Most Hollywood blockbusters today depend upon special effects (SFX) for their visual impact. One of the most widely-used techniques is "greenscreening", in which multiple elements are filmed in front of a plain green background and then are “composited” together in one scene. But the techniques of SFX compositing go all the way back to the beginnings of cinema.
"Hidden History" is a diary series that explores forgotten and little-known areas of history.
When motion photography first appeared back in the late 19th century, the sheer sight of “moving pictures” was a sensation to audiences. The first cinema productions, such as those made by Lumiere in Paris, depicted short scenes like railroad engines rushing towards the viewer, or a man with a gun firing it at the audience. It was reported at the time that these were so shocking that audience members would sometimes faint.
Over time, however, as motion pictures became more familiar, movie-makers needed new techniques to produce new effects that would continue to dazzle and amaze their audiences. (A process that continues in Hollywood today.)
One of the most significant pioneers was George Melies (pronounced “may-laze”), who worked in France. Cinema producers had already mastered the technique of the “double exposure”, in which a piece of film was shot with elements of a scene, then the film was rewound to the beginning and shot again to add new elements. But Melies added a significant new improvement: using pieces of glass that had been painted black, called a “matte”, Melies could block light from entering the camera and carefully prevent specific portions of the film from being exposed while he shot a scene, and then by rewinding and shooting again, this time with the rest of the scene blacked out, he was able to add new elements precisely where he wanted them. With this, he was able to produce what were, at that time, spectacular effects: in his famous “A Man of Heads”, shot in 1898, Melies was able to create a scene of a magician who would sequentially take his head off and set them on the table, where they would all sing together while he played a banjo.
The double exposures of Melies’s matte technique were all done inside the camera. This however produced two problems that Melies had not been able to solve: during his matte shots, the camera could not move at all, and none of the actors being shot could cross from a matted area into a non-matte.
But by 1918 a new process had been worked out, by a cinematographer named Pat Williams, that eliminated the painted glass mattes and allowed the actual compositing to be done in a darkroom instead, avoiding both of these problems. William’s technique was called a "traveling matte". In this process, the actors would be filmed against a plain black background, and then this piece of film would be shot again on high-contrast film to produce a “scene" in which the entire background was black and the actors were pure white. In effect the negative of this sequence acted as a matte, allowing light to pass through certain portions of the image and blocking it at others. Perhaps the most famous early films to use the traveling matte technique was “The Invisible Man”, produced in 1933.
With the traveling matte, SFX were now free to move anywhere within the screen.
The high-contrast technique used in the traveling matte, however, made it difficult to capture fine detail, and it also had problems if there were a lot of shadows in the shot. So in 1925, an improved version of the Williams process was developed by C. Dodge Dunning. Dunning’s technique used a series of filters to shoot the actors in bright yellow light, and to shoot a plain background in bright blue. This could then be split into two separate pieces of black and white film to make the foreground element and the traveling matte. The Dunning bluescreen process was first used in the groundbreaking 1933 film, “King Kong”.
But just as the Dunning technique was developed, the film industry was already being altered by an important new development: color film. The earliest color films all used a similar technique: the camera essentially shot three different colors (red, blue and yellow), and then combined these with black to form the finished full-colored sequence. None of the existing traveling matte techniques would work with this.
It wasn’t until 1940 that a good process for compositing colored film sequences was developed by FX artist Larry Butler. It was first used in the film “The Thief of Baghdad”. In Butler's technique, the actors were shot against a plain blue background, and the FX department would then use that sequence to produce a black and white traveling matte in a process similar to the Williams technique. To complete the sequence, this matte was then passed through an "optical printer", a specialized camera that was able to take several pieces of film (including each of the three color separations) and project them all, in layers, onto a single strip of film, producing a completed composite image.
For the next 40 years, blue screen traveling mattes were the state of the art in the film industry. (Disney did develop a technically-superior process utilizing a yellow screen and used it for "The Absent-Minded Professor" and "Mary Poppins", but the camera was so expensive that only one was ever built.)
When George Lucas began work on “Star Wars” in 1975, however, he ran smack into one of the difficulties that surrounded the traveling matte technique: if you had multiple moving elements in your scene, it was very difficult to make their motions match, since each element had to be shot and matted separately in its own sequence.
Fortunately for Lucas, the computer age had already begun, and cinematographer John Dykstra rigged together a computer-controlled camera that had the capability, once its motion was captured and stored in memory, to faithfully reproduce the same identical shot over and over again, as many times as was needed. By combining the computer-controlled camera with blue screen traveling mattes, “Star Wars” was able to produce on-screen SFX that still look good forty years later.
The computer revolution of the 1980s, though, also revolutionized film-making. Film cameras were replaced by digital cameras, and the entire time-consuming process of color separations, optical printers, and traveling mattes was replaced by digital editing. And central to this was a process called “chromakey". We know it today as "green screening".
In this technique, elements such as actors or digital models are shot against a plain green background (the color green was selected both because it shows up brightly in digital recordings, making it easier to work with, and also because normal human skin tones do not have much "green" element to them). Using a series of computer filters, the green can then be removed, and each element can then be digitally layered on top of each other and flattened into a final sequence.
One of the early movies to successfully use digital green screening was “Death Becomes Her”, made in 1992.
Today virtually all of the big Hollywood FX spectaculars are shot with green screens and digitally edited.
NOTE: As some of you already know, all of my diaries here are draft chapters for a number of books I am working on. So I welcome any corrections you may have, whether it's typos or places that are unclear or factual errors. I think of y'all as my pre-publication editors and proofreaders. ;)
