I've Been Playing with the "Color Enhance" option in Gimp

Gimp is a free open source image editor similar to Photo Shop. The latest version is Gimp 2.8.2 and can be downloaded via Partha.com . Be sure you also download the plugins.  There is a newer beta version, however I don't recommend it yet, since there are still some issues with it. Gimp is very simple to use and to me it's easier to use than Photoshop.