Diffing images with git

git-imgdiff.sh

#!/bin/bash

DIFF_PATH=/tmp/diff.png
MONTAGE_PATH=/tmp/montage.png
rm -rf $DIFF_PATH $MONTAGE_PATH

# Try to diff the images and create a montage with the original on
# the left, diff in the middle and the new one on the right.
DIFF=$(compare $2 $1 png:- > $DIFF_PATH)

# XXX: for some reason IG exits with 1 when it successfully creates the diff
if [[ $? == 1 ]]; then
  montage -label Original $2 -label Diff $DIFF_PATH -label New $1 \
    -tile x1 -geometry '433x+4+4>' $MONTAGE_PATH
else
  # If the images have different sizes the diff will fail.
  # In this case, create a montage with just the original and the new one.
  montage -label Original $2 -label New $1 \
    -tile x1 -geometry '650x+4+4>' $MONTAGE_PATH
fi

if [[ $? == 0 ]]; then
  display $MONTAGE_PATH> /dev/null 2>&1
fi

setup.sh

git config --global core.attributesfile '~/.gitattributes'

echo '*.png diff=image' > ~/.gitattributes

git config --global diff.image.command '~/git-imgdiff.sh'

apt-get install imagemagick