Volume III, 2003
Dr. Yap Siong Chua
In order to represent real-world images with a computer, a program has to relate three-dimensional images on a two-dimensional monitor screen. Several ways of doing this exist with varying degrees of realism. One of the most successful methods can be grouped in a "screen-to-world method" of viewing, which is also known as "ray-tracing."
This computer graphics technology simulates light rays within a 3D environment. Since light rays have predictable physical properties, the raytracing algorithm can attempt to calculate the exact coloring of each ray/object intersection at any given pixel. Advanced levels of ray tracing allow light rays to bounce from object to object, mimicking what they do in real life.
"Local illumination" represents the basic form of ray tracing. It only takes into account the relationship between light sources and a single object, but does not consider the effects that result from the presence of multiple objects. For instance, a light source can be intersected by another surface and therefore be obscured to any point behind that surface. Similarly, light can be contributed not by a light source, but by a reflection of light from some other object. The local illumination model does not visually show this reflection of light. Therefore, special techniques have to be used to represent these effects. In real life there are often multiple sources of light and multiple reflecting objects that interact with each other in many ways.
"Global illumination," the more advanced form of ray tracing, adds to the local model by reflecting light from surrounding surfaces to the object. A global illumination model is more comprehensive, more physically correct, and it produces more realistic images.
Ray tracing is an essential subject when it comes to computer graphics. It combines issues of efficiency and realism, thus finding a favorable balance of the time and effort involved to make realistic three dimensional images. In the process of researching the many different ways of implementing a ray tracer, the study began with local illumination and graduated to global illumination, using some pre-established techniques and the development of new techniques.
Rupard, Jason, "Ray Tracing And Global Illumination" (2003). All Volumes (2001-2008). Paper 105.