Explore the history of Chroma Key. Everything from blue screen to green screen!
This time on tips and tricks we’re gonna take a look at the history of Chroma Key, how the process began, and how film producers used this process over the years to help them cinematically. Everything from blue screen to green screen, this time on tips and tricks.
The history of Chroma Keying is based on the need to have the control and convenience of shooting on a set married with the beauty of shooting on location. Location shooting, ranging from the extremely difficult – say the middle of the ocean – to the impossible – say a battle scene in deep space – are the prime instances where Chroma Keying comes into play. The idea of being able to separate the foreground and seamlessly integrate another background has driven some of the best minds in the film and TV business to come up with various solutions over the years.
Originally developed in the 1930s by RKO Radio Picture, producers used a process that combines two or more images into one known as a traveling mat. This process was pioneered by Linwood Dunn. He used traveling mat and double exposure to create transitions in such films as the 1933 musical Flying Down to Rio. The effects of double exposure had been known for some time, but Dunn’s attempt at minimizing the background of the second exposure by using a traveling mat took a big leap forward in believability. The process involved projecting the background image onto a counter mat and then optically re-photographing the result. While not perfect as you can see some bleed through in the airplane, it was pretty impressive for 1933, and the audiences bought into the effect.
Special effects mastermind Larry Butler is largely credited with the creation of blue screen during a fantasy film, The Thief of Baghdad. Released in 1940 by London Films, the film was the first of its kind to feature dazzling special effects as well as Technicolor. When color film became available it opened the door to new advances in Keying, and The Thief of Baghdad was the first film to use the Chroma Key process. By using three strips of film, one for red, one for green, and one for blue, Butler was able to arrange the original negative and newly printed positive strips in such a way that the blue negative and green positive film strips created a pretty solid mat that could be composited with new footage shot against a blue screen. These were all run through an optical printer so that the final film print would show the finished composite. While not yet a perfect Key due to the limitations of the equipment at the time, the basic concept was used in color film compositing until the advent of digital technology.
Arthur Windermere began to develop even more blue screen techniques by creating the ultraviolet traveling mat process in the 1958 adaptation of the Ernest Hemingway novel, The Old Man and the Sea. Unfortunately the process was extremely time-consuming, as the film had to be combined one frame at a time.
The Chroma Key process was finally perfected by Richard Edlund after he created a quad-optical printer for The Empire Strikes Back in 1980. The quad-optical printer was the key to taking a rough analog process, making it easier and much more accurate with better results for the final shot. Two projectors, a film camera, and a beam splitter combined the images together one frame at a time. This part of the process had to be very carefully controlled to ensure the absence of black lines. During the 1980s many computers were used to control the optical printer to get it just right.
The switch from blue screen to green screen largely reflects the switch to video in the late ‘70s. Although blue screen is very complementary to human skin tone and better with film due to the blue emulsion layer film strips contain, green screen became the favorite in the video world because digital cameras retain more detail in the green color channel. It also requires less light and has a higher luminance value than blue. In the past decade the use of green has become more dominant in video special effects. Also, the green background is favored over blue for outdoor shooting, where the blue sky might appear in the frame and could accidentally be replaced in the process.
CGI, or computer generated imagery, is now used for the majority of Hollywood releases. The principle is the same as working with the green screen, the only difference being the backgrounds are constructed on a computer instead of shooting an existing location.
The effort that generations of filmmakers put into special equipment and techniques in order to pull a good Key was intense and difficult, requiring both artistic sense and a technical mastery of the media. So the next time you shoot some green screen footage and simply click the Chroma Key effect with your mouse, spare a thought for those uncelebrated men behind the scenes who made the whole process possible.