GRASS VALLEY zodiak, User Manual

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Zodiak User Manual 49
Keying
Clip and Gain
The Clip and Gain operation selects a threshold of the selected key cut
video that will be used to cut the hole in the background video. Clip con-
trols the threshold, and Gain controls the softness of the key edges and any
translucent areas. High portions of the key cut signal specifies what video
is retained, and low portions determine what video is removed. Interme-
diate levels specify a soft blend of the background and fill video
(
Figure 16 ).
Figure 16. Key Clip, Gain, and Key Control Signal
Clip and Gain control is appropriate for high gain keys (see below), to
easily adjust where the relatively hard transition from background to fill
occurs. In this mode, changing the Clip control moves the threshold up and
down without affecting Gain, which is adjusted separately with its own
Gain control.
High Gain, Low Gain, and Unity Gain
A high gain key has a narrow range, creating harder key edges. A low gain
key has a wider range, creating softer key edges. Linear keys typically use
minimal gain (also called unity gain) to completely preserve the soft edges
of the keys (
Figure 17 ). Note that the Zodiak system also supports keys that
go below unity gain.
Figure 17. Keying Gain Values
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Key Cut
Signal
Key Control
Signal
Key Control
Signal
Inverted
(Hole Cutter)
Video
Retained
Mix of
Background
and Fill Video
Video
Removed
Background Video
Removd
Background Video
Retained
Clip
Gain
0
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High Gain Low Gain
Clip
Gain
Gain
Gain
Clip
Unity Gain
Clip