In practice, video inspired image compression techniques (i.e. HEVC Main Still Picture) will do a significantly better job on that masonry brickwork image. The

In practice, video inspired image compression techniques (i.e. HEVC Main Still Picture) will do a significantly better job on that masonry brickwork image. The algorithm is already looking for patches of image that have moved by possibly hundreds of pixels (to sub pixel accuracy) both within a single frame, and across multiple frames. Basically, it'll find a patch of image that, when shifted horizontally and vertically by a certain amount, looks pretty close to the patch of image that it's trying to encode. The compressor will then say "just copy that region that you decompressed half a frame ago to here first, and now the residual values I give you are differences between the first patch and the second." Even if the brick / mortar phase is slightly off (e.g. from perspective or lens effects), this will give you about an order of magnitude more compression efficiency (and perceptual quality) than anything that tries to use color depth to preserve edges.