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Basic Green Screen Question

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Tara Sennott
Basic Green Screen Question
on Feb 2, 2016 at 4:10:33 am


I'm building a set out of theater flats, and one of the flats will have a window in it. I'm hoping to put a green screen behind the window so I can later add some stock footage. We will be shooting with a steadicam in this space so the cameras angle to the green screen will be changing constantly. Someone told me this will cause problems when trying to add the footage in post?

How can I take the right precautions of setting up the green screen and lighting it correctly so that I won't have any issues in post? I've attached an image of what I'd like it to look like in post. (Note: walls in the room are green so I'll be using a blue screen)

Thanks to anyone who can help me out!

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Tudor "Ted" Jelescu
Re: Basic Green Screen Question
on Feb 2, 2016 at 8:11:15 am

No pic attached- without seeing it though I can suggest you make sure you can get some good track points and then you can use AE's 3d camera tracker to get a camera solve and use that to comp in your footage. For a more realistic result though I would break your background in several layers and set them in 3d space to get parallax

Tudor "Ted" Jelescu
Senior VFX Artist

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Kalle Kannisto
Re: Basic Green Screen Question
on Feb 2, 2016 at 10:51:34 am

I'm afraid the biggest issue in post is going to be the time you're going to be spending on this one thing. It can turn out to be much longer than the time you'll spend editing the piece. For a realistic result you'll have to 3D camera track the steadycam shots and like Ted suggests, use several layers for the view out the window. Just camera tracking the footage can take days and days.

If this is a long piece, I'd look for a practical solution, i.e. actually putting something behind the window, or having it covered up with curtains for the most part and then only use the blue-screened view when absolutely necessary. It will save possibly hundreds of hours in trying to make a believable view out the window if it is frequently in frame.

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Jon Doughtie
Re: Basic Green Screen Question
on Feb 2, 2016 at 10:05:09 pm

What Kalle said. If it is possible, a practical solution will likely be much less painful in the long run than an AE-tracked solution, assuming your window is purely background and not scene-critical.

If what you see out the window is scene-critical, then be patient; it will take some extra effort to get the desired result.

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Tara Sennott
Re: Basic Green Screen Question
on Feb 5, 2016 at 11:43:48 pm

Thanks for your response.

Here is the image:

I'm not sure if this would change your response...but if I didn't want the green screen to have a realistic look, and wanted it to look sort of cheesy then would I have to do all this more complicated stuff?

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Spencer Tweed
Re: Basic Green Screen Question
on Feb 3, 2016 at 2:11:44 am

It depends what you want to put out there and how featured your window is. I've gotten away with making sure your blue screen is as far away from the window as possible and than adding some tracking markers in a few horizontal rows (try black gaff tape, or anything else that will be nice and visible in camera but not too large on screen). Depending on the shot you might not need much parallax and just tracking the points could be enough. Keeping your blue screen far away also minimizes spill on your set.

As an additional suggestion make sure you actually have glass or plexi in there - you can use the real reflections to your advantage and key through them with what we call a "soft matte" (basically just don't key your footage all the way through, but spill suppress the hell out of it).

If the window is close to camera and your steadicam is going all over the place then you will need to do a 3D track as the other guys have suggested. For this I still suggest putting your blue screen as far back as you can, then add a few c-stands with bright tape or trackers on the ends of them at different depths outside your window (assuming the window is quite large in frame) this can help with your track if you don't mind the additional roto/paint cleanup you'll have to do.

Hope some of that helps! It would be good to see a still.

- Spencer

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