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The Art of Green Screen Lighting


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#1 Simon Bjork

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Posted 11 May 2009 - 03:50 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...


Floor

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?


(this is a repost from the lighting forum, I felt like it belonged here more. Maybe delete the other one?)
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#2 Scott Fritzshall

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Posted 11 May 2009 - 02:01 PM

One good technique I've heard for doing floors is to have some sort of mirrored surface that the actors stand on; this reflects the greenscreen down to their feet without needing to be lit, and plus you can get the actors' reflections if you need that. Most of the time, though, when people are doing keying on the floors, they just lay down some crappy blue or greenscreen fabric and don't even bother to light it differently. You're probably going to have to rotoscope everything from the waist down regardless, so I don't even know if it's worth the worry.

Lighting-wise, frankly if you're putting a lot of effort into it you're in the minority. Getting it evenly lit is the most important thing. I personally think that one stop under tends to be best, but I've heard people saying that one stop over is optimal for RED; I haven't used it yet though so I can't confirm or deny.
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#3 Stuart Brereton

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Posted 11 May 2009 - 04:39 PM

The most important factors in lighting green screen are that it is evenly lit in all areas that are behind the action, and that it is exposed so as to maximize saturation and minimize spill.
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#4 Saul Rodgar

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Posted 11 May 2009 - 09:57 PM

I prefer blue chroma than green. It gives me better results overall. I use daylight balanced fixtures with it and it is easier to deal with in post.
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#5 Will Earl

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Posted 12 May 2009 - 12:05 PM

One way I've seen which works well to cut down on spill is to flag off areas of the greenscreen which aren't actually being used - especially on big greenscreen stages spill is much more problematic from green that is being reflected from off to the side of the actor rather than from behind the actor. Obviously flagging off sections of green can be a problem if the actor decides to walk in front of a section of greenscreen that has been covered in black, so some thought does need to go into this. Also the time taken to flag off sections (especially on a large stage) needs to be taken into consideration.
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Visual Products

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Broadcast Solutions Inc

Rig Wheels Passport

Glidecam