Spotlight Greenscreening?

B

BitterJester

Member
Let's say we're shooting in an apartment with flat, off-white walls. The walls are supposed to have fuzzy "holes" in them that fade in and out, revealing a different world behind the wall.

I wonder if we can achieve this effect by focusing some green lights on the flat wall, and dimming them in and out, with the intention of keying out the green in post.

Let's pretend there are no issues with light control or brightness, and we're able to cast a near-perfect circle of green light onto a flat wall. Would the dimming of the green light create the "fading hole" effect I'm hoping for? Does this sound like a good strategy? Are there smarter alternatives?
 
in principle it should work, greenscreening doesn't care how the green was created. Find a green gel spotlight and give it a try - as you've already guessed, light control or brightness will make or break it, I do worry that this technique would be even more susceptible to those problems than normal greenscreen.
 
If the wall is pretty homogeneous and you want just a hole, couldn't you just superimpose the hole later in post? Like make a mask in After Effects and fade the hole up and down per what your story needs? Green screen stuff might be unnecessary.

I don't know necessarily if you want to fade a green light to simulate holes. You might run into problems keying out the green when the light is nearly off.
 
I would take a shot of the wall with you rcamera. then greenscreen out the whole wall. The problem with your original ideas is that as the light "dims" it will move more toward black and away from "green" this will make it more difficult to key. It's be easier just to remove the whole wall and add it back in AE, then make holes in the wall using the pen -mask tool in AE
 
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