TL;DR

Using ImageMagick to crop one or more images from the command line.

Do you know ImageMagick? It’s an amazing set of command-line tools for doing image manipulation. It allows doing a lot - I mean really a lot - of things, although not always simple things are simple.

Anyway, this time I needed to do some cropping.

Usually when I do this with a GUI I set one corner, draw a rectangle up to the diagonally opposite corner, and there goes the cropping. It turns out that the input required by ImageMagick is somehow different:

• size (width and height) of the rectangle to cut, and
• offset (x and y) of the upper-left corner (assuming that y increases downwards).

Hence, a couple of points (5, 7) and (27, 33) become 23x27+5+7.

After the first half time… it becomes shell script time! So here we go:

I hope the comments make sense.

The list of files to crop is provided in the standard input, so that this can be piped in the shell. There are two positional arguments: two points (in the x,y form, like e.g. 19,72) and an optional substitution suitable for sed, to generate the name of the cropped file.

The names of cropped files are printed on standard output, for further processing down the line.

The cropped images are produced with +repage, which means that there is no virtual canvas preserved and it just works.

Well, I guess it’s all for today… I hope you will enjoy!