2008

Photon count increased to 50,000 (in Global Light Properties group) for greater detail
in the caustics.
Global Illumination with the mental ray Renderer
Global illumination enhances the realism in rendered images by simulating
all light interreflection effects in a scene (except caustics on page 6066 ). It
generates such effects as "color bleeding," where for example, a white shirt
next to a red wall appears to have a slight red tint.
The mental ray renderer offers two distinct toolsets for achieving global
illumination:
photon tracing on page 6100 and final gathering on page 6104 .
The primary difference between the two is that photon tracing goes from the
light source toward the ultimate illuminated target (taking bounces into
account), and final gathering goes the opposite way: from the illuminated
surface toward the light source. You can use either of these toolsets separately,
or combine them for optimal rendered results.
6072 | Chapter 18 Rendering