'posterize applies a type of color reduction on images, ignoring the less significative bits of each color channel, the result having flat colors zones instead of gradual transitions.
result: posterize value (image!) depth (integer!)
where 'depth is between 1 and 7, with 1 keeping only 8 colors, and 7 with the less noticeable effect. The result is darker so a brightness correction would be appropriate: for the strongest setting, with depth = 1 (8 colors), half the brightness is lost, so applying a VID 'effect like “multiply 255” would do the trick.
Other 'depth values:
- depth = 0 or less gives a black result (0 bit/color channel),
- depth = 8 does nothing (8 bits/color channel as the original),
- depth > 8 gives a false color effect (but darker so one should compensate with 'multiply or similar).