The effect produced when a photographic image is displayed or printed with a small number of colors or shades of gray. For example, displaying color photographs or video with 16 colors produces a visible posterization, but the images are discernible. At 256 colors, the flesh tones on color images are only mildly posterized. For realistic flesh tones, it takes 65K colors. For absolute realism, it requires 16M colors. See
pixelated.
This Image Has 128 Colors
These examples show how an image posterizes as fewer colors are used. The colors are halved in each of the following.