This isn't about the Carta vs Pearl display or full vs fast screenupdate.
It's about a small malfunction in the full screen update procedure in Pocketbook.
So it's not a Coolreader bug; it's also reproducable at the build-in Adobe and FBreader.
And it's a minor issue but nevertheless excists.
Personally, I prefer quality vs speed.
And speed is a relative term; an user invention is still necessary to 'turn' a page.
You can exhibit the phenomenon yourself:
Make sure you have backlight on at max setting and set 'Display update mode' to 'Don't use fast updates'.
Choose a dark, bold font and set it's size at max (nowadays you can get to 150
and perhaps even embold the font even more (Font settings -> Font embolding). Now start turn pages and look accurate and you can exhibit some light ghosting from the previous page in the dark portion of the text.
When you carry out the same experiment and set 'Display update mode' to 'Always use fast updates' and manually refresh after a turned page (program either 'Full screen update' or 'Invert display' as a Tap action) and you will witness a more even, darker black text.
Although not a lot people will read with this font settings, this phenomenon will still be present at smaller sizes and to put it plain simple: the contrast on a Pocketbook could be a notch better.
As earlier said, it's due to how Pocketbook executes a full screen refresh at page turn:
- step 1: the new page is displayed inverted
- step 2: just before step 3, the old page is briefly displayed inverted
- step 3: the new page is displayed normal
Look at the pictures in the attachment (build-in Adobe reader) to see wath I'm try to explain...