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green gels on lights for green screen shoots?

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Omar Torresola
green gels on lights for green screen shoots?
on Nov 23, 2011 at 8:44:57 am

A co worker in a production company has told me that the best DPs lit their green screen with green gels on the lights. He claims that putting green gels with daylight bulbs will produce a green-er background. Please help me settle this with some technical reasoning. I'm afraid I don't understand why would one method be superior than the other.


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Mark Suszko
Re: green gels on lights for green screen shoots?
on Nov 23, 2011 at 8:10:02 pm

Well, this topic has come up before, and there are two camps. My thinking is that while you might gain in color saturation by filtering the light, you lose more of the overall power of the light to cover a sufficient area evenly thru reducing overall output from the filtration.

Moreover, if you are shining green lights at a green wall, unless the light is perfectly even, you're creating two shades of green where the pigment on the wall overrides the colored light.

You also may get spill problems from gelled lights that you would not see from full spectrum lights.

The fact that I have never seen anybody else doing that also tells me something.


I once, for a lark, gelled a Lowel 1K with some heavy green and lit up a white wall with it, and then used that as a chromakey source in the field. It worked *okay*, but wasn't really as saturated as I needed, nor could it cover enough area evenly using just one light.

You know, the green doesn't have to be as bright as a neon sign on Broadway or Times Square. To work well it just has to be maybe a stop different from the talent and well-saturated, but most important of all, EVEN. I have keyed with the good Rosco chromakey paint that costs like it is made from Fabrege' Eggs, and I have pulled excellent keys from a plastic picnic table cover from the Dollar Store. Evenness was always the overriding factor.


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Todd Terry
Re: green gels on lights for green screen shoots?
on Nov 23, 2011 at 8:36:03 pm

[Mark Suszko] "The fact that I have never seen anybody else doing that also tells me something."

Yeah, I've only seen that done about once or twice ever. There's really not much point in it... if you have a true green background, it's really only reflecting the green portion of the light spectrum. If you gel a light green, then the instrument is only transmitting green... the same that's being reflected. It's not going to do much to make a truly green screen any "greener"... and just more likely to cause some spill issues if any of that light happens to stray anywhere it shouldn't.

Remember, a green gel doesn't "color" the light green, it just filters out everything that isn't green.

Much like Mark's experiment (although with blue), it was not uncommon on television newscast sets in the 1970s era to have a white or pale background flat what was washed with blue-gelled light for behind-the-anchors key graphics, back when that was in vogue. Those blue instruments would be turned on or off depending on whether it was a key shot. This was about the same era that you saw a lot of news backdrops that were a big montage of the television station's logo, but painted with two slightly different shades of blue paint. You used to see that ALL the time. Very "Action Newsish." Complete with Ron Burgundy.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Mark Suszko
Re: green gels on lights for green screen shoots?
on Nov 23, 2011 at 11:04:50 pm

Your Ron Burgundy mention brings to mind...

Trying to remember if it was WBBM TV Ch.2 sportscaster Johnny Morris or Maybe Bruce Roberts in Chicago, late 70's/ early 80's, that used to have the worst collection of wildly patterened polyester sportcoats, and he was always doing chromakey bits where part of the day's jacket would key through. The guys in the control room may have had to take up (more) drinking, trying to keep up with his coats and the keyer controls:-) I think they finally gave up keying him and put him at a desk:-)


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Steve Kownacki
Re: green gels on lights for green screen shoots?
on Nov 24, 2011 at 12:04:26 am

I've never heard of that but I have used complementary gels on the subject's backlight. See thread here http://mobi.creativecow.net/thread/47/858572. Better to incense the distance as Dennis stated.

Steve






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Steve Kownacki
Re: green gels on lights for green screen shoots?
on Nov 24, 2011 at 12:07:52 am

That's increase the distance. Incense may help. Editing posts on my Droid2 doesn't recognize my password.

Steve






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Alan Lloyd
Re: green gels on lights for green screen shoots?
on Nov 24, 2011 at 7:38:14 pm

That was Bruce Roberts.


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Scott Sheriff
Re: green gels on lights for green screen shoots?
on Nov 24, 2011 at 4:47:38 am

My two cents
I spent a lot of time working broadcast in the analog era where chroma keys were not nearly as good as they are now, and you had to work real hard at it. I can tell you that in my experience there are a lot of things that go into pulling a good key, but colored gels in the cyc lights illuminating the CK wall ain't one of them. The green (or blue) doesn't have to be the perfect shade, or even be that heavily saturated, but evenness of illumination is the real secret. There are several reasons gels will make this more difficult, not easier. Offsetting colored gels on the backlights can sometimes help kill CK spill on the talent, but even that often introduces more problems then it solves.

Scott Sheriff
Director
http://www.sstdigitalmedia.com


"If you think it's expensive to hire a professional to do the job, wait until you hire an amateur." ---Red Adair

Where were you on 6/21?


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Mark D'Agostino
Re: green gels on lights for green screen shoots?
on Nov 29, 2011 at 4:49:26 pm

Now from the "minority" camp...We've been doing green screen work for many years, since Ultimatte v.3. A couple years ago we took the time to very carefully compare a green screen painted with Rosco paint and lit with "white" light and the same with green gels on the light. We indeed did see a difference in the ease of pulling a clean key and do choose to light with green gels now. However, we only do this on small green screen setups where we don't see floor and have enough room room for separation. We've also use magenta minusgreen gels on back lights.
Regardless of whether you choose to do this or not I agree that it is critical to light the screen evenly and at a proper level and using a quality green screen paint.

Mark D'Agostino
http://www.synergeticproductions.com


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Todd Terry
Re: green gels on lights for green screen shoots?
on Nov 29, 2011 at 5:35:32 pm

I'm surprised there was much of a difference, Mark. Ultimatte is so good it will usually pull razor sharp keys even with pretty dirty setups. But hey, whatever works best for ya!

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Bob Cole
Re: green gels on lights for green screen shoots?
on Dec 22, 2011 at 11:49:41 pm

I don't recommend green-gelled light sources, due to the danger that green light might hit your subject, which would affect your key. In fact I'd look at the green background as a potential source of green light and make sure your subject is far enough away, and the background is not over-lit.

Bob C


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Mark D'Agostino
Re: green gels on lights for green screen shoots?
on Dec 23, 2011 at 2:14:13 pm

I understand your concerns Bob but the issue of green spill is only a problem if the LD is sloppy and the screen is too close. I've never had that problem and the green gels have helped us pull keys easier. I do however only use this method on small green screens up to a medium shot...usually an interview.

Mark D'Agostino
http://www.synergeticproductions.com


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Bob Cole
Re: green gels on lights for green screen shoots?
on Dec 23, 2011 at 2:42:01 pm

I'm open to trying it. Which green gel do you use? I'm impressed that you limit its use to optimal conditions, minusgreen backlight. Light wants to go everywhere, which is why my first reaction was skepticism. Why exactly do you NOT use green gels on head-to-toe shots?


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Mark D'Agostino
Re: green gels on lights for green screen shoots?
on Dec 23, 2011 at 2:57:17 pm

After testing several we had best luck with Rosco's "Chroma Green" #389. What we found was the added green lowers the red channel giving more separation. If I had KinoFlos for this I'd probably use their green tubes in the fixtures for the same reason. I don't use gels for head-to-toe because then I'd definitely be splashing green gelled light on the feet. If I left the light on the floor surrounding the feet "white" then the floor green wouldn't match the background/wall green.
By the way, I use Rosco green paint in our studio, A Wescott green screen for small location shots and occasionally a giant roll of green photographer's paper backdrop when I want a seamless floor-to-wall screen on-location,(my least preferred).

Mark D'Agostino
http://www.synergeticproductions.com


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