Ever since posting my Natron mural tutorial, I’ve gotten lots of questions about the process of using the color channels of footage as an alpha channel. It can definitely be a confusing technique, especially if you’re new to compositing. I thought it’d be a good idea to make a short tutorial going over that process specifically.
Channel matte in Natron 
Luma matte in Blender
I did the same tutorial in both Natron and Blender, so whatever you’re more comfortable compositing in, you’re covered. Both videos are below.
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