GRASS VALLEY zodiak, User Manual

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46 Zodiak User Manual
Section 2 — Concepts
Keying
Keying inserts part of one picture into another to create a composite pic-
ture. Keying involves three signals:
• Background,
• Key cut, used to specify where to cut a hole in the background, and
• Key fill, used to fill the hole in the background. The fill can be an
incoming video signal or it can be an internally generated matte.
A separate key cut input signal is not necessarily required for keying. For
example, a self key (also called a video key) uses the same input signal for
both key cut and key fill.
The Zodiak system supports the following types of keys:
• Linear Key (fixed and adjustable)
• Luminance Key
• Preset Pattern
• Chroma Key
The Zodiak system also supports self keys and split keys.
Matte Fill Key Example
One of the earliest keying techniques was to use an art card and camera to
perform a luminance key with a matte fill. This type of key is a good
example for explaining basic keying principles because three separate and
independent incoming signals are used.
To insert a green logo into background video, the logo can be printed in
white on black paper and a camera can be focused on it. The signal from the
camera can be selected as the key cut signal and green matte video can be
selected as the key fill signal sent to the keyer. The key cut signal is then
adjusted (clipped) to ignore the black paper and use only the white logo
shape to cut a hole in the background video. The keyer then shapes the key
fill to precisely match the logo-shaped hole cut in the background and fills