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Keys
Keys
A key is an effect in which parts of one picture are inserted into
another to create a composite picture. For example, keys are used
to insert captions, to place a small news scene or graphic over the
shoulder of a newscaster, or to place the image of a weather
reporter in front of a weather map. There are several types of keys,
each of which serves a different purpose. These will be briefly
described on the following pages.
Luminance Key
A luminance key, shown in Figure 3-3, uses the brightness
information in one picture, called the key source to cut a hole in
another picture, called the background. A third picture, called the
fill, is inserted into the hole to fill it. A clip control allows the
operator to set the level of key source brightness that will cut the
hole so that any part of the picture that is lower in brightness than
the clip setting is ignored and will not cut the hole. The operator
can also invert the key so that dark areas of the source cut the hole
instead of bright areas.
GVG
News
GVG
News
Key Source
Fill Video
Background with Key and Fill Inserted
Figure 3-3. Luminance Key Example