Keying Refinement Filters
The Matte Magic and Spill Suppression filters help you refine composites that use transparency mattes to merge one image with another. The Keyer and Luma Keyer filters have much of this functionality. Matte Magic and Spill Suppression are refinement filters to let you manipulate mattes you create via other means.
Matte Magic
The Matte Magic filter lets you manipulate the edges of a matte by shrinking, feathering, and eroding them to improve difficult keys.
Parameters in the Inspector
Shrink: Use this slider to manipulate the contrast of the matte in a way that renders translucent regions of the keyed matte more translucent while shrinking the matte.
Feather: Use this slider to blur the keyed matte, softening the edges by a uniform amount.
Erode: Drag this slider to the right to gradually increase transparency from the edge of the solid portion of the key inward.
Levels: Use this grayscale gradient to alter the contrast of any matte or alpha channel, by dragging three handles that set the black point, white point, and bias (distribution of gray values between the black point and white point). Adjusting the contrast of a matte can be useful for manipulating translucent areas of the key to make them more solid (by lowering the white point) or more translucent (by raising the black point). Dragging the Bias handle right erodes translucent regions of the key, while dragging the Bias handle left makes translucent regions of the key more solid.
Black, White, Bias: Click the disclosure triangle in the Levels row to reveal sliders for the Black, White, and Bias parameters. These sliders, which mirror the settings of the Levels handles described above, allow you to keyframe the three Levels parameters (via the Add Keyframe button to the right of each slider). Keyframing the Black, White, and Bias parameters may yield a better key, one that adapts to changing blue screen or green screen conditions.
Mix: Use this slider to set the percentage of the original image to be blended with the filtered image. 100% is the filtered image, while 0% is the original, unfiltered image.
HUD Controls
The HUD contains the following controls: Shrink, Feather, and Erode.
Spill Suppression
When you key an image that was shot against a blue screen or green screen, some color will have reflected 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 difficult to eliminate from the foreground subject you’re trying to preserve.
Unlike the spill suppression controls found in the Keyer filter, which automatically neutralize the color being keyed, the Spill Suppressor filter 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 benefit 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 effect 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 reflection 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 filtered image. 100% is the filtered image, while 0% is the original, unfiltered image.
HUD Controls
The HUD contains the following controls: Color, Level, Tint, and Saturation.