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:
“A film is a petrified fountain of thought.”
—Jean Cocteau (1889–1963)
“The vanity of men, a constant insult to women, is also the ground for the implicit feminine claim of superior sensitivity and morality.”
—Patricia Meyer Spacks (b. 1929)
“A true politeness does not result from any hasty and artificial polishing, it is true, but grows naturally in characters of the right grain and quality, through a long fronting of men and events, and rubbing on good and bad fortune.”
—Henry David Thoreau (1817–1862)