A chroma key compositing filter.

This filter supports a number of different modes:

• Automatic - decide which keying method to use based on the supplied color. If the supplied color is near: red, green or blue then use that a method that is specific to that color, otherwise use the Nearest Color method.
• Red - Use a keying method that is specific to the color red.
• Green - Use a keying method that is specific to the color green.
• Blue - Use a keying method that is specific to the color blue.
• Nearest Color - Use a keying method that will key against the supplied color using a distance model.
• Chroma Color - Use a keying method that will key against the supplied color using chroma angles.
• Position - Use the Nearest Color method by sampling the color of the pixel at the specified location. The color paramter is ignored with this mode.