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[libpng15] Multiple transform bug fixes plus a work-round for double gamma

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correction.
This commit is contained in:
John Bowler
2011-11-16 14:26:34 -06:00
committed by Glenn Randers-Pehrson
parent 36f5884359
commit 18c5cfafeb
5 changed files with 477 additions and 45 deletions
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50
pngrtran.c
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@@ -1465,6 +1465,28 @@ png_init_read_transformations(png_structp png_ptr)
}
#endif /* PNG_READ_BACKGROUND_SUPPORTED && PNG_READ_EXPAND_16_SUPPORTED */
#if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
(defined(PNG_READ_SCALE_16_TO_8_SUPPORTED) || \
defined(PNG_READ_STRIP_16_TO_8_SUPPORTED))
if ((png_ptr->transformations & (PNG_16_TO_8|PNG_SCALE_16_TO_8)) &&
(png_ptr->transformations & PNG_COMPOSE) &&
!(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
png_ptr->bit_depth == 16)
{
/* On the other hand, if a 16-bit file is to be reduced to 8-bits per
* component this will also happen after PNG_COMPOSE and so the background
* color must be pre-expanded here.
*
* TODO: fix this too.
*/
png_ptr->background.red = (png_uint_16)(png_ptr->background.red * 257);
png_ptr->background.green =
(png_uint_16)(png_ptr->background.green * 257);
png_ptr->background.blue = (png_uint_16)(png_ptr->background.blue * 257);
png_ptr->background.gray = (png_uint_16)(png_ptr->background.gray * 257);
}
#endif
/* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the
* background support (see the comments in scripts/pnglibconf.dfa), this
* allows pre-multiplication of the alpha channel to be implemented as
@@ -1512,6 +1534,16 @@ png_init_read_transformations(png_structp png_ptr)
#ifdef PNG_READ_BACKGROUND_SUPPORTED
if (png_ptr->transformations & PNG_COMPOSE)
{
/* Issue a warning about this combination: because RGB_TO_GRAY is
* optimized to do the gamma transform if present yet do_background has
* to do the same thing if both options are set a
* double-gamma-correction happens. This is true in all versions of
* libpng to date.
*/
if (png_ptr->transformations & PNG_RGB_TO_GRAY)
png_warning(png_ptr,
"libpng does not support gamma+background+rgb_to_gray");
if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
{
/* We don't get to here unless there is a tRNS chunk with non-opaque
@@ -1726,7 +1758,13 @@ png_init_read_transformations(png_structp png_ptr)
else
/* Transformation does not include PNG_BACKGROUND */
#endif /* PNG_READ_BACKGROUND_SUPPORTED */
if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE
#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
/* RGB_TO_GRAY needs to have non-gamma-corrected values! */
&& ((png_ptr->transformations & PNG_EXPAND) == 0 ||
(png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
#endif
)
{
png_colorp palette = png_ptr->palette;
int num_palette = png_ptr->num_palette;
@@ -2165,12 +2203,22 @@ png_do_read_transformations(png_structp png_ptr, png_row_infop row_info)
#ifdef PNG_READ_GAMMA_SUPPORTED
if ((png_ptr->transformations & PNG_GAMMA) &&
#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
/* Because RGB_TO_GRAY does the gamma transform. */
!(png_ptr->transformations & PNG_RGB_TO_GRAY) &&
#endif
#if (defined PNG_READ_BACKGROUND_SUPPORTED) ||\
(defined PNG_READ_ALPHA_MODE_SUPPORTED)
/* Because PNG_COMPOSE does the gamma transform if there is something to
* do (if there is an alpha channel or transparency.)
*/
!((png_ptr->transformations & PNG_COMPOSE) &&
((png_ptr->num_trans != 0) ||
(png_ptr->color_type & PNG_COLOR_MASK_ALPHA))) &&
#endif
/* Because png_init_read_transformations transforms the palette, unless
* RGB_TO_GRAY will do the transform.
*/
(png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
png_do_gamma(row_info, png_ptr->row_buf + 1, png_ptr);
#endif