@schuhumi: I'll be mildly curious to know, once people with a PW4/KOA2/KT4 try this, whether ordered dithering actually behaves as expected

.
It *should* (and it certainly does on similar Kobo HW), but when we enabled it in KOReader, we got reports about extremely broken quantization... :/.
(It's fairly easy to check with the fbink CLI tool and a random image, FWIW

).