GIMP, the GNU Image Manipulation Program, is a serious, powerful, practical image processing program that rivals the famous Adobe Photoshop. Not that there’s anything wrong with Photoshop – it’s a non-Microsoft product too – but a version of Photoshop for Linux does not exist. Originally a unix app, GIMP has been ported to Microsoft Windows. Having used it on Windows and on Linux, I can report no noticable difference in functionality between the two. GIMP has filters to blur and sharpen and apply many kinds of art effects, tools to select by rectancle, oval, color, tools to add text and draw shape (though it falls short of being a good paint program), adjust brightness, contrast, saturation etc. or more general curve-adjusment with a histogram display, and so on and so on. GIMP can do layers, with adjustable transparency and many ways to combine them e.g. add, multiply, brightest, etc. Layers can be used to split a color image into RGB or HSV channels, and recombine them into color. There are more features than can be mentioned here – it is hard to think of a useful feature Photoshop has the GIMP doesn’t have. In comparing the two, you’ll find the main difference in the user interface “feel”. In GIMP you generally right-click in your image window to bring up a menu of commands, filters and everything. Certain tools and general commands are always available in a toolbox window, but this does *not* feature most of the commands you would use everyday. The only thing I didn’t like about GIMP is that it did crash on occasion when I worked on huge images (satellite photos of Earth, typically several thousand pixels wide and tall.) But then, Photoshop too crashed about as often.
If you need to work on images with a professional tool, and contemplate getting rid of your Windows/Photoshop setup and going over to Linux, but have doubts about not using Photoshop, first get GIMP for Windows and try it. You’ll still have Photoshop and won’t need to change operating systems while evaluating GIMP. When you’re satisfied that GIMP will work for you, then you can go whole hog for an all-Linux system. By the way, installation of GIMP for either operating system was very easy; if you’ve ever installed anything before, you can install GIMP.