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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 directly lets you evaluate
the parts of the generated matte. Areas in the matte that appear white are visible in
the final 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).
Viewing the alpha channel makes it easier to spot unwanted holes in the key, or areas
of the key that aren’t transparent enough.
• Original: When selected, the rightmost button displays the original, unkeyed image in
the Canvas. This view is useful to sample colors from the original image.
Fill Holes: Use this slider adjust solidity in regions of marginal transparency throughout
a key. This parameter is useful when you’re satisfied with the edges of your keyed matte,
but you have unwanted holes in the interior of the foreground subject that you can’t
eliminate using the Strength parameter without ruining your edges. Higher slider values
fill more holes in the solid areas of the keyed subject.
Edge Distance: Use this slider to adjust how close to the edge of your keyed subject the
effect of the Fill Holes parameter gets. Decreasing this parameter brings the solid,
nontransparent area of the matte closer to the edge of the subject being keyed, sacrificing
translucence at the edges in favor of filling unwanted holes at the edge of the keyed
subject, or retrieving areas of semitransparent detail, such as hair, smoke, or reflections.
Increasing this parameter pushes the filled 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. Increasing this parameter too much may introduce
regions of unwanted translucence in parts of the subject that should be solid.
Spill Level: Use this slider to set how much spill suppression is applied to the keyed
subject. Spill suppression is a color correction that neutralizes the green or blue colored
light that often bounces off a green screen or blue screen background and tints the edges
of a subject during a shoot. Consequently, it becomes more difficult to separate the
foreground subject from the background during the keying process. Spill suppression is
applied when you add the Keyer filter.
With spill suppression
Without spill suppression
642 Chapter 13 Keying