IETF Fax working group Graham Klyne
Request for comments: nnnn 5GM/Content Technologies
Category: Work-in-progress Lloyd McIntyre
Xerox Corporation
October 1998
Expires: April 1999
Content feature schema for Internet fax
<draft-ietf-fax-feature-schema-01.txt>
Status of this memo
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[[INTENDED STATUS: This document specifies an Internet standards
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Copyright Notice
Copyright (C) The Internet Society 1998. All Rights Reserved.
Abstract
This document defines a content feature schema that is a profile of
the media feature registration mechanisms [1,2,3] for use in
performing capability identification between extended Internet fax
systems [5].
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This document does not describe any specific mechanisms for
communicating capability information, but does presume that any
such mechanisms will transfer textual values. It specifies a
textual format to be used for describing Internet fax capability
information.
Table of contents
1. Introduction ............................................2
1.1 Organization of this document 3
1.2 Terminology and document conventions 3
1.3 Revision history 3
1.4 Unfinished business 4
2. Fax feature schema syntax ...............................4
3. Internet fax feature tags ...............................4
3.1 Image Size 5
3.2 Resolution 5
3.3 Media type 6
3.4 Paper Size 6
3.5 Colour and greyscale 6
3.6 Coding 7
3.7 Colour model 8
3.8 Preferred units 8
4. Examples ................................................8
4.1 Simple mode Internet fax system 8
4.2 High-end black-and-white Internet fax system 9
4.3 Grey-scale Internet fax system 9
4.4 Full-colour Internet fax system (JPEG) 9
4.5 Full-colour Internet fax system (MRC) 9
4.6 Sender and receiver feature matching 9
5. Security considerations .................................12
5.1 Threats 12
6. Full copyright statement ................................12
7. Acknowledgements ........................................13
8. References ..............................................13
9. Authors' addresses ......................................15
Appendix A: Feature registrations ..........................15
1. Introduction
This document defines a content feature schema that is a profile of
the media feature registration mechanisms [1,2,3] for use in
performing capability identification between extended Internet fax
systems [5].
This document does not describe any specific mechanisms for
communicating capability information, but does presume that any
such mechanisms will transfer textual values. It specifies a
textual format to be used for describing Internet fax capability
information.
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The range of capabilities that can be indicated are based on those
covered by the TIFF file format for Internet fax [7] and Group 3
facsimile [6]. A companion document [4] describes the relationship
and mapping between this schema and Group 3 fax capabilities.
1.1 Organization of this document
Section 2 specifies the overall syntax for fax feature descriptions
by reference to the media feature registration and syntax documents
[1,2].
Section 3 enumerates the feature tags that are to be recognized and
processed by extended Internet fax systems, according to their
capabilities.
Appendix A contains additional feature tag registrations for media
features that are specific to fax and for which no applicable
registration already exists. These are presented in the form
prescribed by the media feature registration procedure [1].
1.2 Terminology and document conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The term "eifax system" is used to describe any software, device or
combination of these that conforms to the specification "Extended
Facsimile Using Internet Mail" [5].
NOTE: Comments like this provide additional nonessential
information about the rationale behind this document.
Such information is not needed for building a conformant
implementation, but may help those who wish to understand
the design in greater depth.
1.3 Revision history
00a 28-Sep-1998 Initial draft.
01a 12-Oct-1998 Incorporated review comments. Described feature
tag for differential x/y resolution ratio.
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1.4 Unfinished business
- Review terminology (especially eifax).
- Finalize feature set
- Supply examples
- Supply new feature registrations
2. Fax feature schema syntax
The syntax for the fax feature schema is described by "A syntax for
describing media feature sets" [2]. This in turn calls upon media
feature tags that may be registered according to the procedure
described in "Media Feature Tag Registration Procedure" [1].
NOTE: Media feature registration provides a base
vocabulary of features that correspond to media handling
capabilities. The feature set syntax provides a
mechanism and format for combining these to describe
combinations of features that may be handled by eifax
systems.
3. Internet fax feature tags
This section enumerates and briefly describes a number of feature
tags that are defined for use with Extended Internet Fax (eifax)
systems and applications. These tags may be used also by other
systems and applications that support corresponding capabilities.
The feature tags presented below are those that an eifax system is
expected to recognize its ability or non-ability to handle.
Definitive descriptions of feature tags are indicated by reference
to their registration per the 'conneg' registration procedure [1]
(some of which are appended to this document)
NOTE: The presence of a feature tag in this list does
not mean that an eifax system must have that capability;
rather, it must recognize the feature tag and deal with
it according to the capabilities that it does have.
Further, an eifax system is not prevented from
recognizing and offering additional feature tags. The
list below is intended to provide a minimum vocabulary
that all eifax systems can use in a consistent fashion.
If an unrecognized or unused feature tag is received, the
feature set matching rule (described in [2]) operates so
that tag is effectively ignored.
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3.1 Image Size
Feature tag name Legal values
---------------- ------------
pix-x <Integer> (>0)
pix-y <Integer> (>0)
Reference: "Media Features for Display, Print, and Fax" [3].
[[[GK: The use of pixels as a measure of fax image size is
currently under discussion: should we use pixels or some physical
unit of measure? In my opinion, we should use physical dimensions
rather than pixels, because when a device (like a fax) offers a
range of resolutions, these are not generally reflected in the
physical image size, though they would affect the pixel size.
Thus, using physical dimensions, it is not necessary to specify a
different image size with each resolution option.]]]
3.2 Resolution
Feature tag name Legal values
---------------- ------------
dpi <Integer> (>0)
dpi-xyratio <Rational> (>0)
Reference: "Media Features for Display, Print, and Fax" [3], and
this document appendix A.
If 'dpi-xyratio' is present and not equal to 1 then the horizontal
resolution (x-axis) is indicated by the 'dpi' feature value, and
the vertical resolution (y-axis) is the value of 'dpi' divided by
'dpi-xyratio'.
For example, the basic Group 3 fax resolution of 200*100dpi might
be indicated as:
(& (dpi=200) (dpi-xyratio=200/100) )
[[[Handling of differential x- and y- resolutions is currently
under discussion.]]]
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3.3 Media type
Feature tag name Legal values
---------------- ------------
ua-media screen
screen-paged
stationery
transparency
envelope
envelope-plain
continuous
Reference: "Media Features for Display, Print, and Fax" [3].
NOTE: Where the recipient indicates specific support for
hard copy or soft copy media type, a sender of colour
image data may wish to adjust the colour components (e.g.
per the related rules of ITU recommendation T.42 [9]) to
improve rendered image quality on that medium.
3.4 Paper Size
Feature tag name Legal values
---------------- ------------
paper-size A4
A3
B4
letter
legal
Reference: "Media Features for Display, Print, and Fax" [3].
3.5 Colour and greyscale
Feature tag name Legal values
---------------- ------------
grey <Integer>
(Typically 2,16,256,65536,16777216)
color <Integer>
(Typically 16,256,65536,16777216)
Reference: "Media Features for Display, Print, and Fax" [3].
NOTE: a bi-level (i.e. black-and-white only) fax image or
capability is indicated by the feature value 'grey=2'.
This is indicates the rendering capabilities of a
recipient or requirements of a document, and does not of
itself indicate a coding scheme.
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3.6 Coding
Feature tag name Legal values
---------------- ------------
image-coding MH
MR
MMR
JBIG-2-Level (bi-level)
JBIG-M-Level (multi-level)
JPEG
MRC
strip-size <Integer>
image-interleave Strip
Plane
color-subsampling <Boolean>
MRC-level <Integer> [1-7]
The 'strip-size' feature may be used with JBIG and MRC coding, and
indicates the maximum number of scan lines in an image strip. For
JBIG receivers the legal constraints are:
(strip-size=128)
(strip-size>=0)
The later being equivalent to no restriction. For MRC coded image
receivers, the legal constraints are:
(strip-size=[0..256])
(strip-size>=0)
For a receiver that can handle both JBIG and MRC images, the strip-
size constraints may need to be related to the image coding, as in
this example:
(| (& (image-coding=JBIG-2-LEVEL) (strip-size=128) )
(& (image-coding=JBIG-M-LEVEL) (strip-size=128) )
(& (image-coding=MRC) (strip-size=[0..256]) )
Where it may vary, the actual maximum strip size for a given file
is indicated in the image data.
The 'MRC-level' feature is used only if the 'image-coding' feature
includes MRC.
Reference: this document, appendix A.
[[[GK: color subsampling is proposed to be changed to a token, thus
allowing subsampling capabilities other than 4:1:1.]]]
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3.7 Colour model
Feature tag name Legal values
---------------- ------------
color-space CIELAB (per T.42 [9])
Palette (per T.43 [10])
custom-illuminant <Boolean>
custom-gamut <Boolean>
Reference: this document, appendix A.
3.8 Preferred units
Feature tag name Legal values
---------------- ------------
preferred-unit metric
inch
NOTE: this feature is really provided for interactions
that involve legacy fax machines. TIFF images used for
Internet fax (per RFC 2301 [7]) always contain inch-based
measurements.
The value of this feature does not affect in any way the
units used for expressing other feature values; e.g.
resolution is always measured in dots per inch.
Reference: this document, appendix A.
4. Examples
Some of the examples contain comments introduced by '--...'. These
are not part of the allowed capability description syntax. They
are included here to explain some of the constructs used.
<<<Suggested example subjects follow>>
4.1 Simple mode Internet fax system
This example describes the capabilities of a typical simple mode
Internet fax system. Note that TIFF application S is required to
be supported by such a system.
(& ( dpi=200 )
( dpi-xyratio=[200/100,200/200] )
( grey=2 )
( paper-size=A4 )
( image-coding=MH )
( ua-media=stationery ) )
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4.2 High-end black-and-white Internet fax system
This would include support for B/W JBIG and be equivalent to what
is sometimes called "Super G3", except that Internet fax
functionality would be added.
(& (| (& (dpi=200) (dpi-xyratio=200/100) ) -- 200*100
(& (dpi=200) (dpi-xyratio=1) ) -- 200*200
(& (dpi=300) (dpi-xyratio=1) ) -- 300*300
(& (dpi=400) (dpi-xyratio=1) ) ) -- 400*400
( grey=2 )
( paper-size=[A4,B4] )
( image-coding=[MH,MR,MMR,JBIG-2-LEVEL] ) )
4.3 Grey-scale Internet fax system
This is the previous example extended to handle grey scale multi-
level images. In keeping with Group 3 fax, this capability
requires equal x- and y- resolutions for a multi-level image.
(& (| (& (dpi=200) (dpi-xyratio=200/100) (grey=2) )
(& (dpi=200) (dpi-xyratio=1) )
(& (dpi=300) (dpi-xyratio=1) )
(& (dpi=400) (dpi-xyratio=1) ) )
( grey<=256 )
( paper-size=[A4,B4] )
( image-coding=[MH,MR,MMR,JBIG-2-LEVEL,JPEG,JBIG-M-LEVEL] ) )
4.4 Full-colour Internet fax system (JPEG)
<<<to be provided>>>
4.5 Full-colour Internet fax system (MRC)
<<<to be provided>>>
4.6 Sender and receiver feature matching
This example considers sending a document to a high-end black-and-
white fax system with the following capabilities:
(& (| (& (dpi=200) (dpi-xyratio=200/100) ) -- 200*100
(& (dpi=200) (dpi-xyratio=1) ) -- 200*200
(& (dpi=300) (dpi-xyratio=1) ) -- 300*300
(& (dpi=400) (dpi-xyratio=1) ) ) -- 400*400
( grey=2 ) (color=0)
(| (& (paper-size=A4) (ua-media=[stationery,transparency]) )
(& (paper-size=B4) (ua-media=continuous) ) )
( image-coding=[MH,MR,JBIG-2-LEVEL] ) )
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Turning to the document itself, assume it is available to the
sender in three possible formats, A4 high resolution, B4 low
resolution and A4 high resolution colour, described by:
(& ( dpi=300 ) ( dpi-xyratio=1 )
( grey=2 )
( paper-size=A4 )
( image-coding=[MMR,JBIG-2-LEVEL] ) )
(& ( dpi=200 ) (dpi-xyratio=200/100)
( grey=2 )
( paper-size=B4 )
( image-coding=[MH,MR] ) )
(& ( dpi=300 ) ( dpi-xyratio=1 )
( color<=256 )
( paper-size=A4 )
( image-coding=JPEG ) )
These three image formats can be combined into a composite
capability statement by a logical-OR operation (to describe format-
1 OR format-2 OR format-3):
(| (& ( dpi=300 ) ( dpi-xyratio=1 )
( grey=2 )
( paper-size=A4 )
( image-coding=[MMR,JBIG-2-LEVEL] ) )
(& ( dpi=200 ) (dpi-xyratio=200/100)
( grey=2 )
( paper-size=B4 )
( image-coding=[MH,MR] ) )
(& ( dpi=300 ) ( dpi-xyratio=1 )
( color=42 )
( paper-size=A4 )
( image-coding=JPEG ) ) )
This could be simplified, but there is little gain in doing so at
this point.
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The composite document description can be matched with the receiver
capability description, according to the rules in [2], to yield the
result:
(| (& ( dpi=300 ) ( dpi-xyratio=1 )
( grey=2 )
( paper-size=A4 )
( ua-media=[stationery,transparency] )
( image-coding=JBIG-2-LEVEL ) )
(& ( dpi=200 ) (dpi-xyratio=200/100)
( grey=2 )
( paper-size=B4 )
( ua-media=continuous )
( image-coding=[MH,MR] ) ) )
Points to note about the feature matching process:
o The colour document option is eliminated because the receiver
cannot handle either colour (indicated by '(color=0)') or JPEG
coding.
o The high resolution version of the document with '(dpi=300)' must
be send using '(image-coding=JBIG-2-LEVEL)' because this is the
only available coding of the image data that the receiver can use
for high resolution documents.
o The low-resolution version of the document can be sent with
either MH or MR coding as the receiver can deal with either of
these for low resolution documents.
o The high resolution variant of the document is available only for
A4, so that is the paper-size used in that case. Similarly the
low resolution version is sent for B4 paper.
o Even though the sender may not understand the 'ua-media' feature
tag, and does not mention it, the matching rules preserve the
constraint that the B4 document is rendered with
'(ua-media=continuous)', and the A4 document may be rendered with
'(ua-media=[stationery,transparency])'.
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5. Security considerations
The points raised below are in addition to the general security
considerations for extended Internet fax [5], and others discussed
in [2,8,11,12,13]
5.1 Threats
Negotiation mechanisms reveal information about one party to other
parties. This may raise privacy concerns, and may allow a
malicious party to make better guesses about the presence of
specific security holes.
Most of these considerations pertain to capabilities information
getting into the hands of someone who wanted to abuse it. This
document specifies a list of capabilities which will help a sender
determine what image files characteristics can be processed by the
recipient, not mechanisms for their publication. Implementors and
users should try to ensure that these capabilities are provided to
appropriate persons, systems and agents.
1. Unsolicited bulk mail: if it is known that a recipient can
process certain types of images, they may be targeted by bulk
mailers that want to send such images.
<<<more to be provided>>>
6. Full copyright statement
Copyright (C) The Internet Society 1998. 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.
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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.
7. Acknowledgements
The authors gratefully acknowledge the following persons who made
comments on earlier versions of this memo: James Rafferty, Dan
Wing, [[...]].
8. References
[1] "Media Feature Tag Registration Procedure"
Koen Holtman, TUE
Andrew Mutz, Hewlett-Packard
Ted Hardie, NASA
Internet draft: <draft-ietf-conneg-feature-reg-03.txt>
Work in progress, July 1998.
[2] "A syntax for describing media feature sets"
Graham Klyne, 5GM/Content Technologies
Internet draft: <draft-ietf-conneg-feature-syntax-00.txt>"
Work in progress, September 1998.
[3] "Media Features for Display, Print, and Fax"
Larry Masinter, Xerox PARC
Koen Holtman, TUE
Andrew Mutz, Hewlett-Packard
Dan Wing, Cisco Systems
Internet draft: <draft-ietf-conneg-media-features-02.txt>
Work in progress, September 1998.
[4] "Internet fax feature mapping from Group 3 fax"
Lloyd McIntyre, Xerox Corporation
Graham Klyne, 5GM/Content Technologies
Internet draft: <draft-ietf-fax-feature-T30-mapping-00.txt>
Work in progress, August 1998.
[5] "Extended Facsimile Using Internet Mail
Larry Masinter, Xerox Corporation
Dan Wing, Cisco Systems
Internet draft: <draft-ietf-fax-eifax-04.txt>
Work in progress, September 1998.
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[6] "Procedures for document facsimile transmission in the general
switched telephone network"
ITU-T Recommendation T.30
International Telecommunications Union
July 1996
[7] RFC 2301, "File format for Internet fax"
L. McIntyre,
R. Buckley,
D. Venable, Xerox Corporation
S. Zilles, Adobe Systems, Inc.
G. Parsons, Northern Telecom
J. Rafferty, Human Communications
March 1998.
[8] RFC 2305, "A Simple Mode of Facsimile Using Internet Mail"
K. Toyoda
H. Ohno
J. Murai, WIDE Project
D. Wing, Cisco Systems
March 1998.
[9] T.42 (custom illuminant, gamut)
[10] T.43 (JBIG for colour/grey)
[11] "Scenarios for the Delivery of Negotiated Content"
T. Hardie, NASA Network Information Center
Internet draft: <draft-ietf-http-negotiate-scenario-02.txt>
Work in progress, November 1997.
[12] "Requirements for protocol-independent content negotiation"
G. Klyne, Integralis Ltd.
Internet draft: <draft-ietf-conneg-requirements-00.txt>
Work in progress, March 1998.
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9. Authors' addresses
Graham Klyne
5th Generation Messaging Ltd. Content Technologies Ltd.
5 Watlington Street Forum 1, Station Road
Nettlebed Theale
Henley-on-Thames, RG9 5AB Reading, RG7 4RA
United Kingdom United Kingdom.
Telephone: +44 1491 641 641 +44 118 930 1300
Facsimile: +44 1491 641 611 +44 118 930 1301
E-mail: GK@ACM.ORG
Lloyd McIntyre
Xerox Corporation
Mailstop PAHV-305
3400 Hillview Ave.
Palo Alto, CA 94304 USA
Telephone: +1-650-813-6762
Facsimile: +1-650-845-2340
E-mail: Lloyd.McIntyre@pahv.xerox.com
Appendix A: Feature registrations
[[[This appendix contains registrations of media features, that are
specific to fax and for which no applicable registration already
exists.]]]
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