For information about keying in general, including links to tutorials and other resources, see Keying introduction and resources.
The Color Difference Key effect creates transparency from opposite starting points by dividing an image into two mattes, Matte Partial A and Matte Partial B. Matte Partial B bases the transparency on the specified key color, and Matte Partial A bases transparency on areas of the image that don’t contain a second, different color. By combining the two mattes into a third matte, called the alpha matte, the Color Difference Key creates well-defined transparency values.
The Color Difference Key produces high-quality keying for all well-lit footage items shot against a bluescreen or greenscreen and works especially well with images that contain transparent or semitransparent areas, such as smoke, shadows, or glass.
This effect works with 8-bpc and 16-bpc color.