rfc2880.txt

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Network Working Group                                        L. McIntyre
Request for Comments: 2880                             Xerox Corporation
Category: Informational                                         G. Klyne
                                                    Content Technologies
                                                             August 2000


                   Internet Fax T.30 Feature Mapping

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   This document describes how to map Group 3 fax capability
   identification bits, described in ITU T.30 [6], into the Internet fax
   feature schema described in "Content feature schema for Internet fax"
   [4].

   This is a companion to the fax feature schema document [4], which
   itself defines a profile of the media feature registration mechanisms
   [1,2,3], for use in performing capability identification between
   extended Internet fax systems [5].

Table of Contents

   1. Introduction .............................................3
      1.1 Organization of this document ........................3
      1.2 Terminology and document conventions .................3
      1.3 Discussion of this document ..........................4
   2. Combining feature tags ...................................4
      2.1 Relationship to Group 3 fax ..........................5
      2.2 Feature set descriptions .............................5
      2.3 Examples .............................................5
        2.3.1 Data resource example ............................6
        2.3.2 Recipient capabilities example ...................6
   3. Survey of media-related T.30 capability bits .............6
      3.1 DIS/DTC bit 15 (resolution) ..........................6
      3.2 DIS/DTC bit 16 (MR coding) ...........................7
      3.3 DIS/DTC bits 17,18 (width) ...........................7
      3.4 DIS/DTC bits 19,20 (length) ..........................7



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      3.5 DIS/DTC bit 31 (MMR coding) ..........................7
      3.6 DIS/DTC bit 36 (JBIG multi-level coding) .............8
      3.7 DIS/DTC bit 37 (plane interleave) ....................8
      3.8 DIS/DTC bits 41,42,43 (resolution) ...................8
      3.9 DIS/DTC bits 44,45 (preferred units) .................9
      3.10 DIS/DTC bit 68 (JPEG) ...............................9
      3.11 DIS/DTC bit 69 (colour) .............................9
      3.12 DIS/DTC bit 71 (bits/sample) .......................10
      3.13 DIS/DTC bit 73 (no subsampling) ....................10
      3.14 DIS/DTC bit 74 (custom illuminant) .................10
      3.15 DIS/DTC bit 75 (custom gamut) ......................10
      3.16 DIS/DTC bits 76,77 (paper size) ....................11
      3.17 DIS/DTC bit 78 (JBIG bi-level coding) ..............11
      3.18 DIS/DTC bit 79 (JBIG stripe size) ..................11
      3.19 DIS/DTC bit 92,93,94 (MRC maximum functional mode) .11
      3.20 DIS/DTC bit 95 (MRC stripe size) ...................12
      3.21 DIS/DTC bit 97 (resolution) ........................12
      3.22 DIS/DTC bit 98 (resolution) ........................12
   4. Summary of T.30 capability dependencies .................12
      4.1 Image coding ........................................13
        4.1.1 Bi-level coding .................................13
        4.1.2 Multi-level coding ..............................14
        4.1.3 MRC format ......................................14
      4.2 Resolution and units ................................15
      4.3 Colour capabilities .................................17
      4.4 Document size .......................................18
   5. Mapping T.30 capabilities to fax feature schema .........18
      5.1 Image coding ........................................20
        5.1.1 Bi-level coding .................................20
        5.1.2 Multi-level coding ..............................21
        5.1.3 MRC format ......................................23
      5.2 Resolution and units ................................23
      5.3 Colour capabilities .................................24
      5.4 Document size .......................................26
   6. Examples ................................................26
      6.1 Common black-and-white fax machine ..................27
        6.1.1 Corresponding Internet fax capabilities .........29
      6.2 Full-featured color fax machine .....................30
   7. Security Considerations .................................34
   8. Acknowledgements ........................................34
   9. References ..............................................34
   10. Authors' Addresses .....................................36
   Full Copyright Statement ...................................37








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RFC 2880           Internet Fax T.30 Feature Mapping         August 2000


1. Introduction

   This document describes how to map Group 3 fax capability
   identification bits, described in ITU T.30 [6], into the Internet fax
   feature schema described in "Content feature schema for Internet fax"
   [4].

   This is a companion to the fax feature schema document [4], which
   itself defines a profile of the media feature registration mechanisms
   [1,2,3], for use in performing capability identification between
   extended Internet fax systems [5].

1.1 Organization of this document

   Section 2 introduces the mechanisms that combine feature tag
   constraints to describe complex recipient capabilities.

   Section 3 surveys Group 3 fax (T.30) capability bits that relate to
   media handling capabilities.

   Section 4 describes the dependencies between Group 3 fax (T.30)
   capability bits.  These are presented in a decision table format [16]
   with descriptive text in place of the action bodies.

   Section 5 describes a formal mechanism for converting Group 3 fax
   (T.30) capability masks to fax feature schema statements.  The
   conversion process is driven by the decision tables introduced
   previously, using fax feature schema statements and combining rules
   in the action bodies.

   Section 6 presents an example of a Group 3 fax (T.30) capability
   mask, and uses the formal mechanism described previously to convert
   that into a corresponding fax feature schema statement.

1.2 Terminology and document conventions

   eifax system
             is used to describe any software, device or combination
             of these that conforms to the specification "Extended
             Facsimile Using Internet Mail" [5].

   Feature   is used as defined in [15].  (See also section 2 of this
             memo.)

   Feature tag
             is used as defined in [15].  (See also section 2.)





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   Feature collection
             is used as defined in [2].  (See also section 2.)

   Feature set
             is used as defined in [2].  (See also section 2.)

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:

       [e-mail]

   To subscribe to this list, send a message with the body 'subscribe'
   to "[e-mail]".

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

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

2. Combining feature tags

   A fax document can be described by media features.  Any single media
   feature value can be thought of as just one component of a feature
   collection that describes some instance of a document (e.g.  a
   printed fax, a displayed image, etc.).  Such a feature collection
   consists of a number of media feature tags (each per [1]) and
   associated feature values.

   A feature set contains a number of feature collections.  Thus, a
   feature set can describe a number of different fax document
   instances.  These can correspond to different treatments of a single
   document (e.g. different resolutions used for printing a given fax),
   a number of different documents subjected to a common treatment (e.g.
   the range of different images that can be rendered on a given
   display), or some combination of these (see examples below).

   Thus, a description of a feature set can describe the rendering
   requirements of a fax document or the capabilities of a receiving
   eifax system.









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2.1 Relationship to Group 3 fax

   A "feature tag" can be compared with a single bit in a T.30 DCS
   frame, describing a specific attribute of a specific fax document.

   A "feature collection" corresponds to a complete T.30 DCS frame,
   describing a range of attributes of a specific fax document.

   A "feature set" corresponds to a DIS or DTC frame, describing the
   range of document attributes that can be accepted by a given fax
   machine.

   Within T.30 DIS/DTC frames, dependencies between the various
   capabilities are implicit in the definitions of the capabilities.
   E.g. multi-level coding (DIS/DTC bit 68) requires support for
   200*200dpi resolution (DIS/DTC bit 15).  In the feature set
   description framework used by eifax systems [1,2,3,4] such
   dependencies between different features are expressed explicitly.
   Later sections of this memo describe how the implicit dependencies of
   T.30 are expressed using the media feature set notation.

2.2 Feature set descriptions

   The general approach to describing feature sets, described more fully
   in [2], is to use functions ("predicates") that, when applied to a
   feature collection value, yield a Boolean value that is TRUE if the
   feature collection describes an acceptable fax document instance,
   otherwise FALSE.

                      P(F)
        P(F) = TRUE <- : -> P(F) = FALSE
                       :
            +----------:----------+  This box represents some
            |          :          |  universe of fax documents (F)
            | Included : Excluded |  from which some acceptable subset
            |          :          |  is selected by the predicate P.
            +----------:----------+
                       :

2.3 Examples

   In the examples below the following notation is used:

      (x ? y)             tests feature tag 'x' for some relationship
                          with value 'y'.

      (| p1 p2 ... pn )   represents the logical-OR of predicates 'p1',
                          'p2' up to 'pn'.



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      (& p1 p2 ... pn )   represents the logical-AND of predicates
                          'p1', 'p2' up to 'pn'.

2.3.1 Data resource example

   The following expression uses the syntax of [2] to describe a data
   resource that can be displayed either:
   (a)  as a 750x500 pixel image using 15 colours, or
   (b)  at 150dpi on an A4 page.

      (| (& (pix-x=750) (pix-y=500) (color=15) )
         (& (dpi>=150) (papersize=A4) ) )

2.3.2 Recipient capabilities example

   The following expression describes a receiving system that has:
   (a)  a screen capable of displaying 640*480 pixels and 16 million
        colours (24 bits per pixel), 800*600 pixels and 64 thousand
        colours (16 bits per pixel) or 1024*768 pixels and 256 colours
        (8 bits per pixel), or
   (b)  a printer capable of rendering 300dpi on A4 paper.

      (| (& (| (& (pix-x<=640)  (pix-y<=480) (color<=16777216) )
               (& (pix-x<=800)  (pix-y<=600) (color<=65535) )
               (& (pix-x<=1024) (pix-y<=768) (color<=256) ) )
            (media=screen) )
         (& (dpi=300)
            (media=stationery) (papersize=A4) ) )

3. Survey of media-related T.30 capability bits

   The following sections refer to T.30 DIS/DTC bits identified and
   described in Table 2/T.30 and accompanying notes [6].  Bit numbers
   that are not referenced below are considered to be not related to
   media features, hence not relevant to the Internet fax feature
   schema.

         NOTE: some of the DIS/DTC bits identified below are
         documented in revisions of the T.30 specification that
         may be not yet publicly available from the ITU.

3.1 DIS/DTC bit 15 (resolution)

   All Group 3 fax systems are required to support a basic resolution of
   200*100dpi (dots per inch) or 8*3.85dpmm (dots per millimetre).

   Setting this bit indicates additional support for 200*200dpi or
   8*7.7dpmm.



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   For multi-level images, 200*200dpi is the basic resolution, and this
   bit must be set.  The other basic resolution options apply to bi-
   level images only.

   See also: bits 44,45.

3.2 DIS/DTC bit 16 (MR coding)

   All Group 3 fax systems are required to support Modified Huffman (MH)
   1-dimensional coding for bi-level images.  (A bi-level image is one
   with just two pixel states such as black and white, as opposed to a
   grey-scale or colour image.)

   Setting this bit indicates additional support for Modified Read (MR)
   2-dimensional coding for bi-level images.