Grass Valley LGK-3901 - Manual (Page 35)

GUIDE TO INSTALLATION AND OPERATION
LGK-3901/DSK-3901 | 29
4.8.5 Keying Parameters
The following Keying Parameters may be adjusted for both internal graphics (LGK-3901 only) and external graphics
(LGK-3901/DSK-3901).
4.8.5.1 Source
The Key source may be chosen from the following:
• Separate Key The key data is derived from the luminance content (Y value) of the separate Key.
• Self Key The key data is derived from the luminance content (Y value) of the Fill signal itself.
• None The key for an image is set to white so that there is no image transparency.
4.8.5.2 Clip, Gain and Transparency
Once the Key Source is selected, the Key signal is processed with Clip, Gain and Transparency to alter the mapping
between Key input luminance to Key output values. Transparency modifies the maximum key value as follows:
4.8.5.3 Type
Once the Key Output is generated, the Type controls the combining of the Background and Fill video signals. The
LGK-3901/DSK-3901 supports both Linear and Full keying types.
Linear keying is used where the Fill signal has been pre-computed to match the Key signal. In this case, the Fill has
already been cut by its own key external to the LGK-3901/DSK-3901. The card computes (1 - Key) and uses this to
“cut a hole” in the Background signal. The Fill is then simply added to this.