Only a single program was used to safely compress all textures in MTG.
* `optipng -o7 -zm1-9 -nc -strip all -clobber %%f`
The key command used is -nc, which stops color mode changes. I.e. any RGBA textures will remain RGBA textures, with none being changes to 8-bit indexed mode.
utils/optimize_textures.sh performs this compression automatically, assuming optipng is installed.
This fixes all cases where the color profile was broken, and
libpng warns about. It also makes almost all textures indexed
instead of RGB where possible (textures that don't have
semi-transparent pixels).
