Bedienungsanleitung Nikon LS3510 (Seite 70 von 87) (Englisch)

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7-6 Scanning for Reproduction

Software Reference for Scanners

overly neutral halftone of medium-percentage black dots., a rainbow effect will

appear where the colored dot midtones break above the gray replacement point.

Also, in dark areas, where a large percentage of common color YMC inks

have been replaced with black, the depth of the ink (the richness) goes flat because

there is low ink surface volume on the page. When the same density is produced

using YMC or YMCK then there is a greater quantity of ink laid down and the

richness or depth is immediately apparent. Flemish painters like Rembrandt

realized this and used the oil medium to build up a shadow area to maximum black

using many layers of colors on top of each other. If they had simply used a black

pigment, there would have been no depthoor penetration of the shadows, no

content. In the above example, the lack of depth in the deep shadows of our

printed image would contrast greatly with the more robust layers of color which

formed the neutral lower-midtones even though they are lighter densities. Also,

this GCR technique, when badly handled, generally leads to a severe tone break

that is not necessarily due to a lack of bits in the digital representation, but due

rather to the jump from four color to one color, being set at a level where their is a

natural break forming in the image shading content, such as strongly defined dark

shadows which merge with the lighter side of a contrasty subject. Portraits that are

low-key and contrasty are the worst candidates for this type of color correction. It

is best to avoid or reduce the use of GCR when printing difficult subjects like

faces (especially on short runs where the cost of ink is not a major component of

the job), since the tone breaks will always appear adjacent to continuous midtones

in a face that requires a delicate gradation balance.

Finally, for gray replacement in the midtones, it is generally true that using

several screens of small dot size fills in the pattern of holes between variable high

contrast dots better than a single large size dot pattern. The surface effect that you

may detect from bad GCR is simply the lack of more diverse layers of ink, where a

single screen of medium black dots does not have the same surface sheen as

several screens laid down at different angles with smaller colored dots. The latter

is easier on the eyes, and in the lower midtones, the dot pattern is harder to detect.

In any multiplexed representation system, it is always better to increase the

frequency of the sampling, i.e.. lots of smaller dots are better than fewer larger

dots. When viewed from a certain distance they both appear to be the same shade.

Of course, there is a natural limit to this in that the finest controllable printing dot

in an ink litho system is difficult to produce at finer than a 1/200th of an inch

screen size.

At that size, the accuracy of the dot size is harder to control because the

capillary action of the paper has already caused it to bleed sideways to perhaps

twice its original size. Normally the dot gain as it is commonly called, is limited to

2-5% on film and perhaps as high as 10-15% with ink and paper. This dot gain

produces a muddy, desaturated and low definition result. The effect cannot be seen

on a film dot proof such as a 3M Match Print® or Dupont Chromalin®. These

proofs use a light sensitive color pigmented emulsion to reproduce the dots from

the original separation films. Because the dots are photographically “hard”, they

don’t bleed by capillary action, their gain is limited to the photographic gain

caused by the irradiation of exposure and processing.

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Nikon LS3510 Seite 70

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