Was just about to ask the refresh time, I specifically chose this one due to it's faster refresh time (1 s) compared to color displays: https://shop.pimoroni.com/products/inky-what?variant=2121402...
You pretty much do two full refreshes, and then some. The first one drives the pigment (red,yellow) layers, and then the black ones.
Why does the refresh time depend on the size of the region updated? Forgive my ignorance—I'm imagining that the limiting factor would be the time it takes for the grains to physically flip over, because they all flip concurrently.
Only one row at a time has voltage applied to it. In one update, the image is scanned out multiple times, so it appears as if all pixels were changing simultaneously (and perhaps they do, if the electrodes have significant capacitance.)
With fewer rows to update, each row gets a push more often, flipping the grains faster.
Hypothesizing a bit here: maybe it's like flash, where erasing is slow and has to be done in large chunks, but once a large chunk is erased small chunks can be written (once) quickly.
Re:Reasonably priced color e-ink display
by sparker72678 on Monday July 20, 2020 @01:37PM
(#23900073)
And the dithering isn't even that great, as not all color combinations are easily-mixed, given their varied densities.
• In monochrome panels, you can get 16 shades, and a full refresh in under a second (with partial refresh much faster, as tight as very few milliseconds for small areas, or commonly 30fps full-screen update if you’re willing to compromise a bit on image quality).
• In colour panels, you don’t seem to get shades or rapid refresh: seven colours means you get a seven colour palette, so you’ll have to use dithering to get any in-between colours; and you don’t get partial updates at all: even the fastest coloured panels take a couple of seconds to update the image, and the more colours you add the slower it is.
If I’m wrong about these and there are colour panels with more interesting colour or partial refresh, I’m interested to hear. I just haven’t seen any, and have done some looking.
The long and the short of it is that colour e-ink displays are only useful for display use, not for individual devices like ebook readers or computer displays.