Media Features for Display, Print, and Fax
Six named tags that let a device say how big, sharp and colorful its screen or paper is.
Masinter, L., Wing, D., Mutz, A., and K. Holtman, "Media Features for Display, Print, and Fax", RFC 2534, DOI 10.17487/RFC2534, March 1999, <https://www.rfc-editor.org/info/rfc2534>.
@misc{rfc2534,
series = {Request for Comments},
number = 2534,
howpublished = {RFC 2534},
publisher = {RFC Editor},
doi = {10.17487/RFC2534},
url = {https://www.rfc-editor.org/info/rfc2534},
author = {L. Masinter and D. Wing and A. Mutz and K. Holtman},
title = {{Media Features for Display, Print, and Fax}},
pagetotal = 9,
year = 1999,
month = mar,
} RFC text
Contents
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, 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
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.
AI ELI5
On this page
§1Purpose of the Media Features
The work was originally motivated by web browsers needing to send their display characteristics to the web server, so the server could choose an appropriate representation. The RFC defines common media features by which a recipient informs a sender about how it handles messages, using the registration form of RFC 2506.
Variants would typically be higher or lower resolution images. For a printer, the result is higher quality output. For a small screen device such as a cellphone or portable digital assistant, the result is faster transmission.
If a tiny phone and a big printer both ask for a picture, each should get the version that suits it. To do that, they first have to say what they can handle.
§2.1Size and Resolution Tags
The pix-x and pix-y tags give the horizontal and vertical display size of the recipient in pixels, for display or print. Their value type is a signed integer. The RFC's example is that a web application for a 240x480 display might use different HTML pages than one for a 1024x768 display.
The dpi tag gives the resolution the recipient can display or print without loss, in pixels per inch. Its value type is rational, so SI-based devices fit: dpi=19558/100 represents 77 dots per centimeter. Printing and fax applications typically choose a representation by resolution rather than pixel size. The tag only covers uniform resolution, even though some devices have non-square pixels.
One tag tells how many dots wide and tall the screen is. Another tells how finely packed the dots are.
§2.2Device Media and Paper Size
The ua-media tag says what kind of media the recipient's device uses. It is a token with an equality relationship. Values include screen (a refreshable display), screen-paged (a display that cannot scroll), stationery (separately cut opaque sheets), transparency, envelope, envelope-plain and continuous (continuously connected opaque sheets). A typical use is choosing between a rendition meant to be printed and one meant to be displayed.
The paper-size tag is also a token with an equality relationship. Typical values are letter (8.5x11.0 inches), a4 (210x297 mm), b4 (250x353 mm), a3 (297x420 mm) and legal (8.5x14 inches). The RFC notes that absolute resolution and pixel sizes are more precise and predictable, but some applications find paper size useful in addition. Not all of the paper may have a printable area.
One tag says whether the output is a screen, a sheet of paper or an envelope. Another names the paper size, like A4 or letter.
§2.3The Color Tag
The color tag indicates a gross level of capability to handle color, chosen from a limited set of tokens with an equality relationship. The values are binary (black-and-white or other bi-level), grey (more than two levels of intensity), limited (a small number of colors, at most a few under 32), mapped (colors mapped to a multi-component color space, enough levels to show a continuous tone photograph but in a more limited space) and full (full continuous tone color).
The RFC suggests that web applications may choose between color, grey or binary representations, and gives the example of someone preparing different restaurant direction maps for each kind of value. The intended usage is listed as COMMON.
This tag says how many colors something can show, from only black and white all the way up to a full-color photo.
- binaryBi-level — Black-and-white, or other bi-level capability.
- greyGreyscale — More than two levels of intensity.
- limitedFew colors — A small number of colors, such as a highlight printer or pen plotter.
- mappedMapped color — Pixel values mapped to a multi-component color space.
- fullFull color — Full continuous tone color capability.
§3Examples of Use
The RFC gives illustrative examples. The syntax for combining features is purely illustrative and not normative.
pix-x<=1024, pix-y<=768might be used for a 1024x768 display.dpi=300might be used for a 300 dpi printer.paper-size=a4indicates the display size is 210x297mm.
You write short notes like 'dpi=300' to say 'my printer is this sharp'.
§4Registration
The document calls for registering the feature tags pix-x, pix-y, dpi, ua-media, paper-size and color as per RFC 2506. Each registration lists an ASN.1 identifier; the identifiers appear as 1.3.6.1.8.1.1 through 1.3.6.1.8.1.6, and the IANA section says they should be assigned and replaced in the body of the registration.
The tags go into an official list so everybody uses the same names.
§5Security Considerations
The only concern the RFC raises is that wrong media feature information attributed to a recipient might cause a sender to send content the recipient cannot actually process, which would cause a denial of service.
If someone lies about what a device can show, it may be sent something it cannot use.