The visible texture in a film photograph. In black-and-white film, the image is made of tiny particles of metallic silver. Where these particles group together, they form a pattern that the eye sees as grain. In color film, the silver is removed and the image is made of dye clouds, which also create grain, usually softer.
High-ISO films have bigger grain than low-ISO films. Grain also becomes more visible when you make large enlargements. In digital photography, the similar effect is called noise.
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