What Is Occlusion in Graphics?
Occlusion, more commonly known as ambient occlusion, is a computer graphics technique used to approximate the effect of global illumination by taking into account the occlusion, or blocking, of light caused by other geometry in a scene.
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Global Illumination Versus Local Illumination
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Local illumination models calculate the illumination value, or light value, at a point based on the angle from the light source. These methods are not dependent on other objects in the scene. Global illumination, on the other hand, incorporates the effect of surrounding objects on the illumination value at a point, and is therefore more realistic.
Method of Implementation
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The ambient occlusion value at a point on a surface is calculating by shooting rays in all directions out of the surface. Rays that do not hit an object add to the brightness at the point, while rays that are blocked by objects do not add any brightness. As a result, surface areas that are surrounded by geometry appear quite dark while surfaces not blocked at all appear very bright.
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Significance
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Ambient occlusion techniques greatly enhance the realism of a scene without the computational cost of full global illumination techniques. Hayden Landis, Ken McGaugh and Hilmar Koch received the 2010 Scientific and Technical Academy Award for their work on ambient occlusion.
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