Green screen: what it is and how it works

The green screen, also called chroma key, is a technique used in photography and film. It consists in placing a subject in front of a green backdrop, which in the post-production phase will be replaced by another background: the subject will then fit into the setting you prefer.

Why is it green?

Green is the chosen color because it contrasts with most everyday objects. In film productions, it has gradually been noticed that it is very difficult for the complexion or hair color of a subject to be of this color.
In post-production, the subject is then “separated” from the background (which is normally green, but can also be blue in the case of night scenes) through the chroma key technique, or color key. It’s a feature present in main editing softwares, which “erases” the green screen and turns it into transparent. Always in the post-production phase, the new background will be chosen and integrated in place of the transparency, leaving the subject in the foreground. The chosen set can be fixed or moving, existing in nature or non-existent, and with this it will be possible to add other stage elements such as other characters, or special effects such as explosions. Generally, the new background will be either previously filmed material or a new product processed digitally with the help of computer graphics.

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In any case, the green screen can be changed virtually during post-production with special software, but also on a film set with real special effects. The chroma key technique allows to create a mix between reality and fiction, to manipulate reality in order to make it something completely new. It is therefore no wonder that cinema has grasped its potential.

The rules of the green screen

The green screen is the name that has been given for convenience to the background, but this does not necessarily have to be a panel: it can even be a wall, a cloth, or even a kind of suit.

There is also the possibility for the subject to wear a green screen and to replace it in post-production with a particular disguise, which in post-production can become an armor, the coat of an animal, a superhero suit or whatever you prefer. The important thing is that it does not present wrinkles or reflections that can spoil the result and make it difficult to erase. There were also examples of more imaginative and original green screens, where the green effect to be erased was even made with a liquid.

It’s also crucial that the subjects do not wear anything green. These details would risk being transformed into transparent areas that should not be erased. The light must then be different between the green screen and the subject, and the illumination of the screen must be homogeneous. Another important aspect to consider is the quality of the shot, so you need to control sharpness and saturation of the screen.

Experts advise to buy a diffuser of light and lights from many watts, but if you want to make a green screen more “homemade” a white sheet will be enough to standardize the light, erase the shadows and bring out the subject.

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The advantages of the green screen

Once you have the right equipment to make the technique without imperfections, the green screen has many advantages in its use. The green screen is in fact cheaper than finding and traveling to a certain location together with the crew and equipment. The green screen also allows you to recreate post-production settings that wouldn’t normally be accessible to the public.

However, it also offers many possibilities at the level of imagination, integrating scenes and elements that are not real in the narration and transforming anthropomorphic characters into fantastic creatures. The possibilities of the green screen extend to many areas. You can make videos that will be uploaded to social networks or YouTube, but you can also use it for an original and different corporate video.

Which productions use green screens?

The first use of the technique dates back to 1940 in The Thief of Baghdad, a film by John Huston that won the Oscar for special effects. In fact, at first the screen used was blue. Only after 1970 the use of green screens began to spread, mainly because of digital technologies.

Since its invention, its potential has been exploited by major fantasy and science fiction sagas. From The Matrix to Star Wars, Game of Thrones, Lord of the Rings and the Marvel Cinematic Universe, the green screen has built fantasy worlds and characters. The Star Wars saga has used the green screen as a real pioneer of this avant-garde technique. The film even won an Oscar, dubbing the success of Larry Clarke, the author of the special effects in the Bagdad Thief.

The green screen is a versatile tool, which can be used not only in cinema or advertising but also, for example, in news and weather forecasts. During the broadcasts, the presenter is in fact in front of a green panel that is replaced live with the weather map.

With our professional equipment, we make videos with green screens and take care of their post-production: do you want to know more? Let’s meet each other!