Ordered Dithering with Arbitrary or Irregular Colour Palettes

This is very obvious during animation, where pixels will appear to jitter between frames. It also makes files harder to compress.

my strat is

1. ordered dither frames 1 and 2
2. diff the ordered dithering versions
3. make an error-diffusion version of 1 and 2
4. for frame 2 only replace the pixels that changed in the ordered dithering diff