Instruction Manual

Chapter 13 Keying 509
Spill Suppression
When you key an image that was shot against a blue screen or green screen, some color will
have reected from the screen to illuminate the edges, or even the interior, of the foreground
subject. This unwanted coloration of the subject is called spill, and can be dicult to eliminate
from the foreground subject you’re trying to preserve.
Unlike the spill suppression controls found in the Keyer lter, which automatically neutralize
the color being keyed, the Spill Suppression lter lets you deal with this problem by manually
choosing the color to be neutralized.
Parameters in the Inspector
•
Color: Use this control to sample the color to suppress in the keyed image. Click the color
well and choose a hue from the Colors window, or use the eyedropper to sample a color in
the Canvas.
•
Level: Use this slider to adjust the amount of spill removal applied to the keyed image.
Tip: Green screen clips typically benet from a lower spill-level setting than blue screen
clips. Good starting points to try are 46% for green and 73% for blue, although you’ll need to
customize these values for your composites.
•
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 control) lightens edge fringing that is too dark. The White point handle (on the
right side of the 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 eect on
the subject.
•
Black, White: Click the disclosure triangle in the Spill Contrast row to reveal sliders for the
Black and White point parameters. These sliders, which mirror the settings of the Spill Contrast
handles described above, allow you to keyframe the Black point and White point parameters
(via the Add Keyframe button to the right of each slider).
•
Tint: Use this slider to restore the natural color of the keyed foreground subject. Because
Spill Suppression controls eliminate blue or green spill by desaturating subtle blue or green
fringing and reection on the subject, the Tint slider lets you add hues to restore the natural
color of the subject. Overdoing this parameter results in over-tinting the subject with the
complementary color of the hue being suppressed—magenta if green, and orange if blue.
•
Saturation: Use this slider to alter the range of hues introduced by the Tint slider (when the
Tint slider is used at moderate levels).
Tip: The best order in which to use these controls is to adjust Tint before you
adjust Saturation.
•
Mix: Use this slider to set the percentage of the original image to be blended with the ltered
image. 100% is the ltered image, while 0% is the original, unltered image.
Use masks to aid keying eects
Garbage masks
Keying is rarely a one-step process. Although adding a keying lter is the rst step, there is
usually additional work that must be done to create a good key that retains detail around the
edge of your subject. You can use the mask tools and alpha channel lters presented in this
section to turn a decent key into a great one.
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