Color separation

The most common model of subtractive color synthesis is the CMYK printing system — cyan , magenta , yellow , and key (black) . In addition to the subtractive scheme, the theory of color reproduction is additive . It assumes not the subtraction of the color components from the “white” flow, but the summation of multi-colored flows into a single resulting flow. One of the variants of the additive scheme is the RGB model - red , green , blue . If the subtractive scheme is used in the printing industry (with “zero” in white paper ), then the additive one (with a larger color gamut ) is used in televisions, monitors, etc., where the screen is turned off black.

Color separation is the process of decomposing a full-color image into 3 RGB planes, 4 CMYK planes, or into a larger number of planes. With each plane with the help of a photo-automatic machine , a photographic film can be drawn, from which, in turn, printing plates can be made for various paints, again using a photo-process . With color separation, additional data processing is possible, for example, in order to reduce moire .

Color separation in modern printing - the process of preparing color images for printing in several colors. This technology uses the principle of subtractive color synthesis, assuming that the material reflecting or transmitting light (for example, paper or transparent film) is applied layers of colored dyes, each of which "subtracts" from the white color its share of the spectrum.

Traditionally, color separation was carried out in printing houses using optical filters and a raster system. At present, the process of rasterization and color separation is automated and implemented programmatically for prepress preparation of images, in particular, in the Adobe Photoshop graphic editor. Color separation here is a transformation of a color image into four color separations, of which four offset printing plates are made , successively applying colored printing ink on paper, forming a full-color image on the print.

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  Rgb

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  CMYK

In color film photography , as well as in film cinema , color separation results in three color separation monochrome images on separate films or in separate layers of a multi-layer photosensitive photographic material ^[3] . Separation into components occurs by means of light filters or due to selective spectral sensitivity ^{[4] of the} emulsion . The very first methods of color separation in photography and cinema involved the simultaneous shooting of two or three black-and-white negatives with the separation of the luminous flux by color-separating prisms and light filters. The first color film systems "Sinekolor" and "Technicolor" included shooting on two or three films.

In addition to these technologies, there was a raster film "Dufikolor" and lentikuryurye photographic materials with a lens raster deposited on the substrate and performing color separation together with color light filters installed in the shooting lens ^[5] . The resolution of such photo-film materials was unsatisfactory and these processes by Kodak and Agfa were forgotten in the mid-1930s.

The color photo also used three negatives, taken through color filters and the subsequent combination of color-separated colored images. However, the equipment for such photographs and films was too cumbersome and difficult to operate, and after the appearance of colored multi-layer films, it was practically out of use. In the color multilayer films both methods are used: part of the photosensitive layers of different spectral sensitivity are located under the color filtering layers that cut off part of the light spectrum . During laboratory processing in the photosensitive layers dyes of different colors are formed, depending on the color of the radiation to which the layer is sensitized . This is how a color image is obtained, consisting of several (most often three) color separations. In a negative-positive process, the three photosensitive layers perceive the primary colors used in the additive method of color synthesis, that is, red, green, and blue. And the dyes formed in the layers give an image of colors that are complementary to those that are reproducible and are used in substractive synthesis, that is, yellow, magenta, and cyan. Color separation occurs twice - in the production of negative and positive , resulting in a positive form of colors that are additional to the colors of the negative and coincide with the colors of the subject. With the reversing process, color separation occurs only once during the shooting. Therefore, the quality of the color rendition of the image obtained on reversible films is much higher than that obtained by the negative-positive process ^[6] . In the case of hydrotypical production of films (Technikolor technology) on film or photographs, after color separation, three color-separated matrices are obtained, from which sequential printing onto blank film with additional colors is performed.

In digital photography and digital cinema, color separation occurs using a Bayer filter in photosensitive matrices or three layers with different spectral sensitivity in multilayer Foveon X3 matrices. Color separation is performed on the primary colors used in additive color synthesis. To obtain the colors of the subtractive method used in the printing industry, digital image processing is performed by a computer .

In the very first color transmitting television cameras, color separation took place with the help of dichroic prisms or mirrors, with the help of which three monochrome images of primary colors were obtained on three or four transmitting tubes . Later, transmitting tubes appeared ^[7] , which carried out internal color separation using lattice light filters ^[8] . With the advent of semiconductor CCDs, high-end professional video cameras are still equipped with a color separation system and three matrices.

In cheaper and compact one-matrix devices, color separation occurred using a Bayer grille, as in digital cameras that appeared later. Modern video cameras and, especially, digital cameras , almost do not use the cumbersome prism color separation system, which imposes restrictions on the use of certain types of optics, and are based on the Bayer lattice . Some types of TV film projectors and film scanners also use a three-matrix color separation system.

• N. D. Panfilov, A. A. Fomin. Section Three. Photographic materials // Quick reference for amateur photographer. - M .: "Art", 1985. - S. 90-122. - 367 s. - 100 000 copies

• Color correction methods
• ICC color separation profiles