Apple Final Cut Pro 7 - Manual (Page 1227)

With a high-quality DV camera and good lighting, it’s possible to pull a reasonable key
using DV clips, but you cannot expect the kind of subtleties around the edges of a keyed
subject that you can get with uncompressed or minimally compressed footage. For
example, while you may be able to preserve smoke, reflections, or wisps of hair when
keying uncompressed footage, with equivalent DV footage this probably won’t be possible.
On the other hand, if your foreground subject has slicked-back hair and a crisp suit, and
if there are no translucent areas to worry about, you may be able to pull a perfectly
acceptable key.
Using Proper Lighting
The lighting you use when shooting blue- or green-screen footage plays a crucial role in
determining whether or not you’ll be able to key out the background easily.
• Blue or green background: Should be evenly lit, with no exceptionally bright areas (hot
spots) or shadows. The material you use for the background screen should be smooth,
with no bumps or wrinkles.
• Video signal: Should have a minimum of film or video grain, since the “noisiness” that
grain introduces can make it more difficult to pull a good key. Video can get grainy in
low-light situations, so the lighting on your background screen should be bright enough
that you don’t have to turn up the gain of your video camera.
• Lighting of foreground subject: Should have close to a 1:1 ratio to the lighting of the
background screen. This avoids overexposing or underexposing the background screen
when the foreground subject is correctly lit.
Once your background blue or green screen is properly lit, you should concentrate on
lighting the foreground subject to match the scene into which you’re going to
composite it. It’s especially important to make sure that the contrast between the
shadows and highlights of your subject’s lighting is correct. While you can use the
Final Cut Pro color correction filters to easily adjust the color and overall brightness of
your subject, contrast is not so easy to change. This is not to say that you need to light
your foreground subject flatly. Just make sure that the direction, quality, and contrast
of the lighting you use works for the scene your subject will inhabit.
• Distance between foreground subject and background screen: It’s a good idea to have
some distance between the foreground subject and the background screen, to reduce
the amount of colored light bouncing off the background blue or green screen and
“spilling” on the foreground subject. In general, position your subject 5 to 10 feet away
from the background screen.
1227 Chapter 72 Keying, Mattes, and Masks