WHAT IS A BLUE SCREEN? (In the Entertainment industry.)

Blue Screen Star Wars / Photo Credit: CBS Studios - Prospect 7 - IMPS

WHAT IS A BLUE SCREEN? (In the Entertainment industry.)

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WHAT IS A BLUE SCREEN? 

Generally, the only difference between using a green screen as a background and using a blue screen as a background is the color itself—but more filmmakers are moving from blue to green for other specific reasons: The use of digital cameras. ... Using green instead of blue results in less noise when keying out the footage. The filmmaking technique of shooting foreground action against an evenly-lit monochromatic background for the purpose of removing the background from the scene and replacing it with a different image or scene. The visual effect resulting from this technique as well as the colored screen itself, especially blue.

Blue was originally used for TV chroma keying special effects because human skin tone contains very little blue, and because the film industry used blue backgrounds for similar purposes. The color blue was tied to the blue emulsion layer of film having comparable grain and detail in comparison to the red and green layers of the emulsion. In television and digital filmmaking, however, green has become the favored color because of some practical considerations, and because lousy compression algorithms used in both analog and digital TV distribution retain more detail in the green channel. The choice of color is up to the effects artists and the needs of the specific shot. Whereas the blue screen was introduced to the television industry by the film industry, the use of green screen visual effects has been introduced to the film industry as electronic imaging has augmented and replaced the use of chemical film stock in cinema. Also, the green background is favored over blue for outdoor filming where the blue sky might appear in the frame and could accidentally be replaced in the process. Although green and blue are the most common in part because red, green and blue components are used to encode the visible light spectrum, any key color can be used. Red is avoided for human subjects due to its prevalence in white skin tones, but can be often used for objects and scenes which do not involve people.

Why do movies use blue screens?

In the movie/weather/gaming industry, green and blue screens are used. Blue screens are used in place of green screens because it's generally easier to chroma-key. The color is softer than in a green screen. However, green screens are still more commonly used because of multiple reasons.

The illusion is created by a special effects technique known as traveling matte or blue screen. This technique allows actors and scale models to find themselves in totally imaginary situations -- in space ships, dangling from rope bridges over gorges, flying through the air (a la Superman) -- and have it look completely real in the theater. The technique is used so often now that you don't even realize it. An optical printer with two projectors, a film camera and a 'beam splitter', was used to combine the actor in front of a blue screen together with the background footage, one frame at a time. ... Some films make heavy use of chroma key to add backgrounds that are constructed entirely using computer-generated imagery (CGI).

Processing a blue backdrop

Before electronic chroma keying, compositing was done on (chemical) film. The camera color negative was printed onto high-contrast black and white film, using either a filter or the color sensitivity of the black and white film to limit it to the blue channel. Assuming this film was a negative it produced clear where the blue matte screen was, black elsewhere, except it also produced clear for any white objects (since they also contained blue). Removing these spots could be done by a suitable double-exposure with the color positive, and many other techniques. The end result was a clear background with an opaque shape of the subject in the middle. This is called a female matte, similar to an alpha matte in digital keying. Copying this film onto another high-contrast negative produced the opposite 'male matte'. The background negative was then packed with the female matte and exposed onto a final strip of film, then the camera negative was packed with the male matte was double-printed onto this same film. These two images combined together creates the final effect.

Major factors

The most important factor for a key is the color separation of the foreground (the subject) and background (the screen) – a blue screen will be used if the subject is predominately green (for example plants), despite the camera being more sensitive to green light.

In analog color TV, color is represented by the phase of the chroma subcarrier relative to a reference oscillator. Chroma key is achieved by comparing the phase of the video to the phase corresponding to the pre-selected color. In-phase portions of the video are replaced by the alternate background video.

In digital color TV, color is represented by three numbers (red, green, blue intensity levels). Chroma key is achieved by a simple numerical comparison between the video and the pre-selected color. If the color at a particular point on the screen matches (either exactly, or in a range), then the video at that point is replaced by the alternate background.

Lighting

In order to create an illusion that characters and objects filmed are present in the intended background scene, the lighting in the two scenes must be a reasonable match. For outdoor scenes, overcast days create a diffuse, evenly colored light which can be easier to match in the studio, whereas direct sunlight needs to be matched in both direction and overall color based on time of day.

A studio shot taken in front of a green screen will naturally have ambient light the same color as the screen, due to its light scattering. This effect is known as spill. This can look unnatural or cause portions of the characters to disappear, so must be compensated for, or avoided by using a larger screen placed far from the actors.

Camera

The depth of field used to record the scene in front of the colored screen should match that of the background. This can mean recording the actors with a larger depth of field than normal.

Sources, References & Credits: Google, Wikipedia, Wikihow, WikiBooks, Pinterest, IMDB, Linked In, Indie Wire, Film Making Stuff, Hiive, Film Daily, New York Film Academy, The Balance, Careers Hub, The Numbers, Film Maker, TV Guide Magazine, Blurb, Media Match, Quora, Creative Skill Set, Chron, Investopedia, Variety, No Film School, How Stuff Works, WGA, BBC, Daily Variety, The Film Agency, Best Sample Resume, How Stuff Works, Bright Hub, Career Trend, Producer's Code of Credits, Truity, Production Hub, Producers Guild of America, Film Connection, Variety, Wolf Crow, Get In Media, Production Beast, Sony Pictures, Warner Bros, UCAS, Frankenbite, Realty 101, Liberty Me, Careers Hub, Sokanu, Raindance, Film Connection, My Job Search, Prospects, David Mullich, Gear Shift, Video University, Oxford Dictionaries’, Boredom Therapy, The Bold Italic, Nicholas Persac, The Guardian, Jones on art, Allison Meier,

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Blue Screen Star Wars / Photo Credit: CBS Studios - Prospect 7 - IMPS