Cel-shading or toon shading is a type of non-photorealistic rendering designed to make 3-D computer graphics appear to be flat by using less shading color instead of a shade gradient or tints and shades. Cel-shading is often used to mimic the style of a comic book or cartoon or give it a distinctive paper-like texture. There are similar techniques that can make an image look like a sketch, an oil painting or an ink painting. It is somewhat recent, appearing from around the beginning of the twenty-first century. The name comes from cels (short for celluloid), the transparent sheets of acetate, which are painted on for use in traditional 2D animation. (Wikipedia)
