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Chroma Key - Not How but How Much

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Mark Carrara
Chroma Key - Not How but How Much
on Feb 14, 2008 at 5:03:01 pm

I work for a school District and we want to create a green screen (chroma key) studio for our applied video class. We are starting with an empty classroom, no lights so we can go with any lights we need (of course money is a big deal). We do not need full length shots, mainly knees up standing or sitting behind a desk.

Here is my thoughts on layout, a 8ft tall by 12ft wide screen, painted chroma green (Rosco paint). Hanging from the ceiling , 4ft in front of the screen will be a bank of lights pointing down at a 45degree angle. I would like to go with fluorescents for several reasons. Because we are a school building our own lights would add to the educational experience, plus it is less expensive.

In reading posts two points come out - light it evenly and not too much light. Lighting it evenly seems to be the easy task, as has been suggested check on a waveform monitor. Now after all of that preliminary stuff the question.

How much light is enough? Is there a rule of thumb as to the number of lumens or lux or whatever we need to properly light a screen for a good key?

Mark


Mark Carrara
Technology Coordinator
School District of Gilman
Gilman, WI


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Vincent Becquiot
Re: Chroma Key - Not How but How Much
on Feb 14, 2008 at 5:35:05 pm

I usually try to keep the screen at around 40-45 IREs, after proper exposure on the talent. That should give you a more saturated green and less spill.

Vince



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Carey Harrison
Re: Chroma Key - Not How but How Much
on Feb 14, 2008 at 9:32:54 pm

Hi Mark,
Sounds like you have a good plan. I rewired a few 2' x 4' drop ceiling flo fixtures for our green screen (wall) and they work quite well. The light is soft and even and well within my budget. Make sure that the ballasts don't "flicker" and you'll be fine. I will light just a bit hotter than Vince (50-55 IRE) but the goal , as he stated, is good saturation without too much spill. Good Luck!

CH

http://www.nightglassimagecenter.com/

http://www.lightsandcameras.com/


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