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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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