Images to be added.
With Physically-Based Compositing (PBC) we refer to the process of outputting individual lighting components from the renderer in a global illumination context to be then summed in compositing safely.
Let's first review the two ways of reconstructing and tweaking a global illumination image in compositing:
Classic Compositing | Physically-Based Compositing | |
---|---|---|
Global Illumination | Yes | Yes |
Image Layer Type | Shading Components | Individual Lights Components |
Image Layer Examples |
| lights, light groups, incandescence, environment |
Compositing Operation | Sum | Sum |
Affects all light paths | No | Yes |
In a Classic Compositing scenario where shading components are being output, the artist will be adding them up to "reconstruct" the beauty image:
beauty_color = diffuse
+
specular
+ indirect_diffuse
+ indirect_specular
+ subsurface
However, due to the presence of Global Illumination, light bounces everywhere in the scene, therefore any coloring operation in a directly lit component, such as grading (G) the diffuse, would require a second operation to compensate its effect in the indirectly lit components:
beauty_color = diffuse(G)
+ specular
+ indirect_diffuse(G)
+ indirect_specular
+ subsurface(G)
beauty_color = light_1
+ light_2
+ light_group_A
+ light_Group_B
+ incandescence
+ environment
A grading operation on light_2 in compositing will not require tweaking of any other component:
beauty_color = light_1
+ light_2(G)
+ light_group_A
+ light_Group_B
+ incandescence
+ environment
In 3Delight light & light groups are mutually exclusive: a light put in group1 cannot be added to another group and cannot be output independently to ensure a correct compositing.