This article needs additional citations for verification .(September 2008) |
The sodium vapor process (occasionally referred to as yellowscreen) is a photochemical film technique for combining actors and background footage. It originated in the British film industry in the late 1950s and was used extensively by Walt Disney Productions in the 1960s and 1970s as an alternative to the more common bluescreen process. Wadsworth E. Pohl is credited with the invention or development of both of these processes (Patent US3133814A [1] ), and received (with Ub Iwerks and Petro Vlahos) an Academy Award in 1965 for the sodium vapor process as used in the film Mary Poppins . [2] [3] [4] [5]
The process is not very complicated in principle. An actor is filmed performing in front of a white screen that is lit with powerful sodium vapor lights. This light has a narrow color spectrum, that falls neatly into a chromatic notch between the various color sensitivity layers of color film. In this way the yellow color does not register on the red, green, or blue layers. [5] This allows the complete range of colors to be used, not only in costumes, but also in makeup and props. A camera with a beam-splitter prism is used to expose two separate film elements. The main element is the regular color negative film insensitive to sodium light and the other a fine-grain black-and-white film that is extremely sensitive to the specific wavelength produced by the sodium vapor. [5]
This second film element is used to create a matte, as well as a counter-matte, for use during compositing on an optical printer. These complementary mattes allow the various image elements to be cleanly isolated, so that as they are re-exposed onto a single fresh piece of negative, one at a time and in jigsaw fashion, the various images do not show through one another (as they would using simple double exposure). Acquiring the matte film element (as a first-generation original) at the same time as the live action makes a much better fit during optical printing, because it requires fewer separate, duplicate film generations than does bluescreen (though both processes degrade the image and introduce more "error" to the resulting matte) in the process of achieving sufficiently dense mattes. This increased accuracy ultimately renders the matte "lines" almost invisible, though as with bluescreen, its use may be signaled by hard separation or mismatched coloration and contrast between elements, or in this case, a telltale white/yellow fringe. [2]
Disney made one sodium vapor camera. 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.[ citation needed ] 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 its color negative film, Eastmancolor, which led to Hollywood's discontinuation of Technicolor cameras in 1954.
At the time of its use, the sodium process yielded cleaner results than did bluescreen, which was subject to noticeable color spill (a blue tint around the edges of the matte). The increased accuracy allowed for the compositing of materials with finer detail, such as hair or Mary Poppins' veiled hat. It was also useful that the "sodium yellow" light (and its removal via the matte) had a negligible effect on human skin tones. [2] As the bluescreen process improved, the sodium vapor process was abandoned; its screen and lamps monopolizing huge studios and incurring a higher cost.[ citation needed ] It was also reported that only three of the required prisms were produced. [6]
The first use of the process was in the J. Arthur Rank Organisation's Plain Sailing in 1956. [2] It was used in Disney's short Donald and the Wheel , [7] and the films The Parent Trap and Mary Poppins . It was also used for the Ray Harryhausen film First Men In The Moon , produced by Columbia Pictures. This was the only film Ray made in Cinemascope. He needed an alternate method of getting his stop motion characters together onto screen as his traditional methods did not fit the anamorphic lens process. 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.
The process was used in the 1970s for scenes in Island at the Top of the World , Gus , The Apple Dumpling Gang , Bedknobs and Broomsticks , Freaky Friday , Escape to Witch Mountain , Pete's Dragon , and The Black Hole . The last known use of the process was in the 1990 film Dick Tracy. [8]
On April 7, 2024, production studio Corridor Digital published a video showcasing a modern implementation of the sodium vapor process using a custom filter setup developed by Paul Debevec. [6]
This setup had the following steps:
35 mm film is a film gauge used in filmmaking, and the film standard. In motion pictures that record on film, 35 mm is the most commonly used gauge. The name of the gauge is not a direct measurement, and refers to the nominal width of the 35 mm format photographic film, which consists of strips 1.377 ± 0.001 inches (34.976 ± 0.025 mm) wide. The standard image exposure length on 35 mm for movies is four perforations per frame along both edges, which results in 16 frames per foot of film.
Chroma key compositing, or chroma keying, is a visual-effects and post-production technique for compositing (layering) two or more images or video streams together based on colour hues. The technique has been used in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture, and video game industries. A colour range in the foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as colour keying, colour-separation overlay, or by various terms for specific colour-related variants such as green screen or blue screen; chroma keying can be done with backgrounds of any colour that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from any human skin colour. No part of the subject being filmed or photographed may duplicate the colour used as the backing, or the part may be erroneously identified as part of the backing.
Traditional animation is an animation technique in which each frame is drawn by hand. The technique was the dominant form of animation of the 20th century, until there was a shift to computer animation in the industry, such as digital ink and paint and 3D computer animation.
A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm.
Compositing is the process or technique of combining visual elements from separate sources into single images, often to create the illusion that all those elements are parts of the same scene. Live-action shooting for compositing is variously called "chroma key", "blue screen", "green screen" and other names. Today, most compositing is achieved through digital image manipulation. Pre-digital compositing techniques, however, go back as far as the trick films of Georges Méliès in the late 19th century, and some are still in use.
The multiplane camera is a motion-picture camera that was used in the traditional animation process that moves a number of pieces of artwork past the camera at various speeds and at various distances from one another. This creates a sense of parallax or depth.
Cinecolor was an early subtractive color-model two-color motion picture process that was based upon the Prizma system of the 1910s and 1920s and the Multicolor system of the late 1920s and the 1930s. It was developed by William T. Crispinel and Alan M. Gundelfinger, and its various formats were in use from 1932 to 1955.
Petro Vlahos was an American engineer and inventor, considered to be one of the pioneering scientific and technical innovators of the motion picture and television industries. He is remembered in particular for creating the Ultimatte process, which refined the colour process known as chroma keying. In recognition of his contributions, he was awarded multiple Oscars, as well as an Emmy Award.
Mattes are used in photography and special effects filmmaking to combine two or more image elements into a single, final image. Usually, mattes are used to combine a foreground image with a background image. In this case, the matte is the background painting. In film and stage, mattes can be physically huge sections of painted canvas, portraying large scenic expanses of landscapes.
A front projection effect is an in-camera visual effects process in film production for combining foreground performance with pre-filmed background footage. In contrast to rear projection, which projects footage onto a screen from behind the performers, front projection projects the pre-filmed material over the performers and onto a highly reflective background surface.
Rear projection is one of many in-camera effects cinematic techniques in film production for combining foreground performances with pre-filmed backgrounds. It was widely used for many years in driving scenes, or to show other forms of "distant" background motion.
Reverse bluescreen is a visual effects technique pioneered by Jonathan Erland of Apogee Inc.(John Dykstra's company) for shooting the flying sequences in the film Firefox. Its objective is to enable the matting of subjects that confound the conventional process, such as those exhibiting reflective surfaces. It derives its name from the fact that it reverses, or inverts, the basic bluescreen process. Erland received a Scientific and Engineering Award from the Academy of Motion Picture Arts and Sciences for this technique.
In cinematography, bipacking, or a bipack, is the process of loading two reels of film into a camera, so that they both pass through the camera gate together. It was used both for in-camera effects and as an early subtractive colour process.
Color motion picture film refers both to unexposed color photographic film in a format suitable for use in a motion picture camera, and to finished motion picture film, ready for use in a projector, which bears images in color.
Primatte is a brand of chroma key software used in motion picture, television and photographic host applications to remove solid colored backgrounds and replace them with transparency to facilitate ‘background replacement’. It uses a unique algorithm based on three multi-faceted polyhedrons floating in RGB colorspace that are used to isolate color regions in the foreground image. Primatte is often referred to as a compositing technology and is usually used as a plug-in for host products such as Adobe After Effects, Adobe Photoshop, Autodesk Media and Entertainment Inferno or Flame, Eyeon Fusion and several other compositing and editing software packages.
The Prizma Color system was a color motion picture process, invented in 1913 by William Van Doren Kelley and Charles Raleigh. Initially, it was a two-color additive color system, similar to its predecessor, Kinemacolor. However, Kelley eventually transformed Prizma into a bi-pack color system that itself became the predecessor for future color processes such as Multicolor and Cinecolor.
Articles related to the field of motion pictures include:
Technicolor is a family of color motion picture processes. The first version, Process 1, was introduced in 1916, and improved versions followed over several decades.
The Williams process or Williams doublematting process is a matte creation technique patented by the American cinematographer Frank D. Williams in 1918. Unlike prior matte techniques, it allowed for the integration of the actors' movements with previously shot backgrounds.
Wadsworth Egmont Pohl was an American engineer and inventor who won a Technical Award in 1964, and was credited with the invention or development of the Sodium vapor process and the bluescreen process.