The GIMP is a full featured digital photo editing package available for free on the Open Sofware Licence. It really is a great program packed with quality tools and filters. There is now an excellent CMYK Plug in for The GIMP which is great for correcting colors and even creating Duotones. Many of the filters are unique to The GIMP and its worth having this program even if you have PhotoShop.
If you haven't already done so please read my
Essential Background Info tutorial and our
Color Page these pages go into some detail about Raster or Bitmap Images and color formats such as RGB and CMYK.
Below are some of the many uses for Digital Photo Editing Programs.