One more relevant use case: I've found Floyd-Steinberg dithering to be somewhat useful in compressing scanned JPEG paper notes at 600dpi (~1.5-2.5MB per page) t

One more relevant use case: I've found Floyd-Steinberg dithering to be somewhat useful in compressing scanned JPEG paper notes at 600dpi (~1.5-2.5MB per page) to 1-bit PNG (100-300KB). At full scale, there is no loss in readability and in fact I think I prefer the aesthetic quality of the 1-bit PNG. However, at <50% zoom, the dithered version was way less readable than a 2-bit PNG of slightly higher file size, so I ended up not compressing to 1-bit. Edit: I was wrong, my (ex-) image viewer was at fault at 50% zoom. Viewing in other apps, the dithered version is visually no different from the 2-bit version. I bet the difference is even less with a HiDPI screen.