jloutsch/kfxgen v5.20.0 on GitHub

kfxgen is a Calibre plugin that turns EPUB books into Amazon's KFX format, with a working Kindle table of contents.

What's new in 5.20.0

Ten fixes since 5.19.0, each one compared with Kindle Previewer 4.0.3, Amazon's own converter, on the same book.

Pictures

A large PNG picture is saved as a JPEG when that is smaller, as Amazon does. In a 12-book library sample, those pictures shrank from 36.4 MB to 11.5 MB. Pictures with transparency stay PNG.
A picture inside a table cell's words stays in the line.
A picture on its own line inside a paragraph sits where Amazon puts it: with the text after a single line break, as its own block after a blank line.
A link aimed at such a picture lands on it.

Tables

Header cells are centred unless the book sets their alignment, and a header the book sets to normal weight is no longer bold.
Plain cells are no longer forced to the left. They follow the reader's default, as in Amazon's books; checked on a Kindle Paperwhite.

Navigation

When kfxgen rebuilds a Contents page, the page's own section headings (such as "Part One") are kept, in place.
Heading stops follow the order in which each heading level first appears.

Tech debt paid down

Some earlier table fixes were measured against Amazon output made from test pages without a document type. Amazon's converter reads those in an older compatibility mode that aligns tables differently.
Those rules were re-checked the way real books are read, and corrected. The test pages are fixed too. One right-to-left rule is filed for the same correction (#605).

Still open:

The full list, with issue numbers, is in CHANGELOG.md.

Download kfxgen-plugin-5.20.0.zip from the Assets below.
In Calibre, open Preferences → Plugins → Load plugin from file, and choose the zip.
Restart Calibre.

Or from the command line:

calibre-customize -a kfxgen-plugin-5.20.0.zip

Then convert any book to KFX.