What Is Chroma Key and How Does It Work?

Chroma key is the movie magic that permits presenters to talk in front of landmarks that are thousands of miles away, astronauts to float in space, and superheroes to fight extraterrestrial invaders from the comfort of their home or office studio. But what is chroma key, and how does it work?

The Screen Is Green

Chroma key uses a process known as compositing. Two images or videos are combined into one, allowing for amazing effects. This is achieved by first filming a subject in front of a flat, single-colored screen. Most often, the color is a vibrant green, which is why you’ve likely heard of a “green screen” technique or effect. A computer program is then used to remove anything that’s the same color as the screen. You can then replace that newly blank space with anything, whether that be still or moving images or computer-generated imagery. This can add a visually exciting touch to any presentation, training video, or the like.

An Old Cinematic Trick

The technique of using screens to create special effects goes back to the earliest days of filmmaking. Directors would use black drapes, traveling mattes (large painted backdrops), and double exposure as far back as the 1890s. This could give the illusion of movement, as in the 1903 film The Great Train Robbery, or invisibility, as in the great Universal Pictures monster movie The Invisible Man. Modern chroma key effects are much more elaborate and convincing, however, seamlessly blending what’s imaginary with what’s real. One early chroma key technology success was a little film you may have heard of—The Empire Strikes Back. This film required a colossal amount of work with chroma key and blue screens to composite all those roaring space battles.

Setting up a Green Screen

While it can produce what look like super-futuristic, high-tech effects, setting up a green screen is a fairly simple process. You can convert almost any place into a film studio with a portable green screen set up. If you have a dedicated space available for filming, you can treat a room or section of wall, ceiling, and floor with chroma key paint or cover a space with our line of Pro Matte® IV green screen flooring. Stick with quality chroma key products rather than cheap kits if you want to ensure your work looks professional. As for software, there are plenty of video editing programs out there, such as After Effects, iMovie, and others, depending on your budget.

Why Green Screens?

With hope, the above explanations will answer the questions, what is chroma key, and how does it work? But why green screens? The answer is simple! There are no green-skinned or (generally) green-haired people. At least not as green as the tint and hue used in producing green screen backdrops. Performers and speakers working with green screens avoid wearing green, or else they can become transparent and end up having the secondary image projected onto themselves. Unless the production requires transparency, this is not usually the intended effect!

Jun 18 2021