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Secondary Outputs (AOVs)


Introducing Secondary Outputs

Another feature of RenderMan for Maya is the ability to generate secondary outputs (also called Arbitrary Output Variables, or AOVs). While rendering, RenderMan for Maya can output additional data (specular highlights, reflections, shadows, etc.) into separate image files, called secondary outputs. These outputs are not rendered in multiple passes, but are created at the same time the main image is being rendered

Secondary outputs are useful for compositing. It can be more efficient to adjust certain effects in compositing (such as tweaking specularity) than rendering the image over and over again. Secondary outputs can also be used to create special effects. RenderMan for Maya provides controls to generate exactly the kinds of secondary outputs required.

For more information about workflow associated with creating secondary outputs refer to the Secondary Outputs Tutorial. What follows here is an overview of the basic outputs and how they are combined to create your final image.


About Outputs

Here is a list of shadingmodel outputs. These additive terms are required to reconstruct the beauty render. They all must be passed through layering operations.

AmbientConstant
The (surface?) shaders' constant "built-in" ambient illumination
AmbientLight
Illumination from ambient lights
Backscattering
Total contribution of backscattering effects
DiffuseDirect
Unoccluded diffuse response to direct lights
DiffuseDirectShadow
Diffuse response that is shadowed (subtract this from DiffuseDirect)
DiffuseEnvironment
Diffuse response from environments
DiffuseIndirect
Diffuse response reflected from other objects
Incandescence
Total contribution of incandescent effects
Refraction
Total contribution of refraction effects
Rim
Total contribution of rim effect
SpecularDirect
Specular response from direct lights
SpecularDirectShadow
Specular response that is shadowed, subtract this from SpecularDirect
SpecularEnvironment
(Unoccluded) specular response from environments
SpecularIndirect
Specular light reflected from other objects (coherent reflections)
Subsurface
Total contribution of subsurface scattering
Translucence
Total contribution of cheap/thin translucence

The recipe for compositing your beauty image is a simple additive process using these outputs:

	result = SpecularDirect - SpecularDirectShadow + SpecularIndirect + 
		 SpecularEnvironment + AmbientConstant + AmbientLight + 
		 DiffuseDirect + Translucence - DiffuseDirectShadow + 
		 DiffuseIndirect + DiffuseEnvironment + Backscattering + 
		 Subsurface + Rim + Refraction + Incandescence
	

Additionally, there are “ancillary outputs” that are not used to create the beauty render but can be useful for other compositing tasks:

SpecularColor
Color used to scale specular illumination
DiffuseColor
Color used to scale ambient and diffuse illumination
OcclusionDirect
Occlusion of direct illumination (shadows)
OcclusionIndirect
Occlusion of indirect (ambient) illumination

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