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#1 william koon

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Posted 04 March 2007 - 03:15 AM

I intend to shoot a couple of scenes in a hall on blue screen for CGI's purposes. The blue screen will cover the background as well as the floor. Please help solving a few questions I have as follow :
(1) Must the blue screen be evenly lit ? If so, how do I light the floor evenly as a few talents will use the space and cast shadows on the floor?
(2) How far the talents must be away from the blue screen at the background? Again, how to solve this distance on the floor?
(3) How effective is the CGI if the talents are to be lit in low key?
Thnx
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#2 Will Earl

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Posted 04 March 2007 - 03:53 AM

Ideally you should try and light the bluescreen as flat and even as possible, however don't stress getting the bluescreen lighting perfect it if it affects the quality of the hero lighting.

There's no defined distance as to how far away you should place the talent from a bluescreen, keep a reasonable distance of say 1 metre.

Most keyers can handle shadows, however most productions will try and avoid bluescreen floors as ground-interaction in VFX is still hard to pull off convincingly.

As long as you can match the lighting of the CG elements with the on-set photography then it doesn't matter what type of lighting you go for.
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#3 Pedro Millan

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Posted 04 March 2007 - 04:23 AM

As far as i know, the talents must be in a distance where no blue light is reflected.
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#4 Ram Shani

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Posted 04 March 2007 - 05:47 AM

the distance from the screen is to avoid spill of the blue on the subject which make it hard to key

so dont light the screen to strong (comen practice is one stop under )

to halp that you can add alittel cto to the backlight if its blue and alittel -green (magenta) if its green screen

to light the floor you can use chaina balles or space light

or any top soft light

1 meter is to close it will be very hard to control the spill from the screen



the distance from the screen is to avoid spill of the blue on the subject which make it hard to key

so don't light the screen to strong (common practice is one stop under )

to help that you can add a littel cto to the back light if its blue and little -green (magenta) if its green screen

to light the floor you can use china balls or space light

or any top soft light

1 meter is to close it will be very hard to control the spill from the screen
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#5 Will Earl

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Posted 04 March 2007 - 04:35 PM

I should have said minimal distance of 1 metre, Ram is correct - ideally you should keep it as far away as possible. But then again I've gotten use to looking at bluescreen elements that forgo any of the luxuries that are commonly asked for in bluescreen photography.
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#6 Stephen Williams

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Posted 04 March 2007 - 04:39 PM

I should have said minimal distance of 1 metre, Ram is correct -


Hi Will,

If the talent is standing on the blue screen the distance will go to zero in any case! LOL.

Stephen
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#7 william koon

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Posted 05 March 2007 - 10:20 PM

Hi Will,

If the talent is standing on the blue screen the distance will go to zero in any case! LOL.

Stephen

Thnx all for the effort and inputs. Infact my real problem will be the floor blue/green screen as mentioned by Stephen 'zero' distance. What are the alternatives?
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#8 william koon

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Posted 27 March 2007 - 08:42 PM

the distance from the screen is to avoid spill of the blue on the subject which make it hard to key

so dont light the screen to strong (comen practice is one stop under )

Why one stop under is required?
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#9 Scott Fritzshall

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Posted 27 March 2007 - 09:33 PM

Why one stop under is required?

Mostly so that less light is bouncing back onto your subjects. The brightness of your bluescreen can vary as long as it's even. Often you'll want to vary the brightness based on what's going to be replacing it- if you've got a very dark background, for instance, you might want to light the bluescreen 2 stops under.
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#10 Adam Paul

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Posted 28 March 2007 - 05:32 AM

Mostly so that less light is bouncing back onto your subjects. The brightness of your bluescreen can vary as long as it's even. Often you'll want to vary the brightness based on what's going to be replacing it- if you've got a very dark background, for instance, you might want to light the bluescreen 2 stops under.


Why should it make a difference since the blue is there just to create a vacuum or empty space when removed allowing you to replace it with whatever you want?
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#11 Chad Stockfleth

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Posted 28 March 2007 - 10:03 AM

Shadows are a fact of life when standing on greenscreen. Try to keep them from being too hard, and make sure you can see seperation (a defined line) between the feet and the floor. Post can usually handle it.

I'm not sure of lighting the screen 2 stops under....it shouldn't make a difference since it's going to disappear. In fact, lighting it darker seems like it would be more troublesome. I'd stick with a stop under, making sure it isn't reflecting on the talent. A cunning use of flags and light and you should be fine.

Good Luck!
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#12 John Holland

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Posted 28 March 2007 - 10:08 AM

Is this film ,HD ,video ? i think it makes a difference when lighting the blue screen and how much under or over you go .
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#13 william koon

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Posted 29 March 2007 - 03:05 AM

Is this film ,HD ,video ? i think it makes a difference when lighting the blue screen and how much under or over you go .

I intend to go for HD. Pls also advise the differences in film and video.
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#14 Walter Graff

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Posted 29 March 2007 - 09:34 AM

The key to chromakey is color. You are trying to light the screen for hue not intensity, hence why you don't try to light it brightly, rather simply to enhance it's color value for camera. Yes even is always better. You can use a light meter for that and/or zebras in the camera to see what parts are brighter or darker. The reason most folks talk about a stop under has to do with the glow of the screen. The more light you use the more the color reflects off that screen. And that could mean more spill on your talent. So if you light the screen slightly under to even with the value on your talent you'll usually have an easier time. As for shadows, they are inevitable, but if your talent is lit with softer light and the intensities of the shadows created are not so dark, it is not a problem. The key to learning to light chromakey is to know how the post production process works. If you are shooting video that means doing a small sample shot, then taking it to post and learning how to cut the key and seeing what works and what does not. Lighting chromakey without knowing how the edit process works first hand is like learning to drive from reading the driving manual only, but no actual behind the wheel experience. People ask when to use blue and when to use green. Actually you can use any color. Lately I have been doing white (luminance key) for headshot projects. Usually experience and knowing what the background plate will be helps you decide. For instance if you have a undersea background, blue would be a better choice as any imperfections in cutting the key can be more easily masked.


I have two introductory articles on lighting screens and a more detailed instructional DVD on my site.

http://www.bluesky-w...reenscreen.html

http://www.bluesky-w...reenscreen2.htm

http://www.bluesky-web.com/008.html
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Aerial Filmworks

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