11 Jan 2014

The History of VFX Part V: Optical Effects

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Raiders of the lost Ark Raiders of the lost Ark Lucasfilm Ltd

Index

Having charted the story of VFX in cinema in the first four parts, Andy Stout turns his attention to detailing the various techniques used over the past century, starting with optical effects. Dismiss them at your peril; after all this is how they made 2001

 
At its heart, most VFX of the optical era involves combining elements shot at different times and different scales into the one frame. To do this and prevent one image looking uncomfortably ghostlike (unless, of course, a ghost was exactly what you were after) you need a matte. The very earliest mattes were static and blocked out whole areas of the exposed negative in what effectively amounts to a split screen process. That’s not to say they weren’t highly sophisticated though.

Remember the last scene in Raiders of the Lost Ark when the Ark of the Covenant is abandoned in a Brobdingnagian warehouse that seemingly stretches on to infinity? That’s a matte painting right there, and it’s on screen for over half a minute.

Mattes - learning to travel

The first mattes (and some of the last) used by the VFX industry were painted glass sheets. Glass had been used by still photographers for years to tweak their shots, and while it worked well with film it wasn’t an easy process: locked off cameras of the early film era necessitated sandbags on the camera legs to ease the problems of vibration and judder, while the artist drawing the picture had to pretty much guess the lighting conditions that the final scene would be filmed under.

Hence original negative matte painting was developed. This simply uses a black-painted piece of glass or even cardboard placed inside a matte box in front of the lens to block out an area and prevent that part of the negative being exposed. The film is then kept in the fridge, with a couple of frames snipped off and projected back through a special camera onto an easel for the artist to add the required elements. Various tests are undertaken to match exposure levels, and then the whole thing is then shot again and developed.

Travelling mattes then took things to the next level. What is required here is to shoot two elements – a background and an actor, typically – and then produce a background image that contains an unexposed hole exactly the same size and shape as the moving actor. The actor element is then slotted into the hole and, providing both scenes have been lit carefully and in the same way, the illusion that he or she is performing in front of the background is convincingly created. That’s the idea anyway.

Working with film this takes several, finicky stages to produce a composite and several different, equally finicky processes were developed that refined it as the industry progressed. The Williams Process, patented in 1918, shot the actor in front of an evenly lit black screen and then copied it a number of times to produce a clear background with a black, moving silhouette. This was then bi-packed with the desired background element and printed, but not developed, to a new piece of film. This was then bi-packed in turn with film showing the correctly exposed foreground/opaque background, and the whole thing run through the printer and re-exposed.

Laborious

It was laborious but it was also effective, and was used for nigh on two decades in the industry.

The colour method that first gained widespread usage was the Dunning-Pomeroy process, which also happily shifted the production of the necessary mattes to an in-camera process. The background scene was printed to produce a positive B&W image and then dyed to give an orange and white version. This positive was then bi-packed with ordinary unexposed black and white negative in a specially designed camera that could run both together. Meanwhile, the foreground was set up in the studio to be bathed in orange light and a bluescreen was placed in the background.

All this meant that during shooting the orange foreground elements passed safely through the O&W film to produce a normally exposed image, while the light from the blue screen was absorbed by the orange areas, effectively enabling the actors to operate as their own travelling mattes.



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Andy Stout

Andy has spent over two decades writing about all aspects of the broadcast and film industries for a variety of high-profile industry publications on both sides of the Atlantic. During that time the industry has moved from 4:3 SD to 16:9 SD to HD and now on to 4K HDR. He's getting kind of curious to see where it goes next.

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