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.
Some GPUs cause visual bugs when mip-mapping is used with indexed textures
that use alpha. Because leaves are sometimes rendered opaque it is even
more important to keep these as RGBA to preserve the correct background
colour.
