I am creating an overlay for a video clip. In the overlay, there will be a light emitting object. I want this light to affect the subject in the video, but not the entire surface of the video clip. My plan is to model the character in the clip and then render only the light hitting that model. I've not found a way to do so. Simpler version. I have a cube and a plane. The cube emits light. I only want the light to show on the plane and not the plane itself. I have tried for hours to no avail. Any ideas?

After reading the answers, I tried more and this is what I came up with. Pretty close. nodes Renders as: render

Difficult to show what I'm looking for without being able to do it.

  • $\begingroup$ Have you thought about baking a light on a plane as a texture and then using it as a factor between diffuse/emission and transparent shaders? $\endgroup$ – Paul Gonet Oct 14 '15 at 19:20

Depending on whether or not you plan on simulating the materials of the subject, perhaps a setup like this would work:

enter image description here

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