Changing the color type might help as well:
pngcrush -c 2
removes the alpha channel (for colour images that don't need transparency) and:
pngcrush -c 0
removes the colour channel as well (for grayscale images).
Changing the color type might help as well:
pngcrush -c 2
removes the alpha channel (for colour images that don't need transparency) and:
pngcrush -c 0
removes the colour channel as well (for grayscale images).