GRASS VALLEY zodiak, Руководство пользователя

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Zodiak User Manual 47
Keying
it with green matte video. This creates a green logo inserted into the back-
ground (
Figure 15 ). Because luminance values of the key cut signal are
used to cut the hole in the background this is called a luminance key.
Figure 15. Matte Fill Luminance Keying Example
In this keying discussion illustrations rather than actual screen images are
used for simplicity, and because the printing process has difficulty cap-
turing the subtleties of soft key edges.
Shaping Video
In the matte key example above, the key fill signal was a full raster color
that did not match the shape of the key cut signal. This key fill signal is
accurately called non-shaped video, but may also be referred to as unshaped
video since both signal types are processed identically during keying.
Some external devices (e.g., character generators) provide a key cut signal
and an already processed companion key fill signal. A key fill signal that
correctly matches the key cut signal is called shaped video. During keying,
properly shaped key fill video can be summed with a background signal
(with a hole cut) and achieve the desired result. When the shaping is per-
formed by the source device, the Zodiak system can use a standard clip and
gain setting defined during system configuration to create the key cut
control signal, and so relieve the operator of having to adjust clip and gain
manually.
If a key fill does not match the hole in the background (like in the matte key
example above), the key fill needs to be shaped by the switcher. By multi-
plying the key fill signal with the key control signal the unwanted areas of
the fill can be made black, shaping the video to match the hole before it is
Key Cut
Key Fill
Background
Background with Matte Key Inserted
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