Datavideo TVS-1000 Instruction Manual page 51

The Show alpha matte view
The intended result is to make the mask background colour as close to perfect black as possible.
In order to do that the Black Level slider should be moved until black is distributed as evenly as
possible on the mask background.
A view after a Black level adjustment
If the slider is moved to the extremes, the other objects will lose their properties and become
non-transparent; this is why the function should be applied sparingly so that small differences
are still discernible in the distribution of the black background.
The next step is to obtain a uniform distribution of white on objects which will remain fully non-
transparent. This uneven distribution may arise from the fact that the colours of the object may
have colour components close to the keying colour. In this case an adjustment can be made using
the function known as White Level.
By moving the slider from the maximum value to the left, you can obtain a perfect distribution of
white on a given object.
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