RFC2534 - Media Features for Display, Print, and Fax

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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.

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.

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.

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.

- 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.

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:

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.

7. References

[REG] Holtman, K., Mutz, A. and T. Hardie. "Feature Tag Registration
Procedures", BCP 31, RFC2506, 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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Copyright (C) The Internet Society (1999). All Rights Reserved.

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