Multi-pass rendering
Multi-pass images give digital compositor a great
deal of control over the look of the shot. Compositor can make an overall improvement to each pass as well as adjust the final composite more artistically. In addition, compositor can take advantage of a specific pass by interactively relighting the scene, adding motion blur or even retexturing the CG elements without spending extra time re-rendering them in the 3D software.
The most often used multi-passes are: Beauty pass, diffuse pass, specular pass, reflection, refraction, shadow pass, depth pass, normal pass, ambient occlusion pass, ID pass, motion vector, etc. These separated render passes can be seamlessly combined together later on through the use of mathematic formulas in digital compositing software. See Figure 11.