Code: Select all
convert in.png -crop 40x40%+10%+10% out.png
My first thought was
Code: Select all
convert in.png -chop 10x10% -crop 40x40%+0+0 out.png
Obviously something like (40%/(1-10%)=44.4%)
Code: Select all
convert in.png -chop 10x10% -crop 44.4x44.4%+0+0 out.png
If all my images happened to be the same size, I could just convert the offsets to pixels. But it was not meant to be.