Grass Valley Kalypso User Manual V.15.0 - Manual (Page 81)

Kalypso — User Manual 81
Keying
the fill can be made black, shaping the video to match the hole before it is
summed with the background. Key fill video must be shaped using the key
cut signal actually used to create the hole in the background. Video shaped
with a different key cut signal will not key correctly.
The Kalypso system, as well as some external devices like DPMs, can also
divide a shaped video signal by its own key signal. The result is called
unshaped video. For optimum image quality, shaping and unshaping oper-
ations should be minimized. In general, devices should be installed and
configured in a manner that prevents them from having to unshape
incoming video just to reshape it again afterwards.
Specifying whether source signals are shaped or unshaped is part of the
Kalypso system configuration process (source definition). Properly shaped
video is an important aspect of keying. See Properly and Improperly Shaped
Video
on page 91 for more information.
Note that an unshaped signal viewed directly will show harsh edge arti-
facts due to dividing by a small number. This is normal and expected.
Keying this signal will clean up its appearance.
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 signals.
Setting Gain too high can cause ragged key edges.
The Kalypso system provides two methods for adjusting the key control
signal, Clip and Gain, and Clip Hi and Clip Lo. Note that the same basic
keying process is controlled by either of these methods.
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 con-
trols the threshold, and Gain controls the softness of the key edges and any
translucent areas. High portions of the key cut signal specifies what video
is retained, and low portions determine what video is removed. Interme-
diate levels specify a soft blend of the background and fill video
(
Figure 55 ).