How do I batch trim images 50% to the left with automator?

Question

I know I can batch trim images with automator for 50% horizontal, but then it get's trimmed on both sides... I need it to get 50% trimmed on just the left/right side.

Answer 1

I don't know about Automator; I'd use bash (on the command-line) for this sort of thing.

If you have ImageMagick installed (you should be able to get it from homebrew), you can use convert to cut off one side or another of an image.

This will give you the left-hand side of the image (so it will cut off the right half):

convert input.png -crop 50%x100%+0+0 output.png

becomes

This will give you the right-hand side (cut off the left half of the image):

convert input.png -gravity east -crop 50%x100%+0+0 output.png

becomes

To act on every file ending with .png in a given directory, you can put it in a bash for loop:

for f in *.png; do convert "$f" -crop 50%x100%+0+0 "${f%.*}-cropped.png"; done

To do so recursively (every *.png in the working directory, and every *.png in any sub-directories), use globstar:

shopt -s globstar; for f in **/*.png; do convert "$f" -crop 50%x100%+0+0 "${f%.*}-cropped.png"; done

All of these will create a separate output file (in these examples, for every file.png there will be created a file-cropped.png). To work on files without creating a separate output, use mogrify (the companion tool of convert). Of course, this will over-write your existing files, so be careful in its use. Mogrify is able to take multiple inputs from the command-line, so there is no need to use a for loop here:

mogrify -crop 50%x100%+0+0 *.png
##  Recursively:
shopt -s globstar; mogrify -crop 50%x100%+0+0 **/*.png

If you are working with a truly huge number of files (thousands), the above globs may choke; in that case, you should use find:

##  For convert:
find . -type f -name '*.png' -execdir bash -c 'convert "$0" -crop 50%x100%+0+0 "${0%.*}-cropped.png"' '{}' \;

##  For mogrify:
find . -type f -name '*.png' -execdir mogrify -crop 50%x100%+0+0 '{}' \;

You can put any of this stuff into a bash script like so:

#!/usr/bin/env bash
for f in *.png; do convert "$f" -crop 50%x100%+0+0 "${f%.*}-cropped.png"; done
exit 0

Or, a nicer-looking version:

#!/usr/bin/env bash
for f in *.png; do
  convert "$f" -crop 50%x100%+0+0 "${f%.*}-cropped.png"
done
exit 0

...save that in a plaintext file called something like crop-left.sh and set it as executable:

chmod u+x crop-left.sh

To use it from the command-line, it would be

./crop-left.sh

I don't know how to fit this into Automator, since I've never used that program, but it probably can be done.