The Difference Matte effect creates transparency by comparing a source clip with a difference clip, and then keying out pixels in the source image that match both the position and color in the difference image. Typically, it’s used to key out a static background behind a moving object, which is then placed on a different background. Often the difference clip is simply a frame of background footage (before the moving object has entered the scene). For this reason, the Difference Matte Key effect is best used for scenes that have been shot with a stationary camera and an unmoving background.

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Difference Matte effect

A.

Original image

B.

Background image

C.

Image on second track

D.

Final composite image