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3-15
Chroma Key
Chroma Key
A chroma key is a key in which a particular color that you select in
the background of a scene is detected and replaced with a new
background scene. This gives the illusion that foreground objects
are positioned in front of a new background. For example, the fill
video selected on the Key bus may be a weather reporter standing
in front of a blue wall, and the new background video may be a
weather map (Figure 3-3). The completed chroma key consists of
the weather map background where the blue wall used to be and
the reporter foreground fill everywhere else. This creates the
illusion that the reporter is standing in front of the weather map.
A convenient feature of the chroma keyer is automatic setup. This
feature sets up the key for you when you identify the background
color that you want to replace. You simply position a cursor over
the color using the joystick and press the
AUTO SETUP button in
the Chroma Key/Chroma Key Setup Menu. (On the Model 2200,
you can use the AUTO SETUP button on the Chroma Keyer
Subpanel.)In most cases, this function yields a very good chroma
key, which you can use as is or to fine tune as desired using the
Keyer controls and the Chroma Key Menu controls.
The chroma keyer includes background and foreground
suppression. Background suppression replaces the old
background color with black before adding in the new
background. This ensures that the old background color is
completely removed from the scene, resulting in a cleaner key.
Foreground suppression is essentially a second chroma keyer that
allows you to detect and remove the background color and its
variations that “splash” onto foreground objects, as sometimes
happens when the foreground object is placed near the
background. The detected foreground “splash” color is replaced
with a neutral color and luminance value that restores the natural
color of the foreground object.