I installed ImageMagick via this script:
install_im.sh at master from masterkain’s ImageMagick-sl – GitHub
Start that then put in a movie b/c you’ll be there a while. At some point in there, it asks for your password though so…
Then I just ran this command in the dir w/ the pngs:
mogrify -scale 23.7% *.png
Worked nicely.