Instruction Manual

Chapter 13 Keying 506
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Luma Rollo: Use this slider to adjust the linearity of the fallo between the Luma control’s
tolerance and softness handles. Modifying this parameter changes the softness of the matte
around the edges in regions that are aected most by the Luma control. Decreasing the Luma
Rollo value makes the slope between the two handles of the Luma control more linear, which
visibly increases edge softness. Increasing this value makes the slope between the handles of
the Luma control steeper, sharpening the edges of the matte and making them more abrupt.
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View: Use these buttons to switch among three keying preview modes in the Canvas, useful
for rening your key.
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Composite: When selected, the leftmost button displays the nal composited image in the
Canvas, with the keyed foreground subject isolated against a transparent background, which
lets layers underneath show through.
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Matte: When selected, the middle button displays the grayscale matte, or alpha channel,
generated by the keying operation. Viewing the alpha channel lets you evaluate the parts of
the generated matte. Areas in the matte that appear white are visible in the nal composite;
areas that appear black are transparent; and areas with shades of gray are semitransparent
(lighter grays being more solid, and darker grays being more translucent). Viewing the alpha
channel makes it easier to spot unwanted holes in the key, or areas of the key that aren’t
transparent enough.
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Original: When selected, the rightmost button displays the original, unkeyed image in
the Canvas.
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 do not alter
the range of values sampled to create the keyed matte. Instead, they alter the matte generated
by the Luma and Luma Rollo controls, letting you shrink, expand, soften, or invert the matte to
achieve a better composite.
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Fill Holes: Use this slider to adjust solidity in regions of marginal transparency throughout a
key. This parameter is useful when you’re satised with the edges of your keyed matte but
have unwanted holes in the interior of the foreground subject that you can’t eliminate using
the Strength parameter without ruining edges. Higher slider values ll more holes in the solid
areas of the keyed subject.
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Edge Distance: Use this slider to adjust how close to the edge of your keyed subject the eect
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, sacricing translucence at the
edges in favor of lling unwanted holes at the edge of the keyed subject, or retrieving areas
of semitransparent detail, such as hair, smoke, or reections. Raising this parameter pushes
the lled 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.
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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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