Photographic Reduction

the process of reducing the optical density of a photographic image by removing part of the metallic silver (for black-and-white photographic materials); also, the selective partial bleaching of the blue, yellow, or purple hues (for monopack color film).

Reduction of black-and-white photographic materials is based on partial oxidation of the metallic silver that produces the photographic image. The silver is converted into soluble salts, which are subsequently washed out of the photographic emulsion. A distinction is made among subtractive (or surface), proportional, and superproportional reduction. The solutions used in subtractive photographic reduction remove equal amounts of metallic silver from all areas of the image. In this type of process the contrast remains unchanged or is weakened slightly. Sub-tractive photographic reduction is used to remove various kinds of fogging and to correct overexposed negatives and sound tracks of variable width. In proportional reduction the largest quantity of metallic silver is removed from the areas of the photographic image that have the highest optical density (conversely, the removal of silver from areas of very low optical density is insignificant). This type of reduction is used to correct overdeveloped negatives and sound tracks with variable density and to provide uniform weakening of the image contrast. In superproportional reduction the metallic silver is removed mainly from the image areas with high optical density. Superproportional photographic reduction is used to correct very dense negatives having a high degree of contrast.

Photographic reduction makes it possible to improve the quality of overexposed and overdeveloped negatives. However, complete compensation of errors in exposure and development cannot be achieved. In some cases the method of photographic reduction is used to remove the image from individual areas of prints. The photographic reduction of colored images has the purpose of improving the color balance.