Adobe 25510629 - After Effects CS3 Professional, Руководство пользователя

Страница: 61 / 130

Creating and assigning sources and virtual sets 61
Lighting:
Whenever possible, light the backdrop separately from the foreground subject. This
requires moving the subject as far from the backdrop as possible to create space for two
separate lighting zones that don’t interfere with each other. If this brings areas beyond the
edges of the backdrop into view, you can delete them with Mask Painter tool or by cropping
the edges. Just keep the subject entirely in front of the backdrop. For more information, see
“Painting a mask” on page 84 or “Cropping the edge of a frame” on page 84 .
Lighting on the backdrop should be as even as possible, without hotspots or shadows.
Umbrella reflectors and soft box diffusers are ideal for providing the desired results. A light
meter or in-camera zebra pattern indicator can help ensure that the backdrop is evenly lit and
deeply saturated.
Reducing spill
Colored light spilling from the background onto the subject can interfere with getting a
convincing key. Although spill suppression features in Ultra can greatly reduce color spill
problems, being careful while you’re shooting is better yet. Keep the following points in mind:
The larger the background, the more significant this issue tends to be. That’s because
every square inch of colored background reflects light of the background’s color.
In wide shots with the subject standing on a color screen, the floor also becomes a source
of bounced light. To minimize spill from the floor, reduce the amount of key color
flooring in front of the subject. One way to accomplish this is to place a black drop cloth
immediately in front of the farthest point forward that the subject’s feet will reach. You
can use the Input Cropping controls to trim out everything in front of the subject’s feet.
A nearby white wall beside the background or behind the camera can compound the
problem by bouncing more colored light back onto the subject. To minimize this
problem, set up the key backdrop in an area without nearby light-colored walls.
Choosing the subject’s wardrobe
Ultra does not know whether a green pixel is part of the backdrop or the subject’s necktie, so
ensure that the subject isn’t wearing anything that’s too close to the color of the backdrop.
Otherwise, you’ll be looking right through the subject to the virtual set behind.
TIP
For each clip that you record and then key and composite in Ultra, ensure that you get at
least a few frames that show only the keying background as it will be lit and framed for
the shot. Frames with nothing in the foreground let you use the Set Key method, which
not only produces the highest quality key but is also the easiest to use. For more
information, see
“Set Key” on page 78 .