Digital compositing

The basic operation used in digital compositing is known as alpha blending, where an opacity value, 'α', is used to control the proportions of two input pixel values that end up a single output pixel.

If this operation has to be done in real time video games, there is an easy trick to boost performance.

If all layers of an image change regularly but many layers still need to be composited (such as in distributed rendering), the commutativity of a compositing operator can still be exploited to speed up computation through parallelism even when there is no gain from pre-computation.

In general, we can build a tree of pair-wise compositing operations with a height that is logarithmic in the number of layers.

The most historically significant nonlinear compositing system was the Cineon, which operated in a logarithmic color space, which more closely mimics the natural light response of film emulsions (the Cineon System, made by Kodak, is no longer in production).

Compositing often also includes scaling, retouching and colour correction of images.

Software which incorporates a node based interface include Natron, Shake, Blender, Blackmagic Fusion, and Nuke.

Nodes are a great way to organize the effects in a complex shot while maintaining a grip on the smaller details.