A short history of keying
Discovery of the matteThe second effect, and the one that concerns us most here, was the matte, used with a double exposure. It was discovered that if you exposed the film (by shooting a scene) and then wound the film back into the camera, you could expose a new image over the top. Filmmakers like Méliès saw that if you left parts of the scene dark in the first exposure, then you could align some action to happen in that space on the second exposure. The India Rubber Head (1901) was a case in point. (See if you can find a version to see on YouTube if the above link has moved.)From the still at the head of this article you can get the idea. An alchemist/scientist places a version of his own head on a table and begins to inflate it with bellows. Conveniently there is a black shadowy archway where this double exposure happens. The head ‘expands’ by having the camera move closer in the second exposure. Filmmakers soon started experimenting with Matte boxes- simple bits of card over the lens that stopped portions of the film being exposed to light the first time, and then inverted this on the second exposure.
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Visual Effects for Guerrilla Filmmakers
Colour Separation processesAs film grew in commercial importance, there were many variants of this process created; but essentially it’s the antecedent of what happens today digitally. When colour film started gaining ground (around 1918-1936) clever new methods to separate foreground and different background were invented. One particular method was the Blue Screen Colour Difference process. Invented by Petro Vlahos it became the basis for the most widely used methods of getting a travelling matte until digital techniques were possible in the 80s. The process demanded a very pure blue backlit background. The film negative produced was copied onto black and white filmstock through a blue filter, which allows only red and green to expose the film, so the blue area is transparent. However there is always likely to be a bit of blue on the foreground character so this black and white film was combined with the original negative to make a new high contrast matte, but this time through a special green filter. By now the blue screen is clear and the foreground character totally black. This ‘male matte’ is then copied to a negative ‘female matte’. There are several other stages to this- each one with other film prints. Aren’t you glad we now do this digitally?The advantage of this system was detail- around hair for instance, and it recorded semi-transparent objects like a glass of water or reflections on a window very well. The system was even used in Superman (1978) -although Superman’s costume was blue, they were able to pull a decent key through this method.
Now it’s all digitalIn the digital age we still use some of these tricks to pull a decent key, although it all happens now at the tweak of a mouse, we don’t have to wait overnight for film to be processed through chemicals. However, we sometimes still need to look at the individual Red, Green or Blue channels of a foreground image to make a matte work. It can still be laborious to get your key as convincing as you want it to be.YouTube is a great place to look for early cinema firsts, like Georges Méliès or Petro Vlahos’ work. It’s been said that many of the first pioneers of cinematography shared similar characteristics to today’s guerrilla filmmakers; the ability to experiment, make do with what they found around them, and inventiveness. Just like today, the field was wide open for newcomers to create things never seen before. As an example have a look at this film about the first colour film ever invented. If you find any interesting clips about any of the subjects in this article, why don’t you share them with all of us?Next we’ll see how Justin Hunt from Ember films creates a great green screen image which you’ll have a chance to key very soon.
Visual Effects for Guerrilla Filmmakers
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