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:
“You should look straight at a film; that’s the only way to see one. Film is not the art of scholars but of illiterates.”
—Werner Herzog (b. 1942)
“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)
“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)