Convert image format/postprocessing

[Efreak]

A large number of older webcomics have large png and jpg files (some nicely optimized, some not). It would be nice to have an alternative for long-term archiving, to save space, such as converting files to webp automatically, as they're downloaded. Currently I'm using cbxconverter, but that's a windows only gui program that (at least on my laptop) takes longer to process each image than it takes to download it and can only be run after the comic has been zipped, not while it downloads.

[Efreak]

If this is an unwanted feature, it would also be nice to have a more general post-processing function to run a custom command/script on each downloaded file, and another on each directory after any given comic is complete

For individual post-processing, it would allow

• convert image to webp
  • convert -trim $image $image.webp && rm $image
• reduce image quality
  • convert -quality=75 $image.jpg.

For post-processing on directories, this would allow

• creating customized cbz files
  • for a in 01 02 03 do; zip -m -0 $(dirname $PWD)_20$a.cbz 20$a*; done
• exporting files
  • calibredb -add $filename.cbz -series '$ComicName'