Color Management

A range of measures involving color management are

required at the prepress and print stage to produce a

multicolor print that gives the best possible reproduction

of the original.

The reproduction must be correct for tone and color

values. The “ correct tone value” means that the observer

cannot determine any difference in tonal progression

compared to the original or that the desired reproduction

curve for tone value is adhered to. A print

has the “ correct color value” if the reproduction gives

the best match for color to the original. If the color

space of the original differs from that reproducible in

print, then appropriate adjustments must be made. In

special cases, the use of special inks or “house colors”

provides an alternative.

The requirement of the proof is to simulate the expected

result of the printed job (not to produce the best

possible reproduction using the selected proofing

process, which may be better than that of the job).

Color values over the whole job must provide a consistent match to the ok-sheet within the chosen D E visual tolerances (see sec. 1.4.1).

Deviations in tone and color values during prepress and

print are caused by deviations from the ideal in the actual transfer characteristic curves. For example, a print shows a characteristic dot gain in comparison to the film or the printing plate caused by an enlargement of the halftone dot due to the printing process and by light entrapment (“light gathering”). To avoid producing a distorted print as a result of this dot gain, tone value must be reduced at the prepress stage by exactly the same amount, thereby compensating for the effect.

Dot gain is recorded quantitatively in the print characteristic curve. It is dependent predominantly on the printing process, the press, the printing conditions, the ink, screen ruling, the halftone process and the substrate.

Consequently, if a job is to be printed on a different

press than originally intended, new printing

plates might need to be produced if the print characteristic curves deviate too much from one another. The same is particularly true when changing to a different printing technology.

Similar effects to the print characteristic curve, albeit

over a different range and sometimes to a much lesser

extent, are produced by the characteristic curves of the

spectral light sensitivity and gradation of film material

for color separations, the spectral absorption and

transmission properties of real printing inks and color

filters, the whiteness of the substrate, its opacity and

light scattering properties, and so forth.

Measures to compensate for all of these effects may

be taken if the type and degree of deviation are known

and the means to counteract them in a defined manner

are present. For example, the system of characteristic

curves (see sec. 3.1.3.5) allows the required repro characteristic

curve as well as the printing and platemaking

curves to be produced from the target reproduction

curve, resulting in a reproduction with the correct tone

value on the printed sheet.

The type and degree of deviation of the print from

the original are determined with the aid of gray scales,

halftone squares and colorimetric areas, which are produced

during platemaking and printed out and then

measured using a densitometer or spectrophotometer.

Correction of tone value is necessary to:

• reduce the density range of the original to that

which can be reproduced in print,

• compensate for the dot gain appearing in the print

by accurately measured dot loss in prepress,

• compensate for variations in tone value associated

with platemaking,

• simulate the dot gain of the print at the proofing

stage.

Influencing color value in the sense of color correction

is necessary to:

• compensate for the uneven spectral distribution of

the illuminant light used in the production of color

separations,

• take account of the irregular spectral light sensitivity

of the film material,

• counteract the effect of unacceptably low main re-

flectance (faulty transmission, grayness) and secondary

reflectance (faulty absorption, desaturation)

of the individual printing inks in the colored

image,

• take account of the imperfect transparency of the

printing ink,

• compensate for the spectral deficiency of the filter

color,

• produce gray balance across the whole tonal range,

• take account of the conditions for ink acceptance in

the print for a prescribed color sequence,

• simulate the optical properties of the substrate in

the proof.

Mastering the large number of influencing parameters

is achieved by broad standardization of materials and

processes including the control processes (Europe

Scale for printing inks, recommended color sequence

for multicolor printing, suggested values for solid tone

densities of the standard process colors in the print for

different types of substrate, etc., see sec. 13.2.3).

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