Part 1, Part 2, Part 3, Part 4, Part 5, [download the Unity3D package]
If you are using Unity3D you may be familiar with image effects. They are scripts which, once attached to a camera, alter its rendering output. Despite being presented as standard C# scripts, the actual computation is done using shaders. So far, materials have been applied directly to geometry; they can also be used to render offscreen textures, making them ideal for postprocessing techniques. When shaders are used in this fashion, they are often referred as screen shaders.