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shooting green screen from inside a vehicle


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#1 William Fritzberg

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Posted 23 November 2006 - 04:51 PM

Hi,

I'm a film student at UBC and am doing a short which includes several surreal scenes using green screens and a bus. So far those i have talked have rommended placing the screen atleast ten feet away and lighting it equally. However, I am worried about window reflections and spill that might end up on our actor inside the bus. Also we will be shooting with dv.

any suggestions or advice?

william
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#2 Jamie Metzger

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Posted 23 November 2006 - 06:11 PM

Typical lighting for a greenscreen you need that kind of distance. Talk to a vfx person about this. You can get away with any kind of evenly lit material that isn't the same color as the person's outfit, expecially if they cross the screen.

If you are going to shoot "DV" shoot the highest quality of dv possible, like on a dvx (minimum) and an HVX 200 would be prime.
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#3 Albert Smith

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Posted 23 November 2006 - 07:11 PM

If you are shooting SD DV Video I would try as hard as you can to avoid using a greenscreen. It is damn near impossible to get a good key from DV footage, I'm not saying you cant, its just a lot of work and your deffinetly going to need some good third party software.I think if your going to have actuall windows in the bus and a screen behind those windows your going to have a big problem with reflections and just the light your putting something inbetween the camera and the greenscreen and its just going to make it even harder, A possibility would be to keep the shots static and then just mask out the windows in post thats not too hard to do but the shots need to be completly static then...or your going to be working frame by frame. but yea deffinetly set the screen back as far as you can from the bus to take away all the spill problems. Good luck, green screens are hell if you ask me haah, I hate the damn things.
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#4 craig aftanas

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Posted 24 November 2006 - 12:19 AM

are you worried about green spill on the action?

it was suggested to me the other day that adding a wiff of magenta to the back light would 'help' to cancel out any green spill on the action. might be a no brainer but it made me go 'oh yeah!'
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#5 Michael Collier

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Posted 24 November 2006 - 01:07 AM

With mini-DV be warry of using a high f-stop. The lens will go very soft when wide open. If you can get a waveform monitor I would recomend using it. If not you can go to serious magics site and download a test version of DV Rack, which will give you a makeshift waveform/vectrascope. The demo lasts about a month, and after that you can buy it if you want. That way you can accuratley set the greenscreens level (around 45 IRE with a consistent lighting). If your far enough away, the light in the bus should not affect the green.
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#6 David Cox

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Posted 24 November 2006 - 03:40 AM

DV (and HDV and HD-CAM) record only one quarter of the colour resolution (3:1:1) , so this makes it unsuitable for green screen work. The software doing the keying is basically using a low resolution image to generate the matte, and this leads to blocky edges and lost fine detail.

Just for your green screen shots, if you can get your images recorded onto something else it would give you an advantage. For example the panasonic P2 cards or a teathered digi beta recorder will record 4:2:2, so you will get double the colour info.

Other than that, make your green screen as flat and evenly lit as possible. A computer doesn't "know" the difference between variations in the green screen that you want to key out (shadows, folds, light fall off) and the ones you want to keep (reflections on the glass, foreground motion blur). The more even the green, the better your key.

David Cox
Baraka Post Production
www.baraka.co.uk
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