The computation costs of ray tracing make it particularly unsuitable for animations because of the large number of images that must be rendered. 3D Studio, the workhorse of computer animation software, does not even provide true ray tracing. POV, the Persistence of Vision Ray Tracer, provides an excellent introduction to ray tracing. Visit the Computer Art Lab at Wire Frame University to pick up a copy. Scan Line Conversion Scan Line rendering sacrifices reflections and shadows for increased render speeds.
More speed is achieved by eliminating hidden faces from consideration before rendering.
Without shadows and reflections, the three dimensional information from hidden faces is not necessary. Scan line rendering can create images in a fraction of the time full ray tracing requires. Several other rendering methods can be used to obtain really fast pictures of a scene. Such images are almost never used for final production images, but are invaluable while a project is being developed. Flat Shading with No Mapping Disables surface mapping, polygon smoothing, and ray tracing.