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Another mixing light question: this time for green screen

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Fernando Mol
Another mixing light question: this time for green screen
on Jan 29, 2010 at 11:26:32 pm

Hi,

I'll have to do some head shots with green screen. I own two set of lights that I use depending on the shooting. Photo flood lamps (with 3200 bulbs right now) and a kit of three fluorescent daylight lamps.

I have made some green screen in the past, but I was wondering if (by any chance) does anyone have illuminated a green screen and a subject with different color temperatures before.

I know I can just go and buy some daylight photo floods or some 3200 fluorescent lights to make them all even, but the idea came to me and... well, here I am making my question.

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Bill Davis
Re: Another mixing light question: this time for green screen
on Jan 29, 2010 at 11:44:39 pm

Fernando,

If you can keep most of the spill from the greenscreen OFF your talent, you should be fine. All your keyer cares about is that the GS lighting produces an even and consistent single color - no matter really, what that color is.

That leaves you lighting the subject with tungsten. Which has been done for decades.

The only issue you'll have is if, for example, your talent has a shiny cheek, or shiny black hair, or anything else which would reflect the GS background and cause a "carve out" to appear on the talent's outline. You can't blame the keyer for that - it's just keying what it "sees" as green.

This is why separation is so important. The more "forward" your talent is, the weaker the spill from the key background will be on the talent - as the light follows the inverse square rule and moving the talent from 2 feet in front of the background to 6 feet drops the spill intensity by a factor of 9. Moving the talent out from 2 feet to 8 feet drops that spill intensity by a factor of 16. More depth from camera to subject to GS will ALWAYS make for a better key right up to the distance where the log relationship makes further separation insignificant.



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Fernando Mol
Re: Another mixing light question: this time for green screen
on Jan 31, 2010 at 3:55:08 pm

Great advice.

Thank you, Bill

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Richard Crowley
Re: Another mixing light question: this time for green screen
on Feb 1, 2010 at 2:19:18 pm

Color temperature (and accuracy, "CRI" Color Rendering Index) are important for most lighting situations. But when you are lighting a chroma screen (green or blue), then neither temperature nor CRI are even factors to consider.

I have successfully used inexpensive "shop lights" from Home Depot for lighting green-screen. They are not suitable for general lighting because of their bad CRI, particularly their prominent green spike. But that same green spike becomes a benefit when lighting green screens (but not blue screens).


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