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Once and for all: GREEN SCREEN!


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#1 Simon Bjork

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Posted 08 May 2009 - 03:14 AM

Green screens, can't live with them, can't live without them.

People have problems with green screens every day. We hear from the compositors about green spill, too dark, too bright, wrong color of green, uneven screen and so on. All I ever hear about green screen is a compromise. Should have done this better, should have done that better. But we never do.

I thought we should collect our experiences in one post, so it would be easy to share problems and get good ideas.


Color

From tests we have done, it's clear that we pull the best key from a green-screen that's lit with Kino-Flos' and green tubes. The colour-range of the green becomes very narrow, and it's easy for i.e. Keylight to find a good key, especially in trouble areas like hair.

Tungsten doesn't give a good key at all, at least not with the RED-camera. The screen is no longer green, it's got reds and blues in it aswell. To avoid this you'd have to filter the camera or the lights with a blue filter to get it to around 5000K, with gives a pretty good key. Problem is you loose a stop or so in exposure.

HMI seem to give a good key as well, not as good as green tubes, but still good. Problem is that it's expensive.


Set-up

From my experience we seem to get the best screen when we hang Kini-Flos in a truss, pointing down to the screen. About eight or so i a row to get the entire 15 meter wide screen. From that you can get about 5.6 at 320 ASA. It's not completely even, but I think it would be possible to adjust them in another angle or attach a 1-bank or 2-bank under them in another angle. Any other ideas that has worked really well? We have been using a couple of HMIs with Chimeras as well, but compared to the kinos, it hasn't gotten the screen very even.

I guess 5.6 at the screen would be okey, even with a blue filter and even if your doing say 50fps. On a lens that is 2.2 or so, you could still have your screen one stop over as people seem to like. Is that even true from your experience?


Floor

Say we get the screen lit in a good way. Often people require to see the floor aswell. Here is were the problem starts. One thing the compositing programs likes is a screen lit with green tubes. One this the compositing programs doesn't like is to have two different types of green. Sure, it's no problem to pull two keys, one for the floor and one for the screen, but it is a problem with the fading area in between. So from what I have seen and heard, it might not be a good idea to use green tubes at the screen and say spacelights for the floor, as they produce different types of green. So what are our options then?

I'm basing everything of that you're using your ambient light for the scene to light the floor, I mean, how would you do it in any other way?

Light everything with spacelights, screen and floor. Problem is that you need a lot of spacelights to fill a studio, it takes a lot of power, and you'd have to use a blue filter to get a better key (at least with RED-camera, resulting in that you loose a stop, resulting that you need even more space lights). And do spacelights even look good?

Light everything with flourecents in the cealing, hundreds of them to produce a really soft light, for the ambience and for the floor. But will it give me a good enough exposue?

Bounce some big HMIs in a silk to get and even light for the floor.

Bounce with really big Tungsten to get an even light for the floor.

Use FinnLights.

This really seem to be the the hardest part...


Conclusion

I don't know. And it's frustrating. Is there any other types of lights you have used that seem to produce a good result? Both for the screen and for the floor.

Can it really be this hard?


(I know there are other posts about this, but it seemed like a good idea to write this in a new post. Please feel free to move it if it belongs somewhere else)
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#2 Arturo Querzoli

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Posted 18 February 2010 - 02:37 PM

Hey, this is a great topic and I think people should add info on it! Thank you for what's already posted, and be sure I'll add on as problems/ solutions come up;-)
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#3 David Desio

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Posted 24 February 2010 - 02:21 PM

I work on a green screen alot and I haven't tried the kino green bulb thing yet. What I use are a bunch of 1k cyc floods with 216 in each to get my cyc wall lit. Then I have 6 1k spacelights hung over the floor and a chicken coop built around them to keep'em from spilling everywhere. That gets me almost where I need to be. For the subject I light them completely seperate from everything else and try for them to be about 2 stops under the cyc. I like to use a bounced tungsten key, or daylight depending on what we're compositing, then 4'4bank kino for the fill, though recently I've been foregoing the fill light and using a white board to catch the spill from the key and give them a lift on the fill side. Then I use 2 arri 650 fresnels for the backlight, on on each side. To minimize spill I will cover most of the floor in cardboard and leave just enough room for the talent if we are seeing head to toe.

I've found that the light from the key will add luminance to the floor and while it may not be completely even, I have never had any trouble pulling a key. I know that you are supposed to try for absolute eveness in the green screen but sometimes time contraints get in the way of that.

What kind of problems did you have in the key whe you were all tungsten?

The main problems I've faced are noise in the blacks (Due to studio limitations I'm usually shooting at a 2.8/4 split) and dirty shadows under the feet.
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Glidecam

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The Slider

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Aerial Filmworks

Broadcast Solutions Inc

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rebotnix Technologies

Opal

Willys Widgets

Tai Audio

Gamma Ray Digital Inc