Apple Final Cut Pro 6 - Manual (Page 1224)

Chapter 20 Keying, Mattes, and Masks 439
II
13 Finally, you’re ready to insert the background image. Make sure that the clip you’re
editing into your sequence to use as the background image appears in a video track
below the foreground clip being keyed.
14 To really make the foreground and background look as if they were shot together, it
may be necessary to perform additional compositing steps such as blurring the
background to make it look out of focus, color correcting the foreground subject to
have the same color temperature as the background, or using motion effects to move
the foreground subject. Even with a successful key, these are the details that make a
composite look like a finished shot.
The background image
now appears.
The background image
is placed below the
foreground clip that
was keyed.