nice idea, I think it is somewhat more in line with the keep it simple option, as I e.g. have no idea what a hilbert curve for an arbitrary size rectangle look

nice idea, I think it is somewhat more in line with the keep it simple option, as I e.g. have no idea what a hilbert curve for an arbitrary size rectangle looks like. And you still get compression for x and y directions (though no run length encoding the vertical, perhaps a further addition). I quite like this approach of defining a few compression methods, see which one works best, and apply that one. I used a similar strategy for time series compression where I would take a chunk of data, apply z few different compression algorithms on it (RLE, delta RLE, etc) and just keep which ever one was smallest. Of course here it is done on a per pixels basis, and I used arbitrary size chunks. The latter is trivial to parallelize. Same could be applied here though, split the image in half and compress both parts independently