ABSTRACT
Compositing images shot against one background over a new background is one of the trickier visual effects tasks. It requires separating the foreground elements from the original background they were shot against. Even if the foreground comes with its own alpha channel, getting it to blend nicely with its new background can still be a challenge. This chapter gives an overview of the keyers After Effects offers, and focuses on using the preferred Keylight plug-in. The process of keying footage means creating an alpha channel that isolates the objects or actions that are needed from the background they were originally shot against. A number of techniques can be used to accomplish this separation. The most common technique is based on color keying. In addition to keying, other terms include chroma keying, Ultimatte and bluescreen or greenscreen.
