Quote:
Originally Posted by davidfor
The only one that has a problem is the grayscale PNG with 16 levels.
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This reminds me... I think there is a minor bug in the image display code that also affects pdf's.
I think there is a quantization error in converting grey scale in general to what the eink screen needs. At a guess without any experimentation, it feels like they are doing a direct threshold conversion without any dithering. The result is that images with even distribution of colors look fine, but in a few edge cases some strange artifacts show up.
For example, I have a pdf that is probably from a scanned document. When I tried to read it on my kobo, there was a huge smear down the middle that looked like something was stuck to the scanner and made the document unreadable. When I view the pdf on my laptop, I can see the smear, but it is very faint.
I checked other documents from the same source, and they had the smear, but it was a slightly different shade of grey that did not render on the kobo and the document was readable.
My guess is that the smear sometimes falls into the same bucket as the text due to the way the colors are quantized. I didn't think about it much at the time, I should try to generate a test case.