Nuke-Remove green screen

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Our teacher taught us how to use the smart nodes to snap the green screen.

1-Keylight (screen colour-absorbing green，screen gain Adjustment range size。view composite to check the result of background

2-IBKcolor(clean fg for main things,clean bg for bg colour)

3-Primatte

4-Constant node (absorbing background colour, merge node minus bg colour）merge divide