9.5.2

890 • CHAPTER 18
THE SHADERS • 891
Algorithm
Species which illumination model Lumas will use. The drop-down list provides for two choices:
Internal, which is the standard Lambertian model, and Oren Nayar, which provides for a roughness
variable allowing the user to go from simple surfaces (0 Roughness, identical to Lambertian), to
complex rough surface (1+ Roughness, which provides a matt surface, such as linen or dirt).
Roughness
Dictates how rough the Oren Nayar illumination model will be. Zero is no roughness while 100% or
greater is very rough. Experimentation is required to fully understand this parameter. This option is
only available if Oren Nayar is selected in the Algorithm drop-down list.
Illumination
Scales the Color to produce attenuation in the illumination of the surface (this simply means it makes
the color darker when the value is close to zero and brighter when the value is closer to 100% or
above).
If you are using the Oren Nayar illumination algorithm, you may want to bump up the illumination by
about 10% to 20% because it renders darker usually. Appropriate values are between 0% to 200%.
Contrast
Provides contrast for the result of the Color. Zero causes no effect, 0% - 100% causes standard
contrast, above 100% causes a wrap contrast (the values that go above 100% wrap around to 0%
again, used to create the Candy materials), negative values provide an inverse contrast that simulates
materials that seem luminescent, such as silver. Appropriate values are -500% to 500%.
Specular pages
The three specular highlights controlled by the Specular channels are added to the color of the surface.
All three Specular channels share the same parameter set, described below.
Active
Here you can enable or disable the three specular highlights individually.