G is for Greenscreen

by Graham Edwards

G is for Greenscreen - The Cinefex VFX ABCIn the VFX ABC, the letter “G” stands for “Greenscreen”.

You’re standing on a film set. What do you see? Cameras? Lights? A craft service table laden with muffins? A hundred people standing around waiting for something to happen?

Look hard, and you may also see something else: a piece of visual effects technology so commonplace that the eye just skitters over it, barely even registering it’s there – strangely appropriate, because the object’s sole function is to appear completely invisible to the camera.

I’m talking, of course, about the humble greenscreen.

Everyone knows what a greenscreen does. When you point a camera at it, the flat primary colour creates a blank space into which those clever visual effects artists can put anything they like. The greenscreen is a blank canvas ready and waiting to be painted with a spectacular Himalayan panorama, a brooding alien cityscape, a speeding freeway … whatever the backdrop, green is queen.

But can its reign continue? To find out, I asked a panel of VFX professionals whether they thought greenscreens would still be around in ten years time. Before they offer their thoughts on the future of greenscreen, however, let’s take a moment to consider its past.

Greenscreen composite from "Avengers Assemble"

Before and after greenscreen composite from “Avengers Assemble” by ILM

Greenscreen Past

The history of greenscreen is really the history of compositing, which the Cinefex VFX ABC explored in C is for Composite. Still, it never hurts to refresh the memory.

A fundamental discipline of visual effects is the combining of one image with another in a sort of kinetic collage. Typically, this involves cutting the moving image of an actor out of one shot and pasting it into the background of another. To do this effectively, you need a foolproof way of making a moving mask that precisely matches the actor’s constantly-changing silhouette. This mask is known as a travelling matte.

Ever since the early days of cinema, filmmakers have experimented with different ways of creating travelling mattes. One of the earliest solutions is still in use today: filming an actor in front of a coloured screen.

Technicolor bluescreen composite from "The Thief of Bagdad"

“The Thief of Bagdad” features some of the earliest Technicolor bluescreen composites

Developed in the 1930s, the Dunning Process used a blue screen, and required the actors to be illuminated with yellow light. Coloured filters were used to separate foreground from background, but the process only worked in black and white. The arrival of colour film led to more complicated systems of filters and optical printers being used to isolate the actors against the bright blue screens.

Why blue? Because the cool colour of the screen was at the opposite end of the spectrum to the warm skin tones of the actors standing in front of it; the contrast made it easier to create a good matte. You just had to make sure the wardrobe department didn’t dress your leading lady in a bright blue evening gown, or else she’d disappear before your eyes.

Preparing a bluescreen shot for "Ghostbusters"

Preparing a bluescreen shot for “Ghostbusters”, in which the Stay-Puft Marshmallow Man was composited into live-action plates shot in New York

In the ‘60s and ‘70s, Disney had great success with yellow screens lit by sodium vapour lights, used in films such as Mary Poppins. But for the most part the colour of choice remained blue. Once digital techniques came on the scene, however, blue began giving way to green.

So why the colour shift? One reason is that many digital cameras are configured using a Bayer Pattern, in which there are twice as many green sensors as either red or blue; these cameras are naturally more sensitive to the green end of the spectrum. And greenscreens often perform better outdoors, in environments where a traditional bluescreen might blend with the sky.

In many situations, however, the bluescreen is still the filmmaker’s best option – it just depends on the demands of the individual shot.

"White House Down" bluescreen composite

This composite shot by Crazy Horse Effects from “White House Down” proves the traditional bluescreen is still alive and kicking

Greenscreen Present

In the old days, lighting a bluescreen was a big deal. Because the optical department was reliant on delicate photochemical processes, it was vital that the blue colour captured in the original photography was as flat and clean as possible. For that reason, most bluescreen shots were set up on the soundstage, under carefully controlled conditions.

The effectiveness of modern colour separation tools – and the trend towards smaller set builds augmented by digital extensions – has led to a more relaxed approach. You’ll find greenscreens of all shapes and sizes on many location shoots, filling in the gaps between buildings or blocking off the ends of streets. Entire sets might be built and covered in greenscreen material, allowing actors to clamber over blocky toytown structures which will be replaced in post-production by entire digital environments.

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Smaller greenscreens are used within the sets, or even on the bodies of the actors. Wondering what to display on that bank of monitors in the spaceship’s control room? No problem – just set the screens to green and drop in the funky graphics later. Need to alter the anatomy of your lead actor’s head? Easy – just give him a greenscreen bald cap and get VFX to track in the tentacles.

With a greenscreen, you really can do anything.

In fact, greenscreens have become so familiar that even Joe Public – who’s more interested in popcorn than post-production – understands broadly what they do. Granted, the only key he knows is the one that fits his front door, and he might wonder why the rotoscope department is always griping that there might as well not be a greenscreen there at all – “Gee whiz, the thing doesn’t run to the edge of the set, and it’s not even lit properly, I mean, these things aren’t magic carpets, you know!” Nevertheless, the greenscreen has become a universal shorthand for “visual effects go here”. If there’s a single image that symbolises the visual effects industry for the outside world, the greenscreen is it.

It’s an icon for people within the industry too. Take a look at all the VFX professionals you follow on social media. How many of their online avatars are bright green squares? Quite a few, right?

The Go Green movement rose up over a year ago with an agenda to raise awareness of inequalities within the visual effects industry – in particular the effect of nationally-granted subsidies across an international marketplace. The movement is still going strong, and the symbolic power of the greenscreen remain at the heart of its campaign.

There just no escaping it: the greenscreen is a dominant force in visual effects. In fact, it’s hard to imagine what filmmaking would be like without it.

Greenscreen Future

Let’s fast-forward ten years to a movie set of the near future. Look – there’s the camera. Mind your head on the lights. Hmm, looks like we could do with a fresh batch of muffins on the craft service table.

Now, let’s look for the greenscreens. Ten years on, are they still around? If not, what new technology has come along to replace them?

Here’s what our panel of visual effects experts had to say:

Visual effects technology continues to progress and develop at a high rate. Even now our teams have had to become adept at working around lack of green screen when time constraints/filming schedule prohibit its use. Having said that, I think in ten years time, greenscreen or an equivalent will still be needed when actors are in frame. I can see a time when greenscreen could be replaced with live feeds that can still be keyed off, but have the massive advantage of providing actors with on-set feedback. It would be an interesting development that would be beneficial both for us and for the wider production. – Jeff Clifford, Head of R&D, Double Negative

We’ll probably be using more sophisticated systems for real-time keying on location in order to visualize complex visual effects shots, but the reality is that green (or blue) screens are still very useful, and will likely continue to be for the foreseeable future. We are still coming up with better ways to light actors on green screen to make the integration better. But there are techniques that will likely revolutionize this, ie real-time rendering and the motion capture of performances. I can imagine a not-too-distant future in which we can create 100% photo-real characters, captured in real-time and rendered on a 100% digital environment. – Aladino Debert, Creative Director and VFX Supervisor, Advertising & Games, Digital Domain

I’m pretty sure that in 10 years we won’t be using color difference matting with green or blue screens any more. Future VFX youngsters will feel about this technique much the way we feel about using miniatures today. Cameras which capture depth data are already available. When the resolution of these channels increases, we’ll place set extensions and digital creatures not just behind the plate, but within it. This will complete the deep compositing idea. Meanwhile, I guess, VFX artists will continue spending their time on rotoscoping plates, where it was not possible or too expensive to setup a green screen. – Sven Martin, VFX Supervisor, Pixomondo

Yes, I believe we will still be using greenscreens. Manual rotoscoping is an art form in itself, but even the best roto artist will never match the precision of a greenscreen key. It’s impossible to determine the exact colour and opacity of a hair at a given pixel using even the best rotoscoping system, and to be consistent and accurate over the entire image and a whole sequence of images. Other software solutions which have attempted to extract foregrounds from their backing have been promising, but thus far have proven to be either temporally inconsistent, or simply less precise than a greenscreen. Rear projection has recently been tried again with stunning success in Oblivion. With improvements in projectors (increased dynamic range) I can see this idea being used more often. It does have its disadvantages though; you need to know in advance exactly what you want in the background. Rather than an end to greenscreen use, I hope we will see a hybrid solution: the continued development of the technology and an amalgamation of ideas targeting the same problem. A more intelligent keyer might consider not only colour, but depth, focus, disparity and other image factors to compute whether a pixel is solid foreground, solid background, spill, or transparent foreground. But it seems like it will be a long time before there is a set of circumstances in which a greenscreen would not be at least part of the solution. – Charlie Tait, Head of Compositing, Weta Digital

We will definitely still be using green and blue screens in 10 years time. Technology and techniques are improving, but some classes of problem just require them, and will for the foreseeable future. – Ken McGaugh, VFX Supervisor, Double Negative

I anticipate still using greenscreen insofar as there will be a need to extract live performance from unwanted background. It will be more electronically procedural, with less burden on set-up and lighting to specifications. I think on-set needs will be more forgiving. – Joe Bauer, VFX Supervisor, HBO’s Game of Thrones

Yes, we will still be using greenscreens. There will be advances in technology that will simplify the process, but I don’t think enough of an advance to automate the cutting of mattes. I also don’t believe all advances in technology will be accessible to every filmmaker. However, I do feel this is where 3D stereo technology will come in handy, with further exploration of depth maps. This is probably the area that will bring about the eventual elimination of green screen. – Lon Molnar, Owner & VFX Supervisor, Intelligent Creatures

I would love to see a day when we could do “deep” filming: somehow map out depth and use this to help automate our composites. This is years away from being a reality. Often there are times we choose to not use a blue or green screen, opting to rotoscope instead, but blue and green screens are here for the next 10 years and beyond. – Geoff Scott, VFX Supervisor, Intelligent Creatures

Bluescreen set-up from "Return of the Jedi"

Cameraman Don Dow attends to the miniature sail barge while assistant Patrick McArdle prepares the Vistarama motion control camera, in this bluescreen set-up from “Return of the Jedi”

Conclusion

Well, the consensus seems to be that greenscreens – and blue – aren’t going anywhere anytime soon. Still, given that I can already download an app to my smartphone that will scan an object, isolate it from its background and derive 3D geometry from the data, the dream of “deep filming” may be closer than we think.

Until it becomes a reality, however, the greenscreen seems likely to dominate as the VFX background of choice, and thus will continue to be what it’s always been: the original field of dreams.

Avengers Assemble photographs © 2012 by Marvel Entertainment. Ghostbusters photograph copyright © 1984 by Columbia Pictures Industries Inc. Prometheus photographs copyright © 2012 by Twentieth Century Fox. White House Down photographs © 2013 by Columbia Pictures. Return of the Jedi photograph copyright © 1983 by Lucasfilm Ltd.

3 thoughts on “G is for Greenscreen

  1. While our product, Primatte, has had a good run for the last 17 years and seems to still be popular, we are constantly looking for ways to get better results with it. Our last release, Version V, had a lot of new features that simplified the chromakeying process and, we think, made the product easier and faster to use. We will continue to look for ways to improve it and welcome any suggestions from users as to how we might do that.
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  2. Pingback: G is for Greenscreen | PIXOMONDO

  3. Make a very good key is barely has hard as it was 15 years ago, (when i started)… it is one of the area where the inovation and progress his the poorest.
    i though, 15 years ago, that the Zcam will be all over the place now, but it seems that people what to spend time in developing Hi-deph/rate/rez, etc..
    Too bad for the guys who waste so much time in rotoscoping everything :)

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