The use of a green screen as a special effects tool in movies may seem like a modern invention, but using coloured backgrounds to combine foreground action with fantastic backgrounds is a technique which dates back to the 1930s.

Various methods were used to combine foregrounds with specially prepared backgrounds since the early days of cinema, but it wasn’t until colour photography became popular in the 1940s and 1950s that solid coloured backgrounds came into their own for special effects work.

Blue Beginnings

Special effects technicians chose the colour blue for the backgrounds which were to be replaced in the films of the 1940s. This was because it was one of the least common colour in nature, meaning it reduced the chances of something disappearing when filmed in front of it – after the processing of the film was complete. Green was equally as good but wouldn’t become the background colour of choice until decades later.

During this time the various methods for replacing the blue background with a more exciting one relied on a range of techniques for processing film. These were much more complicated than the digital techniques of today.

Films like The Ten Commandments (1956) famously used the Blue Screen technique.

Much like today the subject was filmed in front of a blue green, but many more steps were involved to remove the background. The positive film that was produced during filming had to be transferred onto two more, black and white, film strips through a red and blue filter. When the resulting positive black and white films were combined the new film could be used as a mask. This mask would block out light hitting the blue background so that only the foreground would be transferred onto another strip of film, with transparent film surrounding it.

The last step would be to combine the desired background film, with the foreground film, onto a final strip of film. In total this early method required eight steps, sometimes more, to get to the finished composited film clip.

Yellow Years

Movie studios developed a similar method in the 1950s, but which used a bright yellow background instead of a blue one. Two strips of film were exposed at the same time, instead of one, to produce a mask which could be used to combine the foreground and background elements. The film Mary Poppins features the most famous example of this method, combining live actors with animated backgrounds.

Although this method produced excellent results, and was much simpler, it required specialised equipment that wasn’t compatible with the lenses which had started to become the standard for filmmaking at the time. Movie studios turned back to blue because of this, creating an improved blue screen method which matched the quality of the yellow screen composites – this new blue screen method was a lot more complicated than the original and required a total of 12 film elements to get to the final composited image.

Turning Green

It wasn’t until the late 1990s that green became the default colour for creating composited images.

A Virtual Television Studio, image by Phrontis, CC BY-SA 3.0

As digital post-production became more popular green became the logical choice for special effects backgrounds. Not only was green easier to light, but it was a less common colour for costumes (especially for TV weathermen) and looked brighter on electronic displays. The colour green is now firmly associated with Hollywood movies, but blue is still widely used. The new digital methods of blue and green screen compositing became known as chroma keying.

Chromakey Today

Today new technologies, new software and high-resolution digital cameras are making the green screen technique more accessible than ever.

Green Screen Submarine uses a custom web app to remove green pixels from images, creating a composite picture which puts someone in an incredible place.

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