Graininess

graininess [′grān·ē·nəs]

(graphic arts)

A mottled effect in film caused by clumping of the silver particles.

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Graininess 

the inhomogeneity of a uniformly exposed and developed photographic layer observed in an enlarged photographic image. At high magnification the form of the primary blackening structure (microgranular structure) may be seen; it consists of individual silver “grains” which are produced by the reducing action of the developer on the microscopic crystals of silver halide in the photographic material. The size of the grains is usually greater than the size of the silver halide crystals from which they are formed, reaching several microns (μ). The secondary blackening structure, which itself is called graininess (also macrograininess, granularity, or photographic noise), is observed at low magnifications (5–30 ×). It is produced by the superposition of the projections of individual silver grains located at different depths of the very thin (7–26 μ) developed layer, by the combined reduction of several randomly adhering microscopic crystals of silver halide, and sometimes by the accretion of silver grains in the process of their formation during developing.

Graininess lowers the quality of a photographic image by reducing the aesthetic impression of still pictures produced by printing from a small negative and in motion-picture images on a screen by making it more difficult (or even impossible) to recognize fine details in complicated pictures, particularly technical photographs, and by complicating the microphotometric processing of spectrograms, astronomical photographs, and other kinds of special photographic images. Graininess is primarily determined by the size of the microscopic silver halide crystals; it increases sharply with the degree of exposure and development of the layer. However, it usually is not highly dependent on the composition of the developer. Photographic images produced on low-sensitivity materials with the smallest possible exposures and a low degree of development are the least grainy.

IU. N. GOROKHOVSKII