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Mattes and masks are often used in graphic pipelines to create transitions, layouts, and more complex composites. Mask images are also used for projection and LED mapping. We can use this approach to create transitions between two images or videos.
We’ve already seen that we can mask elements with the Composite and Multiply TOPs. We can also use the Matte TOP for more control. We can think of the Matte TOP, which has three inputs, as having a behavior of the first input over the second input with the alpha of the third. A over B with the alpha of C.
Instead of the alpha channel of the third image, we might instead use the luminance of the matte image or any high contrast monochrome image.