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Define Ray Tracing

Ray Tracing is a rendering technique which produces three-dimensional, photo-realiistic images with reflection, shading, and perspecitve. While it produces very high quality images, it requires a very large number of computer calculations, and is therefore not a very fast process.

Using Ray Tracing, the computer mathematically models the light rays as they bounce around a virtual world of objects that you design. For each pixel on the viewing window a ray is calculated to see if it hits any object in the virual world. If it does, rays of light from the light source (or sources) are calcualted to detmine if the object is in darkness, in shadow, or in direct light from the defined light source. The reflectiveness of the the surface as well as ambient light are calculated. For each ray calculated from the view screen, many additional rays may be calculated before the final lighting, reflection, refraction, and finally color or the final pixel may be determined.

Ambient light is light that comes from the light source after it bouces off at least one other object. If you look into a dark area of the room, like under a table, there is no direct light there yet you can still see clearly. The light in such an area is ambient light reflected from the floor, walls, and other objects in the room. Ambient light can produce more realistic pictures, but understandably increases the length of time needed to create (or render) each picture. It is for this reason a lot of software that does ray tracing simulate ambient light by having all objects put out so much ambient light rather than calculate the light.

Reflectiveness and light refraction as well as the color of the light itself also greatly effect a picture. Fog is created or simulated by creating a pattern of points in space that refract the light. The density of the points controls the density of the fog. The refraction of light is simply the bending of light to change its direction. If light is refracted enough it is said to be reflected. Reflection is when all the light changes direction after hitting an object. When ray tracing how reflective an object is determines how shiny the object is. By making an object more reflective it appears to be smoother and more shiny.

Objects that allow light to pass through them and just refract the light are used to make ghostlike objects or objects that appear like glass. If a ripple pattern is added to the glass then it is a pretty good imitation of water.

The color of an object is controlled by its lighting and coloring. Several shading algorithms or sets of computer instructions have been created that allow for the controlled shading of objects. This is what helps create the 3D effect and helps create perspective. How much light a point on an object is getting controls how bright the object is at that point. The color of the light will also effect the overall color at a given point on an object. All of these these are used when calcualating the color.

When all this is put together, along with additional techiques not discussed here, you can create some very good and realistic pictures. Please let me know if you have questions or would like more information on the subject.

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