However, while film grains are randomly distributed and have size variation, image sensor cells are of same size and are arranged in a grid, so direct comparison of film and digital resolutions is not straightforward. Thus, like film grain, physical pixel size represents the compromise between resolution and sensitivity. CCD cell), the pixels just as small-grain film has better resolution but less sensitivity than large-grain film, so will an image sensor with more elements result in an image with better resolution but less light per pixel. In digital cameras, the closest physical equivalents of film grains are the individual elements of the image sensor (e.g. Recording Kodak Film 1000 ASA, Amsterdam, Graffiti 1996.ĭigital photography does not exhibit film grain, since there is no film for any grain to exist within. Selwyn's observation (known as Selwyn's law) that, for a not too small aperture, the product of RMS granularity and the square root of aperture area tends to be independent of the aperture size. Selwyn granularity įilm grain is also sometimes quantified in a way that is relative independent of size of the aperture through which the microdensitometer measures it, using R. The standard 0.048 mm aperture size derives from a drill bit used by an employee of Kodak. When the particles are large, fewer are averaged in the standard area, so there is a larger random fluctuation, and a higher granularity number. When the particles of silver are small, the standard aperture area measures an average of many particles, so the granularity is small. Granularity is sometimes quoted as "diffuse RMS granularity times 1000", so that a film with granularity 10 means an rms density fluctuation of 0.010 in the standard aperture area. Granularity, or RMS granularity, is a numerical quantification of film-grain noise, equal to the root-mean-square (rms) fluctuations in optical density, measured with a microdensitometer with a 0.048 mm (48-micrometre) diameter circular aperture, on a film area that has been exposed and normally developed to a mean density of 1.0 D (that is, it transmits 10% of light incident on it).
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