extract images

[milahu]

use darkmode to find jpg images with white background

darkmode: reader settings -> page color: black
create 2 screenshots of every page: light + dark
text changes color, images dont change color
take difference of light and dark screenshots
difference is black -> text
difference is white -> image

bonus points for detecting QR codes, and converting them to sharp SVG images

example

magick compare light.png dark.png -compose src -highlight-color black -lowlight-color white diff.png

light.png

dark.png

diff.png

todo: find large white boxes in diff.png and use them to extract images from light.png

image processing is much simpler in python
first attempt: align-pages.py