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Versions: 00 01 02 03 04 05 RFC 2531

IETF Fax working group                                    Graham Klyne
Request for comments: nnnn                    5GM/Content Technologies
Category: Work-in-progress                              Lloyd McIntyre
                                                     Xerox Corporation
                                                        8 January 1999
                                                    Expires: July 1999


               Content feature schema for Internet fax
                <draft-ietf-fax-feature-schema-05.txt>


Status of this memo

  This document is an Internet-Draft.  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''.

  To view the entire list of current Internet-Drafts, please check
  the "1id-abstracts.txt" listing contained in the Internet-Drafts
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  (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au
  (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US
  West Coast).

  [[INTENDED STATUS:  This document specifies an Internet standards
  track protocol for the Internet community, and requests discussion
  and suggestions for improvements.  Please refer to the current
  edition of the "Internet Official Protocol Standards" (STD 1) for
  the standardization state and status of this protocol.
  Distribution of this memo is unlimited.]]

Copyright Notice

  Copyright (C) The Internet Society 1998.  All Rights Reserved.

Abstract

  This document defines a content feature schema that is a profile of
  the media feature registration mechanisms [1,2,3] for use in
  performing capability identification between extended Internet fax
  systems [5].



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  This document does not describe any specific mechanisms for
  communicating capability information, but does presume that any
  such mechanisms will transfer textual values.  It specifies a
  textual format to be used for describing Internet fax capability
  information.















































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Table of contents

  1. Introduction ............................................4
     1.1 Organization of this document                        4
     1.2 Terminology and document conventions                 4
  2. Fax feature schema syntax ...............................5
  3. Internet fax feature tags ...............................5
     3.1 Image size                                           6
     3.2 Resolution                                           6
     3.3 Media type                                           7
     3.4 Paper Size                                           7
     3.5 Color capability                                     8
     3.6 Color model                                          9
     3.7 Image coding                                         11
  4. Examples ................................................13
     4.1 Simple mode Internet fax system                      13
     4.2 High-end black-and-white Internet fax system         14
     4.3 Grey-scale Internet fax system                       14
     4.4 Full-color Internet fax system                       15
     4.5 Full-color Internet fax system (MRC)                 16
     4.6 Sender and receiver feature matching                 16
  5. IANA considerations .....................................19
  6. Security considerations .................................19
     6.1 Capability descriptions and mechanisms               19
     6.2 Specific threats                                     19
  7. Full copyright statement ................................20
  8. Acknowledgements ........................................20
  9. References ..............................................20
  10. Authors' addresses .....................................23
  Appendix A: Feature registrations ..........................24
     A.1 Image size                                           24
     A.2 Resolution aspect ratio                              26
     A.3 Color levels                                         28
     A.4 Color space                                          30
     A.5 CIELAB color depth                                   33
     A.6 CIELAB color gamut                                   35
     A.7 Image file structure                                 38
     A.8 Image data coding                                    40
     A.9 Image coding constraint                              42
     A.10 JBIG stripe size                                    44
     A.11 Image interleave                                    46
     A.12 Color subsampling                                   48
     A.13 MRC availability and mode                           50
     A.14 MRC maximum stripe size                             52
  Appendix B: TIFF mode descriptions .........................54
  Appendix C: Revision history ...............................55





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1. Introduction

  This document defines a content feature schema that is a profile of
  the media feature registration mechanisms [1,2,3] for use in
  performing capability identification between extended Internet fax
  systems [5].

  This document does not describe any specific mechanisms for
  communicating capability information, but does presume that any
  such mechanisms will transfer textual values.  It specifies a
  textual format to be used for describing Internet fax capability
  information.

  The range of capabilities that can be indicated are based on those
  covered by the TIFF file format for Internet fax [7] and Group 3
  facsimile [6].  A companion document [4] describes the relationship
  and mapping between this schema and Group 3 fax capabilities.

1.1 Organization of this document

  Section 2 specifies the overall syntax for fax feature descriptions
  by reference to the media feature registration and syntax documents
  [1,2].

  Section 3 enumerates the feature tags that are to be recognized and
  processed by extended Internet fax systems, according to their
  capabilities.

  Appendix A contains additional feature tag registrations for media
  features that are specific to fax and for which no applicable
  registration already exists.  These are presented in the form
  prescribed by the media feature registration procedure [1].

1.2 Terminology and document conventions

  The term "extended Internet fax system" is used to describe any
  software, device or combination of these that conforms to the
  specification "Extended Facsimile Using Internet Mail" [5].

  "capability exchange" describes any transfer of information between
  communicating systems that is used to indicate system capabilities
  and hence determine the form of data transferred.  This term covers
  both one-way and two-way transfers of capability information.

  "capability identification" is a particular form of capability
  exchange in which a receiving system provides capability
  information to a sending system.





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  "capability description" is a collection of data presented in some
  specific format that describes the capabilities of some
  communicating entity.  It may exist separately from any specific
  capability exchange mechanism.

       NOTE:  Comments like this provide additional nonessential
       information about the rationale behind this document.
       Such information is not needed for building a conformant
       implementation, but may help those who wish to understand
       the design in greater depth.

2. Fax feature schema syntax

  The syntax for the fax feature schema is described by "A syntax for
  describing media feature sets" [2].  This in turn calls upon media
  feature tags that may be registered according to the procedure
  described in "Media Feature Tag Registration Procedure" [1].

       NOTE:  Media feature registration provides a base
       vocabulary of features that correspond to media handling
       capabilities.  The feature set syntax provides a
       mechanism and format for combining these to describe
       combinations of features.  This memo indicates those
       features that may be associated with extended Internet
       fax systems.

3. Internet fax feature tags

  This section enumerates and briefly describes a number of feature
  tags that are defined for use with extended Internet fax systems
  and applications.  These tags may be used also by other systems and
  applications that support corresponding capabilities.

  The feature tags presented below are those that an extended
  Internet fax system is expected to recognize its ability or non-
  ability to handle.

  Definitive descriptions of feature tags are indicated by reference
  to their registration per the media feature registration procedure
  [1] (some of which are appended to this document)

       NOTE:  The presence of a feature tag in this list does
       not mean that an extended Internet fax system must have
       that capability;  rather, it must recognize the feature
       tag and deal with it according to the capabilities that
       it does have.






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       Further, an extended Internet fax system is not prevented
       from recognizing and offering additional feature tags.
       The list below is intended to provide a basic vocabulary
       that all extended Internet fax systems can use in a
       consistent fashion.

       If an unrecognized or unused feature tag is received, the
       feature set matching rule (described in [2]) operates so
       that tag is effectively ignored.

3.1 Image size

  Feature tag name    Legal values
  ----------------    ------------
  size-x              <Rational> (>0)
  size-y              <Rational> (>0)

  Reference:  this document, Appendix A.

  These feature values indicate a rendered document size in inches.

  Where the actual size is measured in millimetres, a conversion
  factor of 10/254 may be applied to yield an exact inch-based value.

3.2 Resolution

  Feature tag name    Legal values
  ----------------    ------------
  dpi                 <Integer> (>0)
  dpi-xyratio         <Rational> (>0)

  Reference: "Media Features for Display, Print, and Fax" [3], and
  this document appendix A.

  If 'dpi-xyratio' is present and not equal to 1 then the horizontal
  resolution (x-axis) is indicated by the 'dpi' feature value, and
  the vertical resolution (y-axis) is the value of 'dpi' divided by
  'dpi-xyratio'.

  For example, the basic Group 3 fax resolution of 200*100dpi might
  be indicated as:

     (& (dpi=200) (dpi-xyratio=200/100) )

  When describing resolutions for an MRC format document, the
  complete set of usable resolutions is listed.  However, there are
  some restrictions on their use:  (a) 100dpi resolution can be used
  only with multi-level images, and (b) any multi-level image
  resolution is required to be an integral sub-multiple of the
  applicable mask resolution.


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3.3 Media type

  Feature tag name    Legal values
  ----------------    ------------
  ua-media            screen
                      screen-paged
                      stationery
                      transparency
                      envelope
                      envelope-plain
                      continuous

  Reference: "Media Features for Display, Print, and Fax" [3].

       NOTE: Where the recipient indicates specific support for
       hard copy or soft copy media type, a sender of color
       image data may wish to adjust the color components (e.g.
       per the related rules of ITU recommendation T.42 [9]) to
       improve rendered image quality on that medium.

3.4 Paper Size

  Feature tag name    Legal values
  ----------------    ------------
  paper-size          A4
                      A3
                      B4
                      letter
                      legal

  Reference: "Media Features for Display, Print, and Fax" [3].





















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3.5 Color capability

  Feature tag name    Legal values
  ----------------    ------------
  color               Binary  (bi-level only)
                      Limited (a limited number of colors)
                      Mapped  (palette or otherwise mapped color)
                      Grey    (grey-scale only)
                      Full    (full continuous-tone color)

  Reference: "Media Features for Display, Print, and Fax" [3].

  The intention here is to give a broad indication of color handling
  capabilities that might be used, for example, to select among a
  small number of available data resources.

  The value of this feature also gives an indication of the more
  detailed color handling features that might be applicable (see next
  section).

  'Binary' indicates blank-and-white, or other bi-level capability.
  No further qualifying feature tags are required.

  'Limited' indicates a small number of distinct fixed colors, such
  as might be provided by a highlight printer, pen plotter or limited
  color display.  The 'color-levels' tag should be used to indicate
  the number of distinct colors available.

       NOTE:  No ability to indicate any specific or named color
       is implied by this option.

       Some devices might use different intensity levels rather
       than different hues for distinction.

  'Mapped' indicates that pixel color values are mapped in some
  specifiable way to a multi-component color space.  The 'color-
  levels' tag may be used to indicate the number of distinct colors
  available;  in its absence, sufficient levels to display a
  photographic image should be assumed.

  'Grey' indicates a continuous tone grey-scale capability.

  'Full' indicates full continuous tone color capability.

  For 'Mapped', 'Grey' and 'Full' color, additional feature tags
  (section 3.6) may be used to further qualify the color
  reproduction.





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3.6 Color model

  Feature tag name    Legal values
  ----------------    ------------
  color-levels        <integer>   (>2)
  color-space         Device-RGB  (device RGB)
                      Device-CMY  (device CMY)
                      Device-CMYK (device CMYK)
                      CIELAB      (LAB per T.42 [9])
                      (may be extended by further registrations)
  CIELAB-L-depth      <integer>   (>0)
  CIELAB-a-depth
  CIELAB-b-depth
  CIELAB-L-min        <integer>
  CIELAB-L-max
  CIELAB-a-min
  CIELAB-a-max
  CIELAB-b-min
  CIELAB-b-max

  Reference: this document, appendix A.

  The general model for image handling (both color and non-color) is
  described here from a receiver's perspective;  a similar model
  operates in the reverse direction for a scan/send perspective:

       raw bit        pixel         color         physical
       stream  -(A)-> values -(B)-> values -(C)-> rendition

   -   "raw bit stream" is a stream of coded bits

  (A)  indicates image coding/decoding (MH,MR,MMR,JPEG,JBIG,etc.)

   -   "pixel values" are a single numeric value per picture element
       that designates the color of that element.

  (B)  indicates pixel-to-color value mapping

   -   "color values" have a separate numeric value for each color
       component (i.e. L*, a*, b* in the case of CIELAB indicated
       above.)

  (C)  indicates how the color values are related to a physical
       color.  This involves interpretation of the color value with
       respect to a color model (e.g. RGB, L*a*b*, CMY, CMYK) and a
       color space (which is typically recipient-dependent).

   -   "physical rendition" is a color value physically realized on a
       display, printer or other device.



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  There are many variables that can be applied at each stage of the
  processing of a color image, and any may be critical to meaningful
  handling of that image in some circumstances.  In other
  circumstances many of the variables may be implied (to some level
  of approximation) in the application that uses them (e.g. color
  images published on a Web page).

  The color feature framework described here is intended to allow
  capability description at a range of granularity:  feature tags
  which correspond to implied (or "don't care" or "unknown") feature
  values may simply be omitted from a capability description.

  Grey scale and bi-level images are handled within this framework as
  a special case, having a 1-component color model.  The following
  features are used for describing color capabilities:

  'color-levels' indicates the number of distinct values for each
  picture element, and applies to all but bi-level images.  For bi-
  level images, a value of 2 is implied.

  'color-space' is used mainly with 'Mapped' and 'Full', but could be
  used with other modes if the exact color used is significant.  Two
  kinds of color space can be distinguished:  device-dependent and
  calibrated.  Device dependent spaces are named here as 'Device-
  xxx', and are used to indicate a color space that is defined by the
  receiving device.  Calibrated color spaces presume the existence of
  a rendering system that is calibrated with respect to an indicated
  definition, and is capable of processing the device-independent
  color information accordingly.

  A color-handling receiver should indicate any appropriate device
  color space capability in addition to any calibrated color spaces
  that it may support.  A calibrated color space should be used when
  precise color matching is required in the absence of specific
  knowledge of the receiving system.

       NOTE:  In practice, although they appear to be separate
       concepts, the color model and color space cannot be
       separated.  In the final analysis, a color model (RGB,
       CMY, etc.) must be defined with respect to some color
       space.

  'CIELAB-L-depth', 'CIELAB-a-depth' and 'CIELAB-b-depth' indicate
  the number of different values that are possible for the L*, a* and
  b* color components respectively, and are significant only when
  colors are represented in a CIELAB color space.  These features
  would be used with palettized color, or with full color where each
  color component has a different number of possible values.




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  The 'CIELAB-x-min' and 'CIELAB-x-max' values indicate a color gamut
  (i.e. a range of color values that are used or may be rendered).  A
  gamut may be indicated in terms of the CIELAB color space even when
  colors are represented in some other space.

3.7 Image coding

  Feature tag name    Legal values
  ----------------    ------------
  image-file-         TIFF-S
  structure           TIFF-F
                      TIFF-J
                      TIFF-C
                      TIFF-L
                      TIFF-M
                      (may be extended by further registrations,
                      to cover non-TIFF image file structures)
  image-coding        MH
                      MR
                      MMR
                      JBIG
                      JPEG
                      (may be extended by further registrations)
  image-coding-       JBIG-T85    (bi-level, per ITU T.85)
  constraint          JBIG-T43    (multi-level, per ITU T.43)
                      JPEG-T4E    (per ITU T.4, Annex E)
                      (may be extended by further registrations)
  JBIG-stripe-size    <Integer>
  image-interleave    Stripe
                      Plane
  color-subsampling   "1:1:1"     (no color subsampling)
                      "4:1:1"     (4:1:1 color subsampling)
  MRC-mode            <Integer> (0..7)   (per ITU T.44 [15])
  MRC-max-stripe-size <Integer>

  Reference: this document, appendix A.

  'image-file-structure' defines how the coded image data is wrapped
  and formatted.  Options defined here are the various profiles of
  TIFF-FX, per RFC 2301 [7].  These options apply to overall
  formatting of the image data (TIFF file format, byte ordering, bit
  ordering, etc.) and do not define specific image coding issues that
  are covered by other aspects of the TIFF-FX profile specifications.

  'image-coding' describes how the raw image data is compressed and
  coded as a sequence of bits.  These are generic tags that may apply
  to a range of file formats and usage environments.





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  'image-coding-constraint' describes how the raw image data coding
  method is constrained to meet a particular operating environment.
  Options defined here are JBIG and JPEG coding constraints that
  apply in typical Group 3 fax environments.

  The 'JBIG-stripe-size' feature may be used with JBIG image coding,
  and indicates the number of scan lines in each stripe except the
  last in an image.  The legal constraints are:

     (JBIG-stripe-size=128)
     (JBIG-stripe-size>=0)

  The latter being equivalent to no restriction.

  The 'MRC-mode' feature is used to indicate the availability of MRC
  (mixed raster content) image format capability, and also the MRC
  mode available.  A zero value indicates MRC is not available, a
  non-zero value indicates the available MRC mode number.

  An MRC formatted document is actually a collection of several
  images, each of which is described by a separate feature
  collection.  An MRC-capable receiver is presumed to be capable of
  accepting any combination of contained images that conform to the
  MRC construction rules and declared image-coding capabilities.

  Within an MRC-formatted document, multi-level coders are used for
  foreground and background images (i.e. odd-numbered layers: 1, 3,
  5, etc.) and bi-level coders are used for mask layers (i.e. even
  numbered layers 2, 4, 6, etc.).

       NOTE: an MRC formatted document may appear within a TIFF
       image file structure, so this separate feature is needed
       to capture the full range of possible capabilities.

  The 'MRC-max-stripe-size' feature may be used with MRC coding, and
  indicates the maximum number of scan lines in each MRC stripe.  The
  legal constraints are:

     (MRC-max-stripe-size=[0..256])
     (MRC-max-stripe-size>=0)

  These values indicate upper bounds on the stripe size.  The actual
  value may vary between stripes, and the actual size for each stripe
  is indicated in the image data.








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       NOTE: there are many image coding options here, and not
       all are required in all circumstances.

       Specification of the image-file-structure tag value alone
       is not normally sufficient to describe the capabilities
       of a recipient.  A general rule is that sufficient detail
       should be provided to exclude any unsupported features.

       For extended Internet fax, image-file-structure and
       image-coding should always be specified, together with
       additional values described above as needed to clearly
       indicate which feature tag values are supported and which
       are not.  (See also the examples in section 4.)

4. Examples

  Some of the examples contain comments introduced by '--...'.  These
  are not part of the allowed capability description syntax.  They
  are included here to explain some of the constructs used.

  The level of detail captured here reflects that used for capability
  identification in Group 3 facsimile.

4.1 Simple mode Internet fax system

  This example describes the capabilities of a typical simple mode
  Internet fax system.  Note that TIFF application S is required to
  be supported by such a system.

     (& (color=Binary)
        (image-file-structure=TIFF-S)
        (dpi=200)
        (dpi-xyratio=[200/100,200/200])
        (paper-size=A4)
        (image-coding=MH) (MRC-mode=0)
        (ua-media=stationery) )
















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4.2 High-end black-and-white Internet fax system

  This would include support for B/W JBIG and be equivalent to what
  is sometimes called "Super G3", except that Internet fax
  functionality would be added.

     (& (color=Binary)
        (image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
        (| (& (dpi=200) (dpi-xyratio=200/100) )    -- 200*100
           (& (dpi=200) (dpi-xyratio=1) )          -- 200*200
           (& (dpi=204) (dpi-xyratio=204/391) )    -- 204*391
           (& (dpi=300) (dpi-xyratio=1) ) )        -- 300*300
        (| (image-coding=[MH,MR,MMR])
           (& (image-coding=JBIG)
              (image-coding-constraint=JBIG-T85)
              (JBIG-stripe-size=128) ) )
        (MRC-mode=0)
        (paper-size=[A4,B4]) )

4.3 Grey-scale Internet fax system

  This is the previous example extended to handle grey scale multi-
  level images.  In keeping with Group 3 fax, this example requires
  equal x- and y- resolutions for a multi-level image.

     (& (| (& (color=Binary)
              (image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
              (| (image-coding=[MH,MR,MMR])
                 (& (image-coding=JBIG)
                    (image-coding-constraint=JBIG-T85)
                    (JBIG-stripe-size=128) ) )
              (| (& (dpi=200) (dpi-xyratio=200/100) )
                 (& (dpi=200) (dpi-xyratio=1) )
                 (& (dpi=204) (dpi-xyratio=204/391) )
                 (& (dpi=300) (dpi-xyratio=1) ) ) )
           (& (color=Grey)
              (image-file-structure=[TIFF-C,TIFF-L])
              (color-levels<=256)
              (color-space-CIELAB)
              (| (& (image-coding=JPEG)
                    (image-coding-constraint=JPEG-T4E) )
                 (& (image-coding=JBIG)
                    (image-coding-constraint=JBIG-T43)
                    (JBIG-stripe-size=128)
                    (image-interleave=stripe) ) )
              (dpi=[100,200,300])
              (dpi-xyratio=1) ) )
        (MRC-mode=0)
        (paper-size=[A4,B4]) )



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4.4 Full-color Internet fax system

  This adds 16-bit full-color to the previous example.

     (& (| (& (color=Binary)
              (image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
              (| (image-coding=[MH,MR,MMR])
                 (& (image-coding=JBIG)
                    (image-coding-constraint=JBIG-T85)
                    (JBIG-stripe-size=128) ) )
              (| (& (dpi=200) (dpi-xyratio=200/100) )
                 (& (dpi=200) (dpi-xyratio=1) )
                 (& (dpi=204) (dpi-xyratio=204/391) )
                 (& (dpi=300) (dpi-xyratio=1) ) ) )
           (& (| (& (color=Grey) (color-levels<=256) )
                 (& (color=Full) (color-levels<=65536)
                    (color-subsampling=["1:1:1","4:1:1"]) ) )
              (image-file-structure=[TIFF-C,TIFF-L])
              (color-space=CIELAB)
              (| (& (image-coding=JPEG)
                    (image-coding-constraint=JPEG-T4E) )
                 (& (image-coding=JBIG)
                    (image-coding-constraint=JBIG-T43)
                    (JBIG-stripe-size=128)
                    (image-interleave=stripe) ) )
              (dpi=[100,200,300])
              (dpi-xyratio=1) ) )
        (MRC-mode=0)
        (paper-size=[A4,B4]) )























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4.5 Full-color Internet fax system (MRC)

     (& (| (& (color=Binary)
              (image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
              (MRC-mode=0)
              (image-coding=[MH,MMR])
              (| (& (dpi=200) (dpi-xyratio=[200/100,1]) )
                 (& (dpi=204) (dpi-xyratio=204/391) )
                 (& (dpi=300) (dpi-xyratio=1) )
                 (& (dpi=400) (dpi-xyratio=1) ) ) )
           (& (image-file-structure=[TIFF-C,TIFF-L])
              (| (& (color=Grey) (color-levels<=256) )
                 (& (color=Full) (color-levels<=65536)
                    (color-subsampling=["1:1:1","4:1:1"]) ) )
              (color-space=CIELAB)
              (MRC-mode=0)
              (image-coding=JPEG)
              (image-coding-constraint=JPEG-T4E)
              (dpi=[100,200,300,400])
              (dpi-xyratio=1) )
           (& (image-file-structure=TIFF-M)
              (MRC-mode=1) (MRC-max-stripe-size=[0..256])
              (image-coding=[MH,MMR,JPEG])
              (| (color=Binary)
                 (& (color=Grey) (color-levels<=256) )
                 (& (color=Full) (color-levels<=65536)
                    (color-subsampling=["1:1:1","4:1:1"]) ) )
              (color-space=CIELAB)
              (dpi=[100,200,300,400])
              (dpi-xyratio=1) ) )
        (paper-size=[A4,B4]) )

4.6 Sender and receiver feature matching

  This example considers sending a document to a high-end black-and-
  white fax system with the following receiver capabilities:

     (& (| (& (dpi=200) (dpi-xyratio=200/100) )    -- 200*100
           (& (dpi=200) (dpi-xyratio=1) )          -- 200*200
           (& (dpi=300) (dpi-xyratio=1) )          -- 300*300
           (& (dpi=400) (dpi-xyratio=1) ) )        -- 400*400
        (color=Binary)
        (| (& (paper-size=A4) (ua-media=[stationery,transparency]) )
           (& (paper-size=B4) (ua-media=continuous) ) )
        (image-coding=[MH,MR,JBIG]) )







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  Turning to the document itself, assume it is available to the
  sender in three possible formats, A4 high resolution, B4 low
  resolution and A4 high resolution color, described by:

     (& (dpi=300) (dpi-xyratio=1)
        (color=Binary)
        (paper-size=A4)
        (image-coding=[MMR,JBIG]) )

     (& (dpi=200) (dpi-xyratio=200/100)
        (color=Binary)
        (paper-size=B4)
        (image-coding=[MH,MR]) )

     (& (dpi=300) (dpi-xyratio=1)
        (color=Mapped) (color-levels<=256)
        (paper-size=A4)
        (image-coding=JPEG) )

  These three image formats can be combined into a composite
  capability statement by a logical-OR operation (to describe
  format-1 OR format-2 OR format-3):

     (| (& (dpi=300) (dpi-xyratio=1)
           (color=Binary)
           (paper-size=A4)
           (image-coding=[MMR,JBIG]) )
        (& (dpi=200) (dpi-xyratio=200/100)
           (color=Binary)
           (paper-size=B4)
           (image-coding=[MH,MR]) )
        (& (dpi=300) (dpi-xyratio=1)
           (color=Mapped) (color-levels=42)
           (paper-size=A4)
           (image-coding=JPEG) ) )

  This could be simplified, but there is little gain in doing so at
  this point.














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  The composite document description can be matched with the receiver
  capability description, according to the rules in [2], to yield the
  result:

     (| (& (dpi=300) (dpi-xyratio=1)
           (color=Binary)
           (paper-size=A4)
           (ua-media=[stationery,transparency])
           (image-coding=JBIG) )
        (& (dpi=200) (dpi-xyratio=200/100)
           (color=Binary)
           (paper-size=B4)
           (ua-media=continuous)
           (image-coding=[MH,MR]) ) )

  Points to note about the feature matching process:

  o  The color document option is eliminated because the receiver
     cannot handle either color (indicated by '(color=Mapped)') or
     JPEG coding (indicated by '(image-coding=JPEG)').

  o  The high resolution version of the document with '(dpi=300)' must
     be send using '(image-coding=JBIG)' because this is the only
     available coding of the image data that the receiver can use for
     high resolution documents.  (The available 300dpi document
     codings here are MMR and JBIG, and the receiver capabilities are
     MH, MR and JBIG.)

  o  The low-resolution version of the document can be sent with
     either MH or MR coding as the receiver can deal with either of
     these for low resolution documents.

  o  The high resolution variant of the document is available only for
     A4, so that is the paper-size used in that case.  Similarly the
     low resolution version is sent for B4 paper.

  o  Even though the sender may not understand the 'ua-media' feature
     tag, and does not mention it, the matching rules preserve the
     constraint that the B4 document is rendered with
     '(ua-media=continuous)', and the A4 document may be rendered with
     '(ua-media=[stationery,transparency])'.

  Finally, note that when matching an MRC document description, the
  description of each component sub-image must match the capabilities
  of the intended receiver.







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5. IANA considerations

  Appendix A of this document calls for registrations of feature tags
  in the "IETF tree", as defined in section 3.1.1 of "Media Feature
  Tag Registration Procedure" [1] (i.e. these feature tags are
  subject to the "IETF Consensus" policies described in RFC 2434
  [21]).

  ASN.1 identifiers should be assigned for each of these registered
  feature tags and replaced in the body of the registration.

6. Security considerations

  The points raised below are in addition to the general security
  considerations for extended Internet fax [5], and others discussed
  in [2,8,11,12,13]

6.1 Capability descriptions and mechanisms

  Negotiation mechanisms reveal information about one party to other
  parties.  This may raise privacy concerns, and may allow a
  malicious party to make better guesses about the presence of
  specific security holes.

  Most of these concerns pertain to capability information getting
  into the hands of someone who may abuse it.  This document
  specifies capabilities that help a sender to determine what image
  characteristics can be processed by the recipient, not mechanisms
  for their publication.  Implementors and users should take care
  that the mechanisms employed ensure that capabilities are revealed
  only to appropriate persons, systems and agents.

6.2 Specific threats

  1.  Unsolicited bulk mail:  if it is known that a recipient can
      process certain types of images, they may be targeted by bulk
      mailers that want to send such images.















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7. Full copyright statement

  Copyright (C) The Internet Society 1999.  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 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
  WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

8. Acknowledgements

  The authors gratefully acknowledge the contributions of the
  following persons who commented on earlier versions of this memo:
  James Rafferty, Dan Wing, Robert Buckley, Mr Ryuji Iwazaki.  The
  following contributed ideas upon which some of the features
  described here have been based:  Larry Masinter, Al Gilman, Koen
  Holtman.

9. References

[1]  "Media Feature Tag Registration Procedure"
     Koen Holtman, TUE
     Andrew Mutz, Hewlett-Packard
     Ted Hardie, NASA
     Internet draft: <draft-ietf-conneg-feature-reg-03.txt>
     Work in progress, July 1998.

[2]  "A syntax for describing media feature sets"
     Graham Klyne, 5GM/Content Technologies
     Internet draft: <draft-ietf-conneg-feature-syntax-00.txt>"
     Work in progress, September 1998.


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[3]  "Media Features for Display, Print, and Fax"
     Larry Masinter, Xerox PARC
     Koen Holtman, TUE
     Andrew Mutz, Hewlett-Packard
     Dan Wing, Cisco Systems
     Internet draft: <draft-ietf-conneg-media-features-02.txt>
     Work in progress, September 1998.

[4]  "Internet fax feature mapping from Group 3 fax"
     Lloyd McIntyre, Xerox Corporation
     Graham Klyne, 5GM/Content Technologies
     Internet draft: <draft-ietf-fax-feature-T30-mapping-00.txt>
     Work in progress, August 1998.

[5]  "Extended Facsimile Using Internet Mail
     Larry Masinter, Xerox Corporation
     Dan Wing, Cisco Systems
     Internet draft: <draft-ietf-fax-eifax-04.txt>
     Work in progress, September 1998.

[6]  "Procedures for document facsimile transmission in the general
     switched telephone network"
     ITU-T Recommendation T.30 (1996)
     International Telecommunications Union
     July 1996

[7]  RFC 2301, "File format for Internet fax"
     L. McIntyre,
     R. Buckley,
     D. Venable, Xerox Corporation
     S. Zilles, Adobe Systems, Inc.
     G. Parsons, Northern Telecom
     J. Rafferty, Human Communications
     March 1998.

[8]  RFC 2305, "A Simple Mode of Facsimile Using Internet Mail"
     K. Toyoda
     H. Ohno
     J. Murai, WIDE Project
     D. Wing, Cisco Systems
     March 1998.

[9]  "Continuous-tone color representation method for facsimile"
     ITU-T Recommendation T.42 (1996)
     International Telecommunications Union
     (Covers custom illuminant, gamut)






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[10] "Colour and gray-scale image representation using lossless coding
     scheme for facsimile"
     ITU-T Recommendation T.43 (1997)
     International Telecommunications Union.
     (Covers JBIG for colour/grey images)

[11] "Scenarios for the Delivery of Negotiated Content"
     T. Hardie, NASA Network Information Center
     Internet draft: <draft-ietf-http-negotiate-scenario-02.txt>
     Work in progress, November 1997.

[12] "Requirements for protocol-independent content negotiation"
     G. Klyne, Integralis Ltd.
     Internet draft: <draft-ietf-conneg-requirements-00.txt>
     Work in progress, March 1998.

[13] "Standardization of Group 3 facsimile terminals for document
     transmission"
     ITU-T Recommendation T.4 (1996)
     International Telecommunications Union
     (Covers basic fax coding formats: MH, MR)

[14] "Facsimile coding schemes and coding control functions for Group
     4 facsimile apparatus"
     ITU Recommendation T.6
     International Telecommunications Union
     (Commonly referred to as the MMR standard; covers extended 2-D
     fax coding format)

[15] "Mixed Raster Content (MRC)"
     ITU-T Recommendation T.44
     International Telecommunications Union

[16] "Information technology - Digital compression and coding of
     continuous-tone still image - Requirements and guidelines"
     ITU-T Recommendation T.81 (1992) | ISO/IEC 10918-1:1993
     International Telecommunications Union
     (Commonly referred to as JPEG standard)

[17] "Information technology - Coded representation of picture and
     audio information - Progressive bi-level image compression"
     ITU-T Recommendation T.82 (1993) | ISO/IEC 11544:1993
     International Telecommunications Union
     (Commonly referred to as JBIG1 standard)








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[18] "Application profile for Recommendation T.82 - Progressive bi-
     level image compression (JBIG1 coding scheme for facsimile
     apparatus)"
     ITU-T Recommendation T.85 (1995)
     International Telecommunications Union
     (Covers bi-level JBIG)

[19] "Colorimeter, 2nd ed."
     CIE Publication No. 15.2
     1986.
     (Defines CIELAB color space;  use with fax is further constrained
     by T.42 [9].)

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

[21] RFC 2434, "Guidelines for Writing an IANA Considerations Section
     in RFCs"
     T. Narten, IBM
     H. Alvestrand, Maxware
     October 1998.

10. Authors' addresses

  Graham Klyne
  5th Generation Messaging Ltd.    Content Technologies Ltd.
  5 Watlington Street              Forum 1, Station Road
  Nettlebed                        Theale
  Henley-on-Thames, RG9 5AB        Reading, RG7 4RA
  United Kingdom                   United Kingdom.
  Telephone: +44 1491 641 641      +44 118 930 1300
  Facsimile: +44 1491 641 611      +44 118 930 1301
  E-mail: GK@ACM.ORG

  Lloyd McIntyre
  Xerox Corporation
  Mailstop PAHV-121
  3400 Hillview Ave.
  Palo Alto, CA 94304 USA
  Telephone: +1-650-813-6762
  Facsimile: +1-650-845-2340
  E-mail: Lloyd.McIntyre@pahv.xerox.com







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Appendix A: Feature registrations

A.1 Image size

  -  Media Feature tag name(s):

       size-x
       size-y

  -  ASN.1 identifiers associated with these feature tags:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       These feature tags indicate the size of a displayed, printed
       or otherwise rendered document image;  they indicate
       horizontal (size-x) and vertical (size-y) dimensions.

       The unit of measure is inches (to be consistent with the
       measure of resolution defined by the feature tag 'dpi').

       Where the actual size is available in millimetres, a
       conversion factor of 10/254 may be applied to yield an exact
       inch-based value.

  -  Values appropriate for use with these feature tags:

       Rational (>0)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Print and display applications where different media choices
       will be made depending on the size of the recipient device.

  -  Examples of typical use:

       This example describes the maximum scanned image width and
       height for Group 3 fax: 215x297 mm (8.46x11.69 inches):

       (size-x<=2150/254)
       (size-y<=2970/254)








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  -  Related standards or documents:

       The memo "Media Features for Display, Print, and Fax" [3]
       describes features (pix-x, pix-y) for measuring document size
       in pixels.

       Fax applications should declare physical dimensions using the
       features defined here.

  -  Considerations particular to use in individual applications,
     protocols, services, or negotiation mechanisms:

       Where no physical size is known or available, but a pixel size
       is known, a notional size should be declared based upon known
       pixel dimensions and a notional resolution of (say) 100dpi

       For example, to describe a 640x480 pixel display:

          (& (size-x<=640/100) (size-y<=480/100) (dpi=100) )

       The notional 100dpi resolution is used as it represents a
       fairly typical resolution for a pixel-limited display.
       Reducing the rational numbers to canonical form gives the
       following equivalent expression:

          (& (size-x<=32/5) (size-y<=24/5) (dpi=100) )

  -  Interoperability considerations:

       For interoperability with other (non-fax) applications that
       use only pixel-based measurements, pixel dimensions (pix-x,
       pix-y) may be declared in addition to physical measurements.

  -  Related feature tags:

       pix-x                 [3]
       pix-y                 [3]
       dpi                   [3]
       dpi-xyratio           [this document]

  -  Intended usage:

       Common

  -  Author/Change controller:

       IETF





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A.2 Resolution aspect ratio

  -  Media Feature tag name(s):

       dpi-xyratio

  -  ASN.1 identifier associated with this feature tag:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature is used to indicate differential horizontal and
       vertical resolution capability.  In the absence of this
       feature, horizontal and vertical resolutions are presumed to
       be the same.

       When this feature tag is specified, any declared resolution
       (dpi) is presumed to apply to the horizontal axis, and the
       vertical resolution is obtained by dividing that declared
       resolution by the resolution ratio.

       The value of this feature is a pure number, since it
       represents the ratio of two resolution values.

  -  Values appropriate for use with this feature tag:

       Rational (>0)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Internet fax, and other print or display applications that
       must handle differential horizontal and vertical resolution
       values.

  -  Examples of typical use:

       The following example describes a fax resolution of 204 dpi
       horizontally by 391 dpi vertically:

       (& (dpi=204) (dpi-xyratio=204/391) )

  -  Related standards or documents:

       The memo "Media Features for Display, Print, and Fax" [3]
       describes a feature (dpi) for measuring document resolution.





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  -  Interoperability considerations:

       When interoperating with an application that does not
       recognize the differential resolution feature, resolution
       matching may be performed on the basis of the horizontal
       resolution only, so aspect ratio information may be lost.

  -  Related feature tags:

       dpi                   [3]
       size-x                [this document]
       size-y                [this document]

  -  Intended usage:

       Internet fax

  -  Author/Change controller:

       IETF
































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A.3 Color levels

  -  Media Feature tag name(s):

       color-levels

  -  ASN.1 identifier associated with this feature tag:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature tag is used to indicate a number of different
       image data pixel color values.

       When mapped (palettized) color is used, this is generally
       different from the number of different colors that can be
       represented through the color mapping function.

       This feature tag is used in conjunction with a 'color' feature
       having a value other than 'Binary'.

  -  Values appropriate for use with this feature tag:

       Integer  (>=2)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Color image printing or display applications where the data
       resource used may depend upon color handling capabilities of
       the recipient.

  -  Examples of typical use:

       To describe recipient capabilities:
       (& (color=limited) (color-levels<=6) )
       (& (color=grey)    (color-levels<=64) )
       (& (color=mapped)  (color-levels<=240) )
       (& (color=full)    (color-levels<=16777216) )

       To describe capabilities used by a document:
       (& (color=limited) (color-levels=4) )
       (& (color=grey)    (color-levels=48) )
       (& (color=mapped)  (color-levels=100) )
       (& (color=full)    (color-levels=32768) )






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  -  Related standards or documents:

       The memo "Media Features for Display, Print, and Fax" [3]
       describes a feature (color) for indicating basic color
       capabilities.

  -  Interoperability considerations:

       The actual number of color values used by a document does not,
       in general, exactly match the number that can be handled by a
       recipient.  To achieve a feature match, at least one must be
       declared as an inequality.

       It is recommended that a recipient declares the number of
       color values that it can handle as an inequality (<=), and a
       data resource declares the number of colors that it uses with
       an equality, as shown in the examples above.

  -  Security considerations:

     - Privacy concerns, related to exposure of personal information:
          Where feature matching is used to select content applicable
          to the physical abilities of a user, unusual values for this
          feature tag might give an indication of a user's restricted
          abilities.

  -  Related feature tags:

       color                 [3]
       color-space           [this document]

  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF













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A.4 Color space

  -  Media Feature tag name(s):

       color-space

  -  ASN.1 identifier associated with this feature tag:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature indicates a color space.

       A color space value provides two types of information:
       o  the color model used to represent a color value, including
          the number of color components
       o  a mapping between color values and their physical
          realizations

       Device color space values are defined for applications where
       the general color representation used is significant, but
       exact color rendering is left to the device used.  Device
       color spaces defined here have values of the form 'Device-
       xxx'.

       Calibrated color space values are provided for use with a
       rendering system that is calibrated with respect to some
       indicated definition, and capable of processing device-
       independent color information accordingly.

  -  Values appropriate for use with this feature tag:

       Token

       Device color      Device-RGB   (device dependent RGB)
       spaces:           Device-CMY   (device dependent CMY)
                         Device-CMYK  (device dependent CMYK)

       Calibrated color  CIELAB       (per T.42 [9])
       space:

                         (may be extended by further registrations)

       'Color-space=CIELAB' indicates the CIE L*a*b* colour space,
       using CIED50 illuminant and its perfectly diffuse reflecting
       white point (per T.42 [9]).





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  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Color image printing and display applications where the data
       resource used may depend upon color handling capabilities of
       the recipient.

       Scanning applications where the data transferred may depend
       upon the image generation capabilities of the originator.

  -  Examples of typical use:

       To describe rendering or scanning capabilities:

       (color-space=[Device-RGB,CIELAB])

       To describe capabilities assumed by a document for which
       approximate color reproduction is required:

       (color-space=Device-RGB)

       To describe capabilities assumed by a document for which exact
       color reproduction is required:

       (color-space=CIELAB)

  -  Related standards or documents:

       CIELAB color space is defined in [19]

       CIELAB use for fax is described in ITU T.42 [9]

  -  Interoperability considerations:

       A color-handling receiver should indicate at any appropriate
       device color space capability, in addition to any calibrated
       color spaces that it may support.

       Calibrated color spaces are intended to be used when precise
       color matching is required;  otherwise, if applicable, a
       device color space (color-space=Device-xxx) should be
       indicated.

       Documents for which exact color matching is not important
       should indicate a device color space capability, if
       applicable.

       These principles allow sender/receiver feature matching to be
       achieved when exact color matching is not required.



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  -  Security considerations:

     - Privacy concerns, related to exposure of personal information:
          Where feature matching is used to select content applicable
          to the physical abilities of a user, unusual values for this
          feature tag might give an indication of a user's restricted
          abilities.

     - Denial of service concerns related to consequences of
       specifying incorrect values:
          Failure to indicate a generic color space capability for a
          device may lead to failure to match color space for an
          application or document that does not require an exact color
          match.

  -  Related feature tags:

       color                 [3]

  -  Related media types or data formats:

       TIFF-FX               [7]

  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF





















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A.5 CIELAB color depth

  -  Media Feature tag name(s):

       CIELAB-L-depth
       CIELAB-A-depth
       CIELAB-B-depth

  -  ASN.1 identifiers associated with these feature tags:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       These feature tags indicate a color depth capability;  i.e.
       the level of detail to which an individual CIELAB color
       component can be specified.  They define the number of
       distinct values possible for each of the color components L*,
       a* and b*.

       Typically, this feature would be used with 'color=mapped', and
       possibly 'color=grey' or 'color=full', to indicate the number
       of distinct colors that can be realized.

  -  Values appropriate for use with these feature tags:

       Integer (>0)

  -  These feature tags are intended primarily for use in the
     following applications, protocols, services, or negotiation
     mechanisms:

       Color image printing and display applications where the data
       resource used may depend upon color handling capabilities of
       the recipient.

       Scanning applications where the data transferred may depend
       upon the image generation capabilities of the originator.














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  -  Examples of typical use:

       To describe rendering or scanning capabilities:

       (& (color=mapped) (color-levels<=240)
          (CIELAB-L-depth<=128)
          (CIELAB-a-depth<=128)
          (CIELAB-b-depth<=128) )
       (& (color=full) (color-levels<=16777216)
          (CIELAB-L-depth<=256)
          (CIELAB-a-depth<=128)
          (CIELAB-b-depth<=128) )

       To describe capabilities assumed by a document:

       (& (color=mapped) (color-levels=200)
          (CIELAB-L-depth=32)
          (CIELAB-a-depth=32)
          (CIELAB-b-depth=32) )
       (& (color=full) (color-levels=32768)
          (CIELAB-L-depth=128)
          (CIELAB-a-depth=32)
          (CIELAB-b-depth=32) )

  -  Related standards or documents:

       The memo "Media Features for Display, Print, and Fax" [3]
       defines a feature (color) for indicating basic color
       capabilities.

       CIELAB color space is defined in [19]

       CIELAB use for fax is described in ITU T.42 [9]

  -  Related feature tags:

       color                 [3]
       color-levels          [this document]
       color-space           [this document]

  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF




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A.6 CIELAB color gamut

  -  Media Feature tag name(s):

       CIELAB-L-min
       CIELAB-L-max
       CIELAB-a-min
       CIELAB-a-max
       CIELAB-b-min
       CIELAB-b-max

  -  ASN.1 identifiers associated with these feature tags:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       These feature indicate a supported range of color values, by
       indicating minimum and maximum values used for each color
       component in a CIELAB color space.

       'CIELAB-L-min' and 'CIELAB-L-max' are the minimum and maximum
       values of the L* component.

       'CIELAB-a-min' and 'CIELAB-a-max' are the minimum and maximum
       values of the a* component.

       'CIELAB-b-min' and 'CIELAB-b-max' are the minimum and maximum
       values of the b* component.

  -  Values appropriate for use with this feature tag:

       Rational

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Color image printing and display applications where the data
       resource used may depend upon detailed color handling
       capabilities of the recipient.

       Scanning applications where the data transferred may depend
       upon the detailed color image generation capabilities of the
       originator.








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  -  Examples of typical use:

       To describe rendering or scanning capabilities:

       (& (CIELAB-L-min>=0)
          (CIELAB-L-max<=100)
          (CIELAB-a-min>=-75)
          (CIELAB-a-max<=+75)
          (CIELAB-b-min>=-85)
          (CIELAB-b-max<=+85) )

       To describe capabilities required by a document:

       (& (CIELAB-L-min=20)
          (CIELAB-L-max=80)
          (CIELAB-L-min=-35)
          (CIELAB-L-max=+55)
          (CIELAB-L-min=-45)
          (CIELAB-L-max=+65) )

  -  Related standards or documents:

       CIELAB color space is defined in [19]

       CIELAB use for fax is described in ITU T.42 [9]

  -  Interoperability considerations:

       When describing a recipient's capabilities, the minimum and
       maximum color component values that can be rendered should be
       indicated by inequalities as shown in the examples above.

       When describing a document, the actual minimum and maximum
       color component values used should be indicated, as shown
       above.

  -  Security considerations:

     - Privacy concerns, related to exposure of personal information:
          Where feature matching is used to select content applicable
          to the physical abilities of a user, unusual values for this
          feature tag might give an indication of a user's restricted
          abilities.

  -  Related feature tags:

       color                 [3]
       color-space           [this document]




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  -  Related media types or data formats:

       TIFF-FX               [7]

  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF








































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A.7 Image file structure

  -  Media Feature tag name(s):

       image-file-structure

  -  ASN.1 identifier associated with this feature tag:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature indicates a file structure used for transfer and
       presentation of image data.

       It does not indicate image data coding:  that is described by
       separate feature tags (image-coding, etc.).

  -  Values appropriate for use with this feature tag:

       Token

       TIFF-FX profiles  TIFF-S
       [7]:              TIFF-F
                         TIFF-J
                         TIFF-C
                         TIFF-L
                         TIFF-M

                         (may be extended by further registrations,
                         to cover non-TIFF image file structures)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Internet fax, and other print or display applications that
       transfer image data.

  -  Examples of typical use:

       See Appendix B of this memo.











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  -  Considerations particular to use in individual applications,
     protocols, services, or negotiation mechanisms:

       This tag is intended to provide information about an image
       file structure.  Information about image data coding is
       provided by other tags.

       In the case of TIFF-FX image data, there are a number of image
       file format constraints that are imposed by the various usage
       profiles defined in RFC 2301 [7].  The purpose of the 'image-
       file-structure' feature tag is to capture those file format
       constraints.

       Registration of additional image file structure tags should
       focus similarly on image file structure issues, not raw image
       data compression and coding.  As a guide, an image file
       structure may contain image data coded in a variety of ways,
       and carries information to describe that coding separately
       from MIME content-type labelling, etc.

  -  Related feature tags:

       image-coding          [this document]

  -  Related media types or data formats:

       TIFF-FX               [7]
       TIFF V6.0 (Adobe)     [20]

  -  Intended usage:

       Internet fax
       Image scanning/rendering applications

  -  Author/Change controller:

       IETF















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A.8 Image data coding

  -  Media Feature tag name(s):

       image-coding

  -  ASN.1 identifier associated with this feature tag:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature tag indicates a form of image data compression
       and coding used.

       It identifies a generic image coding technique used, without
       regard to any specific profiling of that technique that may be
       applied.  Values for this feature are generally applicable
       across a wide range of image transfer applications.

       This information is distinct from the image file structure and
       MRC information conveyed by the 'image-file-structure' tags.

  -  Values appropriate for use with this feature tag:

       Token             MH
                         MR
                         MMR
                         JBIG
                         JPEG

                         (may be extended by further registrations)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Internet fax, and other applications that transfer image data.

  -  Examples of typical use:

       See Appendix B of this memo.











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  -  Related standards or documents:

       MH, MR:     ITU T.4 [13]
       MMR:        ITU T.6 [14]
       JPEG:       ITU T.81 [16]
       JBIG:       ITU T.82 [17]

  -  Interoperability considerations:

       To establish the correct conditions for interoperability
       between systems, capabilities to handle the generic image
       coding technique and the specific image coding constraints
       must be established.

  -  Related feature tags:

       image-coding-constraint  [this document]
       JBIG-stripe-size         [this document]
       image-interleave         [this document]

  -  Related media types or data formats:

       TIFF-FX                  [7]

  -  Intended usage:

       Internet fax
       Image scanning/rendering applications

  -  Author/Change controller:

       IETF




















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A.9 Image coding constraint

  -  Media Feature tag name(s):

       image-coding-constraint

  -  ASN.1 identifier associated with these feature tags:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature tag qualifies the 'image-coding' feature with a
       specific profile or usage constraints.

       Values for this feature are generally specific to some given
       value of 'image-coding' and also to some restricted
       application or class of applications.

  -  Values appropriate for use with this feature tag:

       Token             JBIG-T85    (bi-level, per ITU T.85)
                         JBIG-T43    (multi-level, per ITU T.43)
                         JPEG-T4E    (per ITU T.4, Annex E)

                         (may be extended by further registrations)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Internet fax, and other applications that transfer image data.

       The specific values for this feature indicated above are
       intended for use with Internet fax.

  -  Examples of typical use:

       See Appendix B of this memo.

  -  Related standards or documents:

       JBIG-T85:   ITU T.85 [18]
       JBIG-T43:   ITU T.43 [10]
       JPEG-T4E:   ITU T.4 Annex E [13]








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  -  Interoperability considerations:

       To establish the correct conditions for interoperability
       between systems, capabilities to handle the generic image
       coding technique and the specific image coding constraints
       must be established.

  -  Related feature tags:

       image-coding             [this document]
       JBIG-stripe-size         [this document]
       image-interleave         [this document]

  -  Related media types or data formats:

       TIFF-FX                  [7]

  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF



























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A.10 JBIG stripe size

  -  Media Feature tag name(s):

       JBIG-stripe-size

  -  ASN.1 identifier associated with these feature tags:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature is a specific usage constraint that is applied to
       JBIG image coding (image-coding=JBIG), and indicates the
       allowable size for each stripe of an image, except the last.

       A stripe of a JBIG image is a delimited horizontal band of
       compressed image data that can be decompressed separately from
       the surrounding data.

  -  Values appropriate for use with this feature tag:

       Integer  (>0)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Internet fax, and other applications that transfer image data.

  -  Examples of typical use:

       (JBIG-stripe-size=128)
       (JBIG-stripe-size>0)

  -  Related standards or documents:

       JBIG:       ITU T.82 [17]
       JBIG-T85:   ITU T.85 [18]
       JBIG-T43:   ITU T.43 [10]













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  -  Considerations particular to use in individual applications,
     protocols, services, or negotiation mechanisms:

       In the case of Internet fax, the specific constraints allowed
       for a receiver are those given as examples above.

       Specifying a stripe size that is not limited (JBIG-stripe-
       size>0) means that an entire page of image data is encoded as
       a single unit.  This may place considerable demands on the
       memory of a receiving system, as the entire stripe needs to be
       buffered in memory.

  -  Interoperability considerations:

       To establish the correct conditions for interoperability
       between systems, capabilities to handle the generic image
       coding technique and the specific image coding constraints
       must be established.

  -  Related feature tags:

       image-coding             [this document]
       image-coding-constraint  [this document]
       image-interleave         [this document]

  -  Related media types or data formats:

       TIFF-FX                  [7]

  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF















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A.11 Image interleave

  -  Media Feature tag name(s):

       image-interleave

  -  ASN.1 identifier associated with this feature tag:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature indicates an image interleave capability.

       It may be used with JBIG images (image-coding=JBIG) to
       indicate color plane interleaving of either stripes or entire
       image planes.

  -  Values appropriate for use with this feature tag:

       Token             Stripe
                         Plane

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Internet fax, and other applications that transfer image data.

  -  Examples of typical use:

       (image-interleave=stripe)
       (image-interleave=[stripe,plane])

  -  Considerations particular to use in individual applications,
     protocols, services, or negotiation mechanisms:

       Specifying a plane interleave means that an entire page of
       image data must be buffered in order to generate render the
       image.  This may place considerable demands on the memory of a
       sending or receiving system.

  -  Related feature tags:

       image-coding             [this document]
       JBIG-stripe-size         [this document]

  -  Related media types or data formats:

       TIFF-FX                  [7]



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  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF












































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A.12 Color subsampling

  -  Media Feature tag name(s):

       color-subsampling

  -  ASN.1 identifier associated with this feature tag:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature tag indicates whether color information may be
       subsampled with respect to luminance data.

       It is used with continuous color images (color=full), color
       spaces that use separate luminance and color components
       (e.g. color-space=LAB), and image file structures that support
       color subsampling.

  -  Values appropriate for use with this feature tag:

       String            "1:1:1"
                         This value indicates a full set of color
                         component samples for each luminance
                         component sample.

                         "4:1:1"
                         This value indicates a set of color samples
                         for each luminance sample.

                         (may be extended by further registrations)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Color image printing and display applications where the data
       resource used may depend upon color handling capabilities of
       the recipient.

       Scanning applications where the data transferred may depend
       upon the image generation capabilities of the originator.

  -  Examples of typical use:

       (& (color=full) (color-space=[LAB,CIALAB])
          (color-subsampling=["1:1:1","4:1:1"]) )





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  -  Related feature tags:

       color                 [3]
       color-space           [this document]
       image-file-structure  [this document]

  -  Related media types or data formats:

       TIFF-FX               [7]

  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF


































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A.13 MRC availability and mode

  -  Media Feature tag name(s):

       MRC-mode

  -  ASN.1 identifier associated with this feature tag:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature is used to indicate the availability of MRC
       (mixed raster content) image format capability, and also the
       MRC mode available.  A zero value indicates MRC is not
       available, a non-zero value (in the range 1..7) indicates the
       available MRC mode number.

       An MRC formatted document is actually a collection of several
       images, each of which is described by a separate feature
       collection.  An MRC-capable receiver is presumed to be capable
       of accepting any combination of contained images that conform
       to the MRC construction rules, where each such image matches
       the separately declared resolution, color capability, color
       model, image coding, and any other capabilities.

          NOTE: an MRC formatted document may appear within a
          TIFF image file structure.

          Within an MRC-formatted document, multi-level coders
          are used for foreground and background images (i.e.
          odd-numbered layers: 1, 3, 5, etc.) and bi-level coders
          are used for mask layers (i.e. even numbered layers 2,
          4, 6, etc.).

  -  Values appropriate for use with this feature tag:

       Integer (0..7)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Internet fax, and other applications that transfer image data.

  -  Examples of typical use:

       See Appendix B of this document.





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  -  Related standards or documents:

       ITU T.44 [15]

  -  Interoperability considerations:

       To establish the correct conditions for interoperability
       between systems, capabilities to handle the MRC mode and any
       contained image coding techniques must be established.

  -  Related feature tags:

       image-coding             [this document]
       MRC-max-stripe-size      [this document]

  -  Related media types or data formats:

       TIFF-FX                  [7]

  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF

























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A.14 MRC maximum stripe size

  -  Media Feature tag name(s):

       MRC-max-stripe-size

  -  ASN.1 identifier associated with this feature tag:

       [[[New assignments by IANA]]]

  -  Summary of the media features indicated:

       This feature may be used with MRC coding (MRC-mode>=1), and
       indicates the maximum number of scan lines in each MRC stripe.

       The value given indicates an upper bound on the stripe size.
       The actual value may vary between stripes, and the actual size
       for each stripe is indicated in the image data.

  -  Values appropriate for use with this feature tag:

       Integer (>0)

  -  The feature tag is intended primarily for use in the following
     applications, protocols, services, or negotiation mechanisms:

       Internet fax, and other applications that transfer image data.

  -  Examples of typical use:

       (MRC-max-stripe-size=[0..256])
       (MRC-max-stripe-size>=0)

  -  Considerations particular to use in individual applications,
     protocols, services, or negotiation mechanisms:

       For Internet fax, the legal constraints for an image receiver
       are those given as examples above.

  -  Related feature tags:

       MRC-mode              [this document]

  -  Related media types or data formats:

       TIFF-FX               [7]






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  -  Intended usage:

       Internet fax
       Color image scanning/rendering applications

  -  Author/Change controller:

       IETF












































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Appendix B: TIFF mode descriptions

  This appendix contains descriptions of the TIFF modes defined by
  RFC 2301 [7], presented as feature set expressions in the form
  defined by "A syntax for describing media feature sets" [2] and
  using the feature schema introduced by this document.

  These may be taken as illustrations of the feature set combinations
  that are required for the corresponding TIFF profiles described by
  RFC 2301.

     (Tiff-S) :-
          (& (image-file-structure=TIFF-S)
             (color=Binary)
             (image-coding=MH) (MRC-mode=0) )

     (Tiff-F) :-
          (& (image-file-structure=TIFF-F)
             (color=Binary)
             (image-coding=MH) (MRC-mode=0) )

     (TIFF-J) :-
          (& (image-file-structure=TIFF-J)
             (color=Binary)
             (image-coding=JBIG) (MRC-mode=0) )

     (TIFF-C) :-
          (& (image-file-structure=TIFF-C)
             (color=Grey)
             (image-coding=JPEG) (MRC-mode=0) )

     (TIFF-L) :-
          (& (image-file-structure=TIFF-L)
             (color=Grey)
             (image-coding=JBIG) (MRC-mode=0) )

     (TIFF-M) :-
          (& (image-file-structure=TIFF-M)
             (color=[Binary,Grey])
             (image-coding=[MH,JPEG]) (MRC-mode>=1) )

  The feature sets described above are minimum requirements for the
  corresponding TIFF modes.  Thus, MR and MMR image coding are not
  mandatory with TIFF mode F, and would be indicated by combining the
  expression for (TIFF-F) with (image-coding=MR) and/or
  (image-coding=MMR).





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  Similarly, limited, mapped or full color are not mandatory with the
  grey/color TIFF modes (C, L and M), and would be indicated by
  combining the corresponding expression with (color=limited),
  (color=mapped) and/or (color=full).

  TIFF profile M is a composite structure that can combine image data
  coding options from other profiles:  the description above
  indicates mandatory features;  other options may be indicated by
  combining TIFF-M with other options (e.g. color= limited, mapped or
  full, and image-coding= MR, MMR or JBIG).

  Support for multiple TIFF profiles may be indicated by combining
  their expressions with the OR operator; e.g.

     (| (TIFF-F) (TIFF-S) (TIFF-J) )

  indicates support for all black-and-white modes.

Appendix C: Revision history

  00a  28-Sep-1998  Initial draft.

  01a  12-Oct-1998  Incorporated review comments.  Described feature
                    tag for differential x/y resolution ratio.  Added
                    some examples.

  01b  19-Oct-1998  Updated section 3.6 on image coding.  Added
                    Appendix B containing feature expressions for the
                    TIFF modes from RFC 2301.

  02a  26-Oct-1998  Update examples.  Add separate stripe size
                    features for JBIG and MRC.

  02b  30-Oct-1998  Update examples.  Add text clarifying the
                    description of MRC documents (as a set of feature
                    collections describing multiple contained images).
                    Add text describing constrains on resolution and
                    image coding usage within an MRC document.

  02c  11-Nov-1998  Add ITU references.  Added terminology:
                    "capability exchange", "capability identification"
                    and "capability description".  Update JBIG and MRC
                    stripe size tags.  Move subsampling to colour
                    section.  Remove preferred-unit tag.  Add T.4,
                    T.6, T.44 and T.81 references.

  02d  16-Nov-1998  Update colour handling features, reflecting
                    proposed changes to the media features memo [3].
                    Update the image coding capability framework.
                    Updated TIFF mode descriptions in Appendix B.


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  03a  17-Nov-1998  Replace use of 'pix-x', 'pix-y' with 'size-x',
                    'size-y'.  Add registrations in Appendix A.

  03b  08-Dec-1998  Remove normative language and reference to RFC2119
                    (normative statements will be in the main fax
                    protocol draft).  Revise structure of colour
                    features, and removed color-palette feature.
                    Define colour feature tags specific to CIELAB
                    model and colour space.

  04a  14-Dec-1998  Update examples to reflect revised feature tags.
                    Revise description of MRC document in section 3.7.
                    Clarified interpretation of 'color=fixed'.  Change
                    feature value 'color=fixed' to 'color=limited'.

  05a  04-Jan-1999  Incorporate WG last-call comments:  change
                    references to MRC-stripe-size to MRC-max-stripe-
                    size;  similarly references to MRC-maximum-stripe-
                    size.  Change "eifax" to "extended Internet fax".
                    Added guidance note for image coding feature
                    usage.  Added IANA consideration comments to
                    Appendix A.

  05b  08-Jan-1999  Added new section for IANA considerations;
                    removed references to fax working group from
                    registration change control sections.  Remove JPEG
                    from TIFF-L auxiliary predicate.  Clarify
                    description of MRC receiver capabilities in
                    section A.13.  Remove 'color=full' from (TIFF-C)
                    and (TIFF-M) predicates, and add some explanatory
                    text.  Remove 'color=limited' from (TIFF-L)
                    predicate.

  05c  08-Jan-1999  Minor revisions to TIFF profile illustrations and
                    descripions in Appendix B.  Reformatted
                    description of 'color=limited' in section 3.5 to
                    clarify that this does not indicate support for
                    specific named colors.














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