THOMSON GRASS VALLEY KayakDD-1, User Manual

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KayakDD - Digital Production Switcher
2.10.1 Matte Fill Key Example
One of the earliest keying techniques was to use an art card and camera to perform a
luminance key with a matte fill. This type of key is a good example for explaining basic
keying principles because three separate and independent incoming signals are used.
To insert a green logo into background video, the logo can be printed in white on black
paper and a camera can be focused on it. The signal from the camera can be selected
as the key cut signal and green matte video can be selected as the key fill signal sent
to the keyer. The key cut signal is then adjusted (clipped) to ignore the black paper and
use only the white logo shape to cut a hole in the background video. The keyer then
shapes the key fill to precisely match the logo-shaped hole cut in the background and
fills it with green matte video. This creates a green logo inserted into the background
(
Figure 8 ). Because luminance values of the key cut signal are used to cut the hole in
the background this is called a luminance key.
Figure 8 Matte Fill Luminance Keying Example
In this keying discussion illustrations rather than actual screen images are used for
simplicity, and because the printing process has difficulty capturing the subtleties of
soft key edges.
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