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597Final Cut Pro User Guide
• Luma: Drag the adjustable handles in this grayscale gradient to modify the isolated
range of the luma channel (the range of brightness and darkness) that also helps
define the keyed matte. The upper handles (which appear only in Manual mode)
adjust the tolerance (core transparency) of the luma channel’s contribution to
the key. The lower handles adjust the softness (edge transparency) of the luma
channel’s contribution to the key. The Graph mode governs which handles are
adjustable. In Scrub Boxes mode, you can adjust only the lower softness handles,
which modify the range of brightness and darkness affecting the edge transparency
of the matte. In Manual mode, you can also adjust the upper tolerance handles,
which modify core transparency within the luma channel of the matte. By default, the
slope of the left and right sides of the Luma graph has a slight “S” curve. You can
modify the shape of the curve by adjusting the Luma Rolloff slider (described below).
Note: The luma softness handles may extend past the outer boundaries of the
Luma control. This is due to the floating-point precision of the Keyer effect and is
expected. To reveal out-of-bounds handles and then move them, drag the slope line
of the Luma graph.
• Chroma Rolloff: Use this slider to adjust the linearity of the chroma rolloff slope
(displayed in the small graph to the left of the Chroma control). Chroma rolloff
modifies the softness of the matte around the edges of regions that are affected
most by the Chroma control. Lowering this value makes the slope of the graph more
linear, which softens the edges of the matte. Raising this value makes the slope of
the graph steeper, which sharpens the edges of the matte.
• 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.
• 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.