6.2. The Ray Tracing Technique   

The ray tracing technique attempts to simulate the behaviour of light rays in order to generate an image. In the real world light rays originate from various light sources and are then reflected off or refracted through objects in their path, with a small proportion eventually reaching the viewer's eye. A logical way to simulate this efficiently is to consider only those rays that strike the eye of the viewer. This is achieved by tracing the rays backwards from the viewer into the scene, and following the reflected and transmitted rays generated by these to a level specified by the user.

In order to properly describe this technique, it will be necessary to first describe the behaviour of light rays as they strike the interface between two media. This has been very well described by [KEIT 71] as follows :

When light passing from one homogeneous medium falls on the interface between this and another medium, part of it is reflected and the rest passes into the second medium; the light entering the second medium is then partly or wholly absorbed. Any light that is not absorbed may pass through the medium, and this is referred to as transmitted light.

Therefore, if r=proportion of light reflected, t=proportion transmitted, and a=proportion absorbed, then r+t+a=1. When considering ray tracing, the absorbed light (which goes nowhere) is ignored, leaving r+t<=1. The methods of the reflection and transmission of light are described below.