re: Compositing -- Chroma Key vs. Color Key

I haven't done too much major compositing in my work experience so I'm reading up more on it. I noticed that in the Apple Pro Series book, Chroma Key is the recommended device for doing blue- and green-screen work, but Color Key isn't even mentioned. I've been using Color Key for years to do background replacement. What is the difference between the two?

Subjectively - chroma key seems to be a better keyer in the specified vector ranges. It operates with chroma smoother, spill supress and matte choker well.

On other systems, like Red the Chroma Key is actually a combination of all of these, and it porvides a selection set for a broader range of chroma vectors than color key.

Perhaps Graeme can give an objective pointer at the differences

Ian