The Gimp is a free program that allows you to manipulate images, such as combining single-filter images from the telescope to create a full color image.
The Gimp can be downloaded from www.gimp.org and is available for Mac, Windows, and Linux, as well as in several different languages.
Important note: The Gimp does not recognize FITS files, so you must process the data with Iris or DS9 and save the data as .JPG before importing them into The Gimp.
