2011

Table Of Contents
Benefits of Indirect Illumination
Indirect illumination techniques, like global illumination and final gathering,
enhance the realism of a scene by simulating radiosity, or the interreflection
of light in a scene.
Global illumination (GI) provides effects such as color bleeding. For example,
if a red countertop is next to a white wall, the white wall gets a slightly pink
tint. You might also think its a minor detail, but if the pink tint is missing
from the image, the image looks fake, even though it might be hard to point
out precisely why. This effect is not possible with ordinary ray-tracing
calculations.
To calculate global illumination, the renderer uses photon maps, a technique
to generate the indirect illumination effects and global illumination. A side
effect of using a photon map is rendering artifacts such as dark corners and
low-frequency variations in the lighting. You can reduce or eliminate these
artifacts by turning on final gathering, which increases the number of rays
used to calculate global illumination.
When preparing for a finished rendering, make sure you have specified the
drawing units you want to use before you make any GI settings. Changing
drawing units after youre satisfied with the global illumination will adversely
affect the rendering results.
The accuracy and intensity of global illumination is controlled by the number
of photons generated, the sampling radius, and its trace depth. This example
shows the effects of a low number of photons and a sampling radius set too
small.
2136 | Chapter 46 Render 3D Objects for Realism