Creating a cartoon shading effect
Toon shading (also called Celshading) is a non-photorealistic technique that is intended to mimic the style of shading often used in hand-drawn animation. There are many different techniques that are used to produce this effect. In this recipe, we'll use a very simple technique that involves a slight modification to the ambient and diffuse shading model.
The basic effect is to have large areas of constant color with sharp transitions between them. This simulates the way that an artist might shade an object using strokes of a pen or brush. The following image shows an example of a teapot and torus rendered with toon shading.
The technique presented here involves computing only the ambient and diffuse components of the typical ADS shading model, and quantizing the cosine term of the diffuse component. In other words, the value of the dot product normally used in the diffuse term is restricted to a fixed number of possible values. The following table illustrates...
