Wandering mask

There were many varieties of self-masking, improved as the development of cinema technology. One of the most famous techniques was the “Williams mask” and “Dunning-Pomeroy's banner” ^[2] . All these technologies were based on the creation of an additional mask film containing a moving image that obscures a part of the frame that coincides along the contour with the objects of the survey. A significant part of these processes involved the use of a mask not when shooting, but when printing an intermediate counter in two exposures.

In the USSR, a method called “additive transparency” was invented by the combined camera operator Boris Gorbachev and was first used in the film “ Cinderella ” ^{[3] [4]} . The technology was used in black and white cinema, and included the filming of a blue-lit actor scene on a red background. However, the speedy spread of color in cinema no longer allowed using the previous method and B. K. Gorbachev in collaboration with film engineer V. I. Omelin ( NIKFI ) practically re-passed the whole technology using other materials: this way the red background was replaced with a translucent infrared screen illumination of low-voltage lamps and adjustable angle of inclination from 20 ° to 35 °, which allowed the cameraman to illuminate the gaming scene from any side, without fear of falling reflected glare from the glossy side of the screen into the lens of the camera; instead of the former blue light, standard white with heat filters, only slightly tinted in blue ^[5] . The optical part of the TKS camera also underwent significant alteration: a special lens and a block of prisms with corrected chromatic aberration for near infrared rays and the corresponding illumination of optical elements ^[6] .
A patent for a similar method was obtained in 1936 by L. Plansky, but the technology with an infra-screen was finally formed only by the end of the 40s ^[7] .

The roaming mask method introduced in Soviet film studios allowed creating a combined image that was no different from the usual one ^[8] and existed until the mid-1990s - the last was the operator Vladimir Vasilyev , who shot the shots for Shirley Myrli ^[9] . After this picture, the screen at Mosfilm was disassembled, the laboratory with the equipment for processing the mask film was destroyed.
In the United States, this technology was used until the end of the 1950s , when a more flexible kind of stray mask replaced, providing for a combined image of objects shot on a blue background, with subsequent optical overlap ^[8] . The necessary mask and countermask were created by printing on a contrasting black and white film from a color negative through red and blue light filters, and the final image was obtained by sequential printing of the actor's plan and background onto the general double negative ^[10] . In this case, the shooting blue background could be of any size and fit in an arbitrary place in the scene, without requiring complex lighting fixtures. This technology made it possible to obtain a combined image only after counter-capturing, in contrast to the infra-screen, which provided the finished original negative ^[11] . The technical perfection of the Kodak film at that time allowed for multiple reprinting of the image, and the blue screen technology quickly displaced the infra-screen from foreign film production ^[8] . In the USSR, its own version of this process was developed by Lenfilm studio experts and was first used for combined shots of the paintings The Adventures of Sherlock Holmes and Dr. Watson: The Baskervil dog , The Passion for Mordos and The Testament of Professor Dowell ^[12] .

A further development of the stray mask and the “blue screen” was the technology of automatic repetition of the camera movement , due to which the combination of various components in one frame can be combined with camera panning , its arbitrary movement and using the zoom lens . Before the advent of such a technique, the wandering mask required a fixed fixation of the camera, reducing the dynamics of the screen image. With the advent of digital technology Digital Intermediate , the methods of combined shooting, similar to the chroma key technique, have replaced the methods of stray masks. In this case, the actors are shot on a single-color background of a bright color, most often blue or green, followed by a digital substitution of the background color with another image. This technology eliminates complex photochemical and copying processes, but requires strict control over the colors of costumes and decoration elements in the main image. In the case of the coincidence of the color of any parts with the background color, the background in the final image will appear through them, which requires manual frame-by-frame correction ^[13] .

However, technological simplicity and the ability to control the chromakey process put it out of competition with traditional film technicians. Currently, optical methods of stray mask are not used. Modern developments in the field of the light field camera allow replacing the chromakey with a more advanced technique that does not limit the color of the objects being shot and does not require any screens. Thus, the digital movie camera Lytro Cinema simultaneously with the image file generates a depth map, on the basis of which you can assign the distance from which the captured image is replaced with a different background ^[14] .

The process, suitable for black-and-white movies, is based on the screening of the emulsion with silver and the Sabatier effect . The acting scene is filmed on a black background, after which the exposed film appears , but is not fixed . As a result, the unexposed areas of the background on the emulsion remain photosensitive, and a mask of developed metallic silver is formed on the exposed ones ^[15] . The film processed in this way is dried in the dark and again exposed to the background image. The areas exposed during the first exposure, shielded by the developed silver, are practically not illuminated by the background, while the rest of the frame space fixes a new image. After the second manifestation and final fixation, both images are combined on the received negative. The simplicity of the technology made it possible to use it even in amateur cinema and on reversed films. However, a number of drawbacks turned out to be unavoidable: a contour often formed at the border of two exposures due to diffusion of the products of oxidation of the first developer ^[16] .

In 1916, Frank Williams invented a method of obtaining a combined image in the laboratory with several films. The technology became possible after the appearance of the “Bell-Howell 2709” film camera in 1912 , for the first time equipped with a counter-grab , which sharply increased the accuracy of film motion ^[17] . The essence of the process consists in the production of moving masks and countermasks on two additional films, through which the printing of the combined counter- print occurs. There were two options for shooting the actor's scene - on a black and white background. In either case, the scene is illuminated taking into account obtaining a negative density normal, and from it a positive is printed on a high-contrast film in order to get a silhouette image of the actors on a transparent background. If at the first counter-cracking it is not possible to obtain a high-quality mask and counter-mask, the process of counter-cracking is repeated ^[18] . Sometimes, to increase the optical density of silhouettes, the positive was additionally processed in an amplifier solution ^[19] . With the positive mask obtained on a contrast film, a negative countermask is printed, which represents the transparent silhouettes of actors on an opaque black background ^[20] .

The combination of the actor's scene with the background occurs during the subsequent printing of the intermediate positive by the “ bipack ” method. At the same time, a positive film is folded with a mask, through which the background image from another negative is printed. After the first exposure, the positive film is rewound to the beginning and is folded with a countermask, through which the actor's scene is printed. The negative of the actor's stage, the mask and the countermask are synchronized with the frame accuracy of the marks made when printing both mask films, which ensures an exact match of the moving contours. After the manifestation on a positive film, a combined image is formed, containing the actor's stage and background. Sometimes, instead of a brightly lit white background, black was used, in which case a countermask was printed from a negative. The method has been successfully used by many film studios for several decades, including in the film Gold Rush by Charlie Chaplin ^[17] .
The main disadvantage of the method was the difficulty of combining the contours of the masks and the negative of the actor's scene due to the strong shrinkage of the films of those years on the nitrocellulose substrate during their laboratory processing . The unpredictability of the finite image size often led to the appearance of a border between the actors and the background ^[19] . However, the technology subsequently became the basis for the modern “ blue screen ” method in color cinema ^[21] .

The technology was developed in 1927 by Dodge Dunning and Roy Pomeroy ( Eng. C. Dodge Dunning, Roy J. Pomeroy ) and is based on the Bipack method ^[22] . Panchromatic film is exhibited in a special movie camera through a pre-printed positive background, virirovanny in red. The acting scene, illuminated by an orange-red light, is filmed against a blue-green uniform background. As a result, the red image of actors freely passes through the background film, and the blue-green light from the background is delayed by it, depending on the intensity of the red dye, printing the image from a positive ^[23] . At the same time, the blue-green background could not get on the image of the actors, excluding the "x-ray" through them, typical of the usual double exposure. Compared to the Williams mask, the process provided a better image of the actors directly taken to the original negative. In addition, the accuracy of contour alignment did not depend on the shrinkage of the film. The only drawback of the method was the additional stage of copying the image of the background that fell on the negative from the intermediate positive. In addition, the accuracy of the balance of two images for light and exposure strongly depended on the nuances of the background film viri- nation, and the result could be monitored only after laboratory processing . Nevertheless, the process was widely used in black and white cinema, and one of the earliest films with its use was Wilhelm Murnau 's “ Sunrise ” ^[17] . In the later picture “ King Kong ”, the banner is combined with the latest techniques of puppet animation , photo - transposition and frame-by-frame stunt printing at the time ^[23] .

The method for color and black-and-white cinema (developed by the operator B. Gorbachev with the participation of NIKFI engineer V. Omelin) was first implemented at Mosfilm , where in 1953 a unique 8x12 meter infrared screen was installed in the large pavilion of the Main building Laboratory processing of the infrachromatic film mask has been established. Three more smaller screens appeared on studios in Kiev , Odessa , and on Lenfilm ^[3] . For filming were used special movie camera , which allowed to shoot simultaneously on two films . For these purposes, cameras of the TKS series ^[24] were released, as well as the wide-format camera “Maska-70” 1KFSh ^[25] . With the help of such devices, the first of the two exposures required for obtaining a combined image was carried out. As in other technologies of the wandering mask, the difficulty was that the scene was first shot with actors who did not see the background on which the action takes place ^[26] .

First exposure

For the first exposure to a special film camera TKS charged two film, folded substrate to each other. Exposure of the films took place through a special light-splitting prism, creating images on the emulsion of each of the films, exactly the same in size ^[24] . At the same time, one of the films is black-and-white infrachromatic , that is, sensitive to infrared radiation. The second, black and white panchromatic or color multilayer film registers the visible image. For the shooting, the actors and part of the decoration were placed in front of a sloping background infra-screen uniformly illuminated by sources of infrared radiation to the light ^[27] . In the process of exposure on an infrachromatic film, an image of an infrared background is formed, because a light filter is installed in the frame window in front of it, which delays visible radiation and transmits infrared light. The second film, insensitive to infrared light, registers the image of actors and part of the scenery against a black screen. To prevent illumination of the infrachromatic film by the game image, all devices that illuminate the scene are put on light filters that detain infrared rays. Visible light on the infra-screen is allowed, because its tilt directs the reflection up. After shooting, the second film is sent to storage ^[28] , and the infrachromatic film immediately appears in a reversible process to a high contrast ratio . As a result, it produces a dense silhouette mask with a transparent background in place of an infrared screen.

Second Exposition

For background shooting, a developed mask and a negative film with a hidden game image were charged into a film camera using the bipack method, that is, with emulsions pressed together ^[28] . In this case, the developed film was located closer to the lens. For this, most movie cameras suitable for shooting on two films are suitable, including the Soviet cameras of the KSM, KSK and PSC series ^[25] . At the same time, it is necessary to observe frame-by-frame alignment accuracy, for which, at the first exposure, special cuttings were made on both films ^[28] . In the second exposure, only the background was shot, on which the action should take place, and the operator had the opportunity to precisely assemble the mask and the background, as he observed the mask image in the loop . Some devices are equipped with a special lamp, which can be inserted instead of a magnifying glass, and through the shooting lens to project the image of the mask on the background to be removed for alignment ^[29] . Проявленная инфракрасная плёнка выполняет роль маски, защищающей скрытое изображение актёров от экспонирования фоном. В результате после проявления на второй киноплёнке получается изображение актёров и части декораций, точно совмещённое с произвольным фоном. Причём, если актёр по ходу сцены должен «заходить» за участки фона, на их месте при съёмке первой экспозиции устанавливаются каше , также освещённые инфракрасным светом. В результате возможно полное «погружение» актёров в вымышленную сцену: они могут заходить за деревья и колонны, что неосуществимо при рирпроекции .

Такая техника съёмки требовала специальных навыков и знания техники бипак. Одна из сложностей состояла в необходимости точной подгонки снимаемых в первую и вторую экспозицию сцен по экспозиции и цветовому балансу. Кроме того, помимо синхронизации важно совпадение направления и характера в освещении обеих сцена. Потому такие эпизоды От и До снимались имеющим специальную подготовку оператором комбинированных съёмок , заранее прикреплявшимся к съёмочной группе .

Метод блуждающей маски позволял снимать невозможные в реальности сочетания актёров и фонов, например полёт на ковре-самолёте в «Старике Хоттабыче» ^[30] и панночки в « Вие », всевозможные волшебные превращения в « Садко », « Сказке о потерянном времени », « Сказке о царе Салтане ». Кроме того, разномасштабное совмещение в одном кадре актёров, снятых с разной крупностью, например Головы воина-великана и Руслана в « Руслане и Людмиле ». Сцены, связанные с риском для жизни, также были сняты этим способом в картинах: « Высота » ^{[8] [31]} , « Люди на мосту », « Непридуманная история ». На инфраэкране снято много эпизодов и кадров, для съёмки которых в обычных условиях потребовалась бы организация сложных экспедиций или выезда за границу ^[8] , больших массовок или постройка дорогих декораций. Это фильмы « Человек человеку », « Мексиканец », « Адмирал Ушаков », « Воскресение », « Человек ниоткуда », « Ленин в Польше », « Экипаж » ^[32] .

In the 1950s, the so-called “sodium process” ( English Sodium vapor process ) became popular in the UK, which was also called the “yellow screen” technology. The method was based on shooting the actor's scene against a white screen illuminated by sodium discharge lamps . The spectral composition of such a light source has a narrow yellow maximum, and is located between the photosensitivity zones of different photo emulsions of color negative film. As a result, the background is not displayed on the negative, affecting only the second, black and white film, the light on which is directed from the lens using a beam-splitting prism ^[33] .

After shooting on the exposed color film, a hidden image of the actor's scene is obtained, and on the black-and-white display, a contouring wandering mask. Later, it was used for printing, during which the background from another positive was imprinted on the unexposed areas of the color film. With the exception of the second exposure, which was carried out in a film copy machine, the process was close to the Soviet infra-screen, giving the finished image in the original negative. In addition, compared with the more common "blue screen", yellow gave a better combination of the plot, without any contours around the actors. Due to its merits, technology was used until the end of the 1980s. The last film, a series of scenes which was created in the technique of “sodium process”, in 1990 became “ Dick Tracy ” ^[34] .

The most advanced technology of the wandering mask, used until the advent of digital cinema. The method is a further development of the “Williams mask”, which on modern films is deprived of its main drawback, unavoidable on old nitrate photographic materials with great shrinkage. The part of the frame intended for replacement with another image is colored blue, or draped with the same fabric ^{[* 1]} . The color of the replaced background is selected for reasons of its maximum actinicity for the upper blue-sensitive layer of color film, and zero actinicity for the lower red-sensitive ^[35] . As a result, in the developed color negative, the optical density of the background in the blue-sensitive layer is maximum, and in the red-sensitive one it is close to the density of the veil . Thus, in the first one, the principle of the light background of the Williams mask works, and in the second - the opposite one, which totally excludes the effect of the brightness of individual parts of the actor's scene on the quality of separation ^[21] .

The laboratory stage of the process begins with the printing of a black-and-white mask and countermask from the color negative of the actor's scene. First, on the black-and-white orthochromatic film from a negative, illuminated through a blue light filter , the so-called “blue- light ” intermediate positive is printed. The yellow dye in combination with the color of the blue filter added to it makes the corresponding fragments of the negative opaque, preventing the display of a positive film on the background areas. As a result, in a positive way, the image of the actors is printed on a transparent background. The finished positive is folded with a negative by the bipack method, and a countermask is printed on them through a red light filter on a panchromatic film, which also manifests itself to maximum contrast . On the counter-mask, the transparent silhouettes of the actors are placed on an opaque background. The mask is printed with a countermask and represents an image of opaque silhouettes on a transparent background. The final stage involves the optical printing of a color negative double , which combines images of actors and background. The first ones are printed through a mask from the intermediate positive of the actor's scene, made from the original negative, and the background is imprinted through the countermask onto the rest of the frame from another interpositive ^[10] .

In the Soviet film industry, due to the low quality of the negative film, a different manufacturing sequence was used for the manufacturing of a walking mask ^[36] . First, through the red light filter, a red-matched positive was printed on the panchromatic film through a red light filter, which was shown to maximum contrast. The resulting positive contained a reversed image of a red-sensitive layer of negative, where the blue background looks transparent. Then, on a positive black and white film from the same negative, a “blue” positive was printed through a blue light filter. After the exposure, the unmanifested film was rewound to the beginning, and the second exposition was printed with a red-faced positive, additionally exposing the bright red-orange areas of the actors' image. After contrasting manifestation on a positive film, a primary mask is formed, which is a silhouette image of the actors on a transparent background. Its optical density and contrast are insufficient, and therefore it is used as an intermediate for the subsequent printing of the countermask and already from it - the working mask. Printing is carried out with compensation of halos of light scattering in order to exclude a mismatch of contours, which leads to the appearance of a border around the actor's scene ^[36] .

Compared with other technologies of the wandering mask, the most significant disadvantage of the “blue screen” method is considered to receive the combined image not in the original negative, but in the counter-effect , which reduces the photographic image quality. However, modern films can reduce these losses to a minimum, and the predictability of the results obtained eliminates the need to re-shoot costly scenes due to marriage during complex manipulations with a negative ^[11] . Compared to infra-mask, the matching of the background and the actor's scene with the exposition that occurs during the printing process is greatly simplified. Shooting does not require precision equipment and special qualifications of the cameraman , and the blue background is easily placed in any part of the scene being shot and can be of arbitrary sizes ^{[37] [38]} .

• Rearrangement
• Front projection
• Camera motion control

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