2008

■ 2.0 (The default.) The energy decays at an inverse square rate. That is, a
photon's energy is the inverse of the square of the distance from the light
source: 1/distance 2.
In the real world, light decays at an inverse square rate (Decay=2.0), but this
gives strictly realistic results only if you provide a realistic value for the energy
of the light. Other values of Decay can help you adjust indirect illumination
without worrying about physical accuracy.
NOTE Decay values of less than 1.0 are not recommended, and can cause
rendering artifacts.
Geometry Properties group
All Objects Generate & Receive GI and Caustics When on, at rendering time,
all objects in the scene can generate and receive caustics and global
illumination, regardless of their local object properties settings. When off, an
object's local object properties determine whether it generates or receives
caustics or global illumination. Turning this on is an easy way to ensure that
caustics and global illumination are generated, though it can increase rendering
time. Default=off.
This setting does not alter the object's local object properties settings for mental
ray. When you turn off All Objects Generate & Receive GI And Caustics, the
prior object properties settings are in effect once again.
Final Gather Rollout (mental ray Renderer)
Rendering menu > Render > Render Scene dialog > Indirect Illumination panel
> Final Gather rollout
Main toolbar > Render Scene > Render Scene dialog > Indirect Illumination
panel > Final Gather rollout
Note: The Indirect Illumination panel appears only when the mental ray
renderer is the currently active renderer.
Final gathering is a technique for estimating global illumination for a given
point by either sampling a number of directions over the hemisphere over
that point (such a set of samples is called a final gather point), or by averaging
a number of nearby final gather points since final gather points are too
expensive to compute for every illuminated point. In the former case, the
6104 | Chapter 18 Rendering