Nuke 101: Professional Compositing and Visual Effects, Second Edition

7. Keying

Keying is the process of creating a matte (an image that defines a foreground area) by asking the compositing system to look for a range of colors in the image. This is also sometimes called extracting a key. It’s a procedural method, which makes keying a lot faster than rotoscoping, for example. However, it has its own problems.

You have to shoot specifically for keying because you have to place the foreground object in front of a single-color screen. The color of the screen can’t include any of the colors of the foreground object because the computer will be asked to remove this color. Usually this is done with either a blue or green backing—called a bluescreen or greenscreen, respectively. Usually the color you choose is related ...