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RFC 2879 - Content Feature Schema for Internet Fax (V2)


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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 RFC 2531.

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 RFC 2531 ..........................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 RFC 2531.

   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 RFC 2301 [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 RFC 2301 [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 RFC 2531 [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 RFC 2434 [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", 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 T.30 Feature Mapping",
        RFC 2880, July 2000.

   [5]  Masinter, L. and D. Wing, RFC 2532, "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 (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", 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)

   [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",
        RFC 2703, 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, RFC 2434, October 1998.

   [22] Klyne, G. and L. McIntyre, "Content feature schema for Internet
        fax", RFC 2531, 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 RFC 2301 [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 RFC 2301 [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
   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 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 RFC 2531

   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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