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[devel] Use the old scaling method for background if png_set_chop_16() was

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called.
This commit is contained in:
Glenn Randers-Pehrson 2011-06-14 06:30:12 -05:00
parent 550bab03fb
commit 7dffa41643
3 changed files with 17 additions and 0 deletions
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2
ANNOUNCE
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@ -198,6 +198,8 @@ Version 1.5.4beta02 [June 14, 2011]
Added png_set_chop_16() API, to match inaccurate results from previous
libpng versions.
Removed the ACCURATE and LEGACY options (they are no longer useable)
Use the old scaling method for background if png_set_chop_16() was
called.
Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
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2
CHANGES
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@ -3461,6 +3461,8 @@ Version 1.5.4beta02 [June 14, 2011]
Added png_set_chop_16() API, to match inaccurate results from previous
libpng versions.
Removed the ACCURATE and LEGACY options (they are no longer useable)
Use the old scaling method for background if png_set_chop_16() was
called.
Send comments/corrections/commendations to png-mng-implement at lists.sf.net
(subscription required; visit

13
pngrtran.c
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@ -1453,6 +1453,9 @@ png_init_read_transformations(png_structp png_ptr)
* The PNG_BACKGROUND_EXPAND code above does not expand to 16 bits at
* present, so that case is ok (until do_expand_16 is moved.)
*/
if (png_ptr->transformations & PNG_CHOP_16_TO_8)
{
# define CHOP(x) (x)=((png_uint_16)(((png_uint_32)(x)*255+32895) >> 16))
CHOP(png_ptr->background.red);
CHOP(png_ptr->background.green);
@ -1460,6 +1463,16 @@ png_init_read_transformations(png_structp png_ptr)
CHOP(png_ptr->background.gray);
# undef CHOP
}
else /* Use pre-libpng-1.5.4 inaccurate "ACCURATE" scaling */
{
# define CHOP(x) ((png_uint_16)((2*(png_uint_32)(x) + 257)/514))
CHOP(png_ptr->background.red);
CHOP(png_ptr->background.green);
CHOP(png_ptr->background.blue);
CHOP(png_ptr->background.gray);
# undef CHOP
}
}
#endif
/* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the