png_get_tRNS
Name
png_get_tRNS -- get transparency data for images
Synopsis
png_uint_32
png_get_tRNS
(png_structp
png_ptr, png_infop
info_ptr, png_bytep *
trans, int *
num_trans, png_color_16p *
trans_values);
Description
png_get_tRNS() shall obtain the transparency data for paletted images and
image types that don't need a full alpha channel from info_ptr.
For a paletted image, the function retrieves the transparency values
stored in the same order as the palette colors, starting from index 0.
For non-paletted images, the function retrieves the single color value
which is treated as fully transparent. If the transparency information is
valid, i.e. PNG_INFO_tRNS bit is set for info_ptr->valid:
*trans shall be set to the transparency values for a paletted image. Values for
the data shall be in range [0,255], ranging from fully transparent to fully
opaque, respectively.
*num_trans shall be set to the number of transparency values
*trans_values shall be set to the single color value specified for non-paletted
images.
Return Value
Returns PNG_INFO_tRNS on successful return, 0 otherwise.