Use arbitrary greyscale image as dithering matrix. Operates the same way as the standard bayer matrix does for ordered dithering.
Allow the user to create their own artistic dither patterns.
Side benefit of also allowing use of other bayer matrix sizes (I like love the dither levels of 2x2 bayer but find the higher dither levels of larger bayer matrices to be rather ugly).
eg. standard 16x16 bayer matrix image: https://raw.githubusercontent.com/tromero/BayerMatrix/master/images/bayer16tile2.png