5

Luma keys are most effective when you’re keying a subject with a range of lightness
different from the area you’re turning transparent. For example, if you’re keying a black
background, the foreground subject should not have have deep shadows or dark areas
that might get keyed with the background. Generally speaking, shadows and highlights
in the image usually make this a difficult filter for pulling a perfect key.
Luma Keyer
The Luma Keyer filter appears to have similar controls to the Keyer filter. However, because
the Luma Keyer generates keys based on a simple range of lightness in an image, rather
than a range of color and lightness, its controls are simpler.
Parameters in the Inspector
Luma: Drag the handles of this grayscale gradient to adjust tolerance and softness in the
matte. When you first apply the Luma Keyer filter to an image layer in Motion, the Luma
control displays two handles: a Tolerance handle in the upper right, and a Softness handle
in the lower left.
Dragging the top handle to the left reveals a second tolerance handle. Together, these
handles define the range of image lightness used to define the core transparency of the
resulting matte. The range of lightness turned transparent is indicated by a checkerboard
pattern behind the gradient.
Two handles under the gradient define the softness, or edge transparency, of the key.
(The second softness handle may not be visible until you drag the two tolerance handles
left.) Dragging either of the lower softness handles further out and away from the upper
tolerance handles results in a key with softer edges. You can also drag the slope in the
graph to adjust the softness handles.
Invert: Select this checkbox to reverse which area is transparent and which is opaque.
660 Chapter 13 Keying