This process is commonly referred to as chromogenic development. After the silver has been formed, exhausted agents reach with dye couplers to simultaneously form colored dye images, which represent the complementary color to the wavelengths of light that were originally recorded by the film. This step is common to all color photographic materials regardless of whether they ultimately produce positive or negative images on film or paper. When color negative film is processed, the first step (color developer) is designed to initiate reduction of silver halide salts in each of the three emulsion layers into metallic silver that produces a negative image. In general, the shelf life of diluted color process chemicals is far less than those used for black & white film processing. The stability of chemical solutions is also a factor in color processing, because sensitive combinations must be mixed immediately prior to use to avoid rapid deterioration of the components. Although the basic steps are similar in nature, color processes require more steps and greater temperature control than do black & white processes. Processing color film requires considerably more effort and attention than does black & white film. The image was recorded on Fujicolor Superia 100 color negative film and processed using the Kodak C-41 technique at 37.8 degrees centigrade. A Kodak Wratten CC10M magenta color compensating filter was used in the light path to eliminate a green cast present in background of the stained specimen. The staining mixture consists of safranin O (nuclei, chromosomes and cell walls), fast green (cytoplasm and cellulose cell walls), crystal violet (starch), and orange G (acidophilic cytoplasm).
The specimen employed in this discussion is a brightfield color photomicrograph of a quadruple-stained thin section of longitudinal tracheids derived from loblolly pine. Color negative film has an orange mask that is used to help control contrast and correct for deficiencies in green and red-sensitive layers when the negatives are printed. Bleach is then utilized to remove all of the silver metal, and each layer is left with only a color image. The blue-sensitive layer of the original film forma a yellow image, while the green and red-sensitive layers form magenta and cyan images, respectively. The result is the formation of three dye layers, one from each of the subtractive primary colors : cyan, magenta, and yellow. While doing this, the developer also oxidizes and combines with dye couplers that are either built into the emulsion layers or added during development. When negative film is processed, the developer converts light-sensitive crystallites of silver halide (usually the bromide salt) compounds in the emulsion layers into metallic silver.
Subsequently, the negative is printed, usually onto color photographic paper, to yield a positive color print. Color negative film produces an image that is complementary with respect to colors and density of the original microscopic viewfield. Other colors will react with two or more of the emulsion layers to reproduce that color when the negative is printed.
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