EP0676285B1 - Colour management in a sheet-fed rotary offset printing machine - Google Patents

Abstract

A group of measured fields (as well as a process for using the measured fields) is provided for determining color data of a printed product, especially for color management in the rotary offset printing of single editions, with a plurality of measured fields, which are printed on a printed product to be checked or on a primary print in such a way that they can be optically scanned. The group of measured fields includes a first combination measured field, in which the fundamental colors are superprinted with their nominal degrees of surface coverage (Fc1, Fm1, Fy1). Additional combination measured fields are provided, in which the fundamental colors are superprinted at varied nominal degrees of surface coverage {(Fc2=Fc1+ DELTA Fc2, Fm1, Fy1), (Fc1, Fm3=Fm1+ DELTA Fm3, Fy1), (Fc1, Fm1, Fy4=Fy1+ DELTA Fy4)}, wherein each fundamental color is varied at least once, and at least one other fundamental color is varied in each additional combination measured field. Additionally at least one single-color full-tone field is provided for each fundamental color. Further, at least one single-color half-tone field is provided for each fundamental color, wherein first single-color half-tone fields have, in their corresponding fundamental color, a degree of surface coverage (Fc1, Fm1, Fy1) that corresponds to that of the same color in the first combination measured field, and/or second single-color half-tone fields have, in their corresponding fundamental color, a degree of surface coverage (Fc2, Fm3, Fy4) that corresponds to the varied degree of surface coverage of the same color in the additional combination measured fields.

Description

The basic idea of color management is that color templates in digital prepress are defined independently of output devices and materials. The colors are therefore described in a colorimetric coordinate system standardized by the Commission Internationale de l'Eclairage (CIE), such as XYZ, CIELAB or CIELUV. If multicolored images of this type are output on paper using a system calibrated in terms of color management, this ensures that the color appearance of the output is always the same, regardless of the output process used.

• die farbliche Erscheinung mehrfarbig gedruckter Bilder auch im Zeitungsoffset-Auflagendruck systematisch erfasst,
• zufällige Abweichungen unterdrückt oder ausgeregelt und
• systematische Abweichungen kompensiert werden können.

Computer color printers, digital color copiers and digital proofing devices are currently used as calibratable output systems. It is advantageous to extend the concept of color management to conventional printing processes such as newspaper offset. The chain of effects consisting of printing form production and the printing process is treated like any other calibratable output device. Until that happens, however, the conditions must be created for that

• the color appearance of multicolor printed images is also systematically recorded in newspaper offset production,
• random deviations suppressed or corrected and
• systematic deviations can be compensated.

Numerous solutions are known today for monitoring and controlling the coloring in multicolor offset printing.

EP 0 196 431 B1, for example, describes a method and a device for achieving a uniform printing result on a multi-color offset printing machine that works in an autotypical manner. This solution is characterized by the measurement of ink layer thicknesses (solid ink densities) and halftone dot sizes (area coverage) at measuring fields, which are also printed for each printing ink in each inking zone of the press. The ink guide actuators on the printing press are set automatically on the basis of these densitometric measured values.

The need to print several measuring fields in each inking zone has meant that the above-mentioned method has so far only been used in commercial offset printing. In commercial offset printing, the measuring fields can be printed outside the type area, ie on an edge, which is then cut away. This requirement is not met in newspaper offset. No margin is cut away here, any measuring fields that are also printed must be accommodated within the type area and thus take up space that could otherwise be used by advertisements or editorial contributions. Newspaper publishers are therefore reluctant to accept the measuring fields.

Another obstacle to the use of the above method in newspaper offset is the high level of equipment and manpower that arises when measuring the measuring fields. Should the web offset measurement be online, i.e. happen automatically on the running web, an optical measuring head with automatic positioning is necessary for each web side. If the measurement were instead carried out with commercially available hand-held densitometers or hand-held spectrophotometers, additional personnel would have to be employed in view of the large number of measuring fields and the time required for manual measuring device positioning, especially for the purpose of quality data acquisition. A systematically carried out quality data acquisition cannot prevail in newspaper offset print run, as long as it is associated with high investment costs or large additional personnel requirements.

The method described in EP 0 196 431 B1 has a further disadvantageous property in that features which have no direct relation to the color appearance of the printed product are measured with the solid and screen density of the individual colors. This deficiency can be countered by the fact that so-called combination measuring fields, i.e. Measuring fields in which the primary colors involved in the printing are printed on one another in a raster tone, provided and measured colorimetrically.

Colorimetric measurement values obtained in this way can refer to the XYZ color space, which is based on the sensitivity function of the average human eye, or to the color spaces CIELUV or CIELAB derived from the XYZ system, all of which have been standardized by the CIE (Commission Internationale de l'Eclairage) .

The colorimetric measurement on combination measuring fields has the advantage that it enables a statement about the interaction of all colors involved in a multicolor printing. The colorimetric measurement values directly say something about how the combination measuring field or the printed product appears in color to the human viewer. Another advantage is that the combination measuring fields can be replaced by image locations with a suitable image structure, if necessary. In contrast to densitometric methods, the disadvantage of colorimetric measurement methods is that they do not provide direct information about the process control. A deviation in the color location, for example, does not allow any conclusions to be drawn about how the ink guide on the printing press has to be corrected in order to reduce the deviation.

Methods have been developed by means of which deviations in the color location can be converted into variations in the layer thicknesses or the densities of the individual colors involved in the printing. For example, EP 0 321 402 A1 and EP 0 408 507 A1 describe linear transformations for converting variations in full tone or screen density into variations in the color location of combination measuring fields in the CIELUV or CIELAB color spaces.

These transformations make it possible, for example, to calculate, from a deviation of the color location from a combination measuring field on a sample sheet, the change in the solid density of individual color measuring fields, which is necessary to compensate for the deviation of the color location in the combination measuring field. The strategy pursued is therefore to correct undesirable deviations in the color location of combination measuring fields exclusively by suitable changes in the ink layer thicknesses of the colors involved in the printing process.

The limitation to changes in the color layer thicknesses in EP 0 408 507 A1 appears somewhat arbitrary. Basically, the correction of color location deviations can also be achieved by a suitable change in the area coverage of the individual printing inks. This can be done, for example, in digital prepress when the color separations are calculated. This possibility is particularly interesting if the color location deviations observed for a specific combination measuring field are to a large extent systematic, ie not exclusively random. Another advantage is that a change in the area coverage of the printing inks is often easier to master when calculating the color separations than a change in the ink layer thicknesses carried out on the printing press. The idea of taking individual printing characteristics of individual inking units into account when calculating the color separations is already known from DE 42 09 165 A1. However, there is no reference to colorimetric measurement values at combination measuring fields or image points.

• Die notwendige Anzahl der Messfelder sollte reduziert werden, damit die Messfelder im Satzspiegel der Zeitung weniger Platz beanspruchen.
• Der gerätemässige und personelle Aufwand zum Ausmessen der Messfelder soll verkleinert werden.
• Die Verfahren sollten in Zukunft auf einer statistischen Kontrolle aufbauen. Messfelder werden dann nur in wenigen repräsentativen Farbzonen mitgedruckt und die Ergebnisse auf den gesamten Druckprozess extrapoliert. Dies kommt beiden vorhin aufgeführten Forderungen entgegen.
• Das Messen an Bildstellen mit einem geeigneten Bildaufbau soll das Mitdrucken und Ausmessen von speziellen Messfeldern so weit wie möglich unnötig machen.
• Aus derselben Messung sollten sowohl farbmetrische als auch densitometrische Messwerte resultieren. Dadurch kann gleichzeitig eine Aussage über die farbliche Erscheinung des Druckerzeugnisses und über die Möglichkeiten zu ihrer Korrektur sowohl in der Druckvorstufe wie an der Druckmaschine abgeleitet werden.

From what has been said so far, it can be concluded that the methods for quality data acquisition and process optimization known today and primarily intended for commercial offset print run cannot be transferred unchanged to newspaper offset print run. This explains why it is still common practice in newspaper offset today to monitor and control the coloring through the trained but subjective eye of the printer. For use in newspaper offset production, it is desirable to improve the objective processes discussed above, in particular in the following respects:

• The necessary number of measuring fields should be reduced so that the measuring fields in the type area of the newspaper take up less space.
• The device-related and personnel expenditure for measuring the measuring fields should be reduced.
• In the future, the procedures should be based on statistical control. Measuring fields are then only printed in a few representative color zones and the results are extrapolated to the entire printing process. This complies with both of the above requirements.
• Measuring at image points with a suitable image structure should make the printing and measuring of special measuring fields as unnecessary as possible.
• Both colorimetric and densitometric measurements should result from the same measurement. As a result, a statement about the color appearance of the printed product and about the possibilities for its correction can be derived both in the prepress stage and on the printing press.

The object of the invention is to provide measuring fields for recording color data of a printed product which are suitable for color management in web offset production and whose use in color management in particular enables a method which satisfies individual, several and preferably all of the requirements set out above . The method and the measuring fields developed for this purpose, or the measuring field group or arrangement, should also be usable in newspaper offset print runs.

This object is achieved by a measuring field group according to claim 1 and a method according to claims 2 or 3. The subclaims represent expedient, not completely self-evident designs. The solution is characterized by the special requirements of newspaper printing, but this does not in any way preclude a useful application in other areas, such as web offset printing.

• Die farbliche Erscheinung einer im mehrfarbigen Übereinanderdruck bedruckten Fläche ist bei gegebenem Papier und Farbmaterial durch das Zusammenwirken der Farbschichtdicke und des effektiven Flächendeckungsgrades aller übereinanderliegenden Druckfarben bestimmt.
• Durch farbmetrische Messung an einem Kombinationsmessfeld, d.h. an einem Messfeld, in welchem mehrere Faden in Raster- oder Volltönen übereinandergedruckt sind, wird die kombinierte Wirkung der beteiligten Druckfarben durch eine einzige optische Antastung erfasst.
• Der Beitrag der einzelnen Farbe kann am besten durch ihre Schichtdicke und die Rasterpunktgrösse charakterisiert werden. Das densitometrische Äquivalent dazu sind die Volltondichte und der effektive Flächendeckungsgrad im Druck. Diese zwei Kenngrössen werden in Herkömmlichen Prüfverfahren pro beteiligte Druckfarbe durch Dichtemessung je an einem einfarbigen Kontrollfeld im Voll-und Rasterton gemessen. Die Berechnung des Flächendeckungsgrades aus Voll-und Rastertondichte geschieht üblicherweise nach der allgemeinbekannten Formel von Murray-Davies.
• Basiert die Qualitätsdatenerfassung im Offset-Auflagendruck ausschliesslich auf densitometrischen Messungen, so müssen pro Druckfarbe also mindestens zwei einfarbige Messfelder mitgedruckt werden. Diese Messfelder sind einzeln einer Dichtemessung zu unterziehen. Will man zusätzlich auch noch über das Zusammenwirken der Farbschichten Auskunft bekommen, so sind zur Bestimmung der Farbannahme zusätzliche densitometrische Messungen an weiteren zwei- und dreifarbigen Kombinationsmessfeldern notwendig. Im dreifarbigen Übereinanderdruck ergibt dies beispielsweise mindestens zehn optische Antastungen.
• Eine Verkleinerung des Aufwandes ergibt sich, wenn anstelle der Volltondichte und des Flächendeckungsgrades einer Farbe ihre Rastertondichte betrachtet wird. Die Rastertondichte gibt die kombinierte Wirkung der beiden anderen Einflussgrössen wieder. Allerdings ist dann eine differenzierte Betrachtung nach den Ursachen von Variationen schwieriger.
• Zwischen den an einem Kombinationsmessfeld ermittelten farbmetrischen Werten auf der einen Seite sowie den densitometrischen Kennwerten Volltondichte und Flächendeckungsgrad der Einzelfarben auf der anderen Seite besteht ein gesetzmässiger Zusammenhang. Dieser Zusammenhang ist generell kompliziert. Er lässt sich jedoch vereinfachen, wenn nur Variationen der interessierenden Grössen um einen bestimmten Arbeitspunkt betrachtet werden, was in der Druckereipraxis in Anbetracht der einschlägigen Standardisierungsanstrengungen meistens genügt.

The method according to the invention is based on the following considerations:

• The color appearance of a surface printed in multicolored overprint is determined for a given paper and color material by the interaction of the ink layer thickness and the effective area coverage of all superimposed printing inks.
• By colorimetric measurement on a combination measuring field, ie on a measuring field in which several threads are printed one above the other in halftone or full tones, the combined effect of the printing inks involved is recorded by a single optical probe.
• The contribution of the individual color can best be characterized by its layer thickness and the dot size. The densitometric equivalent to this is the solid color density and the effective area coverage in the print. These two parameters are measured in conventional test methods for each printing ink involved by density measurement on a single-color control field in full tone and screen tone. The calculation of the area coverage from full and grid density is usually done according to the well-known Murray-Davies formula.
• If the quality data acquisition in offset production is based exclusively on densitometric measurements, at least two monochrome measuring fields must be printed with each printing ink. These measuring fields are to be individually subjected to a density measurement. If you also want to get information about the interaction of the color layers, additional densitometric measurements on further two and three-color combination measuring fields are necessary to determine the color acceptance. In three-color overprinting, this results in at least ten optical probes, for example.
• The effort is reduced if instead of the solid color density and the area coverage of a color its grid density is considered. The grid density reflects the combined effect of the two other influencing variables. However, it is then more difficult to differentiate between the causes of variations.
• Between the colorimetric values determined on a combination measuring field Values on the one hand and the densitometric parameters of solid color density and area coverage of the individual colors on the other hand are legally related. This relationship is generally complicated. However, it can be simplified if only variations of the sizes of interest around a certain working point are considered, which is usually sufficient in printing practice in view of the relevant standardization efforts.

• Der systematische Zusammenhang zwischen den Variationen von farbmetrischen Kennwerten an Kombinationsmessfeldern und Variationen von Volltondichte und Flächendeckungsgrad der Einzelfarben wird an Eichdrucken für gegebenes Papier, Farbmaterial, eine bestimmte Druckmaschine und einen Arbeitspunkt empirisch bestimmt. Der Arbeitspunkt charakterisiert sich zweckmässigerweise durch die nominellen Flächendeckungsgrade der Einzelfärben im Kombinationsmessfeld, d.h. die Flächendeckungsgrade, welche das Kombinationsmessfeld auf den Filmvorlagen oder den Druckplatten aufweist.
• Das Ergebnis der Auswertung der Eichdrucke bildet somit pro Arbeitspunkt eine Transformationsfunktion, welche Variationen der Volltondichte in den Einzelfarbenvolltonfeldern und Variationen der effektiven Flächendeckungsgrade in den Einzelfarbenrasterfeldern in Variationen des Farbortsvektors des Kombinationsmessfeldes umrechnet.
• Ein Nebenergebnis der Auswertung der Eichdrucke ist eine Zerlegung der Variationen des Farbortsvektors nach den sie erzeugenden Ursachen, d.h. nach den Variationen der Volltondichte in den Einzelfarbenvolltonfeldern und den Variationen der effektiven Flächendeckungsgrade in den Einzelfarbenrasterfeldern. Aus dieser Zerlegung kann weiter das statistische Verhältnis der ursachenbezogenen Beiträge der Variationen des Farbortsvektors abgeleitet werden.
• Auf dem hinsichtlich seiner farblichen Erscheinung zu kontrollierenden und zu optimierenden Druckerzeugnis wird sodann lediglich das Kombinationsmessfeld mitgedruckt und farbmetrisch ausgemessen. Aus diesem gemessenen Ist-Farbort wird durch Subtraktion eines vorgegebenen Soll-Farbortes die Farborts-Abweichung oder Farborts-Variation berechnet.
• Die Farborts-Variation am Druckerzeugnis wird nun einerseits durch eine Verstellung der Farbführungsstellglieder an der Druckmaschine und andererseits durch eine Veränderung der Flächendeckungsgrade beim Herstellen der Farbauszüge kompensiert. Die Verstellung der Farbführungsstellglieder eignet sich dabei vorzugsweise zur Kompensation der zufälligen Anteile der Farborts-Variation, während sich die Veränderung der Flächendeckungsgrade beim Herstellen der Farbauszüge ausschliesslich zur Kompensation der systematischen, d.h. über mehrere Druckaufträge unveränderlichen, Anteile der Farborts-Variation anbietet.

The following procedure is suggested:

• The systematic relationship between the variations in colorimetric parameters on combination measuring fields and variations in solid color density and area coverage of the individual colors is empirically determined on calibration prints for given paper, ink material, a specific printing machine and a working point. The operating point is expediently characterized by the nominal areas of coverage of the individual colors in the combination measurement field, ie the areas of coverage which the combination measurement area has on the film templates or the printing plates.
• The result of the evaluation of the calibration prints therefore forms a transformation function for each working point, which converts variations of the solid color density in the single-color full-tone fields and variations of the effective area coverage in the single-color grid fields into variations of the color locus vector of the combination measuring field.
• A by-product of the evaluation of the calibration prints is a decomposition of the variations of the color locus vector according to the causes that generated it, ie according to the variations of the solid color density in the single color solid tone fields and the variations of the effective area coverage in the single color halftone fields. The statistical relationship of the cause-related contributions of the variations in the color locus vector can also be derived from this decomposition.
• On the printed product to be checked and optimized with regard to its color appearance, only the combination measuring field is then also printed and measured colorimetrically. From this measured actual color location, the color location deviation or color location variation is calculated by subtracting a predetermined target color location.
• The color location variation on the printed product is now compensated on the one hand by adjusting the ink guide actuators on the printing press and on the other hand by changing the area coverage when producing the color separations. The adjustment of the ink guide actuators is preferably suitable for compensating for the random proportions of the color location variation, while the change in the area coverage when producing the color separations is only suitable for compensating for the systematic portions of the color location variation, ie unchangeable over several print jobs.

For color management, measuring fields and / or image points serving as measuring fields are also printed and optically scanned after printing. The returned light is evaluated.

According to the invention, the printed product to be checked and a number of calibration prints produced with specifically different ink layer thicknesses each have a first combination measuring field, in which the basic colors, usually the three colors cyan, magenta and yellow, are overprinted with the nominal area coverage (F _c1 , F _m1 , F _g1 ) are.

, F_m1, F_g1), (F_c1, ${\text{F}}_{\text{m3}}{\text{= F}}_{\text{m1}}{\text{+ΔF}}_{\text{m3}}$

, F_g1), (F_c1, F_m1, ${\text{F}}_{\text{g4}}{\text{= F}}_{\text{g1}}{\text{+ΔF}}_{\text{g4}}$

) übereinandergedruckt sind. In jedem dieser zusätzlichen Kombinationsmessfelder ist jeweils zumindest eine andere Grundfarbe variiert, beispielsweise die erste Grundfarbe um den Wert ΔF_c2 im zweiten, die zweite Grundfarbe um den Wert ΔF_m3 im dritten und die dritte Grundfarbe um den Wert ΔF_g4 im vierten Feld. Die Anzahl der zusätzlichen Kombinationsmessfelder und die Anzahl der Farben pro Kombinationsmessfeld entspricht bevorzugterweise der Anzahl der Grundfarben.The calibration prints also have combination measuring fields in which the basic colors with the nominal area coverage ( ${\text{F}}_{\text{c2}}{\text{= F}}_{\text{c1}}{\text{+ ΔF}}_{\text{c2}}$

, F _m1 , F _g1 ), (F _c1 , ${\text{F}}_{\text{m3}}{\text{= F}}_{\text{m1}}{\text{+ ΔF}}_{\text{m3}}$

, F _g1 ), (F _c1 , F _m1 , ${\text{F}}_{\text{g4}}{\text{= F}}_{\text{g1}}{\text{+ ΔF}}_{\text{g4}}$

) are printed on top of each other. In each of these additional combination measuring fields, at least one other primary color is varied, for example the first primary color by the value ΔF _c2 in the second, the second primary color by the value ΔF _m3 in the third and the third primary color by the value ΔF _g4 in the fourth field. The number of additional combination measuring fields and the number of colors per combination measuring field preferably corresponds to the number of basic colors.

The calibration prints additionally have at least one individual color grid in the basic colors for each basic color, which in its respective color has an area coverage that corresponds to that of the same color in the first combination measuring field. They preferably additionally have at least one different individual color grid for each primary color. The area coverage of the other single-color grid corresponds to the varied area coverage of the corresponding additional combination measurement area. In the above nomenclature, the individual color grid fields in the preferred embodiment thus have the areas of coverage F _c1 , F _c2 , F _m1 , F _m3 , F _g1 and F _g4 .

Furthermore, the calibration prints additionally contain at least one each Single-color full-tone field per basic color; preferably exactly one per basic color.

The calibration print or prints can be printed separately or also in the printed product. The measuring fields form a measuring field group, which is preferably arranged in the form of a measuring field block.

Advantageously, the color locus vectors R ₁ , R ₂ , R ₃ and R _{4 can be determined} in a selected colorimetric coordinate system on these calibration prints by measurement with a color measuring device on the combination measuring fields. In the individual _{color raster fields} , the effective area coverage in the pressure F _ec1 , F _ec2 , F _em1 , F _em3 , F _eg1 , F _eg4 and likewise in the single color full tone fields by densitometric measurement with a filter characteristic corresponding to the individual field can also be determined by densitometric or other measurements _Vc1 , D _Vm1 , D _Vg1 can be determined.

The color locus vectors, the solid color densities and the effective area coverage of the calibration prints are used according to the invention to determine two transformation functions A and B, which are a variation ΔD _{V1 of} the solid color in the individual color solid tone fields caused by a change in the color layer thicknesses or a variation ΔF _{e1 of} the effective area coverage in the individual areas Convert single color grid fields with the nominal area coverage F _c1 , F _m1 and F _g1 into variations of the color locus vector of the first combination measuring field with the nominal area coverage (F _c1 , F _m1 , F _g1 ).

In the method according to the invention, the color locus vector in the selected coordinate system is repeatedly determined on the printed product to be checked by measurement with a color measuring device on the first combination measuring field, and for that one predefined target color locus vector-related deviation of the color locus vector ΔR ₁₁ determined on the printed product, a combination of a variation ΔD _{V11 of} the solid color in existing or imagined single color solid color fields caused by changing the ink layer thicknesses and a variation ΔF _{e11 of} the effective area coverage in existing or imaginary single color _{grid area fields} with the nominal nominal area independent of this calculated.

According to the invention, the deviation ΔR _{11 of} the color locus vector corresponds exactly to the combined effect of the variations ΔD _V11 and ΔF _e11 via the transformation functions A and B.

The invention is further characterized in that the deviation of the color locus vector ΔR ₁₁ on the printed product is corrected in the sense that on the one hand the calculated variation ΔD _{V11 of} the solid ink densities by adjusting the ink guide actuators on the printing press and on the other hand the calculated variation ΔF _{e11 of} the effective area coverage a change in the area coverage when the color separations are made to disappear; further in that the

bzw. $\underline{{\text{ΔR}}_{\text{11}}}\text{=}\underline{\underline{\text{A}}}\underline{{\text{ΔD}}_{\text{V11}}}\text{+}\underline{\underline{\text{B}}}\underline{{\text{ΔF}}_{\text{e11}}}$

gilt.Transformation functions A and B are linear, ie are characterized by two 3x3 matrices A and B and that the relationship $\underset{}{{\text{ΔR}}_{}}$$\underline{{}_{\text{1}}}\text{=}\underline{\underline{\text{A}}}\underline{{\text{ΔD}}_{\text{V1}}}\text{+}\underline{\underline{\text{B}}}\underline{{\text{ΔF}}_{\text{e1}}}$

respectively. $\underline{{\text{<figure-callout id="11" label="ΔR" filenames="imgf0001.png" state="{{state}}">ΔR</figure-callout>}}_{\text{11}}}\text{=}\underline{\underline{\text{A}}}\underline{{\text{ΔD}}_{\text{V11}}}\text{+}\underline{\underline{\text{B}}}\underline{{\text{ΔF}}_{\text{e11}}}$

applies.

gilt wobei A ΔD _V11 dem zufälligen Anteil von ΔR ₁₁ entspricht und B ΔF _e11 den systematischen, d.h. über mehrere aufeinanderfolgende Druckaufträge konstanten Anteil von ΔR ₁₁ repräsentiert.Furthermore, it is advantageous that for a deviation ΔR ₁₁ of the color locus vector determined on the printed product, a combination of a variation ΔD _{V11 of} the solid densities caused by changing the ink layer thicknesses and a variation ΔF _{e11 of} the area coverage _levels independent of this is calculated in such a way that $\underline{{\text{ΔR}}_{\text{11}}}\text{=}\underline{\underline{\text{A}}}\underline{{\text{ΔD}}_{\text{V11}}}\text{+}\underline{\underline{\text{B}}}\underline{{\text{ΔF}}_{\text{e11}}}$

applies where A ΔD _V11 corresponds to the random part of ΔR ₁₁ and B ΔF _{e11 represents} the systematic part of ΔR ₁₁ , ie constant part of ΔR ₁₁ over several successive print jobs.

It is also advantageous that for a deviation ΔR ₁₁ of the color locus vector determined on the printed product, a variation ΔD _{V11 of} the solid densities caused by a change in the ink layer thicknesses is calculated, the variation ΔR ₁₁ corresponding exactly to the effect of the variation ΔD _V11 via the transformation function A and that the deviation of the color locus vector ΔR ₁₁ on the printed product is corrected in the sense that the calculated variation ΔD _{V11 of} the solid densities is made to disappear by adjusting the ink guide actuators on the printing press.

Finally, it is also advantageous that for a deviation ΔR ₁₁ of the color locus _vector determined on the printed product, a variation ΔF _{e11 of} the effective area coverage in existing or imagined individual color grid _fields with the nominal area coverage degrees F _c1 , F _m1 , and F _{g1 is} calculated, independent of changes in the ink layer thicknesses , wherein the variation ΔR ₁₁ corresponds exactly to the effect of the variation ΔF _e11 via the transformation function B alone and that
the deviation of the color location vector ΔR ₁₁ on the printed product is corrected in the sense that the calculated variation ΔF _{e11 of} the effective area coverage is compensated for as a result of a change in the area coverage independent of variations in the ink layer _thickness when producing the color separations.

The invention can be used with advantage in web offset printing.

A measuring field group for recording color data of a printed product, in particular for color management in web offset production printing, has a plurality of measuring fields, which can be optically scanned on a printed product to be checked or on Calibration print are printed.

According to the invention, this measurement field group includes a first combination measurement field in which the basic colors with their nominal area coverage are printed one on top of the other, additional combination measurement fields in which the basic colors are printed with different nominal area coverage, each basic color being varied at least once in every additional combination measurement field, Furthermore, additional single-color grids in the primary colors, the first single-color grids in their respective primary colors having an area coverage that corresponds to that of the same color in the first combination measurement area. Preferably, second individual color grid fields are provided, which have an area coverage in their respective primary color that corresponds to the varied area coverage of the same color in the additional combination measurement areas and finally additionally at least one individual color solid field for each primary color.

The functioning of the method according to the invention will now be explained with reference to FIG. 1.

• In einem ersten dreifarbigen Kombinationsmessfeld 1 sind die Grundfarben Cyan, Magenta und Gelb mit den nominellen Flächendeckungsgraden (F_c1, F_m1, F_g1) übereinandergedruckt. In drei weiteren Kombinationsmessfeldern 2, 3 und 4 sind ebenfalls die Grundfarben Cyan, Magenta und Gelb übereinander gedruckt und zwar mit den nominellen Flächendeckungsgraden ( ${\text{F}}_{\text{c2}}{\text{=F}}_{\text{c1}}{\text{+ΔF}}_{\text{c2}}$
  
  , F_m1, F_g1), (F_c1, ${\text{F}}_{\text{m3}}{\text{=F}}_{\text{m1}}{\text{+ΔF}}_{\text{m2}}$
  
  , F_g1) und (F_c1, F_m1, ${\text{F}}_{\text{g4}}{\text{=F}}_{\text{g1}}{\text{+ΔF}}_{\text{g4}}$
  
  ). Bezogen auf Kombinationsmessfeld 1 ist also in jedem der Kombinationsmessfelder 2, 3 und 4 der nominelle Flächendeckungsgrad genau einer Grundfarbe variiert, d.h. in Kombinationsmessfeld 2 derjenige von Cyan um ΔF_c2, in Kombinationsmessfeld 3 derjenige von Magenta um ΔF_m3 und in Kombinationsmessfeld 4 derjenige von Gelb um ΔF_g4. ΔF_c2, ΔF_m3 und ΔF_g4 dürfen dabei sowohl positives wie negatives Vorzeichen aufweisen.
• Drei weitere Einzelfarbenfelder 5, 6 und 7 enthalten die Volltöne von Cyan, Magente und Gelb.
• Sechs Einzelfarbenfelder sind mit Rastertönen bedruckt, und zwar Feld 8 und 11 in Cyan mit den nominellen Flächendeckungsgraden F_c1 und F_c2, Feld 9 und 12 in Magenta mit den nominellen Flächendeckungsgraden F_m1 und F_m3 sowie Feld 10 und 13 in Gelb mit den nominellen Flächendeckungsgraden F_g1 und F_g4.

A calibration print 20 contains a measuring field block consisting of 13 measuring fields:

• In a first three-color combination measuring field 1, the basic colors cyan, magenta and yellow are printed with the nominal area coverage (F _c1 , F _m1 , F _g1 ). In three further combination measuring fields 2, 3 and 4, the basic colors cyan, magenta and yellow are also printed on top of each other, with the nominal area coverage ( ${\text{F}}_{\text{c2}}{\text{= F}}_{\text{c1}}{\text{+ ΔF}}_{\text{c2}}$
  
  , F _m1 , F _g1 ), (F _c1 , ${\text{F}}_{\text{m3}}{\text{= F}}_{\text{m1}}{\text{+ ΔF}}_{\text{m2}}$
  
  , F _g1 ) and (F _c1 , F _m1 , ${\text{F}}_{\text{g4}}{\text{= F}}_{\text{g1}}{\text{+ ΔF}}_{\text{g4}}$
  
  ). In relation to combination measuring field 1, the nominal area coverage of exactly one basic color is varied in each of combination measuring fields 2, 3 and 4, i.e. in combination measuring field 2 that of cyan by ΔF _c2 , in combination measuring field 3 that of magenta by ΔF _m3 and in combination measuring field 4 that of yellow by ΔF _g4 . ΔF _c2 , ΔF _m3 and ΔF _g4 may have both positive and negative signs.
• Three further single color fields 5, 6 and 7 contain the full tones of cyan, magente and yellow.
• Six single-color fields are printed with halftone tones, namely fields 8 and 11 in cyan with the nominal area coverage levels F _c1 and F _c2 , fields 9 and 12 in magenta with the nominal area coverage levels F _m1 and F _m3 as well as field 10 and 13 in yellow with the nominal areas Area coverage F _g1 and F _g4 .

The printed product 30 to be checked and optimized in the edition contains at least the combination measuring field 1 of the measuring fields described, in which the basic colors cyan, magenta and yellow with the nominal area coverage (F _c1 , F _m1 , F _g1 ) are _overprinted . In principle, an image point with an identical image structure can also serve as a combination measuring field.

The calibration print 20 is used in particular with regard to the color material, the color layer thickness and the dot gain, i.e. the enlargement of the area coverage from the film template or the printing plate to the print, printed under standardized conditions. These conditions were set for the print run, for example by UGRA in Switzerland or FOGRA in Germany. It does not matter for the principle of operation whether the method according to the invention is used in newspaper or commercial web offset. The only essential is the requirement that the calibration print 20 according to the same standard as the edition, i.e. the printed product to be checked and optimized is produced.

Further calibration prints 21, 22 and 23 also contain a measuring field block. With regard to the arrangement of the measuring fields and their image structure, the measuring field blocks of the calibration prints 20 to 23 are identical. The calibration prints 21, 22 and 23 are produced in a way that deviates from the applicable printing standard in that the color layer thickness of exactly one of the basic colors cyan, magenta and yellow is varied for each calibration print compared to the calibration print 20. On the calibration print 21 the color layer thickness differs from cyan, that of magenta on the calibration print and that of yellow on the calibration print 23. In principle, the deviations can go in the positive or negative direction.

A further condition must be observed when producing the calibration prints 20 to 23. In addition to the measuring field blocks, the calibration prints must also have other areas printed with all primary colors, so that sufficient color acceptance is guaranteed at the location of the measuring field block in the paper running direction. The design of these areas is free. Analogous considerations apply with regard to the ink acceptance for the printed product 30.

• die mit Änderungen der Farbschichtdicken verbundenen Variationen der Volltondichte von Cyan, Magenta und Gelb sowie
• die von Änderungen der Farbschichtdicken unabhängigen Variationen der effektiven Flächendeckungsgrade von Cyan, Magenta und Gelb im Druck.

With the help of calibration prints 20 to 23, the two most important influences on the color appearance of the combination measuring field 1 can now be determined quantitatively. They are

• the variations in solid ink density of cyan, magenta and yellow associated with changes in the color layer thicknesses as well
• the variations of the effective area coverage of cyan, magenta and yellow in the print independent of changes in the ink layer thickness.

The influence of the ink layer thickness is expressed in the differences between colorimetric and densitometric measurement values between the different calibration prints. The influence of the variations in the degree of surface coverage, which are independent of changes in the ink layer thicknesses, however, is noticeable in the differences in the measured values between the different measuring fields on one and the same calibration print.

• eine erste Transformationsfunktion A, welche eine durch Änderung der Farbschichtdicken bedingte Variation der Volltondichten in die dadurch resultierende Variation des Farbortes des Kombinationsmessfeldes umrechnet sowie
• eine zweite Transformationsfunktion B, welche eine von Änderungen der Farbschichtdicken unabhängige Variation der effektiven Flächendeckungsgrade in die dadurch resultierende Variation des Farbortes des Kombinationsmessfeldes abbildet.

When determining the dependence of the color appearance of the combination measuring field 1 on the solid color densities and the area coverage of the primary colors, it is a matter of determining two transformation functions, namely:

• a first transformation function A, which converts a variation in the solid densities caused by changing the ink layer thicknesses into the resulting variation in the color location of the combination measuring field and
• a second transformation function B, which maps a variation of the effective area coverage independent of changes in the ink layer thicknesses into the resulting variation in the color location of the combination measuring field.

In general, the transformation functions A and B are non-linear. Since we usually deal with relatively small variations around a standardized operating point in printing practice, it is permissible to linearize the relationships. In the interest of clarity, the method according to the invention is explained below using a linearized model. This does the generalizing wording in the claims to linear and non-linear systems does not break.

• Es wird ein farbmetrisches Koordinatensystem, vorzugsweise XYZ, für die farbmetrischen Messungen festgelegt. Prinzipiell sind auch CIELAB oder CIELUV möglich. Wichtig ist, dass für die Angabe aller farbmetrischen Messwerte immer dasselbe System benutzt wird. Der Einfachheit halber basieren die weiteren Ausführungen beispielhaft auf Normfarbwerten XYZ.
• An den Kombinationsmessfeldern 1 bis 4 von Eichdruck 20 werden die Normfarbwerte XYZ gemessen. Es resultieren vier Farbortsvektoren $$\underline{\text{R}}\text{=}\left[\begin{array}{c}\text{X}\\ \text{Y}\\ \text{Z}\end{array}\right]$$
  
  und zwar R ₁ für Messfeld 1, R ₂ für Messfeld 2, R ₃ für Messfeld 3 und R ₄ für Messfeld 4.
• An den Einzelfarbenfeldern 5 bis 13 von Eichdruck 20 werden Farbdichten gemessen und mithilfe der allgemein bekannten Gleichung von Murray-Davies die effektiven Flächendeckungsgrade in den Messfeldern 8 bis 13 berechnet. Es resultieren dabei drei Volltondichtewerte, und zwar D_Vc1 für Messfeld 5, D_Vm1 für Messfeld 6 und D_Vg1 für Messfeld 7. Weiter ergeben sich sechs Werte für den effektiven Flächendeckungsgrad im Druck, und zwar F_ec1 für Messfeld 8, F_ec2 für Messfeld 11, F_em1 für Messfeld 9, F_em2 für Messfeld 12, F_eg1 für Messfeld 10 und F_eg4 für Messfeld 13.
• Am Kombinationsmessfeld 1 der Eichdrucke 21 bis 23 werden die Normfarbwerte XYZ gemessen. Es resultieren drei Farbortsvektoren $$\underline{\text{R}}\text{=}\left[\begin{array}{c}\text{X}\\ \text{Y}\\ \text{Z}\end{array}\right]$$
  
  und zwar R ₂₁ für Eichdruck 21, R ₂₂ für Eichdruck 22 und R ₂₃ für Eichdruck 23.
• Am Einzelfarbenfeld 5 des Eichdrucks 21 wird die Volltondichte für Cyan gemessen. Es resultiert der Wert D_Vc2.
• Am Einzelfarbenfeld 6 des Eichdrucks 22 wird die Volltondichte für Magenta gemessen. Es resultiert der Wert D_Vm3.
• Am Einzelfarbenfeld 7 des Eichdrucks 23 wird die Volltondichte für Gelb gemessen. Es resultiert der Wert D_Vg4.
• Mit den Definitionen $$\underline{\underline{{\text{ΔR}}_{\text{Dv}}}}\text{:=[}\underline{{\text{<figure-callout id="21" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{21}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\underline{{\text{R}}_{\text{22}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\underline{{\text{R}}_{\text{23}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\text{],}$$
  
  
  $$\underline{\underline{{\text{ΔR}}_{\text{Fe}}}}\text{:=[}\underline{{\text{R}}_{\text{2}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\underline{{\text{R}}_{\text{3}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\underline{{\text{R}}_{\text{4}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\text{] und}$$
  
  
  lassen sich die linearisierten Zusammenhänge zwischen den gemessenen Grössen durch die folgenden zwei Gleichungen darstellen: $$\underline{\underline{{\text{ΔR}}_{\text{Dv}}}}\text{=}\underline{\underline{{\text{AΔD}}_{\text{v}}}}\underline{\underline{{\text{ΔR}}_{\text{Fe}}}}\text{=}\underline{\underline{{\text{BΔF}}_{\text{a}}}}$$
  
• Hier stehen die beiden 3x3-Matrizen A und B für die gesuchten Transformationsfunktionen A und B. Um zu den Transformationsfunktionen zu gelangen, müssen wir also die beiden letzten Gleichungen nur noch nach A und B auflösen: $$\underline{\underline{\text{A}}}\text{=}\underline{\underline{{\text{ΔR}}_{\text{Dv}}{\text{ΔD}}_{\text{v}}{}^{\text{-1}}}}\underline{\underline{\text{B}}}\text{=}\underline{\underline{{\text{ΔR}}_{\text{Fe}}{\text{ΔF}}_{\text{e}}{}^{\text{-1}}}}$$
  

The following procedure is suitable for determining the transformation functions A and B:

• A colorimetric coordinate system, preferably XYZ, is defined for the colorimetric measurements. In principle, CIELAB or CIELUV are also possible. It is important that the same system is used for all colorimetric measurements. For the sake of simplicity, the further explanations are based, for example, on standard color values XYZ.
• The standard color values XYZ are measured on the combination measuring fields 1 to 4 of calibration print 20. Four color locus vectors result $$\underline{\text{R}}\text{=}\left[\begin{array}{c}\text{X}\\ \text{Y}\\ \text{Z.}\end{array}\right]$$
  
  namely R ₁ for measuring field 1, R ₂ for measuring field 2, R ₃ for measuring field 3 and R ₄ for measuring field 4.
• Color densities are measured on the individual color fields 5 to 13 of calibration print 20 and the effective area coverage in the measuring fields 8 to 13 is calculated using the generally known Murray-Davies equation. This results in three full-tone density _values , namely D _Vc1 for measuring field 5, D _Vm1 for measuring field 6 and D _Vg1 for measuring field 7. There are also six values for the effective area coverage in the print, namely F _ec1 for measuring field 8, F _ec2 for measuring field 11, F _em1 for measuring field 9, F _em2 for measuring field 12, F _eg1 for measuring field 10 and F _eg4 for measuring field 13.
• The standard color values XYZ are measured on the combination measuring field 1 of the calibration prints 21 to 23. The result is three color locus vectors $$\underline{\text{R}}\text{=}\left[\begin{array}{c}\text{X}\\ \text{Y}\\ \text{Z.}\end{array}\right]$$
  
  namely R ₂₁ for calibration pressure 21, R ₂₂ for calibration pressure 22 and R ₂₃ for calibration pressure 23.
• The solid color density for cyan is measured on the individual color field 5 of the calibration print 21. The result is D _Vc2 .
• The solid color density for magenta is measured on the individual color field 6 of the calibration print 22. The result is D _Vm3 .
• The solid color density for yellow is measured on the individual color field 7 of the calibration print 23. The result is D _Vg4 .
• With the definitions $$\underline{\underline{{\text{ΔR}}_{\text{Dv}}}}\text{: = [}\underline{{\text{<figure-callout id="21" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{21}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\underline{{\text{R}}_{\text{22}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\underline{{\text{R}}_{\text{23}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\text{],}$$
  
  
  $$\underline{\underline{{\text{ΔR}}_{\text{Fe}}}}\text{: = [}\underline{{\text{R}}_{\text{2nd}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\underline{{\text{R}}_{\text{3rd}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\underline{{\text{R}}_{\text{4th}}}\text{-}\underline{{\text{<figure-callout id="1" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{1}}}\text{] and}$$
  
  
  the linearized relationships between the measured quantities can be represented by the following two equations: $$\underline{\underline{{\text{ΔR}}_{\text{Dv}}}}\text{=}\underline{\underline{{\text{AΔD}}_{\text{v}}}}\underline{\underline{{\text{ΔR}}_{\text{Fe}}}}\text{=}\underline{\underline{{\text{BΔF}}_{\text{a}}}}$$
  
• Here the two 3x3 matrices A and B stand for the transformation functions A and B we are looking for. To get to the transformation functions, we only have to solve the last two equations for A and B : $$\underline{\underline{\text{A}}}\text{=}\underline{\underline{{\text{ΔR}}_{\text{Dv}}{\text{ΔD}}_{\text{v}}{}^{\text{-1}}}}\underline{\underline{\text{B}}}\text{=}\underline{\underline{{\text{ΔR}}_{\text{Fe}}{\text{ΔF}}_{\text{e}}{}^{\text{-1}}}}$$
  

By evaluating the calibration prints 20 to 23, we now have the quantitative relationship between variations in the solid density of the primary colors, which are caused by changes in the ink layer thicknesses, and variations in the area coverage of the primary colors, which are independent of changes in the ink layer thicknesses, on the one hand, and variations in the color locus vector in the Combination measuring field 1 determined.

According to the method just described, the matrix B is calculated on the basis of the matrices ΔR _Fe and ΔF _e . ΔR _Fe and ΔF _e are defined by measured values that originate from calibration pressure 20 alone. This means that the matrix B can be determined completely on the basis of a single calibration pressure. In an extension of the method, it would be possible to determine a separate matrix B for several calibration prints and then to average the B over all B's . This measure could reduce the influence of random measurement errors.

The transformation functions obtained from the calibration prints can now be used to advantage if the quality of production prints is to be monitored and optimized. The prerequisite for this is that the combination measuring field 1 is also printed in the printed product with the same nominal area coverage for cyan, magenta and yellow.

. Der Soll-Farbortsvektor kann sowohl ein von einer gegebenen Vorlage stammender Messwert sein als auch direkt von der digitalen Druckvorstufe herkommen.The color locus vector R ₁₁ in the combination measuring field 1 is measured on samples of the printed product 30 taken by sampling by measurement with a color measuring device. By referring to a predetermined target color locus vector R ₀ , the color locus deviation is then calculated $\underline{{\text{<figure-callout id="11" label="ΔR" filenames="imgf0001.png" state="{{state}}">ΔR</figure-callout>}}_{\text{11}}}\text{=}\underline{{\text{<figure-callout id="11" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{11}}}\text{-}\underline{{\text{R}}_{\text{0}}}$

. The target color locus vector can either be a measurement value originating from a given template or come directly from the digital prepress.

If one follows ΔR ₁₁ over a longer period of time, ie over several productions, and forms the mean value ΔR _11M , in most cases ΔR _11M will differ from zero. In conventional processes for controlling the color in offset printing, ΔR _{11M would} now be compensated for in every edition by adjusting the ink guide actuators on the printing press. If we now adopt the basic idea of color management in offset printing, we do not compensate for the systematic color locus deviation ΔR _11M by setting the printing press but by producing the color separations in the prepress stage by specifically influencing the area coverage.

• Man bestimmt mithilfe der Transformationsfunktion B eine von Änderungen der Farbschichtdicke unabhängige Variation
  
  der effektiven Flächendeckungsgrade in Cyan, Magenta und Gelb: $$\underline{{\text{ΔF}}_{\text{e11}}}\text{=}\underline{\underline{{\text{B}}^{\text{-1}}{\text{ΔR}}_{\text{11M}}}}\text{.}$$
  
• Mithilfe der für den Druckprozess gültigen Druckkennlinien lassen such dann die Änderungen der nominellen Flächendeckungsgrade von Cyan, Magenta und Gelb im Farbauszug bestimmen, welche notwendig sind, um die systematische Farbortsabweichung ΔR _11M zu kompensieren.

The following procedure is suitable for this:

• The transformation function B is used to determine a variation which is independent of changes in the ink layer thickness
  
  the effective area coverage in cyan, magenta and yellow: $$\underline{{\text{ΔF}}_{\text{e11}}}\text{=}\underline{\underline{{\text{B}}^{\text{-1}}{\text{ΔR}}_{\text{11M}}}}\text{.}$$
  
• With the help of the printing characteristics that are valid for the printing process, we can then determine the changes in the nominal area coverage of cyan, magenta and yellow in the color separation, which are necessary to compensate for the systematic color location deviation ΔR _11M .

übrig. Diese müssen ebenfalls ausgeglichen werden. Das erfindungsgemässe Verfahren ermöglicht es, an Druckmaschinen mit farbzonenorientiert arbeitenden Farbwerken folgendermassen vorzugehen:

• Man bestimmt mithilfe der Transformationsfunktion A eine durch Änderungen der Farbschichtdicke bedingte Variation
  
  der Volltondichten in Cyan, Magenta und Gelb: $$\underline{{\text{ΔD}}_{\text{v11}}}\text{=}\underline{\underline{\text{A}}}{\text{}}^{\text{-1}}\underline{\underline{{\text{ΔR}}_{\text{11Z}}}}\text{.}$$
  
• Durch Verstellung der Farbführungsstellglieder an der Druckmaschine werden die Farbschichtdicken so geregelt, dass ΔD _v11 gegen null geht. Für das Ausregeln von ΔD _v11 sind zwei Lösungen denkbar:
  • Falls die Volltondichten von Cyan, Magenta und Gelb auf dem Druckerzeugnis 30 direkt gemessen werden können, so brauchen nur die Volltondichte-Sollwerte um -ΔD_vc11, -ΔD_vm11 bzw. -ΔD_vg11 verändert zu werden. Eine manuelle oder automatische Regelung auf die neuen Volltondichte-Sollwerte bringt dann ΔD _v11 zum Verschwinden.
  • Falls auf dem Druckerzeugnis 30 keine Volltondichten gemessen werden können, werden die Volltondichtevariationen ΔD_vc11, ΔD_vm11 bzw. ΔD_vg11 mit den auf die Farbzone, welche das Kombinationsmessfeld 1 enthält, bezogenen Flächendeckungssummen von Cyan, Magenta bzw. Gelb gewichtet. Dies ergibt ein direktes Mass für die Veränderung der in der Farbzone geführten Farbmengen der Grundfarben, welche zur Kompensation der Volltondichtevariation ΔD _v11 führt. Die Veränderung der Farbmengen kann wiederum durch einen manuellen Eingriff oder durch automatische Steuerung erfolgen.

If the systematic color locus deviation is compensated, random color locus deviations still remain $\underline{{\text{ΔR}}_{\text{11T}}}\text{=}\underline{{\text{ΔR}}_{\text{11}}}\text{-}\underline{{\text{ΔR}}_{\text{11M}}}$

left. These must also be balanced. The method according to the invention makes it possible to proceed as follows on printing presses with inking units which operate in an ink-zone-oriented manner:

• With the help of the transformation function A, a variation due to changes in the color layer thickness is determined
  
  of solid ink densities in cyan, magenta and yellow: $$\underline{{\text{ΔD}}_{\text{v11}}}\text{=}\underline{\underline{\text{A}}}{}^{\text{-1}}\underline{\underline{{\text{ΔR}}_{\text{11T}}}}\text{.}$$
  
• By adjusting the ink guide actuators on the printing press, the ink layer thicknesses are controlled so that ΔD _{v11 goes} to zero. Two solutions are conceivable for the correction of ΔD _v11 :
  • If the full tone densities of cyan, magenta and yellow can be measured directly on the printed product 30, then only the full tone density setpoints need to be changed by -ΔD _vc11 , -ΔD _vm11 or -ΔD _vg11 . Manual or automatic control to the new full-tone density setpoints then causes _{ΔD v11} to disappear.
  • If no full-tone densities can be measured on the printed product ₃₀ , the full-tone density variations ΔD _vc11 , ΔD _vm11 or ΔD vg11 are _weighted with the area coverage _amounts of cyan, magenta or yellow related to the ink _zone which contains the combination measuring _field 1. This gives a direct measure of the change in the amount of color of the primary colors, which leads to the compensation of the solid density variation _{ΔD v11} . The change in the amount of color can again be done by manual intervention or by automatic control.

With the application of the method according to the invention that has just been described, it has been shown that variations in the color location vector R ₁₁ in the combination measuring field 1 on the printed product 30 result from a combination of changes in the ink layer thicknesses of the basic colors cyan, magenta and yellow and changes in the nominal area coverage when producing the color separations in the Prepress can be compensated.

• Auf praxisüblichen mehrfarbigen Druckerzeugnissen gibt es in derselben Farbzone immer mehrere sich durch die nominellen Flächendeckungsgrade der Grundfarben unterscheidende Mischfarbtöne zu drucken. Diese Situation ist gleichwertig damit, dass das Druckerzeugnis 30 in derselben Farbzone mehrere Messfelder mit unterschiedlichem Bildaufbau hat.
• Für alle diese Messfelder wird nun gefordert, dass die Farbortsvariationen durch Verstellen der Farbführungsstellglieder an der Druckmaschine ausgeregelt werden. Im Normalfall wird jedes Messfeld eine andere Farbortsvariation aufweisen und deshalb eine andere Korrektur der Maschineneinstellung verlangen. Diese Bedingung kann nie erfüllt werden, so dass schlussendlich ein Kompromiss gefunden werden muss, durch den zwar die Farbortsvariationen in allen Kombinationsmessfeldern etwas reduziert aber niemals gleichzeitig zum verschwinden gebracht werden.
• In dieser Beziehung weist nun das erfindungsgemässe Verfahren einen bedeutenden Vorteil auf, indem es über die Veränderung der nominellen Flächendeckungsgrade beim Herstellen der Farbauzszüge individuelle Korrekturen für jedes Messefeld oder jede Bildstelle entsprechend dem Bildaufbau erlaubt. Auf diese Weise können die systematischen Anteile der Farbortsvariation vollständig kompensiert werden.

In contrast, previously known methods for compensating the color location variations are based solely on influencing the color guidance on the printing press. This has a decisive disadvantage compared to the method according to the invention, which is to be illuminated here somewhat:

• There are always several mixed colors to be printed in the same color zone on standard multicolored printed products, which differ by the nominal area coverage of the primary colors. This situation is equivalent to the fact that the printed product 30 has several measurement fields with different image structures in the same color zone.
• For all of these measuring fields, it is now required that the color location variations are corrected by adjusting the ink guide actuators on the printing press. Normally, each measuring field will have a different color location variation and therefore require a different correction of the machine setting. This condition can never be met, so that ultimately a compromise has to be found by which the color location variations in all combination measuring fields are somewhat reduced, but never made to disappear at the same time.
• In this regard, the method according to the invention has an important advantage in that it allows individual corrections for each measuring field or each image location in accordance with the image structure by changing the nominal area coverage when producing the color separations. In this way, the systematic parts of the color location variation can be fully compensated.

The compensation of the systematic color location variations by changing the nominal area coverage when producing the color separations in the prepress is particularly interesting in connection with newer color zone-less printing press concepts. These printing presses are stable with regard to the consistency of the ink guide over several runs, but can hardly be controlled by adjusting the ink guide actuators. Correction of color location deviations by influencing the nominal area coverage in prepress is the method of choice here.

The method according to the invention makes it possible to use an image location with a suitable image structure instead of the combination measuring field 1 on the printed product 30. The space occupied by the combination measuring field 1 on the printed product can thereby be saved.

• Es ist problemlos möglich, zur Bestimmung der Transformationsfunktion B beispielsweise das erste gute Exemplar der Auflage anstelle des Eichdrucks 20 zu verwenden.
• Die Transformationsfunktion A lässt sich dann ebenfalls aufgrund von weiteren drei Exemplaren, die der Auflage entnommen werden, ermitteln, sofern über die Auflage genügend grosse Schwankungen der Volltondichte der Grundfarben vorkommen. Die Auswertung erfolgt durch eine Verallgemeinerung des oben angegebenen Rechenschemas, welche darin besteht, dass die Matrix ΔD _v keine Diagonalmatrix ist, sondern in allen Spalten je eine Variation der Volltondichten von Cyan, Magenta und Gelb enthält:
  
  Eine Verbesserung der Schätzgenauigkeit der Transformationsfunktion A ist dadurch zu erreichen, dass eine grössere Anzahl von Stichproben aus der Auflage ausgewertet wird. Die Spaltenzahl der Matrizen ΔR _Dv und ΔD _v vergrössert sich dann entsprechend der Anzahl der zusätzlich ausgewerteteten Stichproben. Die dadurch entstehende Matrixgleichung ist dann allerdings überbestimmt und muss mithilfe der Methoden der Ausgeleichsrechnung nach A aufgelöst werden.

Another sensible application of the method according to the invention is that the complete measurement field block of the calibration prints 20 to 23 is also printed in the printed product 30, so that the actual calibration prints can be dispensed with.

• It is easily possible to use, for example, the first good copy of the edition instead of the calibration print 20 to determine the transformation function B.
• The transformation function A can then also be determined on the basis of a further three copies taken from the edition, provided that there are sufficiently large fluctuations in the solid color density of the primary colors over the edition. The evaluation is carried out by a generalization of the above-mentioned calculation scheme , which consists in that the matrix ΔD _{v is} not a diagonal matrix, but contains a variation of the full tone densities of cyan, magenta and yellow in all columns:
  
  An improvement in the estimation accuracy of the transformation function A can be achieved by evaluating a larger number of samples from the edition. The number of columns in the matrices ΔR _Dv and ΔD _v then increases in accordance with the number of additionally evaluated samples. The resulting matrix equation is then, however overdetermined and must be resolved using the methods of the compensation calculation according to A.

For the method according to the invention, it does not matter what type of measuring device the measurement data is collected with. For example, it is in principle open whether densitometric values are determined using a densitometer, a spectrophotometer, a video camera or any other suitable device. Analogously, colorimetric measurements with spectrophotometers, three-range color measuring devices, video cameras or other suitable devices are possible without breaking the invention. Furthermore, it does not matter which tools are used to further process the measurement data.

The method according to the invention can also be extended in the direction of four-color overprinting, in that a proportion of the printing ink black is also permitted in the combination measuring fields on the calibration prints 20 to 23 and the printed product 30. The only condition is that the nominal area coverage of black is the same in all four combination measuring fields.

Claims (17)

1. A group of measuring fields for the acquisition of colour data on a printed product, in particular for colour management in rotary offset production printing, having a plurality of measuring fields which are printed, so as to be capable of being optically scanned, on a printed product to be checked or a calibration print,
   characterised by

   a) a first combination measuring field (1) in which the primary colours are overprinted with their nominal dot percentages (P_c1, P_m1, P_y1),

   b) additional combination measuring fields (2, 3, 4) in which the primary colours are overprinted with varied nominal dot percentages {( ${\text{P}}_{\text{c2}}{\text{= P}}_{\text{c1}}{\text{+ ΔP}}_{\text{c2}}$

   

   , P_m1, P_y1), (P_c1, ${\text{P}}_{\text{m3}}{\text{= P}}_{\text{m1}}{\text{+ ΔP}}_{\text{m3}}$

   

   , P_y1), (P_c1, P_m1, ${\text{P}}_{\text{y4}}{\text{= P}}_{\text{y1}}{\text{+ ΔP}}_{\text{y4}}$

   

   )}, each primary colour being varied at least once and in each additional combination measuring field (2, 3, 4) at least one other primary colour being varied,

   c) additionally at least one single-colour full-tone field (5, 6, 7) for each primary colour and

   d) additionally at least one single-colour halftone field (8,11; 9,12; 10,13) for each primary colour, first single halftone colour fields [sic] (8, 9, 10) possessing in their respective primary colour a dot percentage (P_c1, P_m1, P_y1) which corresponds to that of the same colour in the first combination measuring field (1) and/or second single halftone colour fields [sic] (11, 12, 13) possessing in their respective primary colour a dot percentage (P_c2, P_m3, P_y4) which corresponds to the varied dot percentage of the same colour in the additional combination measuring fields (2, 3, 4).
2. A method for colour management in rotary offset production printing, in which

   a) measuring fields and/or image areas serving as measuring fields are concomitantly printed and

   b) optically scanned after the printing operation and

   c) the reflected light is evaluated,
   characterised in that

   d) a group of measuring fields according to Claim 1 is used.
3. A method for colour management in rotary offset production printing, in which

   a) measuring fields and/or image areas serving as measuring fields are concomitantly printed and

   b) optically scanned after the printing operation and

   c) the reflected light is evaluated,
   characterised in that

   d) the printed product (30) to be checked and a plurality of calibration prints (20, 21, 22, 23) produced with specifically different ink film thicknesses each contain a first combination measuring field (1) in which the primary colours, in particular the three colours cyan, magenta and yellow, are overprinted with their nominal dot percentages P_c1, P_m1, P_y1,

   e) the calibration prints (20, 21, 22, 23) additionally have combination measuring fields (2, 3, 4) in which the primary colours are overprinted with the nominal dot percentages ( ${\text{P}}_{\text{c2}}{\text{= P}}_{\text{c1}}{\text{+ ΔP}}_{\text{c2}}$

   

   , P_m1, P_y1), (P_c1, ${\text{P}}_{\text{m3}}{\text{= P}}_{\text{m1}}{\text{+ ΔP}}_{\text{m3}}$

   

   , P_y1), (P_c1, P_m1, ${\text{P}}_{\text{y4}}{\text{= P}}_{\text{g1}}{\text{+ ΔP}}_{\text{g4}}$

   

   ), each primary colour being varied at least once and in each additional combination measuring field (2, 3, 4) at least one other primary colour being varied,

   f) the calibration prints (20, 21, 22, 23) additionally have, for each primary colour, at least one single-colour full-tone field (5, 6, 7) and

   g) the calibration prints (20, 21, 22, 23) additionally have, for each primary colour at least one single-colour halftone field (8,11; 9,12; 10,13), first single halftone colour fields [sic] possessing in their respective primary colour a dot percentage (P_c1, P_m1, P_y1) which corresponds to that of the same colour in the first combination measuring field (1) and/or second single halftone colour fields [sic] (11, 12, 13) possessing in their respective primary colour a dot percentage (P_c2, P_m3, P_y4) which corresponds to the varied dot percentage of the same colour in the additional combination measuring fields (2, 3, 4).
4. A method according to Claim 3, characterised in that the calibration prints (20, 21, 22, 23) are used

   a) to determine, by measurement with a colour-measuring instrument, on the combination measuring fields (1, 2, 3, 4) in each case the colour location vectors R ₁, R ₂, R ₃ and R ₄ in a chosen colorimetric coordinate system,

   b) to determine, in the single-colour full-tone fields, the full-tone density values D_fc1, D_fm1, D_fy1 by densitometric measurement using a filter characteristic corresponding to the individual field and

   c) to determine, in the single-colour halftone fields (8,11; 9,12; 10,13), the effective dot percentages in the print P_ec1, P_ec2, P_em1, P_em3, P_ey1 and P_ey4 by densitometric or other measurements.
5. A method according to Claim 4, characterised in that the colour location vectors (R ₁, R ₂, R ₃ and R ₄), the full-tone densities (D_fc1, D_fm1, D_fy1) and the effective dot percentages (P_ec1, P_ec2, P_em1, P_em3, P_ey1, P_ey4) of the calibration prints (20, 21, 22, 23) are used to determine two transformation functions A and B which respectively convert a variation $$\underline{{\text{ΔD}}_{\text{f11}}}\text{=}\left[\begin{array}{c}{\text{ΔD}}_{\text{fc1}}\\ {\text{ΔD}}_{\text{fm1}}\\ {\text{ΔD}}_{\text{fy1}}\end{array}\right]$$

   

   of the full-tone density in the single-colour full-tone fields which is caused by changing the ink film thicknesses and a variation $$\underline{{\text{ΔP}}_{\text{e11}}}\text{=}\left[\begin{array}{c}{\text{ΔP}}_{\text{ec1}}\\ {\text{ΔP}}_{\text{em1}}\\ {\text{ΔP}}_{\text{ey1}}\end{array}\right]$$

   

   of the effective dot percentages in the single-colour halftone fields with the nominal dot percentages (P_c1, P_m1 and P_y1) which are independent thereof into variations of the colour location vector ΔR of the first combination measuring field (1) with the nominal dot percentages (P_c1, P_m1, P_y1).
6. A method according to Claim 5, characterised in that

   a) the printed product (30) to be checked is used repeatedly to determine, by measurement with a colour-measuring instrument, on the first combination measuring field (1) the colour location vector R ₁₁ in a chosen coordinate system and

   b) for the deviation, in relation to a preset desired colour location vector R ₀, of the colour location vector $\underline{\text{ΔR}}{\text{}}_{\text{11}}\text{=}\underline{\text{R}}{\text{}}_{\text{11}}\text{-}\underline{\text{R}}{\text{}}_{\text{0}}$

   

   determined on the printed product (30), a combination of a variation $$\underline{{\text{ΔD}}_{\text{f11}}}\text{=}\left[\begin{array}{c}{\text{ΔD}}_{\text{fc11}}\\ {\text{ΔD}}_{\text{fm11}}\\ {\text{ΔD}}_{\text{fy11}}\end{array}\right]$$

   

   of the full-tone density in existing or imaginary single-colour full-tone fields which is caused by changing the ink film thicknesses and a variation $$\underline{{\text{ΔP}}_{\text{e11}}}\text{=}\left[\begin{array}{c}{\text{ΔP}}_{\text{ec11}}\\ {\text{ΔP}}_{\text{em11}}\\ {\text{ΔP}}_{\text{ey11}}\end{array}\right]$$

   

   of the effective dot percentages in existing or imaginary single-colour halftone fields with the nominal dot percentages P_c1, P_m1, P_y1 which is independent thereof is calculated.
7. A method according to Claim 6, characterised in that the deviation ΔR ₁₁ corresponds exactly to the combined effect of the variations ΔD _f11 and ΔP _e11 via the transformation functions A and B.
8. A method according to Claim 6 or 7, characterised in that the deviation of the colour location vector ΔR ₁₁ on the printed product is corrected in a way that, on the one hand, the calculated variation ΔD _f11 of the full-tone densities is made to disappear by adjustment of the ink supply actuators on the printing machine and, on the other hand, the calculated variation ΔP _e11 of the effective dot percentages is made to disappear by a change of the dot percentages during the production of the colour separations.
9. A method according to one of Claims 3 to 8, characterised in that the transformation functions A and B are linear, i.e. characterised by two 3x3 matrices A and B, and in that, respectively the relation $\underline{\text{ΔR}}{\text{}}_{\text{1}}\text{=}\underline{\underline{\text{A}}}\underline{\text{ΔD}}{\text{}}_{\text{f1}}\text{+}\underline{\underline{\text{B}}}\underline{\text{ΔP}}{\text{}}_{\text{e1}}$

   

   and $\underline{\text{ΔR}}{\text{}}_{\text{11}}\text{=}\underline{\underline{\text{A}}}\underline{\text{ΔD}}{\text{}}_{\text{f11}}\text{+}\underline{\underline{\text{B}}}\underline{\text{ΔP}}{\text{}}_{\text{e11}}$

   

   holds true.
10. A method according to Claim 9, characterised in that, for a deviation ΔR ₁₁ of the colour location vector determined on the printed product, a combination of a variation ΔD _f11 of the full-tone densities which is caused by changing the ink layer thicknesses and a variation ΔP _e11 of the dot percentages which is independent thereof is calculated in such a way that simultaneously $\underline{\text{ΔR}}{\text{}}_{\text{11}}\text{=}\underline{\underline{\text{A}}}\underline{\text{ΔD}}{\text{}}_{\text{f11}}\text{+}\underline{\underline{\text{B}}}\underline{\text{ΔP}}{\text{}}_{\text{e11}}$

    

    holds true, where A ΔD _f11 corresponds to the random proportions of ΔR ₁₁ and B ΔP _e11 represents the systematic proportions of ΔR ₁₁, i.e. that which is constant over several successive print jobs.
11. A method according to one of Claims 3 to 8, characterised in that, for a deviation ΔR ₁₁ of the colour location vector determined on the printed product, a variation ΔD _f11 of the full-tone densities which is caused by changing the ink film thicknesses is calculated, where the variation ΔR ₁₁ corresponds exactly to the effect of the variation ΔD _f11 via the transformation function A, and in that
    the deviation of the colour location vector ΔR ₁₁ on the printed product is corrected in a way that the calculated variation ΔD _f11 of the full-tone densities is made to disappear by adjustment of the ink supply actuators on the printing machine.
12. A method according to one of Claims 3 to 8, characterised in that, for a deviation ΔR ₁₁ of the colour location vector determined on the printed product, a variation ΔP _e11 of the effective dot percentages in existing or imaginary single-colour halftone fields with the nominal dot percentages P_c1, P_m1 and P_y1 which is independent of changes of the ink film thicknesses is calculated, where the variation ΔR ₁₁ corresponds exactly to the effect of the variation ΔP _e11 via the transformation function B alone, and in that
    the deviation of the colour location vector ΔR ₁₁ on the printed product is corrected in a way that the calculated variation ΔP _e11 of the effective dot percentages is compensated during the production of the colour separations as a result of a change of the dot percentages which is independent of a change of the ink film thickness.
13. A method according to one of Claims 3 to 12, characterised in that the combination measuring field on the printed product is an image area.
14. A method according to one of Claims 3 to 13, characterised in that the combination measuring fields on the calibration prints and the printed product are also printed with a halftone in black, in addition to cyan, magenta and yellow, the nominal dot percentage of black being the same in all the combination measuring fields.
15. A method according to one of Claims 3 to 14, characterised in that the colorimetric and/or densitometric measurements are carried out using a spectrophotometer.
16. A method according to one of Claims 3 to 14, characterised in that the densitometric measurements are carried out using a densitometer.
17. A method according to one of Claims 3 to 14, characterised in that the colorimetric measurements are carried out using a three-colour colorimeter.

Images