Grain is defined as
the subjective salt-and-pepper appearance
of a negative, slide, or print resulting from clumps of metallic silver
or clouds of color dyes congregating together in the image.
Generally, grain is most apparent in the
clear mid-tones that lack much pictorial detail.
Information about Granularity
Grain is an observable structural aspect
of a negative, slide, or print. It is the measured variation in the
distribution of an otherwise uniform silver deposit or dye cloud.
Grain growth is linked to film speed. As
film sensitivity increases, and corresponding ISO numbers go up, so
usually does the appearance of grain. We can generalize that faster
films are grainier than slower ones.
The issue of what is acceptable or
objectionable grain becomes important only when an image is magnified
sufficiently for the grain pattern to become visible.
Color films, print or slide, contain no
residual silver in their finished forms because the dyes forming the
color image create dye clouds at locations previously occupied by
developed silver clumps. Depending on the nature of the former silver
inhabitants and the composition of the new color dye clouds, what
appears as grain in black-and-white images can be seen in color
negatives and transparencies as well.
Grain or even dye clouds are not
necessarily visible to the naked eye. What we see are not individual
grains but groups of grains or dyes at different strata within the
emulsion layer of the Elm or print. The degree of visible graininess is
also a function of how regularly or randomly the grains of silver are
distributed. An observer may not perceive grain in a certain image if
it is arranged in a regular, repeating pattern. However, the same
observer might see a second image as grainier than the first even
though it contains fewer silver particles by actual count-simply
because its architecture scattered the silver grains randomly.
It has been a long-standing goal of film
designers to create emulsions and papers with regular, uniform, and
repeating grain patterns composed of identically shaped crystals in an
ever-thinner emulsion substrate.
It is important to point out that in film
design, as in fashion design, thin is good. The thinner the emulsion,
the more it can potentially resolve. Also, since thin emulsions tend to
cause less light scatter than thicker ones, they can contribute more
readily to the perception of fine grain.
Color films and prints display what
appears to be grain in much the same way that black-and-white material
does. However, the manner in which grain-like structures are produced
in color films and prints is quite different from black-and-white, but
the resulting image-degrading effects are similar for both.