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[devel] Make the 16-to-8 scaling accurate. Dividing by 256 with no rounding is

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wrong (high by one) 25% of the time. Dividing by 257 with rounding is
    wrong in 128 out of 65536 cases. Getting the right answer all the time
    without division is easy.
This commit is contained in:
John Bowler
2011-06-10 23:24:58 -05:00
committed by Glenn Randers-Pehrson
parent cc2770850a
commit b2bee3374c
12 changed files with 81 additions and 55 deletions
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libpng.3
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@@ -5047,6 +5047,12 @@ In libpng-1.5.3 we reinitialized the zlib stream for each type of data.
We added five png_set_text_*() functions for setting the parameters to
use with textual data.
Prior to libpng-1.5.3, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
option was off by default, and slightly inaccurate scaling occurred.
This option can no longer be turned off, and 16-to-8 scaling is always
accurate. This change will result in some different results while
reading 16-bit images, with some of the pixels no longer being off-by-one.
B. Changes to the build and configuration of libpng
Details of internal changes to the library code can be found in the CHANGES