File: png-sTER-proposal-20070329

It is proposed to revise the sTER chunk specification to add a
recommendation about background treatment.

It is proposed to revise
Extensions to the PNG 1.2 Specification, Version 1.3.0, as follows:

A. Change document version to 1.3.1.

C. Divide paragraph 3.6 into three subparagraphs

3.6.1 sTER chunk specification

      [existing text in paragraph 3.6, except the final 2 paragraphs]

3.6.2 sTER chunk recommendations for encoders

      [final two paragraphs of existing paragraph 3.6]

3.6.3 sTER chunk recommendations for decoders

When the image is transparent or is presented in a manner that
does not cover the entire PNG area, the decoder should take care to
present a coherent background.  One way to achieve this is to
simply take the background behind the spot where the stereo image is
expected to be placed.  In the special cases when left and 
right images need to be displayed side by side or top over bottom, use for 
both images the background behind leftmost or topmost image.
Another solution is to use a simple solid color behind both images.



D. Add to the Appendix: Revision History

       * 30 April 2007 (version 1.3.1):

             * Added sTER chunk recommendations for decoders.