Image Editing with the GIMP

Adobe Photoshop has become a verb among digital photographers. Computer image editing is at a point were you can manipulate pictures to the point where you have no idea what the original was.  Popular Photography has an image editing contest going right now, with pictures from previous year's contests, if you want some examples. The trouble with Photoshop, is that it costs a small fortune. Luckily for us, the open source world has produced a reasonable alternative, GIMP (GNU Image Manipulation Program). Gimp is best run on a Unix like (Linux, etc) machine, though there is a Windows port. The trouble with both the GIMP and Photoshop is the learning curve. Both programs take considerable effort to learn (and a hefty CPU with lots of RAM, or lots of patience). While it is hard to do the stuff requested by the Popular Photography contest, there is plenty of documentation on the web to get you started using GIMP to clean up your day to day digital pictures. I took some pictures with a point and shoot digital the other day, in auto mode (which didn't use the settings I would have), and while looking for better noise reduction plugins I stumbled across some sites that people might find useful:

The obvious place to start learning GIMP, would be the official documentation.  If you are not already familiar with image editing software, you might prefer to look at some tutorials on Gimp.org.
As a photographer, I have found that the GIMP for photographers site has some more generally useful tips. This site also has some (some of them more odd) short tutorials that might be useful under certain  conditions.
GimpTalk.com has some discussion forums as well as a bunch of tutorials, plugins and scripts.

On the topic of Plugins and Scripts, GIMP has a plugin interface as well as scripting support for Perl and a proprietary language. The GIMP Plugin Registry has a lot of these available for download. A few of them have windows binaries, which can be put in the plugins subdirectory of your GIMP install directory, but many need to be compiled (good luck with that on Windows). For Linux/UNIX users, this is simple (assuming you have a recent copy of gcc installed). Just run the make script packaged with the plugin or run "gimptool --install plugin.c". If you use GIMP-2.X then you might have to use gimptool-2.0. For fixing my pictures, I found that the Dcam Noise2 plugin helps a lot with noise due to high sensor sensitivity settings. Besides noise removal plugins, there are a wide variety of other enhancement, artistic and file format plugins available. If you find a GIMP script-fu script, these can be installed on a Linux/UNIX machine using "gimptool --install-script script.scm"

If you have a Digital Camera that can produce a image saved in a RAW format, you will almost certainly want to be able to take advantage of the improved quality this can offer.  Dave Coffin's dcraw library/converter seems to be the standard way of opening most RAW format images on Linux. It comes with a GIMP plugin. This site lists some alternatives, particularly if you have a Nikon DSLR, but talks about packages that can read other RAW formats as well. If you are a Windows user, you can try some of the tools based on dcraw, but you are probably better off with your camera manufacturer's software or some other commercial program.

If you want to do some sort of batch image processing ImageMagick may be better for you.

Happy Image Editing. Maybe I will post some of my own GIMP tips in a little while, but for now this should get you started.