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How A Green Screen Works: Everything You Need To Know

How A Green Screen Works: Everything You Need To Know

how to use green screen

A green screen is a large green background against which scenes of a film are shot. Later during the post production process, with the help of visual effects (VFX) these shots are layered and composited over a separately filmed background. Thus, the green screen used to achieve such an effect is also known as  CGI (computer graphics) green screen. 

During the early years of using this technique,  blue screens were more popular. The reason behind using a blue screen was it worked better with celluloid film. But as technology evolved and celluloid was replaced by high-end digital, green screen due to its visual properties was more suited to this new medium. At present green screens are not only limited to motion pictures cinematography. They’re commonly used in television broadcasts, video games, and music video production. The green screen technique is one of the oldest processes in the history of filmmaking that has revolutionized the method of  image making.

 

What is the Use of a Green Screen?

Green screen facilitates a film production to use whatever background images are required in the background according to the demand of the story. Here are some upsides for filmmakers to using the green screen :

1. When the desired background for a fantasy, alien, historic, futuristic or hard-to-access location is beyond budget, a green screen becomes a helpful and cost effective approach. It allows the production to depict disparate locations and sequences. This helps in enhancing filmmaking possibilities and language.

2. It makes the appearance of two actors sharing the same screen space possible when each of them has been shot separately using a green screen. You needn’t spend all that extra money rescheduling  a shoot.

3. It helps to enlarge or shrink a character relative to their background or even make them fly like a superhero.

4. Shooting action sequences in risky locations where access becomes difficult or dangerous, green screen technology helps protect actors from perilous environments. The actor can shoot the scene within the safety of a studio set with a green screen in the background.

5. Green screen technology helps to create sequences that take place in outer space.

6. In  news and weather reports green screens are used behind the news presenter.

The following video explains how green screen technology is used in filmmaking.

 

Why Only a Green Screen is Used, Not Any Other Color?

Blue screens have been used in filmmaking since the 1930s. But green screens are considered as standard in the film industry because of the following reasons: 

  • The color green is not commonly found in human skin tones. 
  • It is less common in costuming and props than the color blue.
  • Nowadays, all the films are shot digitally. The cleanness and luminescence of green color in digital images provides lesser noise than blue color.
  • During the process of shooting, blue screens have a lower luminosity as compared to green screens. So, a blue background will  require a camera to a higher f-stop, which will hinder shooting a large scene with a lot of visual effects.

So, in comparison, a green screen is preferred to a blue screen. Moreover, during the process of editing, the technician finds it easier to key in on the green value. This helps him/her to isolate the characters, and then replace them with separate background footage. This is the reason why green screen is used for editing.

 

Brief History of Green Screen in Cinema

Green screens have been used in movies since the 1940s and continue to be used in current filmmaking practices too. 

In the year 1898, George Albert Smith, a French filmmaker, used a black cloth to make objects disappear. American filmmaker, Edwin S. Porter, utilized this technique in his film The Great Train Robbery (1903). He painted train windows in the background with black color so that he could add the backdrop of the passing locations later in the film.

In the year 1918, another American filmmaker Frank Williams developed the technique of traveling matte. It is a method of combined filming that involves the use of an opaque silhouette called the traveling matte. Here a moving actor or other object is filmed on special ‘masking film’ as background. Later, the background is replaced with moving images that are appropriate to the story.

Fifteen years later, in 1933, filmmaker James Whale took advantage of this technique to make a character disappear in his film The Invisible Man.

The following video explains the use of compositing in early days of filmmaking.

 

With the evolution and developments of new digital camera and video editing software, it is the cinematography technique and the keying technology that has evolved. However, the bright green canvas is still the same. It has not changed over the years of filmmaking.

 

How Does a Green Screen Work?

When a green screen is used during the process of filmmaking, it serves as background. This background is removed and replaced with a suitable backdrop during post production. One should keep in mind the following steps to achieve the green screen effect:

Step 1: A green screen is placed in the background and the actors perform their action in the foreground. If required, props may also be placed in the foreground.

Step 2: The entire action is captured in a digital camera. 

Step 3: The footage is imported using a non-linear editing software. The background color of green is made transparent. So, now we are left with the actors and props in the foreground.

Step 4: The background is then subjected to compositing using chroma keying and replaced with visual effects to create the appropriate background.

 

Some important processes that are key to a professionally executed green screen technology:

Chroma Keying: This process transforms all areas of the image or video of any specific color into a transparent layer. It is also popularly called chroma key compositing, color keying, or simply keying.

Luma Keying: This process sets layer transparency based on the brightness or luminance level. While it can be used to overlay video for dramatic effects or smooth transitions, it’s most commonly used in editing still images.

Color Correction: When certain areas of the characters absorb or reflect that color, which is typically blue or green, it results in color spill. Mild cases of a color spill, affected edges and areas can be easily color corrected to eliminate or minimize the effects of the green screen.

 

How to Make a Green Screen for Low-Budget, Independent Productions?

Though the green screen technology is considered cheaper than actual world alternatives, it is nonetheless time-consuming, cumbersome and at times expensive. Ideally this technology is not  suited for a low-budget or independent film. But creating a green screen for shooting low-budget and independent films may not not always be an expensive or mammoth task. One requires a good material for the screen and a location spacious enough to do justice to the scene. 

It is very important to keep in mind the following factors:

1. The green screen used in the background should be of a single and solid color of green. This will facilitate the process of keying during the post production.

2. Both foreground and background should be illuminated consistently. One shouldn’t be brighter than the other. Any difference in the intensity of lighting will ruin all efforts.

3. The foreground and background should be illuminated with soft and even lighting. If the shadow of the character or prop in foreground creates a shadow in the background, it will be a cumbersome task to remove it during post production.

4. The characters and props must be a few feet in front of the screen during the shooting. It is essential that the subjects must be lit by three-point lighting.

5. The distance of the camera from the subject that is the depth of field in both foreground and background footage should match.

6. The camera should be in a static position and remain stable. If  the camera makes any movement, it’ll disturb the contrast and the stability in the background. Hence, changing focus or zooming during the shoot will disrupt the background stability.

7. Most importantly, the actors’ costumes or color of props should not have the same color as the screen behind them. If they’re the same color, the color of the costume and props too will have to be replaced during post-production.

This video explains how to light a green screen with minimal resources to achieve a professional result.

 

Common Mistakes Filmmakers Make With Green Screens

Here are some very basic but essential things to keep in mind when using a green screen:

1. Shadows on the green screen

Shadows or the dark area on the green screen make it difficult to key them out perfectly. This kind of situation arises when the subject is too close to the green screen or due to very strong lighting, especially strong frontal lighting. This can be avoided by placing the subject further from the green background and avoiding using a single light source.

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2. Uniform Lightning

The foreground and background should always be evenly lit. If this isn’t done properly there will still be dark and light areas in the background. Hence, complicating the chroma key process. This can be avoided by assigning the job to a person who is in charge of the design and execution of the lighting plan on set.

 

3. Excess Lighting

Too much lighting can create green edges that can appear around the subject. This will create visible green fuzzy edges around the subject. If the subject is an actor, it may appear that there is a green halo or a green reflection on their skin. This will not only look very unappealing but is also a pain in image post-production.

 

4. Disappearing green objects

One should avoid having green things on the subject or on any property within the set that would be in the final product. Moreover, the subject should avoid wearing any green clothes, makeup, or accessories otherwise, the subject will end up disappearing after image editing. Because chroma keying means eliminating all green hues from images or footage. In case one requires green objects in their frame, use a blue screen or a plain white background.

 

Green Screen Examples In Movies

Here are examples of seven films that have utilized the green screen in an innovative wayThese films display how cinematic storytelling can achieve new heights when technology and creativity merge. Most of these won Academy Awards for their immense creative contribution to the world of visual effects in filmmaking.

 

1. The Thief of Bagdad (1940)

The Thief of Bagdad is a British Technicolor film that used blue screen to create the world of historical fantasy. The film made the first use of the manual bluescreen technique in the history of cinema. The special effects comprise only matte painting and optical printing, all of which helped filmmaker Alexander Korda deliver a naive enthusiasm and fanciness to the narrative.

 

2. The Empire Strikes Back (1980) 

With George Lucas’s The Empire Strikes Back, keying softwares made their debut in filmmaking. The Empire Strikes Back is a space saga on an epic scale that is the sequel of Star Wars (1977).

In this clip, the process of achieving visual effects in the film is explained. We observe that the background screen is blue and not green because the spaceship models used have a green tint in them. Had the background been green, it would’ve been difficult to perform keying during  post production.

 

3. Who Framed Roger Rabbit (1988)

Who Framed Roger Rabbit is a  live-action/animated comedy mystery film directed by Robert Zemeckis. The special effects used in the film create a seamless fusion of live-action and traditional hand-drawn animation. Such creative choices creates a fantasy world within the film where the line between reality and fantasy gets blurred. This video clip shows how this groundbreaking effect was achieved.

 

4. Titanic (1997)

A tale of tragedy and survival, James Cameron’s Titanic showed the world how visual effects can be used to enhance a film’s emotional impact. In this video, we observe how the massive iceberg that ravaged the ship was created in post production with the use of the green screen technology.

 

5. The Matrix (1999)

The science fiction world created by The Wachowskis in their sophomore The Matrix has earned a cult status over the years in terms of how visual effects can become another character in storytelling. The green color tone in the film signifies the difference between the real and virtual worlds. This clip explains how the visual world of the film was created with green screen technology.

 

6. Captain America: The Winter Soldier (2014)

Captain America: The Winter Soldier is the ninth film in the Marvel Cinematic Universe. The film is directed by Anthony and Joe Russo. Without the use of visual effects the narrative of the film would appear unengaging and lose its spirit. This video explains how the Marvel Universe was created through visual effects and green screen technology.

 

7. Padmavat (2018)

Sanjay Leela Bhansali is one of the most visionary filmmakers of Indian cinema. His impeccable vision for the minutest of details in the production design to extremely evocative lensing helps him capture the film’s period with perfection. In this video we get an idea how, along with the visual effects team, he created the landscape and milieu of his magnum opus set in the 13th-century.