The inventor of the “blue screen” film technique as it is used today, Petro Vlahos, has died at the age of 96. This posting is based on the interesting BBC tribute to him. I am glad to say the article links to Google versions of two of his patents (this is unusual).
A blue screen is used in filming where actors are combined in film editing with action or other backgrounds to give a seamless effect. A not very good version was available when Vlahos was asked to see if he could improve the process. Some objects would appear to glow, and that was clearly annoying and hardly realistic. Vlahos later said that he spent six months thinking about it, much of it looking out at Hollywood Boulevard.
He came up with a technique that involved a matte which is transparent whenever the blue screen is used but is opaque in other sequences in the film. The blue, green and red parts are separated and then combined in a certain order. It seems that rather than the actors being superimposed on a background, which I'd assumed, it’s the other way round, which sounds mysterious to me (I do love the magic of the “movies” after all).
His Composite color photography patent was applied for in 1959 and the technique was first used in Ben Hur.
A more complicated variation was also patented as Composite photography utilizing sodium vapor illumination.
Both patents were assigned to the Motion Picture Research Council but the article states that this second technique was developed for Disney. Actors were filmed against a white background with sodium lamps which made a yellow glow bounce off the background.
The camera filmed two separate images (or “film stock”) simultaneously. A prism on the camera would cause one film stock to split the yellow light from other colours and send it to a black and white film stock to create a matte.
The other film stock would record in normal colour without any yellow glow. This produced a very clean effect, and was typically used when actors were apparently interacting with cartoon characters as in Mary Poppins and Bedknobs and Broomsticks.
Vlahos later formed a company, Ultimatte, to develop more techniques.
This is a list of Vlahos’ patents.