film

film - Film grain

Photograph by dev nullon Flickr.

When the grains are large, fewer are averaged in the standard area, so there is a larger random fluctuation, and film Film grain a higher granularity number. The standard 0.048 mm aperture size derives from a drill bit used by an employee of Kodak. Film film 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 Selwyn granularity is defined as: where σ is the RMS granularity and a is the film James Bond film series aperture area. The images below show an example of extreme film grain: Rallycross car pictured on an Agfa 1000 RS slide Detail of the same photo Digital photography does not exhibit film grain, since there is no film for any grain to exist within.

The effect of film grain can be simulated in some digital photo manipulation programs, such as Photoshop, adding grain to a digital image after it is taken. In digital photography, image noise sometimes appears as a grain-like effect. . Film grain or granularity is the random optical texture of processed photographic film due to the presence of small grains of a metallic silver developed from silver halide that have received enough photons. Granularity, or RMS granularity, is a numerical quantification of film-grain noise, equal to the root-mean-square (rms) fluctuations in optical density, 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. When the grains are small, the standard aperture area measures an average of many grains, so the granularity is small.

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 be independent of the aperture size.