Instruction Manual

Chapter 13 Keying 508
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Screen: Superimposes lighter portions of the background layer over wrapped areas of the
keyed foreground layer. Good for creating an aggressive light wrap eect.
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Overlay: Combines the background layer with the wrapped areas of the keyed foreground
layer so overlapping dark portions become darker, light portions become lighter, and colors
become intensied.
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Hard Light: Acts like the Overlay composite mode, except that colors become muted.
Additional controls
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Preserve RGB: Select this checkbox to preserve smooth graphics and text. Some images may be
rendered as if they have an alpha channel, even though they don’t. A good example is white
text on a black background. Rasterized text in most images is antialiased properly, and further
modication to the RGB channels by the Luma Keyer can degrade the quality of the edges.
Selecting the Preserve RGB checkbox adds transparency to the image without modifying the
RGB channels, leaving smoothly aliased text or graphics visually intact.
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Mix: Use this slider to set the percentage of the original image to be blended with the keyed
image. 100% is the fully keyed image, while 0% is the original, unkeyed image.
Keying renement lters
Matte Magic
The Matte Magic lter lets you manipulate the edges of a matte by shrinking, feathering, and
eroding them to improve dicult keys. The Keyer and Luma Keyer lters have much of the same
functionality. Matte Magic is a renement lter to let you manipulate mattes you create via
other means.
Parameters in the Inspector
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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.
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Feather: Use this slider to blur the keyed matte, softening the edges by a uniform amount.
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Erode: Drag this slider to the right to gradually increase transparency from the edge of the
solid portion of the key inward.
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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.
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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.
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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.
67% resize factor