Grass Valley Kayenne XL Package v.7.0.4 - Manual (Page 53)

Kayenne XL Package — User Manual 51
Keying
Chroma keys are performed by suppressing the backing color in the fore-
ground scene, cutting a hole in the background, and then combining the
two processed signals. When conditions are ideal, complete suppression of
the backing color is possible and the hole cut in the background will match
the suppressed foreground, permitting these two signals to be added suc-
cessfully.
This is called an additive chroma key (used when the system Foreground
Reshaping feature is off). When conditions do not permit adequate backing
color suppression, the foreground with its backing color suppressed can be
multiplied by the keying signal to prevent contaminating areas of the back-
ground outside the keyed area. This is called a multiplicative chroma key
(used when the system Foreground Reshaping feature is on). Setting up a
successful chroma key setup involves many more adjustments than other
keys. No amount of adjustment, however, can overcome problems caused
by an improperly set up studio chroma key scene.
Primary and Secondary Color Suppression
As described above, chroma key primary color suppression replaces the
old backing color with black before replacing it with the new background
video. It usually has a very low selectivity and therefore suppresses a wide
range of colors. The goal is to suppress as much of the backing color as pos-
sible without affecting foreground regions.
Secondary suppression is essentially a second chroma keyer that can be
used to deal with areas where the backing color passes through some trans-
lucent portion of the foreground object, like smoke or liquid. This also
includes hair since fine detail often mixes with the backing color. The goal
of secondary suppression is to restore the natural color of the foreground
object. In general, medium to high selectivity values will be used.
Primary and secondary suppression adjustments are used to select the hue
to be replaced and for adjusting the luminance and chrominance levels in
the areas of the picture where suppression is applied.
Flare Suppression
Flare suppression can be used to compensate for backing color reflected
onto foreground objects, or for lens flare (backing color reflections within
the camera lens). In these cases, the foreground object will take on a slight
greenish or bluish tint. Flare suppression subtracts a slight amount of the
primary suppression color from the foreground.
Chroma Key Shadow Generator
The Kayak HD system has a shadow generator that can be used to include
shadows that fall on the backing area of the scene in the background.