Use a garbage matte

A garbage matte (or junk matte) removes unneeded portions of the scene, resulting in a rough area that contains only the subject that you want to keep. When you are working with a poorly lit or uneven color screen (for example, a bluescreen or greenscreen), sketching a garbage matte around the subject can greatly reduce the amount of work that you have to do in keying out the background. However, if you spend a lot of time making a perfect garbage matte that exactly outlines the subject—essentially rotoscoping—you lose the time-saving advantage of keying.

  1. Create a mask to roughly outline a subject.
  2. Apply one or more keying effects to mask out the remainder of the background.
  3. Apply Matte effects as necessary to fine-tune the matte.

Aharon Rabinowitz provides a video tutorial on the Creative COW website that shows how to create a super-tight garbage matte using Auto-trace.