As per Relevance of the word describe, we have this rfc below:
Network Working Group G.
Request for Comments: 2531 5GM/Content
Category: Standards Track L.
Xerox
March 1999
Content Feature Schema for Internet
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
Copyright
Copyright (C) The Internet Society (1999). All Rights Reserved
This document defines a content feature schema that is a profile
the media feature registration mechanisms [1,2,3] for use
performing capability identification between extended Internet
systems [5].
This document does not describe any specific mechanisms
communicating capability information, but does presume that any
mechanisms will transfer textual values. It specifies a
format to be used for describing Internet fax capability information
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RFC 2531 Content Feature Schema for Internet Fax March 1999
Table of
1. Introduction .............................................3
1.1 Organization of this document............................3
1.2 Terminology and document conventions.....................3
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 Color capability.........................................6
3.6 Color model..............................................8
3.7 Image coding............................................10
4. Examples ................................................12
4.1 Simple mode Internet fax system.........................12
4.2 High-end black-and-white Internet fax system............12
4.3 Grey-scale Internet fax system..........................13
4.4 Full-color Internet fax system..........................13
4.5 Full-color Internet fax system (MRC)....................14
4.6 Sender and receiver feature matching....................15
5. IANA Considerations .....................................17
6. Security Considerations .................................17
6.1 Capability descriptions and mechanisms..................17
6.2 Specific threats........................................18
7. Acknowledgements ........................................18
8. References ..............................................18
9. Authors' Addresses ......................................21
Appendix A: Feature registrations ..........................22
A.1 Image size..............................................22
A.2 Resolution aspect ratio.................................24
A.3 Color levels............................................25
A.4 Color space.............................................27
A.5 CIELAB color depth......................................30
A.6 CIELAB color gamut......................................32
A.7 Image file structure....................................34
A.8 Image data coding.......................................36
A.9 Image coding constraint.................................38
A.10 JBIG stripe size.......................................39
A.11 Image interleave.......................................41
A.12 Color subsampling......................................42
A.13 MRC availability and mode..............................43
A.14 MRC maximum stripe size................................45
Appendix B: TIFF mode descriptions .........................47
Appendix C: Revision history ...............................49
Full Copyright Statement ...................................51
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RFC 2531 Content Feature Schema for Internet Fax March 1999
1.
This document defines a content feature schema that is a profile
the media feature registration mechanisms [1,2,3] for use
performing capability identification between extended Internet
systems [5].
This document does not describe any specific mechanisms
communicating capability information, but does presume that any
mechanisms will transfer textual values. It specifies a
format to be used for describing Internet fax capability information
The range of capabilities that can be indicated are based on
covered by the TIFF file format for Internet fax [7] and Group 3
facsimile [6]. A companion document [4] describes the
and mapping between this schema and Group 3 fax capabilities
1.1 Organization of this
Section 2 specifies the overall syntax for fax feature
by reference to the media feature registration and syntax
[1,2].
Section 3 enumerates the feature tags that are to be recognized
processed by extended Internet fax systems, according to
capabilities
Appendix A contains additional feature tag registrations for
features that are specific to fax and for which no
registration already exists. These are presented in the
prescribed by the media feature registration procedure [1].
1.2 Terminology and document
The term "extended Internet fax system" is used to describe
software, device or combination of these that conforms to
specification "Extended Facsimile Using Internet Mail" [5].
"capability exchange" describes any transfer of information
communicating systems that is used to indicate system
and hence determine the form of data transferred. This term
both one-way and two-way transfers of capability information
"capability identification" is a particular form of
exchange in which a receiving system provides capability
to a sending system
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RFC 2531 Content Feature Schema for Internet Fax March 1999
"capability description" is a collection of data presented in
specific format that describes the capabilities of some
entity. It may exist separately from any specific
exchange mechanism
NOTE: Comments like this provide additional
information about the rationale behind this document.
information is not needed for building a
implementation, but may help those who wish to understand
design in greater depth
2. Fax feature schema
The syntax for the fax feature schema is described by "A syntax
describing media feature sets" [2]. This in turn calls upon
feature tags that may be registered according to the
described in "Media Feature Tag Registration Procedure" [1].
NOTE: Media feature registration provides a base vocabulary
features that correspond to media handling capabilities.
feature set syntax provides a mechanism and format for
these to describe combinations of features. This memo
those features that may be associated with extended Internet
systems
3. Internet fax feature
This section enumerates and briefly describes a number of
tags that are defined for use with extended Internet fax systems
applications. These tags may be used also by other systems
applications that support corresponding capabilities
The feature tags presented below are those that an extended
fax system is expected to recognize its ability or non-ability
handle
Definitive descriptions of feature tags are indicated by reference
their registration per the media feature registration procedure [1]
(some of which are appended to this document
NOTE: The presence of a feature tag in this list does not
that an extended Internet fax system must have that capability
rather, it must recognize the feature tag and deal with
according to the capabilities that it does have
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RFC 2531 Content Feature Schema for Internet Fax March 1999
Further, an extended Internet fax system is not prevented
recognizing and offering additional feature tags. The list
is intended to provide a basic vocabulary that all
Internet fax systems can use in a consistent fashion
If an unrecognized or unused feature tag is received, the
set matching rule (described in RFC2533 [2]) operates so that
is effectively ignored
3.1 Image
Feature tag name Legal
---------------- ------------
size-x (>0)
size-y (>0)
Reference: this document, Appendix A
These feature values indicate a rendered document size in inches
Where the actual size is measured in millimetres, a
factor of 10/254 may be applied to yield an exact inch-based value
3.2
Feature tag name Legal
---------------- ------------
dpi (>0)
dpi-xyratio (>0)
Reference: "Media Features for Display, Print, and Fax" [3], and
document appendix A
If 'dpi-xyratio' is present and not equal to 1 then the
resolution (x-axis) is indicated by the 'dpi' feature value, and
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
indicated as
(& (dpi=200) (dpi-xyratio=200/100) )
When describing resolutions for an MRC format document, the
set of usable resolutions is listed. However, there are
restrictions on their use: (a) 100dpi resolution can be used
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RFC 2531 Content Feature Schema for Internet Fax March 1999
with multi-level images, and (b) any multi-level image resolution
required to be an integral sub-multiple of the applicable
resolution
3.3 Media
Feature tag name Legal
---------------- ------------
ua-media
screen-
envelope-
Reference: "Media Features for Display, Print, and Fax" [3].
NOTE: Where the recipient indicates specific support for hard
or soft copy media type, a sender of color image data may wish
adjust the color components (e.g. per the related rules of
recommendation T.42 [9]) to improve rendered image quality on
medium
3.4 Paper
Feature tag name Legal
---------------- ------------
paper-size A
A
B
Reference: "Media Features for Display, Print, and Fax" [3].
3.5 Color
Feature tag name Legal
---------------- ------------
color Binary (bi-level only
Limited (a limited number of colors
Mapped (palette or otherwise mapped color
Grey (grey-scale only
Full (full continuous-tone color
Reference: "Media Features for Display, Print, and Fax" [3].
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The intention here is to give a broad indication of color
capabilities that might be used, for example, to select among a
number of available data resources
The value of this feature also gives an indication of the
detailed color handling features that might be applicable (see
section).
'Binary' indicates black-and-white, or other bi-level capability.
further qualifying feature tags are required
'Limited' indicates a small number of distinct fixed colors, such
might be provided by a highlight printer, pen plotter or
color display. The 'color-levels' tag should be used to indicate
number of distinct colors available
NOTE: No ability to indicate any specific or named color
implied by this option
Some devices might use different intensity levels rather
different hues for distinction
'Mapped' indicates that pixel color values are mapped in
specifiable way to a multi-component color space. The 'color-levels
tag may be used to indicate the number of distinct colors available
in its absence, sufficient levels to display a photographic
should be assumed
'Grey' indicates a continuous tone grey-scale capability
'Full' indicates full continuous tone color capability
For 'Mapped', 'Grey' and 'Full' color, additional feature
(section 3.6) may be used to further qualify the color reproduction
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3.6 Color
Feature tag name Legal
---------------- ------------
color-levels (>2)
color-space Device-RGB (device RGB
Device-CMY (device CMY
Device-CMYK (device CMYK
CIELAB (LAB per T.42 [9])
(may be extended by further registrations
CIELAB-L-depth (>0)
CIELAB-a-
CIELAB-b-
CIELAB-L-min
CIELAB-L-
CIELAB-a-
CIELAB-a-
CIELAB-b-
CIELAB-b-
Reference: this document, appendix A
The general model for image handling (both color and non-color)
described here from a receiver's perspective; a similar
operates in the reverse direction for a scan/send perspective
raw bit pixel color
stream -(A)-> values -(B)-> values -(C)->
- "raw bit stream" is a stream of coded
(A) indicates image coding/decoding (MH,MR,MMR,JPEG,JBIG,etc.)
- "pixel values" are a single numeric value per picture
that designates the color of that element
(B) indicates pixel-to-color value
- "color values" have a separate numeric value for each
component (i.e. L*, a*, b* in the case of CIELAB
above.)
(C) indicates how the color values are related to a
color. This involves interpretation of the color value
respect to a color model (e.g. RGB, L*a*b*, CMY, CMYK) and
color space (which is typically recipient-dependent).
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- "physical rendition" is a color value physically realized on
display, printer or other device
There are many variables that can be applied at each stage of
processing of a color image, and any may be critical to
handling of that image in some circumstances. In other
many of the variables may be implied (to some level of approximation
in the application that uses them (e.g. color images published on
Web page).
The color feature framework described here is intended to
capability description at a range of granularity: feature tags
correspond to implied (or "don't care" or "unknown") feature
may simply be omitted from a capability description
Grey scale and bi-level images are handled within this framework as
special case, having a 1-component color model. The
features are used for describing color capabilities
'color-levels' indicates the number of distinct values for
picture element, and applies to all but bi-level images. For bi
level images, a value of 2 is implied
'color-space' is used mainly with 'Mapped' and 'Full', but could
used with other modes if the exact color used is significant.
kinds of color space can be distinguished: device-dependent
calibrated. Device dependent spaces are named here as 'Device-xxx',
and are used to indicate a color space that is defined by
receiving device. Calibrated color spaces presume the existence of
rendering system that is calibrated with respect to an
definition, and is capable of processing the device-independent
information accordingly
A color-handling receiver should indicate any appropriate
color space capability in addition to any calibrated color
that it may support. A calibrated color space should be used
precise color matching is required in the absence of
knowledge of the receiving system
NOTE: In practice, although they appear to be separate concepts
the color model and color space cannot be separated. In the
analysis, a color model (RGB, CMY, etc.) must be defined
respect to some color space
'CIELAB-L-depth', 'CIELAB-a-depth' and 'CIELAB-b-depth' indicate
number of different values that are possible for the L*, a* and b
color components respectively, and are significant only when
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RFC 2531 Content Feature Schema for Internet Fax March 1999
are represented in a CIELAB color space. These features would
used with palettized color, or with full color where each
component has a different number of possible values
The 'CIELAB-x-min' and 'CIELAB-x-max' values indicate a color
(i.e. a range of color values that are used or may be rendered).
gamut may be indicated in terms of the CIELAB color space even
colors are represented in some other space
3.7 Image
Feature tag name Legal
---------------- ------------
image-file- TIFF-
structure TIFF-
TIFF-
TIFF-
TIFF-
TIFF-
(may be extended by further registrations
to cover non-TIFF image file structures
image-coding
(may be extended by further registrations
image-coding- JBIG-T85 (bi-level, per ITU T.85)
constraint JBIG-T43 (multi-level, per ITU T.43)
JPEG-T4E (per ITU T.4, Annex E
(may be extended by further registrations
JBIG-stripe-size
image-interleave
color-subsampling "1:1:1" (no color subsampling
"4:1:1" (4:1:1 color subsampling
MRC-mode (0..7) (per ITU T.44 [15])
MRC-max-stripe-size
Reference: this document, appendix A
'image-file-structure' defines how the coded image data is
and formatted. Options defined here are the various profiles
TIFF-FX, per RFC 2301 [7]. These options apply to overall
of the image data (TIFF file format, byte ordering, bit ordering
etc.) and do not define specific image coding issues that are
by other aspects of the TIFF-FX profile specifications
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'image-coding' describes how the raw image data is compressed
coded as a sequence of bits. These are generic tags that may
to a range of file formats and usage environments
'image-coding-constraint' describes how the raw image data
method is constrained to meet a particular operating environment
Options defined here are JBIG and JPEG coding constraints that
in typical Group 3 fax environments
The 'JBIG-stripe-size' feature may be used with JBIG image coding
and indicates the number of scan lines in each stripe except the
in an image. The legal constraints are
(JBIG-stripe-size=128)
(JBIG-stripe-size>=0)
The latter being equivalent to no restriction
The 'MRC-mode' feature is used to indicate the availability of
(mixed raster content) image format capability, and also the MRC
available. A zero value indicates MRC is not available, a non-
value indicates the available MRC mode number
An MRC formatted document is actually a collection of several images
each of which is described by a separate feature collection.
MRC-capable receiver is presumed to be capable of accepting
combination of contained images that conform to the MRC
rules and declared image-coding capabilities
Within an MRC-formatted document, multi-level coders are used
foreground and background images (i.e. odd-numbered layers: 1, 3, 5,
etc.) and bi-level coders are used for mask layers (i.e.
numbered layers 2, 4, 6, etc.).
NOTE: an MRC formatted document may appear within a TIFF
file structure, so this separate feature is needed to capture
full range of possible capabilities
The 'MRC-max-stripe-size' feature may be used with MRC coding,
indicates the maximum number of scan lines in each MRC stripe.
legal constraints are
(MRC-max-stripe-size=[0..256])
(MRC-max-stripe-size>=0)
These values indicate upper bounds on the stripe size. The
value may vary between stripes, and the actual size for each
is indicated in the image data
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RFC 2531 Content Feature Schema for Internet Fax March 1999
NOTE: there are many image coding options here, and not all
required in all circumstances
Specification of the image-file-structure tag value alone is
normally sufficient to describe the capabilities of a recipient
A general rule is that sufficient detail should be provided
exclude any unsupported features
For extended Internet fax, image-file-structure and image-
should always be specified, together with additional
described above as needed to clearly indicate which feature
values are supported and which are not. (See also the examples
section 4.)
4.
Some of the examples contain comments introduced by '--...'.
are not part of the allowed capability description syntax. They
included here to explain some of the constructs used
The level of detail captured here reflects that used for
identification in Group 3 facsimile
4.1 Simple mode Internet fax
This example describes the capabilities of a typical simple
Internet fax system. Note that TIFF application S is required to
supported by such a system
(& (color=Binary
(image-file-structure=TIFF-S
(dpi=200)
(dpi-xyratio=[200/100,200/200])
(paper-size=A4)
(image-coding=MH) (MRC-mode=0)
(ua-media=stationery) )
4.2 High-end black-and-white Internet fax
This would include support for B/W JBIG and be equivalent to what
sometimes called "Super G3", except that Internet fax
would be added
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RFC 2531 Content Feature Schema for Internet Fax March 1999
(& (color=Binary
(image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
(| (& (dpi=200) (dpi-xyratio=200/100) ) -- 200*100
(& (dpi=200) (dpi-xyratio=1) ) -- 200*200
(& (dpi=204) (dpi-xyratio=204/391) ) -- 204*391
(& (dpi=300) (dpi-xyratio=1) ) ) -- 300*300
(| (image-coding=[MH,MR,MMR])
(& (image-coding=JBIG
(image-coding-constraint=JBIG-T85)
(JBIG-stripe-size=128) ) )
(MRC-mode=0)
(paper-size=[A4,B4]) )
4.3 Grey-scale Internet fax
This is the previous example extended to handle grey scale multi
level images. In keeping with Group 3 fax, this example
equal x- and y- resolutions for a multi-level image
(& (| (& (color=Binary
(image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
(| (image-coding=[MH,MR,MMR])
(& (image-coding=JBIG
(image-coding-constraint=JBIG-T85)
(JBIG-stripe-size=128) ) )
(| (& (dpi=200) (dpi-xyratio=200/100) )
(& (dpi=200) (dpi-xyratio=1) )
(& (dpi=204) (dpi-xyratio=204/391) )
(& (dpi=300) (dpi-xyratio=1) ) ) )
(& (color=Grey
(image-file-structure=[TIFF-C,TIFF-L])
(color-levels<=256)
(color-space-CIELAB
(| (& (image-coding=JPEG
(image-coding-constraint=JPEG-T4E) )
(& (image-coding=JBIG
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe) ) )
(dpi=[100,200,300])
(dpi-xyratio=1) ) )
(MRC-mode=0)
(paper-size=[A4,B4]) )
4.4 Full-color Internet fax
This adds 16-bit full-color to the previous example
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(& (| (& (color=Binary
(image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
(| (image-coding=[MH,MR,MMR])
(& (image-coding=JBIG
(image-coding-constraint=JBIG-T85)
(JBIG-stripe-size=128) ) )
(| (& (dpi=200) (dpi-xyratio=200/100) )
(& (dpi=200) (dpi-xyratio=1) )
(& (dpi=204) (dpi-xyratio=204/391) )
(& (dpi=300) (dpi-xyratio=1) ) ) )
(& (| (& (color=Grey) (color-levels<=256) )
(& (color=Full) (color-levels<=65536)
(color-subsampling=["1:1:1","4:1:1"]) ) )
(image-file-structure=[TIFF-C,TIFF-L])
(color-space=CIELAB
(| (& (image-coding=JPEG
(image-coding-constraint=JPEG-T4E) )
(& (image-coding=JBIG
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe) ) )
(dpi=[100,200,300])
(dpi-xyratio=1) ) )
(MRC-mode=0)
(paper-size=[A4,B4]) )
4.5 Full-color Internet fax system (MRC
(& (| (& (color=Binary
(image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
(MRC-mode=0)
(image-coding=[MH,MMR])
(| (& (dpi=200) (dpi-xyratio=[200/100,1]) )
(& (dpi=204) (dpi-xyratio=204/391) )
(& (dpi=300) (dpi-xyratio=1) )
(& (dpi=400) (dpi-xyratio=1) ) ) )
(& (image-file-structure=[TIFF-C,TIFF-L])
(| (& (color=Grey) (color-levels<=256) )
(& (color=Full) (color-levels<=65536)
(color-subsampling=["1:1:1","4:1:1"]) ) )
(color-space=CIELAB
(MRC-mode=0)
(image-coding=JPEG
(image-coding-constraint=JPEG-T4E
(dpi=[100,200,300,400])
(dpi-xyratio=1) )
(& (image-file-structure=TIFF-M
(MRC-mode=1) (MRC-max-stripe-size=[0..256])
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(image-coding=[MH,MMR,JPEG])
(| (color=Binary
(& (color=Grey) (color-levels<=256) )
(& (color=Full) (color-levels<=65536)
(color-subsampling=["1:1:1","4:1:1"]) ) )
(color-space=CIELAB
(dpi=[100,200,300,400])
(dpi-xyratio=1) ) )
(paper-size=[A4,B4]) )
4.6 Sender and receiver feature
This example considers sending a document to a high-end black-and
white fax system with the following receiver 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
(color=Binary
(| (& (paper-size=A4) (ua-media=[stationery,transparency]) )
(& (paper-size=B4) (ua-media=continuous) ) )
(image-coding=[MH,MR,JBIG]) )
Turning to the document itself, assume it is available to the
in three possible formats, A4 high resolution, B4 low resolution
A4 high resolution color, described by
(& (dpi=300) (dpi-xyratio=1)
(color=Binary
(paper-size=A4)
(image-coding=[MMR,JBIG]) )
(& (dpi=200) (dpi-xyratio=200/100)
(color=Binary
(paper-size=B4)
(image-coding=[MH,MR]) )
(& (dpi=300) (dpi-xyratio=1)
(color=Mapped) (color-levels<=256)
(paper-size=A4)
(image-coding=JPEG) )
These three image formats can be combined into a composite
statement by a logical-OR operation (to describe format-1 OR format-2
OR format-3):
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RFC 2531 Content Feature Schema for Internet Fax March 1999
(& (dpi=300) (dpi-xyratio=1)
(color=Binary
(paper-size=A4)
(image-coding=[MMR,JBIG]) )
(& (dpi=200) (dpi-xyratio=200/100)
(color=Binary
(paper-size=B4)
(image-coding=[MH,MR]) )
(& (dpi=300) (dpi-xyratio=1)
(color=Mapped) (color-levels=42)
(paper-size=A4)
(image-coding=JPEG) ) )
This could be simplified, but there is little gain in doing so
this point
The composite document description can be matched with the
capability description, according to the rules in [2], to yield
result
(& (dpi=300) (dpi-xyratio=1)
(color=Binary
(paper-size=A4)
(ua-media=[stationery,transparency])
(image-coding=JBIG) )
(& (dpi=200) (dpi-xyratio=200/100)
(color=Binary
(paper-size=B4)
(ua-media=continuous
(image-coding=[MH,MR]) ) )
Points to note about the feature matching process
o The color document option is eliminated because the
cannot handle either color (indicated by '(color=Mapped)') or
coding (indicated by '(image-coding=JPEG)').
o The high resolution version of the document with '(dpi=300)'
be send using '(image-coding=JBIG)' because this is the
available coding of the image data that the receiver can use
high resolution documents. (The available 300dpi document
here are MMR and JBIG, and the receiver capabilities are MH,
and JBIG.)
o The low-resolution version of the document can be sent with
MH or MR coding as the receiver can deal with either of these
low resolution documents
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RFC 2531 Content Feature Schema for Internet Fax March 1999
o The high resolution variant of the document is available only
A4, so that is the paper-size used in that case. Similarly
low resolution version is sent for B4 paper
o Even though the sender may not understand the 'ua-media'
tag, and does not mention it, the matching rules preserve
constraint that the B4 document is rendered with '(ua
media=continuous)', and the A4 document may be rendered with '
(ua-media=[stationery,transparency])'.
Finally, note that when matching an MRC document description,
description of each component sub-image must match the
of the intended receiver
5. IANA
Appendix A of this document calls for registrations of feature
in the "IETF tree", as defined in section 3.1.1 of "Media Feature
Registration Procedure" [1] (i.e. these feature tags are subject
the "IETF Consensus" policies described in RFC 2434 [21]).
ASN.1 identifiers should be assigned for each of these
feature tags and replaced in the body of the registration
6. Security
The points raised below are in addition to the general
considerations for extended Internet fax [5], and others discussed
[2,8,11,12,13]
6.1 Capability descriptions and
Negotiation mechanisms reveal information about one party to
parties. This may raise privacy concerns, and may allow a
party to make better guesses about the presence of specific
holes
Most of these concerns pertain to capability information getting
the hands of someone who may abuse it. This document
capabilities that help a sender to determine what
characteristics can be processed by the recipient, not mechanisms
their publication. Implementors and users should take care that
mechanisms employed ensure that capabilities are revealed only
appropriate persons, systems and agents
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RFC 2531 Content Feature Schema for Internet Fax March 1999
6.2 Specific
1. Unsolicited bulk mail: if it is known that a recipient
process certain types of images, they may be targeted by
mailers that want to send such images
7.
The authors gratefully acknowledge the contributions of the
persons who commented on earlier versions of this memo:
Rafferty, Dan Wing, Robert Buckley, Mr Ryuji Iwazaki. The
contributed ideas upon which some of the features described here
been based: Larry Masinter, Al Gilman, Koen Holtman
8.
[1] Holtman, K., Mutz, A. and T. Hardie, "Media Feature
Registration Procedure", BCP 31, RFC 2506, March 1999.
[2] Klyne, G., "A Syntax for Describing Media Feature Sets",
2533, March 1999.
[3] Masinter, L., Holtman, K., Mutz, A. and D. Wing, "Media
for Display, Print, and Fax", RFC 2534, March 1999.
[4] McIntyre, L. and G. Klyne, "Internet fax feature mapping
Group 3 fax", Work in Progress
[5] Masinter, L. and D. Wing, "Extended Facsimile Using
Mail", RFC 2532, March 1999.
[6] "Procedures for document facsimile transmission in the
switched telephone network", ITU-T Recommendation T.30 (1996),
International Telecommunications Union, July 1996.
[7] McIntyre, L., Buckley, R., Venable, D., Zilles, S., Parsons, G
and J. Rafferty, "File format for Internet fax", RFC 2301,
1998.
[8] Toyoda, K., Ohno, H., Murai, J. and D. Wing, "A Simple Mode
Facsimile Using Internet Mail", RFC 2305, March 1998.
[9] "Continuous-tone color representation method for facsimile
ITU-T Recommendation T.42 (1996),
Telecommunications Union, (Covers custom illuminant, gamut).
Klyne & McIntyre Standards Track [Page 18]
RFC 2531 Content Feature Schema for Internet Fax March 1999
[10] "Colour and gray-scale image representation using
coding scheme for facsimile", ITU-T Recommendation T.43 (1997),
International Telecommunications Union. (Covers JBIG
colour/grey images).
[11] Hardie, T., "Scenarios for the Delivery of Negotiated Content",
Work in Progress
[12] Klyne, G., "Requirements for protocol-independent
negotiation", Work in Progress
[13] "Standardization of Group 3 facsimile terminals for
transmission", ITU-T Recommendation T.4 (1996),
Telecommunications Union, (Covers basic fax coding formats: MH
MR).
[14] "Facsimile coding schemes and coding control functions for
4 facsimile apparatus", ITU Recommendation T.6,
Telecommunications Union, (Commonly referred to as the
standard; covers extended 2-D fax coding format).
[15] "Mixed Raster Content (MRC)", ITU-T Recommendation T.44,
International Telecommunications Union
[16] "Information technology - Digital compression and coding
continuous-tone still image - Requirements and guidelines",
ITU-T Recommendation T.81 (1992) | ISO/IEC 10918-1:1993,
International Telecommunications Union, (Commonly referred to
JPEG standard).
[17] "Information technology - Coded representation of picture
audio information - Progressive bi-level image compression",
ITU-T Recommendation T.82 (1993) | ISO/IEC 11544:1993,
International Telecommunications Union, (Commonly referred to
JBIG1 standard).
[18] "Application profile for Recommendation T.82 - Progressive bi
level image compression (JBIG1 coding scheme for
apparatus)", ITU-T Recommendation T.85 (1995),
Telecommunications Union, (Covers bi-level JBIG).
[19] "Colorimeter, 2nd ed.", CIE Publication No. 15.2, 1986.
(Defines CIELAB color space; use with fax is
constrained by T.42 [9].)
Klyne & McIntyre Standards Track [Page 19]
RFC 2531 Content Feature Schema for Internet Fax March 1999
[20] Tag Image File Format, Revision 6.0, Adobe
Association
/pdffiles/tiff6.pdf>, June 1992.
[21] Narten, T. and H. Alvestrand, "Guidelines for Writing an
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
Klyne & McIntyre Standards Track [Page 20]
RFC 2531 Content Feature Schema for Internet Fax March 1999
9. Authors'
Graham
5th Generation Messaging Ltd. Content Technologies Ltd
5 Watlington Street Forum 1, Station
Nettlebed
Henley-on-Thames, RG9 5AB Reading, RG7 4
United Kingdom United Kingdom
Phone: +44 1491 641 641 +44 118 930 1300
Facsimile: +44 1491 641 611 +44 118 930 1301
EMail: GK@ACM.
Lloyd
Xerox
Mailstop PAHV-121
3400 Hillview Ave
Palo Alto, CA 94304
Phone: +1-650-813-6762
Facsimile: +1-650-845-2340
EMail: Lloyd.McIntyre@pahv.xerox.
Klyne & McIntyre Standards Track [Page 21]
RFC 2531 Content Feature Schema for Internet Fax March 1999
Appendix A: Feature
A.1 Image
- Media Feature tag name(s):
size-
size-
- ASN.1 identifiers associated with these feature tags
1.3.6.1.8.1.7
1.3.6.1.8.1.8
- Summary of the media features indicated
These feature tags indicate the size of a displayed, printed
otherwise rendered document image; they indicate
(size-x) and vertical (size-y) dimensions
The unit of measure is inches (to be consistent with
measure of resolution defined by the feature tag 'dpi').
Where the actual size is available in millimetres, a
factor of 10/254 may be applied to yield an exact inch-
value
- Values appropriate for use with these feature tags
Rational (>0)
- The feature tag is intended primarily for use in the
applications, protocols, services, or negotiation mechanisms
Print and display applications where different media
will be made depending on the size of the recipient device
- Examples of typical use
This example describes the maximum scanned image width
height for Group 3 fax: 215x297 mm (8.46x11.69 inches):
(size-x<=2150/254)
(size-y<=2970/254)
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- Related standards or documents
The memo "Media Features for Display, Print, and Fax" [3]
describes features (pix-x, pix-y) for measuring document
in pixels
Fax applications should declare physical dimensions using
features defined here
- Considerations particular to use in individual applications
protocols, services, or negotiation mechanisms
Where no physical size is known or available, but a pixel
is known, a notional size should be declared based upon
pixel dimensions and a notional resolution of (say) 100
For example, to describe a 640x480 pixel display
(& (size-x<=640/100) (size-y<=480/100) (dpi=100) )
The notional 100dpi resolution is used as it represents
fairly typical resolution for a pixel-limited display
Reducing the rational numbers to canonical form gives
following equivalent expression
(& (size-x<=32/5) (size-y<=24/5) (dpi=100) )
- Interoperability considerations
For interoperability with other (non-fax) applications that
only pixel-based measurements, pixel dimensions (pix-x, pix-y
may be declared in addition to physical measurements
- Related feature tags
pix-x [3]
pix-y [3]
dpi [3]
dpi-xyratio [this document
- Intended usage
- Author/Change controller
Klyne & McIntyre Standards Track [Page 23]
RFC 2531 Content Feature Schema for Internet Fax March 1999
A.2 Resolution aspect
- Media Feature tag name(s):
dpi-
- ASN.1 identifier associated with this feature tag
1.3.6.1.8.1.9
- Summary of the media features indicated
This feature is used to indicate differential horizontal
vertical resolution capability. In the absence of
feature, horizontal and vertical resolutions are presumed to
the same
When this feature tag is specified, any declared
(dpi) is presumed to apply to the horizontal axis, and
vertical resolution is obtained by dividing that
resolution by the resolution ratio
The value of this feature is a pure number, since it
the ratio of two resolution values
- Values appropriate for use with this feature tag
Rational (>0)
- The feature tag is intended primarily for use in the
applications, protocols, services, or negotiation mechanisms
Internet fax, and other print or display applications that
handle differential horizontal and vertical resolution values
- Examples of typical use
The following example describes a fax resolution of 204
horizontally by 391 dpi vertically
(& (dpi=204) (dpi-xyratio=204/391) )
- Related standards or documents
The memo "Media Features for Display, Print, and Fax" [3]
describes a feature (dpi) for measuring document resolution
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- Interoperability considerations
When interoperating with an application that does not
the differential resolution feature, resolution matching may
performed on the basis of the horizontal resolution only,
aspect ratio information may be lost
- Related feature tags
dpi [3]
size-x [this document
size-y [this document
- Intended usage
Internet
- Author/Change controller
A.3 Color
- Media Feature tag name(s):
color-
- ASN.1 identifier associated with this feature tag
1.3.6.1.8.1.10
- Summary of the media features indicated
This feature tag is used to indicate a number of
image data pixel color values
When mapped (palettized) color is used, this is
different from the number of different colors that can
represented through the color mapping function
This feature tag is used in conjunction with a 'color'
having a value other than 'Binary'.
- Values appropriate for use with this feature tag
Integer (>=2)
Klyne & McIntyre Standards Track [Page 25]
RFC 2531 Content Feature Schema for Internet Fax March 1999
- The feature tag is intended primarily for use in the
applications, protocols, services, or negotiation mechanisms
Color image printing or display applications where the
resource used may depend upon color handling capabilities
the recipient
- Examples of typical use
To describe recipient capabilities
(& (color=limited) (color-levels<=6) )
(& (color=grey) (color-levels<=64) )
(& (color=mapped) (color-levels<=240) )
(& (color=full) (color-levels<=16777216) )
To describe capabilities used by a document
(& (color=limited) (color-levels=4) )
(& (color=grey) (color-levels=48) )
(& (color=mapped) (color-levels=100) )
(& (color=full) (color-levels=32768) )
- Related standards or documents
The memo "Media Features for Display, Print, and Fax" [3]
describes a feature (color) for indicating basic
capabilities
- Interoperability considerations
The actual number of color values used by a document does not
in general, exactly match the number that can be handled by
recipient. To achieve a feature match, at least one must
declared as an inequality
It is recommended that a recipient declares the number of
values that it can handle as an inequality (<=), and a
resource declares the number of colors that it uses with
equality, as shown in the examples above
- Security considerations
- Privacy concerns, related to exposure of personal information
Where feature matching is used to select content applicable
the physical abilities of a user, unusual values for
feature tag might give an indication of a user's
abilities
Klyne & McIntyre Standards Track [Page 26]
RFC 2531 Content Feature Schema for Internet Fax March 1999
- Related feature tags
color [3]
color-space [this document
- Intended usage
Internet
Color image scanning/rendering
- Author/Change controller
A.4 Color
- Media Feature tag name(s):
color-
- ASN.1 identifier associated with this feature tag
1.3.6.1.8.1.11
- Summary of the media features indicated
This feature indicates a color space
A color space value provides two types of information
o the color model used to represent a color value,
the number of color
o a mapping between color values and their
Device color space values are defined for applications
the general color representation used is significant, but
color rendering is left to the device used. Device
spaces defined here have values of the form 'Device- xxx'.
Calibrated color space values are provided for use with
rendering system that is calibrated with respect to
indicated definition, and capable of processing device
independent color information accordingly
- Values appropriate for use with this feature tag
Klyne & McIntyre Standards Track [Page 27]
RFC 2531 Content Feature Schema for Internet Fax March 1999
Device color Device-RGB (device dependent RGB
spaces: Device-CMY (device dependent CMY
Device-CMYK (device dependent CMYK
Calibrated color CIELAB (per T.42 [9])
space
(may be extended by further registrations
'Color-space=CIELAB' indicates the CIE L*a*b* colour space
using CIED50 illuminant and its perfectly diffuse
white point (per T.42 [9]).
- The feature tag is intended primarily for use in the
applications, protocols, services, or negotiation mechanisms
Color image printing and display applications where the
resource used may depend upon color handling capabilities
the recipient
Scanning applications where the data transferred may
upon the image generation capabilities of the originator
- Examples of typical use
To describe rendering or scanning capabilities
(color-space=[Device-RGB,CIELAB])
To describe capabilities assumed by a document for
approximate color reproduction is required
(color-space=Device-RGB
To describe capabilities assumed by a document for which
color reproduction is required
(color-space=CIELAB
- Related standards or documents
CIELAB color space is defined in [19]
CIELAB use for fax is described in ITU T.42 [9]
Klyne & McIntyre Standards Track [Page 28]
RFC 2531 Content Feature Schema for Internet Fax March 1999
- Interoperability considerations
A color-handling receiver should indicate at any
device color space capability, in addition to any
color spaces that it may support
Calibrated color spaces are intended to be used when
color matching is required; otherwise, if applicable, a
color space (color-space=Device-xxx) should be indicated
Documents for which exact color matching is not
should indicate a device color space capability, if applicable
These principles allow sender/receiver feature matching to
achieved when exact color matching is not required
- Security considerations
- Privacy concerns, related to exposure of
information
Where feature matching is used to select content
to the physical abilities of a user, unusual values for
feature tag might give an indication of a user's
abilities
- Denial of service concerns related to consequences
specifying incorrect values
Failure to indicate a generic color space capability for
device may lead to failure to match color space for
application or document that does not require an exact
match
- Related feature tags
color [3]
- Related media types or data formats
TIFF-FX [7]
- Intended usage
Internet
Color image scanning/rendering
- Author/Change controller
Klyne & McIntyre Standards Track [Page 29]
RFC 2531 Content Feature Schema for Internet Fax March 1999
A.5 CIELAB color
- Media Feature tag name(s):
CIELAB-L-
CIELAB-A-
CIELAB-B-
- ASN.1 identifiers associated with these feature tags
1.3.6.1.8.1.12
1.3.6.1.8.1.13
1.3.6.1.8.1.14
- Summary of the media features indicated
These feature tags indicate a color depth capability; i.e.
level of detail to which an individual CIELAB color
can be specified. They define the number of distinct
possible for each of the color components L*, a* and b*.
Typically, this feature would be used with 'color=mapped',
possibly 'color=grey' or 'color=full', to indicate the
of distinct colors that can be realized
- Values appropriate for use with these feature tags
Integer (>0)
- These feature tags are intended primarily for use in
following applications, protocols, services, or
mechanisms
Color image printing and display applications where the
resource used may depend upon color handling capabilities
the recipient
Scanning applications where the data transferred may
upon the image generation capabilities of the originator
- Examples of typical use
To describe rendering or scanning capabilities
(& (color=mapped) (color-levels<=240)
(CIELAB-L-depth<=128)
(CIELAB-a-depth<=128)
(CIELAB-b-depth<=128) )
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RFC 2531 Content Feature Schema for Internet Fax March 1999
(& (color=full) (color-levels<=16777216)
(CIELAB-L-depth<=256)
(CIELAB-a-depth<=128)
(CIELAB-b-depth<=128) )
To describe capabilities assumed by a document
(& (color=mapped) (color-levels=200)
(CIELAB-L-depth=32)
(CIELAB-a-depth=32)
(CIELAB-b-depth=32) )
(& (color=full) (color-levels=32768)
(CIELAB-L-depth=128)
(CIELAB-a-depth=32)
(CIELAB-b-depth=32) )
- Related standards or documents
The memo "Media Features for Display, Print, and Fax" [3]
defines a feature (color) for indicating basic
capabilities
CIELAB color space is defined in [19]
CIELAB use for fax is described in ITU T.42 [9]
- Related feature tags
color [3]
color-levels [this document
color-space [this document
- Intended usage
Internet
Color image scanning/rendering
- Author/Change controller
Klyne & McIntyre Standards Track [Page 31]
RFC 2531 Content Feature Schema for Internet Fax March 1999
A.6 CIELAB color
- Media Feature tag name(s):
CIELAB-L-
CIELAB-L-
CIELAB-a-
CIELAB-a-
CIELAB-b-
CIELAB-b-
- ASN.1 identifiers associated with these feature tags
1.3.6.1.8.1.15
1.3.6.1.8.1.16
1.3.6.1.8.1.17
1.3.6.1.8.1.18
1.3.6.1.8.1.19
1.3.6.1.8.1.20
- Summary of the media features indicated
These feature indicate a supported range of color values,
indicating minimum and maximum values used for each
component in a CIELAB color space
'CIELAB-L-min' and 'CIELAB-L-max' are the minimum and
values of the L* component
'CIELAB-a-min' and 'CIELAB-a-max' are the minimum and
values of the a* component
'CIELAB-b-min' and 'CIELAB-b-max' are the minimum and
values of the b* component
- Values appropriate for use with this feature tag
- The feature tag is intended primarily for use in the
applications, protocols, services, or negotiation mechanisms
Color image printing and display applications where the
resource used may depend upon detailed color
capabilities of the recipient
Klyne & McIntyre Standards Track [Page 32]
RFC 2531 Content Feature Schema for Internet Fax March 1999
Scanning applications where the data transferred may
upon the detailed color image generation capabilities of
originator
- Examples of typical use
To describe rendering or scanning capabilities
(& (CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(CIELAB-a-min>=-75)
(CIELAB-a-max<=+75)
(CIELAB-b-min>=-85)
(CIELAB-b-max<=+85) )
To describe capabilities required by a document
(& (CIELAB-L-min=20)
(CIELAB-L-max=80)
(CIELAB-L-min=-35)
(CIELAB-L-max=+55)
(CIELAB-L-min=-45)
(CIELAB-L-max=+65) )
- Related standards or documents
CIELAB color space is defined in [19]
CIELAB use for fax is described in ITU T.42 [9]
- Interoperability considerations
When describing a recipient's capabilities, the minimum
maximum color component values that can be rendered should
indicated by inequalities as shown in the examples above
When describing a document, the actual minimum and
color component values used should be indicated, as
above
- Security considerations
- Privacy concerns, related to exposure of
information
Where feature matching is used to select content
to the physical abilities of a user, unusual values for
feature tag might give an indication of a user's
abilities
Klyne & McIntyre Standards Track [Page 33]
RFC 2531 Content Feature Schema for Internet Fax March 1999
- Related feature tags
color [3]
color-space [this document
- Related media types or data formats
TIFF-FX [7]
- Intended usage
Internet
Color image scanning/rendering
- Author/Change controller
A.7 Image file
- Media Feature tag name(s):
image-file-
- ASN.1 identifier associated with this feature tag
1.3.6.1.8.1.21
- Summary of the media features indicated
This feature indicates a file structure used for transfer
presentation of image data
It does not indicate image data coding: that is described
separate feature tags (image-coding, etc.).
- Values appropriate for use with this feature tag
Klyne & McIntyre Standards Track [Page 34]
RFC 2531 Content Feature Schema for Internet Fax March 1999
TIFF-FX profiles TIFF-
[7]: TIFF-
TIFF-
TIFF-
TIFF-
TIFF-
(may be extended by further registrations
to cover non-TIFF image file structures
- The feature tag is intended primarily for use in the
applications, protocols, services, or negotiation mechanisms
Internet fax, and other print or display applications
transfer image data
- Examples of typical use
See Appendix B of this memo
- Considerations particular to use in individual applications
protocols, services, or negotiation mechanisms
This tag is intended to provide information about an image
structure. Information about image data coding is provided
other tags
In the case of TIFF-FX image data, there are a number of
file format constraints that are imposed by the various
profiles defined in RFC 2301 [7]. The purpose of the 'image
file-structure' feature tag is to capture those file
constraints
Registration of additional image file structure tags
focus similarly on image file structure issues, not raw
data compression and coding. As a guide, an image
structure may contain image data coded in a variety of ways
and carries information to describe that coding separately
MIME content-type labelling, etc
- Related feature tags
image-coding [this document
- Related media types or data formats
TIFF-FX [7]
TIFF V6.0 (Adobe) [20]
Klyne & McIntyre Standards Track [Page 35]
RFC 2531 Content Feature Schema for Internet Fax March 1999
- Intended usage
Internet
Image scanning/rendering
- Author/Change controller
A.8 Image data
- Media Feature tag name(s):
image-
- ASN.1 identifier associated with this feature tag
1.3.6.1.8.1.22
- Summary of the media features indicated
This feature tag indicates a form of image data compression
coding used
It identifies a generic image coding technique used,
regard to any specific profiling of that technique that may
applied. Values for this feature are generally
across a wide range of image transfer applications
