This script can effectively convert ANY image files to ANY other imagefiles.
It's simply using the pillow library to convert images.
This is the lightweight repo, my test files aren't included.
python convert.py
make sure you have pillow in your python environment
pip install pillow
keep in mind the filesize of the .ppm images in this repo are massive in filesize.
du -sh images/
452M images/
use the lightweight branch if you want to avoid cloning with my test images.