More commonly known as green screen
or blue screen
(though that one also has a different meaning
), the process by which a subject filmed on a camera can be seamlessly inserted into a scene generated by other means. It relies on filming the subject in front of a solid-color background — any color will do, so long as it's not used in the foreground — and adjusting the editing system to replace that color with the background signal.
The main methods of controlling the background for live-action shots are, in increasing order of technological sophistication:
- Finding one that already exists, and film on location.
- Build a set.
- Film the background separately, and project it onto a screen behind the actors while filming, typically via rear projection.
- Double-exposing the film, which results in a slightly transparent foreground but is cheap.
- The old analog Matte Shot, done with precise blocking of the camera frame.
- Chroma Key.
The background inserted via Chroma Key can be any visual image. CGI is the most common today, but it can be other live action footage, models, stop motion or cel animation just as easily.
The color used is now entirely arbitrary. Blue was a popular choice in the early days of color motion pictures, because it is complementary to the reds found in human skin. Green became popular because digital editing systems can isolate green with less light in the background, and because lime green is less common than bright blue in costumingnote
Magenta is sometimes used, as is black, but the latter is problematic, as it's almost impossible to shoot a person without having some black visible on their person, in eyes or shadows.
If any part of an actor or prop is colored the same as the background, that part will disappear. Thus, sometimes the background color is chosen because of the colors to be used in the foreground action. The original run of Doctor Who
, for instance, used green or yellow backgrounds even when blue was the most common color at The BBC
, because a large number of its effects shots involved the TARDIS, a timeship that takes the form of a blue police phone box. The problem with using yellow was that foreground objects and actors always had a prominent yellow fringe around them. Normally, wardrobe and prop designers simply avoid using greens in the capture range, but this is not always possible; you'll occasionally see bloopers where weather forecasters have part of the meteorology map show up on their ties, for example.
The invisibility effect can be used intentionally to allow a performer, or part of his body, to interact with props while remaining unseen. A garment that can be used for this purpose is a one-piece jumpsuit in the background color, with a full-face mask, and a mesh eye piece, called a "gimp suit" or, in the case of a blue background, a "blueberry" in the trade. Performers in recent Jim Henson
Productions shows have used these suits to perform with puppets without having to raise them above their heads. The suit looks like a Ninja outfit, and that is not a coincidence, as it serves the same purpose as the black outfits traditionally worn by Japanese stagehands. See notes at Ninja
Almost all productions use Chroma Key at some point, but there are some standout examples. Also notable for causing occasional unintentional hilarity
- when background and foreground are poorly matched, or the SFX budget is low, the effect is anything but seamless
It can be fairly tricky to create a viable Chroma-Key effect, especially with amateur equipment — often, it requires fiddling with hue and saturation, and even then, there is often a faint, tell-tale 'border' around the subject where the green-screen footage and the 'real' actor don't match up.
- Used in Nike's The LeBrons commercials for the eponymous family based on LeBron James, as seen in this one.
- The first film to use the chroma key process was The Thief of Bagdad back in 1940. It was invented by Larry Butler, who won the Oscar for it.
- The 1943 version of H.G. Wells's The Invisible Man used the black velvet effect in close-ups where Griffin removed his bandages.
- Sky Captain and the World of Tomorrow (2004) had almost no real sets or props, relying on Chroma Key in every shot.
- As did the film adaptation of Sin City, in order to re-create all those stylistic comic-book-style backgrounds and lighting motiffs.
- MirrorMask does the same, in a very very trippy way.
- As did Labyrinth, in the "Chilly Down" sequence.
- The Movie adaptation of Frank Miller's 300 was filmed almost entirely in Chroma Key. The Movie of Alan Moore's Watchmen (by the same director) uses a combination of chroma key and traditional sets.
- The live-action movie of Speed Racer was filmed almost entirely on green screen to give it an anime-style effect.
- The Star Wars prequels helped pioneer the idea of minimal set design through Chroma Key.
- The fact that only blue screen was available for A New Hope caused Luke's squadron to be changed from Blue to Red to avoid problems with blue markings.
- Also in Return of the Jedi, the only reason Luke's new lightsaber is green is because the battle that takes place on Tatooine happens to have a bright blue sky. In some early trailers, Luke's saber is blue, but they chose to change it to green so it would show up against the sky properly.
- In the original editions of the original trilogy, you'll notice that whenever R2-D2 is in space, his panels are painted black instead of blue to accommodate the chroma key effect. This was digitally fixed years later for the special edition versions.
- In filming the first Superman movie, the costume had to be teal in blue screen effects, and then color corrected after the shots were composited.
- In Superman III, there is a short instant where you can see him flying through a canyon sporting the teal outfit.
- The opening scenes of Groundhog Day demonstrate this - the woman is wearing a blue blouse when she steps in front of the chroma key camera, and all that can be seen are her head and hands in front of the satellite picture.
- Quite possibly the best use of chroma key occurs throughout Walt Disney's Darby O'Gill and the Little People. Two remarkable examples are the moments where Darby plays "The Fox Chase" on a fiddle to an audience of dancing leprechauns and, most notably, the Banshee sequence.
- Puma Man has some very unconvincing green screen work, but that's part of its charm.
- Bad chroma key is deliberately invoked in Cloudy with a Chance of Meatballs, when the mayor appears in front of a freeze frame of the Baby Brent Sardines commercial to promote his unveiling.
- Tim Burton's Alice in Wonderland used this extensively. The sets seem to consist of nothing but green walls in the proper shape, along with platforms. Only things the human characters touched actually existed on the set, and most seemed to be green and were textured via CG (The Tea Table seemed to be an exception, due to the hatter walking on and knocking stuff off). The staff comments in the "Making Of" stated it was an "Odd Mix" of Full CGI (too many to list), motion capture characters with the actor's head pasted on, normal actors human (mainly Alice), and edited normal actors (the Red Queen and her giant head).
- The body-suit version was memorably used in Star Trek: First Contact to erase half of the actress playing the Borg Queen during her entrance-in-two-parts.
- At the Walt Disney Studios, Ub Iwerks developed the sodium vapor process, in which the actors were filmed against a white backdrop lit with powerful sodium lights. A special prism in the camera separated the image and exposed it simultaneously on two different film stocks: regular color film, which did not pick up the sodium light, and black and white film sensitive to sodium light, which created the matte. The process was used for most Disney productions, including Song of the South, Mary Poppins and The Black Hole, and was also used for The Birds and a number of Ray Harryhausen's films. Although it provided better results than blue screen, and saved time by creating the matte simultaneously with the foreground footage, the process proved too expensive and was discontinued by the 1980s.
- Used a bit in Who Framed Roger Rabbit, as you can see here.
- In the Harry Potter films, the invisibility cloak is, of course, created with a chroma key green cloak. Chroma key is obviously also used for scenes with Flying Broomsticks and so forth. As as far as sets go, the Potter filmmakers tend to prefer building real sets and usually just use chroma key to fill in scenery out a window, for example. However, there have been at least two all-CGI sets in the series, the Hall of Prophecy from Order of the Phoenix (because they couldn't do the scene where all the shelves crash down for real) and the Chamber of Secrets in Deathly Hallows, Part 2 (the original Chamber set from The Chamber of Secrets was real, but wasn't saved after filming).
- As mentioned above, Ray Harryhausen used the sodium vapor process on a number of his films. For instance, it's used to achieve some of the scale effects in The Three Worlds of Gulliver. More subtly, in Jason and the Argonauts, in the scene where Jason is talking to Medea at the stern of the Argo, you have to look closely to realize that they were filmed in the studio with location footage of the rest of the ship matted in behind them.
- In Chitty Chitty Bang Bang, blue screen was obviously used for the Flying Car scenes. Obvious because you can see blue matte lines around the actors in several shots.
- The Amazing Bulk is filmed entirely in Chroma Key.
- In Stuck On You, a 'blueberry' suit is used to keep Bob out of Walt's scenes on Honey and the Beaze
- In Wayne's World, when the Show Within a Show moves into a studio, they gain the ability to use Chroma Key, which Wayne demonstrates for the audience by "travelling" to New York City, Hawaii, Texas, and... Delaware. "Hi... I'm in Delaware."
- Repo Chick was filmed almost entirely on a green screen. The actors were then composited onto model railways and toy cars instead of more realistic backgrounds.
- Referred to in Tom Clancy's novel Debt of Honor as a ruse.
- Troy Rising: Tyler Vernon uses this and relayed broadcasting for misdirection to protect him against alien invaders that want him dead, while giving a televised interview.
- The music video "Shine On Me" by Chris Dane Owens abuses the hell out of it.
- Or, as the page puts it, abuses it "like a free bag of heroin."
- Yes's video for "Leave It", while groundbreaking for its time, has some notable Chroma Key issues with the white shirts on the white background. (Most notably at 2:58 in the video)
- Used in "Friday", as Rebecca Black herself Lampshaded in her appearance on "Funny or Die". ("I'm talking about riding in a car with a 13-year-old driver, whether on the road or on a windless green screen cityscape.")
- The video made to promote Strawbs' album Grave New World makes extensive use of Chroma Key, with no pretense at making the compositions look realistic. For instance, one scene shows a dancer performing in front of aerial Stock Footage of clouds, while another has the band hovering over Piccadilly Circus.
- Tori Amos's videos tend to use a lot of Chroma Key effects, to the point where she once quipped "I seem to live my life on green screen."
- The FMV for Wing Commander III: Heart of the Tiger was filmed exclusively on greenscreen, predating Star Wars by a good half a decade (and stealing Mark Hamill from them while they were at it). WC4 made the shift to actual sets.
- Homestar Runner makes fun of this in the Strong Bad E-Mail redesign, where Strong Bad imagines what his room would look like if he replaced the walls with a green screen. It backfired when he imagined frolicking through the bread aisle of a grocery store, as due to his eyes also being green, they vanished ("Oh, bread aisle! Warm me with your enriched, bleached bosom! And please, give me back my sight"). It then freaked him out when he saw the green-clad Coach Z walk in, appearing as nothing more than a floating head.
- Technically, all of this is impossible, but keep in mind, this is also a series where computer viruses can bend "reality" by, presumably, spreading to the creators' machines and messing up the Flash file, not to mention Homestar states he's Behind the Black in almost every Strong Bad Email.
- Parodied on King of the Hill, Luanne is hired as weather girl not because of her acting, but because her conservative blue dress with a white top melds perfectly with the background.
- News folk use this technique when presenting the weather, often using a special pointing device which the computer can track to appear to interact with the weatherboard by drawing lines and arrows. One particular segment has a host who enjoys taking further advantage of the technique: he wears a blue suit skeleton costume on Halloween.
- When Harry Carey worked at WGN covering the Chicago Cubs, during the postgame show he and the play-by-play commentator would sit in front of a blue screen showing the crowd at Wrigley Field. Carey, whose Catch Phrase was "Holy Cow!", had a little plastic cow which had some blue dots on it, making it "holey" so you could see "through" it to the shot behind them.
- Here's a tip. At a couple of tourist spots like the John Hancock Center in Chicago, they may have a green screen backdrop that you stand in front of so that a souvenir photo can be taken of you. Wear a shirt matching the color of the chroma screen. When you look at your souvenir photo on the 94th floor sometime later, prepare to laugh out loud seeing that the Chicago skyline imposed in the background also has been imposed onto your shirt.