Why Color Mapping?
Surely you are aware of the fact that an image rendered with GI (and low ray depth) is very bright in some areas and very dark in others. A balanced allocation of color and brightness would be nice in order to be able to achieve a consistent lighting.
Many may think that this can simply be done in Photoshop. Not quite. Most image-editing applications can only work with the limited 24-bit or 48-bit RGB interpolation of the much more precise image.
There are two ways to work around this limitation: