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Stochastic
printing, also called frequency modulation (FM) screening, uses small (10, 20
or 25 Micron), same size dots in a random pattern and varies the density of
the dot to create an image that is closer to continuous tone.
In the reproduction of an image, we scan a continuous tone original
photograph. The scan results in light striking a photosensitive device which
issues a number that digitally represents the tonality of the original image.
Printing a halftone image on paper requires that this number be passed to a
computer, which stores a grid of numbers in a rectangular matrix representing
the original image in digital form.
To convert the digital matrix of numbers into a printed halftone, the
computer sends the grid of numbers to the imagesetter where it is overlaid
with a "virtual" halftone screen, a mathematical matrix. The
computer captures the value of the numbers and passed it to the halftone
generator in the imagesetter.
The numbers can range from 0 to 256, which is translated by the halftone
generator into a halftone "dot". That dot may exist in any of 256
potential values. The dot is actually drawn by the halftone generator that
determines its shape as it grows in size from nonexistence to solid.
Varieties of dot shapes exist, from round or elliptical to diamond shaped. In
addition, straight-line and star-shaped dots are also possible.
Stochastic printing uses a random dot, which takes the mathematical value of
the dot and distributes its components inside the halftone cell. Stochastic
patterns make possible halftone printing without the use of conventional
dots. As a result, problems associated with screening striped or finely
detailed fashion sportswear that would result in a moiré patterns are eliminated.
This also makes it possible to print in more than the conventional four
colors of ink. By removing the barriers of screen angle interference from the
printing process, stochastic printing has made it possible for the use of
more than the basic 4 ink colors. Pantone introduced hexachromatic inks (six
process colors). This allows more accurate reproduction of pastel colors.
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