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Green screen lighting


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#1 Jan Kielland

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Posted 29 August 2006 - 09:51 PM

Hi

I'm a unexperienced DP that is doing a short film. Half the film is going to be shot infront of green screen and I was hoping someone here could help me with the lighting. If I could light my actors similar to the way they did in Sin City that would be fantastic (allthough I know that might be hard).


How much light should I have on the green screen compared to on the actors?
Does anyone have any examples of their own set ups that they could show me?

The short will be shot on interlaced HD then de-interlaced for the green screen.


thanks
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#2 Brian Dzyak

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Posted 30 August 2006 - 12:10 AM

Hi

I'm a unexperienced DP that is doing a short film. Half the film is going to be shot infront of green screen and I was hoping someone here could help me with the lighting. If I could light my actors similar to the way they did in Sin City that would be fantastic (allthough I know that might be hard).
How much light should I have on the green screen compared to on the actors?
Does anyone have any examples of their own set ups that they could show me?

The short will be shot on interlaced HD then de-interlaced for the green screen.
thanks



The action will dictate the size of the green you'll need. Then you can choose the lights you'll need. If you're using a fabric type of green, pull it as tight as possible then get the lights to illuminate it from the front to eliminate shadows from wrinkles. The broader the sources the better. Pull the action as far from the green as possible to keep any green spill from falling on the actors. You should be able to keep your key lights off the background with the liberal use of flags.

Very important: Make time to do a test. Shoot a tape of action against the green under varying conditions and lighting. Give the tape to whoever is doing post and have them run it through the full process. It is far better to discover any problems before the day of the real shoot than for production to have you on the phone with editorial afterwards.

Also, you say that you are inexperienced. It is important for you, your ACs, and Editorial to all understand HD thoroughly. Make sure everyone is on the same page. Don't shoot 24P if you are better off with 23.98P or 59.94I. If you aren't sure of the ramifications of that last sentence, by all means, find out before you do anything else.
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#3 Matthew Parnell

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Posted 30 August 2006 - 05:48 AM

Also try to shoot using as flat a light as possible.
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#4 Stephen Williams

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Posted 30 August 2006 - 05:53 AM

Also try to shoot using as flat a light as possible.


Hi,

On the green yes.
The lighting of the subject should match the look required in the composite.

Stephen
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#5 Jan Kielland

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Posted 30 August 2006 - 08:31 AM

I was planing on alot of backlight, is that a good idea?

The space is supposed to be a post apocalyptic sci fi sports arena.


Thanks for the replys

Jan

I was planing on alot of backlight, is that a good idea?

The space is supposed to be a post apocalyptic sci fi sports arena.


Thanks for the replys

Jan
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#6 Mitch Gross

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Posted 30 August 2006 - 09:32 AM

It is important to light the greenscreen as flatly and evenly as possible. There should be no more than 1/2 stop variation in brightness across the screen. I like to light my greenscreen to about 2/3rd of a stop below my exposure. So if you are lighting to key, (I'll assume from your comments you're shooting on a Sony Z1U), Use the zebras on your camera to find the exposure on the actor (I'd set zebras to 70 as a good basic exposure), see what the F-stop reads and then dial the exposure open by 2/3rd of a stop. Now light the screen so that it creates zebras at this exposure. In practice you'll usually get the exposure on the greenscreen first and then adjust the lighting on the talent relative to that.

You'll always need a bigger screen that you think. To prevent color bleed onto your talent, have them as far from the screen as possible -- at least 7-8 feet. Depending how far you can get back your camera and zoom in, you'll need a very large screen even to do waist-up shots. My greenscreen is 16'x8', and it is just barely big enough for most of the work I do.
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#7 Brian Dzyak

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Posted 30 August 2006 - 10:14 AM

Also, I don't know what your budget is, but if a significant portion of the movie will be greenscreen work, consider finding a production stage that has a curved cyc wall that you can light. You'd have to use a bunch of scoop-type lights and add green gel. Using a space like that will allow head to toe wide shots that you just can't get by using a backdrop.

Again, test as much as possible using different lenses, exposures, movement...anything you think you'll do. Have post do a test on your work and they'll hopefully tell you what works best for them.
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#8 timHealy

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Posted 30 August 2006 - 11:30 AM

It may be worth talking to the people doing your compositing and asking them if they have any input to the exposure question. I have a friend who is a colorist, who seems to differ from anther friend, who is a compositor, about the exposure of a green screen. One says a half stop over and the other says a half stop under.

best

Tim
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#9 Stephen Williams

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Posted 30 August 2006 - 11:39 AM

It may be worth talking to the people doing your compositing and asking them if they have any input to the exposure question. I have a friend who is a colorist, who seems to differ from anther friend, who is a compositor, about the exposure of a green screen. One says a half stop over and the other says a half stop under.

best

Tim


Hi,

IMHO green overexposed is going to be a bad idea, Blue on the other hand.....

Stephen
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#10 John Holland

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Posted 30 August 2006 - 11:55 AM

I have always overexposed blue screen by at least two stops ! but greenscreen , nah . john holland.
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#11 Kevin Zanit

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Posted 30 August 2006 - 09:14 PM

Hmmm, well I tend to underexpose the screen (regardless of color) by one stop. But maybe y'all know something I don't . . . ;)


Kevin Zanit
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#12 Nathan Chaszeyka

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Posted 30 August 2006 - 10:35 PM

Hmmm, well I tend to underexpose the screen (regardless of color) by one stop. But maybe y'all know something I don't . . . ;)
Kevin Zanit


Same here but that has been with DV and DVCProHD. I have had great results. Perhaps the lighting differs when using other formats or film.
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#13 Kevin Zanit

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Posted 31 August 2006 - 12:32 AM

I always underexpose by one stop, even in DV. Essentally ILM told me thats how they want their screens on a project I did, and I have done it that way ever sense.

But, do whatever is working for you.
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#14 Adam j Kennedy

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Posted 31 August 2006 - 11:07 AM

hi i am also about to shoot some on green screen, i know a little about stops and all that, but i need to get something straigt....
so if i light my subject at 5.6 then i need to light my screen at a 4 stop.

is this correct....

im trying to get a low lighting on my subject so will the green screen be lit up enough even if i go 1 stop under the low key light.....

thanks,

adam
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#15 Michael Rizzi

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Posted 31 August 2006 - 01:30 PM

hi i am also about to shoot some on green screen, i know a little about stops and all that, but i need to get something straigt....
so if i light my subject at 5.6 then i need to light my screen at a 4 stop.

is this correct....

im trying to get a low lighting on my subject so will the green screen be lit up enough even if i go 1 stop under the low key light.....

thanks,

adam


That is correct. It's better to underexpose the green than overexpose. Even if it means underexposing by 2 stops versus over by a half a stop. The saturation and evenness (?) of the green is what the post guys appreciate. If the green is too bright, the chroma could start getting too close to your subjects chroma and cause problems.
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#16 Jonathan Bowerbank

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Posted 04 February 2007 - 04:30 PM

I'll be shooting a MiniDV short film soon for a student. There will only be a couple of green screen shots. But I really wanted to pump up the color of the greenscreen. What green gel do you people think is best?

I was assuming CalColor Green 60 or 90 would be best, then backlighting my subject with a CalColor Magenta 15 just if I'm getting any green spill.
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#17 Paul Nordin

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Posted 04 February 2007 - 05:00 PM

I really wanted to pump up the color of the greenscreen. What green gel do you people think is best?


If you can, I would do a couple of simple tests ahead of time to make sure you are going in the right direction for the CG/post person. If the background is evenly lit (per all the others I like 1 stop lower than key) to minimize spill, there shouldn't be a reason to pump up the green. Very clean (as far as DV will go that is) matts can be pulled that way, and pushing the chroma too far can create more problems than they solve some of the time. Do you not have good separation between background and subject? Just wondering what problem you are trying to avoid.

Cheers
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#18 Peter Emery

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Posted 04 February 2007 - 06:22 PM

You need to be careful shooting greenscreen with DV as the format is low on colour space. It was never designed for such things. If at all possible shoot on digibeta. The guy keying the green out in post will thank you for it.
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#19 Ram Shani

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Posted 05 February 2007 - 12:10 AM

i agree the main problem is the color spec in the mini dv/hdv that make the post life hell

from my exp i would say 1 stop under

if you plan to do moves on the screen( dolly cran) you beater to put small cross mark on the screen for traking in post

if you have long shoots avoide shadows on the fluor and you need to light it to

nice artical about color spce:

http://www.dvxuser.c...les/colorspace/
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#20 Matt Sandstrom

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Posted 05 February 2007 - 02:44 AM

color space is really the wrong word. digibeta and dv use the same color space, i.e. the exact same colors and shades can be accurately represented. the difference, as explained in the article, is that dv chroma is sampled at a lower resultion, thus your matte will also have lower resolution, by definition, there's no way to get around that. a lot of the separation is carried by the luminance channel though, especially with green as opposed to blue, so with a good chroma resampler it's not a big deal. a one pixel wide hair for example is separated from the green background not only because it's not green or blue, but because it's brighter. a good keyer will see this. i'm not an expert in either greenscreen llighting nor keying, but i develop final cut plugins in my spare time so i know a lot about how the image data looks and works, from lots and lots of experimenting and analyzing. lighting evenly and avoiding spill is much more important than what format you're shooting on.

/matt
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