C-print

A chromogenic print, also known as a dye coupler print or a silver halide print, is a photographic print made from a color negative, transparency, or digital image and developed using a chromogenic process. They are the most common print for printing color photographs. They are composed of three layers of gelatin, each containing a light-sensitive material and a different dye coupler of subtractive color that together form a full-color image. The light-sensitive material in the print, like in black and white photographic papers, is a silver halide emulsion.

Developing color by using an oxidized developer was first suggested by German chemist Benno Homolka, who, by oxidizing indoxyl and theo-indoxyl, developed insoluble green and red dyes on a latent image. Although Homolka noted that these developers could create beautiful photographic effects, he didn't suggest using this developer in a color photographic process.

The potential of oxidized developers in a color photographic process was first realized by another German chemist, Rudolf Fischer, who, in 1912, filed a patent describing a chromogenic process to develop both positives and negatives. The following year he filed a patent listing various color developers and dye couplers, many of which are still used today. In spite of this, Fischer never created a successful color print due to his inability to prevent the dye couplers from moving between the emulsion layers.

This first solution to this problem, found by Agfa workers Gustav Wilmanns and Wilhelm Schneider, was creating a print made of three layers of gelatin containing subtractive color dye couplers made of long hydrocarbon chains, and carboxylic or sulfonic acid. This turned the dye couplers into micelles which can easily be scattered in the gelatin while loosely tethering to it. Agfa patented both the developer for this print and its photographic process and promptly developed and released Agfacolor Neu, the chromogenic print, a color print film that could be developed using a transparency, in 1936.

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