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Difference

This node produces the difference between two images as a matte. It takes two inputs:

• input B contains the subject with the background, and

• input A contains the background without the subject (a clean plate).

You can use this node to produce a rough matte for a moving subject shot in front of a static background, for example. However, because of lighting discrepancies, grain, and tiny movements of the camera or background, you may need to use other nodes to refine the results.

Inputs and Controls

Connection Type	Connection Name	Function
Input	A	The background without the subject (a clean plate).
	B	The subject with the background.

Control (UI)	Knob (Scripting)	Default Value	Function
Difference Tab
offset	offset	0	Subtract this value from each pixel of the output.
gain	gain	1	Any pixels that are white are set to this color.
output	output	enabled	Enables the associated output channel to the right. Disabling this checkbox is the same as setting the channel to none.
		rgba.alpha	Render the resulting image into this output channel.