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Green Screen outdoors?

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William Mims
Green Screen outdoors?
on Aug 25, 2009 at 1:44:26 pm

The first "Hollywood" studios were sets outside because the only way to get enough light was to use the sun. In using green screen, the problem is always getting the key light direction to match the lighting of the intended background. Has anyone tried placing a green screen outdoors and matching the sun direction that way?

Mims


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Emre Tufekci S.O.A.
Re: Green Screen outdoors?
on Aug 25, 2009 at 2:34:07 pm

We have used green screen outside but it was not for keying out the background using a luminance or chroma matte but as a separator for rotoscoping/tracking software (like mocha). This assisted us in getting tracking mattes that we used to key out the backgrounds. It is difficult to shoot outdoors keying as the light changes so will your matte.

This helped us match the lighting elements of the sun as there were a lot of practical effects used on the outdoor set.

Here is a better example of outdoor green screen and keying. Not for the faint of heart. :)

http://www.studiodaily.com/main/technique/casestudies/6503.html

I hope this helps.

Emre Tufekci
http://www.productionpit.com



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Robin Probyn
Re: Green Screen outdoors?
on Aug 26, 2009 at 11:16:15 am

Watch out for the wind too.. if its a big screen..you,ll need some serious stands.. weights etc



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Steven Bradford
Re: Green Screen outdoors?
on Aug 26, 2009 at 6:11:20 pm

This is a standard technique. It has great advantages and some big disadvantages. It was used for Star Wars in the death star trench scene, and also I believe in parts of the speedbike scene through the trees in Return of the Jedi.

Anyways, it's great for when you need to match sunlit backgrounds. It's fantastic for doing model work of spacecraft, particularly larger models, as it's can be difficult to get that perfect sharp shadow parallel source effect in the studio.

It's also great because it's really easy to get a perfectly even illumination on the screen, that's the same intensity as on the talent. piece of cake really.

If your purpose is not to match sun shadows, it's also great to to it on an overcast day. Or, use the sun as the back light and use the sky as your key on both the background and the talent. I did this once when I had to composite horses against a background. To take the rimlight down, we raised a large full scrim net behind the screen to drop the rimlight down a stop.

The problems, and why this isn't done all the time, are pretty much the same for any outdoor shoot-- the sun moves, weather, and audio problems.

Steven Bradford
http://www.3dstereomedia.com 3D company I've worked with since 1990
http://www.seanet.com/~bradford/ my personal home page, find my greenscreen page there.
http://www.seattlefilminstitute.com the school I teach at.


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William Mims
Re: Green Screen outdoors?
on Aug 27, 2009 at 2:30:48 am

Steven: Thanks, most encouraging and I found your NASA video quite delightful. I am sure you had a lot of fun doing it. I have done stage green screen in L.A. but not outside. In the same vein: I have a feature film to do later and I need a TV station control room b.g. plate if anyone knows of a b.g. plate I could use. There are some out there but they are pretty cheezy.

Mims


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Rick Amundson
Re: Green Screen outdoors?
on Aug 27, 2009 at 2:29:23 pm

I have done numerous green screen shoots both indoors and outdoors and I agree with what has been said by the others. Another good source to learn more about green screen work is the Visual Effects for Directors series from Hollywood Camera Work.

http://www.hollywoodcamerawork.us/index.html

As I said, having done chromakey work for years, I was happy to learn a few new tricks from this series.

Best of luck!

Best of luck!

Rick Amundson
Producer/Director/DP
Screenscape Studios
Bravo Romeo Entertainment
http://www.screenscapestudios.com
http://www.bravoromeo.com
http://www.indeliblemovie.com


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Alan Lloyd
Re: Green Screen outdoors?
on Aug 27, 2009 at 2:14:10 pm

It looks like you're getting some good replies here, I just want to add one - with an example.







The outdoor greenscreen is at about 1:35. And yes, the sun is on the other side for the reverse - it's a no-budget labor of love for a few of us here in MN. (I was inside, doing the lighting for an indoor greenscreen setup for a different scene, while this sequence was being shot.)

It does, though, match the direction of the "sunlight" on the background plates.

They did manage to pull an OK key on both sequences, working off HDV - I think in FCP, though I'm not involved in the editing, I just light some of it.



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