GRASS VALLEY 1200, Installation And Service

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3-8
Section 3 Ñ Functional Description
Scaling
All of the key, video, and control signals must go Òfrom black to whiteÓ
when the signals are sent outside the switcher. Internally the signals are
scaled down. Each place where these signals are sent outside there is a
Scaling circuit to modify the signals appropriately.
Shaped and Unshaped Video
Shaped video is video that has been multiplied by a key signal to create a
partial-raster image that is matted over black. A good example of shaped
video is the fill video output of some character generators, which consists
of characters on a black matte. Typically, the shaped fill video is also
accompanied by a matching key signal that may be used in a keyer to cut a
hole in background video into which the already-shaped fill video may be
inserted.
The 1200 configuration menus ask you to identify video inputs as shaped
or unshaped because the switcher handles those two types of fill video
signals differently. For keying with shaped fill video, the keyer multiplies
only the background video with the key signal to cut a hole in the
background, and then adds the already-shaped fill video into the hole. For
fill video that is not already shaped, the keyer first multiplies both the
background and the fill video with the key to cut a hole in the background
and shape the fill to match the hole. Then the background video and the fill
video are added together to create the finished key.
If you incorrectly identify the type of fill video in the Define Inputs
configuration menu, selecting shaped when you should select unshaped or
vice versa, your keys will have dark lines at the edges or other artifacts.
Changing the video type in the Define Inputs configuration menu will
correct the problem.