"High-end graphics editing in the commercial world has been
defined by Adobe's Photoshop. It is so dominant and so prevalent
that the name is frequently used as a verb, as in the line from the
movie Cheaper by the Dozen "We'll photoshop her in later." In the
free and open source world the standard of comparison is GIMP. GIMP
stands for GNU Image Manipulation Program and was first released in
January of 1996. The latest stable release is version 2.6. Many
people add "The" in front of GIMP when referring to the program
since they think it reads better, but officially it is just GIMP.
(You don't say "The Photoshop", do you?)
"Both Photoshop and GIMP are categorized as raster graphics
editors. A raster graphics image is essentially an n by m array of
pixels where n and m are the dimensions of the image. Each pixel
represents a color and typically consists of three or four
components. Traditional display systems use the three base colors
of red, green and blue (RGB) to create a specific color. The print
industry has traditionally used the four colors cyan, magenta,
yellow and black (CMYK) for their purposes.
"Understanding the image and color basics and the end product
helps when evaluating software. GIMP really shines when it comes to
enhancing or retouching digital photos"