Definitions for "Chroma Key"
The Chroma Key process is based on the Luminance key. In a luminance key, everything in the image over (or under) a set brightness level is "keyed"out and replaced by either another image, or a color from a color generator. Also known as Blue Screen Compositing, the Chroma Key Process was made famous by films such as star wars where spacecraft miniatures were composited onto starfield backgrounds.
A rule for combining two video signals, or two images, based on the color of one image, such as: The output signal/image is taken from signal/image A, except where A contains the chroma key value, where the output is taken from signal/image B, allowing signal/image A and B to be overlayed, with A's chroma key pixels effectively transparent.
A television effect that uses a monochromatic colored background to allow electronic switching to another picture. Deep blue and deep green are commonly used for this purpose when the image involves humans.