Quote:
Originally Posted by jackm8
I'll go and do some proper kfx samples later. I guess that it's best to ignore converting kfx back to epub for this comparison, and just look at kfx on e-ink device for results visible in the end. But this will involve talking photos and a bit of work.
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My interest is seeing that the cover image makes it into the KFX file without a loss of quality. What happens after that in rendering the image on a Kindle device is not under my control so I do not see any point in posting Kindle screen images.
What I meant by asking for an example is any case where the original cover image does not make it into the KFX file unchanged. The easiest way to check for that is by converting from KFX back to EPUB using the command line interface (CLI) of the KFX input plugin. Using that avoids potential image manipulation by calibre itself. If a case can be found I would need to be able to duplicate it myself using your source file to determine the cause.
I previously mentioned one known issue. If the original cover image is not in JPEG File Interchange Format (JFIF) then it will be regenerated by the plugin with a possible loss of quality. I will look into improving that.
In addition calibre's conversion and metadata updating system can impact cover images. I recommend using the KFX Output plugin CLI to avoid those possibilities.
There may still be other cases that I am not aware of. The bulk of the KFX conversion process is performed using Amazon's Kindle Previewer and that might potentially do further image manipulation that only comes into play under certain circumstances.
Quote:
Originally Posted by jackm8
Regarding dithering. You're right that generally dithering images is not ideal, but it is when you do dithering in exactly the same resolution as target device. Then dithering provides best possible results, at least in my experience. The problem with it is that it is very sensitive to jpeg compression, as jpeg compression basically does it's own compression that is similar to dithering, not overwriting dithered results, but adding to it, ultimately causing bad quality.
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I agree that tailoring images to a specific device can make them fragile if any unexpected manipulations occur. I will try to improve what I can but some things may not be under my control.