Media Features for Display, Print, and Fax
Named tags that let a device say what it can display or print, so the sender can pick the right version.
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
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ISO Plain Language
On this page
§1What a Media Feature Is
This work was originally motivated by the requirements from web browsers to send the browser's display characteristics to the web server, so the server could choose an appropriate representation. A media feature is a tag by which a recipient informs a sender of 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. In the case of sending to a printer the result would be higher quality output; in the case of a small screen device such as a cellphone or portable digital assistant the result would be faster transmission.
Media features may be used in many different protocol situations. Each registration in Section 2 follows the form specified in RFC 2506 and gives the feature tag name, the ASN.1 identifier associated with the tag, a summary of what the tag indicates, the values appropriate for it, the applications it is intended for, and examples of typical use. The document calls for registration of the six feature tags pix-x, pix-y, dpi, ua-media, paper-size and color, with an ASN.1 identifier assigned to each and replaced in the body of the registration.
A feature tag is a label with a fixed meaning, so that any two programs agree what it says. A sender reads the labels the receiver sent and chooses the matching version of the document.
- pix-xHorizontal display size — Signed integer, in pixels.
- pix-yVertical display size — Signed integer, in pixels.
- dpiResolution — Rational, in pixels per inch.
- ua-mediaDevice medium — Token, such as screen, stationery or envelope.
- paper-sizePaper size — Token, such as letter, a4 or legal.
- colorColour capability — Token, from binary to full.
§2.1Image Size: pix-x and pix-y
The tags pix-x and pix-y have ASN.1 identifiers 1.3.6.1.8.1.1 and 1.3.6.1.8.1.2. They indicate the display size of the recipient for display or print, measured in pixels, with pix-x giving the horizontal dimension and pix-y the vertical one. The value appropriate for these tags is a signed integer.
They are intended for display and print applications where different media choices are made depending on the size of the recipient device. A web application for use on a 240x480 display might use different HTML pages than one intended for use on a 1024x768 display.
Two numbers say how wide and how tall the screen is, counted in pixels. The sender uses them to pick a page that fits.
§2.2Resolution: dpi
The tag dpi has ASN.1 identifier 1.3.6.1.8.1.3. It indicates the resolution that the recipient can display or print without loss, measured in pixels per inch. Resolution capability is typically represented as dots per inch rather than in SI units, and values for dpi may be expressed as a rational to accommodate resolution of SI-based devices: the RFC gives dpi=19558/100 as the way to represent a resolution of 77 dots per centimeter. The value appropriate for the tag is a rational.
Printing and fax applications typically choose representations of a transmitted document depending on the resolution of the recipient rather than pixel size, for example choosing a version of a printable document to send to a printer. Software applications are typically unaware of the resolution of the display. Devices exist with different resolution in different directions, so that individual pixels are not square, but this feature only encompasses the uniform resolution.
Resolution says how many dots fit into an inch. It matters most for printers and faxes, which choose a sharper or a softer version of a document depending on what the machine can handle.
§2.3Device Medium: ua-media
The tag ua-media has ASN.1 identifier 1.3.6.1.8.1.4. It indicates the recipient's device medium with a simple token. The values are a token with an equality relationship:
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.
Most of the values are useful for printing applications, or to distinguish printing from display. A typical use is selecting between a rendition intended to be printed and one intended to be displayed. Other media values were not included because their utility seemed relative. Interoperability with the Internet Print Protocol means that some additional feature values may need to be registered.
This tag says what the output is: a screen, a sheet of paper, a transparency, an envelope. It is what lets the sender choose a printable version instead of a screen version.
§2.4Paper Size: paper-size
The tag paper-size has ASN.1 identifier 1.3.6.1.8.1.5. For stationery it is often useful to have information about the size of the output. 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. Not all of the paper may have a printable area.
The values are a token with an equality relationship. Typical values are letter at 8.5x11.0 inches, a4 at 210x297 mm, b4 at 250x353 mm, a3 at 297x420 mm, and legal at 8.5x14 inches. The tag seems most useful for the printing application, for example choosing between a4 and letter size renditions of the same printable document.
One more token names the paper: letter, a4, legal and so on, each with its measurements. A sender can then offer the version that matches the paper in the tray.
§2.5Colour and Greyscale: color
The tag color has ASN.1 identifier 1.3.6.1.8.1.6. It indicates a gross level of capability to represent, or need for, handling of colour, out of a limited set of choices. The values are a token with an equality relationship:
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 colours, such as a highlight printer, pen plotter or limited colour display. At the lowest level this implies at least one colour other than black, and at the high end a small number, less than 32, of colours. No implication is made that any particular colour is available;mapped, pixel colour values are mapped in some specifiable way to a multi-component colour 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, the ability, or at least the willingness, to represent a full colour image and present it, with full continuous tone colour capability.
Web applications may choose between colour, grey or binary representations, and fax or printing applications might choose between colour and non-colour renditions. The intended usage of the tag is COMMON.
Five levels of colour, from plain black and white up to a full colour photograph. The tag says how much colour the recipient can take, so the sender does not send a picture it cannot use.
- binaryBlack-and-white or other bi-level capability.
- greyMore than two levels of intensity, for example at least two bits of grey-scale data.
- limitedA small number of colours, fewer than 32 at the high end.
- mappedPixel colours mapped into a more limited colour space.
- fullFull continuous tone colour capability.
§3Examples of Feature Comparison
The RFC gives three example comparisons that show how the features describe 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.The examples read as plain conditions: a screen no wider than 1024 pixels, a printer that does 300 dots per inch, or a sheet of A4 paper.
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.§5Security 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.
If the description of the recipient is wrong, the sender may send something the recipient cannot handle. That is the one security risk the RFC points out.