A green screen is, as you might expect, a large, green screen. They’re used for the visual effects and post-production technique known as ‘chroma-keying.’ This involves placing a subject in front of a green screen for filming and then replacing the “green” in post-production with another background of choice. This background could be anything, from a different colour to an artificial image of New York, or the Solar System, for example.
Why green? Green is the colour that statistically features least in most common filming scenarios, meaning that it is easier to remove in post-production. In other words, it is the colour which makes it easiest to separate the subject from the background.
As a video production company, we use green screens to produce high-quality film all the time. Here are some pointers from our team.
How to set up a green screen
Setting up a green screen begins with choosing the correct size. Green screens can be any size, depending on the requirements of the scene and the background desired. For example, green screens for a single talking-head interview are usually a couple of meters square, while Hollywood blockbusters involving lots of special effects regularly use green screens measuring up to several hundred meters. If you’re shooting a full “head to toe” shot of a person, then the floor also needs to be a chroma green colour. You can buy a green screen from sites such as Backdrop Source, or borrow one from any quality broadcast hire service.
Next, you’ll need to light the screen separately to the subject. It must be lit as evenly as possible and without shadows, which deviates from the common and more creative practice of using lighting to enhance a subject. The subject should be placed several metres from the green screen to ensure that green light doesn’t reflect from the screen onto the subject. This green reflection, known in the business as ‘spill’, can cause issues when it comes to editing the footage. The less green reflected on the subject, the easier the post-production process is. Finally, make sure the subject has a good backlight, sometimes also called a hair light, as this helps to separate them from the green screen.
Tips for shooting green screen
Make sure your subject doesn’t turn up in green clothing. Modern chroma-keying software is very sophisticated, but it’s not magic. If the subject is wearing green, then they risk becoming a ‘floating head’, as their clothing will be edited out along with the green background in post-production.
You should also make sure you clean your green screen. Any dust or dirt on the green screen can cause issues later when the footage is being edited. If your green screen is made of fabric, make sure it is well ironed as creases can also cause problems in post-production.
What are green screens used for?
It’s not always time or cost-effective to shoot on location. Green screens are useful any time you want your subject to appear to be somewhere they aren’t. They’re a staple of Hollywood blockbusters, as they allow for scenery and special effects to be edited in post-production.
Many interviews are filmed against green screens with the background replaced later. Weather reporters also rely on green screens. The map with the weather isn’t actually behind the presenter, and they can’t actually see what they’re gesturing to. Instead, it’s a digital image added through chroma-keying.
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