The More Mattes the Merrier I

Sometimes one keying effect won't do the trick. For instance, you might need one effect to deal with solid foreground objects and another effect for edge details. If this is the case, use your keying effects to generate grayscale mattes, not color images with missing backgrounds. Then combine all the mattes into a single matte, precompose them, and use the precomp as a track matte for the original color image.