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The Circle Effect In Chroma Keying

The circle effect in chroma keying is a technical technique that is used in digital video editing programs. It is used to double a person or with various other objects that are filmed on a green screen. The basic idea of the circle effect is that you are flipping video layers while green screened subject are moving to make them circle each other and pass seamlessly with no visible video distortion. How it works on a basic level is it requires three video clips layered on top of each other. The first clip on the bottom layer is the background image. The next two layers are on top of that. The clip on second layer has subject A and the clip on the third layer has subject B. A is on the left side of the screen and B is on the right side of the screen. A and B start moving to pass each other and switch sides. Subject A passed on top of Subject B. Now what the video editor will do is make a cut to the video clips and switch them from the second to third layers and vice versa. Now when subjects A and B go to pass each other, Subject B will be on the top. This effect can be repeated infinitely or with multiple other subjects.

Apple Computer, Final Cut Pro User’s Manual: Inc., Cupertino, CA. 1999