G is for Greenscreen

Cinefex magazine’s Graham Edwards discusses the history and future of greenscreen, garnering thoughts from VFX experts including Pixomondo’s Sven Martin. Read excerpts from the original article below.


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 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 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.


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.


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


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.


A Good Day to Die Hard photographs ©2013 Twentieth Century Fox Film Corporation.

To read the original article in its entirety and see thoughts by other VFX experts, check out Cinefex’s blog here.