Indirect Illumination versus Global Illumination
Indirect illumination and global illumination are similar. Both effects
are the result of light hitting objects in the scene, then bouncing off
those objects to illuminate other objects in the scene. With both illumination
types, the bounced light can reach areas that direct light from the light
sources could not otherwise reach.
Indirect illumination is the result of light transmitted from a source
onto objects in the scene that are then diffusely spread from one object
to another. Objects send out sampling rays from each pixel in the image
and gather the color information on what the rays hit. More rays result
in more realistic color bleeding and slower performance.
Global illumination is the result of photons being emitted into the
scene by each light source. As the photons bounce around the scene and
hit an object, they store the color information. The distance that the
photons travel and the strength of the effect is determined by the photon
energy. More photons result in more realistic effects and slower performance.
Note the following images. One shows the effect of indirect illumination,
and the other shows the effect of global illumination. The effects produce
similar results. It is recommended that you vary the intensity of lights,
the energy and amount of photons, and the diffuse property of the appearances
to find the combination that produces the best results for your scene.
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