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 |
|
|
| Compositing Operation | Sum | Sum |
| Affects all light paths | No | Yes |
In a Classic Compositing scenario where shading components are being output as image layers, 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 secondary operation to compensate its effect in the indirectly lit components:
beauty_color = diffuse(G)
+ specular
+ indirect_diffuse(G)
+ indirect_specular
+ subsurface(G)
It should appear evident that in such case more relationship-tweaking between the individual components would be necessary in compositng when doing a simple operation such as grading.
In the Physically-Based Compositing scenario however a grading operation would not require any further relationship-tweaking since by outputting Individual Light Components (see Multi-Lights rendering in 3Delight) we always operate on all light paths, for each light, group of lights, for the environment and for incandescent geometry. Given a setup with many lights, he artist will be adding the image layers to "reconstruct" the beauty image:
beauty_color = light_1
+ light_2
+ light_group_A
+ light_Group_B
+ incandescence
+ environment
A grading operation (G) on light_2 in compositing will not require any further relationship-tweaking for any other image layer since we already carry all light paths (direct and indirect) in the light_2 image layer :
beauty_color = light_1
+ light_2(G)
+ light_group_A
+ light_Group_B
+ incandescence
+ environment
In 3Delight, output of light and 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.