I really like the trick of caching previously-seen pixels by value rather than position. Very nifty! I was thinking this would combine well with progressive re

I really like the trick of caching previously-seen pixels by value rather than position. Very nifty! I was thinking this would combine well with progressive rendering (i.e. store pixels in mipmap-style order) so the cache is warmed up with spread of pixels across the image rather than just scanline order. That doesn’t make it parallelizable in the way tiling does, though, hmm. Another tweak that would probably help is having the file specify a rotation (or even a full mapping table) for each component of the hash, so a clever encoder can pick values that minimise collisions. (A fast encoder can just use all-zeroes to get the same behaviour as before.)