July 20, 2013

Watch: Tutorial on What It Takes to Pull Off Great Chroma Keying

Chroma Key LessonWhen I first heard about chroma keying, I had 2 thoughts in my head: "Chroma keying is as easy as getting some bright green fabric at a fabric shop," and  "This process is so complicated I never want to try it." Well, I've learned that it's not difficult enough to shy completely away from, but it's not as simple as I first thought. Either way, once again, Filmmaker IQ lends us a very generous hand and walks us through 5 elements of chroma keying through a helpful tutorial video -- shedding light on things we should consider before we put our subjects in front of that big green (or blue) screen. Check it out after the jump.

As usual, John Hess of Filmmaker IQ hosts this great video tutorial, this time on chroma key. The lesson is broken up into 5 elements: space, the screen, lighting, the camera, and post production.

By considering your working space, using a quality screen, lighting it evenly, using a camera with as little compression as you can get, and finally using a good software keyer, you should be able to pull off a great key. Good chroma keying is a skill, and it will take a little practice, but the reward for your patience and experimentation can be quite liberating. – Another tool for you use in your quest to make something great.

Check out the tutorial below to find out how to make a great chroma key:

Of the 5 elements they cover, here are a couple integral ones to keep in mind. Evaluating the space you have to work with will directly determine the kind of chroma key you can produce. The more space you have, the greater distance you have to pull your subject away from the green screen, eliminating shadows. With less space, talking heads and still shot are possible.

The screen you use, whether it's blue or green, has an effect on your image as well -- for instance, green screens require less light than blue screens. Filmmaker IQ says:

-- many digital cameras use a Bayer pattern of Red Green Blue photosites where there are twice as many green photosites as there are red and blue. This makes digital cameras much more sensitive to green coloring.

To find out what else Filmmaker IQ had to say about chroma keying, in terms of lighting, cameras, and post production, go here.

Have you ever tried chroma key? What worked for you? Let us know in the comments below.

Links: 5 Elements of a Great Chroma Key -- Filmmaker IQ

Your Comment

23 Comments

I like taking a picture of my lit green screen with iOS or Androids 'Snapseed' app and then increase the contrast of the photo. You immediately see where the highlights and shadows are on your screen.

July 20, 2013 at 10:55AM, Edited September 4, 11:21AM

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Vincent

This was very informative... I usually don't think about the space requirements that John brought up early in the video. And the fact that green requires less light than blue is also helpful to us low-budget filmmakers.

July 20, 2013 at 11:05AM, Edited September 4, 11:21AM

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Also, bear in mind that today's shallow depth of field craze increases the difficulty of achieving a clean key. I find f5.6 to f8 perfect. Occasionally I will back light a subject with 1/4 cto to further battle any green screen bounce.

July 20, 2013 at 11:39AM, Edited September 4, 11:21AM

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Dan Barr

I have very little experience with filters, gels, etc. Could you elaborate on what the 1/4 cto does to improve the backlighting?

July 20, 2013 at 1:31PM, Edited September 4, 11:21AM

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Matthew C. Plowman

CTO (color temperature orange) is an orange filter. Backlighting with it will help to neutralize any green reflection on your subject that comes from the green screen.

July 20, 2013 at 1:47PM, Edited September 4, 11:21AM

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James Lewis

1/2 magenta gel will actually neutralize the green spill better than CTO, especially if you're already lighting with tungsten.

July 20, 2013 at 3:16PM, Edited September 4, 11:21AM

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jmg

1/2 magenta is the way to go over CTO

July 20, 2013 at 3:17PM, Edited September 4, 11:21AM

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jmg

Actually, any contrasting color will work its a matter of aesthetic choice. I'm usually shooting with HMIs or Kinos with daylight lamps so I backlight with tungsten or cto my 5600k light source. Nothing beats experimenting and finding what works for you and is visually pleasing to your eye.

July 20, 2013 at 11:34PM, Edited September 4, 11:21AM

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Dan Barr

good tutorial.

July 20, 2013 at 1:58PM, Edited September 4, 11:21AM

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maghox.fr

Great tutorial, we have been doing a lot of green screen shoot and getting better with each indie film project we do.. One great plug in is the Red Giant's Denoiser II that can eliminate video noise without hurting time image so the keyed final would look great. See here: https://vimeo.com/22319830

Love this site. I visit this site hourly now. Lol feel like I'm addictive to nofilmschool.com!

July 20, 2013 at 4:05PM, Edited September 4, 11:21AM

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Johnny Wu

I much prefer Neat Video, I found RG's Denoiser II way too smeary for my tastes.

July 20, 2013 at 4:47PM, Edited September 4, 11:21AM

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Gabe

Question for VFX folks that deal with RAW greenscreen. Do you still need to increase the shutter speed to deal with stuff like motion blur as someone swings their arms around? Does the green still bleed thru even if you are dealing with RAW? (This might apply to objects that may be out of focus in the shot, too.)

July 20, 2013 at 5:21PM, Edited September 4, 11:21AM

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Ben Prater

only if you think green spilled edges are more distracting than an inconsistent shutter angle

July 20, 2013 at 8:16PM, Edited September 4, 11:21AM

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jime

Don't mess with the shutter angle, like the guy above said.

If you have a 422 camera, it'll pretty easily pull a key even from a motion blurred subject, or a girl with curly hair. (Heck, if you have a 444 Panavision Genesis you can key smoke).

I've keyed talking heads with a Nikon D7000 many times with good results (it's 4.2.0), but it was a fight. A lot of matte feathering in post! Easier to buy a C300 instead. :)

July 20, 2013 at 8:41PM, Edited September 4, 11:21AM

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Nice place to start for people who are learning about chroma keying. However, with internet access and more people learning and teaching basic vfx, I feel like a lot of the same information gets recycled over and over, without people really understanding why those choices are made to begin with. This did a little better in terms of education compared to some of the videos I've seen, but the resulting example key, and the main tutorial key, were still pretty poor. Granted, for a training video, nobody is expecting a simple explanation of technique to look like a big-budget type job. I don't consider myself an expert, but I have learned over the years a lot of things that go into a good key. A really really well lit background can result in much less hassle in post, however, even the worst shot stuff, and more importantly mediocre footage can be pulled well if your compositor has a correct understanding of pulling multiple keys, and gently finessing the image. And I have seen carefully shot footage slapped into a crap key, simply because the compositor only learned the plugin approach of "one click" keying. I applaud everyone in the vfx community for helping each other learn. And I recommend that we keep in mind that no training will ever be the last word in compositing.

July 20, 2013 at 8:04PM, Edited September 4, 11:21AM

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Aaron

They left out the most important part - hair. The guy they were shooting was bald, and that is VERY easy to key; long hair, on the other hand, is far harder (especially blond hair against green, since they are close on the colour spectrum), disappointing they didn't include any tips on hair.

July 20, 2013 at 8:11PM, Edited September 4, 11:21AM

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Matt

Best thing to do is just use masks to separate parts of the shot so you can target specific ranges of values in your key to get transparency. Pretty much the only way you can do it unless you have an absurdly evenly lit green screen.

July 20, 2013 at 8:25PM, Edited September 4, 11:21AM

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Gabe

Another possible helpful tip would be if you're shooting stationary talking head and using a dslr, turn the camera 90 degreed to get a vertical composition. This way you're using more pixels than if you shot traditional horizontal and you're not shooting wasting space to the right or left of your subject. Doing this will also help achieve a better key especially using dslr's high compression because you're using more pixels to capture the same subject.

Again, this only works where your subject is a talking head and not using much space to the left or right of them.

July 21, 2013 at 12:53AM, Edited September 4, 11:21AM

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Good for standing, full body "weather cast" type shoots too...

July 21, 2013 at 9:31AM, Edited September 4, 11:21AM

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SpartaBear

in fact the reason film used and uses blue mainly is because our skin does NOT contain the blue pigment.

July 25, 2013 at 3:50PM, Edited September 4, 11:21AM

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bruno

in the old days I used to use an orange backlight to take blue spilling away

July 25, 2013 at 3:52PM, Edited September 4, 11:21AM

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bruno

Keep in mind that if you do Chromakey with After Effects there are many 3rd party filters you can purchase to assist with your key no matter what the object you're trying to key. I've heard of a filter designed to help you key fur, if you are trying to key animals over a background.

July 25, 2013 at 5:05PM, Edited September 4, 11:21AM

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I have one very important question regarding the order of the process... I am preparing for my first short film, a sci*fi drama, and I have no experience but what I have been able to learn online and hands-on. So far my only unanswered question is: Should I shoot the background first or the actors? I have a love scene that is supposed to happen in a lake shore and a fighting scene in the top of mountain. I want the background to look real, and there are a lot of shots and camera angles to mix. Should I first shoot the actors in front of the green screen and then try to match the ratio, angles and shots on the real background, or first get the background shots and then fix that for the actors to perform later?

December 25, 2013 at 2:35PM, Edited September 4, 11:45AM

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Francisco