GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc2531

Network Working Group G. Klyne Request for Comments: 2531 5GM/Content Technologies Category: Standards Track L. McIntyre

                                                   Xerox Corporation
                                                          March 1999
              Content Feature Schema for Internet Fax

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

 This document defines a content feature schema that is a profile of
 the media feature registration mechanisms [1,2,3] for use in
 performing capability identification between extended Internet fax
 systems [5].
 This document does not describe any specific mechanisms for
 communicating capability information, but does presume that any such
 mechanisms will transfer textual values.  It specifies a textual
 format to be used for describing Internet fax capability information.

Klyne & McIntyre Standards Track [Page 1] RFC 2531 Content Feature Schema for Internet Fax March 1999

Table of Contents

 1. Introduction .............................................3
 1.1 Organization of this document............................3
 1.2 Terminology and document conventions.....................3
 2. Fax feature schema syntax ................................4
 3. Internet fax feature tags ................................4
 3.1 Image size...............................................5
 3.2 Resolution...............................................5
 3.3 Media type...............................................6
 3.4 Paper Size...............................................6
 3.5 Color capability.........................................6
 3.6 Color model..............................................8
 3.7 Image coding............................................10
 4. Examples ................................................12
 4.1 Simple mode Internet fax system.........................12
 4.2 High-end black-and-white Internet fax system............12
 4.3 Grey-scale Internet fax system..........................13
 4.4 Full-color Internet fax system..........................13
 4.5 Full-color Internet fax system (MRC)....................14
 4.6 Sender and receiver feature matching....................15
 5. IANA Considerations .....................................17
 6. Security Considerations .................................17
 6.1 Capability descriptions and mechanisms..................17
 6.2 Specific threats........................................18
 7. Acknowledgements ........................................18
 8. References ..............................................18
 9. Authors' Addresses ......................................21
 Appendix A: Feature registrations ..........................22
 A.1 Image size..............................................22
 A.2 Resolution aspect ratio.................................24
 A.3 Color levels............................................25
 A.4 Color space.............................................27
 A.5 CIELAB color depth......................................30
 A.6 CIELAB color gamut......................................32
 A.7 Image file structure....................................34
 A.8 Image data coding.......................................36
 A.9 Image coding constraint.................................38
 A.10 JBIG stripe size.......................................39
 A.11 Image interleave.......................................41
 A.12 Color subsampling......................................42
 A.13 MRC availability and mode..............................43
 A.14 MRC maximum stripe size................................45
 Appendix B: TIFF mode descriptions .........................47
 Appendix C: Revision history ...............................49
 Full Copyright Statement ...................................51

Klyne & McIntyre Standards Track [Page 2] RFC 2531 Content Feature Schema for Internet Fax March 1999

1. Introduction

 This document defines a content feature schema that is a profile of
 the media feature registration mechanisms [1,2,3] for use in
 performing capability identification between extended Internet fax
 systems [5].
 This document does not describe any specific mechanisms for
 communicating capability information, but does presume that any such
 mechanisms will transfer textual values.  It specifies a textual
 format to be used for describing Internet fax capability information.
 The range of capabilities that can be indicated are based on those
 covered by the TIFF file format for Internet fax [7] and Group 3
 facsimile [6].  A companion document [4] describes the relationship
 and mapping between this schema and Group 3 fax capabilities.

1.1 Organization of this document

 Section 2 specifies the overall syntax for fax feature descriptions
 by reference to the media feature registration and syntax documents
 [1,2].
 Section 3 enumerates the feature tags that are to be recognized and
 processed by extended Internet fax systems, according to their
 capabilities.
 Appendix A contains additional feature tag registrations for media
 features that are specific to fax and for which no applicable
 registration already exists.  These are presented in the form
 prescribed by the media feature registration procedure [1].

1.2 Terminology and document conventions

 The term "extended Internet fax system" is used to describe any
 software, device or combination of these that conforms to the
 specification "Extended Facsimile Using Internet Mail" [5].
 "capability exchange" describes any transfer of information between
 communicating systems that is used to indicate system capabilities
 and hence determine the form of data transferred.  This term covers
 both one-way and two-way transfers of capability information.
 "capability identification" is a particular form of capability
 exchange in which a receiving system provides capability information
 to a sending system.

Klyne & McIntyre Standards Track [Page 3] RFC 2531 Content Feature Schema for Internet Fax March 1999

 "capability description" is a collection of data presented in some
 specific format that describes the capabilities of some communicating
 entity.  It may exist separately from any specific capability
 exchange mechanism.
    NOTE: Comments like this provide additional nonessential
    information about the rationale behind this document.  Such
    information is not needed for building a conformant
    implementation, but may help those who wish to understand the
    design in greater depth.

2. Fax feature schema syntax

 The syntax for the fax feature schema is described by "A syntax for
 describing media feature sets" [2].  This in turn calls upon media
 feature tags that may be registered according to the procedure
 described in "Media Feature Tag Registration Procedure" [1].
    NOTE: Media feature registration provides a base vocabulary of
    features that correspond to media handling capabilities.  The
    feature set syntax provides a mechanism and format for combining
    these to describe combinations of features.  This memo indicates
    those features that may be associated with extended Internet fax
    systems.

3. Internet fax feature tags

 This section enumerates and briefly describes a number of feature
 tags that are defined for use with extended Internet fax systems and
 applications.  These tags may be used also by other systems and
 applications that support corresponding capabilities.
 The feature tags presented below are those that an extended Internet
 fax system is expected to recognize its ability or non-ability to
 handle.
 Definitive descriptions of feature tags are indicated by reference to
 their registration per the media feature registration procedure [1]
 (some of which are appended to this document)
    NOTE: The presence of a feature tag in this list does not mean
    that an extended Internet fax system must have that capability;
    rather, it must recognize the feature tag and deal with it
    according to the capabilities that it does have.

Klyne & McIntyre Standards Track [Page 4] RFC 2531 Content Feature Schema for Internet Fax March 1999

    Further, an extended Internet fax system is not prevented from
    recognizing and offering additional feature tags.  The list below
    is intended to provide a basic vocabulary that all extended
    Internet fax systems can use in a consistent fashion.
    If an unrecognized or unused feature tag is received, the feature
    set matching rule (described in RFC2533 [2]) operates so that tag
    is effectively ignored.

3.1 Image size

    Feature tag name    Legal values
    ----------------    ------------
    size-x              <Rational> (>0)
    size-y              <Rational> (>0)
 Reference:  this document, Appendix A.
 These feature values indicate a rendered document size in inches.
 Where the actual size is measured in millimetres, a conversion
 factor of 10/254 may be applied to yield an exact inch-based value.

3.2 Resolution

    Feature tag name    Legal values
    ----------------    ------------
    dpi                 <Integer> (>0)
    dpi-xyratio         <Rational> (>0)
 Reference: "Media Features for Display, Print, and Fax" [3], and this
 document appendix A.
 If 'dpi-xyratio' is present and not equal to 1 then the horizontal
 resolution (x-axis) is indicated by the 'dpi' feature value, and the
 vertical resolution (y-axis) is the value of 'dpi' divided by 'dpi-
 xyratio'.
 For example, the basic Group 3 fax resolution of 200*100dpi might be
 indicated as:
       (& (dpi=200) (dpi-xyratio=200/100) )
 When describing resolutions for an MRC format document, the complete
 set of usable resolutions is listed.  However, there are some
 restrictions on their use: (a) 100dpi resolution can be used only

Klyne & McIntyre Standards Track [Page 5] RFC 2531 Content Feature Schema for Internet Fax March 1999

 with multi-level images, and (b) any multi-level image resolution is
 required to be an integral sub-multiple of the applicable mask
 resolution.

3.3 Media type

    Feature tag name    Legal values
    ----------------    ------------
    ua-media            screen
                        screen-paged
                        stationery
                        transparency
                        envelope
                        envelope-plain
                        continuous
 Reference: "Media Features for Display, Print, and Fax" [3].
    NOTE: Where the recipient indicates specific support for hard copy
    or soft copy media type, a sender of color image data may wish to
    adjust the color components (e.g.  per the related rules of ITU
    recommendation T.42 [9]) to improve rendered image quality on that
    medium.

3.4 Paper Size

    Feature tag name    Legal values
    ----------------    ------------
    paper-size          A4
                        A3
                        B4
                        letter
                        legal
 Reference: "Media Features for Display, Print, and Fax" [3].

3.5 Color capability

 Feature tag name    Legal values
 ----------------    ------------
 color               Binary  (bi-level only)
                     Limited (a limited number of colors)
                     Mapped  (palette or otherwise mapped color)
                     Grey    (grey-scale only)
                     Full    (full continuous-tone color)
 Reference: "Media Features for Display, Print, and Fax" [3].

Klyne & McIntyre Standards Track [Page 6] RFC 2531 Content Feature Schema for Internet Fax March 1999

 The intention here is to give a broad indication of color handling
 capabilities that might be used, for example, to select among a small
 number of available data resources.
 The value of this feature also gives an indication of the more
 detailed color handling features that might be applicable (see next
 section).
 'Binary' indicates black-and-white, or other bi-level capability.  No
 further qualifying feature tags are required.
 'Limited' indicates a small number of distinct fixed colors, such as
 might be provided by a highlight printer, pen plotter or limited
 color display.  The 'color-levels' tag should be used to indicate the
 number of distinct colors available.
    NOTE: No ability to indicate any specific or named color is
    implied by this option.
 Some devices might use different intensity levels rather than
 different hues for distinction.
 'Mapped' indicates that pixel color values are mapped in some
 specifiable way to a multi-component color space.  The 'color-levels'
 tag may be used to indicate the number of distinct colors available;
 in its absence, sufficient levels to display a photographic image
 should be assumed.
 'Grey' indicates a continuous tone grey-scale capability.
 'Full' indicates full continuous tone color capability.
 For 'Mapped', 'Grey' and 'Full' color, additional feature tags
 (section 3.6) may be used to further qualify the color reproduction.

Klyne & McIntyre Standards Track [Page 7] RFC 2531 Content Feature Schema for Internet Fax March 1999

3.6 Color model

    Feature tag name    Legal values
    ----------------    ------------
    color-levels        <integer>   (>2)
    color-space         Device-RGB  (device RGB)
                        Device-CMY  (device CMY)
                        Device-CMYK (device CMYK)
                        CIELAB      (LAB per T.42 [9])
                        (may be extended by further registrations)
    CIELAB-L-depth      <integer>   (>0)
    CIELAB-a-depth
    CIELAB-b-depth
    CIELAB-L-min        <integer>
    CIELAB-L-max
    CIELAB-a-min
    CIELAB-a-max
    CIELAB-b-min
    CIELAB-b-max
 Reference: this document, appendix A.
 The general model for image handling (both color and non-color) is
 described here from a receiver's perspective; a similar model
 operates in the reverse direction for a scan/send perspective:
        raw bit        pixel         color         physical
        stream  -(A)-> values -(B)-> values -(C)-> rendition
  1. "raw bit stream" is a stream of coded bits
   (A)  indicates image coding/decoding (MH,MR,MMR,JPEG,JBIG,etc.)
  1. "pixel values" are a single numeric value per picture element

that designates the color of that element.

   (B)  indicates pixel-to-color value mapping
  1. "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).

Klyne & McIntyre Standards Track [Page 8] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. "physical rendition" is a color value physically realized on a

display, printer or other device.

 There are many variables that can be applied at each stage of the
 processing of a color image, and any may be critical to meaningful
 handling of that image in some circumstances.  In other circumstances
 many of the variables may be implied (to some level of approximation)
 in the application that uses them (e.g. color images published on a
 Web page).
 The color feature framework described here is intended to allow
 capability description at a range of granularity: feature tags which
 correspond to implied (or "don't care" or "unknown") feature values
 may simply be omitted from a capability description.
 Grey scale and bi-level images are handled within this framework as a
 special case, having a 1-component color model.  The following
 features are used for describing color capabilities:
 'color-levels' indicates the number of distinct values for each
 picture element, and applies to all but bi-level images.  For bi-
 level images, a value of 2 is implied.
 'color-space' is used mainly with 'Mapped' and 'Full', but could be
 used with other modes if the exact color used is significant.  Two
 kinds of color space can be distinguished: device-dependent and
 calibrated.  Device dependent spaces are named here as 'Device-xxx',
 and are used to indicate a color space that is defined by the
 receiving device.  Calibrated color spaces presume the existence of a
 rendering system that is calibrated with respect to an indicated
 definition, and is capable of processing the device-independent color
 information accordingly.
 A color-handling receiver should indicate any appropriate device
 color space capability in addition to any calibrated color spaces
 that it may support.  A calibrated color space should be used when
 precise color matching is required in the absence of specific
 knowledge of the receiving system.
    NOTE: In practice, although they appear to be separate concepts,
    the color model and color space cannot be separated.  In the final
    analysis, a color model (RGB, CMY, etc.) must be defined with
    respect to some color space.
 'CIELAB-L-depth', 'CIELAB-a-depth' and 'CIELAB-b-depth' indicate the
 number of different values that are possible for the L*, a* and b*
 color components respectively, and are significant only when colors

Klyne & McIntyre Standards Track [Page 9] RFC 2531 Content Feature Schema for Internet Fax March 1999

 are represented in a CIELAB color space.  These features would be
 used with palettized color, or with full color where each color
 component has a different number of possible values.
 The 'CIELAB-x-min' and 'CIELAB-x-max' values indicate a color gamut
 (i.e. a range of color values that are used or may be rendered).  A
 gamut may be indicated in terms of the CIELAB color space even when
 colors are represented in some other space.

3.7 Image coding

    Feature tag name    Legal values
    ----------------    ------------
    image-file-         TIFF-S
    structure           TIFF-F
                        TIFF-J
                        TIFF-C
                        TIFF-L
                        TIFF-M
                        (may be extended by further registrations,
                        to cover non-TIFF image file structures)
    image-coding        MH
                        MR
                        MMR
                        JBIG
                        JPEG
                        (may be extended by further registrations)
    image-coding-       JBIG-T85    (bi-level, per ITU T.85)
    constraint          JBIG-T43    (multi-level, per ITU T.43)
                        JPEG-T4E    (per ITU T.4, Annex E)
                        (may be extended by further registrations)
    JBIG-stripe-size    <Integer>
    image-interleave    Stripe
                        Plane
    color-subsampling   "1:1:1"     (no color subsampling)
                        "4:1:1"     (4:1:1 color subsampling)
    MRC-mode            <Integer> (0..7)   (per ITU T.44 [15])
    MRC-max-stripe-size <Integer>
 Reference: this document, appendix A.
 'image-file-structure' defines how the coded image data is wrapped
 and formatted.  Options defined here are the various profiles of
 TIFF-FX, per RFC 2301 [7].  These options apply to overall formatting
 of the image data (TIFF file format, byte ordering, bit ordering,
 etc.) and do not define specific image coding issues that are covered
 by other aspects of the TIFF-FX profile specifications.

Klyne & McIntyre Standards Track [Page 10] RFC 2531 Content Feature Schema for Internet Fax March 1999

 'image-coding' describes how the raw image data is compressed and
 coded as a sequence of bits.  These are generic tags that may apply
 to a range of file formats and usage environments.
 'image-coding-constraint' describes how the raw image data coding
 method is constrained to meet a particular operating environment.
 Options defined here are JBIG and JPEG coding constraints that apply
 in typical Group 3 fax environments.
 The 'JBIG-stripe-size' feature may be used with JBIG image coding,
 and indicates the number of scan lines in each stripe except the last
 in an image.  The legal constraints are:
    (JBIG-stripe-size=128)
    (JBIG-stripe-size>=0)
 The latter being equivalent to no restriction.
 The 'MRC-mode' feature is used to indicate the availability of MRC
 (mixed raster content) image format capability, and also the MRC mode
 available.  A zero value indicates MRC is not available, a non-zero
 value indicates the available MRC mode number.
 An MRC formatted document is actually a collection of several images,
 each of which is described by a separate feature collection.  An
 MRC-capable receiver is presumed to be capable of accepting any
 combination of contained images that conform to the MRC construction
 rules and declared image-coding capabilities.
 Within an MRC-formatted document, multi-level coders are used for
 foreground and background images (i.e. odd-numbered layers: 1, 3, 5,
 etc.) and bi-level coders are used for mask layers (i.e. even
 numbered layers 2, 4, 6, etc.).
    NOTE: an MRC formatted document may appear within a TIFF image
    file structure, so this separate feature is needed to capture the
    full range of possible capabilities.
 The 'MRC-max-stripe-size' feature may be used with MRC coding, and
 indicates the maximum number of scan lines in each MRC stripe.  The
 legal constraints are:
    (MRC-max-stripe-size=[0..256])
    (MRC-max-stripe-size>=0)
 These values indicate upper bounds on the stripe size.  The actual
 value may vary between stripes, and the actual size for each stripe
 is indicated in the image data.

Klyne & McIntyre Standards Track [Page 11] RFC 2531 Content Feature Schema for Internet Fax March 1999

    NOTE: there are many image coding options here, and not all are
    required in all circumstances.
    Specification of the image-file-structure tag value alone is not
    normally sufficient to describe the capabilities of a recipient.
    A general rule is that sufficient detail should be provided to
    exclude any unsupported features.
    For extended Internet fax, image-file-structure and image-coding
    should always be specified, together with additional values
    described above as needed to clearly indicate which feature tag
    values are supported and which are not.  (See also the examples in
    section 4.)

4. Examples

 Some of the examples contain comments introduced by '--...'.  These
 are not part of the allowed capability description syntax.  They are
 included here to explain some of the constructs used.
 The level of detail captured here reflects that used for capability
 identification in Group 3 facsimile.

4.1 Simple mode Internet fax system

 This example describes the capabilities of a typical simple mode
 Internet fax system.  Note that TIFF application S is required to be
 supported by such a system.
    (& (color=Binary)
       (image-file-structure=TIFF-S)
       (dpi=200)
       (dpi-xyratio=[200/100,200/200])
       (paper-size=A4)
       (image-coding=MH) (MRC-mode=0)
       (ua-media=stationery) )

4.2 High-end black-and-white Internet fax system

 This would include support for B/W JBIG and be equivalent to what is
 sometimes called "Super G3", except that Internet fax functionality
 would be added.

Klyne & McIntyre Standards Track [Page 12] RFC 2531 Content Feature Schema for Internet Fax March 1999

    (& (color=Binary)
       (image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
       (| (& (dpi=200) (dpi-xyratio=200/100) )    -- 200*100
          (& (dpi=200) (dpi-xyratio=1) )          -- 200*200
          (& (dpi=204) (dpi-xyratio=204/391) )    -- 204*391
          (& (dpi=300) (dpi-xyratio=1) ) )        -- 300*300
       (| (image-coding=[MH,MR,MMR])
          (& (image-coding=JBIG)
             (image-coding-constraint=JBIG-T85)
             (JBIG-stripe-size=128) ) )
       (MRC-mode=0)
       (paper-size=[A4,B4]) )

4.3 Grey-scale Internet fax system

 This is the previous example extended to handle grey scale multi-
 level images.  In keeping with Group 3 fax, this example requires
 equal x- and y- resolutions for a multi-level image.
    (& (| (& (color=Binary)
             (image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
             (| (image-coding=[MH,MR,MMR])
                (& (image-coding=JBIG)
                   (image-coding-constraint=JBIG-T85)
                   (JBIG-stripe-size=128) ) )
             (| (& (dpi=200) (dpi-xyratio=200/100) )
                (& (dpi=200) (dpi-xyratio=1) )
                (& (dpi=204) (dpi-xyratio=204/391) )
                (& (dpi=300) (dpi-xyratio=1) ) ) )
          (& (color=Grey)
             (image-file-structure=[TIFF-C,TIFF-L])
             (color-levels<=256)
             (color-space-CIELAB)
             (| (& (image-coding=JPEG)
                   (image-coding-constraint=JPEG-T4E) )
                (& (image-coding=JBIG)
                   (image-coding-constraint=JBIG-T43)
                   (JBIG-stripe-size=128)
                   (image-interleave=stripe) ) )
             (dpi=[100,200,300])
             (dpi-xyratio=1) ) )
       (MRC-mode=0)
       (paper-size=[A4,B4]) )

4.4 Full-color Internet fax system

 This adds 16-bit full-color to the previous example.

Klyne & McIntyre Standards Track [Page 13] RFC 2531 Content Feature Schema for Internet Fax March 1999

    (& (| (& (color=Binary)
             (image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
             (| (image-coding=[MH,MR,MMR])
                (& (image-coding=JBIG)
                   (image-coding-constraint=JBIG-T85)
                   (JBIG-stripe-size=128) ) )
             (| (& (dpi=200) (dpi-xyratio=200/100) )
                (& (dpi=200) (dpi-xyratio=1) )
                (& (dpi=204) (dpi-xyratio=204/391) )
                (& (dpi=300) (dpi-xyratio=1) ) ) )
          (& (| (& (color=Grey) (color-levels<=256) )
                (& (color=Full) (color-levels<=65536)
                   (color-subsampling=["1:1:1","4:1:1"]) ) )
             (image-file-structure=[TIFF-C,TIFF-L])
             (color-space=CIELAB)
             (| (& (image-coding=JPEG)
                   (image-coding-constraint=JPEG-T4E) )
                (& (image-coding=JBIG)
                   (image-coding-constraint=JBIG-T43)
                   (JBIG-stripe-size=128)
                   (image-interleave=stripe) ) )
             (dpi=[100,200,300])
             (dpi-xyratio=1) ) )
       (MRC-mode=0)
       (paper-size=[A4,B4]) )

4.5 Full-color Internet fax system (MRC)

    (& (| (& (color=Binary)
             (image-file-structure=[TIFF-S,TIFF-F,TIFF-J])
             (MRC-mode=0)
             (image-coding=[MH,MMR])
             (| (& (dpi=200) (dpi-xyratio=[200/100,1]) )
                (& (dpi=204) (dpi-xyratio=204/391) )
                (& (dpi=300) (dpi-xyratio=1) )
                (& (dpi=400) (dpi-xyratio=1) ) ) )
          (& (image-file-structure=[TIFF-C,TIFF-L])
             (| (& (color=Grey) (color-levels<=256) )
                (& (color=Full) (color-levels<=65536)
                   (color-subsampling=["1:1:1","4:1:1"]) ) )
             (color-space=CIELAB)
             (MRC-mode=0)
             (image-coding=JPEG)
             (image-coding-constraint=JPEG-T4E)
             (dpi=[100,200,300,400])
             (dpi-xyratio=1) )
          (& (image-file-structure=TIFF-M)
             (MRC-mode=1) (MRC-max-stripe-size=[0..256])

Klyne & McIntyre Standards Track [Page 14] RFC 2531 Content Feature Schema for Internet Fax March 1999

             (image-coding=[MH,MMR,JPEG])
             (| (color=Binary)
                (& (color=Grey) (color-levels<=256) )
                (& (color=Full) (color-levels<=65536)
                   (color-subsampling=["1:1:1","4:1:1"]) ) )
             (color-space=CIELAB)
             (dpi=[100,200,300,400])
             (dpi-xyratio=1) ) )
       (paper-size=[A4,B4]) )

4.6 Sender and receiver feature matching

 This example considers sending a document to a high-end black-and-
 white fax system with the following receiver capabilities:
    (& (| (& (dpi=200) (dpi-xyratio=200/100) )    -- 200*100
          (& (dpi=200) (dpi-xyratio=1) )          -- 200*200
          (& (dpi=300) (dpi-xyratio=1) )          -- 300*300
          (& (dpi=400) (dpi-xyratio=1) ) )        -- 400*400
       (color=Binary)
       (| (& (paper-size=A4) (ua-media=[stationery,transparency]) )
          (& (paper-size=B4) (ua-media=continuous) ) )
       (image-coding=[MH,MR,JBIG]) )
 Turning to the document itself, assume it is available to the sender
 in three possible formats, A4 high resolution, B4 low resolution and
 A4 high resolution color, described by:
    (& (dpi=300) (dpi-xyratio=1)
       (color=Binary)
       (paper-size=A4)
       (image-coding=[MMR,JBIG]) )
    (& (dpi=200) (dpi-xyratio=200/100)
       (color=Binary)
       (paper-size=B4)
       (image-coding=[MH,MR]) )
    (& (dpi=300) (dpi-xyratio=1)
       (color=Mapped) (color-levels<=256)
       (paper-size=A4)
       (image-coding=JPEG) )
 These three image formats can be combined into a composite capability
 statement by a logical-OR operation (to describe format-1 OR format-2
 OR format-3):

Klyne & McIntyre Standards Track [Page 15] RFC 2531 Content Feature Schema for Internet Fax March 1999

    (& (dpi=300) (dpi-xyratio=1)
       (color=Binary)
       (paper-size=A4)
       (image-coding=[MMR,JBIG]) )
    (& (dpi=200) (dpi-xyratio=200/100)
       (color=Binary)
       (paper-size=B4)
       (image-coding=[MH,MR]) )
    (& (dpi=300) (dpi-xyratio=1)
       (color=Mapped) (color-levels=42)
       (paper-size=A4)
       (image-coding=JPEG) ) )
 This could be simplified, but there is little gain in doing so at
 this point.
 The composite document description can be matched with the receiver
 capability description, according to the rules in [2], to yield the
 result:
    (& (dpi=300) (dpi-xyratio=1)
       (color=Binary)
       (paper-size=A4)
       (ua-media=[stationery,transparency])
       (image-coding=JBIG) )
    (& (dpi=200) (dpi-xyratio=200/100)
       (color=Binary)
       (paper-size=B4)
       (ua-media=continuous)
       (image-coding=[MH,MR]) ) )
 Points to note about the feature matching process:
 o  The color document option is eliminated because the receiver
    cannot handle either color (indicated by '(color=Mapped)') or JPEG
    coding (indicated by '(image-coding=JPEG)').
 o  The high resolution version of the document with '(dpi=300)' must
    be send using '(image-coding=JBIG)' because this is the only
    available coding of the image data that the receiver can use for
    high resolution documents.  (The available 300dpi document codings
    here are MMR and JBIG, and the receiver capabilities are MH, MR
    and JBIG.)
 o  The low-resolution version of the document can be sent with either
    MH or MR coding as the receiver can deal with either of these for
    low resolution documents.

Klyne & McIntyre Standards Track [Page 16] RFC 2531 Content Feature Schema for Internet Fax March 1999

 o  The high resolution variant of the document is available only for
    A4, so that is the paper-size used in that case.  Similarly the
    low resolution version is sent for B4 paper.
 o  Even though the sender may not understand the 'ua-media' feature
    tag, and does not mention it, the matching rules preserve the
    constraint that the B4 document is rendered with '(ua-
    media=continuous)', and the A4 document may be rendered with '
    (ua-media=[stationery,transparency])'.
 Finally, note that when matching an MRC document description, the
 description of each component sub-image must match the capabilities
 of the intended receiver.

5. IANA Considerations

 Appendix A of this document calls for registrations of feature tags
 in the "IETF tree", as defined in section 3.1.1 of "Media Feature Tag
 Registration Procedure" [1] (i.e. these feature tags are subject to
 the "IETF Consensus" policies described in RFC 2434 [21]).
 ASN.1 identifiers should be assigned for each of these registered
 feature tags and replaced in the body of the registration.

6. Security Considerations

 The points raised below are in addition to the general security
 considerations for extended Internet fax [5], and others discussed in
 [2,8,11,12,13]

6.1 Capability descriptions and mechanisms

 Negotiation mechanisms reveal information about one party to other
 parties.  This may raise privacy concerns, and may allow a malicious
 party to make better guesses about the presence of specific security
 holes.
 Most of these concerns pertain to capability information getting into
 the hands of someone who may abuse it.  This document specifies
 capabilities that help a sender to determine what image
 characteristics can be processed by the recipient, not mechanisms for
 their publication.  Implementors and users should take care that the
 mechanisms employed ensure that capabilities are revealed only to
 appropriate persons, systems and agents.

Klyne & McIntyre Standards Track [Page 17] RFC 2531 Content Feature Schema for Internet Fax March 1999

6.2 Specific threats

 1.  Unsolicited bulk mail:  if it is known that a recipient can
     process certain types of images, they may be targeted by bulk
     mailers that want to send such images.

7. Acknowledgements

 The authors gratefully acknowledge the contributions of the following
 persons who commented on earlier versions of this memo: James
 Rafferty, Dan Wing, Robert Buckley, Mr Ryuji Iwazaki.  The following
 contributed ideas upon which some of the features described here have
 been based: Larry Masinter, Al Gilman, Koen Holtman.

8. References

 [1]  Holtman, K., Mutz, A. and T. Hardie, "Media Feature Tag
      Registration Procedure", BCP 31, RFC 2506, March 1999.
 [2]  Klyne, G., "A Syntax for Describing Media Feature Sets", RFC
      2533, March 1999.
 [3]  Masinter, L., Holtman, K., Mutz, A. and D. Wing, "Media Features
      for Display, Print, and Fax", RFC 2534, March 1999.
 [4]  McIntyre, L. and G. Klyne, "Internet fax feature mapping from
      Group 3 fax", Work in Progress.
 [5]  Masinter, L. and D. Wing, "Extended Facsimile Using Internet
      Mail", RFC 2532, March 1999.
 [6]  "Procedures for document facsimile transmission in the general
      switched telephone network", ITU-T Recommendation T.30 (1996),
      International Telecommunications Union, July 1996.
 [7]  McIntyre, L., Buckley, R., Venable, D., Zilles, S., Parsons, G.
      and J. Rafferty, "File format for Internet fax", RFC 2301, March
      1998.
 [8]  Toyoda, K., Ohno, H., Murai, J. and D. Wing, "A Simple Mode of
      Facsimile Using Internet Mail", RFC 2305, March 1998.
 [9]  "Continuous-tone color representation method for facsimile"
      ITU-T Recommendation T.42 (1996), International
      Telecommunications Union, (Covers custom illuminant, gamut).

Klyne & McIntyre Standards Track [Page 18] RFC 2531 Content Feature Schema for Internet Fax March 1999

 [10] "Colour and gray-scale image representation using lossless
      coding scheme for facsimile", ITU-T Recommendation T.43 (1997),
      International Telecommunications Union. (Covers JBIG for
      colour/grey images).
 [11] Hardie, T., "Scenarios for the Delivery of Negotiated Content",
      Work in Progress.
 [12] Klyne, G., "Requirements for protocol-independent content
      negotiation", Work in Progress.
 [13] "Standardization of Group 3 facsimile terminals for document
      transmission", ITU-T Recommendation T.4 (1996), International
      Telecommunications Union, (Covers basic fax coding formats: MH,
      MR).
 [14] "Facsimile coding schemes and coding control functions for Group
      4 facsimile apparatus", ITU Recommendation T.6, International
      Telecommunications Union, (Commonly referred to as the MMR
      standard; covers extended 2-D fax coding format).
 [15] "Mixed Raster Content (MRC)", ITU-T Recommendation T.44,
      International Telecommunications Union.
 [16] "Information technology - Digital compression and coding of
      continuous-tone still image - Requirements and guidelines",
      ITU-T Recommendation T.81 (1992) | ISO/IEC 10918-1:1993,
      International Telecommunications Union, (Commonly referred to as
      JPEG standard).
 [17] "Information technology - Coded representation of picture and
      audio information - Progressive bi-level image compression",
      ITU-T Recommendation T.82 (1993) | ISO/IEC 11544:1993,
      International Telecommunications Union, (Commonly referred to as
      JBIG1 standard).
 [18] "Application profile for Recommendation T.82 - Progressive bi-
      level image compression (JBIG1 coding scheme for facsimile
      apparatus)", ITU-T Recommendation T.85 (1995), International
      Telecommunications Union, (Covers bi-level JBIG).
 [19] "Colorimeter, 2nd ed.", CIE Publication No. 15.2, 1986.
      (Defines CIELAB color space;  use with fax is further
      constrained by T.42 [9].)

Klyne & McIntyre Standards Track [Page 19] RFC 2531 Content Feature Schema for Internet Fax March 1999

 [20] Tag Image File Format, Revision 6.0, Adobe 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.

Klyne & McIntyre Standards Track [Page 20] RFC 2531 Content Feature Schema for Internet Fax March 1999

9. Authors' Addresses

 Graham Klyne
 5th Generation Messaging Ltd.    Content Technologies Ltd.
 5 Watlington Street              Forum 1, Station Road
 Nettlebed                        Theale
 Henley-on-Thames, RG9 5AB        Reading, RG7 4RA
 United Kingdom                   United Kingdom.
 Phone:     +44 1491 641 641      +44 118 930 1300
 Facsimile: +44 1491 641 611      +44 118 930 1301
 EMail:     GK@ACM.ORG
 Lloyd McIntyre
 Xerox Corporation
 Mailstop PAHV-121
 3400 Hillview Ave.
 Palo Alto, CA 94304 USA
 Phone:     +1-650-813-6762
 Facsimile: +1-650-845-2340
 EMail: Lloyd.McIntyre@pahv.xerox.com

Klyne & McIntyre Standards Track [Page 21] RFC 2531 Content Feature Schema for Internet Fax March 1999

Appendix A: Feature registrations

A.1 Image size

  1. Media Feature tag name(s):
       size-x
       size-y
  1. ASN.1 identifiers associated with these feature tags:
       1.3.6.1.8.1.7
       1.3.6.1.8.1.8
  1. 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.
  1. Values appropriate for use with these feature tags:
       Rational (>0)
  1. 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.
  1. 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)

Klyne & McIntyre Standards Track [Page 22] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. 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.
  1. 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) )
  1. 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.
  1. Related feature tags:
       pix-x                 [3]
       pix-y                 [3]
       dpi                   [3]
       dpi-xyratio           [this document]
  1. Intended usage:
       Common
  1. Author/Change controller:
       IETF

Klyne & McIntyre Standards Track [Page 23] RFC 2531 Content Feature Schema for Internet Fax March 1999

A.2 Resolution aspect ratio

  1. Media Feature tag name(s):
       dpi-xyratio
  1. ASN.1 identifier associated with this feature tag:
       1.3.6.1.8.1.9
  1. 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.
  1. Values appropriate for use with this feature tag:
       Rational (>0)
  1. 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.
  1. 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) )
  1. Related standards or documents:
       The memo "Media Features for Display, Print, and Fax" [3]
       describes a feature (dpi) for measuring document resolution.

Klyne & McIntyre Standards Track [Page 24] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. 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.
  1. Related feature tags:
       dpi                   [3]
       size-x                [this document]
       size-y                [this document]
  1. Intended usage:
       Internet fax
  1. Author/Change controller:
       IETF

A.3 Color levels

  1. Media Feature tag name(s):
       color-levels
  1. ASN.1 identifier associated with this feature tag:
       1.3.6.1.8.1.10
  1. Summary of the media features indicated:
       This feature tag is used to indicate a number of different
       image data pixel color values.
       When mapped (palettized) color is used, this is generally
       different from the number of different colors that can be
       represented through the color mapping function.
       This feature tag is used in conjunction with a 'color' feature
       having a value other than 'Binary'.
  1. Values appropriate for use with this feature tag:
       Integer  (>=2)

Klyne & McIntyre Standards Track [Page 25] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. 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.
  1. 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) )
  1. Related standards or documents:
       The memo "Media Features for Display, Print, and Fax" [3]
       describes a feature (color) for indicating basic color
       capabilities.
  1. Interoperability considerations:
       The actual number of color values used by a document does not,
       in general, exactly match the number that can be handled by a
       recipient.  To achieve a feature match, at least one must be
       declared as an inequality.
       It is recommended that a recipient declares the number of color
       values that it can handle as an inequality (<=), and a data
       resource declares the number of colors that it uses with an
       equality, as shown in the examples above.
  1. Security considerations:
  1. 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.

Klyne & McIntyre Standards Track [Page 26] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Related feature tags:
       color                 [3]
       color-space           [this document]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

A.4 Color space

  1. Media Feature tag name(s):
       color-space
  1. ASN.1 identifier associated with this feature tag:
       1.3.6.1.8.1.11
  1. 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.
  1. Values appropriate for use with this feature tag:
       Token

Klyne & McIntyre Standards Track [Page 27] RFC 2531 Content Feature Schema for Internet Fax March 1999

       Device color      Device-RGB   (device dependent RGB)
       spaces:           Device-CMY   (device dependent CMY)
                         Device-CMYK  (device dependent CMYK)
       Calibrated color  CIELAB       (per T.42 [9])
       space:
                         (may be extended by further registrations)
       'Color-space=CIELAB' indicates the CIE L*a*b* colour space,
       using CIED50 illuminant and its perfectly diffuse reflecting
       white point (per T.42 [9]).
  1. 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.
  1. 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)
  1. Related standards or documents:
       CIELAB color space is defined in [19]
       CIELAB use for fax is described in ITU T.42 [9]

Klyne & McIntyre Standards Track [Page 28] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Interoperability considerations:
       A color-handling receiver should indicate at any appropriate
       device color space capability, in addition to any calibrated
       color spaces that it may support.
       Calibrated color spaces are intended to be used when precise
       color matching is required; otherwise, if applicable, a device
       color space (color-space=Device-xxx) should be indicated.
       Documents for which exact color matching is not important
       should indicate a device color space capability, if applicable.
       These principles allow sender/receiver feature matching to be
       achieved when exact color matching is not required.
  1. Security considerations:
  1. 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.
  1. 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.
  1. Related feature tags:
       color                 [3]
  1. Related media types or data formats:
       TIFF-FX               [7]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

Klyne & McIntyre Standards Track [Page 29] RFC 2531 Content Feature Schema for Internet Fax March 1999

A.5 CIELAB color depth

  1. Media Feature tag name(s):
       CIELAB-L-depth
       CIELAB-A-depth
       CIELAB-B-depth
  1. ASN.1 identifiers associated with these feature tags:
       1.3.6.1.8.1.12
       1.3.6.1.8.1.13
       1.3.6.1.8.1.14
  1. Summary of the media features indicated:
       These feature tags indicate a color depth capability; i.e.  the
       level of detail to which an individual CIELAB color component
       can be specified.  They define the number of distinct values
       possible for each of the color components L*, a* and b*.
       Typically, this feature would be used with 'color=mapped', and
       possibly 'color=grey' or 'color=full', to indicate the number
       of distinct colors that can be realized.
  1. Values appropriate for use with these feature tags:
       Integer (>0)
  1. 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.
  1. 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) )

Klyne & McIntyre Standards Track [Page 30] RFC 2531 Content Feature Schema for Internet Fax March 1999

       (& (color=full) (color-levels<=16777216)
          (CIELAB-L-depth<=256)
          (CIELAB-a-depth<=128)
          (CIELAB-b-depth<=128) )
       To describe capabilities assumed by a document:
       (& (color=mapped) (color-levels=200)
          (CIELAB-L-depth=32)
          (CIELAB-a-depth=32)
          (CIELAB-b-depth=32) )
       (& (color=full) (color-levels=32768)
          (CIELAB-L-depth=128)
          (CIELAB-a-depth=32)
          (CIELAB-b-depth=32) )
  1. 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]
  1. Related feature tags:
       color                 [3]
       color-levels          [this document]
       color-space           [this document]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

Klyne & McIntyre Standards Track [Page 31] RFC 2531 Content Feature Schema for Internet Fax March 1999

A.6 CIELAB color gamut

  1. Media Feature tag name(s):
       CIELAB-L-min
       CIELAB-L-max
       CIELAB-a-min
       CIELAB-a-max
       CIELAB-b-min
       CIELAB-b-max
  1. ASN.1 identifiers associated with these feature tags:
       1.3.6.1.8.1.15
       1.3.6.1.8.1.16
       1.3.6.1.8.1.17
       1.3.6.1.8.1.18
       1.3.6.1.8.1.19
       1.3.6.1.8.1.20
  1. 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.
  1. Values appropriate for use with this feature tag:
       Rational
  1. 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.

Klyne & McIntyre Standards Track [Page 32] RFC 2531 Content Feature Schema for Internet Fax March 1999

       Scanning applications where the data transferred may depend
       upon the detailed color image generation capabilities of the
       originator.
  1. Examples of typical use:
       To describe rendering or scanning capabilities:
       (& (CIELAB-L-min>=0)
          (CIELAB-L-max<=100)
          (CIELAB-a-min>=-75)
          (CIELAB-a-max<=+75)
          (CIELAB-b-min>=-85)
          (CIELAB-b-max<=+85) )
       To describe capabilities required by a document:
       (& (CIELAB-L-min=20)
          (CIELAB-L-max=80)
          (CIELAB-L-min=-35)
          (CIELAB-L-max=+55)
          (CIELAB-L-min=-45)
          (CIELAB-L-max=+65) )
  1. Related standards or documents:
       CIELAB color space is defined in [19]
       CIELAB use for fax is described in ITU T.42 [9]
  1. 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.
  1. Security considerations:
  1. 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.

Klyne & McIntyre Standards Track [Page 33] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Related feature tags:
       color                 [3]
       color-space           [this document]
  1. Related media types or data formats:
       TIFF-FX               [7]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

A.7 Image file structure

  1. Media Feature tag name(s):
       image-file-structure
  1. ASN.1 identifier associated with this feature tag:
       1.3.6.1.8.1.21
  1. 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.).
  1. Values appropriate for use with this feature tag:
       Token

Klyne & McIntyre Standards Track [Page 34] RFC 2531 Content Feature Schema for Internet Fax March 1999

       TIFF-FX profiles  TIFF-S
       [7]:              TIFF-F
                         TIFF-J
                         TIFF-C
                         TIFF-L
                         TIFF-M
                         (may be extended by further registrations,
                         to cover non-TIFF image file structures)
  1. 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.
  1. Examples of typical use:
       See Appendix B of this memo.
  1. Considerations particular to use in individual applications,

protocols, services, or negotiation mechanisms:

       This tag is intended to provide information about an image file
       structure.  Information about image data coding is provided by
       other tags.
       In the case of TIFF-FX image data, there are a number of image
       file format constraints that are imposed by the various usage
       profiles defined in RFC 2301 [7].  The purpose of the 'image-
       file-structure' feature tag is to capture those file format
       constraints.
       Registration of additional image file structure tags should
       focus similarly on image file structure issues, not raw image
       data compression and coding.  As a guide, an image file
       structure may contain image data coded in a variety of ways,
       and carries information to describe that coding separately from
       MIME content-type labelling, etc.
  1. Related feature tags:
       image-coding          [this document]
  1. Related media types or data formats:
       TIFF-FX               [7]
       TIFF V6.0 (Adobe)     [20]

Klyne & McIntyre Standards Track [Page 35] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Intended usage:
       Internet fax
       Image scanning/rendering applications
  1. Author/Change controller:
       IETF

A.8 Image data coding

  1. Media Feature tag name(s):
       image-coding
  1. ASN.1 identifier associated with this feature tag:
       1.3.6.1.8.1.22
  1. 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.
  1. Values appropriate for use with this feature tag:
       Token             MH
                         MR
                         MMR
                         JBIG
                         JPEG
                         (may be extended by further registrations)
  1. 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.

Klyne & McIntyre Standards Track [Page 36] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Examples of typical use:
       See Appendix B of this memo.
  1. 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]
  1. 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.
  1. Related feature tags:
       image-coding-constraint  [this document]
       JBIG-stripe-size         [this document]
       image-interleave         [this document]
  1. Related media types or data formats:
       TIFF-FX                  [7]
  1. Intended usage:
       Internet fax
       Image scanning/rendering applications
  1. Author/Change controller:
       IETF

A.9 Image coding constraint

  1. Media Feature tag name(s):
       image-coding-constraint
  1. ASN.1 identifier associated with these feature tags:
       1.3.6.1.8.1.23

Klyne & McIntyre Standards Track [Page 37] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. 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.
  1. 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)
  1. 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.
  1. Examples of typical use:
       See Appendix B of this memo.
  1. Related standards or documents:
       JBIG-T85:   ITU T.85 [18]
       JBIG-T43:   ITU T.43 [10]
       JPEG-T4E:   ITU T.4 Annex E [13]
  1. 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.
  1. Related feature tags:
       image-coding             [this document]
       JBIG-stripe-size         [this document]
       image-interleave         [this document]

Klyne & McIntyre Standards Track [Page 38] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Related media types or data formats:
       TIFF-FX                  [7]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

A.10 JBIG stripe size

  1. Media Feature tag name(s):
       JBIG-stripe-size
  1. ASN.1 identifier associated with these feature tags:
       1.3.6.1.8.1.24
  1. 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.
  1. Values appropriate for use with this feature tag:
       Integer  (>0)
  1. 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.
  1. Examples of typical use:
       (JBIG-stripe-size=128)
       (JBIG-stripe-size>0)

Klyne & McIntyre Standards Track [Page 39] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Related standards or documents:
       JBIG:       ITU T.82 [17]
       JBIG-T85:   ITU T.85 [18]
       JBIG-T43:   ITU T.43 [10]
  1. 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.
  1. 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.
  1. Related feature tags:
       image-coding             [this document]
       image-coding-constraint  [this document]
       image-interleave         [this document]
  1. Related media types or data formats:
       TIFF-FX                  [7]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

Klyne & McIntyre Standards Track [Page 40] RFC 2531 Content Feature Schema for Internet Fax March 1999

A.11 Image interleave

  1. Media Feature tag name(s):
       image-interleave
  1. ASN.1 identifier associated with this feature tag:
       1.3.6.1.8.1.25
  1. 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.
  1. Values appropriate for use with this feature tag:
       Token             Stripe
                         Plane
  1. 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.
  1. Examples of typical use:
       (image-interleave=stripe)
       (image-interleave=[stripe,plane])
  1. Considerations particular to use in individual applications,

protocols, services, or negotiation mechanisms:

       Specifying a plane interleave means that an entire page of
       image data must be buffered in order to generate render the
       image.  This may place considerable demands on the memory of a
       sending or receiving system.
  1. Related feature tags:
       image-coding             [this document]
       JBIG-stripe-size         [this document]

Klyne & McIntyre Standards Track [Page 41] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Related media types or data formats:
       TIFF-FX                  [7]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

A.12 Color subsampling

  1. Media Feature tag name(s):
       color-subsampling
  1. ASN.1 identifier associated with this feature tag:
       1.3.6.1.8.1.26
  1. 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.
  1. Values appropriate for use with this feature tag:
       String            "1:1:1"
                         This value indicates a full set of color
                         component samples for each luminance
                         component sample.
                         "4:1:1"
                         This value indicates a set of color samples
                         for each luminance sample.
                         (may be extended by further registrations)

Klyne & McIntyre Standards Track [Page 42] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. 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.
  1. Examples of typical use:
       (& (color=full) (color-space=[Device-RGB,CIELAB])
          (color-subsampling=["1:1:1","4:1:1"]) )
  1. Related feature tags:
       color                 [3]
       color-space           [this document]
       image-file-structure  [this document]
  1. Related media types or data formats:
       TIFF-FX               [7]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

A.13 MRC availability and mode

  1. Media Feature tag name(s):
       MRC-mode
  1. ASN.1 identifier associated with this feature tag:
       1.3.6.1.8.1.27

Klyne & McIntyre Standards Track [Page 43] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. 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.).
  1. Values appropriate for use with this feature tag:
       Integer (0..7)
  1. 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.
  1. Examples of typical use:
       See Appendix B of this document.
  1. Related standards or documents:
       ITU T.44 [15]
  1. 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.

Klyne & McIntyre Standards Track [Page 44] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Related feature tags:
       image-coding             [this document]
       MRC-max-stripe-size      [this document]
  1. Related media types or data formats:
       TIFF-FX                  [7]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

A.14 MRC maximum stripe size

  1. Media Feature tag name(s):
       MRC-max-stripe-size
  1. ASN.1 identifier associated with this feature tag:
       1.3.6.1.8.1.28
  1. 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.
  1. Values appropriate for use with this feature tag:
       Integer (>0)
  1. 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.

Klyne & McIntyre Standards Track [Page 45] RFC 2531 Content Feature Schema for Internet Fax March 1999

  1. Examples of typical use:
       (MRC-max-stripe-size=[0..256])
       (MRC-max-stripe-size>=0)
  1. 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.
  1. Related feature tags:
       MRC-mode              [this document]
  1. Related media types or data formats:
       TIFF-FX               [7]
  1. Intended usage:
       Internet fax
       Color image scanning/rendering applications
  1. Author/Change controller:
       IETF

Klyne & McIntyre Standards Track [Page 46] RFC 2531 Content Feature Schema for Internet Fax March 1999

Appendix B: TIFF mode descriptions

 This appendix contains descriptions of the TIFF modes defined by RFC
 2301 [7], presented as feature set expressions in the form defined by
 "A syntax for describing media feature sets" [2] and using the
 feature schema introduced by this document.
 These may be taken as illustrations of the feature set combinations
 that are required for the corresponding TIFF profiles described by
 RFC 2301.
    (Tiff-S) :-
         (& (image-file-structure=TIFF-S)
            (color=Binary)
            (image-coding=MH) (MRC-mode=0) )
    (Tiff-F) :-
         (& (image-file-structure=TIFF-F)
            (color=Binary)
            (image-coding=MH) (MRC-mode=0) )
    (TIFF-J) :-
         (& (image-file-structure=TIFF-J)
            (color=Binary)
            (image-coding=JBIG) (MRC-mode=0) )
    (TIFF-C) :-
         (& (image-file-structure=TIFF-C)
            (color=Grey)
            (image-coding=JPEG) (MRC-mode=0) )
    (TIFF-L) :-
         (& (image-file-structure=TIFF-L)
            (color=Grey)
            (image-coding=JBIG) (MRC-mode=0) )
    (TIFF-M) :-
         (& (image-file-structure=TIFF-M)
            (color=[Binary,Grey])
            (image-coding=[MH,JPEG]) (MRC-mode>=1) )
 The feature sets described above are minimum requirements for the
 corresponding TIFF modes.  Thus, MR and MMR image coding are not
 mandatory with TIFF mode F, and would be indicated by combining the
 expression for (TIFF-F) with (image-coding=MR) and/or (image-
 coding=MMR).

Klyne & McIntyre Standards Track [Page 47] RFC 2531 Content Feature Schema for Internet Fax March 1999

 Similarly, limited, mapped or full color are not mandatory with the
 grey/color TIFF modes (C, L and M), and would be indicated by
 combining the corresponding expression with (color=limited),
 (color=mapped) and/or (color=full).
 TIFF profile M is a composite structure that can combine image data
 coding options from other profiles: the description above indicates
 mandatory features; other options may be indicated by combining
 TIFF-M with other options (e.g. color= limited, mapped or full, and
 image-coding= MR, MMR or JBIG).
 Support for multiple TIFF profiles may be indicated by combining
 their expressions with the OR operator; e.g.
      (| (TIFF-F) (TIFF-S) (TIFF-J) )
 indicates support for all black-and-white modes.

Klyne & McIntyre Standards Track [Page 48] RFC 2531 Content Feature Schema for Internet Fax March 1999

Appendix C: Revision history

 00a  28-Sep-1998  Initial draft.
 01a  12-Oct-1998  Incorporated review comments.  Described feature
                   tag for differential x/y resolution ratio.  Added
                   some examples.
 01b  19-Oct-1998  Updated section 3.6 on image coding.  Added
                   Appendix B containing feature expressions for the
                   TIFF modes from RFC 2301.
 02a  26-Oct-1998  Update examples.  Add separate stripe size features
                   for JBIG and MRC.
 02b  30-Oct-1998  Update examples.  Add text clarifying the
                   description of MRC documents (as a set of feature
                   collections describing multiple contained images).
                   Add text describing constrains on resolution and
                   image coding usage within an MRC document.
 02c  11-Nov-1998  Add ITU references.  Added terminology: "capability
                   exchange", "capability identification" and
                   "capability description".  Update JBIG and MRC
                   stripe size tags.  Move subsampling to colour
                   section.  Remove preferred-unit tag.  Add T.4, T.6,
                   T.44 and T.81 references.
 02d  16-Nov-1998  Update colour handling features, reflecting
                   proposed changes to the media features memo [3].
                   Update the image coding capability framework.
                   Updated TIFF mode descriptions in Appendix B.
 03a  17-Nov-1998 Replace use of 'pix-x', 'pix-y' with 'size-x', '
                   size-y'.  Add registrations in Appendix A.
 03b  08-Dec-1998  Remove normative language and reference to RFC2119
                   (normative statements will be in the main fax
                   protocol draft).  Revise structure of colour
                   features, and removed color-palette feature. Define
                   colour feature tags specific to CIELAB model and
                   colour space.
 04a  14-Dec-1998  Update examples to reflect revised feature tags.
                   Revise description of MRC document in section 3.7.
                   Clarified interpretation of 'color=fixed'.  Change
                   feature value 'color=fixed' to 'color=limited'.

Klyne & McIntyre Standards Track [Page 49] RFC 2531 Content Feature Schema for Internet Fax March 1999

 05a  04-Jan-1999  Incorporate WG last-call comments:  change
                   references to MRC-stripe-size to MRC-max-stripe-
                   size;  similarly references to MRC-maximum-stripe-
                   size.  Change "eifax" to "extended Internet fax".
                   Added guidance note for image coding feature usage.
                   Added IANA consideration comments to Appendix A.
 05b  08-Jan-1999  Added new section for IANA considerations; removed
                   references to fax working group from registration
                   change control sections.  Remove JPEG from TIFF-L
                   auxiliary predicate.  Clarify description of MRC
                   receiver capabilities in section A.13.  Remove '
                   color=full' from (TIFF-C) and (TIFF-M) predicates,
                   and add some explanatory text.  Remove
                   'color=limited' from (TIFF-L) predicate.
 05c  08-Jan-1999  Minor revisions to TIFF profile illustrations and
                   descripions in Appendix B.  Reformatted description
                   of 'color=limited' in section 3.5 to clarify that
                   this does not indicate support for specific named
                   colors.

Klyne & McIntyre Standards Track [Page 50] RFC 2531 Content Feature Schema for Internet Fax March 1999

Full Copyright Statement

 Copyright (C) The Internet Society (1999).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Klyne & McIntyre Standards Track [Page 51]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2531.txt · Last modified: 1999/03/11 23:23 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki