The Difference tool lets you generate a matte image from two source images with the same background, but different foreground elements. This allows you to remove an image from one context and add it to another. You can even generate a composite image while creating the difference matte.
When you generate a difference matte, the difference between corresponding pixels of the two source images is calculated. The value of the pixel in the back image is subtracted from the value of the corresponding pixel in the front image, and the resulting value is used in the difference matte.
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.