Apple Motion 5.1.1 - Manual (Page 494)

Chapter 13 Keying 494
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Luma Rolloff: Use this slider to adjust the linearity of the luma rolloff slope (the ends of the
bell-shaped luma curve displayed in the Luma control). Luma rolloff modifies the softness of
the matte around the edges of regions that are affected most by the Luma control. Lowering
this value makes the slope between the upper and lower handles in the Luma control more
linear, which increases edge softness in the matte. Raising this value makes the slope steeper,
sharpening the edges of the matte and making them more abrupt.
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Fix Video: Select this checkbox to apply subpixel smoothing to the chroma components of the
image, reducing the jagged edges that result from keying compressed media using 4:2:0, 4:1:1,
or 4:2:2 chroma subsampling. Although selected by default, this checkbox can be deselected if
subpixel smoothing degrades the quality of your keys.
Matte Tools controls
Click the disclosure triangle in the Matte Tools row to reveal controls for post-processing the
transparency matte generated by the previous sets of parameters. These parameters don’t alter
the range of values sampled to create the keyed matte. Instead, they alter the matte generated
by the Keyer filter’s basic and advanced controls (the Color Selection parameter group), letting
you shrink, expand, soften, or invert the matte to achieve a better composite.
The Matte Tools group contains the following controls:
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Levels: Use this grayscale gradient to alter the contrast of the keyed matte, 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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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.
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Soften: Use this slider to blur the keyed matte, feathering the edges by a uniform amount.
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Erode: Drag this slider right to gradually increase transparency from the edge of the solid
portion of the key inward.
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