Find all files under a certain size or dimension and then resize

resize.bash

# Find files over 300kb and resize to 300kb

identify -format '%b %h %i\n' ./*.png |
awk '$1 > 300000 {sub(/^[^ ]* [^ ]* /, ""); print}' |
tr '\n' '\0' |
xargs -0 mogrify -define png:extent=300KB

# Find files over 600px width and resize to 600px while keeping ratio

identify -format '%w %h %i\n' ./*.png |
awk '$1 > 600 {sub(/^[^ ]* [^ ]* /, ""); print}' |
tr '\n' '\0' |
xargs -0 mogrify -resize '600'