rfc2534.txt

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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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RFC 2534       Media Features for Display, Print, and Fax     March 1999


   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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RFC 2534       Media Features for Display, Print, and Fax     March 1999


   - 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: