Keys are “holes” that need to be filled.
Special Effects Keys — Luminance Keys
Keys are among the most common and useful special effects. Keys are essentially holes cut into a video picture that are filled with material from another source. Different types of keys rely on different information to determine the shape and nature of the holes and how they are filled. Luminance keys are triggered by differences in brightness (contrast). The hole in the original video is cut according to contrast differences supplied by a programmed source. The pattern the system derives from this source is called the key source or key signal. The figure at the right shows a common use of luminance keys.
Camera 2 is providing the key source — the bright star against ...
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