SHADING

One of the most demanding aspects of computer graphics is to produce realistic shading. The processing required to achieve this is complex and involves the calculation of how an image should look when it is viewed in a variety of lighting conditions. There are several ways of producing an image with shading, each of which trades off the complexity of the software and the realism of the image produced. The basic form of shading, known as flat shading, assigns a color to each of the polygons that comprise an object and then adds effects to represent the position and intensity of a light source.
There are a number of more sophisticated forms of shading that can be used to produce more lifelike effects. One of the well-established techniques is Gouraud shading, invented by Henri Gouraud in 1971, which uses colour approximations to produce smoothly shaded images without requiring excessive time or processing power. A more sophisticated alternative is Phong shading, named after its creator Bui Tuong Phong, which takes a little more processing time and effort but which produces a more lifelike image. More sophisticated, and hence costly, shading techniques are available for the representation of bumpy or wrinkled surfaces, multiple reflections, and transparency.
The processing power required to produce computer graphics continues to grow and the technologies for displaying the images (such as plasma and liquid-crystal displays) are also evolving. It is little more that 40 years since the first computer graphics appeared but they have developed at such a rate that lifelike images can now be routinely included in computer games, commercial software packages, and feature films