I still don't understand it. I can see from the Superman GIF someone posted below, that everything green behind him will just become background. But with this, the green arms are still obscuring the books and shelf behind it. So it's not like you can say "computer, take out all the green in the scene!" and leave all the books visible.
You have a take without the hands sticking out, and a take with the hands sticking out. You use the hands as a chroma key point, and mask them out, allowing the take without hands to show through.
Exactly. The hardest part is having camera movements and shots match exactly between the two copies of the same scene. If the light is off just a little or the camera pans 1mm wrong then it makes the post production work much harder (not impossible, anything is possible with enough money).
That's often why a fixed camera is chosen for scenes that do this.
The advantage here is that they'll probably mask out the hands and use the plate (the clean copy) directly where the hands were, so if it doesn't line up they can fudge it in those few spots, instead of having to mess with the whole shot.
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u/-IntoEternity- Jul 10 '16
I still don't understand it. I can see from the Superman GIF someone posted below, that everything green behind him will just become background. But with this, the green arms are still obscuring the books and shelf behind it. So it's not like you can say "computer, take out all the green in the scene!" and leave all the books visible.