Sodium vapor process
Encyclopedia
The sodium vapor process (occasionally referred to as yellowscreen) is a technique for combining actors and background footage, allowed to be used by The Walt Disney Company
as an alternative to the more common bluescreen process.
The process is not very complicated in principle, even for the early `60's. An actor is filmed performing in front of a white screen which is lit with powerful sodium vapor lights. This particular light is used because it glows in a specific narrow color spectrum that falls neatly into a chromatic notch between the various color sensitivity layers of the film so that the odd yellow color registers neither on the red, green or blue layers.
This allows the complete range of colors to be used not only in costumes, but also in make-up and props. A camera with a beam splitter prism
is used to expose two separate film elements with the main being regular color negative film that is not very sensitive to sodium light, while the other is a fine grain black-and-white film that is extremely sensitive to the specific wavelength produced by the sodium vapor.
This second film element is used to create a matte, which is basically a cut-out around the original color image, so that the regular color footage can later be placed over the matte, removing all the yellowscreen behind the actors and the result combined with another shot without the two images showing through each other. Making the matte film at the same time as the live action makes a much better fit in the post production optical printing, rendering the matte "lines" almost invisible.
Disney reportedly made only one sodium vapor camera because only one working prism was ever produced, despite attempts to replicate it. The camera was a retired Technicolor
three-strip camera modified to use two films, and used normal lenses for the conventional 1.85-1 aspect ratio. First developed in 1932, Technicolor three-strip cameras ran three rolls of black-and-white film past a beam-splitter and a prism to film three strips of film, one for each primary color. In 1952, Eastman Kodak
introduced their first color negative film, Eastmancolor, to the market.
At the time of its use, the sodium process yielded cleaner results than bluescreen, which was subject to noticeable color spill (a blue tint around the edges of the matte). It was also useful that the removal of the monochromatic "Sodium Yellow" had little effect on human skin tones. As the bluescreen process improved, the sodium vapor process was abandoned because the screen and lamps monopolized a huge studio, and its higher cost.
It was used in the Disney films The Parent Trap, Mary Poppins
, Bedknobs and Broomsticks
and Song of the South
. It was also used for the Ray Harryhausen
film Mysterious Island
, produced by Columbia Pictures
. Alfred Hitchcock
's The Birds
(produced by Universal Studios
) used yellow screen, under the direction of Disney animator Ub Iwerks
, in traveling matte shots with birds' rapidly fluttering wings.
It was used in the 1970s for scenes in Island at the Top of the World
, Gus
, The Apple Dumpling Gang
, Freaky Friday
, Escape to Witch Mountain
, Pete's Dragon
, and The Black Hole
. Its last known use was in the 1990 film Dick Tracy.
The Walt Disney Company
The Walt Disney Company is the largest media conglomerate in the world in terms of revenue. Founded on October 16, 1923, by Walt and Roy Disney as the Disney Brothers Cartoon Studio, Walt Disney Productions established itself as a leader in the American animation industry before diversifying into...
as an alternative to the more common bluescreen process.
The process is not very complicated in principle, even for the early `60's. An actor is filmed performing in front of a white screen which is lit with powerful sodium vapor lights. This particular light is used because it glows in a specific narrow color spectrum that falls neatly into a chromatic notch between the various color sensitivity layers of the film so that the odd yellow color registers neither on the red, green or blue layers.
This allows the complete range of colors to be used not only in costumes, but also in make-up and props. A camera with a beam splitter prism
Prism (optics)
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
is used to expose two separate film elements with the main being regular color negative film that is not very sensitive to sodium light, while the other is a fine grain black-and-white film that is extremely sensitive to the specific wavelength produced by the sodium vapor.
This second film element is used to create a matte, which is basically a cut-out around the original color image, so that the regular color footage can later be placed over the matte, removing all the yellowscreen behind the actors and the result combined with another shot without the two images showing through each other. Making the matte film at the same time as the live action makes a much better fit in the post production optical printing, rendering the matte "lines" almost invisible.
Disney reportedly made only one sodium vapor camera because only one working prism was ever produced, despite attempts to replicate it. The camera was a retired Technicolor
Technicolor
Technicolor is a color motion picture process invented in 1916 and improved over several decades.It was the second major process, after Britain's Kinemacolor, and the most widely used color process in Hollywood from 1922 to 1952...
three-strip camera modified to use two films, and used normal lenses for the conventional 1.85-1 aspect ratio. First developed in 1932, Technicolor three-strip cameras ran three rolls of black-and-white film past a beam-splitter and a prism to film three strips of film, one for each primary color. In 1952, Eastman Kodak
Eastman Kodak
Eastman Kodak Company is a multinational imaging and photographic equipment, materials and services company headquarted in Rochester, New York, United States. It was founded by George Eastman in 1892....
introduced their first color negative film, Eastmancolor, to the market.
At the time of its use, the sodium process yielded cleaner results than bluescreen, which was subject to noticeable color spill (a blue tint around the edges of the matte). It was also useful that the removal of the monochromatic "Sodium Yellow" had little effect on human skin tones. As the bluescreen process improved, the sodium vapor process was abandoned because the screen and lamps monopolized a huge studio, and its higher cost.
It was used in the Disney films The Parent Trap, Mary Poppins
Mary Poppins (film)
Mary Poppins is a 1964 musical film starring Julie Andrews and Dick Van Dyke, produced by Walt Disney, and based on the Mary Poppins books series by P. L. Travers with illustrations by Mary Shepard. The film was directed by Robert Stevenson and written by Bill Walsh and Don DaGradi, with songs by...
, Bedknobs and Broomsticks
Bedknobs and Broomsticks
Bedknobs and Broomsticks is a 1971 musical film produced by Walt Disney Productions and released by Buena Vista Distribution Company which combines live action and animation and was released in North America on December 13, 1971...
and Song of the South
Song of the South
Song of the South is a 1946 American musical film produced by Walt Disney and released by RKO Radio Pictures. The film is based on the Uncle Remus cycle of stories by Joel Chandler Harris. The live actors provide a sentimental frame story, in which Uncle Remus relates the folk tales of the...
. It was also used for the Ray Harryhausen
Ray Harryhausen
Ray Harryhausen is an American film producer and special effects creator...
film Mysterious Island
Mysterious Island (1961 film)
Mysterious Island is a 1961 film released by Morningside Productions. Based very loosely upon the novel The Mysterious Island by Jules Verne, the film was produced by Charles H. Schneer and Ray Harryhausen. Directed by Cy Endfield, it was released through Columbia Pictures...
, produced by Columbia Pictures
Columbia Pictures
Columbia Pictures Industries, Inc. is an American film production and distribution company. Columbia Pictures now forms part of the Columbia TriStar Motion Picture Group, owned by Sony Pictures Entertainment, a subsidiary of the Japanese conglomerate Sony. It is one of the leading film companies...
. Alfred Hitchcock
Alfred Hitchcock
Sir Alfred Joseph Hitchcock, KBE was a British film director and producer. He pioneered many techniques in the suspense and psychological thriller genres. After a successful career in British cinema in both silent films and early talkies, Hitchcock moved to Hollywood...
's The Birds
The Birds (film)
The Birds is a 1963 horror film directed by Alfred Hitchcock based on the 1952 short story "The Birds" by Daphne du Maurier. It depicts Bodega Bay, California which is, suddenly and for unexplained reasons, the subject of a series of widespread and violent bird attacks over the course of a few...
(produced by Universal Studios
Universal Studios
Universal Pictures , a subsidiary of NBCUniversal, is one of the six major movie studios....
) used yellow screen, under the direction of Disney animator Ub Iwerks
Ub Iwerks
Ub Iwerks, A.S.C. was a two-time Academy Award winning American animator, cartoonist, character designer, inventor, creator of Mickey Mouse, and special effects technician, who was famous for his work for Walt Disney....
, in traveling matte shots with birds' rapidly fluttering wings.
It was used in the 1970s for scenes in Island at the Top of the World
Island at the Top of the World
The Island at the Top of the World is a 1974 Disney film starring Donald Sinden and David Hartman.-Synopsis:In London in the year 1907, a British aristocrat named Sir Anthony Ross hastily arranges an expedition to the Arctic to search for his lost son Donald...
, Gus
Gus (film)
Gus is a 1976 American film by Walt Disney Productions. Its center character is Gus, a football-playing mule.- Plot :Gus is a film about a football-kicking mule and his trainer "Andy" ....
, The Apple Dumpling Gang
The Apple Dumpling Gang (film)
The Apple Dumpling Gang is a 1975 Disney film about slick gambler Russel Donavan who is duped into taking care of a group of orphan children who eventually strike gold during the California Gold Rush....
, Freaky Friday
Freaky Friday (1976 film)
Freaky Friday is a 1976 American comedy film starring Jodie Foster as Annabel Andrews and Barbara Harris as her mother.The film is based on the novel of the same name by Mary Rodgers, in which mother and daughter switch bodies and get a taste of each others' lives. The cause of the switch is left...
, Escape to Witch Mountain
Escape to Witch Mountain (1975 film)
Escape to Witch Mountain is a 1975 film based on the novel Escape to Witch Mountain by Alexander Key. It was produced by Walt Disney Productions, released by Buena Vista Distribution Company and directed by John Hough.- Plot :...
, Pete's Dragon
Pete's Dragon
Pete's Dragon is a 1977 live-action/animated musical film from Walt Disney Productions and the first Disney film to be recorded in the Dolby Stereo sound system...
, and The Black Hole
The Black Hole
The Black Hole is a 1979 American science fiction film directed by Gary Nelson for Walt Disney Productions. The film stars Maximilian Schell, Robert Forster, Joseph Bottoms, Yvette Mimieux, Anthony Perkins, and Ernest Borgnine, while the voices of the main robot characters are provided by Roddy...
. Its last known use was in the 1990 film Dick Tracy.