[Terry Brown]

Okay, this is a weird one and may not be related to the KFX conversion at all, but I don't know a better place to start than here.

I am using Calibre 5.1.0, KFX Output 1.44.0, Kindle Previewer 3.45 on macOS Catalina, and a 2018 iPad Pro 12.9 with the latest version of the Kindle app.

I convert and side load KFX files to the Kindle app on the iPad. When viewed using Bookerly (but other fonts as well), there are quality issues. The density of the letters is inconsistent. Hard to describe, but there is a variability in the pixel density of different letters, as if the font were being resampled and averaged for display, and thereby losing information, for example. This causes some letters to appear darker, or perhaps different sizes than others. Very disconcerting on a Retina display.

If I instead use a .mobi file converted in Calibre, I do not see this issue. EPUB files viewed in iBooks do not show the issue. It is specific to the KFX format files.

I also do not see the issue on my iPhone 7. I have tried various fonts and font sizes, themes, etc, but still see the issue on the iPad.

I have attached a screen shot from the iPad. Assuming the resolution is good enough, take a look at the word 'that' in the first line of the right column. The 't' and the 'h' are larger and bolder than other letters.

Take a look at the word 'Narveduen' in the third line from the bottom of the right column. Here, the letters 'uen' at the end of the word are thinner than the others.

Interestingly, I do not see this on my iPhone 7.

Does any of this make any sense? Any ideas about what to try or where to go to get suggestions?