Despite the rise of Virtual Production, the green screen remains an indispensable tool in a filmmaker’s toolkit. This technology, known as chroma keying, allows directors to replace or extend the background of a scene, providing endless creative possibilities.
Although you might think that chroma keys are particularly popular in genre movies such as fantasy and sci-fi, where imaginative settings and special effects are critical, they are actually a basic tool for every type of movie. Comedies, dramas, or period films like Peaky Blinders and The Crown heavily use this technique too. The advertisement and news sectors similarly rely on chroma keying.
Chroma Key (by the Oxford English Dictionary) /ˈkrəʊməˌkiː/ A digital technique by which a block of a particular color (often blue or green) in a film or video image can be replaced by another color or image, enabling, for example, a weather forecaster to appear against a background of a computer-generated weather map.
WHY IS IT SO IMPORTANT?
Chroma keying is indispensable in filmmaking for several reasons:
Versatility: It enables the creation of seemingly any scene without the need for expensive sets or dangerous locations. It means you can either extend your set as needed and/or add new elements into the scene itself.
Controlled Environment: Filming in a studio with a green background saves time and money, as you are not dependent on weather conditions. However, green screens can also be used outside or on set.
Cost Efficiency: Filming with green screens can be more cost-effective than building physical sets or even a day in a virtual production cave.
Creative Freedom: Directors can envision and execute scenes that would be impossible to achieve otherwise, allowing them to extend sets, create effects and even make people fly.
Tip: Always have a VFX supervisor on set for proper lighting and technical setup. They handle unexpected changes on the spot, ensuring VFX artists can focus on creating the desired effects instead of spending more time in tasks like keying and refining edges. If you don't have one, we're here to help.
WHY GREEN?
You probably noted that the green used for chroma key is kind of flashy and bright. The reasons behind it are that it’s not a shade usually used on other objects or clothing in the foreground and it’s the furthest color from skin tones.
However, while green is the most common, other colors can also be used, depending on the specific needs of the scene. Here's the rundown:
Green Screen: The most versatile and widely used. Ideal for most scenes due to the high sensitivity of camera sensors to green, and the reasons mentioned before. On the downside, it has a lot of spill* and is not ideal for fine details or blonde hair.
*Spill: When green light reflects onto actors or objects, creating unwanted green hues. This needs to be corrected in post-production to ensure a clean and accurate final image.
Blue Screen: Before green, blue was the industry standard for its cleaner mattes and sharpness around the edges. Today, it’s mostly used when the scene has green elements or when filming at night, as blue is less reflective, making it suitable for darker settings. However, it requires more lighting, which can affect the budget.
Yellow Screen: In this instance, it was not a fabric or a conventional screen, but rather the projection of sodium vapor lights onto a wall, which created the very specific yellow spectrum required. This technique was notably used by Walt Disney from the mid-1950s to the 1970s.
Mary Poppins famously utilized it and won an Academy Award for Special Effects. The technology worked wonders even for translucent elements (which remains a challenge even by today's standards), but it required a prism to separate colors, a technology that is now considered lost—though Corridor Crew recreated it and were blown away by the results.
Sand Screens (The Dune Case): The specific chroma key tone was chosen primarily to seamlessly integrate actors into desert environments while preventing green or blue spillage onto them or other elements such as armor, visors, or any metallic or reflective objects.
But how did it work? It turns out that the opposite shade on the color wheel of the specific sand they used was... blue! This meant that when inverted, they effectively had a blue screen. To ensure its effectiveness, they conducted extensive testing before filming.
OTHER USES OF GREEN IN FILMMAKING
Green screens are not only used as static backgrounds but also in various dynamic and creative ways to achieve special effects in filmmaking.
Actors or stunt performers wear green suits to become invisible in the frame, allowing filmmakers to create the illusion of floating objects or flying people, or to seamlessly integrate CGI characters into live-action scenes.
Additionally, green props like balls or rods are used as placeholders for CGI elements, ensuring actors interact naturally with digital elements that will be added later. For instance, in Shang-Chi, actors worked with a green cushion that vaguely resembled Morris, the six-legged winged furry pet with no eyes.
CONCLUSION
Since the inception of cinema, chroma keying has remained a pivotal tool for filmmakers, facilitating the creation of visually stunning worlds. Despite the rise of virtual production techniques, green screens continue to thrive due to their versatility, cost-effectiveness, and the creative freedom they offer. It is, in fact, not uncommon to incorporate a green background into LED screens for specific shots.
Like any technology, the key lies in knowing when to employ it and when to explore alternatives. With ongoing technological advancements, including AI-assisted keying, the potential for this technology to enhance cinematic storytelling is expanding rapidly and makes it more accessible for indie filmmakers to play around with.
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