The process of selectively overlaying an area of one picture (or clip) onto another. If the switch between the overlaid and background pictures is simply ‘hard’ this can lead to jagged edges of the overlaid, or keyed, pictures. They are usually subjected to further processing to produce ramped, slightly soft, key edges to give a cleaner, more convincing, result. The whole technology of deriving key signals from image data and the color corrections applied to keyed image edges, has greatly expanded through the use of digital technology, so that many operations may be used together, e.g. softening the key, color correcting key spill areas, and much more.

See also: Chroma keying, Digital keying, Linear keying