VIPS's a free image processing system. It aims to be about half way between
Excel and Photoshop. It's obviously much smaller than these two, but it's
not a toy either (about 200k lines of code). It's very bad at photo
retouching, but it's great (much better than programs like Photoshop, I
think) at all the other things you use photoshop for. It's particularly
good with large images (ie. images larger than the amount of RAM in your
machine), and for working with colour.