MNG-0.95c, Draft 66, 19990615

Global bKGD and sBIT

This proposal is with respect to MNG 0.95a (Draft 64).

MNG-0.95c Draft 66 19990615 is created by making the following changes
to MNG-0.95a Draft 64 19990527:

Section 4.2.5, BASI, is modified to add the words shown in
square brackets:

   Top-level gAMA, sRGB, cHRM, iCCP, [bKGD, sBIT,] and sPLT chunks
   are inherited by a BASI datastream in the same manner as by a PNG
   datastream.

Section 4.4.1. SAVE Save information, is modified to add the words
shown in square brackets:

         Known chunks in this category include DEFI, FRAM, BACK, PLTE,
         cHRM, tRNS, fPRI, gAMA, iCCP, pHYs, [bKGD, sBIT,] and sRGB.

Section 4.5.5, Ancillary PNG chunks, is modified to add the
words shown in square brackets:

   The following PNG chunks are also defined at the MNG top level.
   They provide default values to be used in case they are not
   provided in subsequent PNG [or JNG] datastreams.  Any of these chunks
   can be nullified by the appearance of a subsequent empty chunk
   with the same chunk name.  Such empty chunks are not legal PNG
   or JNG chunks and must only appear in the MNG top level.

       * cHRM, gAMA, iCCP, sRGB[, bKGD, sBIT]

   [In the MNG top level, all of these chunks are written as though
   for 16-bit RGBA PNG datastreams.  Decoders are responsible for
   reformatting the chunk data to suit the actual bit depth and color
   type of the datastream that inherits them.]

   A MNG editor that writes PNG or JNG datastreams is expected to
   include the top-level cHRM, gAMA, iCCP, and sRGB chunks in the
   generated PNG or JNG datastreams, if the embedded image does
   not contain its own chunks that define the color space.  When
   it writes the sRGB chunk, it should write the gAMA chunk (and
   perhaps the cHRM chunk), in accordance with the PNG
   specification, even though no gAMA or cHRM chunk is present in
   the MNG datastream.  [It is also expected to write the reformatted
   top-level bKGD chunk in the generated PNG or JNG datastreams, and
   the reformatted sBIT chunk only in generated PNG datastreams, when
   the datastream does not have its own bKGD or sBIT chunks.]


Add paragraph 6.1.16

  [Other ancillary PNG chunks]

  [Any other ancillary PNG chunks that the decoder recognizes when processing
  a PNG datastream should also be recognized and handled when processing
  a delta-PNG datastream.  Any chunks that it does not recognize should
  be processed as instructed by the ORDR, DROP, and DBYK chunks.  MNG
  viewers are free to ignore any ancillary chunks, while MNG editors must
  handle them in accordance with the copying rules.]