Sebastian Lackner sebastian@fds-team.de wrote:
On 27.01.2017 22:28, Vincent Povirk wrote:
else{png_palette[i].red = 0;png_palette[i].green = 0;png_palette[i].blue = 0;}Why is it necessary to pad the palette in this way? Couldn't you just pass the appropriate number of colors?
Clamping to 1 << This->format->bit_depth is necessary (see the comment about newer libpng versions), but padding the palette probably isn't, at least I'm not aware of any test for it.
It still would be a good idea to test this, a standalone application should be fine. Although I'd guess this basically depends on libpng (old vs. new) behaviour, as far as I can see from my own tests WIC in Windows doesn't impose limitations to a PNG palette size.
It should be fine to replace
colors = 1 << This->format->bit_depth;
with
colors = min(This->colors, 1 << This->format->bit_depth);
and to remove the else branch.
That should work, if newer libpng versions accept such palette sizes.