5

Before you adjust these controls, the graphs in the Chroma and Luma controls represent
ranges of color and luma in the image that have been automatically and manually sampled
(using the Refine Key tools and the Strength slider).
• Graph: Select one of two buttons to set how the adjustable graphs in the Chroma and
Luma controls are used to fine-tune a key:
• Scrub Boxes: Select this button to limit the Chroma and Luma controls to adjusting
softness (edge transparency) in the matte you are creating. In Scrub Boxes mode,
you cannot manually adjust tolerance (core transparency), which is determined by
the Keyer filter’s automatic sampling, plus any Sample Color selection boxes you’ve
added in the Canvas. To increase matte tolerance, add more Sample Color selection
boxes or adjust the Strength slider.)
• Manual: Select this button 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 then 0 before you switch into
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 inadvisable 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 afterwards if you feel it’s necessary
to refine your matte using the Chroma and Luma controls. However, after you switch
to Manual mode, do not switch back to Scrub Boxes mode. If you do, you may
experience unexpected combinations of additionally sampled and keyframed values
that might be difficult to control.
• 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.
644 Chapter 13 Keying