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[devel] png_set_background+png_expand_16 did not interwork correctly.

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This problem is present in 1.5.2; if png_set_background is called with
 need_expand false and the matching 16 bit color libpng erroneously just treats
 it as an 8-bit color because of where png_do_expand_16 is in the transform
 list.  This simple fix reduces the supplied colour to 8 bits, so it gets
 smashed, but this is better than the current behavior.
This commit is contained in:
John Bowler 2011-05-18 18:51:24 -05:00 committed by Glenn Randers-Pehrson
parent 8a7ec52c8b
commit db0ed3e62d
1 changed files with 23 additions and 4 deletions
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27
pngrtran.c
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@ -1106,10 +1106,6 @@ png_init_palette_transformations(png_structp png_ptr)
(png_ptr->transformations & PNG_EXPAND)) (png_ptr->transformations & PNG_EXPAND))
{ {
{ {
/* TODO: THIS MUST BE WRONG, because in png_init_read_transformations
* below the background red,green,blue values are used directly in the
* palette case (allowing an out-of-palette background color!)
*/
png_ptr->background.red = png_ptr->background.red =
png_ptr->palette[png_ptr->background.index].red; png_ptr->palette[png_ptr->background.index].red;
png_ptr->background.green = png_ptr->background.green =
@ -1429,6 +1425,29 @@ png_init_read_transformations(png_structp png_ptr)
else else
png_init_rgb_transformations(png_ptr); png_init_rgb_transformations(png_ptr);
#if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
defined(PNG_READ_EXPAND_16_SUPPORTED)
if ((png_ptr->transformations & PNG_EXPAND_16) &&
(png_ptr->transformations & PNG_COMPOSE) &&
!(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
png_ptr->bit_depth != 16)
{
/* TODO: fix this. Because the expand_16 operation is after the compose
* handling the background color must be 8, not 16, bits deep, but the
* application will supply a 16 bit value so reduce it here.
*
* 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.)
*/
# define CHOP(x) ((png_uint_16)((2*(png_uint_32)(x) + 257)/514))
png_ptr->background.red = CHOP(png_ptr->background.red);
png_ptr->background.green = CHOP(png_ptr->background.green);
png_ptr->background.blue = CHOP(png_ptr->background.blue);
png_ptr->background.gray = CHOP(png_ptr->background.gray);
# undef CHOP
}
#endif
/* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the /* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the
* background support (see the comments in scripts/pnglibconf.dfa), this * background support (see the comments in scripts/pnglibconf.dfa), this
* allows pre-multiplication of the alpha channel to be implemented as * allows pre-multiplication of the alpha channel to be implemented as