In this video I install advpng (from AdvanceCOMP) and show how to use it to recompress a bunch of png files.
Installing MacPorts on a Mac: https://youtu.be/N22Ic6ZRPXI
Install advancecomp (using Macports)
sudo port install macports
View Size of Current Directory
du -sh
Find png Files in Directory (recursively)
find ./ -iname '*.png'
Count Files
find ./ -iname '*.png' | wc -l
Batch Optimize png Files
find ./ -iname '*.png' -exec advpng -z4 {} \;