Color keying (also known as chroma keying) is commonly used on television to create the familiar effect of a newsreader or show host backed by a cavalcade of animated graphics. In reality, the well-coiffed telepromtee is standing in front of a big green screen. As part of the broadcast, the green screen is “keyed out" and replaced by the motion graphics necessary for each segment of the program. You can do the same thing in Motion using the Keyer filters.
Important: Keying to isolate a foreground subject is not always easy; it takes time and patience to learn how to use the parameters in each filter to achieve the best effect. Most keys are “pulled” using more than one tool. Good compositing artists usually combine masked keyer filters, matte adjustment filters, spill suppression operations, and garbage or holdout masks to isolate a single subject. The Keyer filter in Motion combines many of these operations within a single set of parameters. Two other Motion keying filters—Matte Magic and Spill Suppression—provide standalone access to these finishing operations. For more information on techniques you can use to improve a key, see Applying Multiple Keys to a Single Subject.
Keying is accomplished using one of two keyer filters in Motion. The Keyer filter is a general purpose color-keying filter that’s capable of blue screen or green screen keying, or keying any range of color you choose. The Luma Keyer generates mattes based on a sampled range of lightness in the image. Both keyer filters, as well as the Matte Magic and Spill Suppression filters, are located in the Keying category of filters in the Motion Library. (For basic information about Motion filters, see Using Filters.)