Second, there are no 8 bit EPD controllers as of now a mortal can buy, which means grays look very bad.
Third, there are inherent physical limitations which make increasing gray resolution of EPDs quite hard. The precision you want, the slower would the refresh rate be.
For a digital picture frame, refresh rate isn't that important. In fact, a "gradual shading" on refresh might even make for a neat transition effect[1].
IMHO it's just the "cartel" (they like to keep the details of driving their displays confidential) of EPD controller companies who haven't produced controllers with more than 16 levels of grayscale, but the material is fundamentally analog and here is proof that if you drive the display directly, you can get at least 32 levels of grayscale if not more:
With a bit of careful calibration, I believe far finer grayscale is possible.
[1] Although EPDs have been around for a long time now, I have yet to see the demoscene do anything with them --- a directly driven display naturally allows for a lot of effects due to it effectively being an "analog write-only memory".
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Second, there are no 8 bit EPD controllers as of now a mortal can buy, which means grays look very bad.
Third, there are inherent physical limitations which make increasing gray resolution of EPDs quite hard. The precision you want, the slower would the refresh rate be.
For a digital picture frame, refresh rate isn't that important. In fact, a "gradual shading" on refresh might even make for a neat transition effect[1].
IMHO it's just the "cartel" (they like to keep the details of driving their displays confidential) of EPD controller companies who haven't produced controllers with more than 16 levels of grayscale, but the material is fundamentally analog and here is proof that if you drive the display directly, you can get at least 32 levels of grayscale if not more:
https://news.ycombinator.com/item?id=16140284
With a bit of careful calibration, I believe far finer grayscale is possible.
[1] Although EPDs have been around for a long time now, I have yet to see the demoscene do anything with them --- a directly driven display naturally allows for a lot of effects due to it effectively being an "analog write-only memory".
EPDs are highly, highly nonlinear in their driving response.
It for a good reason full info behind making LUTs for driving EPD screens is kept as high secret.