path: root/doc/rfc/rfc2534.txt

Network Working Group                                      L. Masinter
Request for Comments: 2534                           Xerox Corporation
Category: Standards Track                                      D. Wing
                                                   Cisco Systems, Inc.
                                                               A. Mutz
                                                 Jutvision Corporation
                                                            K. Holtman
                                                                   TUE
                                                            March 1999


               Media Features for Display, Print, and Fax

Status of this Memo

   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 (1999).  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.



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   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:

     1.3.6.1.8.1.1
     1.3.6.1.8.1.2

   - 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.








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2.2 Resolution

   - Media Feature tag name:

     dpi

   - ASN.1 identifier associated with this feature tag:

     1.3.6.1.8.1.3

   - 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.








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2.3 Registration of 'ua-media'

   - Media Feature tag name(s):

     ua-media

   - ASN.1 identifier associated with this feature tag:

     1.3.6.1.8.1.4

     - 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.





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   - 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:

     1.3.6.1.8.1.5

   - 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.









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2.5 Color and greyscale

   - Media Feature tag name(s):

   color

   - ASN.1 identifier associated with this feature tag:

     1.3.6.1.8.1.6

   - 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:






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     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. Security Considerations

   Inaccurate media feature information ascribed to a recipient might
   cause a sender to subsequently send content that the recipient is not
   actually able to process, thus causing a denial of service.

6. Acknowledgments

   This document is based on a previous memo 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.




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7. References

   [REG] Holtman, K., Mutz, A. and T. Hardie. "Feature Tag Registration
         Procedures", BCP 31, RFC 2506, March 1999.

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

Authors' Addresses

   Larry Masinter
   Xerox Corporation
   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
   Jutvision Corporation
   124 University Avenue Suite 202
   Palo Alto CA 94301

   Phone: +1 650 325 6787
   Fax:   +1 650 325 9337
   Email: mutz@alum.mit.edu


   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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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.
























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