5

• Edge Distance: Use this slider to adjust how close to the edge of your keyed subject
the effect of the Fill Holes parameter gets. Reducing this parameter brings the solid,
nontransparent area of the matte closer to the edge of the subject being keyed,
sacrificing translucence at the edges in favor of filling unwanted holes at the edge of
the keyed subject, or retrieving areas of semitransparent detail, such as hair, smoke, or
reflections. Raising this parameter pushes the filled area of the matte further to the
interior of the subject, away from the edges, adding translucence to regions of the
image that aren’t being keyed aggressively enough. Raising this parameter too much
can introduce regions of unwanted translucence in parts of the subject that should be
solid.
• 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.
• 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 and apply Parameter behaviors to 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.
• 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 to the right to increase edge transparency from the outer edge
of the matte progressively further into the interior of the keyed matte.
Light Wrap: Click the disclosure triangle in the Light Wrap row to reveal controls for
blending color and lightness values from the background layer of your composite with
the keyed foreground layer. Using these controls, you can simulate the interaction of
environmental lighting with the keyed subject, making it appear as if background light
wraps around the edges of a subject.
In Motion, the Light Wrap operation blends light and dark values from the background
with the edges of the keyed foreground subject, and can be used to create color mixing
effects around the edges of the solid part of a key to better marry the background and
foreground layers of your keyed composite.
662 Chapter 13 Keying