Today, most moviegoers are aware that those amazing settings and backgrounds are probably not real. In the past, studios would painstakingly create large painted canvases to create the illusion that the starts were in a fantastical location (for example, the Sahara desert or outer space). Since then, green screen technology has created so many new and fantastic possibilities. But how exactly does it work?
How Does Green Screen Work?
A chroma key, also known as a green screen, is a process that allows media technicians to replace green backgrounds with anything they want. A single color picked from a narrow spectrum is isolated and removed. In this case, vivid green since it’s so different from human skin and clothing.
In order for a green screen to work, the lighting must be even, leaving no room for visible shadows. Once that part is done, though, the process becomes smoother as they can add anything to replace the removed color without affecting the other parts.
In the case of live feed videos, chroma-keying demands hardware capable of recognizing and manipulating multiple video channels (layers that are defined by color). Recorded material can be changed in post-production using video and/or photo editing software.
Alternative Techniques to Green Screen
An alternative technique to even background lighting is a retroreflective background curtain. A ring of bright LEDs is usually also used around the camera lens. This way, the effect will work, regardless of the lighting on set.
Another variant of chroma keying is called yellow screening, where you use a white backdrop and a yellow sodium lamp in addition to the usual stage lighting. Since the sodium light is in a very narrow frequency band, it is much easier to isolate it.
Difference matte is a chroma-keying process that is quite versatile, allowing the use of many colors. This is done by capturing first the background only, then the actual scene is recorded. This way, the background image cancels the backdrop of the shot scene.
Another recent development is something known as the “volume” – known professionally as StageCraft. It basically creates a more dynamic special effects backdrop that completely surrounds the scene being filmed and gives the performers a clearer idea of what the scene will look like in post-production.