Green Screen Lighting

[Ken Lowe]

Hi, I am lighting gaffer shooting a 15 week video drama which includes a fair amount of 'green screen' shooting (flying sequences).

 

The 'screen' is 60' x 25' and is suspended from scaffolding bars and the floor has been painted in green chromakey paint and is 60' x 60'.

 

The lighting set-up suggested by the DOP is 2 rows of 8 x 1Kw Iris 1's to light the screen. One row suspended on a bar at the same height of the screen and the other as a 'ground row' at the base of the screen. Both rows are 10' from the screen and the individual heads are 6' apart with 250 diffusion fitted to make the lighting as even as possible. A 3' high timber board 60' long has been painted to match the floor and is angled at 45 degrees to hide the ground row.

Above the floor area are 4 x 5Kw space lights, equally spaced at 12' to form a square, the nearest 2 lamps to screen are approx 20' away. All 4 space lights have full length black skirts fitted and 250 diff on the colour frame.

 

The 3/4 back lights requested are 5Kw fresi's suspended on the ends of the green screen bar and side lighting the flying rig is a 10Kw fresi. A 2Kw fill is at the side of the camera which is square onto the screen. All the lamps are supplied via dimmer racks.

 

A brief camera test has been shot but the results are not so good, problems with reflective floor paint and the the angled timber causing a not matching green screen, which, incidentially has been dimmed considerably.

 

With out stepping on the DOP's toes does anybody out there have any experience in green screen lighting and make a few suggestion to put forward?

[David Mullen ASC]

All my experience with greenscreen lighting has involved using Kino greenscreen tubes, which is great because it will make any green screen a deep and pure green no matter what.

[Laurent Andrieux]

My advice :

 

Don't over light the backgroung, set it by the keylight, not overexposed.

 

Be carefull it to be lit every where the same value

 

Be carefull with the shades in the foreground, that darken the green screen, like the floor if a cyclo for instance.

 

Put the talents as far as possible from the backgroung. It allows you to be more free for the foreground, without touching the background, keep the foreground from green reflections, that is very important, and to set backlights.

 

If you have some greenish light coming back onto the foreground, it's a real pain in the ass in post.

 

I give you a trick : warm your backlights (I use CTO on a blue screen, may be you should use minus green on a green screen) as to sort of "kill" the eventual coming back of green light.

 

The best is to have the composite element and make a trial with video equipment on the set. It's not always possible.

 

The major work for the dop is to make the foreground match with the included background... The best would be you to see this element so you can make suggestions for the foreground lighting (gels...)

 

Anybody else's advice ?

 

Good luck ! Let us know !

[Michael Nash]

If I'm understanding you correctly, the floor and angled board are not painted green, but instead another color intended to be included as foreground. And you're having a problem with the floor reflecting the green screen. Is that right?

 

If your green screen is lit to the proper luminance, and lit evenly, then there's not much you can do lighting-wise. The reflection on the floor is from the angle of reflection to camera, not spill. You probably can't flag the reflection on the floor without putting flags right in the middle of your screen.

 

So two solutions come to mind. 1 - use a different material for the floor that's not reflective (this depends on production design and what the floor's supposed to look like in the final comp). 2 - Shoot the flying and floor in separate passes. Turn the green screen lights off or even replace the green with black for the floor pass.

 

Does the floor really need to be seen in frame? As luck would have it I'm shooting a green screen flying sequence in a couple days, and the director and I considered shooting the flying person on green screen head to toe for landing and takoff, then compositong the floor in. Of course you have to deal with shadows and precise angles and so on, so we opted to avoid those shots altogether.

[Phil Rhodes]

Hi,

 

Spot meter/waveform monitor essential. In my experience flying is a pain in the neck which takes ages then gives you thirty seconds with a whining, uncomfortable actor, so work fast!

 

Phil

[Ken Lowe]

Thanks to everyone for your comments so far and all that you have said has been taken on board.

 

Michael, just to make it clear, the floor and timber panel hiding the ground row are in fact painted with matt green chromakey paint which is not quite the same shade as the green screen but slightly lighter.

 

On Friday we intend to re-rig the lighting set up, removing the ground row and reinstalling it on the top lighting bar. This lets us remove the timber panel totally and solve one problem. As to the floor, we are going to use 'blacks' (heavy black drapes) to minimise the bounce back from the space lights.

 

All of your suggestions will be tried and I'll let you know the outcome.

 

Thanks again, And I agree Phil, flying is a pain in the arse!!!

[PhilPowers]

hi there- you might want to try using a polariser to reduce the glare from the floor. If you can remove the ground row you will save youself a lot of bother. Phil's sugestion of using a waveform monitor is a excellent one this will help you lots on the day, if you can't get hold of one try Hamlet they make a small in line waveform generator which plugs between you camera and monitor to make your monitor a waveform monitor. Be very careful of using dimmers on individual lamps/heads/lanterns/luminaries this will alter the colour temp and may not give you a good matte.

 

Any just some thoughts and hey what do I know???

 

 

Good luck :)

[Mitch Gross]

One small note is that I find my green screens comp much cleaner when I light them one stop under key.

[Bob Hayes]

When I shoot green screens I try to put small tape ?X?s? on the green screen as tracking points. They seem to work great however when I go in for closer shots they quickly go out of focus. So, how do you handle tracking points on close ups?

[Olivier Egli]

what larent.a said:

 

My advice :

 

Don't over light the backgroung, set it by the keylight, not overexposed.

 

 

this shall be your bible!

Very often novices make the mistake to overlight the greenscreen because they thing that the blooming effect will help the screen to look more even, but this is not so true when you are sitting in the compositing suite.

Clear separation with back- and kickerlight set at 2 stops over key will help separate fore- and background. if you plan on using heavy fill on the actors you need either a big distance to the screen or to flag it down like hell cause it will spill on the screen. kinos are helpful but often prove too weak to light such a bright area, and if you still want to do it it will eat up your budget in no time. If you got it then go on, best way to do it.

Do you have acces to round horizon flooders? they come in casings of 2x1k and have a very soft edge. mount them on the top bar and have them light the screen from above. Do not light the screen from underneath. use side and 3/4 fron light with high output that match the lights on the overhead fixatures and keep them off the actors.

[oscar jimenez]

Hi, just to make my little contribution: Light green to Zone V and make skin tone on Zone 6 ( it depends on what do you want to achieve ) anyway, that's always worked for me, and if possible, backlights with 1/2 minus green. all moder software can "burn" almost any color with no major trouble, commotion ( primatte keyer ) and combustion are 2 very good tools for compositing. Good luck.

If you are shooting in video, green to fall in 2.8 as Zone V works great, just my experience.

Regards

[Laurent Andrieux]

what laurent.a said:

 

"My advice :

 

Don't over light the backgroung, set it by the keylight, not overexposed."

 

this shall be your bible!

 

Thanks, do I really deserve that ? B)

 

The thing is, if level is too high, the color looses it's purity. If you over expose you go to white, that is all the colors alltogether...

 

Oscar : Would you please remind us what reflectance or stops to keylight is zone V ?

 

thanks

[Michael Nash]

Clear separation with back- and kickerlight set at 2 stops over key will help separate fore- and background.

I don't agree that this is always necessary. Backlight may create the illusion of depth and separation when you're looking at flat green background, but doesn't necessarily have anything to do with pulling a clean chroma matte. It's all about the edges and chroma difference, not the illusion of depth. As long as there's enough difference in hue and luminance between your subject and the green screen, you don't need dedicated backlight to help the matte. For example, if your subject is a person with dark hair or dark wardrobe, that's enough of a difference from green at 50% luminance. Adding backlight isn't going to make black wardrobe or blonde hair any more "different" from green than it already is.

 

Instead, model the light on the FG for the final composite, not for the green screen. I find it helpful to light the FG with the green screen lights turned off, so that I can see how the light is behaving on the FG independently of the green BG. Then turn the green screen lights back on and check your exposure levels.

[David Mullen ASC]

Yes, you should only have strong backlight if that matches the lighting in the background to be composited. You don't want to matte a backlit person against a front or side lit landscape.

 

However, some soft back or cross-lighting, not bright but at key, can help reduce green spill onto the subject.

[Bob Hayes]

When green screening night scenes I?ve found it very useful to build an 8x8 solid black and place it behind the actors. This gives my eye a better idea of how my lighting would look with a dark background.

[Bob Hayes]

I was watching the behind the scenes on ?Men in Black II? and it looked like they used green tape X?s for there tracking points. You could still see them enough to get registration points and yet I think they were green enough to easily remove. I?ve always used a color that stands out. Any ideas?

[Michael Nash]

I think the only problem with using a contrasting color for tracking marks would be if the foreground subject has to cross over or overlap one of those marks. Then the edge at that point would probably have to be rotoscoped. Otherwise, tracking marks could be garbage-matted over. Green marks might be close enough to the matte color that the compositors don't have to create a separate garbage matte, and not worry about the edges when a subject overlaps them.

 

On the flying sequences I did recently I had to use some mis-matching green material to cover stands and boxes, and I was surprised how much you can get away with. That bright green gaffer's tape is wonderful stuff as it's easy to see by eye yet saturated enough that it mattes beautifully.

 

But I think the real requirement is what software and/or hardware you're using to do the composite. What might work well for one system might not for another.

[Guest Daniel J. Ashley-Smith]

Hmm, just wondering. Blue and green screening studios aren't always that bright. When shooting with film what?s the best way to compensate? Opening the iris up full isn't a problem in the situation. And the higher the ISO, the more grain.

 

And does the XL1s have the quality to green/blue screen?

[Alvin Pingol]

And does the XL1s have the quality to green/blue screen?

Green yes, blue maybe.

 

That's pretty much how it is with all video, though, since green makes up most of the YUV color space anyway.

 

Also, Canon's green "pixel shift" technology - I don't know whether this would help or hurt how well one will be able to chroma key. I know that the slight pixel offset creates the illusion of a sharper image, but does it shift so much as to create a significant luma/chroma offset, thereby creating chromakey troubles? Anyone? :huh:

[Matthew Poliquin]

A question regarding lighting and the different keying programs used. I have read a number of articles which state that the keying program used can determine how you light the character and screen. Apparently some programs respond better and worse to using a backlight with some minus green on it, and still some programs allow the character/subject to be lit according to the scene, and not requiring any additional lighting on the screen, and that the shadows created are of no worries.

Can someone shed some light into which programs respond better to key lights that cancel out some of the spill, and which programs allow for shadows to be cast on the screen.

 

 

Thank You,

Matthew Poliquin

DP/AC

Santa Monica, CA