Nikon LS-3500 - LS-3510 - Manual (Page 69)

Scanning for Reproduction 7-5
Software Reference for Scanners
transferred to the paper or film. This method yields the highest possible resolution
and image quality, however the runs are limited to roughly 5,000 copies, as
compared to 500,000 for offset plates and 2-3 million for gravure plates.
There are many other forms of printing from Flexography (using rubber
plates) for packaging, to wood and stone cut artists plates. In photography, there is
an even greater variety of printing methods, from black & white carbro and
platinum prints to the very expensive dye transfer process, and more recently to
the thermal dye sublimation process used in the Nikon CP-3000 Full Color digital
printer. This new technique has much in common with the continuous-tone
gravure process in that it uses variable-density ink transfer from constant sized
dots or “cells” rather than variable dot sizes as in halftone reproduction.
Most DTP scanner users are concerned with the lithographic process only,
(although letterpress can also use the negatives produced this way). The most
important aspects for calibrating this process are dot and screen control by angle,
frequency and size (gain). To make good color separations from your scans, you
should have access to a complete output system from image setter, through film
proofing ColorKeys® or Chromalins®, to progressive and press proofs. You
should also be using a densitometer to measure both the film originals before
scanning and the resulting printed pieces. Access to proper separation guides and
step wedges for calibration is essential. If you begin by using a service bureau for
these necessities, then try to stick to the same one.
Above all, use a scientific and calculated approach to calibration. Haphazard
“we’ll-run-it-when-we-like-the-way-it-looks” methods that don’t rely on writing
your data down and consistent measurement techniques, can only lead to costly
revisions every time you start a job. Since the intention is to save time and money,
you must be as professional in your methods as any printing craftsman would.
There is a considerable amount of theory that must be understood before
printing practice can become second nature. For example, let’s look at how Gray
Component Replacement, or GCR works. Understanding the technique will help
you to achieve better results from a variety of source images.
If there is an area of a print where you find equal amounts of cyan, magenta
and yellow inks, you can replace a certain percentage of these with black ink. Of
course, this assumes that equal quantities of cyan, magenta and yellow inks mix to
produce a neutral black. In fact, they do not. This mixing usually results in a
muddy brownish hue or desaturated color rather than a clean neutral gray.
The replacement of colored ink with black ink is a very difficult technique to
master. At one extreme, if you replace all the heavy common densities (shadow
areas) of YMC with heavy densities of K without replacing some component of
the mid-tones densities with neutral, then the result is an unnatural surface and
color effect on the printed piece. In fact, there should always be at least 10-20%
YMC color remaining in all tones from highlight to shadow when printing a
normal color piece. This applies to the 10-20% of highlight dot, in that the neutral
areas should be printed with some component of colored dots. It is immediately
apparent, especially in the midtones, when the dot pattern reverts to a simple,