You load three clips into the Keyer to create a composite: a front clip, a back clip, and a key-in clip. The key-in clip, which is usually the same as the front clip, is used to create the matte for the front clip.
To access the Keyer:
The Keyer appears.
(a) Keyer button (b) Master Keyer button (c) Channel button (d) Luminance button