== 16 color ==
Sometimes framebuffers offer no more than 4 bits per pixel, for these cases we
have a special 16 color version of images. Those images should not contain
alpha channels and use solid color throughout (no gradients etc.).

In the script itself we use a solid color background, the images should use
matching colors when needing to avoid alpha.

Usually the workflow is to take the regular version and replace the alpha,
then possibly also overly colorful elements, save it and convert to 16 colors.
Most of the time you can use drop shadows, but all in all no more than 16
colors can be used, so you will have to make sure the clipped version's drop
is still appearing as expected.

To convert to <= 16 color version use (< when fewer colors found)
  foo=foo; pngtopnm $foo | pnmquant 16 | pnmtopng > 16.png; mv 16.png $foo; rm foo

You may want to check that the output makes sense.
