Comment by namibj

For fast updates / high frame rate, especially also smooth fade from previous to next page, those displays only do black/white. They can typically modulate about 14 levels of gray in-between but reliably (without really bad ghosting, due to strong temperature sensitivity of the pixel's transition response and the display being static so all gray has to be done by carefully interrupting a transition part way through) only from a nice flash-to-black -> flash-to-white -> fade-to-target-greyscale (sometimes one or two alternating full contrast flashes prepended to more intensely equalize the pixels/erase ghosting, but should only be needed every couple dozen page flips in grayscale mode).

I think the nice b/w no-flicker fade transitions chop the transitioning of all changing pixels into small burst/chunks and interleave/alternate the chunks of white-to-black with the chunks of black-to-white, so it's perceptually simultaneous. Or it's actually pulling off some kind of tri-state driving leaving unchanging pixels alone and pulling those that change to either plus or minus polarity depending on what transition direction they are supposed to go in... Sadly IIRC all quite proprietary-gated :(

What that means for djvu is that at least for text-only content on those readers that manage the 300 dpi "threshold" you'd just rasterize to pure 300dpi black/white (1 bit per pixel) comparable to a 300dpi "don't skimp on toner but don't you dare take half a second longer than you must in order to make the text crisp enough for $reader to have no good reason to whine about it being not crisp enough" laser printer job.

Djvu is particularly for displays with more than about 5bits of grayscale as well as for lossy compression of grayscale/color scans. And maybe also some efficiency gains on 1-bit-per-pixel quantized scans, but those aren't usually the target content for these readers, IMO. Might want to try for them, though!