Some useful ImageMagick commands

#!/bin/bash

# Lots of useful transformations: http://www.imagemagick.org/Usage/transform/

# The following command will concatenate vertically all the pngs of the current directory.
# If there are 10 or less images only out.png will be generated,
# otherwise out-0.png, out-1.png, ... files will be generated.
montage -mode concatenate -tile 1x10 *.png out.png

# To ensure that the background is transparent
montage -mode concatenate -background transparent -tile 1x10 *.png out.png

# To create a png with only the transparent channel
convert <image.png> -channel A -separate -combine <output.png>

# To invert the transparent channel, quite useful to create png+jpg sprites
convert <image.png> -channel A -separate -combine -negate <output.png>

# To convert .png to .jpg
convert <image.png> -background black -flatten <output.jpg>

# To crop images:
# W = width, H = height
# SX = horizontal traslation, SY = vertical traslation
convert <image(s)> -crop WxH+SX+SY <output>

# To make transparent channel a bit more transparent
convert -alpha on -channel a -level 100%,10 -negate <input image(s)> <output>