Global illumination
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Global illumination algorithms used in 3D computer graphics are those which, when determining the light falling on a surface, take into account not only the light which has taken a path directly from a light source (direct illumination), but also light which has undergone reflection from other surfaces in the world (indirect illumination).
Images rendered using global illumination algorithms are often considered to be more photorealistic than images rendered using local illumination algorithms. However, they are also much slower and more computationally expensive. A common approach is to compute the global illumination of a scene and store that information with the geometry (ie. radiosity). That stored data can then be used to generate images from different viewpoints for generating walkthroughs of a scene with out having to go through expensive lighting calculations.
Radiosity, ray tracing, beam tracing, cone tracing, Path Tracing, metropolis light transport and photon mapping are examples of algorithms used in global illumination. Which may or may not be used in conjunction with each other by combining algorithms.
These algorithms model diffuse inter-reflection which is a very important part of global illumination, however most of these (exluding radiosity) also model specular inter-reflection too which makes them more accurate algorithms to solve the lighting equation and provide a more realistic globally illuminated scene.
External links
- SplutterFish (http://www.splutterfish.com/) - developers of Brazil, a rendering system based on global illumination. The site has an extensive gallery of contributed images