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[devel] Documented png_set_alpha_mode(), other changes in libpng.3 and

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libpng-manual.txt.
  The cHRM chunk now sets the defaults for png_set_rgb_to_gray() (when negative
    parameters are supplied by the caller), while in the absence of cHRM
    sRGB/Rec 709 values are still used.
  The bKGD chunk no longer overwrites the background value set by
    png_set_background(), allowing the latter to be used before the file
    header is read. It never performed any useful function to override
    the default anyway.

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This commit is contained in:
John Bowler
2011-05-12 21:48:29 -05:00
committed by Glenn Randers-Pehrson
parent ed4d32baa4
commit cb0b29631f
7 changed files with 718 additions and 269 deletions
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65
pngrutil.c
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@@ -1020,6 +1020,33 @@ png_handle_cHRM(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
}
#endif /* PNG_READ_sRGB_SUPPORTED */
#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
/* Store the _white values as default coefficients for the rgb to gray
* operation if it is supported.
*/
if ((png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
{
/* png_set_background has not been called, the coefficients must be in
* range for the following to work without overflow.
*/
if (y_red <= (1<<17) && y_green <= (1<<17) && y_blue <= (1<<17))
{
/* The y values are chromaticities: Y/X+Y+Z, the weights for the gray
* transformation are simply the normalized Y values for red, green and
* blue scaled by 32768.
*/
png_uint_32 w = y_red + y_green + y_blue;
png_ptr->rgb_to_gray_red_coeff = (png_uint_16)(((png_uint_32)y_red *
32768)/w);
png_ptr->rgb_to_gray_green_coeff = (png_uint_16)(((png_uint_32)y_green
* 32768)/w);
png_ptr->rgb_to_gray_blue_coeff = (png_uint_16)(((png_uint_32)y_blue *
32768)/w);
}
}
#endif
png_set_cHRM_fixed(png_ptr, info_ptr, x_white, y_white, x_red, y_red,
x_green, y_green, x_blue, y_blue);
}
@@ -1544,6 +1571,7 @@ png_handle_bKGD(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
png_size_t truelen;
png_byte buf[6];
png_color_16 background;
png_debug(1, "in png_handle_bKGD");
@@ -1600,7 +1628,7 @@ png_handle_bKGD(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
*/
if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
{
png_ptr->background.index = buf[0];
background.index = buf[0];
if (info_ptr && info_ptr->num_palette)
{
@@ -1610,33 +1638,36 @@ png_handle_bKGD(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
return;
}
png_ptr->background.red =
(png_uint_16)png_ptr->palette[buf[0]].red;
png_ptr->background.green =
(png_uint_16)png_ptr->palette[buf[0]].green;
png_ptr->background.blue =
(png_uint_16)png_ptr->palette[buf[0]].blue;
background.red = (png_uint_16)png_ptr->palette[buf[0]].red;
background.green = (png_uint_16)png_ptr->palette[buf[0]].green;
background.blue = (png_uint_16)png_ptr->palette[buf[0]].blue;
}
else
background.red = background.green = background.blue = 0;
background.gray = 0;
}
else if (!(png_ptr->color_type & PNG_COLOR_MASK_COLOR)) /* GRAY */
{
png_ptr->background.red =
png_ptr->background.green =
png_ptr->background.blue =
png_ptr->background.gray = png_get_uint_16(buf);
background.index = 0;
background.red =
background.green =
background.blue =
background.gray = png_get_uint_16(buf);
}
else
{
png_ptr->background.red = png_get_uint_16(buf);
png_ptr->background.green = png_get_uint_16(buf + 2);
png_ptr->background.blue = png_get_uint_16(buf + 4);
background.index = 0;
background.red = png_get_uint_16(buf);
background.green = png_get_uint_16(buf + 2);
background.blue = png_get_uint_16(buf + 4);
background.gray = 0;
}
png_set_bKGD(png_ptr, info_ptr, &(png_ptr->background));
png_set_bKGD(png_ptr, info_ptr, &background);
}
#endif