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green screen and purple lights

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Ted Rosean
green screen and purple lights
on Feb 20, 2008 at 8:28:33 pm

Hello all, my question refers to something I have seen on many DVD extras of movies where there is a lot of green screen. More specifically, while watching the behind the scenes features on movies like '300' or 'Sunshine', you are often able to see the green screen and the set before the background is composited in post. I've noticed, while watching these behind the scenes features, that there are also some purple lights that are illuminating the green screens, particularly around the edges or corners of the green screen. I was wondering if anyone had any insight on why there is purple light mixed in with the green light. My first thought is that it must help out some way with the keying, then I wondered if adding the purple light would key out differently depending on whether the scene was interior or exterior...but then why does adding a different color light to a green screen help key more color? Thank you.



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Bob Cole
Re: green screen and purple lights
on Feb 27, 2008 at 9:27:21 pm

Could these lights have been aimed at the subject, as a rim light to combat fringing, rather than the green screen?

Bob C

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John Fishback
Re: green screen and purple lights
on Feb 28, 2008 at 10:05:07 pm

Bob is right. If you look at a color wheel, purple is opposite of green. When used as a back light, purple reduces green fringing/spill on talent.

John

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Dennis Size
Re: green screen and purple lights
on Mar 3, 2008 at 3:54:29 am

Between the cameras shooting into the lights -- seeing the combination of red and green "sources" at the same time -- and the transmission/reception process, there is most assuredly a slight distortion of color perception. What you're seeing is the simple use of minus green color correction in the sidelights and backlights of the talent. This is a common technique used to counter the affects of the green bounce light hitting the talent to prevent their edge from tearing.

DS



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Ted Rosean
Re: green screen and purple lights
on Mar 5, 2008 at 4:26:32 pm

Hey, thanks for the responses. I guess now that I found a DVD of the movie, it was actually the blue screen that had the purple light on it, but I'm still confused as to why they would light it like that. I have captured the stills of what I am talking about, and would email them as attachments for anyone who wishes to see them and contemplate. I would post them here but I don't know how to put pictures up yet on the forum. My email is Theodore.Rosean@gmail.com .



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