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.
'jungleleaves simple' had completely different leaf colours to
'jungleleaves', now matched.
'leaves simple' had dark green instead of black colour for transparent
pixels (the 'leaves' texture uses black), normally these pixels would
not be rendered as opaque colours but bush nodes now use this texture
and will be rendering it as opaque. The dark green pixels resulted in
a texture lacking in contrast.
