How you light your subject is up to you. Don’t worry about doing the old-fashion Magenta rim light…we don’t need that anymore. Just light the subject as you would for the given scene. One thing that is important, however, is to make sure that both your foreground and green backing are well lit. Often, crews get one right and the other wrong. Looking through the scopes (and you should always be using scopes on a greenscreen stage), you green level in the RGB Parade should be between 70-80% and the foreground white should be around 90% and black should be…black…5% is OK, if it’s over 10% is will start to look washed out and you will eventually have to crush it (there are lots of nuances with the black level but this is an international article so we will leave it there).
A little more about scopes and screen levels. First of all, to repeat…you need scopes. You don’t need hardware scopes but you do need some kind of scopes. You need scopes to properly measure the evenness of the screen and to measure the Green channel’s relationship to the Red and Blue channels.
For evenness, you need a standard luma scope. This scope gives you a reading of the brightness values across the entire plate. The absolute value is not important (40-60 percent is a good start) but a flat line all the way across is. You want this line to be as flat and thin as possible. When this line is wide and uneven, it means there is variation in the screen. Variations mean you need to widen your key target to include more levels of green…often these soft variations coincide with the subtle greens on the edges of your subject…meaning you need to clip them to pull the key…meaning hard edges… which, is well, bad.
Once the screen is even, the RGB Parade can be used to measure green record and it’s relationship to the red and blue record. Clipping is the first thing to check for in the RGB parade. You do not want the green channel peaking over 90%. If it is, you risk clipping light greens. We usually shoot for 70%. These highlights are often on your subjects edges. The second thing to look for in the RGB Parade is the distance between the red, blue, and green channels. We consider 40 points to be a minimum for interviews or close-ups where you don’t see the person’s feet. If this distance is reduced, you will have less contrast in your matte and, as a result, less definition.
In Final Cut Pro…you can see a fairly flat luma scope and plenty of separation between the Green (pegged at 70%) and the Red/Blue channels (at zero). This is a function of using green kinos on a green screen.
What to use for scopes? We use either Conduit or Scopebox. Conduit (once again, our own plug-in) gives us live set keys but Scopebox is a better set of software scopes. If you are on a PC, Adobe’s OnLocation has a good set of scopes to work with. You can also use Final Cut Pro’s scopes BUT you need to capture a sample and view it to check the RGB parade…a pain but a possibility.
So that’s the basic setup. Yes, there’s alot more to talk about but this gets most videographers onto the playing field. In the next installments of this series, we’ll talk about the capturing process, the keying itself, and the final composite.
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
