Visual Effects

Internal effects in Visual Effects
Miniature effect (Models: miniature sets and models, animatronics )
In the field of special effects a miniature effect is a special effect generated by the use of scale models. Scale models are often combined with high speed photography to make gravitational and other effects scale properly.
Where a miniature appears in the foreground of a shot, this is often very close to the camera lens - for example when matte painted backgrounds are used. Since the exposure is set to the object being filmed so the actors appear well lit, the miniature must be over-lit in order to balance the exposure and eliminate any depth of field differences that would otherwise be visible. This foreground miniature usage is referred to as forced perspective. Another form of miniature effect uses stop motion animation.
Use of scale models in the creation of visual effects by the entertainment industry dates back to the earliest days of cinema. Models and miniatures are copies of people, animals, buildings, settings and objects. Miniatures or models are used to represent things that do not really exist, or that are too expensive or difficult to film in reality, such as explosions, floods or fires.
Early History (1900-1976)
French director Georges Méliès incorporated special effects in his 1902 film "Le Voyage dans la Lune" (A Trip to the Moon) — including double-exposure, split screens, miniatures and stop-action.
Some of the most influential visual effects films of these early years such as Metropolis, The Ten Commandments, Citizen Kane, and 2001: A Space Odyssey utilized miniatures.
In the early 1970s, miniatures were often used to depict disasters in such films as The Poseidon Adventure, Earthquake and The Towering Inferno.
The Golden Years (1977 - 1993)
In the days before widespread use of computer generated imagery was practical, miniatures were a common tool in the visual effects artist's arsenal.
Iconic film sequences such as the tanker truck explosion from The Terminator and the bridge destruction in True Lies were achieved through the use of large-scale miniatures.
1993 saw the release of Jurassic Park which for many marked the turning point in the use of computers to create illusions, for which models and miniatures would have previously been employed.
Modern Use
While the use of computer generated imagery has largely overtaken physical models and miniatures in recent years, they are still often employed, especially for projects requiring physical interaction with fire, explosions or water.
Techniques
Kit-Bashing
Carpentry
Vacuum Forming
Molding and Casting
Fiberglass
Welding
Rapid Prototyping
Motion Control Photography
Slurpasaur
Slurpasaur (or Slurposaur) is a nickname given to optically enlarged lizards that are presented as dinosaurs in motion pictures.
In spite of the pioneering work of Willis O'Brien and others in making stop-motion animated dinosaurs since the early days of cinema, producers have used optically enlarged lizards (often with horns and fins glued on) to represent dinosaurs to cut costs as, it was felt, the public saw dinosaurs as being simply giant lizards. The first major use of the 'slurpasaur' was in One Million B.C. (1940) and, indeed, the special effects in this film were re-used often (in, for example, the 1955 movie King Dinosaur). Other notable films with 'slurpasaurs' include Journey to the Center of the Earth and The Lost World (1960). The latter is notable for a 'dinosaur battle' wherein a monitor lizard and a young crocodile fight each other for real. The former is a rare example of lizards actually being convincing in their role- the lizards are supposed to be Dimetrodons and actually look superficially similar to those creatures. The public eventually became too sophisticated to accept 'slurpasaurs' as convincing dinosaurs a factor which (together with the obvious animal cruelty aspect) led to their disappearance from the special effects arsenal.
Audio-Animatronics
Audio-Animatronics is the registered trademark for a form of robotics created by Walt Disney Imagineering for shows and attractions at Disney theme parks, and subsequently expanded on and used by other companies. The robots move and make noise, generally speech or song. An Audio-Animatronic is different from android-type robots in that it works off prerecorded moves and sounds, rather than processing external stimuli and responding to them. Animatronics has become a generic name for similar robots created by firms other than Disney.
Creation and early development
Audio-Animatronics were originally a creation of Lee Adams, who started his career with Disney as an electrician at the Burbank studio and was one of Disney's original Imagineers. The first Disney Audio-Animatronic was the giant squid in the movie 20,000 Leagues Under the Sea, which was created by Adams, based on a book of the same title by Jules Verne. It had pumps connected to the tentecals. When a pump was activated, air filled the tentacles, making them go up. When air left the tentacles, they coiled up. The term "Audio-Animatronics" was first used commercially by Disney in 1961, was filed as a trademark in 1964, and was registered in 1967.
Perhaps the most impressive of the early Audio-Animatronics efforts was The Enchanted Tiki Room, which opened in 1963 at Disneyland, where a room full of tropical creatures synchronize eye and facial action with a musical score entirely by electro-mechanical means. The "cast" of the musical revue used tones recorded on tape which vibrated a metal reed that closed a circuit to trigger a relay which sent a pulse of electricity to a mechanism that causes a pneumatic valve to move a part of the figure's body. The movements of the attraction's birds, flowers and tiki idols were triggered by sound, hence the audio prefix. Figures' movements had a neutral "natural resting position" that the limb/part would return to when there was no electric pulse. The animation was all on/off moves, such as an open/closed eye or beak. On/off movement was called a digital system. Other early examples were the Lincoln Exhibit presented at the State of Illinois Pavilion at the 1964 New York World's Fair. Also at the fair were three other pavilions featuring Audio-Animatronics. They were Pepsi/UNICEF's "it's a small world", General Electric's Carousel of Progress, and Ford's Magic Skyway.
Inner workings
Pneumatic muscles were not powerful enough to move larger objects, like an artificial human arm, so hydraulics were used for large figures. On/off movement would cause an arm to be either up over the artificial man's head (on switch), or down (off switch), but no movement in between. To create realistic in-between movement in large figures, an analog system was used. This gave the figure's limbs/parts a full range of in-between motion, rather than only two positions. The digital system was used with small pneumatic moving limbs (eyelids, beaks, fingers), and the analog system was used for large hydraulic human or animal (arms, heads) moving limbs. To permit a high degree of freedom, the control cylinders resemble typical miniature pneumatic or hydraulic cylinders, but mount the back of the cylinder on a ball joint and threaded rod. This ball joint permits the cylinders to float freely inside the frame, such as when the wrist joint rotates and flexes. Disney's technology is not infallible however; the oil-filled cylinders do occasionally drip or leak. It is sometimes necessary to do makeup touch-up work, or to strip the clothing off a figure due to leaking fluids inside. The Tiki Room remains a pneumatic theatrical set, primarily due to the leakage concerns -- Disney does not want hydraulic fluids dripping down onto the audience during a show.
Because each individual cylinder requires its own control/data channel, the original audio-animatronic figures were relatively simple in design to reduce the number of necessary channels. The first human designs (referred to internally by Disney as series A-1) for example included all four fingers of the hand as one actuator. With modern digital computers and vast data storage, the number of channels is virtually unlimited. The current versions (series A-100) for example now have individual actuators for each finger.
Compliance is a new technology that gives the animatronic figures faster, more realistic motion. In the older figures, a fast limb movement would cause the figure to shake in a weird unnatural way. So, the movements had to be slowed. Speed was sacrificed to gain control. This was frustrating for animators who wanted some faster movements. The new compliance tech allows fast movements with control too. It works by allowing a limb to pass the point where it is commanded to stop, and slow to a stop, instead of an immediate stop. This absorbs shock, much like the shock absorbers on a car or the natural shock absorption in a living body.
The skin of an AA is made from silicone rubber. Because the neck is so much narrower than the rest of the skull, the skull skin cover has a zipper up the back to permit easy removal. The facial appearance is painted onto the rubber, and standard cosmetic makeup is also used. Over time the flexing causes the paint to loosen and fall off, so occasional makeup work and repainting is required. Generally as the rubber skin flexes, the stress causes it to dry and begin to crack. Figures that do not have a high-degree of motion flexibility (such as the older A-1 series Lincoln) may only need the skin to be replaced every 10 years. The most recent A-100 series human AA's (such as for Bill Clinton) also include flexion actuators that move the cheeks and eyebrows to permit more realistic expressions, but the skin wears out more quickly and needs replacement at least every five years. The wig on each human AA is made from natural human hair for the highest degree of realism, but using real hair creates its own problems since the changing humidity and constant rapid motions of the moving AA carriage hardware throughout the day cause the hair to slowly lose its styling, requiring touch-ups before each day's showing.
Variations of Audio-Animatronics
The technology of the AAs at the theme parks around the world vary in their sophistication. They range from the blinking and mouth movents at Walt Disney's Enchanted Tiki Room to full body movement, from the mouth to the tip of the fingers at Stitch's Great Escape! at the Magic Kingdom. Current technologies have paved the way for more elaborate AA figures, such as the 'Ursula head' at Mermaid Lagoon Theater at Tokyo DisneySea, the Indiana Jones figures inside the Indy attractions at both Disneyland & Tokyo DisneySea, the 'swordfighting' pirates inside Disneyland Paris’ version of Pirates of the Caribbean, the "lava/rock monster" inside Journey to the Center of the Earth at Tokyo DisneySea, the "Yeti" inside Expedition Everest at Disney's Animal Kingdom, or the Roz figure in the Disney's California Adventure attraction "Monsters, Inc. Mike & Sulley to the Rescue!". In the case of the Roz figure, Disney makes the figure seemingly 'interact' with guests with help from an unseen ride operator who chooses pre-recorded messages for Roz to 'speak', thereby seeming to ‘react’ to individual guests' unique appearances/clothing. One of the newest figures comes with changes to the classic attraction, "Pirates of the Caribbean" at the two American resorts, both now featuring characters from the Pirates of the Caribbean film series. The Jack Sparrow figure is based on his portrayor Johnny Depp, even featuring his voice and facial mold.
Disney attractions that have utilized Audio-Animatronics
Disneyland Resort
Disneyland
Main Street, U.S.A.
Grand Canyon/Primeval World dioramas (part of the Disneyland Railroad)
Great Moments with Mr. Lincoln (on 'hiatus', with a planned return in 2007)
Adventureland
Walt Disney's Enchanted Tiki Room
Indiana Jones Adventure: Temple of the Forbidden Eye
Jungle Cruise
New Orleans Square
The Haunted Mansion
Pirates of the Caribbean
Club 33 (Inactive as of 2006)
Frontierland
Mark Twain Riverboat
Big Thunder Mountain Railroad
Mine Train Through Nature's Wonderland (since removed)
Critter Country
Splash Mountain
Country Bear Jamboree (since removed)
Fantasyland
"it's a small world"
Matterhorn Bobsleds
Tomorrowland
Star Tours
Buzz Lightyear Astro Blasters
Finding Nemo Submarine Voyage
Submarine Voyage thru Liquid Space (since removed)
Innoventions
America Sings (since removed)
Flight to the Moon (since removed)
Mission to Mars(since removed)
Carousel of Progress (since moved to Walt Disney World's Magic Kingdom)
Parades
Walt Disney's Parade of Dreams
Disney's California Adventure
a bug's land
It's Tough to be a Bug!
Hollywood Pictures Backlot
Jim Henson's Muppet*Vision 3D
Monsters, Inc. Mike & Sulley to the Rescue!
Lucky the Dinosaur
Walt Disney World Resort
The Magic Kingdom
Adventureland
The Enchanted Tiki Room (Under New Management)
Jungle Cruise
Pirates of the Caribbean
Liberty Square
The Hall of Presidents
The Haunted Mansion
Frontierland
Big Thunder Mountain Railroad
Splash Mountain
Country Bear Jamboree
Fantasyland
It's a Small World
Mickey's PhilharMagic
Mickey Mouse Revue (since moved to Tokyo Disneyland)
20,000 Leagues Under the Sea: Submarine Voyage (since removed)
Tomorrowland
The Carousel of Progress
Space Mountain
Stitch's Great Escape!
Buzz Lightyear's Space Ranger Spin
Flight to the Moon (since removed)
Mission to Mars (since removed)
The Timekeeper (since removed)
ExtraTERRORestrial Alien Encounter (since removed)
Epcot
Future World
Spaceship Earth
Innoventions
Universe of Energy
Journey Into Imagination
The Land
Living with the Land
Food Rocks (since removed)
Kitchen Kabaret (since removed)
Horizons (since removed)
Communicore (since removed)
World of Motion (since removed)
World Showcase
The American Adventure
Maelstrom
Gran Fiesta Tour Starring The Three Caballeros
Disney-MGM Studios
Streets of America Area
Star Tours
Jim Henson's Muppet*Vision 3D
Hollywood Blvd. Area
The Great Movie Ride
Disney's Animal Kingdom
Discovery Island
It's Tough to be a Bug!
DinoLand U.S.A.
DINOSAUR (formerly Countdown to Extinction)
Lucky the Dinosaur (since removed)
Asia
Expedition Everest
Tokyo Disney Resort
Tokyo Disneyland
Adventureland
Primeval World diorama (as part of Western River Railroad)
Jungle Cruise
The Enchanted Tiki Room: Get The Fever!
Pirates of the Caribbean
Critter Country
Splash Mountain
Westernland
Country Bear Jamboree
Mark Twain Riverboat
Big Thunder Mountain Railroad
Fantasyland
Cinderella Castle Mystery Tour (since removed)
It's a Small World
The Haunted Mansion / Haunted Mansion Holiday Nightmare
Pooh's Hunny Hunt
The Mickey Mouse Revue
Tomorrowland
Star Tours
Buzz Lightyear's Astro Blasters
Visionarium (since removed)
Meet the World (since removed)
Tokyo DisneySea
Arabian Coast
Sinbad's Storybook Voyage (formerly Sinbad's Seven Voyages)
Magic Lamp Theater
Port Discovery
StormRider
Mermaid Lagoon
Mermaid Lagoon Theater
New York Harbor
Tower of Terror
Lost River Delta
Indiana Jones Adventure: The Temple of the Crystal Skull
Mysterious Island
Journey to the Center of the Earth
20,000 Leagues Under the Sea
Disneyland Resort Paris
Disneyland Park
Frontierland
Phantom Manor
Big Thunder Mountain
Adventureland
Pirates of the Caribbean
Colonel Hathi's Pizza Outpost restaurant (currently semi-operative)
Fantasyland
It's a Small World
La Tanière du Dragon
Discoveryland
Buzz Lightyear Laser Blast
Le Visionarium (since removed)
Les Mystères du Nautilus
Star Tours
Hong Kong Disneyland Resort
Hong Kong Disneyland
Adventureland
Jungle Cruise
Lucky the Dinosaur
Fantasyland
Mickey's PhilharMagic
It's A Small World (Opening 2008)
Tomorrowland
Buzz Lightyear Astro Blasters
Other uses of animatronic figures
Animatronics also gained popularity in the 1980s through use at family entertainment centers such as Showbiz Pizza Place and Chuck E. Cheese's Pizza Time Theatre. They are also used in film and TV special effects. Several passengers and crew of a Pioneer Zephyr are represented in a display of this historic train at Chicago's Museum of Science and Industry. Neatly dressed in the proper style of first class passengers of their era, one remarks upon the casual dress of the visitors.
Matte painting
Matte paintings are used to create "virtual sets" and "digital backlots". They can be used to create entire new sets, or to extend portions of an existing set. Traditional matte painting is done optically, by painting on top of a piece of glass to be composited with the original footage. However this trick is as old, as Film itself (circa 1911). Originally, matte paintings were painted on glass plates, earlier also named glasshot. Two plates of glass are set up parallel to each other at a certain distance. The camera is set up in front of them. On the rear plate, there is a background landscape which is relatively rough, for example a painted Jungle. On the foreground plate, detail-rich elements are painted such as small plants, stones etc. Between the glass plates, one could then encourage a puppet in stop-motion. Nowadays, matte painting is done in computers with the use of a tablet as a drawing device. In a digital environment, matte paintings can also be done in a 3-D environment, allowing for 3-D camera movements. The first film to use a digital matte painting was Die Hard 2: Die Harder. It was used during the last scene, which took place on an airport runway.
Keying (graphics)
In graphics and visual effects, keying is an informal term for compositing two full frame images together, by discriminating the visual information into values of color and light.
Chroma key
A chroma key is the removal of a color from one image to reveal another "behind" it.
Luma key
A luma key similarly applies transparency (or Alpha channel) to regions (pixels) in an image which fall into a particular range of brightness. This technique is less controllable, but can be used on graphic elements. It is particularly useful for realistic fire keying, and was also used for on-screen text, such as programme titles and credits, before the advent of digital compositing.
Difference key
A difference key uses a background plate of the scene that the foreground object is being keyed out of and the software then assesses the source video and any pixels that don't match the grid are obviously meant to be keyed out. For example, if your subject is standing in front of a wall, a photo taken from the camera of the same wall, is used. This must be taken from the same camera angle, focus & distance. The software then compares the video to be keyed with the original photo and generates a mask based upon that difference, hence the name explain well.
Matte key
A matte key uses three images: the two images that will be composited, and a black-and-white third image (called "mask") that dictates the blending of the two, with white revealing one image, black the other, and grey revealing a blend of the two together.
Generally, the "bottom" image is called the beauty, the image that appears on top is the fill and the discriminating element (chroma, luma or matte) is called the key or matte.
Downstream key
A downstream key (or DSK) is a method of Matte keying, so you use three image or video signals. You have the base signal, where the fill signal is keyed on to, using the key signal to control the opacity of the fill signal. This results in a new signal, that you can use as an input for another DSK. This technique is used in television production, where you show the station name in a corner (DSK 1), and need a name title for a guest (DSK 2), while showing subtitles for translation of his/her speech (DSK 3).
Rotoscoping
Rotoscoping is an animation technique in which animators trace over live-action film movement, frame by frame, for use in animated films. Originally, pre-recorded live-action film images were projected onto a frosted glass panel and re-drawn by an animator. This projection
equipment is called a rotoscope, although this device has been replaced by computers in recent years. More recently, the rotoscoping technique has been referred to as interpolated rotoscoping.
History
The technique was invented by Max Fleischer, who used it in his series Out of the Inkwell starting around 1915, with his brother Dave Fleischer dressed in a clown outfit as the live-film reference for the character Koko the Clown.
Fleischer used rotoscope in a number of his later cartoons as well, most notably the Cab Calloway dance routines in three Betty Boop cartoons from the early 1930s, and the animation of Gulliver in Gulliver's Travels (1939). The Fleischer studio's most effective use of rotoscoping was in their series of action-oriented Superman cartoons, in which Superman and the other animated figures displayed very realistic movement. The Leon Schlesinger animation unit at Warner Brothers, producing cartoons geared more towards exaggerated comedy, used rotoscoping only occasionally. Walt Disney and his animators employed it carefully and very effectively in Snow White and the Seven Dwarfs in 1937. Rotoscoping was also used in many of Disney's subsequent animated feature films with human characters, such as Cinderella in 1950. Later, when Disney animation became more stylized (e.g. One Hundred and One Dalmatians, 1961), the rotoscope was used mainly for studying human and animal motion, rather than actual tracing. Rotoscoping was used extensively in China's first animated feature film, Princess Iron Fan (1941), which was released under very difficult conditions during the Second Sino-Japanese War and World War II. It was used extensively in the Soviet Union, where it was known as "Éclair", from the late 1930s to the 1950s; its historical use was enforced as a realization of Socialist Realism. Most of the films produced with it were adaptations of folk tales or poems - for example, The Night Before Christmas or The Tale of the Fisherman and the Fish. Only in the early 1960s, after the Khrushchev Thaw, did animators start to explore very different aesthetics. Ralph Bakshi used the technique quite extensively in his animated movies Wizards (1977), The Lord of the Rings (1978), American Pop (1981), and Fire and Ice (1983). Bakshi first turned to rotoscoping because he was refused by 20th Century Fox for a $50,000 budget increase to finish Wizards, and thus had to resort to the rotoscope technique to finish the battle sequences. (This was the same meeting at which George Lucas was also denied a $3 million budget increase to finish Star Wars.) Rotoscoping was also used in Heavy Metal (1981), the a-ha music video "Take on Me" (1985), and Don Bluth's Titan A.E. (2000). While rotoscoping is generally known to bring a sense of realism to larger budget animated films, the American animation company Filmation, known for its budget-cutting limited TV animation, was also notable for its heavy usage of rotoscope to good effect in series such as Flash Gordon, Blackstar and He-Man and the Masters of the Universe. Smoking Car Productions invented a digital rotoscoping process in 1994 for the creation of its critically-acclaimed adventure video game, The Last Express. The process was awarded U.S. Patent 6061462: Digital Cartoon and Animation Process. In the mid-1990s, Bob Sabiston, an animator and computer scientist veteran of the MIT Media Lab, developed a computer-assisted "interpolated rotoscoping" process which the director Richard Linklater later employed in the full-length feature films Waking Life (2001) and A Scanner Darkly (2006). Linklater licensed the same proprietary rotoscoping process for the look of both films. Linklater is the first director to use digital rotoscoping to create an entire feature film.
Additionally, a 2005-06 advertising campaign by Charles Schwab uses rotoscoping for a series of television spots, under the tagline "Talk to Chuck." This distinctive look is also the work of Bob Sabiston.
Technique
Rotoscoping is decried by some animation purists but has often been used to good effect. When used as an animator's reference tool, it can be a valuable time-saver.
Rotoscope output can have slight deviations from the true line that differ from frame to frame, which when animated cause the animated line to shake unnaturally, or "boil". Avoiding boiling requires considerable skill in the person performing the tracing, though causing the "boil" intentionally is a stylistic technique sometimes used to emphasize the surreal quality of rotoscoping, as in the music video Take on Me. Rotoscoping has often been used as a tool for special effects in live-action movies. By tracing an object, a silhouette (called a matte) can be created that can be used to create an empty space in a background scene. This allows the object to be placed in the scene. However, this technique has been largely superseded by bluescreen techniques. Rotoscoping has also been used to allow a special visual effect (such as a glow, for example) to be guided by the matte or rotoscoped line. One classic use of traditional rotoscoping was in the original three Star Wars films, where it was used to create the glowing lightsaber effect, by creating a matte based on sticks held by the actors. The term "rotoscoping" (typically abbreviated as "roto") is now generally used for the corresponding all-digital process of tracing outlines over digital film images to produce digital mattes. This technique is still in wide use for special cases where techniques such as bluescreen will not pull an accurate enough matte. Rotoscoping in the digital domain is often aided by motion tracking and onion-skinning software. Rotoscoping is often used in the preparation of garbage mattes for other matte-pulling processes.
Examples of rotoscoping
in animated films:
Snow White and the Seven Dwarfs
The 1940s Superman cartoons
A Scanner Darkly
Waking Life
Lord of the Rings
in live action films:
A Fistful of Dollars (title sequence)
Star Wars (lightsaber effects)
Forrest Gump (television sequences)
Godzilla showa and heisei series(rays)
in video games:
Prince of Persia (Among the first application in video gaming)
Another World
Commander Blood
Flashback: The Quest for Identity
The Last Express
Hotel Dusk: Room 215
in music videos:
Take on Me by a-ha
Money for Nothing by Dire Straits
Money for Nothing - Beverly Hillbillies by Weird Al Yankovic
Breaking the Habit by Linkin Park
in television shows:
Delta State
Flash Gordon (Filmation 1978)
American Idol: Idol Gives Back live duet between Celine Dion and Elvis Presley (together on stage with use of rotoscoping)
in commercials
Charles Schwab commercials
Apple iPod commercials
Chroma key (Blue Screen)
Chroma key is a technique for blending two images, in which a color (or a small color range) from one image is removed (or made
transparent), revealing another image behind it. This technique is also referred to as color keying, colour-separation overlay (CSO; primarily by the BBC), greenscreen, and bluescreen. It is commonly used for weather forecast broadcasts, wherein the presenter appears to be standing in front of a large map, but in the studio it is actually a large blue or green background.
History
Prior to the introduction of digital compositing, the process was complex and time consuming known as "traveling matte". The blue screen and and traveling matte method were developed in the 1930s and were used to create special effects for "The Thief of Baghdad," a film produced by Alex Korda. Director of Special Effects was Larry Butler. Mr. Butler's father, William Butler, appeared in more than 260 silent films beginning his career in 1908 at the age of 48, one of the pioneers of early filmmaking. The first Academy Award for best picture was awarded in 1928 for a film called "Wings," a movie about World War I flying aces. William Butler was 68 at the time; he had become interested in special effects. He asked his son, Larry, to drop out of Burbank High School in order to help him work on his contract to do special effects for the sequel to "Wings" called "Dirigible" which appeared in theaters in 1931.
The credit for development of the blue screen is given to Larry Butler, nominated for five academy awards, winner of two, and longtime executive at Columbia pictures. An inventor and widely believed to be a mechanical genuis, Larry Butler won the Academy Award for Special Effects for the Thief of Baghdad in 1940. He had invented the blue screen and traveling matte technique in order to achieve the visual effects which were unprecedented in 1940. He was also the first special effects man to have created these effects in Technicolor, which was in its infancy at the time. In 1950, Warner Bros. employee and ex-Kodak researcher Arthur Widmer began working on an ultra violet traveling matte process. He also began developing bluescreen techniques: one of the first films to use them was the 1958 adaptation of the Ernest Hemingway novella, The Old Man and the Sea, starring Spencer Tracy. The background footage was shot first and the actor or model was filmed against a bluescreen carrying out their actions. To simply place the foreground shot over the background shot would create a ghostly image over a blue-tinged background. The actor or model must be separated from the background and placed into a specially-made "hole" in the background footage. The bluescreen shot was first
rephotographed through a blue filter so that only the background is exposed. A special film is used that creates a black and white negative image — a black background with a subject-shaped hole in the middle. This is called a 'female matte'. The bluescreen shot was then rephotographed again, this time through a red and green filter so that only the foreground image was cast on film, creating a black silhouette on an unexposed (clear) background. This is called a 'male matte'. The background image is then rephotographed through the male matte, and the shot rephotographed through the female matte. An optical printer with two projectors, a film camera and a 'beam splitter' combines the images together one frame at a time. This part of the process must be very carefully controlled to ensure the absence of 'black lines'. During the 1980s, minicomputers were used to control the optical printer. For The Empire Strikes Back, Richard Edlund created a 'quad optical printer' that accelerated the process considerably and saved money. He received a special Academy Award for his innovation. One drawback to the traditional traveling matte is that the cameras shooting the images to be composited can't be easily synchronized. For decades, such matte shots had to be done "locked-down" so that neither the matted subject nor the background would move at all. Later, computer-timed motion control cameras alleviated this problem, as both the foreground and background could be filmed with the exact same camera moves. Petro Vlahos was awarded an Academy Award for his development of these techniques. His technique exploits the fact that most objects in real-world scenes have a color whose blue color component is similar in intensity to their green color component. Zbig Rybczynski also contributed to bluescreen technology. Some films make heavy use of chroma key to add backgrounds that are constructed entirely using computer-generated imagery (CGI). Performances from different takes can even be composited together, which allows actors to be filmed separately and then placed together in the same scene. Chroma key allows performers to appear to be in any location without even leaving the studio.
Computer development also made it easier to incorporate motion into composited shots, even when using handheld cameras. Reference-points can now be placed onto the colored background (usually as a painted grid, X's marked with tape, or equally spaced tennis balls attached to the wall). In post-production, a computer can use the references to adjust the position of the background, making it match the movement of the foreground perfectly. In the past decade, the use of green has become dominant in film special effects. The main reason for this is that green not only has a higher luminance value than blue but also in early digital formats the green channel was sampled twice as often as the blue, making it easier to work with. The choice of color is up to the effects artists and the needs of the specific shot. Red is usually avoided due to its prevalence in normal human skin pigments, but can be often used for objects and scenes which do not involve people. Weathermen often use a field monitor to the side of the screen to see where they are putting their hands. A newer technique is to project a faint image onto the screen.
The process
The principal subject is filmed or photographed against a background consisting of a single color or a relatively narrow range of colors, usually blue or green because these colors are considered to be the furthest away from skin tone. The portions of the video which match the preselected color are replaced by the alternate background video. This process is commonly known as "keying", "keying out" or simply a "key".
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 preselected color. In-phase portions of the video are replaced by the alternate background video.
In digital color TV, color is represented by a triple of numbers (red, green, blue). Chroma key is achieved by a simple numerical comparison between the video and the preselected 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 video.
Clothing
A chroma key subject must not wear clothing similar in color to the chroma key color(s) (unless intentional), because the clothing may be replaced with the background video. An example of intentional use of this is when an actor wears a blue covering over a part of their body to make it invisible in the final shot. This technique is used in the Harry Potter films, to make Harry's cloak appear to be invisible.
Background
Blue is generally used for both weather maps and special effects because it is complementary to human skin tone. However, in many instances, green has become the favored color because digital cameras retain more detail in the green channel and it requires less light than blue. Although green and blue are the most common, any color can be used. Occasionally, a magenta background is used. With better imaging and hardware, many companies are avoiding the confusion often experienced by weather presenters, who must otherwise watch themselves on a monitor to see the image shown behind them, by lightly projecting a copy of the background image onto the blue/green screen. This allows the presenter to accurately point and look at the map without referring to monitors.
Even lighting
The most difficult part of setting up a bluescreen or greenscreen is even lighting and the avoidance of shadow, because it is ideal to have as narrow a color range as possible being replaced. A shadow would present itself as a darker color to the camera and might not register for replacement. This can sometimes be seen in low-budget or live broadcasts where the errors cannot be manually repaired. The material being used affects the quality and ease of having it evenly lit. Materials which reflect light will be far less successful than those that do not. A plastic sheet will reflect light and have a hotspot in the center which will come out as a pale area, while the edges may be darkened. A cotton sheet will absorb more light and have a more even color range. Recently a much simpler and easier way to create an evenly lit background has been developed. By using screens made from a retroreflective fabric illuminated by a ring of LEDs around the camera lens it is possible to produce very even bright blue or green backgrounds whilst only consuming around five watts. Products such as Reflecmedia's Chromatte and LiteRing systems enable chroma key backgrounds to be created very simply and quickly, freeing the user to concentrate on lighting the foreground creatively. The systems are extremely energy efficient and enable users to create virtual studios in areas where space and energy are at a premium.
Srivenkat Bulemoni