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Network Working Group G. Klyne
Request for Comments: 2531 5GM/Content Technologies
Category: Standards Track L. McIntyre
Xerox Corporation
March 1999
Content Feature Schema for Internet 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 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.
Klyne & McIntyre Standards Track [Page 1]
RFC 2531 Content Feature Schema for Internet Fax March 1999
Table of Contents
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
Klyne & McIntyre Standards Track [Page 2]
RFC 2531 Content Feature Schema for Internet Fax March 1999
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.
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 term "extended Internet fax system" is used to describe any
software, device or combination of these that conforms to the
specification "Extended Facsimile Using Internet Mail" [5].
"capability exchange" describes any transfer of information between
communicating systems that is used to indicate system capabilities
and hence determine the form of data transferred. This term covers
both one-way and two-way transfers of capability information.
"capability identification" is a particular form of capability
exchange in which a receiving system provides capability information
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 some
specific format that describes the capabilities of some communicating
entity. It may exist separately from any specific capability
exchange mechanism.
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.
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. This memo indicates
those features that may be associated with extended Internet fax
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 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 extended Internet
fax 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 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 mean
that an extended Internet fax system must have that capability;
rather, it must recognize the feature tag and deal with it
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 from
recognizing and offering additional feature tags. The list below
is intended to provide a basic vocabulary that all extended
Internet fax systems can use in a consistent fashion.
If an unrecognized or unused feature tag is received, the feature
set matching rule (described in RFC2533 [2]) operates so that tag
is effectively ignored.
3.1 Image size
Feature tag name Legal values
---------------- ------------
size-x <Rational> (>0)
size-y <Rational> (>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 conversion
factor of 10/254 may be applied to yield an exact inch-based value.
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) )
When describing resolutions for an MRC format document, the complete
set of usable resolutions is listed. However, there are some
restrictions on their use: (a) 100dpi resolution can be used only
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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 is
required to be an integral sub-multiple of the applicable mask
resolution.
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 color image data may wish to
adjust the color 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 Color capability
Feature tag name Legal values
---------------- ------------
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 handling
capabilities that might be used, for example, to select among a small
number of available data resources.
The value of this feature also gives an indication of the more
detailed color handling features that might be applicable (see next
section).
'Binary' indicates black-and-white, or other bi-level capability. No
further qualifying feature tags are required.
'Limited' indicates a small number of distinct fixed colors, such as
might be provided by a highlight printer, pen plotter or limited
color display. The 'color-levels' tag should be used to indicate the
number of distinct colors available.
NOTE: No ability to indicate any specific or named color is
implied by this option.
Some devices might use different intensity levels rather than
different hues for distinction.
'Mapped' indicates that pixel color values are mapped in some
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 image
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 tags
(section 3.6) may be used to further qualify the color reproduction.
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3.6 Color model
Feature tag name Legal values
---------------- ------------
color-levels <integer> (>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 <integer> (>0)
CIELAB-a-depth
CIELAB-b-depth
CIELAB-L-min <integer>
CIELAB-L-max
CIELAB-a-min
CIELAB-a-max
CIELAB-b-min
CIELAB-b-max
Reference: this document, appendix A.
The general model for image handling (both color and non-color) is
described here from a receiver's perspective; a similar model
operates in the reverse direction for a scan/send perspective:
raw bit pixel color physical
stream -(A)-> values -(B)-> values -(C)-> rendition
- "raw bit stream" is a stream of coded bits
(A) indicates image coding/decoding (MH,MR,MMR,JPEG,JBIG,etc.)
- "pixel values" are a single numeric value per picture element
that designates the color of that element.
(B) indicates pixel-to-color value mapping
- "color values" have a separate numeric value for each color
component (i.e. L*, a*, b* in the case of CIELAB indicated
above.)
(C) indicates how the color values are related to a physical
color. This involves interpretation of the color value with
respect to a color model (e.g. RGB, L*a*b*, CMY, CMYK) and a
color space (which is typically recipient-dependent).
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- "physical rendition" is a color value physically realized on a
display, printer or other device.
There are many variables that can be applied at each stage of the
processing of a color image, and any may be critical to meaningful
handling of that image in some circumstances. In other circumstances
many of the variables may be implied (to some level of approximation)
in the application that uses them (e.g. color images published on a
Web page).
The color feature framework described here is intended to allow
capability description at a range of granularity: feature tags which
correspond to implied (or "don't care" or "unknown") feature values
may simply be omitted from a capability description.
Grey scale and bi-level images are handled within this framework as a
special case, having a 1-component color model. The following
features are used for describing color capabilities:
'color-levels' indicates the number of distinct values for each
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 be
used with other modes if the exact color used is significant. Two
kinds of color space can be distinguished: device-dependent and
calibrated. Device dependent spaces are named here as 'Device-xxx',
and are used to indicate a color space that is defined by the
receiving device. Calibrated color spaces presume the existence of a
rendering system that is calibrated with respect to an indicated
definition, and is capable of processing the device-independent color
information accordingly.
A color-handling receiver should indicate any appropriate device
color space capability in addition to any calibrated color spaces
that it may support. A calibrated color space should be used when
precise color matching is required in the absence of specific
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 final
analysis, a color model (RGB, CMY, etc.) must be defined with
respect to some color space.
'CIELAB-L-depth', 'CIELAB-a-depth' and 'CIELAB-b-depth' indicate the
number of different values that are possible for the L*, a* and b*
color components respectively, and are significant only when colors
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are represented in a CIELAB color space. These features would be
used with palettized color, or with full color where each color
component has a different number of possible values.
The 'CIELAB-x-min' and 'CIELAB-x-max' values indicate a color gamut
(i.e. a range of color values that are used or may be rendered). A
gamut may be indicated in terms of the CIELAB color space even when
colors are represented in some other space.
3.7 Image coding
Feature tag name Legal values
---------------- ------------
image-file- TIFF-S
structure TIFF-F
TIFF-J
TIFF-C
TIFF-L
TIFF-M
(may be extended by further registrations,
to cover non-TIFF image file structures)
image-coding MH
MR
MMR
JBIG
JPEG
(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 <Integer>
image-interleave Stripe
Plane
color-subsampling "1:1:1" (no color subsampling)
"4:1:1" (4:1:1 color subsampling)
MRC-mode <Integer> (0..7) (per ITU T.44 [15])
MRC-max-stripe-size <Integer>
Reference: this document, appendix A.
'image-file-structure' defines how the coded image data is wrapped
and formatted. Options defined here are the various profiles of
TIFF-FX, per RFC 2301 [7]. These options apply to overall formatting
of the image data (TIFF file format, byte ordering, bit ordering,
etc.) and do not define specific image coding issues that are covered
by other aspects of the TIFF-FX profile specifications.
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RFC 2531 Content Feature Schema for Internet Fax March 1999
'image-coding' describes how the raw image data is compressed and
coded as a sequence of bits. These are generic tags that may apply
to a range of file formats and usage environments.
'image-coding-constraint' describes how the raw image data coding
method is constrained to meet a particular operating environment.
Options defined here are JBIG and JPEG coding constraints that apply
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 last
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 MRC
(mixed raster content) image format capability, and also the MRC mode
available. A zero value indicates MRC is not available, a non-zero
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. An
MRC-capable receiver is presumed to be capable of accepting any
combination of contained images that conform to the MRC construction
rules and declared image-coding capabilities.
Within an MRC-formatted document, multi-level coders are used for
foreground and background images (i.e. odd-numbered layers: 1, 3, 5,
etc.) and bi-level coders are used for mask layers (i.e. even
numbered layers 2, 4, 6, etc.).
NOTE: an MRC formatted document may appear within a TIFF image
file structure, so this separate feature is needed to capture the
full range of possible capabilities.
The 'MRC-max-stripe-size' feature may be used with MRC coding, and
indicates the maximum number of scan lines in each MRC stripe. The
legal constraints are:
(MRC-max-stripe-size=[0..256])
(MRC-max-stripe-size>=0)
These values indicate upper bounds on the stripe size. The actual
value may vary between stripes, and the actual size for each stripe
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 are
required in all circumstances.
Specification of the image-file-structure tag value alone is not
normally sufficient to describe the capabilities of a recipient.
A general rule is that sufficient detail should be provided to
exclude any unsupported features.
For extended Internet fax, image-file-structure and image-coding
should always be specified, together with additional values
described above as needed to clearly indicate which feature tag
values are supported and which are not. (See also the examples in
section 4.)
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.
The level of detail captured here reflects that used for capability
identification in Group 3 facsimile.
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.
(& (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 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.
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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 system
This is the previous example extended to handle grey scale multi-
level images. In keeping with Group 3 fax, this example requires
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 system
This adds 16-bit full-color to the previous example.
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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])
(| (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 matching
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 sender
in three possible formats, A4 high resolution, B4 low resolution and
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 capability
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 at
this point.
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)
(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 receiver
cannot handle either color (indicated by '(color=Mapped)') or JPEG
coding (indicated by '(image-coding=JPEG)').
o The high resolution version of the document with '(dpi=300)' must
be send using '(image-coding=JBIG)' because this is the only
available coding of the image data that the receiver can use for
high resolution documents. (The available 300dpi document codings
here are MMR and JBIG, and the receiver capabilities are MH, MR
and JBIG.)
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.
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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])'.
Finally, note that when matching an MRC document description, the
description of each component sub-image must match the capabilities
of the intended receiver.
5. IANA Considerations
Appendix A of this document calls for registrations of feature tags
in the "IETF tree", as defined in section 3.1.1 of "Media Feature Tag
Registration Procedure" [1] (i.e. these feature tags are subject to
the "IETF Consensus" policies described in RFC 2434 [21]).
ASN.1 identifiers should be assigned for each of these registered
feature tags and replaced in the body of the registration.
6. 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]
6.1 Capability descriptions and mechanisms
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 concerns pertain to capability information getting into
the hands of someone who may abuse it. This document specifies
capabilities that help a sender to determine what image
characteristics can be processed by the recipient, not mechanisms for
their publication. Implementors and users should take care that the
mechanisms employed ensure that capabilities are revealed only to
appropriate persons, systems and agents.
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6.2 Specific threats
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.
7. Acknowledgements
The authors gratefully acknowledge the contributions of the following
persons who commented on earlier versions of this memo: James
Rafferty, Dan Wing, Robert Buckley, Mr Ryuji Iwazaki. The following
contributed ideas upon which some of the features described here have
been based: Larry Masinter, Al Gilman, Koen Holtman.
8. References
[1] Holtman, K., Mutz, A. and T. Hardie, "Media Feature Tag
Registration Procedure", BCP 31, RFC 2506, March 1999.
[2] Klyne, G., "A Syntax for Describing Media Feature Sets", RFC
2533, March 1999.
[3] Masinter, L., Holtman, K., Mutz, A. and D. Wing, "Media Features
for Display, Print, and Fax", RFC 2534, March 1999.
[4] McIntyre, L. and G. Klyne, "Internet fax feature mapping from
Group 3 fax", Work in Progress.
[5] Masinter, L. and D. Wing, "Extended Facsimile Using Internet
Mail", RFC 2532, March 1999.
[6] "Procedures for document facsimile transmission in the general
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, March
1998.
[8] Toyoda, K., Ohno, H., Murai, J. and D. Wing, "A Simple Mode of
Facsimile Using Internet Mail", RFC 2305, March 1998.
[9] "Continuous-tone color representation method for facsimile"
ITU-T Recommendation T.42 (1996), International
Telecommunications Union, (Covers custom illuminant, gamut).
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[10] "Colour and gray-scale image representation using lossless
coding scheme for facsimile", ITU-T Recommendation T.43 (1997),
International Telecommunications Union. (Covers JBIG for
colour/grey images).
[11] Hardie, T., "Scenarios for the Delivery of Negotiated Content",
Work in Progress.
[12] Klyne, G., "Requirements for protocol-independent content
negotiation", Work in Progress.
[13] "Standardization of Group 3 facsimile terminals for document
transmission", ITU-T Recommendation T.4 (1996), International
Telecommunications Union, (Covers basic fax coding formats: MH,
MR).
[14] "Facsimile coding schemes and coding control functions for Group
4 facsimile apparatus", ITU Recommendation T.6, International
Telecommunications Union, (Commonly referred to as the MMR
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 of
continuous-tone still image - Requirements and guidelines",
ITU-T Recommendation T.81 (1992) | ISO/IEC 10918-1:1993,
International Telecommunications Union, (Commonly referred to as
JPEG standard).
[17] "Information technology - Coded representation of picture and
audio information - Progressive bi-level image compression",
ITU-T Recommendation T.82 (1993) | ISO/IEC 11544:1993,
International Telecommunications Union, (Commonly referred to as
JBIG1 standard).
[18] "Application profile for Recommendation T.82 - Progressive bi-
level image compression (JBIG1 coding scheme for facsimile
apparatus)", ITU-T Recommendation T.85 (1995), International
Telecommunications Union, (Covers bi-level JBIG).
[19] "Colorimeter, 2nd ed.", CIE Publication No. 15.2, 1986.
(Defines CIELAB color space; use with fax is further
constrained by T.42 [9].)
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[20] Tag Image File Format, Revision 6.0, Adobe Developers
Association,
<ftp://ftp.adobe.com/pub/adobe/devrelations/devtechnotes
/pdffiles/tiff6.pdf>, June 1992.
[21] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 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.
Phone: +44 1491 641 641 +44 118 930 1300
Facsimile: +44 1491 641 611 +44 118 930 1301
EMail: GK@ACM.ORG
Lloyd McIntyre
Xerox Corporation
Mailstop PAHV-121
3400 Hillview Ave.
Palo Alto, CA 94304 USA
Phone: +1-650-813-6762
Facsimile: +1-650-845-2340
EMail: Lloyd.McIntyre@pahv.xerox.com
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Appendix A: Feature registrations
A.1 Image size
- Media Feature tag name(s):
size-x
size-y
- 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 or
otherwise rendered document image; they indicate horizontal
(size-x) and vertical (size-y) dimensions.
The unit of measure is inches (to be consistent with the
measure of resolution defined by the feature tag 'dpi').
Where the actual size is available in millimetres, a conversion
factor of 10/254 may be applied to yield an exact inch-based
value.
- Values appropriate for use with these feature tags:
Rational (>0)
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Print and display applications where different media choices
will be made depending on the size of the recipient device.
- Examples of typical use:
This example describes the maximum scanned image width and
height for Group 3 fax: 215x297 mm (8.46x11.69 inches):
(size-x<=2150/254)
(size-y<=2970/254)
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- Related standards or documents:
The memo "Media Features for Display, Print, and Fax" [3]
describes features (pix-x, pix-y) for measuring document size
in pixels.
Fax applications should declare physical dimensions using the
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 size
is known, a notional size should be declared based upon known
pixel dimensions and a notional resolution of (say) 100dpi
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 a
fairly typical resolution for a pixel-limited display.
Reducing the rational numbers to canonical form gives the
following equivalent expression:
(& (size-x<=32/5) (size-y<=24/5) (dpi=100) )
- Interoperability considerations:
For interoperability with other (non-fax) applications that use
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:
Common
- Author/Change controller:
IETF
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A.2 Resolution aspect ratio
- Media Feature tag name(s):
dpi-xyratio
- 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 and
vertical resolution capability. In the absence of this
feature, horizontal and vertical resolutions are presumed to be
the same.
When this feature tag is specified, any declared resolution
(dpi) is presumed to apply to the horizontal axis, and the
vertical resolution is obtained by dividing that declared
resolution by the resolution ratio.
The value of this feature is a pure number, since it represents
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 following
applications, protocols, services, or negotiation mechanisms:
Internet fax, and other print or display applications that must
handle differential horizontal and vertical resolution values.
- Examples of typical use:
The following example describes a fax resolution of 204 dpi
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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- Interoperability considerations:
When interoperating with an application that does not recognize
the differential resolution feature, resolution matching may be
performed on the basis of the horizontal resolution only, so
aspect ratio information may be lost.
- Related feature tags:
dpi [3]
size-x [this document]
size-y [this document]
- Intended usage:
Internet fax
- Author/Change controller:
IETF
A.3 Color levels
- Media Feature tag name(s):
color-levels
- 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 different
image data pixel color values.
When mapped (palettized) color is used, this is generally
different from the number of different colors that can be
represented through the color mapping function.
This feature tag is used in conjunction with a 'color' feature
having a value other than 'Binary'.
- Values appropriate for use with this feature tag:
Integer (>=2)
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- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Color image printing or display applications where the data
resource used may depend upon color handling capabilities of
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 color
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 a
recipient. To achieve a feature match, at least one must be
declared as an inequality.
It is recommended that a recipient declares the number of color
values that it can handle as an inequality (<=), and a data
resource declares the number of colors that it uses with an
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 to
the physical abilities of a user, unusual values for this
feature tag might give an indication of a user's restricted
abilities.
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- Related feature tags:
color [3]
color-space [this document]
- Intended usage:
Internet fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
A.4 Color space
- Media Feature tag name(s):
color-space
- 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, including
the number of color components
o a mapping between color values and their physical
realizations
Device color space values are defined for applications where
the general color representation used is significant, but exact
color rendering is left to the device used. Device color
spaces defined here have values of the form 'Device- xxx'.
Calibrated color space values are provided for use with a
rendering system that is calibrated with respect to some
indicated definition, and capable of processing device-
independent color information accordingly.
- Values appropriate for use with this feature tag:
Token
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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 reflecting
white point (per T.42 [9]).
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Color image printing and display applications where the data
resource used may depend upon color handling capabilities of
the recipient.
Scanning applications where the data transferred may depend
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 which
approximate color reproduction is required:
(color-space=Device-RGB)
To describe capabilities assumed by a document for which exact
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]
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- Interoperability considerations:
A color-handling receiver should indicate at any appropriate
device color space capability, in addition to any calibrated
color spaces that it may support.
Calibrated color spaces are intended to be used when precise
color matching is required; otherwise, if applicable, a device
color space (color-space=Device-xxx) should be indicated.
Documents for which exact color matching is not important
should indicate a device color space capability, if applicable.
These principles allow sender/receiver feature matching to be
achieved when exact color matching is not required.
- Security considerations:
- Privacy concerns, related to exposure of personal
information:
Where feature matching is used to select content applicable
to the physical abilities of a user, unusual values for this
feature tag might give an indication of a user's restricted
abilities.
- Denial of service concerns related to consequences of
specifying incorrect values:
Failure to indicate a generic color space capability for a
device may lead to failure to match color space for an
application or document that does not require an exact color
match.
- Related feature tags:
color [3]
- Related media types or data formats:
TIFF-FX [7]
- Intended usage:
Internet fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
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RFC 2531 Content Feature Schema for Internet Fax March 1999
A.5 CIELAB color depth
- Media Feature tag name(s):
CIELAB-L-depth
CIELAB-A-depth
CIELAB-B-depth
- 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. the
level of detail to which an individual CIELAB color component
can be specified. They define the number of distinct values
possible for each of the color components L*, a* and b*.
Typically, this feature would be used with 'color=mapped', and
possibly 'color=grey' or 'color=full', to indicate the number
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 the
following applications, protocols, services, or negotiation
mechanisms:
Color image printing and display applications where the data
resource used may depend upon color handling capabilities of
the recipient.
Scanning applications where the data transferred may depend
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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(& (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 color
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 fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
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RFC 2531 Content Feature Schema for Internet Fax March 1999
A.6 CIELAB color gamut
- Media Feature tag name(s):
CIELAB-L-min
CIELAB-L-max
CIELAB-a-min
CIELAB-a-max
CIELAB-b-min
CIELAB-b-max
- 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, by
indicating minimum and maximum values used for each color
component in a CIELAB color space.
'CIELAB-L-min' and 'CIELAB-L-max' are the minimum and maximum
values of the L* component.
'CIELAB-a-min' and 'CIELAB-a-max' are the minimum and maximum
values of the a* component.
'CIELAB-b-min' and 'CIELAB-b-max' are the minimum and maximum
values of the b* component.
- 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:
Color image printing and display applications where the data
resource used may depend upon detailed color handling
capabilities of the recipient.
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Scanning applications where the data transferred may depend
upon the detailed color image generation capabilities of the
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 and
maximum color component values that can be rendered should be
indicated by inequalities as shown in the examples above.
When describing a document, the actual minimum and maximum
color component values used should be indicated, as shown
above.
- Security considerations:
- Privacy concerns, related to exposure of personal
information:
Where feature matching is used to select content applicable
to the physical abilities of a user, unusual values for this
feature tag might give an indication of a user's restricted
abilities.
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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 fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
A.7 Image file structure
- Media Feature tag name(s):
image-file-structure
- 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 and
presentation of image data.
It does not indicate image data coding: that is described by
separate feature tags (image-coding, etc.).
- Values appropriate for use with this feature tag:
Token
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RFC 2531 Content Feature Schema for Internet Fax March 1999
TIFF-FX profiles TIFF-S
[7]: TIFF-F
TIFF-J
TIFF-C
TIFF-L
TIFF-M
(may be extended by further registrations,
to cover non-TIFF image file structures)
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Internet fax, and other print or display applications that
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 file
structure. Information about image data coding is provided by
other tags.
In the case of TIFF-FX image data, there are a number of image
file format constraints that are imposed by the various usage
profiles defined in RFC 2301 [7]. The purpose of the 'image-
file-structure' feature tag is to capture those file format
constraints.
Registration of additional image file structure tags should
focus similarly on image file structure issues, not raw image
data compression and coding. As a guide, an image file
structure may contain image data coded in a variety of ways,
and carries information to describe that coding separately from
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]
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- Intended usage:
Internet fax
Image scanning/rendering applications
- Author/Change controller:
IETF
A.8 Image data coding
- Media Feature tag name(s):
image-coding
- 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 and
coding used.
It identifies a generic image coding technique used, without
regard to any specific profiling of that technique that may be
applied. Values for this feature are generally applicable
across a wide range of image transfer applications.
This information is distinct from the image file structure and
MRC information conveyed by the 'image-file-structure' tags.
- Values appropriate for use with this feature tag:
Token MH
MR
MMR
JBIG
JPEG
(may be extended by further registrations)
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Internet fax, and other applications that transfer image data.
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- Examples of typical use:
See Appendix B of this memo.
- Related standards or documents:
MH, MR: ITU T.4 [13]
MMR: ITU T.6 [14]
JPEG: ITU T.81 [16]
JBIG: ITU T.82 [17]
- Interoperability considerations:
To establish the correct conditions for interoperability
between systems, capabilities to handle the generic image
coding technique and the specific image coding constraints must
be established.
- Related feature tags:
image-coding-constraint [this document]
JBIG-stripe-size [this document]
image-interleave [this document]
- Related media types or data formats:
TIFF-FX [7]
- Intended usage:
Internet fax
Image scanning/rendering applications
- Author/Change controller:
IETF
A.9 Image coding constraint
- Media Feature tag name(s):
image-coding-constraint
- ASN.1 identifier associated with these feature tags:
1.3.6.1.8.1.23
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- Summary of the media features indicated:
This feature tag qualifies the 'image-coding' feature with a
specific profile or usage constraints.
Values for this feature are generally specific to some given
value of 'image-coding' and also to some restricted application
or class of applications.
- Values appropriate for use with this feature tag:
Token JBIG-T85 (bi-level, per ITU T.85)
JBIG-T43 (multi-level, per ITU T.43)
JPEG-T4E (per ITU T.4, Annex E)
(may be extended by further registrations)
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Internet fax, and other applications that transfer image data.
The specific values for this feature indicated above are
intended for use with Internet fax.
- Examples of typical use:
See Appendix B of this memo.
- Related standards or documents:
JBIG-T85: ITU T.85 [18]
JBIG-T43: ITU T.43 [10]
JPEG-T4E: ITU T.4 Annex E [13]
- Interoperability considerations:
To establish the correct conditions for interoperability
between systems, capabilities to handle the generic image
coding technique and the specific image coding constraints must
be established.
- Related feature tags:
image-coding [this document]
JBIG-stripe-size [this document]
image-interleave [this document]
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- Related media types or data formats:
TIFF-FX [7]
- Intended usage:
Internet fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
A.10 JBIG stripe size
- Media Feature tag name(s):
JBIG-stripe-size
- ASN.1 identifier associated with these feature tags:
1.3.6.1.8.1.24
- Summary of the media features indicated:
This feature is a specific usage constraint that is applied to
JBIG image coding (image-coding=JBIG), and indicates the
allowable size for each stripe of an image, except the last.
A stripe of a JBIG image is a delimited horizontal band of
compressed image data that can be decompressed separately from
the surrounding data.
- Values appropriate for use with this feature tag:
Integer (>0)
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Internet fax, and other applications that transfer image data.
- Examples of typical use:
(JBIG-stripe-size=128)
(JBIG-stripe-size>0)
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- Related standards or documents:
JBIG: ITU T.82 [17]
JBIG-T85: ITU T.85 [18]
JBIG-T43: ITU T.43 [10]
- Considerations particular to use in individual applications,
protocols, services, or negotiation mechanisms:
In the case of Internet fax, the specific constraints allowed
for a receiver are those given as examples above.
Specifying a stripe size that is not limited (JBIG-stripe-
size>0) means that an entire page of image data is encoded as a
single unit. This may place considerable demands on the memory
of a receiving system, as the entire stripe needs to be
buffered in memory.
- Interoperability considerations:
To establish the correct conditions for interoperability
between systems, capabilities to handle the generic image
coding technique and the specific image coding constraints must
be established.
- Related feature tags:
image-coding [this document]
image-coding-constraint [this document]
image-interleave [this document]
- Related media types or data formats:
TIFF-FX [7]
- Intended usage:
Internet fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
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RFC 2531 Content Feature Schema for Internet Fax March 1999
A.11 Image interleave
- Media Feature tag name(s):
image-interleave
- ASN.1 identifier associated with this feature tag:
1.3.6.1.8.1.25
- Summary of the media features indicated:
This feature indicates an image interleave capability.
It may be used with JBIG images (image-coding=JBIG) to indicate
color plane interleaving of either stripes or entire image
planes.
- Values appropriate for use with this feature tag:
Token Stripe
Plane
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Internet fax, and other applications that transfer image data.
- Examples of typical use:
(image-interleave=stripe)
(image-interleave=[stripe,plane])
- Considerations particular to use in individual applications,
protocols, services, or negotiation mechanisms:
Specifying a plane interleave means that an entire page of
image data must be buffered in order to generate render the
image. This may place considerable demands on the memory of a
sending or receiving system.
- Related feature tags:
image-coding [this document]
JBIG-stripe-size [this document]
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- Related media types or data formats:
TIFF-FX [7]
- Intended usage:
Internet fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
A.12 Color subsampling
- Media Feature tag name(s):
color-subsampling
- ASN.1 identifier associated with this feature tag:
1.3.6.1.8.1.26
- Summary of the media features indicated:
This feature tag indicates whether color information may be
subsampled with respect to luminance data.
It is used with continuous color images (color=full), color
spaces that use separate luminance and color components (e.g.
color-space=LAB), and image file structures that support color
subsampling.
- Values appropriate for use with this feature tag:
String "1:1:1"
This value indicates a full set of color
component samples for each luminance
component sample.
"4:1:1"
This value indicates a set of color samples
for each luminance sample.
(may be extended by further registrations)
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- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Color image printing and display applications where the data
resource used may depend upon color handling capabilities of
the recipient.
Scanning applications where the data transferred may depend
upon the image generation capabilities of the originator.
- Examples of typical use:
(& (color=full) (color-space=[Device-RGB,CIELAB])
(color-subsampling=["1:1:1","4:1:1"]) )
- Related feature tags:
color [3]
color-space [this document]
image-file-structure [this document]
- Related media types or data formats:
TIFF-FX [7]
- Intended usage:
Internet fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
A.13 MRC availability and mode
- Media Feature tag name(s):
MRC-mode
- ASN.1 identifier associated with this feature tag:
1.3.6.1.8.1.27
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- Summary of the media features indicated:
This feature is used to indicate the availability of MRC (mixed
raster content) image format capability, and also the MRC mode
available. A zero value indicates MRC is not available, a
non-zero value (in the range 1..7) 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. An MRC-capable receiver is presumed to be capable
of accepting any combination of contained images that conform
to the MRC construction rules, where each such image matches
the separately declared resolution, color capability, color
model, image coding, and any other capabilities.
NOTE: an MRC formatted document may appear within a TIFF
image file structure.
Within an MRC-formatted document, multi-level coders are
used for foreground and background images (i.e. odd-
numbered layers: 1, 3, 5, etc.) and bi-level coders are used
for mask layers (i.e. even numbered layers 2, 4, 6, etc.).
- Values appropriate for use with this feature tag:
Integer (0..7)
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Internet fax, and other applications that transfer image data.
- Examples of typical use:
See Appendix B of this document.
- Related standards or documents:
ITU T.44 [15]
- Interoperability considerations:
To establish the correct conditions for interoperability
between systems, capabilities to handle the MRC mode and any
contained image coding techniques must be established.
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RFC 2531 Content Feature Schema for Internet Fax March 1999
- Related feature tags:
image-coding [this document]
MRC-max-stripe-size [this document]
- Related media types or data formats:
TIFF-FX [7]
- Intended usage:
Internet fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
A.14 MRC maximum stripe size
- Media Feature tag name(s):
MRC-max-stripe-size
- ASN.1 identifier associated with this feature tag:
1.3.6.1.8.1.28
- Summary of the media features indicated:
This feature may be used with MRC coding (MRC-mode>=1), and
indicates the maximum number of scan lines in each MRC stripe.
The value given indicates an upper bound on the stripe size.
The actual value may vary between stripes, and the actual size
for each stripe is indicated in the image data.
- Values appropriate for use with this feature tag:
Integer (>0)
- The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
Internet fax, and other applications that transfer image data.
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- Examples of typical use:
(MRC-max-stripe-size=[0..256])
(MRC-max-stripe-size>=0)
- Considerations particular to use in individual applications,
protocols, services, or negotiation mechanisms:
For Internet fax, the legal constraints for an image receiver
are those given as examples above.
- Related feature tags:
MRC-mode [this document]
- Related media types or data formats:
TIFF-FX [7]
- Intended usage:
Internet fax
Color image scanning/rendering applications
- Author/Change controller:
IETF
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RFC 2531 Content Feature Schema for Internet Fax March 1999
Appendix B: TIFF mode descriptions
This appendix contains descriptions of the TIFF modes defined by RFC
2301 [7], presented as feature set expressions in the form defined by
"A syntax for describing media feature sets" [2] and using the
feature schema introduced by this document.
These may be taken as illustrations of the feature set combinations
that are required for the corresponding TIFF profiles described by
RFC 2301.
(Tiff-S) :-
(& (image-file-structure=TIFF-S)
(color=Binary)
(image-coding=MH) (MRC-mode=0) )
(Tiff-F) :-
(& (image-file-structure=TIFF-F)
(color=Binary)
(image-coding=MH) (MRC-mode=0) )
(TIFF-J) :-
(& (image-file-structure=TIFF-J)
(color=Binary)
(image-coding=JBIG) (MRC-mode=0) )
(TIFF-C) :-
(& (image-file-structure=TIFF-C)
(color=Grey)
(image-coding=JPEG) (MRC-mode=0) )
(TIFF-L) :-
(& (image-file-structure=TIFF-L)
(color=Grey)
(image-coding=JBIG) (MRC-mode=0) )
(TIFF-M) :-
(& (image-file-structure=TIFF-M)
(color=[Binary,Grey])
(image-coding=[MH,JPEG]) (MRC-mode>=1) )
The feature sets described above are minimum requirements for the
corresponding TIFF modes. Thus, MR and MMR image coding are not
mandatory with TIFF mode F, and would be indicated by combining the
expression for (TIFF-F) with (image-coding=MR) and/or (image-
coding=MMR).
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Similarly, limited, mapped or full color are not mandatory with the
grey/color TIFF modes (C, L and M), and would be indicated by
combining the corresponding expression with (color=limited),
(color=mapped) and/or (color=full).
TIFF profile M is a composite structure that can combine image data
coding options from other profiles: the description above indicates
mandatory features; other options may be indicated by combining
TIFF-M with other options (e.g. color= limited, mapped or full, and
image-coding= MR, MMR or JBIG).
Support for multiple TIFF profiles may be indicated by combining
their expressions with the OR operator; e.g.
(| (TIFF-F) (TIFF-S) (TIFF-J) )
indicates support for all black-and-white modes.
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Appendix C: Revision history
00a 28-Sep-1998 Initial draft.
01a 12-Oct-1998 Incorporated review comments. Described feature
tag for differential x/y resolution ratio. Added
some examples.
01b 19-Oct-1998 Updated section 3.6 on image coding. Added
Appendix B containing feature expressions for the
TIFF modes from RFC 2301.
02a 26-Oct-1998 Update examples. Add separate stripe size features
for JBIG and MRC.
02b 30-Oct-1998 Update examples. Add text clarifying the
description of MRC documents (as a set of feature
collections describing multiple contained images).
Add text describing constrains on resolution and
image coding usage within an MRC document.
02c 11-Nov-1998 Add ITU references. Added terminology: "capability
exchange", "capability identification" and
"capability description". Update JBIG and MRC
stripe size tags. Move subsampling to colour
section. Remove preferred-unit tag. Add T.4, T.6,
T.44 and T.81 references.
02d 16-Nov-1998 Update colour handling features, reflecting
proposed changes to the media features memo [3].
Update the image coding capability framework.
Updated TIFF mode descriptions in Appendix B.
03a 17-Nov-1998 Replace use of 'pix-x', 'pix-y' with 'size-x', '
size-y'. Add registrations in Appendix A.
03b 08-Dec-1998 Remove normative language and reference to RFC2119
(normative statements will be in the main fax
protocol draft). Revise structure of colour
features, and removed color-palette feature. Define
colour feature tags specific to CIELAB model and
colour space.
04a 14-Dec-1998 Update examples to reflect revised feature tags.
Revise description of MRC document in section 3.7.
Clarified interpretation of 'color=fixed'. Change
feature value 'color=fixed' to 'color=limited'.
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05a 04-Jan-1999 Incorporate WG last-call comments: change
references to MRC-stripe-size to MRC-max-stripe-
size; similarly references to MRC-maximum-stripe-
size. Change "eifax" to "extended Internet fax".
Added guidance note for image coding feature usage.
Added IANA consideration comments to Appendix A.
05b 08-Jan-1999 Added new section for IANA considerations; removed
references to fax working group from registration
change control sections. Remove JPEG from TIFF-L
auxiliary predicate. Clarify description of MRC
receiver capabilities in section A.13. Remove '
color=full' from (TIFF-C) and (TIFF-M) predicates,
and add some explanatory text. Remove
'color=limited' from (TIFF-L) predicate.
05c 08-Jan-1999 Minor revisions to TIFF profile illustrations and
descripions in Appendix B. Reformatted description
of 'color=limited' in section 3.5 to clarify that
this does not indicate support for specific named
colors.
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Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Klyne & McIntyre Standards Track [Page 51]