Generally, what you are looking for is a large, diffuse, light source that will wash over the screen evenly. You can try to use a little Lowell Tota but it will be very hard to get what you want. We use 4’ Kinos. You will need either a 2 bank or a 4 bank of lights, depending on the type of lights you use in the kinos and the strength of your lights in the foreground.
Interestingly enough, it’s really the bulbs that matter. For a short project, you can get shop light fixtures at Walmart for $8.89 and add good bulbs (Kinoflos) to get something that works…for a period of time. What you pay for in a Kinoflo fixture is the ballast…the power supply. A Kinoflo ballast is consistent, flexible and has a high cycle rate (meaning you will never see it flicker). We use kinos because A) we need the features and B) we’d have to charge less if the clients saw Walmart fixtures. That said, I’ve been to many small studios in the US and Africa that employ the Walmart approach with a great deal of success.
We use green kino bulbs. This is sometimes called “green on green” meaning green lights on a green screen. The result is a very, very pure green that is easier to key. In the “olden days” (5 years ago), the methods of removing the green spill was primitive– making this technique less usable. But with plug-ins like Keylight, dvMatte, and Conduit (disclaimer…my company, dvGarage, makes dvMatte and Conduit), despilling is much less onerous than it was in the past. You can use either daylight (56k) or indoor (32k) bulbs but you need to figure out what color your screen is balanced for. Rosco paints are generally balanced for 32k bulbs and Composite Components are often balanced for 56k. If the screen looks a little yellow, you want 56k bulbs. If it looks a little blue, you want 32k bulbs. This is just a rule of thumb. The best way to check this is through scopes, we’ll get to that. If you are using green bulbs…it will always look really green.
Of course, right now, you are probably thinking, “This guy is FULL of IT, If I use green lights, my foreground subject will be all green!” You would be right…if you lit the screen and the subject with the same lights…something we avoid 90% of the time. To make all of this work, you need to A) have proper separation of the subject and the screen (we generally have 10-15 feet between subject and back wall) and B) separate lighting for the subject. The separation of the subject from the backing greatly reduces green lightwrap (often referred to as Green Spill) because less light from above and below are striking the shoulders and legs from oblique angles. The separate lighting eliminates subject shadows on the backing and allows you to balance the lighting for both the subject and the screen independent of each other.
The nice thing about the super-green Kinos is that they are very, very efficient. I regularly light 12x12 green screens with one bulb on either side… and it’s often too much!
Posted by Art Adams on 03/27 at 10:19 PM
Hi - nice article. Good to see someone trying to get people to shoot better greenscreens.
I’d take issue with you on your disparagement of bluescreen.
You assume that the key mostly depends on the chroma backing channel. And therefore, say that blue is a bad choice, because that colour channel (in film or video or HD) is noisy.
I fact, the way I see it (and from my experience), the quality of the key doesn’t depend on the cleanness of channel recording the backing area, but rather, it depends on the colour difference between the fg and the bg. The key, therefore, depends on all three colour channels - in the case of greenscreen, r and b versus b, in the case of bluescreen, r and g versus b, And, in the majority of cases, blue will have far greater difference from the fg than green will.
A well lit, flat bluescreen will in most cases give a much nicer one click key than greenscreen. For similar reasons to the above (colour difference), bluespill is also easier to remove than green.
IMHO! 
Posted by paddy on 03/31 at 11:45 AM
replace one sentence in the middle with:
The key, therefore, depends on all three colour channels - in the case of greenscreen, r and b versus g, in the case of bluescreen, r and g versus b,
Posted by paddy on 03/31 at 11:46 AM
I haven’t shot a blue screen in years and years. The reasons are several:
Blue is the noisiest channel because silicon is least sensitive to blue. Under tungsten light the blue channel has to have gain added to it in order to match the levels of the others, as there is very little blue in tungsten light compared to red and green so it is always noisier. Hit the blue-only button on a monitor while looking at a picture (instead of bars) and you’ll see it easily.
For corporate work, people tend to wear more blue and little or no green.
The green used for keying is brighter than the blue is, so it requires less light—which saves money.
You’re absolutely right that it’s the difference between chroma channels that results in a good key: at least 40 units of separation between the backing color and the next closest color is how I was taught to do it. But I’m sure there’s a difference in edge quality between the noisy blue channel and the relatively clean green channel.
When I first started shooting green screen on video we aimed for 40-50 units, since we thought that, like on film, you should expose for “middle gray” values for maximum saturation. That came from the blue screen days, where you can get a bright blue or a saturated blue but not both at the same time because a bright rich blue is not in film’s color space. Electronically, though, you can really pump up the screen for maximum color difference, which is why 60-70 units works so well.
Posted by Art Adams on 03/31 at 12:57 PM
All things being equal, I know that a nicely saturated bluescreen will give a better result that a nicely saturated green. That is - in the conditions that I have been working in: 35mm (and more recently HD) features using Keylight in Shake, and before that, Cineon.
As I said above, a good key is only partly to do with the backing colour. If the colour difference off blue is greater than off green (and it will be, for most subjects (blue suits excepted)) then that will mean a LESS noisy key. A key is defined by all 3 channels together, not just one.
Green has its own issues. Because it is closer in hue to skin, hair etc, it can be really hard to get rid of green spill without getting a nasty desaturated look, and grey/white speckles in the blacks.
If lighting with tungsten, then, yes, you will need slightly more light for bluescreen than green. Especially if you are doing what you should be doing, which is to put heavy blue filtration on the screen lights. But if you *aren’t* using tungsten on bluescreen (and, to be honest, why would you?!) then there is no reason why you would need more light for bluescreen than for greenscreen.
Re your notes about bright, saturated blues not being in film colour gamut. Maybe in terms of print, but not neg! I live for bright, saturated blues on film! Doesn’t happen often enough, but it does if I have anything to do with the shoot! 
Posted by paddy on 03/31 at 03:23 PM
Actually, under tungsten conditions you can light blue screen with uncorrected HMIs and end up with a lot of saturation.
When I was talking about a noisy blue channel I was speaking about shooting digitally (something I should have made more clear). I haven’t shot blue screen on film in a LOOOOOONG time. And yes, you’re right, blue is much easier to key flesh tone against, and blonde hair, etc., but I haven’t seen blue in years and years. I’m not sure why, but it just isn’t done anymore.
Posted by Art Adams on 03/31 at 03:51 PM
Something to look for on the waveform monitor on page 3: the fact that the edges drop down a little bit is something you can fight and fight and fight, only to discover it’s not the lighting: it’s the lens. Most video zooms show marked edge drop-off starting at fairly modest focal lengths. Usually this isn’t a big issue. Just know that while it looks like the scope is telling you the left and right edges are falling off in brightness, they probably aren’t.
Posted by Art Adams on 03/31 at 04:01 PM
Agreed, you tend to see more green than blue nowadays.
I do remember when greenscreens started to be used, thinking… why? It seemed almost like a fashion at the time, and to me, still does.
My point is that blue should be (re)considered, because in many cases, it can give a better result. A certainly, on big film shows with vfx supervisors who are prepared to do their homework, you still quite often get bluescreen. I believe “300” was mostly blue. King Kong also. Narnia, much of the recent Potters, Watchmen etc.
(BTW - film is just like video in terms of the blue channel ( emulsion layer) being the grainiest. Doesn’t matter - the improved colour separation with foreground still out-weighs this in most cases.)
Horses for courses, I guess.
Posted by paddy on 04/01 at 05:26 AM
You don’t think we’re getting enough separation in the images shown?
With Green on Green, you get about as much as you want for most shots. We can usually key glass without much work.
I find blue always affects the edge noise…requiring work that lowers the detail. It is easier to despill but we don’t have much trouble with that using either Steve Wright’s Unspill macro or Conduit’s Unspill node.
For me it used to be a conditional process but after a few days of side-by-side tests, we decided to stop using bluescreen about 4 years ago.
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Posted by Alex Lindsay on 04/01 at 08:27 PM
The cases shown are in highly controlled conditions, where it is possible to get a very flat screen, perfect lighting, green on green etc. In those conditions, you could probably key off any colour at all.
I’m talking about larger sets/locations, with much messier conditions, a variety of fg material (not just heads), unevenly lit screens etc.
All things being equal, IMHO, on film or
HD I’d choose blue first over green. The reasons why it was the first (only) choice back in the optical days still apply, with digital technology.
Posted by paddy on 04/02 at 03:56 AM
There are still folks that I respect a lot that prefer blue. I just have never worked on a green plate that wish was blue (we shoot a fair bit in “uncontrolled” environments too). I have worked with many blue plates that I wish were green.
I think the big difference with Optical and Digital is the unspill process. Unfortunately, most keyers don’t take advantage of this.
I will say the one place I would be tempted to shoot blue would be in direct sunlight…where the lower luma is often advantageous.
Posted by Alex Lindsay on 04/02 at 09:29 AM
True, green material (esp Composite Components, whose material I adore) can get overexposed in direct sunlight.
Re despilling: I’m a Keylight man. I’ve never come across a better keyer.
Posted by paddy on 04/02 at 10:45 AM
yes, the example shown here has been performed in the ideal conditions, had it not been ideal the results i guess would have been much different!
Posted by mikejons on 04/20 at 12:35 PM
There’s a valid reason to shoot green when using digital sources. Even though the key is a result of a three channel difference, the backing color is the most important when defining the edge.
Chroma subsampling causes blockiness on the edges, if the backing color is other than green (green is carried along the full resolution luma signal, blue and red are not).
This blockiness can be seen especially well with 4:2:0 sources like DV, HDV, XDCAM HD/EX and so on, but it’s there with 4:2:2 sources too. the color channels can of course be filtered to minimize the artifacts, but that doesn’t fully make up for the artifacts. Only with 4:4:4 sources the playing ground is level for all colors.
I made an example image using 3D rendered sources a few years back, compressed to HDV and DV, to point out the difference in optimal situation. Some of the text i wrote back then was a bit, well, guesswork, but the images are still valid, and show the results of varying BG colors well.
http://www.kolumbus.fi/erkki.halkka/HDVKeying/Compression_and_keying.html
Posted by Halsu on 07/22 at 03:35 PM
Yes, good point I guess. I have never comped blue or greenscreen with less than film scans, or 4:4:4 HD.
Posted by paddy on 07/22 at 03:44 PM
Alex: Thank you for the in-depth articles. To Alex and anyone else familiar with green kinos: I ordered some green kinos after reading this article and was surprised to find they are four pin lights when I opened the box, the picture on film tools website showed them as two pin. I say all this to ask: the article mentions affordable fixtures for kino bulbs from Walmart, are these affordable fixtures mentioned four pin or two pin?
Posted by ozdogink on 01/17 at 05:56 PM
