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Old February 26th, 2008, 07:50 AM   #1
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Green screen gels

I just read the "buying green screen link" but let me ask the stupid question. Can a green screen be created by just adding green gels to normal 3200 lights, well diffused and flagged off talent?
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Old February 26th, 2008, 10:38 AM   #2
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I think it's technically possible but probably not too practical. The closest I've heard to somebody doing that was a guy who made a green file in Photoshop and ran it through a video projector mounted overhead high enough to light a screen and not get on the talent. Seems to me a bucket of paint is much easier.
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Old February 26th, 2008, 12:16 PM   #3
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with a gray ( darker is better ), not white background, its technically possible but not worth the time and effort. gray or even close to black will get you more color saturation.

go give filmtools.com a call. they have raw green and blue fabric 60" wide for $15/yard. I bought 2 yards for $30. I'll tape it to a wall and it works great for talking head seated shots, or knees up standing shots. I also have a real 8X8 green screen as well, but this bit of fabric travels well and costs next to nothing. very handy to have. I can also set up the 8X8, and put this piece on the floor. when it gets dirty, I can try to wash it, or just toss it and get another piece.
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Old February 29th, 2008, 11:20 AM   #4
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I use colored gels all the time to turn white cyc cloth into a blue or green screen. The issues are that fresnels hotspot, which means that the color temp is different in the middle of the light than the outer umbra. Cyc lights also can hotspot and if you have enough distance and diffusion the amount of light tends to fall off and get darker as the distance from lamp increases.

It is better to have a colored background lighted with a soft source and I have have seen great results with a chroma key green background lighted by kino green fluorescent lamps.
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Old February 29th, 2008, 11:31 PM   #5
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just because you can make a color TV from a coke bottle and some paper clips doesn't mean you should, or that it will be a good TV. Sure you can tint a white BG wall with gels, but you have to flag all your keys and fills like crazy to keep saturation. a medium gray works far better, but in the end, its not a practical, reliable, or repeatble way of doing _keys_ when you can get a hunk of real green or blue fabric for $30 (60X72inches) which will work vastly better. right tool for the job.
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Old March 1st, 2008, 01:44 AM   #6
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I hauled along my laptop with DVRack HD to a studio greenscreen shoot this morning, it was a real green surface in a 12x12 frame lit with kino-flos with the green tubes.

What a pleasure to bring up the vectorscope and see a single spike of green, no other colors.

That's really the point. There's all kinds of ways to get green, but having red and blue components reflected off the screen just make the post keying that much harder.

Of course many of us have lit less than perfect screens and gotten away with it, sometimes requiring significant post work. But it's risky - one day you'll find you can't cut the key to your satisfaction.

If you look at the spectral transmission charts available at rosco.com for their green gels, you'll see that green is not only green, some red and blue do get through. Reflecting that off a white surface will give you extra colors that you don't want.

I'd done a series of keys in broad daylight with a pretty good screen with decent results. Once it didn't key well at all - it took me a few minutes to figure out that there was a nearby tree with green foliage that must have been putting green light on my subject - never saw it with the eye or in the viewfinder.

How good is good enough? Only you can decide that. What's written in this thread is more of a "best practices" than hard and fast rules.
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Old March 1st, 2008, 07:11 PM   #7
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[QUOTE=Seth Bloombaum;835672]<EDIT>, it was a real green surface in a 12x12 frame lit with kino-flos with the green tubes.

What a pleasure to bring up the vectorscope and see a single spike of green, no other colors.>>>

Yup, that is exactly my experience Seth. It is a great rig for closeups and medium shots. But a frame does not work with full body shots when the talent is moving around. For that you really need a BIG chroma colored cove cyc.

The right tools make it easier, but sometimes people on these boards cannot afford the right tools and do have to use rubber bands, tape and gum. You can pull keys lighting a white cloth/wall using colored gels if you cannot afford the right tools, but it certainly isn't my first choice.
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