Libpng 1.7.0alpha01 - December 10, 2012

This is not intended to be a public release.  It will be replaced
within a few weeks by a public version or by another test version.

Files available for download:

Source files with LF line endings (for Unix/Linux) and with a
"configure" script

   1.7.0alpha01.tar.xz (LZMA-compressed, recommended)
   1.7.0alpha01.tar.gz
   1.7.0alpha01.tar.bz2

Source files with CRLF line endings (for Windows), without the
"configure" script

   lp170a01.7z  (LZMA-compressed, recommended)
   lp170a01.zip

Other information:

   1.7.0alpha01-README.txt
   1.7.0alpha01-LICENSE.txt

Changes since the last public release (1.6.0):

Version 1.7.0alpha01 [December 10, 2012]
  Started 1.7.0 branch from libpng-1.6.0beta33.
  Made 8-bit compose and rgb_to_grayscale accuracy improvements.  These
    changes cause 16-bit arithmetic to be used for 8-bit data in the gamma
    corrected compose and grayscale operations.  The arithmetic errors have
    three sources all of which are fixed in this commit:
    1) 8-bit linear calculations produce massive errors for lower intensity
       values.
    2) The old 16-bit "16 to 8" gamma table code erroneously wrote the lowest
       output value into a table entry which corresponded to multiple output
       values (so where the value written should have been the closest to the
       transformed input value.)
    3) In a number of cases the code to access the 16-bit table did not round;
       it did a simple shift, which was wrong and made the side effects of (2)
       even worse.
  The new gamma code does not have the 16-to-8 problem at the cost of slighly
    more calculations and the algorithm used to minimize the number of
    calculations has been extended to all the 16-bit tables; it has advantages
    for any significant gamma correction.

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Glenn R-P