Global illumination

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 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 without 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, some of which may be used together.

These algorithms model diffuse inter-reflection which is a very important part of global illumination, however most of these (excluding 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.

The algorithms used to calculate the distribution of light energy between surfaces of a scene are closely related to heat transfer simulations performed using finite-element methods in engineering design.

In real-time 3D graphics, global illumination is sometimes approximated by an "ambient" term in the lighting equation.

File:Global illumination.jpg

An example of a global illumination rendering, demonstrating how surface materials are reflected in other surfaces.

See also

• YafRay free rendering software featuring global illumination
• Radiance - highly accurate ray-tracing software system for UNIX computers. Free to non-commercial users.

External links

• PBRT - Literate programming, has a great accompanying book.
• Vray Render - Vray Render website, a new fast, and powerful rendering engine.
• Vraywiki - Vraywiki website.
• SplutterFish - developers of Brazil, a rendering system based on global illumination. The site has an extensive gallery of contributed images
• Perceptuum - good source for photon mapping, and other global illumination techniques.
• Mental Images - Makers of the highly professional renderer MentalRay. The renderer is used in packages such as Softimage XSI, Maya and 3D Studio Max