Grass Valley Kalypso User Manual V.15.0 - Manual (Page 79)

Kalypso — User Manual 79
Keying
those with higher key priorities. The backgrounds always have the lowest
priority. Changes in key priority can be included as a part of a transition.
Like any other transition, the current stack will transition to the key priority
of the next stack. For example, suppose the current stack has Keys 1, 2, and
3 in that key priority order over Background A, and the next stack specifies
key priority order 3, 2, 1. A mix transition will occur between the 1, 2, 3
composite order to the 3, 2, 1 composite order. All three keys will remain
fully keyed over the background, and will mix to their new key priority
order.
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 Kalypso system supports the following types of keys:
• Linear Key (fixed and adjustable)
• Luminance Key
• Preset Pattern
• Chroma Key (option)
The Kalypso 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