Compositing
The process of combining multiple image or video elements into a single final image, using layer blending, masking, and color correction to achieve a seamless result.
Compositing is the post-production process of integrating multiple visual elements into a unified final image. Live-action plates, CG renders, matte paintings, and effects layers are combined to appear as a single coherent scene.
The fundamental principle relies on alpha channel transparency. Porter-Duff operations define 12 operators, such as Over, In, and Out, specifying pixel interaction. The Over operation is C = Cf * αf + Cb * (1 - αf).
- Node-based compositing: Tools like Nuke and Fusion use node graphs for non-destructive workflows where any stage can be modified independently
- Layer-based compositing: After Effects and Photoshop manage elements in layer stacks - intuitive but complex shots become difficult to manage
- Match moving: Camera tracking recreates real-world camera motion in 3D space for precise CG element placement
- Color matching: Harmonizing color temperature, contrast, and grain across elements ensures believable integration
Feature film shots can involve many layers. Real-time compositing is also used in game engines and virtual production with LED volume stages, which can reduce traditional post-production needs.