Quote:
Originally Posted by jhowell
I repeated your test and observed basically the same result. When converting to KFX and back to EPUB the cover image (1704462598893215816_cover.jpg) is identical but the first interior image (1704462598893215816_p0s.jpg) is re-encoded, changing the file size and pixel values slightly.
I then changed the original file so that the contents of the first interior image and cover image were swapped. In that case the interior image converts unchanged and the cover is modified. That shows there is something about the content of some images and not others that triggers the re-encoding process.
I opened the original EPUB using the Kindle Previewer, saved the converted KPF file and examined its contents. The images there were identical to the KFX file that this plugin produces, showing that all of the image manipulations in this case are due to the processing by the Previewer and not this plugin.
It is unclear why this image manipulation is being done in some cases and not others. The Kindle Previewer's conversion process is completely undocumented.
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Yeah, I thought there was something on that side. One part of the problem is undoubtedly just how aged jpeg standard it. It really wasn't designed for high resolutions, certain compressions, and even display medium present today. The other is Kindle Previewer. There are workarounds. Saving everything images in using just the right settings, is one of them. But I think that one of the main problems is how everything clashes on the side of Calibre that most of the people use. Tools do everything as well as possible, and when used using CLI, they provide great results even when used with imperfectly formatted images. Problems start when used in Calibre, where there's a lot of code on top of it, with default settings that are set so that heavy compressions happen.
For my end, I've found at least two fool proof methods. One is export images as black and white profile png, and convert them in faststone to jpeg. There is something about Photoshops jpeg export engine that probably clashes with Kindle Previewer later in the process. The other appears to be skipping Adobe software and using Capture One instead.