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)
“...some small boys came out of the city and jeered at him, saying, “Go away, baldhead! Go away, baldhead!””
—Bible: Hebrew, 2 Kings 2:23.
Elisha--proving that baldness has been a source of sensitivity for centuries, Elisha cursed them and they died.
“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, trans. by Arthur J. Arberry (1955)