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)
“What we think of as our sensitivity is only the higher evolution of terror in a poor dumb beast. We suffer for nothing. Our own death wish is our only real tragedy.”
—Mario Puzo (b. 1920)
“Have We not made the earth as a cradle
and the mountains as pegs?
And We created you in pairs,
and We appointed your sleep for a rest;
and We appointed night for a garment,
and We appointed day for a livelihood.
And We have built above you seven strong ones,
and We appointed a blazing lamp
and have sent down out of the rain-clouds water cascading
that We may bring forth thereby grain and plants,
and gardens luxuriant.”
—Qur’an, “The Tiding” 78:6-16, ed. Arthur J. Arberry (1955)