How to trim screenshots via the commandline

I just had to trim a bunch of screenshots that had some black borders around them. I didn’t want to do this manually or via a GUI, but ideally batch-able via the commandline. Thankfully, that’s one of the many things that ImageMagick can do for you.

I put all my screenshot PNGs into a folder, and then in that folder ran this mogrify command:

magick mogrify -trim -define trim:percent-background=0% -background black -path output/ *.png

I found that I had to add the -define trim:percent-background=0% option to get rid of all black borders, as otherwise on some of the images a very slim one ended up remaining. I also specified the background color with -background black to make sure that it really only trimmed the black borders.

I then could combine the resulting images into a PDF with img2pdf¹:

img2pdf --output output.pdf *.png