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[libpng16] Avoid the double gamma correction warning in the simplified API.

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This allows the --strict option to pass in the pngstest checks
This commit is contained in:
John Bowler
2012-03-18 22:46:28 -05:00
committed by Glenn Randers-Pehrson
parent 2bc76ffaf1
commit eda53e5770
5 changed files with 70 additions and 11 deletions
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64
pngread.c
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@@ -1838,6 +1838,17 @@ png_create_colormap_entry(png_image_read_control *display,
}
}
static int
make_gray_file_colormap(png_image_read_control *display)
{
unsigned int i;
for (i=0; i<256; ++i)
png_create_colormap_entry(display, i, i, i, i, 255, E_FILE);
return i;
}
static int
make_gray_colormap(png_image_read_control *display)
{
@@ -2368,7 +2379,23 @@ png_image_read_colormap(png_voidp argument)
if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
png_error(png_ptr, "rgb[gray] color-map: too few entries");
cmap_entries = make_gray_colormap(display);
/* Ideally this code would use libpng to do the gamma correction,
* but if an input alpha channel is to be removed we will hit the
* libpng bug in gamma+compose+rgb-to-gray (the double gamma
* correction bug). Fix this by dropping the gamma correction in
* this case and doing it in the palette; this will result in
* duplicate palette entries, but that's better than the
* alternative of double gamma correction.
*/
if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
png_ptr->num_trans > 0) && png_gamma_not_sRGB(png_ptr->gamma))
{
cmap_entries = make_gray_file_colormap(display);
data_encoding = E_FILE;
}
else
cmap_entries = make_gray_colormap(display);
/* But if the input has alpha or transparency it must be removed
*/
@@ -2383,18 +2410,38 @@ png_image_read_colormap(png_voidp argument)
* it. Achieve this simply by ensuring that the entry
* selected for the background really is the background color.
*/
if (output_encoding == E_LINEAR)
if (data_encoding == E_FILE) /* from the fixup above */
{
/* The app supplied a gray which is in output_encoding, we
* need to convert it to a value of the input (E_FILE)
* encoding then set this palette entry to the required
* output encoding.
*/
if (output_encoding == E_sRGB)
gray = png_sRGB_table[gray]; /* now E_LINEAR */
gray = PNG_DIV257(png_gamma_16bit_correct(gray,
png_ptr->gamma)); /* now E_FILE */
/* And make sure the corresponding palette entry contains
* exactly the required sRGB value.
*/
png_create_colormap_entry(display, gray, back_g, back_g,
back_g, 0/*unused*/, output_encoding);
}
else if (output_encoding == E_LINEAR)
{
gray = PNG_sRGB_FROM_LINEAR(gray * 255);
/* And make sure the corresponding palette entry matches.
*/
png_create_colormap_entry(display, gray, back_g, back_g,
back_g, 65535, E_LINEAR);
back_g, 0/*unused*/, E_LINEAR);
}
/* The background passed to libpng, however, must be the sRGB
* value.
/* The background passed to libpng, however, must be the
* output (normally sRGB) value.
*/
c.index = 0; /*unused*/
c.gray = c.red = c.green = c.blue = (png_uint_16)gray;
@@ -2657,13 +2704,12 @@ png_image_read_colormap(png_voidp argument)
png_error(png_ptr, "bad data option (internal error)");
break;
case E_FILE:
/* Make no changes */
break;
case E_sRGB:
/* Change to 8-bit sRGB */
png_set_alpha_mode_fixed(png_ptr, PNG_ALPHA_PNG, PNG_GAMMA_sRGB);
/* FALL THROUGH */
case E_FILE:
if (png_ptr->bit_depth > 8)
png_set_scale_16(png_ptr);
break;