Bipack

Last updated March 22, 2024

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 (effects that are nowadays mainly achieved via optical printing) and as an early subtractive colour process.^[1]

Use as a color process

Eastman, Agfa, Gevaert, and DuPont all manufactured bipack film stocks for use in color processes from the 1920s onwards. Two strips of film, one orthochromatic and having a very thin and superficial red dye layer on its emulsion, and one panchromatic, would be exposed together with their emulsions pressed into close contact, the orthochromatic one nearest the lens. The orthochromatic negative ended up reversed from the normal handedness,^[1] but as the two negatives were often contact-printed onto one duplitized film for subsequent color-toning, as in the Prizma process, this often worked to the advantage of the laboratory.

Early color processes such as Prizmacolor, Multicolor, Cinecolor, and Trucolor all used bipack film.

The most famous version of Technicolor, the full-color three-strip Technicolor Process 4 used from 1932 to 1955, exposed two of the three strips—the blue and red images—in bipack. The green record, the highest definition record, was exposed directly.

Alas, certain early color TV transfers were exposed without respect to whether the film was wound conventionally on the reel (A-wind, i.e. emulsion facing toward the hub) or whether the wind was reversed (B-wind) rendering the resulting color image as somewhat faulty, i.e. due to the thickness of the film itself, one primary color was out-of-focus. Later transfers corrected this error.

Use as an in-camera effect

To achieve the in-camera effect, a reel would be made up of pre-exposed and developed film, and unexposed raw film, which would then be loaded into the camera. The exposed film would sit in front of the unexposed film, with the emulsion of both films touching each other, causing the images on the exposed film to be contact-printed onto the unexposed stock, along with the image from the camera lens. This method, in conjunction with a static matte placed in front of the camera, could be used to print angry storm clouds into a background on a studio set. The process differs from optical printing in that no optical elements (lenses, field lenses, etc.) separate the two films. Both films are sandwiched together in the same camera and make use of a phenomenon known as contact printing.^[2]

The process had its beginnings in providing a repeatable method of compositing live action and matte paintings, allowing the painted section of the final image to be completed later, and not tying up the set/sound-stage whilst the artist matched the painting to the set. It also alleviated the considerable difficulties caused by matching shadows on the painting to the set on an open-air set. The process worked equally well for matting-in real water to a model, or a model skyline to live action. The process was also referred to as the Held Take process. Perhaps the most famous example of a held take is the long shot of astronauts clambering down into a lunar excavation in 2001: A Space Odyssey .^[3]

The technique, if used with a camera not specially designed for contact printing, runs the risk of jamming the camera, due to the double thickness of film in the gate, and damaging both the exposed and unexposed stock.^[4] On the other hand, because both strips of film are in contact and are handled by the same film transport mechanism at the same time, registration is kept very precise. Special cameras designed for the process were manufactured by Acme and Oxberry, amongst others, and these usually featured an extremely precise registration mechanism specially designed for the process. These process cameras are usually recognisable by their special film magazines, which look like two standard film magazines on top of each other. The magazines allow the separate loading of exposed and unexposed stock, as opposed to winding the two films onto the same reel.

The bipack process, which is a competing method to optical printing, was used until digital methods of compositing became predominant in the industry. Industrial Light and Magic used a specially-built rig built for The Empire Strikes Back that utilised the method to create matte painting composites.

The Dunning Process

Various improvements and extensions of the process followed, the most famous being Carroll D. Dunning's, an early method built on the bipacking technique and used for creating traveling mattes. It is described thus:

The foreground action is lighted with yellow light only in front of a uniform, strongly lighted blue backing. Panchromatic negative film is used in the camera as the rear component of a bipack in which the front film is a positive yellow dye image of the background scene. This yellow dye image is exposed on the negative by the blue light from the backing areas, but the yellow light from the foreground passes through it and records an image of the foreground at the same time.

The Dunning Process, often in shorthand referred to as "process," was used in many black and white films, most notably King Kong . Its chief limitation was that it could not be used for color cinematography, and the process died out with the increasing move toward production of films in color.

Related Research Articles

Film stock is an analog medium that is used for recording motion pictures or animation. It is recorded on by a movie camera, developed, edited, and projected onto a screen using a movie projector. It is a strip or sheet of transparent plastic film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast and resolution of the film. The emulsion will gradually darken if left exposed to light, but the process is too slow and incomplete to be of any practical use. Instead, a very short exposure to the image formed by a camera lens is used to produce only a very slight chemical change, proportional to the amount of light absorbed by each crystal. This creates an invisible latent image in the emulsion, which can be chemically developed into a visible photograph. In addition to visible light, all films are sensitive to X-rays and high-energy particles. Most are at least slightly sensitive to invisible ultraviolet (UV) light. Some special-purpose films are sensitive into the infrared (IR) region of the spectrum.

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.

The following list comprises significant milestones in the development of photography technology.

<span class="mw-page-title-main">135 film</span> 35 mm photographic film format

135 film, more popularly referred to as 35 mm film or 35 mm, is a format of photographic film with a film gauge of 35 mm (1.4 in) loaded into a standardized type of magazine for use in 135 film cameras.

In photography, a negative is an image, usually on a strip or sheet of transparent plastic film, in which the lightest areas of the photographed subject appear darkest and the darkest areas appear lightest. This reversed order occurs because the extremely light-sensitive chemicals a camera film must use to capture an image quickly enough for ordinary picture-taking are darkened, rather than bleached, by exposure to light and subsequent photographic processing.

Photographic printing is the process of producing a final image on paper for viewing, using chemically sensitized paper. The paper is exposed to a photographic negative, a positive transparency , or a digital image file projected using an enlarger or digital exposure unit such as a LightJet or Minilab printer. Alternatively, the negative or transparency may be placed atop the paper and directly exposed, creating a contact print. Digital photographs are commonly printed on plain paper, for example by a color printer, but this is not considered "photographic printing".

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, though not all, 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.

Panchromatic emulsion is a type of black-and-white photographic emulsion that is sensitive to all wavelengths of visible light. By extension, a panchromatic sensor is an image sensor sensitive to the whole visible spectrum. A panchromatic image is the resulting picture.

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.

<span class="mw-page-title-main">Optical printer</span>

An optical printer is a device consisting of one or more film projectors mechanically linked to a movie camera. It allows filmmakers to re-photograph one or more strips of film. The optical printer is used for making special effects for motion pictures, or for copying and restoring film material.

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.

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.

The sodium vapor process 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, and received an Academy Award in 1965 for the sodium vapor process used in the film Mary Poppins.

In chemistry, orthochromasia is the property of a dye or stain to not change color on binding to a target, as opposed to metachromatic stains, which do change color. The word is derived from the Greek orthos, and chromatic (color). Toluidine blue is an example of a partially orthochromatic dye, as it stains nucleic acids by its orthochromatic color (blue), but stains mast cell granules in its metachromatic color (red).

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.

Duplitized film was a type of motion picture print film stock used for some two-color natural color processes. It was introduced by Eastman Kodak around 1913. The stock was of standard gauge and thickness, but it had a photographic emulsion coated on both sides of the film base instead of on one surface only.

Dye transfer is a continuous-tone color photographic printing process. It was used to print Technicolor films, as well as to produce paper colour prints used in advertising, or large transparencies for display.

In bipack color photography for motion pictures, two strips of black-and-white 35 mm film, running through the camera emulsion to emulsion, are used to record two regions of the color spectrum, for the purpose of ultimately printing the images, in complementary colors, superimposed on one strip of film. The result is a multicolored projection print that reproduces a useful but limited range of color by the subtractive color method. Bipack processes became commercially practical in the early 1910s when Kodak introduced duplitized film print stock, which facilitated making two-color prints.

Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and resolution of the film. Film is typically segmented in frames, that give rise to separate photographs.

Technicolor is a series of color motion picture processes, the first version dating back to 1916, and followed by improved versions over several decades.

References

1 2 Read, Paul; Meyer, Mark-Paul (2000). Restoration of Motion Picture Film. Oxford: Elsevier Science. pp. 43, 310. ISBN 075062793X. OCLC 45352344.
↑ Fielding, Raymond (1972). Techniques of Special Effects of Cinematography (3rd ed.). New York: Hastings House. ISBN 0803870310. OCLC 503765.
↑ Bizony, Piers (1994). 2001: Filming the Future. London: Aurum Press. ISBN 1854103652. OCLC 33009042.
↑ Professional production cameras will accept two thicknesses of film; process cameras will accept three thicknesses of film or two plus a splice.

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[RMPF-1] 1 2 Read, Paul; Meyer, Mark-Paul (2000). Restoration of Motion Picture Film. Oxford: Elsevier Science. pp. 43, 310. ISBN 075062793X. OCLC 45352344.

[2] Fielding, Raymond (1972). Techniques of Special Effects of Cinematography (3rd ed.). New York: Hastings House. ISBN 0803870310. OCLC 503765.

[3] Bizony, Piers (1994). 2001: Filming the Future. London: Aurum Press. ISBN 1854103652. OCLC 33009042.

[4] Professional production cameras will accept two thicknesses of film; process cameras will accept three thicknesses of film or two plus a splice.

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