Greenscreen- how does it actually work?

When we watch movies, we often see characters surrounded by amazing landscapes that just don’t exist in the real world. Actors fly, fight with monsters, jump from buildings on the 10th floor or ride on the backs of dragons. Sometimes the action takes place in a specific location but 200 years earlier or later. Have you ever wondered how movie makers film such shots? Well, we’re here to tell you the secret.

Chroma keying technique

All the special effects happen with the help of backdrops of brightly colored fabric or paint and a process called chroma keying. This term is used to describe the process of removing (keying) the green background in post-production using video editing software. When the green screen background has been keyed, it will be fully transparent. It allows media technicians to easily replace those backgrounds with pretty much anything- from animated weather maps to the view of the ancient city. It’s the actual technique of layering or compositing two images based on color hues. Every color has a chroma range, hence where the terminology comes from.

In the case of meteorologists, a weather graphic is placed, but any image can be transposed. When viewers look at weather maps from their TV screens, there is really only a green background behind the presenter. The maps are created on the computer by the producers. News, telegraphs, and telecasts are produced in a similar way.

Chroma keying isn’t just for backgrounds, it works with objects too. Elaborated animated characters, such as the dragons in “Game of Thrones,” often have bright-green stand-ins that the actors hold and interact with, but which the fully rendered animal replaces during editing. It offers the most natural-looking way to integrate subjects into the video. Instead of putting each visual element in its own frame (a la picture-in-picture), greenscreen lets you blend them. In fact, done correctly no one would ever suspect they were two separate video streams.

Why green color?

You may be wondering if screens have to be green for chromakeying to work. The answer is no. In fact, many movie makers use blue screens. The green screen, however, is the most popular option. Why? The answer lies in the concept of contrast. The screen being used must be different from (in contrast with) the actors being filmed. It doesn’t match any natural skin tone or hair color, so it’s easy to remove without grabbing parts of the person in the foreground. Green, moreover, requires less light for proper exposure and, finally, it appears least often among clothes and props. Of course, blue backgrounds (the so-called Blue Box) are still used, e.g., if the protagonist of the film is a green monster or if the elements of the scenery are also green plants.

The person who takes part in the recording on a green background, cannot have clothes or props in a similar color, because they will eventually be replaced by an alternative image. When working on a green screen, it is also important to use lighting, which must fall evenly on the background and the appropriate positioning of the recorded character. After all, we don’t want the character to cast a shadow on the background, as this can cause a lot of difficulties when cutting it out and inserting the image.

The wide use of greenscreen today

The history of green screen technology dates back to the 1930s. Technology that was primarily reserved for Hollywood blockbusters is now utilized in video marketing, live events, webinars, and commercials.

Virtual events are becoming more and more popular, and audiences expect the quality to get better as well. If we want to meet their expectations, greenscreen and virtual scenery is the solution that allows creating an online event on a completely new level. Video, event, or streaming created using the keying technique, is a great material to publish on any channel, including YouTube. Using greenscreen, we can add interactive elements to any event, which will not let the audience get bored. A presentation with animated statistics or graphs, surveys, quizzes, or the possibility to ask questions and receive live answers will allow participants to take an active part in the event, and not just watch passively.

Given the current working conditions of most people during the global pandemic, it’s a safe bet you’ve had a Zoom meeting or two with coworkers or others who have had cool virtual backgrounds. Green screen is really the same concept but will typically provide a more professional result.

Green Screen Virtual Studio from Jamie Bhalla on Vimeo.