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INTERNET-DRAFT                                          Larry Masinter
draft-ietf-conneg-media-features-04.txt                   Koen Holtman
                                                             Andy Mutz
                                                              Dan Wing
expires in 6 months                                    January 4, 1999

              Media Features for Display, Print, and Fax

Status of this memo

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
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   Copyright (C) The Internet Society (1997).  All Rights Reserved.

Abstract

   This specification defines some common media features for
   describing image resolution, size, color, and image representation
   methods that are common to web browsing, printing, and facsimile
   applications.  These features are registered for use within the
   framework of [REG].

1. Introduction

   This work was originally motivated by the requirements from web
   browsers to send the browser's display characteristics to the web
   server to allow the server to choose an appropriate representation.

   This specification defines some common media features [REG] by
   which a recipient may inform a sender as to the characteristics of
   its message handling.  The sender may then provide the variant of
   the message that is most suitable for the recipient.

   Different variants would typically be higher or lower resolution
   images (for example) as appropriate.  In the case of a sending to a
   printer, the result would be higher quality output.  In the case of
   a small screen device (cellphone, portable digital assistant), the
   result would be faster transmission.

   Media features may be used in many different protocol situations.
   Those defined in this specification can indicate the display or
   printer dimensions, resolution, color capability.  The physical
   dimensions of a display may be inferred from the display size and
   display resolution. In the case of paper output, the paper size may
   be expressed as a token from a list of standard paper sizes.  These
   are presented formally in the Notation section.

2. Media Feature Registrations

   This section defines several media features, using the form
   specified in [REG].

2.1 Image Size

  - Media Feature tag name(s):

    pix-x
    pix-y

  - ASN.1 identifier associated with this feature tag:

    ***New assignments by IANA***

  - Summary of the media features indicated by this feature tag:

    These features indicate the display size of the recipient for
    display or print, measured in pixels; they indicate horizontal
    (pix-x) and vertical (pix-y) dimensions.

  - Values appropriate for use with this feature tag:

    Signed Integer

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

    Display and print applications where different media choices will
    be made depending on the size of the recipient device. For
    example, a web application for use on a 240x480 display might use
    different HTML pages than one intended for use on a 1024x768
    display.

2.2 Resolution

  - Media Feature tag name:

    dpi

  - ASN.1 identifier associated with this feature tag:

    ***New assignments by IANA***

  - Summary of the media features indicated by this feature tag:

    This feature indicates the resolution that the recipient can
    display or print without loss, measured in pixels per inch.
    Typically resolution capability is represented as dots-per-inch
    rather than in SI units [SI]. Values for dpi may be expressed as a
    rational to accomodate resolution of SI-based devices; for example
    dpi=19558/100 can be used to represent a resolution of 77 dots per
    centimeter.

  - 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:

    Printing and fax applications typically choose representations of
    a transmitted document depending on the resolution of the
    recipient rather than pixel size.

  - Examples of typical use:

    Choosing a version of a printable document to send to a printer.

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

    Software applications are typically unaware of the resolution of
    the display. Note that there exist devices with different
    resolution in different directions, i.e., individual pixels are
    not square. However, this feature only encompasses the
    uniform resolution.

2.3 Registration of 'ua-media'

  - Media Feature tag name(s):

    ua-media

   - ASN.1 identifier associated with this feature tag:

    ***New assignments by IANA***

  - Summary of the media features indicated by this feature tag:

    This feature indicates the recipients device media, indicated with
    an simple token.

  - Values appropriate for use with this feature tag:

    Token with an equality relationship. Values include:

    screen           A refreshable display
    screen-paged     a refreshable display which cannot scroll
    stationery       Separately cut sheets of an opaque material
    transparency     Separately cut sheets of a transparent material
    envelope         Envelopes that can be used for conventional
                     mailing purposes
    envelope-plain   Envelopes that are not preprinted and have no
                     windows
    continuous       Continuously connected sheets of an opaque
                     material

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

    Most of the feature values are useful for printing applications,
    or to distinguish printing from display.

  - Examples of typical use:

    This might typically be used for selecting between a rendition
    that is intended to be printed and one that is intended to be
    displayed.

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

    Other media values were not included because their utility seemed
    relative.

  - Interoperability considerations:

    Interoperability with the Internet Print Protocol means that
    some additional feature values may need to be registered.

2.4 Paper Size

  - Media Feature tag name(s):

    paper-size

  - ASN.1 identifier associated with this feature tag:

    ***New assignment by IANA***

  - Summary of the media features indicated by this feature tag:

    For stationery, it is often useful to have information about the
    size of display used.  While it is more precise and predictable to
    use absolute resolution and pixel sizes, some applications find it
    useful to provide paper size in addition to this information. Note
    that not all of the paper may have a printable area.

  - Values appropriate for use with this feature tag:

    Token with an equality relationship. Typical values include:

     letter        8.5x11.0 inches
     a4            210x297 mm
     b4            250x353 mm
     a3            297x420 mm
     legal         8.5x14 inches

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

    This feature tag seems most useful for the printing application.

  - Examples of typical use:

    Choosing between a4 and letter size renditions of the same
    printable document.

2.5 Color and greyscale

  - Media Feature tag name(s):

    color

  - ASN.1 identifier associated with this feature tag:

    ***New assignments by IANA***

  - Summary of the media features indicated by this feature tag:

    This feature indicates a gross level of capability to represent
    (or need for) for handling of color, out of a limited set of
    choices.

  - Values appropriate for use with this feature tag:

    Token with an equality relationship. Values include:

    binary      black-and-white, or other bi-level capability.

    grey        more than two levels of intensity; for example,
                at least two bits of grey-scale data

    limited     availability of a small number of colors, such as
                might be provided by a highlight printer, pen plotter,
                or limited color display. Such capability is useful
                for business graphics. At the lowest level of
                capability, this implies at least one color other than
                black ("highlight color"). At the high end, a small
                number (less than 32) colors. No implication is made
                that any particular color is available.

     mapped     pixel color values are mapped in some specifable way
                to a multi-component color space. Sufficient levels of
                display are available to represent a continuous tone
                photographic image, but the result will be mapped into
                a more limited space.

     full       ability (or at least willingness) to represent a full
                color image and present it. Full continuous tone color
                capability.

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

     Web applications may choose between color, grey, or binary
     representations. Fax or printing applications might choose
     between color and non-color renditions, for example.

   - Examples of typical use:

     Someone preparing a map of directions to a restaurant might
     prepare different maps for each kind of value.

   - Intended usage:
     COMMON


3. Examples of use of features

   The following examples of feature comparison show how these features
   can be used to describe various capabilities. The syntax used to
   express combinations of features is purely illustrative and not
   normative:

   pix-x<=1024, pix-y<=768
      might be used for a 1024x768 display.

   dpi=300
      might be used for a 300 dpi printer.

   paper-size=a4
      indicates the display size is 210x297mm.

4. IANA considerations

   This document calls for registration of the following feature tags,
   as per [REG]: pix-x, pix-y, dpi, ua-media, paper-size, color.
   ASN.1 identifiers should be assigned to each of these and replaced
   in the body of the registration.

5. Acknowledgments

   This document is based on a previous draft co-authored with Lou
   Montoulli. It had benefited from the comments of Graham Klyne, Ho
   John Lee, Brian Behlendorf, Jeff Mogul, Ted Hardie, and Dan Wing.

6. References

   [REG] A. Mutz, T. Hardie. "Feature Tag Registration Procedures",
        draft-ietf-conneg-feature-reg-03.txt, July 1998.

   [SI] ISO 1000:1992 "SI units and recommendations for the use of
        their multiples and of certain other units", International
        Organization for Standardization, 1992.

Author's Addresses

   Larry Masinter
   Xerox Palo Alto Research Center
   3333 Coyote Hill Road
   Palo Alto CA 94304
   Fax +1 650 812 4333
   Email: masinter@parc.xerox.com

   Dan Wing
   Cisco Systems, Inc.
   101 Cooper Street
   Santa Cruz, CA 95060  USA
   Phone: +1 831 457 5200
   Fax:   +1 831 457 5208
   EMail: dwing@cisco.com

   Andrew H. Mutz
   Hewlett-Packard Company
   1501 Page Mill Road 3U-3
   Palo Alto CA 94304, USA
   Fax +1 650 857 4691
   Email: mutz@hpl.hp.com

   Koen Holtman
   Technische Universiteit Eindhoven
   Postbus 513
   Kamer HG 6.57
   5600 MB Eindhoven (The Netherlands)
   Email: koen@win.tue.nl


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