Firmware 3.11.0 and 3.12.0 have a new feature setting:
Code:
[FeatureSettings]
ShouldDither=true
This turns on dithering for certain images, resulting in a smooth transition from one shade of grey to the next, instead of different shades forming distinct bands.
The images I have seen it work for on my Glo are the sleep screen, and the cover page of synced kepubs. It might work for other images too, I haven't tried yet.
It is difficult to get a screenshot to show the difference it makes though, because with ShouldDither=false the screenshot just shows the original colour cover image. But with the ShouldDither=true it shows a dithered greyscale image. There doesn't seem to be a way to get a screenshot showing the undithered greyscale image.
Also beware when reopening a kepub the old cover image may be cached, so you might need to turn the page and then turn back to the cover to see the effect after changing the ShouldDither setting.