Chromogenic


Chromogenic

Chromogenic refers to color photographic processes in which a traditional silver image is first formed, and then later replaced with a colored dye image.

Description

Chromogenic film or paper contains one or many layers of silver halide emulsion, along with dye couplers which are capable of forming visible dyes in combination with processing chemistry. In processing, the silver image of each layer is first developed. In concert with the dye couplers in each layer, the process subsequently forms dyes only in those areas where silver is present.

In full-color chromogenic materials, multiple layers of emulsion are sensitized to different wavelengths of light. Three layers are usually present, generally sensitive to red, green, and blue colored light. Cyan-colored dye is formed on the red-sensitive layer, magenta-colored dye is formed on the green-sensitive layer, and yellow-colored dye is formed on the blue-sensitive layer, following generally the CMY color model.

Some chromogenic black-and-white negative films also exist, mainly to exploit the wide availability of C-41 processing. These films have softer grain and less contrast than traditional silver halide films. In these films, a single emulsion layer has panchromatic sensitivity. The dye image is typically slightly blue because of the choice of dye couplers, and this tends to produce a dark sepia tone when printed on full-color chromogenic paper.

Each microscopic point of chromogenic dye formation is called a dye cloud. After the formation of dyes is complete, the silver image is removed in processing by a specialty photographic fixer called bleach fix or blix. A processing variation called skip bleach, most popular in motion picture negative processing, allows the silver image to be left partially or completely intact, yielding a type of contrast enhancement.

The most common chromogenic processes are C-41 for color and black-and-white negative film, RA-4 for color negative paper (see Type C print), and E-6 for slide film.

A great deal of research effort has been placed by manufacturers, most notably Fujifilm, Ilford Photo, and Kodak, into controlling the color and tonal characteristics of their chromogenic film and paper. The sensitization of the silver halide emulsions, the composition and mixture of the dye couplers, and the chemical interactions of layers upon one another during processing (called interlayer effects), are the subjects of numerous patents. Fujifilm is apparently unique in its use of a fourth (cyan-sensitive) color layer in certain of its negative films.

Like the traditional silver halide process, the main hazardous waste product of chromogenic processing consists of silver compounds dissolved in the used fixer. This waste is usually processed to recover the valuable dissolved silver in metallic form, and to allow safe disposal of the remaining substance. However a history of improper handling of waste fixer has led to environmental contamination. For example, the disposal of untreated waste fixer into the sanitary sewers and storm drains of New York City has led to high levels of dissolved silver in the Hudson River.

References


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Look at other dictionaries:

  • Chromogenic — Chro mo*gen ic, a. (Biol.) Containing, or capable of forming, chromogen; as, chromogenic bacteria. [1913 Webster] …   The Collaborative International Dictionary of English

  • chromogenic — adjective Date: 1859 1. of or relating to a chromogen 2. being a process of photographic film development in which silver halides activate precursors of chemical dyes that form the final image while the silver is removed; also being a film… …   New Collegiate Dictionary

  • chromogenic — /kroh meuh jen ik/, adj. 1. producing color. 2. Chem. pertaining to chromogen or a chromogen. 3. (of bacteria) producing some characteristic color or pigment that is useful as a means of identification. [1880 85; CHROMO + GENIC] * * * …   Universalium

  • chromogenic — adjective a) Describing a process in which a black and white image is replaced by a coloured one b) Containing or producing chromogen …   Wiktionary

  • chromogenic — 1. Denoting a chromogen. 2. Relating to chromogenesis. * * * chro·mo·gen·ic (kro″mo jenґik) producing a pigment or coloring matter …   Medical dictionary

  • chromogenic — adj. produces color; having a characteristic color; (Chemistry) pertaining to a chromogen (organic color producing substance) …   English contemporary dictionary

  • chromogenic — adjective 1》 involving the production of colour or pigments. 2》 Photography denoting a modern process of developing film which uses couplers to produce black and white images of very high definition …   English new terms dictionary

  • chromogenic — chro·mo·gen·ic …   English syllables

  • chromogenic — chro•mo•gen•ic [[t]ˌkroʊ məˈdʒɛn ɪk[/t]] adj. 1) opt producing color 2) chem. pertaining to a chromogen 3) mcr (of bacteria) producing some characteristic color or pigment that is useful as a means of identification • Etymology: 1880–85 …   From formal English to slang

  • chromogenic — /kroʊməˈdʒɛnɪk/ (say krohmuh jenik) adjective 1. producing colour. 2. relating to chromogen or a chromogen. 3. (of bacteria) forming some characteristic colour or pigment, usually valuable in identification …   Australian English dictionary


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