rfc2880.txt

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McIntyre & Klyne             Informational                     [Page 13]

RFC 2880           Internet Fax T.30 Feature Mapping         August 2000


4.1.2 Multi-level coding

   Note: When 37, 69, 73, 79 and 95 are set to "1", the feature
   represented by "0" is also available.  Example: If plane interleave
   is available then stripe interleave is also available.

<------- T.30 bits --------->
15|16|31|36|37|68|69|73|78|79||Description
--+--+--+--+--+--+--+--+--+--++---------------------------------------
 x|  |  |*0| x| 0| x| x|  |  ||No grey or colour (no T.43 or JPEG)
*1|  |  | 0| x| 1| 0| x|  |  ||JPEG, grey scale only
*1|  |  | 0| x| 1| 1| 0|  |  ||JPEG, full colour, subsampling
*1|  |  | 0| x| 1| 1| 1|  |  ||JPEG, full colour, no subsampling
*1|  |  | 1| 0|*1| 0| x|  |  ||T.43, JPEG, grey only, stripe i/l
*1|  |  | 1| 1|*1| 0| x|  |  ||T.43, JPEG, grey only, plane i/l
*1|  |  | 1| 0|*1| 1| 0|  |  ||T.43, JPEG, colour, stripe i/l, s/s
*1|  |  | 1| 0|*1| 1| 1|  |  ||T.43, JPEG, colour, stripe i/l, no s/s
*1|  |  | 1| 1|*1| 1| 0|  |  ||T.43, JPEG, colour, plane i/l, s/s
*1|  |  | 1| 1|*1| 1| 1|  |  ||T.43, JPEG, colour, plane i/l, no s/s
  |  |  |  |  |  |  |  |  |  ||'s/s'    is 4:1:1 L*:a*:b* subsampling
  |  |  |  |  |  |  |  |  |  ||'No s/s' is 1:1:1 L*:a*:b* subsampling
  |  |  |  |  |  |  |  |  |  ||'stripe i/l' is stripe interleave
  |  |  |  |  |  |  |  |  |  ||'plane i/l'  is full-plane interleave
--+--+--+--+--+--+--+--+--+--++---------------------------------------

4.1.3 MRC format

   Multi-level coders, as indicated above, are used for foreground and
   background images within an MRC-format document.  Bi-level codes
   are used for the mask layer.

<---- T.30 bits ------>
15|92|93|94|95|  |  |  ||Description
--+--+--+--+--+--+--+--++---------------------------------------
 x| 0| 0| 0| x|  |  |  ||MRC not accepted
*1| #| #| #| 0|  |  |  ||MRC level, max strip 256 lines
*1| #| #| #| 1|  |  |  ||MRC level, max strip full page
  |  |  |  |  |  |  |  ||### is MRC performance level (1-7, per T.44)
--+--+--+--+--+--+--+--++---------------------------------------












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RFC 2880           Internet Fax T.30 Feature Mapping         August 2000


4.2 Resolution and units

   Support for bi-level coding at least one of 200*100dpi or 8*3.85dpmm
   is required in all cases for Group 3 fax conformance.  For multi-
   level coders (colour/grey) and MRC mask layers the base resolution is
   200*200dpi (i.e. bit 15 must be set).

   When multi-level coders (JPEG or T.43) or MRC are used, only inch-
   based square resolutions are available.  However, the base non-square
   resolution (i.e. 200x100dpi or 8x3.85dpmm) must still be available as
   a capability for use with the mandatory bi-level coder (MH).  Hence,
   any references to metric and non-square resolutions in the table
   below apply only to bi-level coders.

   When describing MRC capabilities, the complete set of usable
   resolutions is listed.  However, there are some restrictions on their
   use:  (a) 100dpi resolution can be used only with multi-level images,
   and (b) any multi-level image resolution is required to be an
   integral sub-multiple of the applicable mask resolution.

   In the following table:
      dpi  = dots per inch
      dpmm = dots per millimetre

   Preferred resolutions are indicated here, even though inch- or mm-
   based units must be accepted, according to the T.30 protocol [6].

























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RFC 2880           Internet Fax T.30 Feature Mapping         August 2000


<------- T.30 bits ------>
15|41|42|43|44|45|68|97|98||Description
--+--+--+--+--+--+--+--+--++-----------------------------------------
 0|  |  | 0| x| x|  |  |  ||Resolution = base only
  |  |  |  |  |  |  |  |  ||
 1|  |  | 0| 0| 0|  |  |  ||Invalid
 1|  |  | 0| 0| 1|  |  |  ||Resolution = 8*3.85dpmm or 8*7.7dpmm
 1|  |  | 0| 1| 0|  |  |  ||Resolution = 200*100dpi or 200*200dpi
 1|  |  | 0| 1| 1|  |  |  ||Resolution = 8*3.85dpmm or 8*7.7dpmm
  |  |  |  |  |  |  |  |  ||        or   200*100dpi or 200*200dpi
  |  |  |  |  |  |  |  |  ||
 0|  |  | 1| 0| 0|  |  |  ||Invalid
 0|  |  | 1| 0| 1|  |  |  ||Resolution = 8*3.85dpmm or 16*15.4dpmm
 0|  |  | 1| 1| 0|  |  |  ||Resolution = 200*100dpi or 400*400dpi
 0|  |  | 1| 1| 1|  |  |  ||Resolution = 8*3.85dpmm or 16*15.4dpmm
  |  |  |  |  |  |  |  |  ||        or   200*100dpi or 400*400dpi
  |  |  |  |  |  |  |  |  ||
 1|  |  | 1| 0| 0|  |  |  ||Invalid
 1|  |  | 1| 0| 1|  |  |  ||Resolution = 8*3.85dpmm or 8*7.7dpmm
  |  |  |  |  |  |  |  |  ||        or   16*15.4dpmm
 1|  |  | 1| 1| 0|  |  |  ||Resolution = 200*100dpi or 200*200dpi
  |  |  |  |  |  |  |  |  ||        or   400*400dpi
 1|  |  | 1| 1| 1|  |  |  ||Resolution = 8*7.7dpmm  or 8*7.7dpmm
  |  |  |  |  |  |  |  |  ||        or   16*15.4dpmm
  |  |  |  |  |  |  |  |  ||        or   200*100dpi or 200*200dpi
  |  |  |  |  |  |  |  |  ||        or   400*400dpi
--+--+--+--+--+--+--+--+--++-----------------------------------------
  | 0|  |  |  |  |  |  |  ||Resolutions as above
  | 1|  |  |  |  |  |  |  ||Also supports 8*15.4dpmm (bi-level only)
  |  |  |  |  |  |  |  |  ||Independent of bits 44,45
--+--+--+--+--+--+--+--+--++-----------------------------------------
  |  | 0|  |  |  |  |  |  ||Resolutions as above
  |  | 1|  |  |  |  |  |  ||Also supports 300*300dpi
  |  |  |  |  |  |  |  |  ||Independent of bits 44,45
--+--+--+--+--+--+--+--+--++-----------------------------------------
  |  |  |  |  |  | x| 0|  ||Resolutions as above
  |  |  |  |  |  |*1| 1|  ||Also 300*300dpi or 400*400dpi (see below)
  |  |  |  |  |  |  |  |  ||(Applies colour, grey-scale or MRC mask)
  |  |  |  |  |  |  |  |  ||(Valid only when bit 42 or 43 is set.)
  |  |  |  |  |  |  |  |  ||(42 => 300dpi, 43=>400dpi)
--+--+--+--+--+--+--+--+--++-----------------------------------------
  |  |  |  |  |  | x|  | 0||Resolutions as above
  |  |  |  |  |  |*1|  | 1||Also 100*100dpi
  |  |  |  |  |  |  |  |  ||(Applies colour or grey-scale only)
  |  |  |  |  |  |  |  |  ||(Independent of bits 44,45)
--+--+--+--+--+--+--+--+--++-----------------------------------------





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RFC 2880           Internet Fax T.30 Feature Mapping         August 2000


4.3 Colour capabilities

   Bit 68 (JPEG) is required for any colour/grey scale mode, and bit 36
   indicates additional T.43 capability.

<------- T.30 bits --->
36|68|69|71|74|75|  |  ||Description
--+--+--+--+--+--+--+--++-----------------------------------------
 0| 0| x|  |  |  |  |  ||No grey scale or colour
 x| 1| 0|  |  |  |  |  ||Grey scale only
 0| 1| 1|  |  |  |  |  ||Full colour capability (CIE L*a*b*)
 1|*1| 1|  |  |  |  |  ||Full and limited colour capability:
  |  |  |  |  |  |  |  || (CIE L*a*b*, palette, RGB 1 bit/colour
  |  |  |  |  |  |  |  ||  and CMY(K)1 bit/colour)
--+--+--+--+--+--+--+--++-----------------------------------------
  | 0|  | x|  |  |  |  ||
  | 1|  | 0|  |  |  |  ||8 bits/pixel and up to 4096 palette entries
  | 1|  | 1|  |  |  |  ||8 or 12 bits/pixel, 65536 palette entries
--+--+--+--+--+--+--+--++-----------------------------------------
  | 0|  |  | x|  |  |  ||
  | 1|  |  | 0|  |  |  ||CIE standard illuminant D50 (per T.42)
  | 1|  |  | 1|  |  |  ||Custom illuminants (definition provided)
--+--+--+--+--+--+--+--++-----------------------------------------
  | 0|  |  |  | x|  |  ||
  | 1|  |  |  | 0|  |  ||Default gamut (per T.42)
  | 1|  |  |  | 1|  |  ||Custom gamuts (definition provided)
--+--+--+--+--+--+--+--++-----------------------------------------
























McIntyre & Klyne             Informational                     [Page 17]

RFC 2880           Internet Fax T.30 Feature Mapping         August 2000


4.4 Document size

   A4 width (215mm) is required as a minimum for Group 3 fax
   conformance.  A Group 3 fax machine must always be able to receive
   an A4 image.


<---- T.30 bits ------>
17|18|19|20|76|77|  |  ||Description
--+--+--+--+--+--+--+--++-----------------------------------------
 0| 0|  |  |  |  |  |  ||Width = 215mm
 1| 0|  |  |  |  |  |  ||Width = 215mm or 255mm
 0| 1|  |  |  |  |  |  ||Width = 215mm, 255mm or 303mm
 1| 1|  |  |  |  |  |  ||Invalid - interpret as (17=0,18=1)
  |  |  |  |  |  |  |  ||(measurements described as scan line length)
  |  |  |  |  |  |  |  ||(corresp. inch measurements: T.4 sect 2.2)
--+--+--+--+--+--+--+--++-----------------------------------------
  |  | 0| 0|  |  |  |  ||Length = 297mm (A4)
  |  | 1| 0|  |  |  |  ||Length = 297mm (A4) or 364mm (B4)
  |  | 0| 1|  |  |  |  ||Length = unlimited
  |  | 1| 1|  |  |  |  ||Invalid
--+--+--+--+--+--+--+--++-----------------------------------------
  |  |  |  | 0| 0|  |  ||Papersize = A4
  |  |  |  | 1| 0|  |  ||Papersize = A4 or NA-Letter
  |  |  |  | 0| 1|  |  ||Papersize = A4 or NA-Legal
  |  |  |  | 1| 1|  |  ||Papersize = A4 or NA-Letter or NA-Legal
  |  |  |  |  |  |  |  ||(These in addition to paper sizes implied
  |  |  |  |  |  |  |  || by bits 17-20 above)
--+--+--+--+--+--+--+--++-----------------------------------------

5. Mapping T.30 capabilities to fax feature schema

   This section follows the structure of the previous section, except
   that the decision tables are restated with feature set expression
   mappings in the action stub.  The feature set expressions use media
   feature tags presented in "Content feature schema for Internet fax"
   [4].

   To construct a feature set expression corresponding to a collection
   of DIS frame bits:

   o  Compare the DIS bits with each decision table in the following
      sections (5.1 to 5.4).  Some decision tables consist of a number
      of sub-tables separated by horizontal lines.

   o  The DIS bits will match exactly one row from each table or sub-
      table:  collect the corresponding feature set expression from the
      action stub (the right hand column of the table).



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RFC 2880           Internet Fax T.30 Feature Mapping         August 2000


   o  In the case of the table in section 5.2, which consists of
      several sub-tables, combine the feature set expressions from each
      sub-table with a logical-OR:  (| s1 s2 ... sn ), where 's1', 's2'
      etc. are the feature set expressions selected from each sub-
      table.  In this way, a single feature set expression is obtained
      for the table.

   o  In the case of the tables in sections 5.3 and 5.4, combine the
      sub-table expressions with a logical-AND:  (& s1 s2 ... sn ).

   o  Combine the feature set expressions for each table as follows:

        (& (| T511 T512 ) T513 T52 T53 T54 )

      where:

      - T511 is the feature set expression obtained from the table in
        section 5.1.1

      - T512 is obtained from the table in section 5.1.2

      - T513 is obtained from the table in section 5.1.3

      - T52 is obtained from the table in section 5.2

      - T53 is obtained from the table in section 5.3

      - T54 is obtained from the table in section 5.4

   The resulting expression is the feature set expression corresponding
   to the DIS bits given.  Remember that there may be other capabilities
   not expressed by the DIS bits that should be incorporated into the
   final feature expression (e.g. TIFF image file structure).

   To do the reverse transformation, match the feature set to each row
   of each decision table using the matching algorithm in RFC 2533 [2],
   and OR together the DIS bit masks for each row whose feature set
   expression is completely contained by (i.e. is a subset of) that
   given (where the bit value in a table is 'x', use '0').

   A feature set A is completely contained by B if the feature set match
   of A and B (obtained by applying the feature set matching algorithm
   in [2]) is equal to A.








McIntyre & Klyne             Informational                     [Page 19]

RFC 2880           Internet Fax T.30 Feature Mapping         August 2000


5.1 Image coding