ABSTRACT
Compositing necessitates the combination of bitmaps, image sequences, videos, and/or procedurally-generated patterns. Whereas a layer-based program simply stacks layers with preference to upper layers, Nuke combines inputs through various "merge" nodes. Regardless of the compositing program used, a layer or input's alpha channel must be considered as it carries pixel transparency information. In the realm of digital image manipulation, alpha is a channel that stores transparency information. The transparency information is often referred to as a matte, where the matte carries grayscale values. Premultiplication is an optional process whereby the red, green, and blue values of a digital image are multiplied by the alpha values within the same image. Nuke automatically recognizes the alpha channels of imported images. However, premultiplication is not recognized unless a person selects the Read node's Premultiplied checkbox. Whereas an alpha channel is often referred to as an alpha matte or a channel that carries matte information, a mask is a device that generates a matte.
