One document matched: draft-ietf-conneg-media-features-02.txt
Differences from draft-ietf-conneg-media-features-01.txt
INTERNET-DRAFT Larry Masinter
draft-ietf-conneg-media-features-02.txt Koen Holtman
Andy Mutz
Dan Wing
expires in 6 months September 7, 1998
Media Features for Display, Print, and Fax
Status of this memo
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Copyright (C) The Internet Society (1997). 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 (in pixels), color capability and bit-depth, or
media type. The physical dimensions of a display can 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:
***New assignments by IANA***
- 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:
***New assignments by IANA***
- 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.
2.3 Registration of 'media'
- Media Feature tag name(s):
ua-media
- ASN.1 identifier associated with this feature tag:
***New assignments by IANA***
- 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. Typical 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:
***New assignment by IANA***
- 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:
String with equality
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
grey
- ASN.1 identifier associated with this feature tag:
***New assignments by IANA***
- Summary of the media features indicated by this feature tag:
The color capabilities of the recipient are indicated with
feature value describing the number of color (or greyscale)
channel bits available.
- Values appropriate for use with this feature tag:
Integer
Values are typically (but not limited to) 2, 8, or 24. For
example: grey=8 indicates a display capable of representing an
image in 256 levels of a single color, while color=8 indicates a
display capable of representing an image with a palette of 256
colors.
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Web applications may choose between color, greyscale, or binary
representations. Fax applications may choose between color
and non-color renditions.
- Examples of typical use:
n/a
- Related standards or documents:
n/a
- Considerations particular to use in individual applications,
protocols, services, or negotiation mechanisms:
n/a
- Interoperability considerations:
n/a
- Security considerations:
n/a
- Privacy concerns, related to exposure of personal information:
n/a
- Denial of service concerns related to consequences of specifying
incorrect values:
n/a
- Additional information:
n/a
- Keywords:
n/a
- Related feature tags:
- Related media types or data formats:
- Related markup tags:
- Name(s) & email address(es) of person(s) to contact for
further information:
- Intended usage:
COMMON
- Author/Change controller:
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
indicates a 1024x768 display
dpi<=72
indicates a 72 dpi display
ua-media=stationery
indicates the display is a cut sheet of opaque material, such as
paper.
paper-size=iso-a4
indicates the display size is 210x297mm.
color<=24
indicates the display supports 24-bit (8-bit/channel) color.
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, grey,
ASN.1 identifiers should be assigned to each of these and replaced
in the body of the registration.
4. Acknowledgments
This document is based on a previous draft co-authored with Lou
Montoulli. It had benefited from the comments of Graham Klyne, Ho
John Lee, Brian Behlendorf, Jeff Mogul, and Ted Hardie.
References
[REG] A. Mutz, T. Hardie. "Feature Tag Registration Procedures",
draft-ietf-conneg-feature-reg-03.txt, July 1998.
[SI] ISO 1000:1992 "SI units and recommendations for the use of
their multiples and of certain other units", International
Organization for Standardization, 1992.
Author's Addresses
Larry Masinter
Xerox Palo Alto Research Center
3333 Coyote Hill Road
Palo Alto CA 94304
Fax +1 415 812 4333
Email: masinter@parc.xerox.com
Dan Wing
Cisco Systems, Inc.
101 Cooper Street
Santa Cruz, CA 95060 USA
Phone: +1 408 457 5200
Fax: +1 408 457 5208
EMail: dwing@cisco.com
Andrew H. Mutz
Hewlett-Packard Company
1501 Page Mill Road 3U-3
Palo Alto CA 94304, USA
Fax +1 415 857 4691
Email: mutz@hpl.hp.com
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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