Even though an object in a scene is not directly lit it will still be visible. This is because light is reflected indirectly from nearby objects. A simple hack that is commonly used to model this indirect illumination is to use of an ambient light source. |
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Lecture 16 | Slide 4 | 6.837 Fall '00 |  |
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Every object in a scene is potentially a source of light. Light may be either be emitted or reflected from objects. Generally, in computer graphics we make a distinction between light emitters and light reflectors. The emitters are called light sources, and the reflectors are usually the objects being rendered. Light sources are characterized by their intensities while reflectors are characterized by their material properties.
Most computer graphic rendering systems only attempt to model the direct illumination from the emitters to the reflectors of the scene. On the other hand most systems ignore the geometry of light emitters, and consider only the geometry of reflectors.
The rationalization behind these simplifications is that most of the light from a scene results from a single bounce of a emitted ray off of a reflective surface. This is, however, a very questionable assumption. In most computer generated pictures you will not see light directly emitted from the light source, nor the indirect illumination from a light reflecting off on surface and illuminating another.
First we will consider some very simple lighting models.
The amount of ambient light that is reflected by an object is independent of the objects position or orientation. Properties often determine how much of this ambient light is reflected.
