Film Sensitivity and Grain
The size of silver halide grains in the emulsion affect film sensitivity; which is related to granularity because larger grains give film greater sensitivity to light. Fine-grain film, such as film designed for portraiture or copying original camera negatives, is relatively insensitive, or "slow", because it requires brighter light or a longer exposure than a "fast" film. Fast films, used for photographing in low light or capturing high-speed motion, produce comparatively grainy images.
Kodak has defined a "Print Grain Index" (PGI) to characterize film grain (color negative films only), based on perceptual just-noticeable difference of graininess in prints. They also define "granularity", a measurement of grain using an RMS measurement of density fluctuations in uniformly exposed film, measured with a microdensitometer with 48 micrometre aperture. Granularity varies with exposure — underexposed film looks grainier than overexposed film.
Read more about this topic: Film Speed
Famous quotes containing the words film, sensitivity and/or grain:
“This film is apparently meaningless, but if it has any meaning it is doubtless objectionable.”
—British Board Of Film Censors. Quoted in Halliwell’s Filmgoer’s Companion (1984)
“The sensitivity of men to small matters, and their indifference to great ones, indicates a strange inversion.”
—Blaise Pascal (1623–1662)
“Raise children for your old age as you would store up grain against famine.”
—Chinese proverb.