User Guide

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Effects
Creating a Luma Key
The luminance axis represents an image’s luminance values from black to white. The transpar-
ency axis represents transparency from opaque to totally transparent.
Initially an image is totally opaque (i.e. the curve is completely flat). In order to key, specify which
part of the image should be transparent (i.e. define a luminance value). Specify how soft the tran-
sition between opaque and transparent should be (i.e. the steepness of the curve between Point A
and Point B).Two points define the curve: Point B is defined by cutoff and foreground, Point A by
threshold and key transparency.
The settings for a simple luma key could be:
w Threshold = 80 (everything “lighter” than the value 80 is keyed)
w Cutoff = 78 (everything “darker” than 78 remains opaque).
Key Transparency defines how transparent the keyed area should be. Foreground defines the
transparency of the “unkeyed” area.
The luminance difference between the two points in the curve defines the hardness or softness of
the transition in between.
A value of 2 would create, for example, a hard transition. To soften it, either raise Threshold
(move Point A to the right) or reduce Cutoff (move Point B to the left).
To increase or decrease keying with both points simultaneously, drag the line between the points.
This maintains the transition softness and makes it easy to specify which part of the frame to key.
Luminance Key: a different image signal is superimposed over areas with
the same luminance