A few weeks ago, a person posted an interesting question on an internet microscopy mailing list: what is the difference between histogram stretching and histogram equalization when applied to microscopy images? The following is a short intuitive review which compares the two. Since this is a short and general description, I will gloss over some details and make some generalizations which may not be true in all cases and implementations.

The first thing to remember is the basic purpose of contrast enhancement. The idea is simple, In a grayscale (black and white) image you are simply trying to take two levels of gray that are close together, and thus visually similar, and move them apart so you can better see the difference between them. You can think of grayscale values in an image as beads on a string, Contrast enhancement simply moves all or some of those beads farther apart.