What Is Keying and How Can You Use It?
Keying refers to the process of turning an area of consistent color or brightness in a
video clip transparent to isolate a foreground subject. The actual keying process results
in the creation of a matte (explained earlier), which is then automatically applied to
composite an image with a background. In television and in movies, keying is used in a
variety of ways to composite actors in front of graphics and other video clips for a
variety of effects.
For example, a weather reporter on television often stands in front of a weather map.
The reporter is actually standing in front of a large blue or green screen, but the color is
made transparent (keyed out), and a map is inserted behind the person, instead.
Generating a matte signal using a color signal is referred to as chroma keying, while
generating a matte signal using a black-and-white signal is called luma keying.
A four-point matte outlining
the image of the woman
The resulting image, with the
Keying, Mattes, and Masks