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[libpng17] Made 8-bit compose and rgb_to_grayscale accuracy improvements.

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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 commit is contained in:
John Bowler
2012-12-10 16:38:43 -06:00
committed by Glenn Randers-Pehrson
parent ac3b4d9b69
commit 3e42c81193
16 changed files with 2318 additions and 1341 deletions
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45
png.h
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@@ -1116,13 +1116,10 @@ PNG_EXPORT(22, void, png_read_info,
#ifdef PNG_TIME_RFC1123_SUPPORTED
/* Convert to a US string format: there is no localization support in this
* routine. The original implementation used a 29 character buffer in
* png_struct, this will be removed in future versions.
* png_struct, this has been removed.
*/
#if PNG_LIBPNG_VER < 10700
/* To do: remove this from libpng17 (and from libpng17/png.c and pngstruct.h) */
PNG_EXPORTA(23, png_const_charp, png_convert_to_rfc1123, (png_structrp png_ptr,
png_const_timep ptime),PNG_DEPRECATED);
#endif
PNG_REMOVED(23, png_const_charp, png_convert_to_rfc1123, (png_structrp png_ptr,
png_const_timep ptime),PNG_DEPRECATED)
PNG_EXPORT(241, int, png_convert_to_rfc1123_buffer, (char out[29],
png_const_timep ptime));
#endif
@@ -1619,22 +1616,8 @@ PNG_EXPORT(66, void, png_set_crc_action, (png_structrp png_ptr, int crit_action,
PNG_EXPORT(67, void, png_set_filter, (png_structrp png_ptr, int method,
int filters));
/* Flags for png_set_filter() to say which filters to use. The flags
* are chosen so that they don't conflict with real filter types
* below, in case they are supplied instead of the #defined constants.
* These values should NOT be changed.
*/
#define PNG_NO_FILTERS 0x00
#define PNG_FILTER_NONE 0x08
#define PNG_FILTER_SUB 0x10
#define PNG_FILTER_UP 0x20
#define PNG_FILTER_AVG 0x40
#define PNG_FILTER_PAETH 0x80
#define PNG_ALL_FILTERS (PNG_FILTER_NONE | PNG_FILTER_SUB | PNG_FILTER_UP | \
PNG_FILTER_AVG | PNG_FILTER_PAETH)
/* Filter values (not flags) - used in pngwrite.c, pngwutil.c for now.
* These defines should NOT be changed.
* These defines match the values in the PNG specification.
*/
#define PNG_FILTER_VALUE_NONE 0
#define PNG_FILTER_VALUE_SUB 1
@@ -1643,6 +1626,26 @@ PNG_EXPORT(67, void, png_set_filter, (png_structrp png_ptr, int method,
#define PNG_FILTER_VALUE_PAETH 4
#define PNG_FILTER_VALUE_LAST 5
/* The above values are valid arguments to png_set_filter() if only a single
* filter is to be used. If multiple filters are to be allowed (the default is
* to allow any of them) then a combination of the following masks must be used
* and the low three bits of the argument to png_set_filter must be 0.
*
* The resultant argument fits in a single byte.
*/
#define PNG_FILTER_NONE (0x08 << PNG_FILTER_VALUE_NONE)
#define PNG_FILTER_SUB (0x08 << PNG_FILTER_VALUE_SUB)
#define PNG_FILTER_UP (0x08 << PNG_FILTER_VALUE_UP)
#define PNG_FILTER_AVG (0x08 << PNG_FILTER_VALUE_AVG)
#define PNG_FILTER_PAETH (0x08 << PNG_FILTER_VALUE_PAETH)
/* Then two convenience values. PNG_NO_FILTERS is the same as
* PNG_FILTER_VALUE_NONE, but this is harmless because they mean the same thing.
*/
#define PNG_NO_FILTERS 0x00
#define PNG_ALL_FILTERS (PNG_FILTER_NONE | PNG_FILTER_SUB | PNG_FILTER_UP | \
PNG_FILTER_AVG | PNG_FILTER_PAETH)
#ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED /* EXPERIMENTAL */
/* The "heuristic_method" is given by one of the PNG_FILTER_HEURISTIC_
* defines, either the default (minimum-sum-of-absolute-differences), or