillOrder=2,
    where the bit order within bytes is reversed before storage (i.e.,
    bits are stored with the Least Significant Bit first).
    Default = 1 (field may be omitted if this is the value)
    Facsimile data appears on the phone line in bit-reversed order
    relative to its description in the relevant ITU compression
    Recommendation. Therefore, a wide majority of facsimile
    implementations choose this natural order for storage. Nevertheless,
    all readers conforming to this specification must be able to read
    data in both bit orders, except in the case of Profile S, which only
    requires support for FillOrder=2 (Least Significant Bit first).

ImageWidth(256)                                            SHORT or LONG
    RequiredByTIFFBaseline
    The number of pixels (columns) per scanline (row) of the image
    No default, must be specified.


Buckley et al.              Expires December 2003              [Page 13]

Internet Draft        File Format for Internet Fax             June 2003


NewSubFileType(254)                                                 LONG
    RequiredByTIFFforFAX
    A general indication of the kind of data contained in this IFD
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for FAX)

PhotometricInterpretation(262)                                     SHORT
    RequiredByTIFFBaseline
    The color space of the image data
    No default, must be specified

ResolutionUnit(296)                                                SHORT
    RequiredByTIFFBaseline
    The unit of measure for resolution. 2 = inch, 3 = centimeter;
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277)                                               SHORT
    RequiredByTIFFBaseline
    The number of color components per pixel; SamplesPerPixel is 1 for a
    black-and-white, grayscale or indexed (palette) image.
    Default =1 (field may be omitted if this is the value)

XResolution(282)                                                RATIONAL
    RequiredByTIFFBaseline
    The horizontal resolution of the image in pixels per resolution
    unit. The ITU-T Recommendations for facsimile specify a small number
    of horizontal resolutions: 100, 200, 300, 400 pixels per inch, and
    80, 160 pixels per centimeter (or 204, 408 pixels per inch). The
    allowed XResolution values for each profile are given in the section
    defining that profile. Per [T.4], it is permissible for applications
    to treat the following XResolution values as being equivalent: <204,
    200> and <400,408> in pixels/inch. These equivalencies were allowed
    by [T.4] to permit conversions between inch and metric based
    facsimile terminals. To insure interoperability, if an application
    accepts any member of the pairs then T.4 requires it to accept both
    (e.g. accept 204 if 200 pixels per inch is accepted). TIFF for
    Facsimile Writers SHOULD express XResolution in inch based units,
    for consistency with historical practice and to maximize
    interoperability. See the table below for information on how to
    convert from an ITU-T metric value to its inch based equivalent
    resolution.
    No default, must be specified

YResolution(283)                                                RATIONAL
    RequiredByTIFFBaseline
    The vertical resolution of the image in pixels per resolution unit.
    The ITU-T Recommendations for facsimile specify a small number of
    vertical resolutions: 100, 200, 300, 400 pixels per inch, and 38.5,
    77, 154 pixels per centimeter (or 98, 196, 391 pixels per inch). The
    allowed YResolution values for each profile are given in the section

Buckley et al.              Expires December 2003              [Page 14]

Internet Draft        File Format for Internet Fax             June 2003


    defining that profile. Per [T.4], it is permissible for applications
    to treat the following YResolution values as being equivalent: <98,
    100>, <196, 200>, and <391, 400> in pixels/inch. These equivalencies
    were allowed by [T.4] to permit conversions between inch and metric
    based facsimile terminals. To insure interoperability, if an
    application accepts any member of the pairs then T.4 requires it to
    accept both (e.g. accept 98 if 100 pixels per inch is accepted).
    TIFF for Facsimile Writers SHOULD express YResolution in inch based
    units, for consistency with historical practice and to maximize
    interoperability. See the table below for information on converting
    from the metric value to its inch based equivalent resolution.
    No default, must be specified

      +-----------------------------+-----------------------------+
      |         XResolution         |         YResolution         |
      +--------------+--------------+--------------+--------------+
      |ResolutionUnit|ResolutionUnit|ResolutionUnit|ResolutionUnit|
      |  =2 (inch)   |   =3 (cm)    |  =2 (inch)   |   =3 (cm)    |
      +--------------+--------------+--------------+--------------+
      |     100      |              |     100      |              |
      +--------------+--------------+--------------+--------------+
      |     204      |      80      |      98      |     38.5     |
      |     200      |              |     100      |              |
      +--------------+--------------+--------------+--------------+
      |     204      |      80      |     196      |      77      |
      |     200      |              |     200      |              |
      +--------------+--------------+--------------+--------------+
      |     204      |      80      |     391      |     154      |
      +--------------+--------------+--------------+--------------+
      |     300      |              |     300      |              |
      +--------------+--------------+--------------+--------------+
      |     408      |     160      |     391      |     154      |
      |     400      |              |     400      |              |
      +--------------+--------------+--------------+--------------+

2.2.3 TIFF fields recommended for all fax profiles

   The TIFF fields listed in this section MAY be used by all fax
   profiles. However, Profile S writers (the minimal fax profile
   described in Section 3) SHOULD NOT use these fields. Recommended
   fields that are profile-specific are described in Sections 3-8.

DateTime(306)                                                      ASCII
    OptionalInTIFFBaseline
    Date/time of image creation in 24-hour format "YYYY:MM:DD HH:MM:SS".
    No default.

DocumentName(269)                                                  ASCII
    OptionalInTIFFExtension(DocumentStorageAndRetrieval)
    The name of the scanned document. This is a TIFF extension field,

Buckley et al.              Expires December 2003              [Page 15]

Internet Draft        File Format for Internet Fax             June 2003


    not a Baseline TIFF field.
    No default.

ImageDescription(270)                                              ASCII
    OptionalInTIFFBaseline
    A string describing the contents of the image.
    No default.

Orientation(274) = 1-8.                                            SHORT
    OptionalinTIFFBaseline
    1: 0th row represents the visual top of the image; the 0th column
    represents the visual left side of the image. See the current TIFF
    spec [TIFF] for further values; Baseline TIFF only requires value=1.
    Default = 1.
    Note: It is recommended that a writer that is aware of the
    orientation include this field to give a positive indication of
    the orientation, even if the value is the default. Writers should
    not generate mirror images, because many readers will not properly
    reverse the image before display or print.

Software(305)                                                      ASCII
    OptionalInTIFFBaseline
    The name and release number of the software package that
    created the image.
    No default.

2.2.4 New TIFF fields recommended for fax profiles

   The new TIFF fields listed in this section MAY be used by all fax
   profiles. However, Profile S writes (the minimal fax profile
   described in Section 3) SHOULD NOT use these fields. In addition,
   support for these new TIFF fields has not been included in historical
   TIFF-F readers described in Section 4 and [TIFF-F]. These fields
   describe "global" parameters of the fax session that created the image
   data. They are optional, not part of the current TIFF specification,
   and are defined in this document.

   The first new field, GlobalParametersIFD, is an IFD that contains
   global parameters and is located in a Primary IFD.

GlobalParametersIFD (400)                                    IFD or LONG
    An IFD containing global parameters. It is recommended that a TIFF
    writer place this field in the first IFD, where a TIFF reader would
    find it quickly.

   Each field in the GlobalParametersIFD is a TIFF field that is legal
   in any IFD. Required baseline fields should not be located in the
   GlobalParametersIFD, but should be in each image IFD. If a conflict
   exists between fields in the GlobalParametersIFD and in the image
   IFDs, then the data in the image IFD shall prevail.

Buckley et al.              Expires December 2003              [Page 16]

Internet Draft        File Format for Internet Fax             June 2003


   Among the GlobalParametersIFD entries is a new ProfileType field
   which generally describes information in this IFD and in the TIFF
   file.

ProfileType(401)                                                    LONG
    The type of image data stored in this IFD.
    0 = Unspecified
    1 = Group 3 fax
    No default

   The following new global fields are defined in this document as IFD
   entries for use with fax applications.

FaxProfile(402) = 0 - 6.                                            BYTE
    The profile that applies to this file; a profile is subset of the
    full set of permitted fields and field values of TIFF for facsimile.
    The currently defined values are:
    0: does not conform to a profile defined for TIFF for facsimile
    1: minimal black & white lossless, Profile S
    2: extended black & white lossless, Profile F
    3: lossless JBIG black & white, Profile J
    4: lossy color and grayscale, Profile C
    5: lossless color and grayscale, Profile L
    6: Mixed Raster Content, Profile M

CodingMethods(403)                                                  LONG
    This field indicates which coding methods are used in the file. A
    value of 1 in a bit location indicates the corresponding coding
    method is used. More than one bit set to 1 means more than one
    coding method is used in the file.
    Bit 0: unspecified compression,
    Bit 1: 1-dimensional coding, ITU-T Rec. T.4 (MH - Modified Huffman),
    Bit 2: 2-dimensional coding, ITU-T Rec. T.4 (MR - Modified Read),
    Bit 3: 2-dimensional coding, ITU-T Rec. T.6 (MMR - Modified MR),
    Bit 4: ITU-T Rec. T.82 coding, using ITU-T Rec. T.85 (JBIG),
    Bit 5: ITU-T Rec. T.81 (Baseline JPEG),
    Bit 6: ITU-T Rec. T.82 coding, using ITU-T Rec. T.43 (JBIG color),
    Bits 7-31: reserved for future use
    Note: There is a limit of 32 compression types to identify standard
    compression methods.

VersionYear(404)                                                    BYTE
    Count: 4
    The year of the standard specified by the FaxProfile field, given as
    4 characters, e.g. '1997'; used in lossy and lossless color
    profiles.

ModeNumber (405)                                                    BYTE
    The mode of the standard specified by the FaxProfile field. A
    value of 0 indicates Mode 1.0; used in Mixed Raster Content profile.

Buckley et al.              Expires December 2003              [Page 17]

Internet Draft        File Format for Internet Fax             June 2003


3. Profile S - Minimal Black-and-White Fax Profile

   This section defines the minimal black-and-white subset of TIFF for
   facsimile. This subset is designated Profile S. All implementations
   of TIFF for facsimile SHALL support the minimal subset.

   Black-and-white mode is the binary fax application most users are
   familiar with today. This mode is appropriate for black-and-white
   text and line art. Black-and-white mode is divided into two levels of
   capability. This section describes the minimal interchange set of
   TIFF fields that must be supported by all implementations in order to
   assure that some form of image, albeit black-and-white, can be
   interchanged. This minimum interchange set is a strict subset of the
   fields and values defined for the extended black-and-white profile
   (TIFF-F or Profile F) in Section 4, which describes extensions to the
   minimal interchange set of fields that provide a richer set of
   black-and-white capabilities.

3.1. Overview

   The minimal interchange portion of the black-and-white facsimile mode
   supports 1-dimensional Modified Huffman (MH) compression, with the
   original Group 3 fax resolutions, commonly called "standard" and
   "fine."

   To assure interchange, this profile uses the minimal set of fields,
   with a minimal set of values. There are no recommended fields in this
   profile. Further, the TIFF file is required to be "little endian,"
   which means that the byte order value in the TIFF header is "II".
   This profile defines a required ordering for the pages in a fax
   document and for the IFDs and image data of a page. It also requires
   that a single strip contain the image data for each page; see Section
   3.5. The image data may contain RTC sequences, as specified in
   Section 3.4.

3.2. Required TIFF Fields

   Besides the fields listed in Section 2.2.1, the minimal black-and-
   white fax profile requires the following fields. The fields listed in
   Section 2.2.1 and the fields and fax-specific values specified in
   this sub- section must be supported by all implementations.

3.2.1 Baseline fields

BitsPerSample(258) = 1.                                            SHORT
    RequiredByTIFFBaseline
    Binary data only.
    Default = 1 (field may be omitted if this is the value)



Buckley et al.              Expires December 2003              [Page 18]

Internet Draft        File Format for Internet Fax             June 2003


Compression(259) = 3.                                              SHORT
    RequiredByTIFFBaseline
    3 = 1- or 2- dimensional coding.
    The value 3 is a TIFF extension value [TIFF]. The T4Options field
    must be specified and its value specifies that the data is encoded
    using the Modified Huffman (MH) compression of [T.4].

FillOrder(266) = 2.                                                SHORT
    RequiredByTIFFBaseline
    2 = Least Significant Bit first

   NOTE: Baseline TIFF readers are only required to support FillOrder =
   1, where the lowest numbered pixel is stored in the MSB of the byte.
   However, because many devices, such as modems, transmit the LSB first
   when converting the data to serial form, it is common for black-and-
   white fax products to use the second FillOrder =2, where the lowest
   numbered pixel is stored in the LSB. Therefore, this value is
   specified in the minimal black-and-white profile.

ImageWidth(256) = 1728.                                    SHORT or LONG
    RequiredByTIFFBaseline
    This profile only supports a page width of 1728 pixels. This width
    corresponds to North American Letter and Legal and to ISO A4 size
    pages.
    No default, must be specified.

NewSubFileType(254) = (Bit 1=1).                                    LONG
    RequiredByTIFFforFAX
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for fax)

PhotometricInterpretation(262) = 0.                                SHORT
    RequiredByTIFFBaseline
    0 = pixel value 1 means black
    No default, must be specified

ResolutionUnit(296) = 2.                                           SHORT
    RequiredByTIFFBaseline
    The unit of measure for resolution. 2 = inch.
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277) = 1.                                          SHORT
    RequiredByTIFFBaseline
    The number of components per pixel; 1 for black-and-white
    Default =1 (field may be omitted if this is the value)

XResolution(282) = 200, 204.                                    RATIONAL
    RequiredByTIFFBaseline



Buckley et al.              Expires December 2003              [Page 19]

Internet Draft        File Format for Internet Fax             June 2003


    The horizontal resolution of the image is expressed in pixels per
    resolution unit. In pixels/inch, the allowed values are 200 and 204,
    which may be treated as equivalent. See Section 2.2.2 for inch-
    metric equivalency.
    No default, must be specified

YResolution(283) = 98, 100, 196, 200.                           RATIONAL
    RequiredByTIFFBaseline
    The vertical resolution of the image is expressed in pixels per
    resolution unit. In pixels/inch, the allowed values are 98, 100,
    196 and 200; 98 and 100 may be treated as equivalent, and 196 and
    200 may be treated as equivalent. See Section 2.2.2 for inch-metric
    equivalency.
    No default, must be specified

3.2.2 Extension fields

T4Options(292) = (Bit 0 = 0, Bit 1 = 0, Bit 2 = 0, 1)               LONG
    RequiredTIFFExtension (when Compression = 3)
    Bit 0 = 0 indicates MH compression.
    Bit 1 must be 0
    Bit 2 = 1 indicates that EOLs are byte aligned, = 0 EOLs not byte
    aligned
    Default is all bits are 0 (applies when EOLs are not byte aligned)

    Note: The T4Options field is required when the Compression field has
    a value of 3. Bit 0 of this field specifies the compression used (MH
    only in this profile). MH coding requires the use of EOL (End of
    Line) codes: Bit 2 indicates whether the EOL codes are byte-aligned
    or not. See Section 3.4 for details.

3.2.3. New Fields

   None.

3.3. Recommended TIFF Fields

   None.

3.4. End of Line (EOL) and Return to Control (RTC)

   TIFF extensions for fax, used in this specification, differ from
   Baseline TIFF in the following ways:
     - a 12-bit EOL sequence MUST precede each line of MH-compressed
       image data. (Baseline TIFF does not use these EOL sequences.)
     - the EOL sequence MAY be byte-aligned, in which case fill bits are
       added so that the EOL sequence ends on a byte boundary, and any
       subsequent image data begins on a byte boundary.
     - if the EOL codes are not byte aligned, the image data MAY be


Buckley et al.              Expires December 2003              [Page 20]

Internet Draft        File Format for Internet Fax             June 2003


       followed by an RTC (Return to Control) sequence, consisting of
       6 consecutive EOLs.

   In conventional fax, an MH-compressed fax data stream for a page
   consists of the following sequence:
      EOL, compressed data (first line), EOL, compressed data, ... ,
      EOL, compressed data (last line), RTC (6 consecutive EOL codes)
   Baseline TIFF does not use EOL codes or Return to Control (RTC)
   sequences for MH-compressed data. However, the TIFF extension field
   T4Options used in this specification for MH compression (Compression
   = 3) requires EOLs.

   Furthermore, Bit 2 in the T4Options field indicates whether or not
   the EOL codes are byte aligned. If Bit 2 = 1, indicating the EOL
   codes are byte aligned, then fill bits have been added as necessary
   before EOL codes so that an EOL code always ends on a byte boundary,
   and the first bit of data following an EOL begins on a byte boundary.
   Without fill bits, an EOL code may end in the middle of a byte. Byte
   alignment relieves application software of the burden of bit-shifting
   every byte while parsing scan lines for line-oriented image
   manipulation (such as writing a TIFF file). Not all TIFF readers
   historically used for fax are able to deal with non-byte aligned.
   data.

   While TIFF extension requires EOL codes, TIFF in fax applications has
   traditionally prohibited RTC sequences. Implementations that want
   common processing and interfaces for fax data streams and Internet
   fax files would prefer that the TIFF data include RTC sequences.

   To reconcile these differences, RTCs are allowed in cases where EOL
   codes are not byte aligned and no fill bits have been added to the
   data. This corresponds to situations where the fax data is simply
   inserted in a strip without being processed or interpreted. RTCs
   should not occur in the data when EOLs have been byte aligned. This
   is formally specified in the next sub-section.

3.4.1. RTC Exclusion

   Implementations which wish to maintain strict conformance with TIFF
   and compatibility with the historical use of TIFF for fax SHOULD NOT
   include the RTC sequence when writing TIFF files. However,
   implementations which need to support "transparency" of T.4-generated
   image data MAY include RTCs when writing TIFF files if the flag
   settings of the T4Options field are set for non-byte aligned data,
   i.e. Bit 2 is 0. Implementors of TIFF readers should be aware that
   there are some existing TIFF implementations for fax that include the
   RTC sequence in MH image data. Therefore, minimal set readers MUST be
   able to process files which do not include RTCs and SHOULD be able to
   process files which do include RTCs.


Buckley et al.              Expires December 2003              [Page 21]

Internet Draft        File Format for Internet Fax             June 2003


3.5. File Structure

   The TIFF header, described in Section 2.1.1, contains two bytes which
   describe the byte order used within the file. For the minimal black-
   and-white profile, these bytes SHALL have the value "II" (0x4949),
   denoting that the bytes in the TIFF file are in LSByte-first order
   (little- endian). The first or 0th IFD immediately follows the
   header, so that offset to the first IFD is 8. The headers values are
   shown in the following table:

          +--------+-------------------+--------+-----------+
          | Offset |   Description     |     Value          |
          +--------+-------------------+--------+-----------+
          |   0    |   Byte Order      |  0x4949 (II)       |
          +--------+-------------------+--------+-----------+
          |   2    |   Identifier      |  42 decimal        |
          +--------+-------------------+--------+-----------+
          |   4    | Offset of 0th IFD |  0x 0000 0008      |
          +--------+-------------------+--------+-----------+

   The minimal black-and-white profile SHALL order IFDs and image data
   within a file as follows: 1) there SHALL be an IFD for each page in a
   multi- page fax document; (2) the IFDs SHALL occur in the same order
   in the file as the pages occur in the document; (3) the IFD SHALL
   precede the image data to which it has offsets; (4) the image data
   SHALL occur in the same order in the file as the pages occur in the
   document; (5) the IFD, the value data and the image data it has
   offsets to SHALL precede the next image IFD; and (6) the image data
   for each page SHALL be contained within a single strip.

   As a result of (6), the StripOffsets field will contain the pointer
   to the image data. With two exceptions, the field entries in the IFD
   contain the field values instead of offsets to field values located
   outside the IFD. The two exceptions are the values for the
   XResolution and YResolution fields, both of which are type RATIONAL
   and require 2 4- byte numbers. These "long" field values SHALL be
   placed immediately after  the IFD which contains the offsets to them,
   and before the image data pointed to by that IFD.

   The effect of these requirements is that the IFD for the first page
   SHALL come first in the file after the TIFF header, followed by the
   long field values for XResolution and YResolution, followed by the
   image data for the first page, then the IFD for second page, etc.
   This is shown in the following figure. Each IFD is required to have a
   PageNumber field, which has value 0 for the first page, 1 for the
   second page, and so on.





Buckley et al.              Expires December 2003              [Page 22]

Internet Draft        File Format for Internet Fax             June 2003


                   +-----------------------+
                   |         Header        |------------+
                   +-----------------------+            | First IFD
                   |      IFD (page 0)     | <----------+ Offset
               +---|                       |------------+
               |   |                       |--+         |
         Value |   +-----------------------+  |         |
        Offset +-->|      Long Values      |  |         |
                   +-----------------------|  | Strip   |
                   |  Image Data (page 0)  |<-+ Offset  |
                   +-----------------------+            | Next IFD
                   |      IFD (page 1)     | <----------+ Offset
               +---|                       |------------+
               |   |                       |--+         |
         Value |   +-----------------------+  |         |
        Offset +-->|      Long Values      |  |         |
                   +-----------------------|  | Strip   |
                   |  Image Data (page 1)  |<-+ Offset  |
                   +-----------------------+            | Next IFD
                   |      IFD (page 2)     | <----------+ Offset
                   +-----------------------+
                   |          :            |

   Using this file structure may reduce the memory requirements in
   implementations. It is also provides some support for streaming, in
   which a file can be processed as it is received and before the entire
   file is received.

3.6 Profile S - Minimal Black-and-White Profile Summary

   The table below summarizes the TIFF fields that comprise the minimal
   interchange set for black-and-white facsimile. The Baseline and
   Extension fields and field values MUST be supported by all
   implementations. For convenience in the table, certain fields which
   have a value that is a sequence of flag bits are shown taking integer
   values that correspond to the flags that are set. An implementation
   should test the setting of the relevant flag bits individually,
   however, to allow extensions to the sequence of flag bits to be
   appropriately ignored. (See, for example, T4Options below.)

      +---------------------------+--------------------------------+
      | Baseline Fields           |  Values                        |
      +---------------------------+--------------------------------+
      | BitsPerSample             | 1                              |
      +---------------------------+--------------------------------+
      | Compression               | 3: 1D Modified Huffman coding  |
      |                           |     set T4Options = 0 or 4     |
      +------------------------------------------------------------+



Buckley et al.              Expires December 2003              [Page 23]

Internet Draft        File Format for Internet Fax             June 2003


      +---------------------------+--------------------------------+
      | FillOrder                 | 2: least significant bit first |
      +---------------------------+--------------------------------+
      | ImageWidth                | 1728                           |
      +---------------------------+--------------------------------+
      | ImageLength               | n: total number of scanlines   |
      |                           | in image                       |
      +---------------------------+--------------------------------+
      | NewSubFileType            | 2: Bit 1 identifies single     |
      |                           | page of a multi-page document  |
      +---------------------------+--------------------------------+
      | PageNumber                | n,m: page number n followed by |
      |                           | total page count m             |
      +---------------------------+--------------------------------+
      | PhotometricInterpretation | 0: pixel value 1 means black   |
      +---------------------------+--------------------------------+
      | ResolutionUnit            | 2: inch                        |
      +---------------------------+--------------------------------+
      | RowsPerStrip              | number of scanlines per strip  |
      |                           | = ImageLength, with one strip  |
      +---------------------------+--------------------------------+
      | SamplesPerPixel           | 1                              |
      +---------------------------+--------------------------------+
      | StripByteCounts           | number of bytes in TIFF strip  |
      +---------------------------+--------------------------------+
      | StripOffsets              | offset from beginning of       |
      |                           | file to single TIFF strip      |
      +---------------------------+--------------------------------+
      | XResolution               | 204, 200 (pixels/inch)         |
      +---------------------------+--------------------------------+
      | YResolution               | 98, 196, 100, 200 (pixels/inch)|
      +---------------------------+--------------------------------+
      | Extension Fields                                           |
      +---------------------------+--------------------------------+
      | T4Options                 | 0: MH coding, EOLs not byte    |
      |                           |               aligned          |
      |                           | 4: MH coding, EOLs byte aligned|
      +---------------------------+--------------------------------+

4. Profile F - Extended Black-and-White fax profile

   This section defines the extended black-and-white profile or Profile
   F of TIFF for facsimile. It provides a standard definition of what
   has historically been known as TIFF Class F and now TIFF-F. In doing
   so, it aligns this profile with current ITU-T Recommendations for
   black-and-white fax and with existing industry practice.
   Implementations of this profile include implementations of Profile S.




Buckley et al.              Expires December 2003              [Page 24]

Internet Draft        File Format for Internet Fax             June 2003


   This section describes extensions to the minimal interchange set of
   fields (Profile S) that provide a richer set of black-and-white
   capabilities. The fields and values described in this section are a
   superset of the fields and values defined for the minimal interchange
   set in Section 3. In addition to the MH compression, Modified READ
   (MR) and Modified Modified READ (MMR) compression as described in
   [T.4] and [T.6] are supported.

   Section 4.1 gives an overview of TIFF-F. Section 4.2 describes the
   TIFF fields that SHALL be used in this profile. Section 4.3 describes
   the fields that MAY be used in this profile. In the spirit of the
   original TIFF-F specification, Sections 4.4 and 4.5 discuss technical
   implementation issues and warnings. Section 4.6 gives an example use
   of TIFF-F. Section 4.7 gives a summary of the required and
   recommended fields and their values.

4.1 TIFF-F Overview

   Though it has been in common usage for many years, TIFF-F has
   previously never been documented in the form of a standard.  An
   informal TIFF-F document was originally created by a small group of
   fax experts led by Joe Campbell.  The existence of TIFF-F is noted in
   [TIFF] but it is not defined.  This document serves as the formal
   definition of the F application of [TIFF] for Internet applications.
   For ease of reference, the term TIFF-F will be used throughout this
   document as a shorthand for the extended black-and-white profile
   of TIFF for facsimile.

   Up until the TIFF 6.0 specification, TIFF supported various "Classes"
   which defined the use of TIFF for various applications. Classes were
   used to support specific applications. In this spirit, TIFF-F has
   been known historically as "TIFF Class F".  Previous informal TIFF-F
   documents [TIFF-F0] used the "Class F" terminology.  As of TIFF 6.0
   [TIFF], the TIFF Class concept has been eliminated in favor of the
   concept of Baseline TIFF.  Therefore, this document updates the
   definition of TIFF-F as the F profile of TIFF for facsimile, by using
   Baseline  TIFF as defined in [TIFF] as the starting point and then
   adding the TIFF extensions to Baseline TIFF which apply for TIFF-F.
   In almost all  cases, the resulting definition of TIFF-F fields and
   values remains  consistent with those used historically in earlier
   definitions of TIFF  Class F.  Where some of the values for fields
   have been updated to provide more precise conformance with the ITU-T
   [T.4] and [T.30] fax recommendations, these differences are noted.








Buckley et al.              Expires December 2003              [Page 25]

Internet Draft        File Format for Internet Fax             June 2003


4.2. Required TIFF Fields

   This section lists the required fields and the values they must have
   to be ITU-compatible. Besides the fields listed in Section 2.2.1, the
   extended black-and-white fax profile SHALL use the following fields.

4.2.1. Baseline fields

BitsPerSample(258) = 1.                                            SHORT
    RequiredByTIFFBaseline
    Binary data only.
    Default = 1 (field may be omitted if this is the value)

Compression(259) = 3, 4.                                           SHORT
    RequiredByTIFFBaseline
    3 = 1- or 2- dimensional coding, must have T4Options field This is
    a TIFF Extension value [TIFF].
    4 = 2-dimensional coding, ITU-T Rec. T.6 (MMR - Modified Modified
    Read, must have T6Options field)) This is a TIFF Extension value.
    Default = 1 (and is not applicable; field must be specified)

   NOTE: Baseline TIFF permits use of value 2 for Modified Huffman
   compression, but data is presented in a form which does not use EOLs,
   and so TIFF for facsimile uses Compression=3 instead. See Sections
   4.4.4, 4.5.1 and 4.5.2 for more information on compression and
   encoding.

FillOrder(266) = 1 , 2.                                            SHORT
    RequiredByTIFFBaseline
    Profile F readers must be able to read data in both bit orders,
    but the vast majority of facsimile products store data LSB
    first, exactly as it appears on the telephone line.
              1 = Most Significant Bit first.
              2 = Least Significant Bit first

ImageWidth(256)                                            SHORT or LONG
    RequiredByTIFFBaseline
    This profile supports the following fixed page widths: 1728, 2592,
    3456 (corresponding to North American Letter and Legal, ISO A4 paper
    sizes), 2048, 3072, 4096 (corresponding to ISO B4 paper size), and
    2432, 3648, 4864 (corresponding to ISO A3 paper size).
    No default; must be specified

   NOTE: Historical TIFF-F did not include support for the following
   widths related to higher resolutions: 2592, 3072, 3648, 3456, 4096
   and 4864. Historical TIFF-F documents also included the following
   values related to A5 and A6 widths: 816 and 1216. Per the most recent




Buckley et al.              Expires December 2003              [Page 26]

Internet Draft        File Format for Internet Fax             June 2003


   version of [T.4], A5 and A6 documents are no longer supported in
   Group 3 facsimile, so the related width values are now obsolete. See
   section 4.5.2 for more information on inch/metric equivalencies and
   other implementation details.

NewSubFileType(254) = (Bit 1=1).                                    LONG
    RequiredByTIFFforFAX
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for fax)

   NOTE: Bit 1 is always set to 1 for TIFF-F, indicating a single page
   of a multi-page image. The same bit settings are used when TIFF-F is
   used for a one page fax image. See Section 4.4.3 for details on
   multi-page files.

PhotometricInterpretation(262) = 0, 1.                             SHORT
    RequiredByTIFFBaseline
    0 = pixel value 1 means black, 1 = pixel value 1 means white.
    This field allows notation of an inverted or negative image.
    No default, must be specified

ResolutionUnit(296) = 2, 3.                                        SHORT
    RequiredByTIFFBaseline
    The unit of measure for resolution. 2 = inch, 3 = centimeter; TIFF-F
    has traditionally used inch-based measures.
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277) = 1.                                          SHORT
    RequiredByTIFFBaseline
    1 = monochrome, bilevel in this case (see BitsPerSample)
    Default =1 (field may be omitted if this is the value)

XResolution(282) = 200, 204, 300, 400, 408                      RATIONAL
    RequiredByTIFFBaseline
    The horizontal resolution of the image is expressed in pixels per
    resolution unit. In pixels/inch, the allowed values are: 200, 204,
    300, 400, and 408. See Section 2.2.2 for inch-metric equivalency.
    No default, must be specified

   NOTE: The values of 200 and 408 have been added to the historical
   TIFF-F values, for consistency with [T.30]. Some existing TIFF-F
   implementations may also support values of 80 pixels/cm, which is
   equivalent to 204 pixels per inch. See section 4.5.2 for information
   on implementation details.

YResolution(283) = 98, 100, 196, 200, 300, 391, and 400       RATIONAL
    RequiredByTIFFBaseline
    The vertical resolution of the image is expressed in pixels per



Buckley et al.              Expires December 2003              [Page 27]

Internet Draft        File Format for Internet Fax             June 2003


    resolution unit. In pixels/inch, the allowed values are: 98, 100,
    196, 200, 300, 391, and 400 pixels/inch.
    See Section 2.2.2 for inch-metric equivalency.
    No default, must be specified

   NOTE: The values of 100, 200, and 391 have been added to the
   historical TIFF-F values, for consistency with [T.30].  Some existing
   TIFF-F implementations may also support values of 77 and 38.5 (cm),
   which are equivalent to 196 and 98 pixels per inch respectively. See
   section 4.5.2 for more information on implementation details.

   NOTE: Not all combinations of XResolution, YResolution and ImageWidth
   are legal. The following table gives the legal combinations and
   corresponding paper size [T.30].

    +--------------+-----------------+---------------------------+
    |   XResolution x YResolution    |         ImageWidth        |
    +--------------+-----------------+---------+--------+--------+
    |      200x100, 204x98           |         |        |        |
    |      200x200, 204x196          |  1728   |  2048  |  2432  |
    |           204x391              |         |        |        |
    +--------------+-----------------+---------+--------+--------+
    |          300 x 300             |  2592   |  3072  |  3648  |
    +--------------+-----------------+---------+--------+--------+
    |     408 x 391, 400 x 400       |  3456   |  4096  |  4864  |
    +--------------+-----------------+---------+--------+--------+
                                     |Letter,A4|   B4   |   A3   |
                                     |  Legal  |        |        |
                                     +---------+--------+--------+
                                     |         Paper Size        |
                                     +---------------------------+


4.2.2. Extension fields

T4Options(292) = (Bit 0 = 0 or 1, Bit 1 = 0, Bit 2 = 0 or 1)        LONG
    RequiredTIFFExtension (when Compression = 3)
    T4Options was also known as Group3Options in a prior version of
    [TIFF].
    Bit 0 = 1 indicates MR compression, = 0 indicates MH compression.
    Bit 1 must be 0
    Bit 2 = 1 indicates that EOLs are byte aligned, = 0 EOLs not byte
    aligned
    Default is all bits are 0 (applies when MH compression is used and
    EOLs are not byte aligned) (See Section 3.2.2.)
    The T4Options field is required when the Compression field has a
    value of 3. This field specifies the compression used (MH or MR) and
    whether the EOL codes are byte-aligned or not. If they are byte



Buckley et al.              Expires December 2003              [Page 28]

Internet Draft        File Format for Internet Fax             June 2003


    aligned, then fill bits have been added as necessary so that the End
    of Line (EOL) codes always end on byte boundaries See Sections 3.4,
    4.5.3 and 4.5.4 for details.

T6Options(293) = (Bit 0 = 0, Bit 1 = 0). LONG
    RequiredTIFFExtension (when Compression = 4)
    Used to indicate parameterization of 2D Modified Modified Read (MMR)
    compression. T6Options was also known as Group4Options in a prior
    version of [TIFF].
    Bit 0 must be 0.
    Bit 1 = 0 indicates uncompressed data mode is not allowed; = 1
    indicates uncompressed data is allowed (see [TIFF]).
    Default is all bits 0. For FAX, the field must be present and have
    the value 0. The use of uncompressed data where compression would
    expand the data size is not allowed for FAX.

   NOTE: MMR compressed data is two-dimensional and does not use EOLs.
   Each MMR encoded image MUST include an "end-of-facsimile-block"
   (EOFB) code at the end of each coded strip; see Section 4.5.6.

4.2.3. New fields

   None.

4.3. Recommended TIFF fields

4.3.1. Baseline fields

   See Section 2.2.3.

4.3.2. Extension fields

   See Section 2.2.3.

4.3.3. New fields

   See Section 2.2.4 and optional fields below.

   Three new, optional fields, used in the original TIFF-F description
   to describe page quality, are defined in this specification.  The
   information contained in these fields is usually obtained from
   receiving facsimile hardware (if applicable). They SHOULD NOT be used
   in writing TIFF-F files for facsimile image data that is error
   corrected or otherwise guaranteed not to have coding errors. Some
   applications need to understand exactly the error content of the
   data.  For example, a CAD program might wish to verify that a  file
   has a low error level before importing it into a high-accuracy
   document. Because Group 3 facsimile devices do not necessarily
   perform error correction on the image data, the quality of a received
   page must be inferred from the pixel count of decoded scan lines. A

Buckley et al.              Expires December 2003              [Page 29]

Internet Draft        File Format for Internet Fax             June 2003


   "good" scan line is defined as a line that, when decoded, contains
   the correct number of pixels. Conversely, a "bad" scan line is
   defined as a line that, when decoded, comprises an incorrect number
   of pixels.

BadFaxLines(326)                                           SHORT or LONG
    The number of "bad" scan lines encountered by the facsimile device
    during reception. A "bad" scanline is defined as a scanline that,
    when decoded, comprises an incorrect number of pixels. Note that
    PercentBad = (BadFaxLines/ImageLength) * 100
    No default.

CleanFaxData(327) = 0, 1, 2.                                       SHORT
    Indicates if "bad" lines encountered during reception are stored in
    the data, or if "bad" lines have been replaced by the receiver.
    0 = No "bad" lines
    1 = "bad" lines exist, but were regenerated by the receiver,
    2 = "bad" lines exist, but have not been regenerated.
    No default.

   NOTE: Many facsimile devices do not actually output bad lines.
   Instead, the previous good line is repeated in place of a bad line.
   Although this substitution, known as line regeneration, results in a
   visual improvement to the image, the data is nevertheless corrupted.
   The CleanFaxData field describes the error content of the data.  That
   is, when the BadFaxLines and ImageLength fields indicate that the
   facsimile device encountered lines with an incorrect number of pixels
   during reception, the CleanFaxData field indicates whether these bad
   lines are actually still in the data or if the receiving facsimile
   device replaced them with regenerated lines.

ConsecutiveBadFaxLines(328)                               LONG or SHORT
    Maximum number of consecutive "bad" scanlines received.  The
    BadFaxLines field indicates only the quantity of bad lines.
    No Default.

   NOTE: The BadFaxLines and ImageLength data indicate only the quantity
   of bad lines. The ConsecutiveBadFaxLines field is an indicator of the
   distribution of bad lines and may therefore be a better general
   indicator of perceived image quality. See Section 4.4.5 for examples
   of the use of these fields.

4.4. Technical Implementation Issues

4.4.1   Strips

   In general, TIFF files divide an image into "strips," also known as
   "bands."  Each strip contains a few scanlines of the image. By using



Buckley et al.              Expires December 2003              [Page 30]

Internet Draft        File Format for Internet Fax             June 2003


   strips, a TIFF reader need not load the entire image into memory,
   thus enabling it to fetch and decompress small random portions of the
   image as necessary.

   The number of scanlines in a strip is described by the RowsPerStrip
   value and the number of bytes in the strip after compression by the
   StripByteCount value.  The location in the TIFF file of each strip is
   given by the StripOffsets values.

   Strip size is application dependent. The recommended approach for
   multi- page TIFF-F images is to represent each page as a single
   strip. Existing TIFF-F usage is typically one strip per page in
   multi-page TIFF-F files. See Sections 2.1.2 and 2.1.3.

4.4.2  Bit Order

   The current TIFF specification [TIFF] does not require a Baseline
   TIFF reader to support FillOrder=2, i.e. lowest numbered 1-bit pixel
   in the least significant bit of a byte. It further recommends that
   FillOrder=2 be used only in special purpose applications.

   Facsimile data appears on the phone line in bit-reversed order
   relative to its description in ITU-T Recommendation T.4.  Therefore,
   a wide majority of facsimile applications choose this natural order
   for data in a file. Nevertheless, TIFF-F readers must be able to read
   data in both bit orders and support FillOrder values of 1 and 2.

4.4.3. Multi-Page

   Many existing applications already read TIFF-F-like files, but do not
   support the multi-page field.  Since a multi-page format greatly
   simplifies file management in fax application software, TIFF-F
   specifies multi-page documents (NewSubfileType = 2) as the standard
   case.

   It is recommended that applications export multiple page TIFF-F files
   without manipulating fields and values.   Historically, some TIFF-F
   writers have attempted to produce individual single-page TIFF-F files
   with modified NewSubFileType and PageNumber (page one-of-one) values
   for export purposes.  However, there is no easy way to link such
   multiple single page files together into a logical multiple page
   document, so that this practice is not recommended.

4.4.4. Compression

   In Group 3 facsimile, there are three compression methods which had
   been standardized as of 1994 and are in common use. The ITU-T T.4
   Recommendation [T.4] defines a one-dimensional compression method



Buckley et al.              Expires December 2003              [Page 31]

Internet Draft        File Format for Internet Fax             June 2003


   known as Modified Huffman (MH) and a two-dimensional method known as
   Modified READ (MR) (READ is short for Relative Element Address
   Designate). In 1984, a somewhat more efficient compression method
   known as Modified Modified READ (MMR) was defined in the ITU-T T.6
   Recommendation [T.6]. MMR was originally defined for use with Group 4
   facsimile, so that this compression method has been commonly called
   Group 4 compression.  In 1991, the MMR method was approved for use in
   Group 3 facsimile and has since been widely utilized.

   TIFF-F supports these three compression methods. The most common
   practice is the one-dimensional Modified Huffman (MH) compression
   method.  This is specified by setting the Compression field value to
   3 and then setting bit 0 of the T4Options field to 0.  Alternatively,
   the two dimensional Modified READ (MR) method, which is much less
   frequently used in historical TIFF-F implementations, may be selected
   by setting bit 0 of the T4Options field to 1.  The value of Bit 2 in
   this field is determined by the use of fill bits.

   Depending upon the application, the more efficient two-dimensional
   Modified Modified Read (MMR)compression method from T.6 may be
   selected by setting the Compression field value to 4 and then setting
   the first two bits (and all unused bits) of the T6Options field to 0.
   More information to aid the implementor in making a compression
   selection is contained in Section 4.5.2.

   Baseline TIFF also permits use of Compression=2 to specify Modified
   Huffman compression, but the data does not use EOLs. As a result,
   TIFF-F uses Compression=3 instead of Compression=2 to specify
   Modified Huffman compression.

4.4.5.  Example Use of Page-quality Fields

   Here are examples for writing the CleanFaxData, BadFaxLines, and
   ConsecutiveBadFaxLines fields:

     1.  Facsimile hardware does not provide page quality
         information: MUST NOT write page-quality fields.
     2.  Facsimile hardware provides page quality information, but
         reports no bad lines.  Write only BadFaxLines = 0.
     3.  Facsimile hardware provides page quality information, and
         reports bad lines.  Write both BadFaxLines and
         ConsecutiveBadFaxLines.  Also write CleanFaxData = 1 or 2 if
         the hardware's regeneration capability is known.
     4.  Source image data stream is error-corrected or otherwise
         guaranteed to be error-free such as for a computer generated
         file:  SHOULD NOT write page-quality fields.





Buckley et al.              Expires December 2003              [Page 32]

Internet Draft        File Format for Internet Fax             June 2003


   TIFF Writers SHOULD only generate these fields when the image has
   been generated from a fax image data stream where error correction,
   e.g. Group 3 Error Correction Mode, was not used.

4.4.6. Practical Guidelines for Writing and Reading Multi-Page TIFF-F
   Files

   Traditionally, historical TIFF-F has required readers and writers to
   be able to handle multi-page TIFF-F files.  Based on the experience
   of various TIFF-F implementors, it has been seen that the
   implementation of TIFF-F can be greatly simplified if certain
   practical guidelines are followed when writing multi-page TIFF-F
   files.

   The structure for a multi-page TIFF-F file will include one IFD per
   page of the document.  In this case, this IFD will define the
   attributes for a single page. A second simplifying guideline is that
   the writer of TIFF-F files SHOULD present IFDs in the same order as
   the actual sequence of pages.  (The pages are numbered within TIFF-F
   beginning with page 0 as the first page and then ascending (i.e. 0,
   1, 2,...). However, any field values over 4 bytes will be stored
   separately from the IFD. TIFF-F readers SHOULD expect IFDs to be
   presented in page order, but be able to handle exceptions.

   Per [TIFF], the exact placement of image data is not specified.
   However, the strip offsets for each strip of image are defined from
   within each IFD.   Where possible, another simplifying guideline for
   the writing of TIFF-F files is to specify that the image data for
   each page of a multi-page document SHOULD be contained within a
   single strip (i.e. one image strip per fax page). The use of a single
   image strip per page is very useful for applications such as store
   and forward messaging, where the file is usually prepared in advance
   of the transmission, but other assumptions may apply for the size of
   the image strip for applications which require the use of "streaming"
   techniques (see section 4.4.7).  In the event a different image strip
   size guideline has been used (e.g. constant size for image strips
   that may be less than the page size), this will immediately be
   evident from the values/offsets of the fields that are related to
   strips.

   A third simplifying guideline is that each IFD SHOULD be placed in
   the TIFF-F file structure at a point which precedes the image which
   the IFD describes.

   In addition, a fourth simplifying guideline for TIFF-F writers and
   readers is to place the actual image data in a physical order within
   the TIFF file structure which is consistent with the logical page
   order.  In practice, TIFF-F readers will need to use the strip



Buckley et al.              Expires December 2003              [Page 33]

Internet Draft        File Format for Internet Fax             June 2003


   offsets to find the exact physical location of the image data,
   whether or not it is presented in logical page order.

   If the image data is stored in multiple strips, then the strips
   SHOULD occur in the file in the same order that the data they contain
   occurs in the facsimile transmission, starting at the top of the
   page.

   TIFF-F writers MAY make a fifth simplifying guideline, in which the
   IFD, the value data and the image data to which the IFD has offsets
   precede the next image IFD. However, this guideline has been relaxed
   (writers MAY rather than SHOULD use it) compared to the other
   guidelines given here to reflect past practices for TIFF-F.

   In the case of the minimal profile, which is also the minimal subset
   of Profile F, the SHOULD's and MAY's of these guidelines become
   SHALL's (see Section 3.5).

   So, a TIFF-F file which is structured using the guidelines of this
   section will essentially be composed of a linked list of IFDs,
   presented in ascending page order, which in turn each point to a
   single page of image data (one strip per page), where the pages of
   image data are also placed in a logical page order within the TIFF- F
   file structure.  (The pages of image data may themselves be stored in
   a contiguous manner, at the option of the implementor).

4.4.7.   Use of TIFF-F for Streaming Applications

   TIFF-F has historically been used for handling fax image files in
   applications such as store and forward messaging where the entire
   size of the file is known in advance.  While TIFF-F may also possibly
   be used as a file format for cases such as streaming applications,
   assumptions may be required that differ from those provided in this
   section (e.g., the entire size and number of pages within the image
   are not known in advance).  As a result, a definition for the
   streaming application of TIFF-F is beyond the scope of this document.

4.5. Implementation Warnings

4.5.1  Uncompressed data

   TIFF-F requires the ability to read and write at least one-
   dimensional T.4 Huffman ("compressed") data.  Uncompressed data is
   not allowed. This means that the "Uncompressed" bit in T4Options or
   T6Options must be set to 0.






Buckley et al.              Expires December 2003              [Page 34]

Internet Draft        File Format for Internet Fax             June 2003


4.5.2. Encoding and Resolution

   Since two-dimensional encoding is not required for Group 3
   compatibility, some historic TIFF-F readers have not been able to
   read such files.  The minimum subset of TIFF-F REQUIRES support for
   one dimensional (Modified Huffman) files, so this choice maximizes
   portability.  However, implementors seeking greater efficiency SHOULD
   use T.6 MMR compression when writing TIFF-F files.  Some TIFF-F
   readers will also support two-dimensional Modified READ files.
   Implementors that wish to have the maximum flexibility in reading
   TIFF-F files should support all three of these compression methods
   (MH, MR and MMR).

   For the case of resolution, almost all facsimile products support
   both standard (98 dpi) vertical resolution  and "fine" (196 dpi)
   resolution. Therefore, fine-resolution files are quite portable in
   the real world.

   In 1993, the ITU-T added support for higher resolutions in the T.30
   recommendation including 200 x 200, 300 x 300, 400 x 400 in dots per
   inch based units.  At the same time, support was added for metric
   dimensions which are equivalent to the following inch based
   resolutions: 391v x 204h and 391v x 408h.  Therefore, the full set of
   inch-based equivalents of the new resolutions are supported in the
   TIFF-F writer, since they may appear in some image data streams
   received from Group 3 facsimile devices.  However, many facsimile
   terminals and older versions of  TIFF-F readers are likely to not
   support the use of these higher resolutions.

   Per [T.4], it is permissible for applications to treat the following
   XResolution values as being equivalent: <204,200> and <400,408>.  In
   a similar respect, the following YResolution values may also be
   treated as being equivalent: <98, 100>, <196, 200>, and <391, 400>.
   These equivalencies were allowed by [T.4] to permit conversions
   between inch and metric based facsimile terminals.

   In a similar respect, the optional support of metric based
   resolutions in the TIFF-F reader (i.e. 77 x 38.5 cm) is included for
   completeness, since they are used in some legacy TIFF-F applications,
   but this use is not recommended for the creation of TIFF-F files by a
   writer.

4.5.3. EOL byte-aligned

   The historical convention for TIFF-F has been that all EOLs in
   Modified Huffman or Modified READ data must be byte-aligned. However,
   Baseline TIFF has permitted use of non-byte-aligned EOLs by default,
   so that a large percentage of TIFF-F reader implementations support



Buckley et al.              Expires December 2003              [Page 35]

Internet Draft        File Format for Internet Fax             June 2003


   both conventions. Therefore, the minimum subset of TIFF-F, or Profile
   S, as defined in Section 3 includes support for both byte-aligned and
   non- byte-aligned EOLs; see Section 3.2.2.

   An EOL is said to be byte-aligned when Fill bits have been added as
   necessary before EOL codes such that EOL always ends on a byte
   boundary, thus ensuring an  EOL-sequence of a one byte preceded by a
   zero nibble: xxxx0000 00000001.

   Modified Huffman compression encodes bits, not bytes. This means that
   the end-of-line token may end in the middle of a byte. In byte
   alignment, extra zero bits (Fill) are added so that the first bit of
   data following an EOL begins on a byte boundary. In effect, byte
   alignment relieves application software of the burden of bit-
   shifting every byte while parsing scan lines for line-oriented image
   manipulation (such as writing a TIFF file).

   For Modified READ compression, each line is terminated by an EOL and
   a one bit tag bit.  Per [T.4], the value of the tag bit is 0 if the
   next line contains two dimensional data and 1 if the next line is a
   reference line.   To maintain byte alignment, fill bits are added
   before the EOL/tag bit sequence, so that the first bit of data
   following an MR tag bit begins on a byte boundary.

4.5.4. EOL

   As illustrated in FIGURE 1/T.4 in [T.4], facsimile documents encoded
   with Modified Huffman begin with an EOL, which in TIFF-F may be byte-
   aligned. The last line of the image is not terminated by an EOL.  In
   a similar respect, images encoded with Modified READ two-dimensional
   compression begin with an EOL, followed by a tag bit.

4.5.5. RTC Exclusion

   Aside from EOLs, TIFF-F files have historically only contained image
   data. This means that applications which wish to maintain strict
   conformance with the rules in [TIFF] and compatibility with
   historical TIFF-F, SHOULD NOT include the Return To Control sequence
   (RTC) (consisting of 6 consecutive EOLs) when writing TIFF-F files.
   However, applications which need to support "transparency" of [T.4]
   image data MAY include RTCs if the flag settings of the T4Options
   field are set for non-byte aligned MH or MR image data.  Implementors
   of TIFF readers should also be aware that there are some existing
   TIFF-F implementations which include the RTC sequence in MH/MR image
   data. Therefore, TIFF-F readers MUST be able to process files which
   do not include RTCs and SHOULD be able to process files which do
   include RTCs.




Buckley et al.              Expires December 2003              [Page 36]

Internet Draft        File Format for Internet Fax             June 2003


4.5.6 Use of EOFB for T.6 Compressed Images

   TIFF-F pages which are encoded with the T.6 Modified Modified READ
   compression method MUST include an "end-of-facsimile-block" (EOFB)
   code at the end of each coded strip. Per [TIFF], the EOFB code is
   followed by pad bits as needed to align on a byte boundary. TIFF
   readers SHOULD ignore any bits other than pad bits beyond the EOFB.

4.6. Example Use of TIFF-F

   The Profile F of TIFF (i.e. TIFF-F content) is a secondary component
   of the VPIM Message, as defined in [VPIM 2].  Voice messaging
   systems can often handle fax store-and-forward capabilities in
   addition to traditional voice message store-and-forward functions.
   As a result, TIFF-F fax messages can optionally be sent between
   compliant VPIM systems, and may be rejected if the recipient system
   cannot deal with fax.

   Refer to the VPIM Specification for proper usage of this content.

4.7. Profile F - Extended Black-and-white Fax Profile Summary

   Recommended fields are shown with an asterisk *.

   Required fields or values are shown with a double asterisk **. If the
   double asterisk is on the field name, then all the listed values are
   required of implementations; if the double asterisks are in the
   Values column, then only the values suffixed with a double asterisk
   are required of implementations.

       +---------------------------+--------------------------------+
       | Baseline Fields           |  Values                        |
       +---------------------------+--------------------------------+
       | BitsPerSample             | 1**                            |
       +---------------------------+--------------------------------+
       | Compression               | 3**: 1D Modified Huffman and   |
       |                           |      2D Modified Read coding   |
       |                           | 4: 2D Modified Modified Read   |
       |                           |    coding                      |
       +---------------------------+--------------------------------+
       | DateTime*                 | {ASCII}: date/time in 24-hour  |
       |                           | format "YYYY:MM:DD HH:MM:SS"   |
       +---------------------------+--------------------------------+
       | FillOrder**               | 1: most significant bit first  |
       |                           | 2: least significant bit first |
       +------------------------------------------------------------+





Buckley et al.              Expires December 2003              [Page 37]

Internet Draft        File Format for Internet Fax             June 2003


       +------------------------------------------------------------+
       | ImageDescription*         | {ASCII}: A string describing   |
       |                           | the contents of the image.     |
       +---------------------------+--------------------------------+
       | ImageWidth                | 1728**, 2048, 2432, 2592,      |
       |                           | 3072, 3456, 3648, 4096, 4864   |
       +---------------------------+--------------------------------+
       | ImageLength**             | n: total number of scanlines   |
       |                           | in image                       |
       +---------------------------+--------------------------------+
       | NewSubFileType            | 2**: Bit 1 identifies single   |
       |                           | page of a multi-page document  |
       +---------------------------+--------------------------------+
       | Orientation               | 1**-8, Default 1               |
       +---------------------------+--------------------------------+
       | PhotometricInterpretation | 0: pixel value 1 means black   |
       |  **                       | 1: pixel value 1 means white   |
       +---------------------------+--------------------------------+
       | ResolutionUnit**          | 2: inch                        |
       |                           | 3: centimeter                  |
       +---------------------------+--------------------------------+
       | RowsPerStrip**            | n: number of scanlines per     |
       |                           | TIFF strip                     |
       +---------------------------+--------------------------------+
       | SamplesPerPixel           | 1**                            |
       +---------------------------+--------------------------------+
       | Software*                 | {ASCII}: name & release        |
       |                           | number of creator software     |
       +---------------------------+--------------------------------+
       | StripByteCounts**         | <n>: number or bytes in TIFF   |
       |                           | strip                          |
       +---------------------------+--------------------------------+
       | StripOffsets**            | <n>: offset from beginning of  |
       |                           | file to each TIFF strip        |
       +---------------------------+--------------------------------+
       | XResolution               | 200, 204**, 300, 400, 408      |
       |                           | (written in pixels/inch)       |
       +---------------------------+--------------------------------+
       | YResolution               | 98**, 196**, 100,              |
       |                           | 200, 300, 391, 400             |
       |                           | (written in pixels/inch)       |
       +---------------------------+--------------------------------+
       | Extension Fields                                           |
       +---------------------------+--------------------------------+







Buckley et al.              Expires December 2003              [Page 38]

Internet Draft        File Format for Internet Fax             June 2003


       +---------------------------+--------------------------------+
       | T4Options                 | 0**: required if Compression   |
       |                           | is Modified Huffman, EOLs are  |
       |                           | not byte aligned               |
       |                           | 1: required if Compression is  |
       |                           | 2D Modified Read, EOLs are     |
       |                           | not byte aligned               |
       |                           | 4**: required if Compression   |
       |                           | is Modified Huffman, EOLs are  |
       |                           | byte aligned                   |
       +---------------------------+--------------------------------+
       | T4Options (continued)     | 5: required if Compression     |
       |                           | is 2D Modified Read, EOLs are  |
       |                           | byte aligned                   |
       +---------------------------+--------------------------------+
       | T6Options                 | 0: required if Compression is  |
       |                           | 2D Modified Modified Read      |
       +---------------------------+--------------------------------+
       | DocumentName*             | {ASCII}: name of scanned       |
       |                           | document                       |
       +---------------------------+--------------------------------+
       | PageNumber**              | n,m: page number followed by   |
       |                           | total page count               |
       +---------------------------+--------------------------------+
       | New Fields                                                 |
       +---------------------------+--------------------------------+
       | BadFaxLines*              | number of "bad" scanlines      |
       |                           | encountered during reception   |
       +---------------------------+--------------------------------+
       | CleanFaxData*             | 0: no "bad" lines              |
       |                           | 1: "bad" lines exist, but were |
       |                           | regenerated by receiver        |
       |                           | 2: "bad" lines exist, but have |
       |                           | not been regenerated           |
       +---------------------------+--------------------------------+
       | ConsecutiveBadFaxLines*   | Max number of consecutive      |
       |                           | "bad" lines received           |
       +---------------------------+--------------------------------+
       | GlobalParametersIFD*      | IFD: global parameters IFD     |
       +---------------------------+--------------------------------+
       | ProfileType*              | n: type of data stored in file |
       +---------------------------+--------------------------------+
       | FaxProfile*               | n: ITU-compatible fax profile  |
       +---------------------------+--------------------------------+
       | CodingMethods*            | n: compression algorithms used |
       |                           | in file                        |
       +---------------------------+--------------------------------+




Buckley et al.              Expires December 2003              [Page 39]

Internet Draft        File Format for Internet Fax             June 2003


5. Profile J - Lossless JBIG Black-and-White Fax profile

   This section defines the lossless JBIG black-and-white profile or
   Profile J of TIFF for facsimile. Implementations of this profile are
   required to also implement Profile S.

   The previous section described the extended interchange set of TIFF
   fields for black-and-white fax, which provided support for the MH, MR
   and MMR compression of black-and-white images. This section adds a
   profile with JBIG compression capability.

5.1. Overview

   This section describes a black-and-white profile that uses JBIG
   compression. The ITU-T has approved the single-progression sequential
   mode of JBIG [T.82] for Group 3 facsimile. JBIG coding offers
   improved compression for halftoned originals. JBIG compression is
   used in accordance with the application rules given in ITU-T Rec.
   T.85 [T.85].

   This profile is essentially the extended black-and-white profile with
   JBIG compression used instead of MH, MR or MMR.

5.2. Required TIFF Fields

   This section lists the required fields and the values they must have
   to be ITU-compatible. Besides the fields listed in Section 2.2.1, the
   extended black-and-white fax profile requires the following fields.

5.2.1. Baseline fields

   The TIFF fields that SHALL be used in this profile are the same as
   those described in Section 4.2.1 for the extended black-and-white
   profile, with two exceptions: the following text replaces the text in
   Section 4.2.1 for the Compression and FillOrder fields.

Compression(259) = 9.                                              SHORT
    RequiredByTIFFBaseline
    9 = JBIG coding. This is a TIFF extension value.
    Default = 1 (and is not applicable; field must be specified).
    Profile J uses ITU-T T.85 profile of T.82; see T82Options field.

FillOrder(266) = 1, 2.                                            SHORT
    RequiredByTIFFBaseline
    1 = Pixels are arranged within a byte such that pixels with lower
    values are stored in the higher-order bits of the byte, i.e. most
    significant bit first (MSB).
    2 = Pixels are arranged within a byte such that pixels with lower
    column values are stored in the lower-order bits of the bytes, i.e.,
    least significant bit first (LSB).

Buckley et al.              Expires December 2003              [Page 40]

Internet Draft        File Format for Internet Fax             June 2003


    Profile J readers must be able to read data in both bit orders.

5.2.2. Extension fields

Same fields as those in Section 2.2.1.

5.2.3. New fields

T82Options(435) = 0                                                 LONG
    Required when Compression = 9
    Individual bits are set to indicate the applicable profile of JBIG
    coding; all bits set to 0 indicates ITU-T T.85 profile of T.82;
    Other values are for further study.
    Default is all bits 0 and field may be omitted if this is the value
    (Field may be omitted in Profile J files.)

    Note: A T.82 decoder can decode a T.85 encoded image when it handles
    the NEWLE     marker code as described Corrigendum 1 in [T.85].

5.3. Recommended TIFF Fields

   See Section 2.2.3 and 2.2.4.

5.4.  Profile J - Lossless JBIG Black-and-white Fax Profile Summary

   Recommended fields are shown with an asterisk *.

   Required fields or values are shown with a double asterisk **. If the
   double asterisk is on the field name, then all the listed values are
   required of implementations; if the double asterisks are in the
   Values column, then only the values suffixed with a double asterisk
   are required of implementations.

       +---------------------------+--------------------------------+
       | Baseline Fields           |  Values                        |
       +---------------------------+--------------------------------+
       | BitsPerSample             | 1**                            |
       +---------------------------+--------------------------------+
       | Compression               | 9**: JBIG coding               |
       +---------------------------+--------------------------------+
       | DateTime*                 | {ASCII}: date/time in 24-hour  |
       |                           | format "YYYY:MM:DD HH:MM:SS"   |
       +---------------------------+--------------------------------+
       | FillOrder**               | 1: most significant bit first  |
       |                           | 2: least significant bit first |
       +---------------------------+--------------------------------+
       | ImageDescription*         | {ASCII}: A string describing   |
       |                           | the contents of the image.     |
       +---------------------------+--------------------------------+


Buckley et al.              Expires December 2003              [Page 41]

Internet Draft        File Format for Internet Fax             June 2003

       +---------------------------+--------------------------------+
       | ImageWidth                | 1728**, 2048, 2432, 2592,      |
       |                           | 3072, 3456, 3648, 4096, 4864   |
       +---------------------------+--------------------------------+
       | ImageLength**             | n: total number of scanlines   |
       |                           | in image                       |
       +---------------------------+--------------------------------+
       | NewSubFileType**          | 2: Bit 1 identifies single     |
       |                           | page of a multi-page document  |
       +---------------------------+--------------------------------+
       | Orientation               | 1**-8, Default 1               |
       +---------------------------+--------------------------------+
       | PhotometricInterpretation | 0: pixel value 1 means black   |
       |  **                       | 1: pixel value 1 means white   |
       +---------------------------+--------------------------------+
       | ResolutionUnit**          | 2: inch                        |
       |                           | 3: centimeter                  |
       +---------------------------+--------------------------------+
       | RowsPerStrip**            | n: number of scanlines per     |
       |                           | TIFF strip                     |
       +---------------------------+--------------------------------+
       | SamplesPerPixel**         | 1                              |
       +---------------------------+--------------------------------+
       | Software*                 | {ASCII}: name & release        |
       |                           | number of creator software     |
       +---------------------------+--------------------------------+
       | StripByteCounts**         | <n>: number of bytes in TIFF   |
       |                           | strip                          |
       +---------------------------+--------------------------------+
       | StripOffsets**            | <n>: offset from beginning of  |
       |                           | file to each TIFF strip        |
       +---------------------------+--------------------------------+
       | XResolution               | 200, 204**, 300, 400, 408      |
       |                           | (written in pixels/inch)       |
       +---------------------------+--------------------------------+
       | YResolution               | 98**, 196**, 100,              |
       |                           | 200, 300, 391, 400             |
       |                           | (written in pixels/inch)       |
       +---------------------------+--------------------------------+
       | Extension Fields                                           |
       +---------------------------+--------------------------------+
       | DocumentName*             | {ASCII}: name of document      |
       |                           |  scanned                       |
       +---------------------------+--------------------------------+
       | PageNumber**              | n,m: page number followed by   |
       |                           | total page count               |
       +---------------------------+--------------------------------+
       | New Fields                                                 |
       +---------------------------+--------------------------------+
       | GlobalParametersIFD*      | IFD: global parameters IFD     |
       +---------------------------+--------------------------------+

Buckley et al.              Expires December 2003              [Page 42]

Internet Draft        File Format for Internet Fax             June 2003


       +---------------------------+--------------------------------+
       | T82Options**              | 0: T.85 profile of T.82        |
       +---------------------------+--------------------------------+
       | ProfileType*              | n: type of data stored in file |
       +---------------------------+--------------------------------+
       | FaxProfile*               | n: ITU-compatible fax profile  |
       +---------------------------+--------------------------------+
       | CodingMethods*            | n: compression algorithms used |
       |                           | in file                        |
       +---------------------------+--------------------------------+

6. Profile C - Base Color Fax profile

6.1. Overview

   This section defines the lossy color profile or Profile C of TIFF for
   facsimile. Implementations of this profile are required to also
   implement Profile S.

   This is the base profile for color and grayscale facsimile, which
   means that all applications that support color fax must support this
   profile. The basic approach is the lossy JPEG compression [T.4, Annex
   E; T.81] of L*a*b* color data [T.42]. Grayscale applications use the
   L* lightness component; color applications use the L*, a* and b*
   components.

   This profile uses a new PhotometricInterpretation field value to
   describe the L*a*b* encoding specified in [T.42]. This encoding
   differs in two ways from the other L*a*b* encodings used in TIFF
   [TIFF, TTN1]: it specifies a different default range for the a* and
   b* components, based on a comprehensive evaluation of existing
   hardcopy output, and it optionally allows selectable range for the
   L*, a* and b* components.

6.2. Required TIFF Fields

   This section lists the required fields, in addition to those given in
   Section 2.2.1, and the values they must support to be compatible with
   ITU-T Rec. T.42 and Annex E in ITU-T Rec. T.4.

6.2.1. Baseline Fields

ImageWidth(256).                                           SHORT or LONG
    This profile supports the following fixed page widths: 864, 1024,
    1216, 1728, 2048, 2432, 2592, 3072, 3456, 3648, 4096, 4864.

NewSubFileType(254) = (Bit 1=1).                                    LONG
    RequiredByTIFFforFAX
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for fax)

Buckley et al.              Expires December 2003              [Page 43]

Internet Draft        File Format for Internet Fax             June 2003


BitsPerSample(258) = 8.                                        SHORT
    Count = SamplesPerPixel
    The base color fax profile requires 8 bits per sample.

Compression(259) = 7.                                              SHORT
    Base color fax profile uses Baseline JPEG compression. Value 7
    represents JPEG compression as specified in [TTN2].

FillOrder(266) = 1 , 2.                                            SHORT
    RequiredByTIFFBaseline
    Profile C readers must be able to read data in both bit orders,
    but the vast majority of facsimile products store data LSB
    first, exactly as it appears on the telephone line.
              1 = Most Significant Bit first.
              2 = Least Significant Bit first

PhotometricInterpretation(262) = 10.                               SHORT
    Base color fax profile requires pixel values to be stored using the
    CIE L*a*b* encoding defined in ITU-T Rec. T.42. This encoding is
    indicated by the PhotometricInterpretation value 10, referred to as
    ITULAB. With this encoding, the minimum sample value is  mapped to 0
    and the maximum sample value is mapped to (2^n - 1), i.e. the
    maximum value, where n is the BitsPerSample value. The conversion
    from unsigned ITULAB-encoded samples values to signed CIE L*a*b*
    values is determined by the Decode field; see Sec. 6.2.3

   NOTE: PhotometricInterpretation values 8 and 9 specify encodings for
   use with 8-bit-per-sample CIE L*a*b* [TIFF] and ICC L*a*b* [TTN1]
   data, but they are fixed encodings, which use different minimum and
   maximum samples than the T.42 default encoding. As currently defined,
   they are not able to represent fax-encoded L*a*b* data.

ResolutionUnit(296) = 2.                                           SHORT
    The unit of measure for resolution. 2 = inch
    ITU-T standards only specify inch-based resolutions for color fax
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277) = 1, 3.                                       SHORT
    1: L* component only, required in base color profile
    3: L*, a*, b* components
    Encoded according to PhotometricInterpretation field

XResolution(282) = 100, 200, 300, 400.                          RATIONAL
YResolution(283) = 100, 200, 300, 400.                          RATIONAL
    The resolution of the image is expressed in pixels per resolution
    unit. In pixels per inch, allowed XResolution values are: 100, 200,
    300, and 400. The base color fax profile requires the pixels to be
    square, hence YResolution must equal XResolution. Base resolution is
    200 pixels per inch and SHALL be supported by all implementations of
    this profile.

Buckley et al.              Expires December 2003              [Page 44]

Internet Draft        File Format for Internet Fax             June 2003


NOTE: The functional equivalence of inch-based and metric-based resolu-
tions is maintained, per Annex E.6.5 in [T.4]. See table in Sec. 2.2.2.

NOTE: Not all combinations of XResolution, YResolution and ImageWidth
are legal. The following table gives the legal combinations for inch-
based resolutions and the corresponding paper sizes [T.30].

    +--------------------------------+---------------------------+
    |   XResolution x YResolution    |         ImageWidth        |
    +--------------------------------+---------------------------+
    |           100 x 100            |   864   |  1024  |  1216  |
    +--------------------------------+---------------------------+
    |           200 x 200            |  1728   |  2048  |  2432  |
    +--------------------------------+---------------------------+
    |           300 x 300            |  2592   |  3072  |  3648  |
    +--------------------------------+---------------------------+
    |           400 x 400            |  3456   |  4096  |  4864  |
    +--------------------------------+---------------------------+
                                     |Letter,A4|   B4   |   A3   |
                                     |  Legal  |        |        |
                                     +---------------------------+
                                     |         Paper Size        |
                                     +---------------------------+

6.2.2 Extension Fields

The JPEG compression standard allows for the a*b* chroma components of
an image to be subsampled relative to the L* lightness component. The
extension fields ChromaSubSampling and ChromaPositioning define the
subsampling. They are the same as YCbCrSubSampling and YCbCrPositioning
in [TIFF], but have been renamed to reflect their applicability to other
color spaces.

ChromaSubSampling(530).                                            SHORT
    Count = 2
    Specifies the subsampling factors for the chroma components of a
    L*a*b* image. The two subfields of this field, ChromaSubsampleHoriz
    and ChromaSubsampleVert, specify the horizontal and vertical
    subsampling factors respectively.

    SHORT 0: ChromaSubsampleHoriz = 1, 2.
    1: equal numbers of lightness and chroma samples horizontally,
    2: twice as many lightness samples as chroma samples horizontally,

    SHORT 1: ChromaSubsampleVert = 1, 2.
    1: equal numbers of lightness and chroma samples vertically,
    2: twice as many lightness samples as chroma samples vertically,

    The default value for ChromaSubSampling is (2,2), which is the
    default for chroma subsampling in color fax [T.4, Annex E]. No

Buckley et al.              Expires December 2003              [Page 45]

Internet Draft        File Format for Internet Fax             June 2003


    chroma subsampling, i.e. ChromaSubSampling = (1,1), is an option
    for color fax

ChromaPositioning(531) = 1.                                        SHORT
    Specifies the spatial positioning of chroma components relative to
    the lightness component.
    1: centered,
    A value of 1 means chrominance samples are spatially offset and
    centered with respect to luminance samples. See the current TIFF
    specification under YcbCr positioning for further information.
    Default = 1, which is what ITU-T T.4, Annex E specifies.

6.2.3. New Fields

Decode(433).                                                   SRATIONAL
    Count = 2 * SamplesPerPixel
    Describes how to map image sample values into the range of values
    appropriate for the current color space. In general, the values are
    taken in pairs and specify the minimum and maximum output value for
    each color component. For the base color fax profile, Decode has a
    count of 6 values and maps the unsigned ITULAB-encoded sample values
    (Lsample, asample, bsample) to signed L*a*b* values, as follows:.

        L* = Decode[0] + Lsample x (Decode[1]-Decode[0])/(2^n -1)
        a* = Decode[2] + asample x (Decode[3]-Decode[2])/(2^n -1)
        b* = Decode[4] + bsample x (Decode[5]-Decode[4])/(2^n -1)

    where Decode[0], Decode[2] and Decode[4] are the minimum values for
    L*, a* and b*; Decode[1], Decode[3] and Decode[5] are the maximum
    values for L*, a* and b*; and n is the BitsPerSample. When n=8,
 L*=Decode[0] when Lsample=0 and L*=Decode[1] when Lsample=255.

    ITU-T Rec. T.42 specifies the ITULAB encoding in terms of a range
    and offset for each component, which are related to the minimum and
    maximum values as follows:

        minimum = - (range x offset) / 2^n - 1
        maximum = minimum + range

    The Decode field default values depend on the color space. For the
    ITULAB color space encoding, the default values correspond to the
    base range and offset, as specified in ITU-T Rec. T.42 [T.42]. The
    following table gives the base range and offset values for
    BitsPerSample=8, and the corresponding default minimum and
    maximum default values for the Decode field, calculated using the
    equations above when PhotometricInterpetation=10.

    Refer to ITU-T Rec. T.42 [T.42] to calculate the range and offset,
    and hence the minimum and maximum values, for other BitsPerSample


Buckley et al.              Expires December 2003              [Page 46]

Internet Draft        File Format for Internet Fax             June 2003


    values.

                       +-----------------------------------------------+
                       | ITU-T Rec. T.42  |           Decode           |
 +---------+-----------|   base values    |       default values       |
 | BitsPer + Component +------------------+----------------------------+
 | -Sample |           |  Range | Offset  |      Min     |     Max     |
 +---------+-----------+--------+---------+--------------+-------------+
 |    8    |    L*     |   100  |    0    |       0      |     100     |
 |         +-----------+--------+---------+--------------+-------------+
 |         |    a*     |   170  |   128   |  -21760/255  |  21590/255  |
 |         +-----------+--------+---------+--------------+-------------+
 |         |    b*     |   200  |    96   |  -19200/255  |  31800/255  |
 +---------+-----------+--------+---------+--------------+-------------+

   For example, when PhotometricInterpretation=10 and BitsPerSample=8,
   the default value for Decode is (0, 100, -21760/255, 21590/255,
   -19200/255, 31800/255). For guidelines on the use of the Decode field,
   see section 5.2.2 of [GUIDE].

6.3. Recommended TIFF Fields

   See Sections 2.2.3. and 2.2.4.

6.4 Profile C - Base Color Fax Profile Summary

   Recommended fields are shown with an asterisk *

   Required fields or values are shown with a double asterisk **. If the
   double asterisk is on the field name, then all the listed values are
   required of implementations; if the double asterisks are in the
   Values column, then only the values suffixed with a double asterisk
   are required of implementations.

       +---------------------------+--------------------------------+
       | Baseline Fields           | Values                         |
       +---------------------------+--------------------------------+
       | BitsPerSample             | 8**: 8 bits per color sample   |
       +---------------------------+--------------------------------+
       | Compression**             | 7: JPEG                        |
       +---------------------------+--------------------------------+
       | DateTime*                 | {ASCII}: date/time in 24-hour  |
       |                           | format "YYYY:MM:DD HH:MM:SS"   |
       +---------------------------+--------------------------------+







Buckley et al.              Expires December 2003              [Page 47]

Internet Draft        File Format for Internet Fax             June 2003


       +------------------------------------------------------------+
       | FillOrder**               | 1: most significant bit first  |
       |                           | 2: least significant bit first |
       +---------------------------+--------------------------------+
       | ImageDescription*         | {ASCII}: A string describing   |
       |                           | the contents of the image.     |
       +---------------------------+--------------------------------+
       | ImageWidth                | 864, 1024, 1216, 1728**, 2048  |
       |                           | 2432, 2592, 3072, 3456, 3648   |
       |                           | 4096, 4864                     |
       +---------------------------+--------------------------------+
       | ImageLength**             | n: total number of scanlines   |
       |                           | in image                       |
       +---------------------------+--------------------------------+
       | NewSubFileType**          | 2: Bit 1 identifies single page|
       |                           | of a multi-page document       |
       +---------------------------+--------------------------------+
       | Orientation               | 1**-8, Default 1               |
       +---------------------------+--------------------------------+
       | PhotometricInterpretation | 10**: ITULAB                   |
       +---------------------------+--------------------------------+
       | ResolutionUnit**          | 2: inch                        |
       +---------------------------+--------------------------------+
       | RowsPerStrip**            | n: number of scanlines per     |
       |                           | TIFF strip                     |
       +---------------------------+--------------------------------+
       | SamplesPerPixel           | 1**: L* (lightness)            |
       |                           | 3: LAB                         |
       +---------------------------+--------------------------------+
       | Software*                 | {ASCII}: name & release number |
       |                           | of creator software            |
       +---------------------------+--------------------------------+
       | StripByteCounts**         | <n>: number or bytes in        |
       |                           | TIFF strip                     |
       +---------------------------+--------------------------------+
       | StripOffsets**            | <n>: offset from beginning     |
       |                           | of file to each TIFF strip     |
       +---------------------------+--------------------------------+
       | XResolution               | 100, 200**, 300, 400 (written  |
       |                           | in pixels/inch)                |
       +---------------------------+--------------------------------+
       | YResolution               | 100, 200**, 300, 400           |
       |                           | (must equal XResolution)       |
       +---------------------------+--------------------------------+







Buckley et al.              Expires December 2003              [Page 48]

Internet Draft        File Format for Internet Fax             June 2003


       +---------------------------+--------------------------------+
       | Extension Fields                                           |
       +---------------------------+--------------------------------+
       | DocumentName*             | {ASCII}: name of scanned       |
       |                           | document                       |
       +---------------------------+--------------------------------+
       | PageNumber**              | n,m: page number followed by   |
       |                           | total page count               |
       +---------------------------+--------------------------------+
       | ChromaSubSampling         | (1,1), (2, 2)**                |
       |                           | (1, 1): equal numbers of       |
       |                           | lightness and chroma samples   |
       |                           | horizontally and vertically    |
       |                           | (2, 2): twice as many lightness|
       |                           | samples as chroma samples      |
       |                           | horizontally and vertically    |
       +---------------------------+--------------------------------+
       | ChromaPositioning         | 1**: centered                  |
       +---------------------------+--------------------------------+
       | New Fields                                                 |
       +---------------------------+--------------------------------+
       | Decode**                  | minL, maxL, mina, maxa, minb,  |
       |                           | maxb: minimum and maximum      |
       |                           | values for L*a*b*              |
       +---------------------------+--------------------------------+
       | GlobalParametersIFD*      | IFD: IFD containing            |
       |                           | global parameters              |
       +---------------------------+--------------------------------+
       | ProfileType*              | n: type of data stored in      |
       |                           | TIFF file                      |
       +---------------------------+--------------------------------+
       | FaxProfile*               | n: ITU-compatible fax profile  |
       +---------------------------+--------------------------------+
       | CodingMethods*            | n: compression algorithms      |
       |                           | used in file                   |
       +---------------------------+--------------------------------+
       | VersionYear*              | byte sequence: year of ITU std |
       +---------------------------+--------------------------------+

7. Profile L - Lossless Color Profile

   This section defines the lossless color profile or Profile L of TIFF
   for facsimile. Implementations of this profile are required to also
   implement Profiles S and C.







Buckley et al.              Expires December 2003              [Page 49]

Internet Draft        File Format for Internet Fax             June 2003


7.1. Overview

   This profile, specified in [T.43] and [T.4] Annex G, uses JBIG to
   losslessly code three types of color and grayscale images: one bit
   per color CMY, CMYK and RGB images; a palettized (i.e. mapped) color
   image; and continuous tone color and grayscale images. The last two
   are multi-level and use the L*a*b* encoding specified in [T.42].

7.1.1. Color Encoding

   While under development, ITU-T Rec. T.43 was called T.Palette, as one
   of its major additions was palette or mapped color images. Baseline
   TIFF only allows RGB color maps, but ITU-T Rec. T.43 requires L*a*b*
   color maps, using the encoding specified in ITU-T Rec. T.42. Palette
   color images are expressed with indices (bits per sample) of 12 bits
   or less, or optionally 13 to 16 bits, per [T.43] and Annex G in
   [T.4]. Profile L files use the color table in the T.43 data stream
   rather than the TIFF ColorMap field.

   Enabling T.43 color maps in TIFF requires the extension field
   Indexed, defined in [TTN1], and the PhotometricInterpretation field
   value 10, defined in Section 6.2.1. The following table shows the
   corresponding PhotometricInterpretation, SamplesPerPixel,
   BitsPerSample and Indexed field values for the different T.43 image
   types.

       +----------------------------------------------------------+
       | Image Type |PhotometricIn| Samples  | Bits Per | Indexed |
       |            |-terpretation| PerPixel |  Sample  |         |
       |------------+-------------+----------+----------+---------|
       |     RGB    |    2=RGB    |     3    |    1     |    0    |
       +----------------------------------------------------------+
       |     CMY    |    5=CMYK   |     3    |    1     |    0    |
       +------------+-------------+----------+----------+---------+
       |     CMYK   |    5=CMYK   |     4    |    1     |    0    |
       +------------+-------------+----------+----------+---------+
       |   Palette  |  10=ITULAB  |     1    |    n     |    1    |
       +------------+-------------+----------+----------+---------+
       |  Grayscale |  10=ITULAB  |     1    |2-8, 9-12 |    0    |
       +------------+-------------+----------+----------+---------+
       |    Color   |  10=ITULAB  |     3    |2-8, 9-12 |    0    |
       +------------+-------------+----------+----------+---------+

7.1.2. JBIG Compression

   T.43 uses the single-progression sequential mode of JBIG, defined in
   ITU-T Rec. T.82. (Other compression methods are for further study.)
   To code multi-level images using JBIG, which is a bi-level
   compression method, an image is resolved into a set of bit-planes,


Buckley et al.              Expires December 2003              [Page 50]

Internet Draft        File Format for Internet Fax             June 2003


   and each bit-plane is then JBIG compressed. For continuous tone color
   and grayscale images, Gray code conversion is used. The Gray code
   conversion is part of the data stream encoding, and is therefore
   invisible to TIFF.

7.2. Required TIFF Fields

   This section lists the required fields, in addition to those in
   Section 2.2.1, and the values they must have to be compatible with
   ITU-T Rec. T.43.

7.2.1. Baseline Fields

ImageWidth(256).                                           SHORT or LONG
    Same page widths as the base color profile; see Section 6.2.1.

NewSubFileType(254) = (Bit 1=1).                                    LONG
    RequiredByTIFFforFAX
    Bit 1 is 1 if the image is a single page of a multi-page document.
    Default = 0 (no subfile bits on, so may not be omitted for fax)

BitsPerSample(258) = 1, 2-8, 9-12.                                 SHORT
    Count = SamplesPerPixel
    RGB, CMY, CMYK: 1 bit per sample
    Continuous tone (L*a*b*): 2-8 bits per sample, 9-12 bits optional
    Palette color: 12 or fewer bits per sample
    Note: More than 8 bits per sample is not baseline TIFF.

Compression(259) = 10.                                             SHORT
    10: ITU-T Rec. T.43 representation, using ITU-T Rec. T.82 (JBIG)
    coding

FillOrder(266) = 1 , 2.                                            SHORT
    RequiredByTIFFBaseline
    Profile L readers must be able to read data in both bit orders,
    but the vast majority of facsimile products store data LSB
    first, exactly as it appears on the telephone line.
              1 = Most Significant Bit first.
              2 = Least Significant Bit first












Buckley et al.              Expires December 2003              [Page 51]

Internet Draft        File Format for Internet Fax             June 2003


PhotometricInterpretation(262) = 2, 5, 10.                         SHORT
    2: RGB
    5: CMYK, including CMY
    10: ITULAB
    Image data may also be stored as palette color images, where pixel
    values are represented by a single component that is an index into a
    color map using the ITULAB encoding. This color map is specified by
    the color palette table embedded in the image data stream. To use
    palette color images, set the PhotometricInterpretation to 10,
    SamplesPerPixel to 1, Indexed to 1, and use the color map in the
    data stream. See Section 7.1.1 for discussion of the color encoding.

ResolutionUnit(296) = 2.                                        SHORT
    The unit of measure for resolution. 2 = inch.
    ITU-T standards only specify inch-based resolutions for color fax
    Default = 2 (field may be omitted if this is the value)

SamplesPerPixel(277) = 1, 3, 4.                                    SHORT
    1: Palette color image, or L*-only if Indexed = 0 and
       PhotometricInterpretation is 10 (ITULAB).
    3: RGB, or L*a*b*, or CMY if PhotometricInterpretation is 5 (CMYK).
    4: CMYK.

XResolution(282) = 100, 200, 300, 400.                          RATIONAL
YResolution(283) = 100, 200, 300, 400.                          RATIONAL
    The resolution of the image is expressed in pixels per resolution
    unit. In pixels per inch, allowed XResolution values are: 100, 200,
    300, and 400. The lossless color fax profile requires the pixels to
    be square, hence YResolution must equal XResolution. Base resolution
    is 200 pixels per inch.

7.2.2. Extension Fields

Indexed(346) = 0, 1.                                               SHORT
    0: not a palette-color image
    1: palette-color image
    This field is used to indicate that each sample value is an index
    into an array of color values specified in the image data stream.
    Because the color map is embedded in the image data stream, the
    ColorMap field is not used in Profile L. Lossless color fax
    profile supports palette-color images with the ITULAB encoding. The
    SamplesPerPixel value must be 1.









Buckley et al.              Expires December 2003              [Page 52]

Internet Draft        File Format for Internet Fax             June 2003


7.2.3. New Fields

Decode(433)                                                    SRATIONAL
    Decode is used in connection with the ITULAB encoding of image data;
    see Section 6.2.3.

7.3. Recommended TIFF Fields

   See Sections 2.2.3. and 2.2.4.

7.4. Profile L - Lossless Color Fax Profile Summary

   Recommended fields are shown with an asterisk *.

   Required fields or values are shown with a double asterisk **. If the
   double asterisk is on the field name, then all the listed values are
   required of implementations; if the double asterisks are in the
   Values column, then only the values suffixed with a double asterisk
   are required of implementations.

        +--------------------+--------------------------------------+
        |   Baseline Fields  |             Values                   |
        +--------------------+--------------------------------------+
        | BitsPerSample      | 1: Binary RGB, CMY(K)                |
        |                    | 8**: 8 bits per color sample         |
        |                    | 9-12: optional                       |
        +--------------------+--------------------------------------+
        | Compression        | 10**: JBIG, per T.43                 |
        +--------------------+--------------------------------------+
        | DateTime*          | {ASCII}:  date/time in the 24-hour   |
        |                    | format "YYYY:MM:DD HH:MM:SS"         |
        +--------------------+--------------------------------------+
        | FillOrder**        | 1: Most significant bit first        |
        |                    | 2: Least significant bit first       |
        +--------------------+--------------------------------------+
        | ImageDescription*  | {ASCII}: A string describing the     |
        |                    | contents of the image.               |
        +--------------------+--------------------------------------+
        | ImageWidth         | 864, 1024, 1216, 1728**, 2048, 2432, |
        |                    | 2592, 3072, 3456, 3648, 4096, 4864   |
        +--------------------+--------------------------------------+
        | ImageLength**      | n: total number of scanlines in image|
        +--------------------+--------------------------------------+
        | NewSubFileType     | 2**: Bit 1 identifies single page of |
        |                    | a multi-page document                |
        +--------------------+--------------------------------------+





Buckley et al.              Expires December 2003              [Page 53]

Internet Draft        File Format for Internet Fax             June 2003


        +--------------------+--------------------------------------+
        | Orientation        | 1**-8, Default 1                     |
        +--------------------+--------------------------------------+
        | PhotometricInter-  | 2: RGB                               |
        | pretation          | 5: CMYK                              |
        |                    | 10**: ITULAB                         |
        +--------------------+--------------------------------------+
        | ResolutionUnit**   | 2: inch                              |
        +--------------------+--------------------------------------+
        | RowsPerStrip**     | n: number of scanlines per TIFF strip|
        +--------------------+--------------------------------------+
        | SamplesPerPixel    | 1**: L* (lightness)                  |
        |                    | 3: LAB, RGB, CMY                     |
        |                    | 4: CMYK                              |
        +--------------------+--------------------------------------+
        | Software*          | {ASCII}: name & release number of    |
        |                    | creator software                     |
        +--------------------+--------------------------------------+
        | StripByteCounts**  | <n>: number or bytes in TIFF strip   |
        +--------------------+--------------------------------------+
        | StripOffsets**     | <n>: offset from beginning of file to|
        |                    | each TIFF strip                      |
        +--------------------+--------------------------------------+
        | XResolution        | 100, 200**, 300, 400 (pixels/inch)   |
        +--------------------+--------------------------------------+
        | YResolution        | equal to XResolution (pixels must be |
        |                    | square)                              |
        +--------------------+--------------------------------------+
        | Extension Fields                                          |
        +--------------------+--------------------------------------+
        | DocumentName*      | {ASCII}: name of scanned document    |
        +--------------------+--------------------------------------+
        | PageNumber**       | n,m: page number followed by total   |
        |                    | page count                           |
        +--------------------+--------------------------------------+
        | Indexed            | 0: not a palette-color image         |
        |                    | 1: palette-color image               |
        +--------------------+--------------------------------------+
        | New Fields                                                |
        +--------------------+--------------------------------------|
        | Decode             | minL, maxL, mina, maxa, minb, maxb:  |
        |                    | minimum and maximum values for L*a*b*|
        +--------------------+--------------------------------------+
        | GlobalParameters   | IFD: global parameters IFD           |
        | IFD*               |                                      |
        +-----------------------------------------------------------+





Buckley et al.              Expires December 2003              [Page 54]

Internet Draft        File Format for Internet Fax             June 2003


        +--------------------+--------------------------------------+
        | ProfileType*       | n: type of data stored in TIFF file  |
        +--------------------+--------------------------------------+
        | FaxProfile*        | n: ITU-compatible fax profile        |
        +--------------------+--------------------------------------+
        | CodingMethods*     | n: compression algorithms used in    |
        |                    | file                                 |
        +--------------------+--------------------------------------+
        | VersionYear*       | byte sequence: year of ITU fax std   |
        +--------------------+--------------------------------------+



8. Profile M - Mixed Raster Content Profile

   This section defines the Mixed Raster Content profile or Profile M
   of TIFF for facsimile. Implementations of this profile are required
   To implement Profiles S and C, and may optionally implement Profiles
   F, J and L.

8.1. Overview

   Unlike previous fax profiles, which use a single coding method and
   resolution for an entire fax page, Mixed Raster Content [T.44]
   enables different coding methods and resolutions within a single
   page. For example, consider a page that contains black-and-white
   text, which is best coded with MMR or JBIG, a color bar chart, best
   coded with JBIG, and a scanned color image, best coded with JPEG.
   Similarly, while spatial resolution of 400 pixels per inch may be
   best for the black-and- white text, 200 pixel per inch is usually
   sufficient for a color image.

   Rather than applying one coding method and resolution to all
   elements, MRC allows multiple coders and resolutions within a page.
   By itself, MRC does not define any new coding methods or
   resolutions. Instead it defines a 3-layer image model for
   structuring and combining the scanned image data. The MRC 3-layer
   model has been applied here using the TIFF format to yield a data
   structure which differs from [T.44] though it applies the same
   coding methods, uses the same compressed image data streams and is
   consistent with the TIFF principle of a single IFD per image.

8.1.1. MRC 3-layer model

   The 3 layers of the MRC model are Foreground and Background, which
   are both multi-level, and Mask, which is bi-level. Each layer may
   appear only once on a page and is coded independently of the other
   two layers. The final image is obtained by using the Mask layer to
   determine if output pixels come from the Foreground layer or the


Buckley et al.              Expires December 2003              [Page 55]

Internet Draft        File Format for Internet Fax             June 2003


   Background layer. When the Mask layer pixel value is 1, the
   corresponding pixel from the Foreground layer is selected; when it
   is 0, the corresponding pixel from the Background layer is selected.
   Details are given in the Introduction of [T.44].

   In our earlier example, the shape of the black-and-white text and
   the mask for the color chart could be in the Mask layer, the color
   of the chart and text in the Foreground layer, and the color image
   in the Background layer.  If a Mask layer pixel has a value of 1,
   the final image pixel will be, depending on the pixel location, from
   either the color chart or text color in the Foreground layer. If a
   Mask layer pixel has a value of 0, the final image pixel will be
   from the color image in the Background layer.

   Each layer is an image and, when present, is represented by at least
   one IFD in a TIFF file. This is consistent with TIFF, which provides
   fields to define the attributes, such as resolution, image size,
   bits per sample, etc., of a single image or layer. The distribution
   of content among layers is determined by the writer, as is the
   choice of coding method, color encoding and spatial resolution for a
   layer.

   Not all pages, and not all parts of a page, require 3 layers. If a
   page consists of only one layer, then that layer is the primary
   image whether it is a Background, Mask, or Foreground layer. If
   there is more than one layer, then the Mask must be one of the
   layers, in which case it is the primary image. In all cases, the
   primary image must be page size.

   MRC [T.44] allows a page to be transmitted as a series of stripes
   with each stripe consisting of 1, 2 or 3 layers. The number of
   scanlines in each stripe can vary over the page. Although [T.44]
   does not allow overlap between images of a single layer, the MRC
   profile permits overlapping IFDs when one of the IFDs is used only
   to define a default image color. According to [T.4] Annex H, stripes
   having more than 1 layer SHOULD NOT be more than 256 lines in length
   unless the capability to receive longer stripes has been negotiated.

   Furthermore, color fax also requires the spatial resolutions of
   Background and Foreground images to be legal fax values that are
   also integer factors of the Mask image resolution. For example, if
   the Mask Layer resolution is 400 pixels per inch, then allowed
   resolutions for the Foreground and Background layers are 100, 200 or
   400 pixels per inch; if the Mask is at 300 pixels per inch, then
   allowed values are 100 and 300. The Foreground and Background layer
   resolutions can be independently set of each other.





Buckley et al.              Expires December 2003              [Page 56]

Internet Draft        File Format for Internet Fax             June 2003


8.1.2. A TIFF Representation for the MRC 3-layer model

   In the TIFF representation of the 3-layer MRC model, each page is
   represented by a single IFD, called the Primary IFD. The nextIFD
   offset associated with a Primary IFD will point to the Primary IFD
   of the next page.  If the page consists of a single layer, then the
   Primary IFD represents that layer. If more than one layer is present,
   the Primary IFD represents the Mask layer and the other layers are
   represented by a set of child IFDs that are referenced through the
   SubIFD extension field [TTN1] of the Primary IFD. To distinguish MRC-
   specific SubIFDs from other SubIFDs, the NewSubFileType field MUST
   have Bit 4 ON, indicating an MRC-related IFD. A new ImageLayer field
   is also introduced that consists of two values that identify the
   layer (Foreground, Background, or Mask) and the order within the
   layer (first, second, ... image of the layer); see Section 8.2.3

   In Profile M, the Primary IFD represents a complete layer and
   corresponds to the primary image described in Section 8.1.1.  There
   must be no other MRC-related IFDs or SubIFDs that contain image data
   corresponding to the layer represented by the Primary IFD.

   MRC [T.44] allows a page to be transmitted as a series of stripes. A
   strip within an IFD in a Profile M file represents a stripe in a
   [T.44] data stream.  The [T.44] stripes of the Primary image are
   represented by a single, multiple-strip IFD; the [T.44] stripes of
   other layers are represented as multiple, single-strip IFDs.

   The layer represented by the Primary IFD may consist of strips of
   image data, but all the strips must be part of the single Primary
   IFD.  For example, if the page consisted of only the Background
   layer, then all strips associated with the Background layer must be
   treated as a single image.  Because MRC allows stripes with variable
   numbers of scanlines, a reader MUST support StripRowCounts field
   because a writer may use it in place of the RowsPerStrip field to
   support a variable number of scanlines in each strip of the Primary
   IFD.  In accordance with [TTN2], each strip shall be independently
   encoded, but coding parameters may not change between strips.

   Layers other than the layer represented by the Primary IFD store
   each strip as a separate IFD, allowing the coding parameters to
   change from strip-to-strip as described by the MRC standard [T.44].
   In all cases, if the Mask layer exists, it shall be represented by a
   single IFD and a single set of coding parameters.

   The use of SubIFDs to store child IFDs is described in [TTN1]. When
   the Mask is the primary image, the Background and Foreground layer
   images are represented with child IFDs that are referenced by the
   SubIFDs field in the Primary IFD.  There are many possible ways to
   represent the Background and Foreground layer images: (1) the
   SubIFD field of the Primary IFD is an array of pointers to all

Buckley et al.              Expires December 2003              [Page 57]

Internet Draft        File Format for Internet Fax             June 2003


   child image IFDs, one entry per child image; (2) the SubIFD field is
   a single pointer to a linked list of all child image IFDs; (3) the
   SubIFD field is an array of two pointers, where the first pointer is
   to a linked list of all Background layer image IFDs, and the second
   pointer is to a linked list of all Foreground layer image IFDs. A
   Profile M writer SHOULD structure the Background and Foreground
   layer images using (3), as shown in the example below. Furthermore,
   the child IFDs representing the Background and Foreground layer
   images SHOULD be ordered in the file in the same order as they occur
   on the page. However, a Profile M reader must scan all available
   child IFDs to locate and identify IFDs associated with MRC layers.

                               (nextIFD)
  PRIMARY IFD PAGE 0  -----------------------> PRIMARY IFD PAGE 1--> ...
            ImageLayer = [2,1]
            NewSubFileType = 18
            SubIFD[0] ---------------------- SubIFD[1]
                 |                                |
                 V                                V
              Child IFD                        Child IFD
                 ImageLayer = [1,1]               ImageLayer = [3,1]
                 NewSubFileType = 16              NewSubFileType = 16
                 |                                |
                 |(nextIFD)                       |(nextIFD)
                 V                                V
              Child IFD                        Child IFD
                 ImageLayer = [1,2]               ImageLayer = [3,2]
                 NewSubFileType = 16              NewSubFileType = 16
                 |                                |
                 |(nextIFD)                       |(nextIFD)
                 V                                V
              Child IFD                        Child IFD
                 ImageLayer = [1,3]               ImageLayer = [3,3]
                 NewSubFileType = 16              NewSubFileType = 16
                 |                                |
                 |(nextIFD)                       |(nextIFD)
                 V                                V
                 0                                0


   The XPosition and YPosition TIFF fields specify the offset to the
   upper-left corner of the IFD in resolution units, which are inches
   in Profile M; see Section 8.2.2. The Primary IFD must not use
   XPosition or YPosition fields.

   MRC [T.44] allows the specification of a default image color that is
   to be applied in the event no image data is transmitted for a given
   stripe and layer. The new field ImageBaseColor is used to store



Buckley et al.              Expires December 2003              [Page 58]

Internet Draft        File Format for Internet Fax             June 2003


   default image color specifications in Profile M, see 8.2.3. By
   setting the StripByteCounts array to zero values, an IFD defining a
   default color but containing no encoded image data can be specified.
   ImageBaseColor can also be used in IFDs that contain encoded image
   data.  In that case, the fields of the IFD must accurately reflect
   the encoding of the image data. If the StripByteCount entry for a
   given strip is 0, then the ImageBaseColor is used for that strip. If
   the encoded image data is ITU L*a*b, the ImageBaseColor is
   interpreted using the encoding parameters of the image data.  If the
   image data is not ITU L*a*b*, the ImageBaseColor is interpreted as
   8-bit ITU L*a*b*; see Section 8.2.3.

8.2. Required TIFF Fields

   This section describes the TIFF fields required, in addition to
   those in Section 2.2.1, to represent MRC fax images. Since MRC
   stores fax data as a collection of images corresponding to layers or
   parts of layers, the coding methods, color encodings and spatial
   resolutions used by previous profiles apply to Profile M. Therefore,
   the descriptions here will typically reference the appropriate
   earlier sections. Fields and values specific to Profile M are
   pointed out.

8.2.1. Baseline Fields

ImageWidth(256).                                           SHORT or LONG
   Same page widths as Profile C, the base color profile; see Section
   6.2.1.  In Profile M, the width of a Foreground or Background image
   in the coded data stream may be less than the page width, unless the
   Background or Foreground is the primary image, in which case the
   width of the coded data stream is the page width. The ImageWidth
   field will always store the actual width of the coded data.

NewSubFileType(254) = 16, 18.                                       LONG
   For Profile M, the NewSubFileType field has two bits that are
   required.  Bit 1 indicates a single page of a multi-page document
   and must be set for the Primary IFD; Bit 4 indicates the MRC imaging
   model as described in ITU-T Recommendation T.44 [T.44], and must be
   set for Primary IFDs and all MRC-specific child IFDs.

BitsPerSample(258) = 1, 2-8, 9-12                                  SHORT
SamplesPerPixel(277) = 1, 3, 4.                                    SHORT
Compression(259) = 1, 3, 4, 7, 9, 10.                              SHORT
   For Mask layer, see Sections 4.2.1 and 5.2.1
   For Foreground and Background layers, see Sections 6.2.1 and 7.2.1
   Compression=1 is not used by previous profiles. An IFD used only to
   specify the default image color for a layer and strip will not have
   any encoded image data associated with it, i.e., the StripByteCounts
   field will contain a 0. Since no image data exists in the IFD, the


Buckley et al.              Expires December 2003              [Page 59]

Internet Draft        File Format for Internet Fax             June 2003


   Compression field shall be set to 1 indicating no compression.  A
   Compression field value of 1 is not allowed for any other IFDs.

FillOrder(266) = 1 , 2.                                            SHORT
RequiredByTIFFBaseline
   Profile M readers must be able to read data in both bit orders, but
   the vast majority of facsimile products store data LSB first,
   exactly as it appears on the telephone line
          1 = Most Significant Bit first.
          2 = Least Significant Bit first

PhotometricInterpretation(262) = 0, 2, 10.                   SHORT
   For Mask layer, 0.  For Foreground and Background layers, see
   Sections 6.2.1 and 7.2.1.

ResolutionUnit(296) = 2.                                           SHORT
   The unit of measure for resolution. 2 = inch
   ITU-T standards only specify inch-based resolutions for color fax
   Default = 2 (field may be omitted if this is the value).

StripByteCounts(279)                                    SHORT or LONG
   In Profile M, it is permissible for the StripByteCounts value for a
   given strip to have a zero entry.  This means there is no encoded
   image data corresponding to that strip.  Instead, the current
   default image color should be used for the strip.  The standard
   default image colors are black for the Foreground layer and White
   for the Background layer.  The ImageBaseColor field can be used to
   specify other default colors, see 8.2.3.

XResolution(282) = 100, 200, 300, 400.                          RATIONAL
YResolution(283) = 100, 200, 300, 400.                          RATIONAL
   The resolution of the image is expressed in pixels per resolution
   unit. In pixels per inch, allowed XResolution values for all layers
   are: 100, 200, 300, and 400. Color fax requires the pixels to be
   square, hence YResolution must equal XResolution for all layers. The
   resolution of Background and Foreground layers must each be an
   integer factor of the Primary image, which is the Mask layer, when
   it is present; see Section 8.4.

8.2.2. Extension Fields

ChromaSubSampling(530).                                            SHORT
ChromaPositioning(531).                                            SHORT
   For Foreground and Background layers, see Section 6.2.2.

Indexed(346) = 0, 1.                                               SHORT
   For Foreground and Background layers: 1 indicates a palette-color
   image, see Section 7.2.2.



Buckley et al.              Expires December 2003              [Page 60]

Internet Draft        File Format for Internet Fax             June 2003

T4Options(292) = 0, 1, 4, 5.                                       SHORT
T6Options(293) = 0.                                                SHORT
   For Mask layer, see Section 4.2.2.

SubIFDs(330).                                                        IFD
   Count = number of child IFDs.  Each value is an offset from the
   beginning of the TIFF file to a child IFD [TTN1].

XPosition(286).                                                 RATIONAL
YPosition(287).                                                 RATIONAL
   Specifies the horizontal and vertical offsets of the top-left of the
   IFD from the top-left of the Primary IFD in resolution units.  For
   example, if the Primary IFD is at 400 pixels per inch, and a
   foreground layer IFD is at 200 pixels per inch and located at pixel
   coordinate (345, 678) with respect to the Primary IFD, the XPosition
   value is 345/400 and the YPosition value is 678/400 in inches.

   The Primary IFD does not use the XPosition or YPosition fields.  The
   XPosition and YPosition values must be specified for MRC child IFDs;
   there is no default value.


8.2.3. New Fields

Decode(433).                                                   SRATIONAL
   For Foreground and Background layers, see Section 6.2.3.

T82Options(435)                                                     LONG
   For Mask layer, see Section 5.2.3.

ImageBaseColor(434).                                               SHORT
   Count = SamplesPerPixel
   In areas of an image layer where no image data is available (i.e.
   where no strips are defined, or where the StripByteCounts entry for
   a given strip is 0), the color specified by ImageBaseColor will be
   used.

   If the ImageBaseColor field is used in an IFD that contains image
   data encoded in ITU L*a*b*, then the ImageBaseColor will be
   interpreted with the color encoding parameters of the image data
   (i.e., color gamut, illuminant, bit/sample, and decode). If the
   ImageBaseColor field is used in an IFD that contains image data that
   is not encoded in ITU L*a*b, then the ImageBaseColor SHALL be
   interpreted as 8 bits/sample, 3 samples/pixel ITU L*a*b*.  If the
   ImageBaseColor field is used in an IFD that contains no encoded
   image data, then the ImageBaseColor SHALL be interpreted as 8
   bits/sample, 3 samples/pixel ITU L*a*b*.  If the fax data stream
   requires a different encoding, then transferring the default color
   value between a TIFF file and fax data stream requires a color
   conversion.


Buckley et al.              Expires December 2003              [Page 61]

Internet Draft        File Format for Internet Fax             June 2003


   A [T.44] stripe may contain a Foreground or Background image less
   than full stripe size, with the rest of the stripe assuming a
   default image color. In this case, the default image color is imaged
   first, followed by the image data. In Profile M, this is represented
   as a child IFD containing no encoded image data but specifying the
   default image color in the ImageBaseColor field.  A second child IFD
   contains the image data. To insure the default image color is imaged
   first, the order value in the ImageLayer field of the IFD defining
   the ImageBaseColor field MUST have a lower value than the order
   value in the ImageLayer field of the IFD defining the image data.

   To define a child IFD specifying a ImageBaseColor but containing no
   encoded image data, create an IFD with the following settings.

      ImageLayer[0]:             specified layer
      ImageLayer[1]:             less than any other IFDs corresponding
                                 to the same layer and strip.
      RowsPerStrip:              strip height
      ImageLength:               strip height
      ImageWidth:                full image width
      BitsPerSample:             8
      PhotometricInterpretation: 10 (ITULAB)
      SamplesPerPixel:           3
      Compression:               1 (none)
      X/YResolution:             that of the Primary IFD
      XPosition:                 0
      YPosition:                 the offset from the top of the page to
                                 the beginning of the strip in the
                                 resolution units of inches
      StripByteCounts:           single 0 value
      StripOffsets:              single 0 entry
      NewSubFileType:            bit 4 O     (MRC)
      ImageBaseColor:            desired color in 8 bit ITULAB

   For the Foreground layer image, the default value for the
   ImageBaseColor field is black. For other cases, including the
   Background layer image, the default value is white.

StripRowCounts(559).                                                LONG
   Count = number of strips
   The number of scanlines stored in a strip. Profile M allows each fax
   strip to store a different number of scanlines. For strips with more
   than one layer the maximum strip size is either 256 scanlines or
   full page size. The 256 maximum SHOULD be used unless the capability
   to receive longer strips has been negotiated. This field replaces
   RowsPerStrip for IFDs with variable-sized strips. Only one of the
   two fields, StripRowCounts and RowsPerStrip, may be used in an IFD.




Buckley et al.              Expires December 2003              [Page 62]

Internet Draft        File Format for Internet Fax             June 2003


ImageLayer (34732).                                                 LONG
   Count = 2
   Image layers are defined such that layer 1 is the Background layer,
   layer 3 is the Foreground layer, and layer 2 is the Mask layer,
   which selects pixels from the Background and Foreground layers. The
   ImageLayer tag contains two values, describing the layer to which
   the image belongs and the order in which it is imaged.

   ImageLayer[0] = 1, 2, 3.
   1: Image is a Background image, i.e., the image that will appear
      whenever the Mask contains a value of 0. Background images
      typically contain low-resolution, continuous-tone imagery.
   2: Image is the Mask layer. In MRC, if the Mask layer is present, it
      must be the Primary IFD and be full page in extent.
   3: Image is a Foreground image, i.e., the image that will appear
      whenever the Mask contains a value of 1. The Foreground image
      generally defines the color of text or lines, but may also
   contain high-resolution imagery.

   ImageLayer[1]:
   1: first image to be imaged in this layer,
   2: second image to be imaged in this layer,
   3: ...

   In Profile M, more than one image can exist in a single layer.
   ImageLayer[1] specifies the order in which images within a single
   layer are to be imaged.  This insures that overlapping images within
   a single layer are imaged correctly.

   If an IFD contains no encoded image data and is used to only specify
   the ImageBaseColor field, the value of ImageLayer[1] must be less
   than that of any other IFD corresponding to the same layer and strip
   to insure the image data is interpreted as on top of the default
   color.

   In Profile M, it is possible to have only a single layer. For
   example, if a page contains only a single continuous-tone
   photograph, then only the Background layer would occur. In this
   case, the Background layer will be stored as the Primary IFD.
   ImageLayer[0] will be 1 indicating Background; ImageLayer[1] will be
   1 since there can be no other IFDs associated with that layer. No
   Mask layer will exist.


8.3. Recommended TIFF Fields

   See Sections 2.2.3. and 2.2.4.




Buckley et al.              Expires December 2003              [Page 63]

Internet Draft        File Format for Internet Fax             June 2003


8.4. Rules and Requirements for Images

   Profile M defines a fundamental set of rules for images in the 3
   layer representation.

   1. If more than one layer exists, then the binary Mask layer SHALL
      be present and be the primary image. The Mask layer SHALL support
      the binary data representations defined in Section 3 and MAY
      support the binary data representations defined in Sections 4 and
      5, with the exception that PhotometricInterpretation MUST be 0.
      If only one layer exists, then the image corresponding to that
      layer is the primary image.

   2. The Primary IFD defines and extends to the entire page boundary;
      all attached model images cannot extend beyond the Primary image.
      Resolution differences may cause some pixels to "hang over" the
      page boundary, but no new pixels should exist completely beyond
      the page extent.

   3. The Background and Foreground images SHALL support the color
      representations defined in Section 6 and MAY support the color
      representations defined in Section 7. These images MAY optionally
      cover only a portion of the strip or page.

   4. Each Primary IFD and each MRC-specific SubIFD must have an
      ImageLayer field to specify which layer the IFD belongs to, and
      the imaging order of that IFD within the layer.

   5. Each Primary IFD must have a NewSubFileType field value set to
      18, indicating a single page of a multi-page document (bit 1) and
      MRC (bit 4).

   6. Each MRC-specific child IFD must have a NewSubFileType field
      value set to 16, indicating MRC (bit 4).

   7. In MRC fax, each layer is transmitted as a sequence of strips.
      If the page consists of a single layer, then all strips shall be
      stored in the single Primary IFD.  In this case, coding
      parameters cannot change between strips.  If the page consists of
      more than one layer, then all strips of the Mask layer shall be
      stored in the single Primary IFD.  All strips of the Foreground/
      Background layers SHALL be stored in separate IFDs, referenced by
      the Primary IFD's SubIFD field, containing an ImageLayer field
      with ImageLayer[0] identifying either Background (layer 1) or
      Foreground (layer 3), and Imagelayer[1] identifying order in
      which images within a single layer are to be imaged. The TIFF
      XPosition and YPosition fields are used to indicate the placement
      of these images with respect to the primary image.



Buckley et al.              Expires December 2003              [Page 64]

Internet Draft        File Format for Internet Fax             June 2003


   8. When the Mask image is present, the resolution of Background and
      Foreground images must each be an integer factor of the Mask
      image. For example, if the Mask image is 400 pixels/inch, then
      the Background or Foreground image may be at 400 pixels/inch
      (400/1), 200 pixels/inch (400/2) or 100 pixels/inch (400/4).

8.5. Profile M - MRC Fax Profile Summary

   Recommended fields are shown with an asterisk *

   Required fields or values are shown with a double asterisk **. If the
   double asterisk is on the field name, then all the listed values are
   required of implementations; if the double asterisks are in the
   Values column, then only the values suffixed with a double asterisk
   are required of implementations.

     +------------------+-----------------------------------------+
     | Baseline Fields  |               Values                    |
     +------------------+-----------------------------------------+
     | BitsPerSample    | 1**: binary mask, RGB, CMY(K)           |
     |                  | 2-8**: bits per color sample            |
     |                  | 9-12: optional 12 bits/sample           |
     +------------------+-----------------------------------------+
     | Compression      | 1: None (ImageBaseColor IFD only)       |
     |                  | 3**: Modified Huffman and Modified Read |
     |                  | 4: Modified Modified Read               |
     |                  | 7**: JPEG                               |
     |                  | 9: JBIG, per T.85                       |
     |                  | 10: JBIG, per T.43                      |
     +------------------+-----------------------------------------+
     | DateTime*        | {ASCII): date/time in the 24-hour format|
     |                  | "YYYY:MM:DD HH:MM:SS"                   |
     +------------------+-----------------------------------------+
     | FillOrder**      | 1: Most significant bit first           |
     |                  | 2: Least significant bit first          |
     +------------------+-----------------------------------------+
     | ImageDescription*| {ASCII}: A string describing the        |
     |                  | contents of the image.                  |
     +------------------+-----------------------------------------+
     | ImageWidth       | 864, 1024, 1216, 1728**, 2048, 2432,    |
     |                  | 2592, 3072, 3456, 3648, 4096, 4864      |
     |                  | Note, legal widths for the Primary IFD. |
     +------------------+-----------------------------------------+
     | ImageLength**    | n: total number of scanlines in image   |
     +------------------+-----------------------------------------+
     | NewSubFileType** | 16, 18:                                 |
     |                  | Bit 1 indicates single page of a multi- |
     |                  | page document on Primary IFD            |
     |                  | Bit 4 indicates MRC model               |
     +------------------+-----------------------------------------+

Buckley et al.              Expires December 2003              [Page 65]

Internet Draft        File Format for Internet Fax             June 2003


     +------------------+-----------------------------------------+
     | Orientation      | 1**-8, Default 1                        |
     +------------------+-----------------------------------------+
     | PhotometricInter | 0**:  WhiteIsZero  (Mask Layer)         |
     | pretation        | 2:  RGB                                 |
     |                  | 10**: ITULAB                            |
     +------------------+-----------------------------------------+
     | ResolutionUnit** | 2: inch                                 |
     +------------------+-----------------------------------------+
     | RowsPerStrip     | n: number or scanlines per strip        |
     +------------------+-----------------------------------------+
     | SamplesPerPixel  | 1**: L* (lightness)                     |
     |                  | 3: RGB, LAB, CMY                        |
     |                  | 4: CMYK                                 |
     +------------------+-----------------------------------------+
     | Software*        | {ASCII}: name & release number of       |
     |                  | creator software                        |
     +------------------+-----------------------------------------+
     | StripByteCounts**| <n>: number or bytes in each strip      |
     +------------------+-----------------------------------------+
     | StripOffsets**   | <n>: offset from beginning of file to   |
     |                  | each TIFF strip                         |
     +------------------+-----------------------------------------+
     | XResolution      | 100, 200**, 300, 400 (written in        |
     |                  | pixels/inch)                            |
     +------------------+-----------------------------------------+
     | YResolution      | equal to XResolution (pixels must be    |
     |                  | square)                                 |
     +------------------+-----------------------------------------+
     | Extension Fields                                           |
     +------------------+-----------------------------------------+
     | T4Options        | 0**: required if Compression is Modified|
     |                  | Huffman, EOLs not byte aligned          |
     |                  | 1: required if Compression 2D Modified  |
     |                  | Read, EOLs are not byte aligned         |
     |                  | 4**: required if Compression Modified   |
     |                  | Huffman, EOLs byte aligned              |
     |                  | 5: required if Compression 2D Modified  |
     |                  | Read, EOLs are byte aligned             |
     +------------------+-----------------------------------------+
     | T6Options        | 0: required if Compression is 2D        |
     |                  | Modified Modified Read                  |
     +------------------+-----------------------------------------+
     | DocumentName*    | {ASCII}: name of scanned document       |
     +------------------+-----------------------------------------+
     | PageNumber**     | n,m: page number followed by total page |
     |                  | count                                   |
     +------------------+-----------------------------------------+



Buckley et al.              Expires December 2003              [Page 66]

Internet Draft        File Format for Internet Fax             June 2003


     +------------------+-----------------------------------------+
     | ChromaSubSampling| (1,1), (2, 2)**                         |
     |                  | (1, 1): equal numbers of lightness and  |
     |                  | chroma samples horizontally & vertically|
     |                  | (2, 2): twice as many lightness samples |
     |                  | as chroma horizontally and vertically   |
     +------------------+-----------------------------------------+
     | ChromaPositioning| 1: centered                             |
     +------------------+-----------------------------------------+
     | Indexed          | 0: not a palette-color image            |
     |                  | 1: palette-color image                  |
     +------------------+-----------------------------------------+
     | SubIFDs          | <IFD>: byte offset to FG/BG IFDs        |
     +------------------+-----------------------------------------+
     | XPosition        | horizontal offset in primary IFD        |
     |                  | resolution units                        |
     +------------------+-----------------------------------------+
     | YPosition        | vertical offset in primary IFD          |
     |                  | resolution units                        |
     +------------------+-----------------------------------------+
     | New Fields                                                 |
     +------------------+-----------------------------------------+
     | Decode           | minL, maxL, mina, maxa, minb, maxb:     |
     |                  | minimum and maximum values for L*a*b*   |
     +------------------+-----------------------------------------+
     | ImageBaseColor   | a,b,c: background color in ITULAB       |
     +------------------+-----------------------------------------+
     | StripRowCounts   | <n>: number of scanlines in each strip  |
     +------------------+-----------------------------------------+
     | ImageLayer       | n, m: layer number, imaging sequence    |
     |                  | (e.g., strip number)                    |
     +------------------+-----------------------------------------+
     | T82Options       | 0: T.85 profile of T.82 coding          |
     +------------------+-----------------------------------------+
     | GlobalParameters | IFD: global parameters IFD              |
     | IFD*             |                                         |
     +------------------+-----------------------------------------+
     | ProfileType*     | n: type of data stored in TIFF file     |
     +------------------+-----------------------------------------+
     | FaxProfile*      | n: ITU-compatible fax profile           |
     +------------------+-----------------------------------------+
     | CodingMethods*   | n: compression algorithms used in file  |
     +------------------+-----------------------------------------+
     | ModeNumber*      | n: version of T.44 standard             |
     +------------------+-----------------------------------------+
     | VersionYear*     | byte sequence: year of ITU fax standard |
     +------------------+-----------------------------------------+




Buckley et al.              Expires December 2003              [Page 67]

Internet Draft        File Format for Internet Fax             June 2003


9. MIME content-types image/tiff and image/tiff-fx

   The MIME content-types image/tiff and image/tiff-fx are used for
   TIFF-FX encoded image data, as defined in this document. [TIFF-REG] and
   [TIFF-FX-REG] describe the registration of these MIME content-types.














































Buckley et al.              Expires December 2003              [Page 68]

Internet Draft        File Format for Internet Fax             June 2003



10. Security Considerations

   This document describes a file format for Internet fax, which is a
   series of profiles of TIFF for facsimile. As such, it does not create
   any security issues not already identified in [TIFF-REG], in its use
   of fields as defined in [TIFF].  There are also new TIFF fields
   defined within this specification, but they are of a purely
   descriptive nature, so that no new security risks are incurred.

   Further, the encoding specified in this document does not in any way
   preclude the use of any Internet security protocol to encrypt,
   authenticate, or non-repudiate TIFF-encoded facsimile messages.

11. References

11.1 Normative References

   [REQ] Bradner, S, "Key words for use in RFCs to Indicate Requirement
   Levels", RFC 2119, March 1997.

   [T.4] ITU-T Recommendation T.4, Standardization of group 3 facsimile
   apparatus for document transmission, October 1997

   [T.6] ITU-T Recommendation T.6, Facsimile coding schemes and coding
   control functions for group 4 facsimile apparatus, November 1988

   [T.30] ITU-T Recommendation T.30 - Procedures for Document Facsimile
   Transmission in the General Switched Telephone Network, June 1996

   [T.42] ITU-T Recommendation T.42, Continuous-tone colour
   representation method for facsimile, February 1996

   [T.43] ITU-T Recommendation T.43, Colour and gray-scale image
   representations using lossless coding scheme for facsimile, February
   1997

   [T.44] ITU-T Recommendation T.44, Mixed Raster Content (MRC), April
   1999.

   [T.81] ITU-T Recommendation T.81, Information technology - Digital
   compression and coding of continuous-tone still images - Requirements
   and guidelines, September 1992

   [T.85] ITU-T Recommendation T.85, Application profile for
   Recommendation T.82 - Progressive bi-level image compression (JBIG
   coding scheme) for facsimile apparatus, August 1995




Buckley et al.              Expires December 2003              [Page 69]

Internet Draft        File Format for Internet Fax             June 2003


   [T.82] ITU-T Recommendation T.82, Information technology - Coded
   representation of picture and audio information - Progressive bi-
   level image compression, March 1995

   [TIFF] Tag Image File Format, Revision 6.0, Adobe Developers
   Association, June 3, 1992,
   ftp://ftp.adobe.com/pub/adobe/devrelations/
   devtechnotes/pdffiles/tiff6.pdf

        The TIFF 6.0 specification dated June 3, 1992 specification (c)
        1986-1988, 1992 Adobe Systems Incorporated. All Rights Reserved.

   [TIFF-F0] TIFF Class F specification, Apr 28, 1990,
   ftp://ftp.faximum.com/pub/documents/tiff_f.txt

   [TIFF-REG] Parsons, G. and Rafferty J., "Tag Image File
   Format (TIFF) - image/tiff MIME Sub-type Registration", RFC 3302,
   September 2002

   [TTN1] Adobe PageMaker 6.0 TIFF Technical Notes, Sept. 14, 1995,
   http://www.adobe.com/supportservice/devrelations/PDFS/TN/TIFFPM6.pdf

   [TTN2] Draft TIFF Technical Note 2, Replacement TIFF/JPEG
   specification, March 17, 1995,
   ftp://ftp.uu.net/graphics/jpeg/

   [TIFF-FX-REG] McIntyre, L., Parsons, G. and Rafferty, J., "Tag Image
   File Format Fax eXtended (TIFF-FX) - image/tiff-fx MIME Sub-type
   Registration", RFC 3250, September 2002

   The ITU-T Recommendations are available at http://www.itu.ch.

11.2 Informative references

   [GUIDE] Cancio, V., Moldovan, M., Tamura, H., and Wing, D.,
   "Implementers Guide for Facsimile Using Internet Mail", RFC 3249,
   September 2002

   [TIFF-F] Parsons, G.  and J. Rafferty, "Tag Image File Format (TIFF)
   - F Profile for Facsimile", RFC 2306, March 1998.

   [VPIM 2] Vaudreuil G. and G. Parsons, "Voice Profile for Internet
   Mail - Version 2", work in progress, draft-ietf-vpim-vpimv2r2-05.txt,
   February 2002







Buckley et al.              Expires December 2003              [Page 70]

Internet Draft        File Format for Internet Fax             June 2003


12. Authors' Addresses

   Robert Buckley                     Dennis Venable
   Xerox Corporation                  Xerox Corporation
   Mailstop 0128-30E                  Mailstop 0128-27E
   800 Phillips Road                  800 Phillips Road
   Webster, NY 14580, USA             Webster, NY 14580, USA
   Voice: +1-585-422-1282             Voice: +1-585-422-3138
   Fax: +1-585-265-8871               Fax: +1-585-422-6117
   Email: rbuckley@crt.xerox.com      Email: dvenable@crt.xerox.com

   Lloyd McIntyre
   10328 S. Stelling Road
   Cupertino, CA 95014 USA
   Voice: +1-408-725-1624
   Email: lloyd10328@pacbell.net

   Glenn S. Parsons                   James Rafferty
   Nortel Networks                    Brooktrout Technology
   P.O. Box 3511, Station C           410 First Avenue
   Ottawa, Ontario K1Y 4H7, Canada    Needham, MA 02494 USA
   Phone: +1-613-763-7582             Phone: +1-781-433-9462
   Fax: +1-613-763-2697               Fax: +1-781-433-9268
   Email:                             Email: jraff@brooktrout.com
   Glenn.Parsons@NortelNetworks.com


























Buckley et al.              Expires December 2003              [Page 71]

Internet Draft        File Format for Internet Fax             June 2003


Annex A:  Summary of TIFF Fields for Internet Fax

   This annex includes tables which list by profile the TIFF fields used
   in the proposed fax file format.  The fields are organized into 3
   categories:

      1)  TIFF Baseline Fields
      2)  TIFF Extension Fields
      3)  New Fields.

   The tables include the allowed values for each fax profile. Entries
   other than explicit numbers are described by:

      n        - single number
      n, m     - 2 numbers
      a, b, c  - 3 numbers
      r        - rational number
      <n>      - array of numbers
      <b>      - byte sequence
      {ASCII}  - string
      IFD      - IFD byte offset
      <IFD>    - array of IFD byte offsets

   A blank entry in the table indicates that the field is not used by
   that particular fax profile.

Table A.1  TIFF Baseline Fields

            +---------------------------------------------------------+
            |                       Fax Profile                       |
            +---------------------------------------------------------|
            | Minimal | Extended |  JBIG  |  Lossy  |Lossless| Mixed  |
 +----------|   B&W   |    B&W   |  B&W   |  Color  | Color  | Raster |
 |   TIFF   |         |          |        |         |        | Content|
 |  Field   |    S    |     F    |   J    |    C    |   L    |   M    |
 +----------+---------+----------+--------+---------+--------+--------+
 | BitsPer  | 1       | 1        | 1      | 8       | 1, 2-8 | 1, 2-8 |
 | Sample   |         |          |        |         | 9-12   | 9-12   |
 +----------+---------+----------+--------+---------+--------+--------+
 | Compres- | 3       | 3, 4     | 9      | 7       | 10     | 3, 4, 7|
 | sion     |         |          |        |         |        | 9,10   |
 +----------+---------+----------+--------+---------+--------+--------+
 | DateTime |         | {ASCII}  | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
 +----------+---------+----------+--------+---------+--------+--------+
 | FillOrder| 2       | 1, 2     | 1, 2   | 1, 2    | 1, 2   | 1,2    |
 +----------+---------+----------+--------+---------+--------+--------+





Buckley et al.              Expires December 2003              [Page 72]

Internet Draft        File Format for Internet Fax             June 2003


 +----------+---------+----------+--------+---------+--------+--------+
 | ImageDes-|         | {ASCII}  | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
 | cription |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Image-   | n       | n        | n      | n       | n      | n      |
 | Length   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Image-   | 1728    | 1728, 2048, 2432  |   864, 1024, 1216, 1728,  |
 | Width    |         | 2592, 3072, 3456  |  2048, 2432, 2592, 3072,  |
 |          |         | 3648, 4096, 4864  |  3456, 3648, 4096, 4864   |
 |          |         | Note, for the Mixed Raster Content M profile  |
 |          |         | these widths apply to the Primary IFD.        |
 +----------+---------+----------+--------+---------+--------+--------+
 | NewSub-  | 2       | 2        | 2      | 2       | 2      | 16, 18 |
 | FileType |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Orien-   | 1       | 1-8      | 1-8    | 1-8     | 1-8    | 1-8    |
 | tation   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Photo-   | 0       | 0, 1     | 0, 1   | 10      | 2, 5,  | 0,     |
 | metric-  |         |          |        |         | 10     | 2,     |
 | Interp-  |         |          |        |         |        | 10     |
 | retation |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Resolu-  | 2       | 2, 3     | 2, 3   | 2, 3    | 2, 3   | 2, 3   |
 | tionUnit |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | RowsPer- | n       | n        | n      | n       | n      | n      |
 | Strip    |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Samples- | 1       | 1        | 1      | 1, 3    | 1, 3, 4| 1, 3, 4|
 | PerPixel |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Software |         | {ASCII}  | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
 +----------+---------+----------+--------+---------+--------+--------+
 | Strip-   | n       | <n>      | <n>    | <n>     | <n>    | <n>    |
 | Byte-    |         |          |        |         |        |        |
 | Counts   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Strip-   | n       | <n>      | <n>    | <n>     | <n>    | <n>    |
 | Offsets  |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | XResolu- | 204     | 200, 204, 300     |    100, 200, 300, 400     |
 | tion     | 200     | 400, 408          |                           |
 +----------+---------+----------+--------+---------+--------+--------+
 | YResolu- | 98, 196 | 98, 196, 100, 200 |    100, 200, 300, 400     |
 | tion     | 100,200 | 300, 391, 400     |                           |
 +----------+---------+----------+--------+---------+--------+--------+



Buckley et al.              Expires December 2003              [Page 73]

Internet Draft        File Format for Internet Fax             June 2003


Table A.2  TIFF Extension Fields

            +---------------------------------------------------------+
            |                       Fax Profile                       |
            +---------------------------------------------------------|
            | Minimal | Extended |  JBIG  |  Lossy  |Lossless| Mixed  |
 +----------|   B&W   |    B&W   |  B&W   |  Color  | Color  | Raster |
 |   TIFF   |         |          |        |         |        | Content|
 |  Field   |    S    |     F    |   J    |    C    |   L    |   M    |
 +----------+---------+----------+--------+---------+--------+--------+
 | Chroma-  |         |          |        | 1       |        | 1      |
 | Position-|         |          |        |         |        |        |
 | ing      |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Chroma-  |         |          |        | <1, 1>  |        | <1, 1> |
 | SubSampl-|         |          |        | <2, 2>  |        | <2, 2> |
 | ing      |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Document-|         | {ASCII}  | {ASCII}| {ASCII} | {ASCII}| {ASCII}|
 | Name     |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Indexed  |         |          |        |         | 0,1    | 0,1    |
 +----------+---------+----------+--------+---------+--------+--------+
 | Page-    | n, m    | n, m     | n, m   | n, m    | n, m   | n, m   |
 | Number   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | SubIFDs  |         |          |        |         |        | <IFD>  |
 +----------+---------+----------+--------+---------+--------+--------+
 | T4Options| 0, 4    | 0, 1,    |        |         |        | 0, 1,  |
 |          |         | 4, 5     |        |         |        | 4, 5   |
 +----------+---------+----------+--------+---------+--------+--------+
 | T6Options|         | 0        |        |         |        | 0      |
 +----------+---------+----------+--------+---------+--------+--------+
 | XPosition|         |          |        |         |        | r      |
 +----------+---------+----------+--------+---------+--------+--------+
 | YPosition|         |          |        |         |        | r      |
 +----------+---------+----------+--------+---------+--------+--------+














Buckley et al.              Expires December 2003              [Page 74]

Internet Draft        File Format for Internet Fax             June 2003


Table A.3   New Fields

            +---------------------------------------------------------+
            |                       Fax Profile                       |
            +---------------------------------------------------------|
            | Minimal | Extended |  JBIG  |  Lossy  |Lossless| Mixed  |
 +----------|   B&W   |    B&W   |  B&W   |  Color  | Color  | Raster |
 |   TIFF   |         |          |        |         |        | Content|
 |  Field   |    S    |     F    |   J    |    C    |   L    |   M    |
 +----------+---------+----------+--------+---------+--------+--------+
 | BadFax-  |         | n        |        |         |        |        |
 | Lines    |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | CleanFax-|         | 0, 1, 2  |        |         |        |        |
 | Data     |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Coding-  |         |          | n      | n       | n      | n      |
 | Method   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Consecu- |         | n        |        |         |        |        |
 | tiveBad- |         |          |        |         |        |        |
 | FaxLines |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Decode   |         |          |        | <r>     | <r>    | <r>    |
 +----------+---------+----------+--------+---------+--------+--------+
 | Fax-     |         |          | n      | n       | n      | n      |
 | Profile  |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Global-  |         | IFD      | IFD    | IFD     | IFD    | IFD    |
 | Parame-  |         |          |        |         |        |        |
 | tersIFD  |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Image-   |         |          |        |         |        | n, m   |
 | Layer    |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | T82-     |         |          | n      |         |        | n      |
 | Options  |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Image-   |         |          |        |         |        | <n>    |
 | BaseColor|         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Mode-    |         |          |        |         |        | n      |
 | Number   |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------|
 | Profile- |         |          | n      | n       | n      | n      |
 | Type     |         |          |        |         |        |        |
 +--------------------------------------------------------------------+




Buckley et al.              Expires December 2003              [Page 75]

Internet Draft        File Format for Internet Fax             June 2003


 +----------+---------+----------+--------+---------+--------+--------+
 | Strip-   |         |          |        |         |        | <n>    |
 | RowCounts|         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+
 | Version- |         |          |        | <b>     |<b>     |        |
 | Year     |         |          |        |         |        |        |
 +----------+---------+----------+--------+---------+--------+--------+












































Buckley et al.              Expires December 2003              [Page 76]

Internet Draft        File Format for Internet Fax             June 2003

Annex B. List of technical edits to RFC2301

   This Annex lists technical differences between this document and
   RFC 2301, the Proposed Standard File Format for Internet Fax.

   +----+---------+-------------------------------------------------+
   | No.| Section |             Technical Edit                      |
   +----+---------+-------------------------------------------------+
   | 1. | 5.2.1   | Added FillOrder=1 to Profile J                  |
   +----+---------+-------------------------------------------------+
   | 2. | 6.2.1   | Constrained ResolutionUnit to 2 (i.e. inch) for |
   |    | 7.2.1   | all color profiles, per ITU-T Recommendations   |
   |    | 8.2.1   |                                                 |
   +----+---------+-------------------------------------------------+
   | 3. | 7.2.1   | Deleted ColorMap field; it re-encoded the color |
   |    | 7.4     | color palette already in the T.43 data stream   |
   +----+---------+-------------------------------------------------+
   | 4. | 7.2.2   | Changed TAG value of Indexed field from 364 to  |
   |    |         | 346 to agree with Section 8.2.2 and Ref. [TTN1] |
   +----+---------+-------------------------------------------------+
   | 5. | 8.2.1   | Added text clarifying the use of ImageWidth     |
   |    |         | when Background or Foreground layer is Primary  |
   |    |         | IFD                                             |
   +----+---------+-------------------------------------------------+
   | 6. | 8.2.3   | Changed field name from DefaultImageColor to    |
   |    |         | ImageBaseColor;                                 |
   +----+---------+-------------------------------------------------+
   | 7. | 8.2.1   | Added Compression=1 for ImageBaseColor IFDs     |
   +----+---------+-------------------------------------------------+
   | 8. | 5.2.1   | Redefined compression = 9 to be T.82 (JBIG);    |
   |    | 5.2.3   | added T82Options field, with a default value (0)|
   |    |         | corresponding to the T.85 application profile   |
   +----+---------+-------------------------------------------------+
   | 9. | 4.3.3   | Added GlobalParametersIFD, ProfileType,         |
   |    | 4.7     | FaxProfile and CodingMethod to the New Fields   |
   |    |         | portion of Profile F, per Sec. 2.2.4            |
   +----+---------+-------------------------------------------------+
   | 10.|  6.2.1  | Deleted BitsPerSample=12 as an option when      |
   |    |6.2.3,6.4| Compression=7 due to lack of interop testing.   |
   |    |Table A.1|                                                 |
   +----+---------+-------------------------------------------------+
   | 11.|8.2.1,8.4| Deleted PhotometricInterpretation=5 in Profile M|
   |    |Table A.1| due to insufficient interop testing.            |
   +----+---------+-------------------------------------------------+
   | 12.|7.2.1,7.4| Deleted BitsPerSample=13-16 for Palette color   |
   |    |8.2.1,8.5| due to lack of interop testing.                 |
   |    |Table A.1|                                                 |
   +----+---------+-------------------------------------------------+
   | 13.| Annex B | Deleted Annex B due to discontinued use of      |
   |    |         | application parameter; Annex C renamed Annex B  |
   +----+---------+-------------------------------------------------+

Buckley et al.              Expires December 2003              [Page 77]

Internet Draft        File Format for Internet Fax             June 2003


Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREI     WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























Buckley et al.              Expires December 2003              [Page 78]


Html markup produced by rfcmarkup 1.111, available from https://tools.ietf.org/tools/rfcmarkup/