Grass Valley Indigo AV Mixer v.1.2.2 - Manual (Page 50)

50 INDIGO AV Mixer User Manual
Section 5 — Basic Operation
Keying
Keying inserts a 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
• 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 fill. 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.
Key Control Signal Adjustment
During keying, the selected key cut signal can be converted into a key
control signal. It is the key control signal that actually cuts the hole in the
background video. Adjusting the key control signal (Clip and Gain) is
essential in the keying process. The art of setting up a good key is to use
just enough Gain to suppress any imperfections in the incoming key sig-
nals. Setting Gain too high can cause ragged key edges.
The INDIGO AV Mixer provides two methods for adjusting the key
control signal:
• Clip and Gain
• Cleanup and Density
Note that both of these methods control the same basic keying process.
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
controls the threshold, and Gain controls the softness of the key edges
and any translucent areas. High portions of the key cut signal specify
what video is retained, and low portions determine what video is
removed. Intermediate levels specify a soft blend of the background
and fill video.
Cleanup and Density
The Cleanup and Density operation influences only one end of the key
area and keeps the other one constant. Cleanup only influences the
background area. Key levels are increasingly limited to black, i.e.
”cleaned”. Noise and slight shadows in this area will disappear.
Density only influences the foreground area. Key levels are increas-
ingly limited to white to the unity value ”1”, which corresponds to the
”dense” foreground.