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Blue/Green Screen Curiosity Question

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Blue/Green Screen Curiosity Question
on Aug 14, 2007 at 7:35:52 pm

There are a lot of people who present a lot of different ways to light a blue/green screen. I have found methods that work relatively well, but I had an idea that makes perfect sense (to me anyway). And why no one has ever mentioned it, I don't know.

What if you took 1 digital projector, or even two from either side and projected pure blue or pure green onto a large screen behind the subject? I would think that would be the most perfectly lit blue/green screen there could be. Any thoughts?

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Todd at Fantastic Plastic
Re: Blue/Green Screen Curiosity Question
on Aug 14, 2007 at 9:34:06 pm

That'd work in theory.

There was a television station here in town that years ago that would turn their neutral colored set background into a keyable background on the fly by flipping off their normal cyc lights and flipping on wallwashers that were heavily blue gelled. Same theory.

I would say the first issue that comes to mind would be to make sure you have a big enough stage space so that you can put your talent far enough away from the wall so you can totally light them independently (as the good Lord intended). If any spill from your talent lighting gets onto the background it's going to wash out your projected "key wall" to a degree.

What might be even cooler is if the projected key wall is REAR projected... that way you could line the axis of the projector up correctly so you don't get any keystoneing and therefore one side brighter than the other. But of course that would take even BIGGER stage space.

Perfect key or matte lighting certainly is an art. I'm constantly amazed at behind-the-scenes footage of big-budget motion pictures where you see a gigantic and high-ceiling stage with everything swathed in blue (or sometimes green)...and the darn thing is absolutely PERFECTLY evenly lit. Then again, those guys have a few more instruments to play with than most of us do.


Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.

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Vincent Becquiot
Re: Blue/Green Screen Curiosity Question
on Aug 18, 2007 at 4:11:55 am

I think the biggest issue there would be the bleeding on the subject. Of course that would depend on how bright the projector is, but the 6500 lumens we use on a regular basis on a rear fast fold sure washes walls around on that start up blue screen.


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Brian Lynn
Re: Blue/Green Screen Curiosity Question
on Aug 20, 2007 at 8:28:47 pm

Rear projection will not give a nice smooth color. Unless you have a very expensive Stuart rear screen, or a similar low-gain Da-Lite or something you will have a gradient color. Rear projection has an inherant "hot spot". If your projector uses a 0.8 lens this hot spot will be center of the screen itself. Most other lenses will place the hot spot at the lower edge of the screen. This also depends on the actual setup... its possible to "ceiling" the projector and move the hot spot to the top edge, or use "Lens Shift" to move the projected image more off center.

I have used a projector for what you would like to do. Your best bet is front projection, onto a surface large enough that your side-keystone won't matter. Place your projector far enough back that you will never see the edges of your keystone raster.

The other option is to overhead "ceiling" mount your projector on a crossbar or other rigging. This will allow you to shoot over your subject, will bounce ambient light into the floor first, and allow to you shoot your blue/green image squarely onto your key surface.

I hope that all makes sense!

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