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• Shrink/Expand: Use this slider to manipulate the contrast of the matte to affect matte
translucence and matte size simultaneously. Drag the slider left to make translucent
regions more translucent while simultaneously shrinking the matte. Drag the slider
right to make translucent regions more solid while simultaneously expanding the matte.
• Soften: Use this slider to blur the keyed matte, feathering the edges by a uniform
amount.
• Erode: Drag this slider right to gradually increase transparency from the edge of the
solid portion of the key inward.
Spill Suppression: Click the disclosure triangle in the Spill Suppression row to reveal
controls for neutralizing a colored light that bounces off the blue screen or green screen
and contaminates the isolated foreground subject. This fringing around the edge of the
subject is called spill, and is difficult to eliminate because it’s part of the subject you’re
trying to preserve.
The Spill Suppression controls work by letting you adjust the color correction that
neutralizes unwanted color in the foreground subject. While the Spill Level slider (described
above) controls how much suppression is applied, the controls in this group let you
customize the quality of suppression being performed.
When first applied, the Keyer filter adds spill suppression to the video clip or image, based
on the dominant color sampled to create the initial key. This automatic spill suppression
desaturates the key color so fringing around the foreground subject appears gray (rather
than blue or green). But if you reduce the Spill Level slider to 0, effectively turning off
spill suppression, the gray fringing turns blue or green (the color of your background),
proving that successful spill suppression is rendering the background a neutral gray.
• Spill Contrast: Use this grayscale gradient to adjust the contrast of the color being
suppressed, using Black and White point handles (and corresponding sliders). Modifying
spill contrast can reduce the gray fringing surrounding a foreground subject. The Black
point handle (on the left side of the gradient control) lightens edge fringing that is too
dark for a successful composite. The White point handle (on the right side of the gradient
control) darkens edge fringing that is too light. Depending on how much spill is
neutralized by the Spill Level slider, these controls may have a greater or lesser effect
on the subject.
647Chapter 13 Keying