Grass Valley XtenDD v.4.2.4 - Manual (Page 79)

2. Panel Operation
2 – 50 Operating Instructions – Rev. 1 / 7.2002
2.7.16 USING ADDITIVE OR LUMINANCE KEY
The operational modes Add and Luminance Key differ in the fading procedure.
In the luminance key mode, foreground and background are faded. In the add key
mode, the background is faded and the foreground is added to the background.
Key Fill Luminance Key
BGND
K
1 – K
Out
Key Fill
Add Key
BGND
1
1 – K
Out
Figure 201: Fading Procedure
When should Additive Key be used?
The additive key is used when the pattern (caption etc.) is available on a black
background or in the Split/Coupled Key mode, a separate key signal is available
which matches to the pattern (caption generator etc.) with respect to contour.
Since only the background is faded out at the place of the key signal with the exact
edge shape and the foreground signal is added to the faded background, both
signals fit without error into each other in the transition area. Precondition is that
the key signal is processed with gain factor 1 which is achieved by actuating the
Auto key with Add Key or max. ccw position of the Gain control. Under the above-
mentioned conditions, this key type leads to the best results. Key sources on black
backgrounds provide the best keying results.
Fill-Signal +[BGD x (1–Key)]
Key Signal
Fill Signal
BGD x (1–Key Signal)
Faded Background
Figure 202: Key Results with Additive Key