Mask (photo)

As a tool for multiple exposure, the mask appeared at the dawn of photography. Oscar Reilander already in 1856 created the photomontage "Two lifestyles", obtained by printing with 30 negatives ^{[6] [7]} . At the same time, Henry Peach Robinson and Gustave Legrey were engaged in similar experiments. The absence of the need for large quantities of positive copies in photography allows the use of masks for photo printing, and not when shooting. In the cinema, due to the restrictions imposed by the technology of replication, masking in the movie camera , which requires increased accuracy in the work of the cameraman , turned out to be more acceptable. Thus, the actor’s scene was combined with the background shot elsewhere, or “doubles” were created on the screen when the actor was talking to himself ^{[8] [9]} . In 1898, Méliès first applied porridge to the cinema, borrowing it from photographic equipment ^[3] . In this way, he combined in one frame images captured in different places and at different times. At first porridge covered one part of the frame, while a scene was shot on the other. Then the film was rewound to the beginning, and with the help of the counter-counter, part of the frame with the already captured image was closed, shooting another scene on unexposed sections. As a result, objects incompatible in real life were combined on the screen. So it was possible to place actors on an arbitrary background or combine them with a reduced layout of large structures. In the painting “The Great Train Robbery ”, the mask was used to combine the interior of the post office with the image of the train in the doorway.

Further development of lamination was the technique of drafting , when instead of an opaque mask, a background painted on glass was installed in front of the lens, which was prospectively combined with the objects of shooting ^[10] . In this way, it was possible to obtain a combined frame in one exposure. However, the main drawback of the technology was the need for a large depth of field , since the difference in distance from the lens to the glass with the picture and to the main subject is very large. It was possible to fix the problem using the technique of subsequent drafting, which appeared thanks to the latest filming machines equipped with a counter-grab . The mechanism sharply increased the accuracy of transportation of film and allowed to perform multiple exposure with high quality. The main scene was shot using the old technology with an opaque mask, and then a large format photograph was printed from the developed section of the captured film. Its parts, not covered with a mask at the time of shooting, were painted over with black ink, forming a countermask. In the rest of the space, the artist drew the desired background, which was shot on an undeveloped film strip with a second exposure ^[11] .

Despite all the conveniences of the painting technique, it had two main drawbacks: the painted background could only be motionless, which reduced the reliability of the image, and the border between the actor’s scene and the background had to go along a fixed line, restricting the freedom of movement of the actors. The problems were solved with the advent of the first technologies of a wandering mask, the role of which was played by an auxiliary film with a silhouette moving image of the actors. The invention was made possible thanks to the bipack method, in which two film films were charged simultaneously in a movie camera. At the same time, the mask mask covered parts of the frame that should not be exposed at the moment, ensuring the combination of the actor's scene and background exactly along a moving path. A gradual improvement in the quality of films made it possible to use the mask not at the time of shooting the original negative , but when printing an intermediate counter-type using a stunt machine . As a result, it was possible to minimize the risk of a fatal marriage, forcing to re-shoot expensive scenes ^[12] .

Most often, the mask is used for combined photo printing , allowing you to combine images from different negatives in a common picture. To do this, the future image format is determined in advance and a mask and countermask are made from sheet opaque material (for example, cardboard or black paper) ^[13] . Their border is determined by the projected image of one of the negatives. The sheet is cut along this line and after that they start printing. A mask is laid on unexposed photo paper through which the first negative is printed. The second negative is printed through the counter mask, which is placed on a sheet of photo paper so that its border coincides with the border of the mask. In this way, you can combine an unlimited number of images on one sheet, but the complexity of the process increases in proportion to their number ^[14] . The method is also suitable in the manufacture of photovignettes and for imprinting frames. In the XIX century, using a mask, landscapes imprinted an image of the sky, which was impossible to obtain directly due to the lack of spectral sensitization of emulsions of those years ^[15] . However, some photographers resorted to the use of combined photo printing to create multi-figure compositions, such as, for example, “Two Lifestyle” by Oscar Reilander ^[6] . Compared to photographing photo prints mounted on a common substrate, mask printing provides significantly higher image quality, since it eliminates counter-copying .

In addition to combining different images, the mask can also be used to adjust exposure in individual areas of the image ^[16] . In this case, translucent masks are applied, superimposed on the right places on the photo paper. Such a mask attenuates the light and brightens the masked area of ​​the print, or allows you to better print fragments of the picture that are not covered by it, while maintaining the normal exposure in the right places. In projection photo printing, photographers use their hands as a mask, blocking the lens light over areas of photo paper that should look lighter than others in the picture. In this case, the mask boundary is unsharp ^[17] . If it is necessary to obtain a sharp border, a mask of transparent painted film or glass is firmly pressed to the photo paper, and its border exactly follows the contours of the screened area. The same effect can be achieved by applying an opaque mask in two exposures: during one of them, the mask is removed, giving light access. To mitigate the contrast of the image, a halftone mask printed on a photographic film from the same negative can be used ^[18] . When a developed film is superimposed with a low-contrast positive image on photo paper, it serves as a light filter “subtracting” the contrast of the negative image projected by the enlarger ^[1] . In some cases, such a mask is specially printed with reduced sharpness to maintain the contour contrast of the print with a reduced overall ^[19] . In photography, this technique was called “ unsharp masking, ” and a filter with the same name ( English Unsharp Mask ) and the principle of action is built into most modern graphic editors , such as Adobe Photoshop ^[20] . Painted translucent masks can be used in color photo printing to correct color reproduction in individual areas of the image ^[21] .

Color Separation Masking

In analog color photography , masks are used that are formed directly in the emulsion, simultaneously with the main image. Such masking is called “internal” and serves to compensate for undesirable shades of dyes synthesized in zone-sensitive photoemulsion layers of chromogenic photographic materials ^[21] . The technology is used only in negative or counter-type color photo and film films , since the yellow-orange color of the mask is unacceptable in the positive. Moreover, instead of colorless color-forming components, colored ones are added to the emulsion, the intensity of decolorization of which during development is directly proportional to the yield of the corresponding dyes ^[22] . As a result, the processed photographic material contains two images: the main negative and low-contrast positive. A negative image consists of dyes, and a positive one consists of unspent color-forming components. The latter serves as a mask, compensating for printing shades of dyes that impair the quality of color separation ^[23] .

In the cinema, three basic techniques of combined shooting through porridge are known.

Intracamera

The earliest concealment method for combined shooting. Using a compendium , masks are installed in front of the lens of the movie camera, the shape of which determines the boundary of the image separation ^[24] . First, one part of the frame is exposed through the mask, and then the other through the mask. After laboratory processing, a combined image is obtained on film. In this way, you can combine two or more images taken at different times in different places. In George Pabst ’s film “Secrets of One Soul” of 1926, creating one of the combined frames required a six-time exposure with the same amount of porridge and counter-cache ^[25] . A variation of the method is the technique of subsequent drafting, when a segment of a film shot through a mask with an actor’s scene is used to create a painted background on a photo print. The areas covered with black ink with the captured scene serve as a countermask during the second exposure ^[11] .

Transparent mask

The production of a combined frame using this technology begins with the usual shooting of the actor’s scene in the pavilion or in kind. Several frames are cut from the captured and processed film, one of which is projected onto the glass. Before this, the glass is painted black, and on top of it - white paint. Focusing on the image projected onto the paint, the artist denotes the line of the future junction of the real scene with the completed one. Then a negative background pattern is applied to the white paint in the selected places, and the rest of the glass space intended for the already captured image is cleaned of the paint. After that, two films are charged into the movie camera using the bipack method: unexposed and over it the negative of the actor’s scene (“transparency”). Before starting the device, the glass with a pattern is illuminated from behind, isolating from the light the surface facing the lens. As a result, an unexposed film is imprinted with a negative image of the actor’s scene, and only in those places where the glass is cleaned of paint. In this case, shaded glass fragments play the role of a mask. After filming the entire length of the negative, the camera is recharged, leaving in it only the undeveloped film, rewound to the beginning. The second exposure takes place with frontal illumination of the pattern on the glass, closed behind black velvet. The latter serves as a countermask, protecting sections of the frame that are already exposed through the negative from unwanted illumination. After laboratory processing of the film, it receives an interpositive of a combined frame consisting of an actor's scene and a painted background.

Photo Shuffle

The photo-shifting technique can be used to create a wandering mask, which is manually drawn frame-by-frame from the working positive of the actor’s scene. The method was used in the science fiction film " Space Odyssey of 2001 " to combine actors with the background of the starry sky. However, with optical film technology, this technology is too time-consuming, and more common in modern digital.

A mask or porridge is used in cached formats for widescreen cinema . At the same time, the academic frame is limited to the top and bottom by using an opaque mask (porridge), which increases the aspect ratio of the screen ^[26] . Porridge can be installed in the frame window of the movie camera at the time of shooting, giving a widescreen negative. In this case, the technology is called “explicit caching”. Sometimes porridge is used when printing film copies or already in a film projector . In this case, the method is called “ hidden caching ” ^[27] . In both cases, the frame height is reduced, giving a widescreen image, and when it is projected, a short-focus lens is used , filling the image with a wider screen than a conventional film copy ^[28] .

On-screen porridge

The technology is used to match images and screens with different aspect ratios . Most commonly used in standard definition television when displaying widescreen movies on a regular screen. In this case, the widescreen image is completed by the black porridge above and below to the screen format, preserving the original frame without cropping ^[29] . Less commonly, the same technology is used to fit a wide-screen movie frame in the classic 1.37: 1 format . The size and location of the porridge are transmitted along with the video using the service codes WSS ( Wide Screen Signaling ) or AFD ( Active Format Description ) ^{[30] [31]} . In the same way, lamination is used in movie releases.

• Cached film
• Image caching

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