Chromogenic was the dominant color photographic process of the twentieth century for prints, negatives, and positive transparencies.  It is a subtractive color process and is based on the ability of certain chemical compounds called dye couplers to react with oxidized developer to form color dyes. 

In earlier color photographic processes the red, green, and blue records are formed individually as separation negatives (carbro, dye imbibition) . Chromogenic materials are composed of three superimposed gelatin silver  layers each spectrally sensitive to red, green, or blue light—this is called an integral tripack.  Each gelatin layer also contains colorless chemical compounds called dye couplers that will form a complimentary subtractive color dye during development. When the exposure is made, a latent image is formed in each gelatin layer corresponding to the colors of the scene. During development, the developing agent reduces the latent image to silver image particles which in turn oxidizes the developing agent. The dye couplers react with the oxidized developing agent to form cyan, magenta or yellow dyes where silver is present. The silver is converted to colorless silver ion in a bleaching bath and then removed in a fixing bath. In some processes the bleach and fix were combined into one bath called a blix bath.

The final image is composed of three superimposed gelatin layers containing either yellow, magenta, or cyan dye resulting in a full color image.

The process was invented due to a series of discoveries. In 1906 German Chemist, Dr. Benno Holmolka, discovered of the principle of dye coupling through his investigation of the latent image as an oxidizing agent. It was the German chemists, Rudolph Fischer and Hans Siegrist who coined the term “color formers” and first patented the integral tripack. Unfortunately they were not able to overcome the problem of the sensitizing dyes and couplers migrating between the layers. This problem was overcome by Leopold Godowsky and Leopold Mannes by incorporating the couplers into the developer and introducing them during development resulting in the 1935 introduction of Kodak’s Kodachrome, a positive transparency film. In 1941 Kodak made a positive print material on an opaque cellulose acetate support using this same technology, also called Kodachrome.  Agfa introduced the first successful chromogenic materials with internal couplers in 1936 with a product called Agfacolor Neu, also a transparency film. Agfa chemists Wilhelm Schneider and Gustav Willmanns overcame the problem of wandering couplers by making coupler molecules with long hydrocarbon chains which ballasted them in the gelatin. This is called the substantive method.  In 1942 Kodak introduced the first negative film and print material called Kodacolor. This internal coupler product used the lipophilic method in which the couplers were coated in an oily organic liquid before being added to the gelatin which kept them from moving between gelatin layers.