Network Working Group G. Klyne
Request for Comments: 2879 Content Technologies
Obsoletes: 2531 L. McIntyre
Category: Standards Track Xerox Corporation
August 2000

Content Feature Schema for Internet Fax (V2)

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 (2000). All Rights Reserved.

Abstract

This document defines a content media feature schema for Internet
fax.

It is a profile of the media feature registration mechanisms [1,2,3]
for use in performing capability identification between extended
Internet fax systems [5]. It replaces and updates the feature schema
defined in RFC2531.

Table of Contents

1. IntrodUCtion .............................................2
1.1 Organization of this document ........................3
1.2 Terminology and document conventions .................3
1.3 Discussion of this document ..........................4
2. Fax feature schema syntax ................................4
3. Internet fax feature tags ................................4
3.1 Image size ...........................................5
3.2 Resolution ...........................................5
3.3 Media type ...........................................6
3.4 Paper Size ...........................................6
3.5 Color capability .....................................7
3.6 Color model ..........................................8
3.7 Image coding ........................................11
3.8 MRC mode ............................................12
4. Examples ................................................13
4.1 Simple mode Internet fax system ....................13

4.2 High-end black-and-white Internet fax system.........14
4.3 Grey-scale Internet fax system ......................14
4.4 Full-color Internet fax system (JPEG only) ..........15
4.5 Full-color Internet fax system (JPEG and JBIG) ......16
4.6 Full-color Internet fax system (MRC) ................17
4.7 Sender and receiver feature matching ................19
5. IANA Considerations .....................................21
6. Security Considerations .................................21
6.1 Capability descriptions and mechanisms ..............21
6.2 Specific threats ....................................21
7. Acknowledgements ........................................22
8. References ..............................................22
9. Authors' Addresses ......................................24
Appendix A: Feature registrations ..........................25
A.1 Image size ..........................................25
A.2 Resolution ASPect ratio .............................27
A.3 Color levels ........................................28
A.4 Color space ........................................30
A.5 CIELAB color illuminant .............................33
A.6 CIELAB color depth ..................................35
A.7 CIELAB color gamut ..................................37
A.8 Image file structure ................................39
A.9 Image data coding ...................................41
A.10 Image coding constraint ............................43
A.11 JBIG stripe size .................................. 44
A.12 Image interleave ...................................46
A.13 Color subsampling ..................................47
A.14 MRC availability and mode ..........................49
A.15 MRC maximum stripe size ............................50
Appendix B: TIFF mode descriptions .........................52
Appendix C: Changes from RFC2531 ..........................57
Full Copyright Statement ...................................58

1. Introduction

This document defines a content media feature schema for Internet
fax.

It is a profile of the media feature registration mechanisms [1,2,3]
for use in performing capability identification between extended
Internet fax systems [5]. It replaces and updates the feature schema
defined in RFC2531.

The media feature description mechanisms do not describe any specific
mechanisms for communicating capability information, but do presume
that any such mechanisms will transfer textual values. In
conjunction with this feature schema, they specify 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.

"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.

1.3 Discussion of this document

Discussion of this document should take place on the Internet fax
mailing list hosted by the Internet Mail Consortium (IMC). Please
send comments regarding this document to:

ietf-fax@imc.org

To subscribe to this list, send a message with the body 'subscribe'
to "ietf-fax-request@imc.org".

To see what has gone on before you subscribed, please see the mailing
list archive at:

http://www.imc.org/ietf-fax/

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 according to 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.

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 [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
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].

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 blank-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.

In the context of Internet fax, 'limited' is interpreted as one-bit-
per-color-sample (RGB, CMY or CMYK), depending on the color space
used.

'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.

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)
color-illuminant <token> (per ITU T.4 [13], E.6.7)
D50
D65
D75
SA
SC
F2
F7
F11
CTnnnn (see below)
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).

- "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 or color model 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.

'color-illuminant' indicates a CIE illuminant, using the same general
form that is used for this purpose by Group 3 fax (as defined in ITU
T.4 [13], section E.6.7). When the illuminant is specified by its
color temperature, the token string 'CTnnnn' is used, where 'nnnn' is
a decimal number that is the color temperature in Kelvins; e.g.
CT7500 indicates an illuminant color temperature of 7500K.

NOTE: ITU T.4 indicates a binary representation for color
temperature values.

In practice, much of the illuminant detail given here
will probably be unused by Internet fax. The only value
likely to be specified is 'D50', which is the default
color illuminant for Group 3 fax.

'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
are represented in a CIELAB color space. These features would be
used with palletized color, or with full color where each color
component has a different number of possible values.

Color depth values relate to the representation of colour values
rather than the resolution of a scanning or rendering device. Thus,
if 256 different L-component values can be represented then the
assertion (CIELAB-L-depth<=256) is used, even if a receiving device
can render only 100 distinct luminance values. (Color rendering
resolution is not covered by this memo.)

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
structure TIFF-limited
TIFF-minimal
TIFF-MRC
TIFF-MRC-limited
(may be extended by further registrations)
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)

Reference: this document, appendix A.

'image-file-structure' defines how the coded image data is wrapped
and formatted. The following options are defined here:

o 'TIFF' indicates image data enclosed and tagged using TIFF
structures described in Adobe's definition of TIFF [20].

o 'TIFF-limited' indicates image data structured using TIFF, but
with the limitations on the placement of Image File Descriptors
(IFDs) indicated in section 4.4.6 of RFC2301 [7].

o 'TIFF-minimal' indicates a TIFF image format that meets the IFD
placement, byte ordering and bit ordering requirements of the
"minimal black and white mode" described in section 3.5 of RFC
2301 [7], also known as TIFF-S.

o 'TIFF-MRC' uses a TIFF image structure [20] augmented with a sub-
IFD structure, described for the "Mixed Raster Content mode" in
section 8.1.2 of RFC2301 [7], also known as TIFF-M. This
provides a file structure to contain composite images constructed
using the MRC model described in T.44 [15] (see tag 'MRC-mode').

o 'TIFF-MRC-limited' is the same as 'TIFF-MRC', except that the
primary IFD (i.e. top-level IFDs, as opposed to sub-IFDs)
placement is constrained in the same way as 'TIFF-limited'.

'image-coding' describes how 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.

NOTE: there are several 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.)

3.8 MRC mode

Feature tag name Legal values
---------------- ------------
MRC-mode <Integer> (0..7) (per ITU T.44 [15])
MRC-max-stripe-size <Integer>

Reference: this document, appendix A.

The 'MRC-mode' feature is used to indicate the availability of MRC
(mixed raster content) image format capability. A zero value
indicates MRC is not available, a non-zero value indicates the
maximum 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 both the MRC
construction rules and the image-coding capabilities declared
elsewhere.

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.). MRC format also imposes constraints
on the resolutions that can be used.

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<=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.

4. Examples

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 profile S is required to be
supported by such a system.

(& (image-file-structure=TIFF-minimal)
(MRC-mode=0)
(color=Binary)
(image-coding=MH) (MRC-mode=0)
( (& (dpi=204) (dpi-xyratio=[204/98,204/196]) )
(& (dpi=200) (dpi-xyratio=[200/100,1]) ) )
(size-x<=2150/254)
(paper-size=A4)

(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.

(& (image-file-structure=TIFF)
(MRC-mode=0)
(color=Binary)
( (& (dpi=204) (dpi-xyratio=[204/98,204/196]) )
(& (dpi=200) (dpi-xyratio=[200/100,1]) )
(& (dpi=300) (dpi-xyratio=1) ) )
( (image-coding=[MH,MR,MMR])
(& (image-coding=JBIG)
(image-coding-constraint=JBIG-T85)
(JBIG-stripe-size=128) ) )
(size-x<=2150/254)
(paper-size=[letter,A4,B4]) )
(ua-media=stationery) )

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.

(& (image-file-structure=TIFF)
(MRC-mode=0)
( (& (color=Binary)
( (image-coding=[MH,MR,MMR])
(& (image-coding=JBIG)
(image-coding-constraint=JBIG-T85)
(JBIG-stripe-size=128) ) )
( (& (dpi=204) (dpi-xyratio=[204/98,204/196]) )
(& (dpi=200) (dpi-xyratio=[200/100,1]) )
(& (dpi=300) (dpi-xyratio=1) ) )
(& (color=Grey)
(color-levels<=256)
(color-space-CIELAB)
(color-illuminant=D50)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
( (& (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) ) )
(size-x<=2150/254)
(paper-size=[letter,A4,B4]) )
(ua-media=stationery) )

4.4 Full-color Internet fax system (JPEG only)

This adds 24-bit full-color to the previous example.

(& (image-file-structure=TIFF)
(MRC-mode=0)
( (& (color=Binary)
(image-coding=[MH,MR,MMR])
( (& (dpi=204) (dpi-xyratio=[204/98,204/196]) )
(& (dpi=200) (dpi-xyratio=[200/100,1]) )
(& (dpi=300) (dpi-xyratio=1) ) ) )
(& (color=grey)
(image-coding=JPEG)
(image-coding-constraint=JPEG-T4E)
(color-levels<=256)
(color-space=CIELAB)
(color-illuminant=D50)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(dpi=[100,200,300]) (dpi-xyratio=1) )
(& (color=full)
(image-coding=JPEG)
(image-coding-constraint=JPEG-T4E)
(color-subsampling=["1:1:1","4:1:1"])
(color-levels<=16777216)
(color-space=CIELAB)
(color-illuminant=D50)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(CIELAB-a-min>=-85)
(CIELAB-a-max<=85)
(CIELAB-b-min>=-75)
(CIELAB-b-max<=125)
(dpi=[100,200,300]) (dpi-xyratio=1) ) )
(size-x<=2150/254)
(paper-size=[letter,A4,B4]) )
(ua-media=stationery) )

4.5 Full-color Internet fax system (JPEG and JBIG)

This adds limited CMY(K), RGB and 16-bit mapped color using JBIG
coding to the previous example.

(& (image-file-structure=TIFF)
(MRC-mode=0)
( (& (color=Binary)
( (image-coding=[MH,MR,MMR])
(& (image-coding=JBIG)
(image-coding-constraint=JBIG-T85)
(JBIG-stripe-size=128) ) )
( (& (dpi=204) (dpi-xyratio=[204/98,204/196]) )
(& (dpi=200) (dpi-xyratio=[200/100,1]) )
(& (dpi=300) (dpi-xyratio=1) ) ) )
(& (color=Limited)
(image-coding=JBIG)
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe)
( (& (color-space=[Device-RGB,Device-CMY])
(color-levels<=8) )
(& (color-space=Device-CMYK)
(color-levels<=16) ) )
(dpi=[100,200,300]) (dpi-xyratio=1) )
(& (color=Mapped)
(image-coding=JBIG)
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe)
(color-levels<=65536)
(color-space=CIELAB)
(color-illuminant=D50)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(CIELAB-a-min>=-85)
(CIELAB-a-max<=85)
(CIELAB-b-min>=-75)
(CIELAB-b-max<=125)
(dpi=[100,200,300]) (dpi-xyratio=1) )
(& (color=grey)
( (& (image-coding=JPEG)
(image-coding-constraint=JPEG-T4E) )
(& (image-coding=JBIG)
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe) ) )
(color-levels<=256)

(color-space=CIELAB)
(color-illuminant=D50)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(dpi=[100,200,300]) (dpi-xyratio=1) )
(& (color=full)
( (& (image-coding=JPEG)
(image-coding-constraint=JPEG-T4E)
(color-subsampling=["1:1:1","4:1:1"]) )
(& (image-coding=JBIG)
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe) ) )
(color-levels<=16777216)
(color-space=CIELAB)
(color-illuminant=D50)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(CIELAB-a-min>=-85)
(CIELAB-a-max<=85)
(CIELAB-b-min>=-75)
(CIELAB-b-max<=125)
(dpi=[100,200,300]) (dpi-xyratio=1) ) )
(size-x<=2150/254)
(paper-size=[letter,A4,B4]) )
(ua-media=stationery) )

4.6 Full-color Internet fax system (MRC)

This adds MRC image structures to the previous example.

(& (image-file-structure=TIFF-MRC)
(MRC-mode<=1) (MRC-max-stripe-size>=0)
( (& (color=binary)
( (image-coding=[MH,MR,MMR])
(& (image-coding=JBIG)
(image-coding-constraint=JBIG-T85)
(JBIG-stripe-size=128) ) )
( (& (dpi=204) (dpi-xyratio=[204/98,204/196]) )
(& (dpi=200) (dpi-xyratio=[200/100,1]) )
(& (dpi=[300,400]) (dpi-xyratio=1) ) ) )
(& (color=limited)
( (& (color-space=[Device-RGB,Device-CMY])
(color-levels<=8) ) )
( (& (color-space=Device-CMYK)
(color-levels<=16) ) )
(image-coding=JBIG)
(image-coding-constraint=JBIG-T43)

(JBIG-stripe-size=128)
(image-interleave=stripe)
(dpi=[100,200,300,400]) (dpi-xyratio=1) )
(& (color=mapped)
(color-levels<=65536)
(image-coding=JBIG)
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe)
(color-space=CIELAB)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(CIELAB-a-min>=-85)
(CIELAB-a-max<=85)
(CIELAB-b-min>=-75)
(CIELAB-b-max<=125) ) )
(color-illuminant=D50)
(dpi=[100,200,300,400]) (dpi-xyratio=1) )
(& (color=grey)
( (& (image-coding=JPEG)
(image-coding-constraint=JPEG-T4E) )
(& (image-coding=JBIG)
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe) ) )
(color-space=CIELAB)
(color-levels<=256)
(color-illuminant=D50)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(dpi=[100,200,300,400]) (dpi-xyratio=1) )
(& (color=full)
( (& (image-coding=JPEG)
(image-coding-constraint=JPEG-T4E)
(color-subsampling=["1:1:1","4:1:1"]) )
(& (image-coding=JBIG)
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe) ) )
(color-levels<=16777216)
(color-space=CIELAB)
(color-illuminant=D50)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(CIELAB-a-min>=-85)
(CIELAB-a-max<=85)
(CIELAB-b-min>=-75)
(CIELAB-b-max<=125)

(dpi=[100,200,300,400]) (dpi-xyratio=1) ) )
(size-x<=2550/254)
(Paper-size=[Letter,A4,B4])
(ua-media=stationery) )

4.7 Sender and receiver feature matching

This example considers sending a document to an enhanced black-and-
white fax system with the following receiver capabilities:

(& ( (& (dpi=200) (dpi-xyatio=200/100) )
(& (dpi=200) (dpi-xyratio=1) )
(& (dpi=300) (dpi-xyratio=1) )
(& (dpi=400) (dpi-xyratio=1) ) )
(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):

( (& (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.

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 repeats the descriptions of feature tags
introduced by RFC2531 [22], with some small revisions. These have
been registered in the "IETF tree", according to the procedure
described 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 RFC2434 [21]).

Appendix section A.5 introduces one new feature tag (color-
illuminant) to be registered according to the same procedure. An
ASN.1 identifier should be assigned for this new tag 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. Implementers and users should take care that the
mechanisms employed ensure that capabilities are revealed only to
appropriate persons, systems and agents.

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", RFC2506, 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", RFC2534, March 1999.

[4] McIntyre, L. and G. Klyne, "Internet Fax T.30 Feature Mapping",
RFC2880, July 2000.

[5] Masinter, L. and D. Wing, RFC2532, "Extended Facsimile Using
Internet Mail", RFC2532, March 1999.

[6] "Procedures for document facsimile transmission in the general
switched telephone network", ITU-T Recommendation T.30 (1999),
International Telecommunications Union, March 1999

[7] McIntyre, L., Buckley, R., Venable, D., Zilles, S., Parsons, G.
and J. Rafferty, "File format for Internet fax", RFC2301, March
1998.

[8] Toyoda, K., Ohno, H., Murai, J. and D. Wing, "A Simple Mode of
Facsimile Using Internet Mail", RFC2305, March 1998.

[9] "Continuous-tone color representation method for facsimile"
ITU-T Recommendation T.42 (1996) International
Telecommunications Union (Covers custom illuminant, gamut)

[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)

[12] Klyne, G., "Protocol-independent Content Negotiation Framework",
RFC2703, September 1999.

[13] "Standardization of Group 3 facsimile terminals for document
transmission", ITU-T Recommendation T.4 (1999), 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].)

[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, RFC2434, October 1998.

[22] Klyne, G. and L. McIntyre, "Content feature schema for Internet
fax", RFC2531, March 1999.

9. Authors' Addresses

Graham Klyne
Content Technologies Ltd.
1220 Parkview,
Arlington Business Park
Theale
Reading, RG7 4SA
United Kingdom.

Phone: +44 118 930 1300
Fax: +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
Fax: +1-650-845-2340
EMail: Lloyd.McIntyre@pahv.xerox.com

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:

size-x: 1.3.6.1.8.1.7
size-y: 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)

- 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

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.

- 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 (palletized) 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)

- 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 (i.e. not both as equalities).

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.

- 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

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]

- Interoperability considerations:

A color-handling receiver should indicate 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

A.5 CIELAB color illuminant

- Media Feature tag name(s):

color-illuminant

- ASN.1 identifier associated with this feature tag:

1.3.6.1.8.1.29

- Summary of the media features indicated:

This feature indicates a color illuminant. This has the
effect of modifying the color space calibration to reflect the
use of different sources of illumination.

A color-illuminant value would normally be used only with a
calibrated color space.

- Values appropriate for use with this feature tag:

Token

CIELAB illuminant D50
values: D65
D75
SA
SC
F2
F7
F11

Defined by color CTnnnn where 'nnnn' is a decimal
temperature: representation of the illuminant
color temperature in Kelvins.

(may be extended by further registrations)

NOTE: The default color illuminant for Group 3 fax is D50.

- 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.

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, or to describe
capabilities assumed by a document for which exact color
handling capabilities are required:

(& (color-space=CIELAB) (color-illuminant=D50) )

- Related standards or documents:

CIELAB color illuminant representations are described in ITU
T.4 [13], Annex E.6.7.

- Interoperability considerations:

A color-handling receiver that supports a calibrated color
space should indicate any constraint on the illuminants it can
handle.

In the absence of a color-illuminant constraint, a receiver is
presumed to accept and deal with any specified illuminant
value.

- 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.6 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:

CIELAB-L-depth: 1.3.6.1.8.1.12
CIELAB-a-depth: 1.3.6.1.8.1.13
CIELAB-b-depth: 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 represented.

NOTE: this feature tag describes the number of values that
can be represented for a color component, and does not
necessarily indicate the number of distinct values that can
be rendered or resolved by a system.

- 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) )
(& (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

A.7 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:

CIELAB-L-min: 1.3.6.1.8.1.15
CIELAB-L-max: 1.3.6.1.8.1.16
CIELAB-a-min: 1.3.6.1.8.1.17
CIELAB-a-max: 1.3.6.1.8.1.18
CIELAB-b-min: 1.3.6.1.8.1.19
CIELAB-b-max: 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.

NOTE: color component values are assumed to be rational
numbers, so a limited gamut does not necessarily indicate
limited color resolution.

- 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.

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-a-min=-35)
(CIELAB-a-max=+55)
(CIELAB-b-min=-45)
(CIELAB-b-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.

- 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.8 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

Image file TIFF
structure TIFF-limited
options: TIFF-minimal
TIFF-MRC
TIFF-MRC-limited

(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.

The following tag values are defined here:

o 'TIFF' indicates image data enclosed and tagged using TIFF
structures described in Adobe's definition of TIFF [20].

o 'TIFF-limited' indicates image data structured using TIFF,
but with limitations on the placement of Image File
Descriptors (IFDs) within the file, which are indicated in
section 4.4.6 of RFC2301 [7].

o 'TIFF-minimal' indicates a TIFF image format that meets the
IFD placement, byte ordering and bit ordering requirements
of the "minimal black and white mode" described in section
3.5 of RFC2301 [7], also known as TIFF-S.

o 'TIFF-MRC' uses a TIFF image structure [20] augmented with a
sub-IFD structure, described for the "Mixed Raster Content
mode" in section 8.1.2 of RFC2301 [7], also known as TIFF-M
(see also tag 'MRC-mode').

o 'TIFF-MRC-limited' is the same as 'TIFF-MRC', except that
the IFD placement is constrained as for 'TIFF-limited'.

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]
MRC-mode [this document]

- Related media types or data formats:

TIFF-FX [7]
TIFF V6.0 (Adobe) [20]

- Intended usage:

Internet fax
Image scanning/rendering applications

- Author/Change controller:

IETF

A.9 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.

- 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.10 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

- 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]

- Related media types or data formats:

TIFF-FX [7]

- Intended usage:

Internet fax
Color image scanning/rendering applications

- Author/Change controller:

IETF

A.11 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)

- 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

A.12 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 or 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]

- Related media types or data formats:

TIFF-FX [7]

- Intended usage:

Internet fax
Color image scanning/rendering applications

- Author/Change controller:

IETF

A.13 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 one set of color component
samples for each 4 luminance samples.

(may be extended by further registrations)

- 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=[LAB,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.14 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

- 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.

- 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.15 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.

- Examples of typical use:

(MRC-max-stripe-size<=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

Appendix B: TIFF mode descriptions

This appendix contains descriptions of the TIFF modes defined by
RFC2301 [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
RFC2301.

TIFF-S has no optional elements, so is presented as a single
feature set. Other profiles are presented as (TIFF-x-base) and
(TIFF-x-full) indicating the minimum and full feature sets
associated with each profile.

(TIFF-S) :-
(& (image-file-structure=TIFF-S)
(color=Binary)
(image-coding=MH) (MRC-mode=0)
( (& (dpi=200)
(dpi-xyratio=[200/100,200/200])
(size-x=1728/200) )
(& (dpi=204)
(dpi-xyratio=[204/98,204/196]
(size-x=1728/204) ) )
(paper-size=A4) )

(TIFF-F-base) :-
(& (image-file-structure=TIFF-F)
(color=Binary)
(image-coding=MH) (MRC-mode=0)
(dpi=204)
(dpi-xyratio=[204/98,204/196])
(size-x=1728/204)
(paper-size=A4) )

(TIFF-F-full) :-
(& (image-file-structure=TIFF-F)
(color=Binary)
(image-coding=[MH,MR,MMR]) (MRC-mode=0)
( (& (dpi=200)
(dpi-xyratio=[200/100,200/200])
(size-x=[1728/200,2048/200,2432/200]) )
(& (dpi=204)
(dpi-xyratio=[204/98,204/196,204/391])
(size-x=[1728/204,2048/204,2432/204]) )
(& (dpi=300)

(dpi-xyratio=300/300)
(size-x=[2592/300,3072/300,3648/300]) )
(& (dpi=400)
(dpi-xyratio=400/400)
(size-x=[3456/400,4096/400,4864/400]) )
(& (dpi=408)
(dpi-xyratio=408/391)
(size-x=[3456/408,4096/408,4864/408]) ) )
(paper-size=[A4, B4, A3, letter, legal]) )

(TIFF-J-base) :-
(& (image-file-structure=TIFF-J)
(color=Binary)
(MRC-mode=0)
(image-coding=JBIG)
(image-coding-constraint=JBIG-T85)
(JBIG-stripe-size=128)
(dpi=204)
(dpi-xyratio=[204/98,204/196])
(size-x=1728/204)
(paper-size=A4) )

(TIFF-J-full) :-
(& (image-file-structure=TIFF-J)
(color=Binary)
(MRC-mode=0)
(image-coding=JBIG)
(image-coding-constraint=JBIG-T85)
(JBIG-stripe-size>0)
( (& (dpi=200)
(dpi-xyratio=[200/100,200/200])
(size-x=[1728/200,2048/200,2432/200]) )
(& (dpi=204)
(dpi-xyratio=[204/98,204/196,204/391])
(size-x=[1728/204,2048/204,2432/204]) )
(& (dpi=300)
(dpi-xyratio=300/300)
(size-x=[2592/300,3072/300,3648/300]) )
(& (dpi=400)
(dpi-xyratio=400/400)
(size-x=[3456/400,4096/400,4864/400]) )
(& (dpi=408)
(dpi-xyratio=408/391)
(size-x=[3456/408,4096/408,4864/408]) ) )
(paper-size=[A4, B4, A3, letter, legal]) )

(TIFF-C-base) :-
(& (image-file-structure=TIFF-C)

(color=grey)
(color-levels<=256)
(MRC-mode=0)
(image-coding=JPEG) (image-coding-constraint=JPEG-T4E)
(color-space=CIELAB)
(CIELAB-L-depth<=101)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(color-illuminant=D50)
(dpi=200) (dpi-xyratio=1)
(size-x=864/100)
(paper-size=A4) )

(TIFF-C-full) :-
(& (image-file-structure=TIFF-C)
(image-coding=JPEG) (image-coding-constraint=JPEG-T4E)
(color-space=CIELAB)
( (& (color=grey)
(color-levels<=4096)
(CIELAB-L-depth<=4096) )
(& (color=full)
(color-levels<=68719476736)
(color-subsampling=["4:1:1","1:1:1"])
(CIELAB-L-depth<=4096)
(CIELAB-a-depth<=4096)
(CIELAB-b-depth<=4096) ) )
(MRC-mode=0)
(dpi=[100,200,300,400]) (dpi-xyratio=1)
(size-x=[864/100,1024/100,1216/100])
(paper-size=[A4, B4, A3, letter, legal]) )

(TIFF-L-base) :-
(& (image-file-structure=TIFF-L)
(MRC-mode=0)
(image-coding=JBIG)
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size=128)
(image-interleave=stripe)
(color=grey)
(color-levels<=256)
(color-space=CIELAB)
(CIELAB-L-depth=101)
(CIELAB-L-min>=0)
(CIELAB-L-max<=100)
(color-illuminant=D50)
(dpi=200) (dpi-xyratio=1)
(size-x=864/100)
(paper-size=A4) )

(TIFF-L-full) :-
(& (image-file-structure=TIFF-L)
(MRC-mode=0)
(image-coding=JBIG)
(image-coding-constraint=JBIG-T43)
(JBIG-stripe-size>0)
(image-interleave=[stripe, plane])
( (& (color=limited)
(color-levels<=8)
(color-space=[Device-RGB, Device-CMY] ) )
(& (color=limited)
(color-levels<=16)
(color-space=Device-CMYK) )
(& (color=mapped)
(color-levels<=65536)
(color-space=CIELAB)
(CIELAB-L-depth<=4096)
(CIELAB-a-depth<=4096)
(CIELAB-b-depth<=4096) )
(& (color=grey)
(color-levels<=4096)
(color-space=CIELAB)
(CIELAB-L-depth<=4096) )
(& (color=full)
(color-space=CIELAB)
(color-levels<=68719476736)
(CIELAB-L-depth<=4096)
(CIELAB-a-depth<=4096)
(CIELAB-b-depth<=4096)
(CIELAB-L-min>=0) ) )
(dpi=[100,200,300,400]) (dpi-xyratio=1)
(size-x=[864/100,1024/100,1216/100])
(paper-size=[A4, B4, A3, letter, legal]) )

(TIFF-M-base) :-
(& (image-file-structure=TIFF-M)
(MRC-mode>=1)
(MRC-max-stripe-size<=256) )

(TIFF-M-full) :-
(& (image-file-structure=TIFF-M)
(MRC-mode>=1) )

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.

TIFF-M is a composite mode and must be used in conjunction with
some other mode to define the particular capabilities of a
receiver; e.g.

( (TIFF-M-base)
(TIFF-S) (TIFF-J-full) (TIFF-C-base) (TIFF-L-full) )

Each sub-image in an MRC image must conform to the capabilities
indicated AND also to any additional constraints imposed by the MRC
structure, such as bi-level mask layer, etc. See sections A.13 and
section 3.7.

Appendix C: Changes from RFC2531

00a 23-Jun-1999 Updated Appendix B with more complete TIFF-FX
profile descriptions. Added note to section 3.5
clarifying the meaning of (color=limited) in the
context of Internet fax. Added note to section
3.6 and A.6 to clarify interpretation of color
depth. In A.6, noted that color gamut is not the
same as color resolution; fixed example. Split
section 3.7 into two sections, dealing with simple
image coding options and MRC composite image
options. Added new feature tag 'color-illuminant'
(sections 3.6, A.5). Added cross-references from
TIFF-M image file structure to MRC-mode tag.
Updated introduction and references.

00b 10-Aug-1999 Bring examples into line with T.30 mapping
document [4], and reorganize to make the
expression structure less complex. Add details of
mailing list for discussion. Added JPEG-only
colour example. Change definition of image-file-
structure tag to indicate more precisely what is
being defined, and to draw out the distinction
between a file structure to contain MRC images
(image-file-structure), and the MRC image model
(MRC-mode).

01a 01-Oct-1999 Update author's address and some references.

01b 05-Jan-2000 Incorporate last-call review comments (all
editorial).

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