Tektronix Grass Valley 3000 - Manual (Page 117)

3-9
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.