There are many movies and television shows that have backgrounds that just don't seem plausible or employ actions that you know can't possibly be real. This is where a green screen comes in. For example, both Alice in Wonderland (2010) and Aquaman (2018) were filmed entirely on a green screen to achieve the effects the directors wanted.
A green screen is a large screen that is green. It has been used in varying capacities since the nineteenth century. Hollywood and other entertainment producers, along with weather stations, are legendary for using this technology. It can technically be any color but is typically a bright green. This color was chosen because it was determined to be the least likely color a person would be wearing. However, if someone is wearing bright green in front of a green screen, whatever they are wearing would disappear. This can become comical because you could end up with just a floating head.
A green screen is part of a special effects process that is called chroma key. This process allows people to use technology that superimposes their subjects over any virtual background of their choice. Chroma keying is also known as color keying and is the process of identifying a specific color in an electronic image and then using software to make that color transparent. This makes it so another image shows through.
A famous example of using green screens is weather stations. The meteorologist will stand in front of a green screen, and then the weather map will be superimposed over the green screen. This makes the green disappear entirely with only the map showing.
Another example is the flying superhero found in movies. While it appears that the superhero is flying through the air, we all know that isn't actually possible. The actor is filmed lying on his stomach in front of a green screen with a fan blowing his hair. Then, a virtual background of moving sky is placed behind him via chroma keying. This creates the effect that he is actually flying through the air.
Photographers are also known for using green screens. It allows them to place the subject of the photo in front of any background of their choice. This can lead to fun photos like someone standing in front of Niagara Falls while having their picture taken in Iowa.
However, professionals in the entertainment, weather, and photography worlds don't have a monopoly on green screens. You can buy or rent portable green screens to use for a home project, or even make one yourself. It can take a normal video and make it much more engaging.
Another benefit of the green screen in movies and television is that it allows unseen crew members to interact with the scene without you being aware of it at all. Crew members will be dressed entirely in bright green (or whatever color screen is being used) and can then appear in front of the green screen without being seen. This could be used for things like making a cup appear to float or having an item be thrown across the room.
You have likely seen many examples of green screens at work. Weather stations use them to superimpose a weather map, so the meteorologist can do the weather forecast. Hollywood and other entertainment use them to create incredible special effects in movies and television shows. It is behind famous movies like The Avengers and The Hobbit. This technology has been around for over a century, but people are finding new and exciting ways to use it all the time.