2011

Table Of Contents
The Difference tool contains the following parameters:
(a) Channels (b) Tolerance value fields for RGB channels (c) Softness fields for RGB
channels (d) Gain and Lift adjustment
The matte is created using Tolerance and Softness values. The Tolerance value
specifies the difference level that is considered black. A high Tolerance value
includes more black in the matte. The Softness value is used to soften the
transition between the light areas and the dark areas of the matte by adjusting
the amount of gray at its edges. Gray information is not included in the matte
when the Softness is zero. Use a high Softness value to increase the gray.
Choose one or more color channels to use for the difference matte, and then
set the tolerance, softness, gain and lift.
Extracting a Key Using the Luma Keyer
The Luma Keyer computes the luminance of the image and removes pixels
based on a threshold value, affecting the alpha channel. The softness value
can be added to set some fall-off for the key. When the softness is 0, only the
pixels that fall within the tolerance range are keyed out. The luminance keyer
can either output a matte or a pixel selection.
The Luma Keyer UI has four controls.
To:Use:
Select the luma or the color channel luminance that will be used to pull
a key.
Channel
518 | Chapter 22 Pulling Keys and Creating Mattes