Here's the process I used to determine the maximum image size:
- Create a 1024x768 file with alternating blocks of 1-pixel lines, making it easy to spot resizing anomalies
- From that file, create a 128x768 horizontal strip and a 1024x128 vertical strip
- Create an epub with these images in different chapters
- Compile the epub with Kindle Previewer (or Kindlegen)
- Transfer the generated .mobi to a connected Kindle /Documents folder
- Open the .mobi on the Kindle
- Take a screenshot of each rendered strip (on the PW, touch upper right and lower left corners at the same time)
- Open each screenshot in an image editor, measure the rendered area
- Create an image with these dimensions (940x658)
- Add an image of that size to the epub, recreate the .mobi with Kindle Previewer
- Confirm lack of resizing anomalies on the Kindle with a magnifying glass
G