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3e42c81193
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.
This directory (contrib/tools) contains tools used by the authors of libpng.
Code and data placed in this directory is not required to build libpng,
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that libpng supports.
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ORIGINAL AUTHORS
The following people have contributed to the code in this directory. None
of the people below claim any rights with regard to the contents of this
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John Bowler <jbowler@acm.org>