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Chapter 19. Lighting > Defining GI, Radiosity, FG, IBL, and HDRI

Defining GI, Radiosity, FG, IBL, and HDRI

These terms are often thrown around, and the meanings of each get confused. Global illumination, otherwise known as diffuse indirect illumination, refers to a range of techniques such as Final Gather and radiosity. Light bounces all around off every surface indirectly. This bouncing of light energy is referred to as radiosity. Various algorithms exist for calculating radiosity, such as matrix, progressive, and wavelet. Specific techniques, such as Monte Carlo, have become well known. Photon maps can be calculated and optimized in a wide range of ways as well.

In Mental Ray, Final Gathering is an accelerated technique of using photon mappings for approximating radiosity. It simulates the emission of radiant light energy using a ray-tracing renderer. This allows any surface to be a light source. These light values are stored in a photon map and are referred to by the renderer when it creates the color for any given surface, rather than calculating it each time an area of surface is shaded.


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