Apple Final Cut Pro X (10.0.9) - Manual (Page 340)

Chapter 12 Keying and compositing 340
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Manual: Select to use the Chroma and Luma controls to adjust the softness (edge
transparency) and tolerance (core transparency) in the matte you are creating. Make sure the
Strength slider is set to a value greater than 0 before you switch to Manual mode; otherwise
the Chroma and Luma controls are disabled. When you switch to Manual mode, the Refine
Key tools and Strength slider become disabled, but samples you’ve made with those
controls continue to contribute to the matte.
Important: When you switch to Manual mode, it’s best not to switch back to Scrub Boxes
mode. For best results, begin keying an image using the Sample Color and Edges tools in
Scrub Boxes mode. Switch to Manual mode afterward if you feel it’s necessary to refine your
matte using the Chroma and Luma controls. However, if you switch back to Scrub Boxes mode,
you may experience unexpected combinations of additionally sampled and keyframed values
that might be difficult to control.
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Chroma: Drag the two graphs in this color wheel control to adjust the isolated range of hue
and saturation that help define the keyed matte. The selected mode governs which graphs
in the color wheel are adjustable. The outer graph controls the softness (edge transparency)
of the matte you’re creating, and can be adjusted in either Scrub Boxes or Manual mode. The
inner graph controls tolerance (core transparency), and is only adjustable when in Manual
mode. Drag any side of either graph to expand or contract the graph’s border, which adds to
or subtracts from the range of hue and saturation contributing to the key. In Manual mode,
you can also drag inside the tolerance graph to adjust its overall position in the color wheel.
To the left of the color wheel, a small graph displays the slope of chroma rolloff, the relative
softness of matte edges in regions most affected by the Chroma control. Dragging the Chroma
Rolloff slider (described below) modifies the shape of this slope.
Tip: It’s possible to zoom in to and pan around the Chroma control to more precisely adjust
the graphs. To zoom in to the Chroma control, move the pointer over the color wheel, and,
holding down the Z key, drag to the left to zoom out or to the right to zoom in. To pan in the
Chroma control, hold down the H key and drag in the color wheel in the direction you want
to move it. To reset the zoom and recenter the Chroma control, move the pointer over the
Chroma control and press Shift-Z.
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Luma: Drag the adjustable handles in this grayscale gradient to modify the isolated range
of the luma channel (the range of lightness 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 lightness 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 behavior. To
reveal and move out-of-bounds handles, drag the slope line of the Luma graph.
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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.