green/blue screen

[F Bulgarelli]

Hello everyone.

 

I was wondering if someone could give me some hints for lighting and shooting green/blue screen.

I will be shooting a music video on 16mm that involves a lot of green screen.

It will be my first time doing something like that.

What should I look for? Should I do green or blue screen?

 

Any help will be greatly appreciated,

 

Francisco

[Stuart Brereton]

Hi,

 

Light the blue/green screen as evenly as possible. Hotspots and shadows will make it more difficult to key. Some people like to add blue or green gels to their lamps to help with colour saturation of the background. Meter the background carefully - it should not read higher than your keylight, in fact 1 or 2 stops less can help minimise spill. Most modern chromakey software doesn't require you to use backlight to remove spill, so don't use it unless it is part of the look you want.

 

There is a ton of info regarding chromakey work on the CML website.

 

Stuart

[Chris Keth]

Hi,

 

Light the blue/green screen as evenly as possible. Hotspots and shadows will make it more difficult to key. Some people like to add blue or green gels to their lamps to help with colour saturation of the background. Meter the background carefully - it should not read higher than your keylight, in fact 1 or 2 stops less can help minimise spill. Most modern chromakey software doesn't require you to use backlight to remove spill, so don't use it unless it is part of the look you want.

 

There is a ton of info regarding chromakey work on the CML website.

 

Stuart

<{POST_SNAPBACK}>

 

 

If you do use a backlight, you can gel it with a little of the complimentary color to whatever screen you use (gel it a little magenta for a green screen, for example) and that can help reduce spill, don't get carried away though. Just a little color.

[John Ealer]

Francisco -

 

Green screen is, very generally speaking, preferable for most situations for reasons like:

 

1. The green sensitive layer of most film stocks has the least grain.

2. The Y/luma (effectively green) channel of most Y'CbCr color-space-using digital formats is often sampled at a higher frequency than the other channels. For instance, Digibeta is 4:2:2, HDCAM is 3:1:1. Ergo, the potential for easier keying using green.

3. Most producers and post production houses have become very used to using green, so there's maximum familiarity with it.

 

Having said that, the choice of color of screen, how bright to light the screen, etc., should be based on the specific needs of the given project. It's always good form to consult the compositors before shooting the greenscreen to make sure everyone's on the same page with the approach to the compositing that will be done.

 

Having said that, some general recommendations from my experience:

 

1. I try to light the screen between 1/2 stop to a stop above key, depending on the subject. Brighter than that increases spill problems, less than that and you start to lose saturation on the screen.

 

2. I usually avoid using green-gelled lights on the screen, not because they aren't a good idea, but because you're rarely given a big enough stage to adequately control the spill from the cyc lights from falling on the actors. At some point in every shoot, a director will come up with an uplanned shot that requires the actor to come way too close to the screen and walk all the way out to camera.

 

3. The color of greenscreens is hardly uniform. Obvioulsy, there's a differnence between chroma-key green and digital green (I usually opt for digital) but different manufacturers of these cloths come up with very different colors.

 

4. Use backlight gently and thoughtfully, unless it's part of your aesthetic. There's nothing worth that a greenscreen element with a moster backlight (for spill control) comp'ed into a darkly lit background. The compositors can get rid of a bit of spill, they can't get rid of your backlight.

 

J

[F Bulgarelli]

Thank you all.

 

Atavist, I understand what you are saying about thet green screen benefits, in which cases a blue screen is more suitable.

 

Thanks

[Stuart Brereton]

1. I try to light the screen between 1/2 stop to a stop above key, depending on the subject. Brighter than that increases spill problems, less than that and you start to lose saturation on the screen.

 

I would have to say that lighting a blue or green screen hotter than your keylight is the wrong way to go. First, it increases the spill onto your actors, and second, overexposing the screen will reduce its' saturation, which you definitely don't want.

 

Underexposing the screen by 1 stop reduces spill considerably, and maintains a good colour saturation.

 

A visit to the cinematography.net archives will give you a huge amount of info on Blue/Greenscreen work.

 

Stuart

Edited January 12, 2005 by Stuart Brereton

[Glenn Hanns]

Francisco -

 

Green screen is, very generally speaking, preferable for most situations for reasons like:

 

1.  The green sensitive layer of most film stocks has the least grain.

 

Having said that, some general recommendations from my experience:

 

1.  I try to light the screen between 1/2 stop to a stop above key, depending on the subject.  Brighter than that increases spill problems, less than that and you start to lose saturation on the screen.

<{POST_SNAPBACK}>

 

1.The green layer is only less sensitive (and thus less grainy) in Daylight stocks NOT tungsten stocks which have about the same sensitivity with the BLUE layer just a little MORE sensitive.

 

1. Yes lighting your screen to 1/2 - 1 stop over helps to get rid of "muddy" keys and does not affect your colour saturation to the point where it becomes a problem.

 

Using traditional incandescent lighting can add too many other color wavelengths (most notably "yellow") to the screen making keying more difficult. A more accurate method would be to simply light the screen using colored gels to filter your light to as close to the color of your screen as possible. Another would be to use a light source that only emits the desired wavelength. Kino Flo makes a lamp called the Kino Flo Super Green that does just that.

 

Move your foreground as far from your background chromakey to reduce spill. By placing your screen at a 45degree angle to your camera you can reduce the amount of chroma bounce back to the subject from your CKey screen light/s.

 

Do not use any diffusion on the lens as this will break up you F/G - B/G edge and affect your key.

[Justin Hayward]

I try to light the screen between 1/2 stop to a stop above key,

 

I usually go at least a half stop under.

 

Mostly, the difference between blue or green is whatever your subject?s color involves. If they have some green? use blue. Or vise versa. Otherwise, I?m not really concerned.

[F Bulgarelli]

Well, my music video just went from the varicam to the DVX100.

Has anyone done green screen with the DVX100?

 

Any comments or suggestions will be greatly appreciated

 

Francisco

[John Ealer]

Tricky. DV, with it's 4:1:1 chroma sampling, makes it very difficult to pull clean mattes. There are color smoothing tools that compositors use to help a bit, but I would lobby hard to at least use DVCPro50. At 4:2:2, it'll deliver much better results.

 

J

[Adam Frisch FSF]

1. Don't overlight, as has been suggested here.

 

2. Watch for spill - the bigger the screen the better.

 

3. If you can, use green or blue Kinos - that'll make it sing like nothing else.

 

4. Maximize camera oreintation for resolution.

[Rik Andino]

One thing to note

You should keep your subject at least 5-to-8 feet away from the screen

As to avoid spills on the subject, that will look like a green glow...

[F Bulgarelli]

Thank you all.

Adam, what do you mean by "maximize camera orientation"

 

John, I'll push for the dvcpro50

 

Francisco

[F Bulgarelli]

Has anyone shot or tested the DVX100 with green screen at different frame/shutter settings.

I'll be shooting a test and I was thinking It might be a good idea to try different shutter angles to look for a way of minimazing blurr.

Also, shoud we shoot 60i or do you think we can benefit from 30p or 24p.

 

Thanks again,

 

Francisco

[Amy Ecklund]

Hi,

Okay I am in desperate need of help, quickly. Green Screen shoot in a week and a half, first time, using dvx100. I have concerns about both lighting and shooting, I have run into sites that claim the camera axis should always be perpendicular to the screen, that all movements should be attempted with backplates. Also, are there any concerns as far as shooting at 24p for green screen.

 

Thanks so much.

[John Sprung]

Green doesn't have any more resolution than red or blue in 4:2:2. It's derived from luminance, which is full resolution, by subtracting off the other color differences, which are half res, so green is also half res. Therefore, compositors who know their stuff routinely look at pulling a luminance key off the green screen. They get a sharper matte if that works, and fall back on the green if it doesn't. Spot meter from the camera and make the green hotter than anything else in the shot.

 

 

 

-- J.S.

[Guest Kai.w]

Thank you all.

Adam, what do you mean by "maximize camera orientation"

 

John, I'll push for the dvcpro50

Francisco

<{POST_SNAPBACK}>

 

I guess he means that if perspectivity allows for it make the subject as big as possible in the frame (you can downscale later) so as to get as much res as possible.

 

Another thing:

if the camera is locked of, also shoot a second image but empty (don't move the camera or lights inbetween), that is without the subject to key (just a couple of frames). You compositor will love you for that...

 

-k

[Brent J. Craig]

Sometimes we will flip the camera sideways when shooting people for compositing, just to fill the negative more.

 

Are the empty plates you mention really all that important for a properly lit green screen? I know clean plates are great to use for difference mattes when dealing with problem situations (like when you can't use a green screen at all) but do editors use them for greenscreens too?

[Guest Kai.w]

Sometimes we will flip the camera sideways when shooting people for compositing, just to fill the negative more.

 

Are the empty plates you mention really all that important for a properly lit green screen? I know clean plates are great to use for difference mattes when dealing with problem situations (like when you can't use a green screen at all) but do editors use them for greenscreens too?

<{POST_SNAPBACK}>

 

In Ultimatte for instance the additional difference plate helps a lot to get good edges.

You sort of get a very clean BG first. It can better decide what is subject and what is BG.

 

-k

[oscar jimenez]

HI, here's my ten cents, even though I think everything has been said already.

I do always work with green screen ( because I have a 20 x 20 ft mathews green screen cloth ) and Im not willing to buy a blue one. If it is video, depending on frame composition ( ms, wide shot ) ill try to make lighting even for background as possible ) I do use 2 kino 10 bank from sides and a small 1k fresnel rigged from high point at middle to balance lightning in the middle of green background. I do always rely on my spot meter rather tan incident ( that is at most situations, not only green screen ) my formula that has always worked for me and have greens sucessfully burned without that "jaggy- noisy " on edges specially on 16mm is GREEN SHOULD BE PLACED AT ZONE V, SO DO LENS STOP. THAT IS IF GREEN IS 5.6 THEN LENS SHOULD BE SET AT 5.6, for desirable fx then everything else should fall where you want to place it. 200 asa / estudio works beautifoul with green/blue backgrouds. 500 asa rather set it as it was 400 asa. for "normal exposure commercial work" if Im shooting white / caucasian people and want skin renedering "natural healthy looking" have them lit one stop from key ( reflected metering, it should fall on Zone VI) bakclight is helpful, having it at least 2 stops ( reflected) from your key stop. If you are working in such a format as DV or DV cam, try to capture footage on a professional DV deck, I have a deck with SDI output / input, and I capture footage at 16 bits when working mattes, keys burn prettty good without jaggy edges and noise. If it is necesary, in telecine or post you can "de-grain" your image ( if shot on 16mm) and will be less noisy)

Hope I did help

Cheers

Oscar

[Jon Rosenbloom]

Oscar, that is definitely ten cents worth, can you translate your method into incident readings?

 

Francisco, I don't think anyone has asked which compositing software will be used on the project. That would be good to know. Also, you are going to shoot the plates first, right???? Last, do whatever you can to get out of mini-dv for this. Chroma keying is based on color, so obviously a system that works in 4:1:1 is going to be inferior to one that works in 4:2:2. Mini-DV might work, but it will make everyone's job more difficult.

 

Also, have a lot of duvateen on hand so you can set up big siders on the green screen, as well as a teaser.

 

Good luck!

Edited March 21, 2005 by J-Ro

[Paul Bruening]

Hello good people,

 

I will be shooting green screen this summer myself. I'm shooting Techniscope on 5274. This is what I intend. I'm going to use Color Composition's green paint cut with an artist's matte acrylic, painted onto ordinary (sanded) hardware store plastic tarp (already has tie-off grommets). I will stretch on a frame and bag down into the deep-end of a local swimming pool. I will submerse the cam in a shallow box with window. I am going to try Jon Erland's trick of using buff visquin (sp?) over the pools surface to break refraction from sun or cloud light. This should give me even lighting accross both human subject and green screen. Am I an idiot? Will this work? What do you anticipate as problems?

 

Thanks,

Paul Bruening