Some useful ImageMagick snippets

I try and stay out of Photoshop as much as possible. For most non-design image manipulation tasks I've found ImageMagick to be very useful, though it can be hard to sort through the documentation to find the transformation you need. Here are the ImageMagick commands I find most useful:

# Flatten a transparent image with a white background:
convert -flatten img1.png img1-white.png

# Make an image transparent
convert -transparent '#FFFFFF' nontransparent.gif transparent.png

# convert an image into tiles
convert -size 3200x3200 tile:single_tile.png final.png

# making a montage from a collection of images
montage -geometry +0+0 -background transparent *png montage.png

# inverting colors
convert before.png -negate after.png

# generating a favicon
convert large_image.png -resize 16x16! favicon.ico

I also once needed to add numbers to a individual parts of a tiled image. I found it easier to script this with Ruby rather than use the shell's looping constructs:

# adding numbers to a tiled image
cmd = (0..324).to_a.inject([]) do |cmd,n| 
  y=(n/25*32)+15; x=((n%25)*32)+15
  cmd << "-draw 'fill red text #{x},#{y} \"#{n}\"'"
end

`convert img.png #{cmd.join(' ')} annotated_img.png`