Keying is the process of isolating a region of an image by selecting pixels of a particular color and making those pixels transparent, or creating an alpha channel where those pixels are located. The main purpose of using the keyer tools in Composite is to generate mattes and remove color spill from a shot.
The two basic approaches to creating an alpha channel are based on:
You can also use garbage masks to key out undesired elements in an image. However, garbage masks will be discussed in a later section as creating garbage masks are a manual operation that involves creating paint objects or the creation and manipulation of splines (rotoscoping)—see Masking Concepts.
