The Radiosity technique involves simulating the lighting distribution throughout an environment, using a physically accurate lighting model.
Radiosity is in no way responsible for the production or rendering of an image. It takes geometry as its input, and generates geometry as its output - the output geometry is an alternative representation of that supplied as input, but subdivided into small 'elements', and with radiosity values attached to each vertex. This geometry can be used for rendering employing any of the standard rendering methods available in solidThinking.
The idea underlying the radiosity technique is to model the distribution of all the light energy in an environment, by applying the conservation of energy at every surface. It should be understood that the radiosity algorithm solves the lighting problem, but not the visibility problem. Once the light distribution has been generated, images can be rendered using standard visibility and shading algorithms.
The advantage of radiosity as a technique is that it accurately models the type of environments where there are matte surfaces which diffusely reflect light in all directions, and onto other matte surfaces; the inside of a building is a very common example of such an environment. It should be noted that many surfaces in an interior environment are lit by no direct illumination at all, and are visible only by light reflected diffusely from other surfaces.
Also, a surface illuminated indirectly may appear to be of a different color than it would appear if lit directly, since color from one surface can "spill" or "bleed" onto another, particularly if bright colors are placed next to more subdued hues.
A number of important effects are simulated by radiosity techniques. Radiosity is able to account for the area of light sources, resulting in accurate soft shadowing. Also, by accounting for secondary illumination, radiosity correctly computes "color bleeding" effects and the indirect illumination of parts of an environment that are not directly lit by a primary light source.
Radiosity is therefore an important technique for architects, builders and lighting engineers, as well as general computer graphics users, and anyone who is interested in creating realistic images.
The disadvantage of the technique is that it is costly in terms of computer time and memory. It is however the only technique that can reproduce physically accurate lighting conditions in a large class of common scenes.
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