EP0668164A1 - Quality data acquisition in a sheet-fed rotary offset printing machine - Google Patents

Abstract

The measurement fields are optically scannable and are printed on a print prodn. to be controlled or on a standard print. A first combination measurement field (1) is involves in which the basic colours, in partic. the three colours cyan, magenta and yellow, are printed one on top of the other with their nominal surface covering degrees (Fct,Fml,Fgl). Additional individual colour raster fields (8,9,10) in the basic colours in their basic colours have a surface covering degree which corresponds to the same colours in the first combination measurement field. The measurement field group contains additional combination measurement fields (2,3,4) in which the basic colours with varied nominal surface print degrees are printed one on top of the other, whereby each basic colour at least once is varied and in each additional combination measurement field at least another basic colour is varied.

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 worthwhile 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 printing,
• - Suppressed or corrected random deviations 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. Characteristic of this solution is 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 printing machine. 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 outside the type area, i.e. be printed 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 color guidance is corrected on the printing press must 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 certain combination measuring field are to a large extent more systematic, i.e. are not exclusively random in nature. 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 beanspru chen.
• - 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 equipment 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 measurement fields for recording color data of a printed product, which are also suitable for quality data acquisition in web offset printing, in particular for statistical quality data acquisition, and whose use in such a method for quality data acquisition in particular enables a method that individual, several and preferably meets all of the above requirements. The method and the measuring fields developed for it should also be able to be used in newspaper offset print runs.

This object is achieved by a measuring field group according to claim 1 and a method according to claims 3, 4 or 5. 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 Farben 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 Flächendekkungsgrades 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 dem densitometrischen Kennwert Rastertondichte 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 an area 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 colors are printed one above the other in halftone or full tones, the combined effect of the printing inks involved is detected 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 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 print runs is based exclusively on densitometric measurements, then at least two monochrome measuring fields must be printed for 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 screen 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.
• - There is a legal relationship between the colorimetric values determined on a combination measuring field on the one hand and the densitometric characteristic value grid tone density of the individual colors on the other. 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 der Rastertondichte 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 Einzelfarben 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 Rastertondichte in den Einzelfarbenrasterfeldern in Variationen des Farbortsvektors des Kombinationsmessfeldes umrechnet und umgekehrt.
• . Auf dem hinsichtlich seiner farblichen Erscheinung zu kontrollierenden 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 Variationen der Rastertondichte der Einzelfarben werden nun durch Umkehrung der gefundenen Transformationsfunktion aus den Variationen des Farbortsvektors des Kombinationsmessfeldes errechnet.

The following procedure is suggested:

• . The systematic relationship between the variations in colorimetric parameters on combination measuring fields and variations in the screen density of the individual colors is empirically determined on calibration prints for given paper, color material, a specific printing press and a working point. The operating point is expediently characterized by the nominal area coverage of the individual colors in the combination measurement field, ie the area coverage that the combination measurement area has on the film templates or the printing plates.
• . The result of the evaluation of the calibration prints thus forms a transformation function for each working point, which converts variations of the screen density in the individual color screen fields into variations of the color location vector of the combination measuring field and vice versa.
• . Then only the combination measuring field is printed on the printed product to be checked for its color appearance 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 variations in the screen density of the individual colors are now calculated by reversing the transformation function found from the variations in the color locus vector of the combination measuring field.

For quality data acquisition, in particular for statistical quality data acquisition, measurement fields and / or image points serving as measurement 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 one or more calibration prints 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 , Fg _i ).

The calibration print or prints additionally have combination measuring fields in which the primary colors with the nominal area coverage (F _c2 = F _c1 + ΔF _c2 , F _m1 , F _g1 ), (F _c1 , F _m3 = F _m1 + ΔF _m3 , F _g1 ) , (F _c1 , F _m1 , Fg ₄ = Fg ₁ + AFg ₄ ) are printed on top of each other. In each of these additional combination measurement 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 AF _m3 in the third and the third primary color by the value AFg ₄ 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 two individual color grids in the primary colors for each primary color, one each in its respective color having an area coverage that of the same color in the first Combination measuring field corresponds. 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 single-color grids therefore have the area coverage F _c1 , F _c2 , F _m1 , F _m3 , Fg ₁ and Fg ₄ . The calibration print or prints can be printed separately or also in the printed product.

Advantageously, the color locus vectors R ₁ , R ₂ , R ₃ and R4 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 respective raster density values D _c1 , D _c2 , D _m1 , D _m3 , Dg ₁ and Dg ₄ can be determined by densitometric measurement with a filter characteristic corresponding to the individual field.

der Rastertondichten in den Einzelfarbenrasterfeldern mit den nominellen Flächendeckungsgraden F_c1, F_m1, Fg_l in Variationen des Farbortsvektors AR des ersten Kombinationsmessfeldes mit den nominellen Flächendeckungsgraden F_c1, F_m1, Fg_l umrechnet.The color locus vectors and the screen density values of one or more calibration prints are used according to the invention for determining a transformation function L, which is a variation

converted the screen density in the individual color grids with the nominal area coverage F _c1 , F _m1 , Fg _l in variations of the color locus AR of the first combination measuring field with the nominal area coverage F _c1 , F _m1 , Fg _l .

According to the invention, the color locus vector R ₁₁ should be determined repeatedly in the selected coordinate system on the printed product to be checked by measurement with a color measuring device on the first combination measuring field.

der Rastertondichten in vorhandenen oder gedachten Einzelfarbenrasterfeldern mit den nominellen Flächendeckungsgraden F_c1, F_m1, Fg₁ umgerechnet werden.Finally, the deviation of the color locus vector ΔOR ₁₁ = R ₁₁ - Ro determined on the printed product based on a predefined target color locus vector Ro can be changed by reversing the transformation function L

the grid density in existing or imagined single-color grids can be converted with the nominal area coverage F _c1 , F _m1 , Fg ₁ .

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 recording quality data in web offset production printing, has a plurality of measuring fields, which are optically scanned and printed on a printed product to be checked or on a calibration print.

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

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, Fg_i) übereinandergedruckt. In drei werteren Kombinationsmessfeldern 2, 3 und 4 sind ebenfalls die Grundfarben Cyan, Magenta und Gelb übereinander gedruckt und zwar mit den nominellen Flächendeckungsgraden (F_c2 = F_c1 +ΔF_c2, F_m1, Fgi), (F_c1, F_m3 = F_m1 +ΔF_m3, F_g1) und (F_c1, F_m1, Fg₄ = F_g1 +AFg₄). 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 DF_c2, in Kombinationsmessfeld 3 derjenige von Magenta um AF_m3 und in Kombinationsmessfeld 4 derjenige von Gelb um AFg₄, ΔF_c2, AF_m3 und AFg₄ dürfen dabei sowohl positives wie negatives Vorzeichen aufweisen.
• - 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 Flächendekkungsgraden Fg_l und Fg₄.

A calibration print 40 contains a measuring field block consisting of 10 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 , Fg _i ). The basic colors cyan, magenta and yellow are also in three other combination measuring fields 2, 3 and 4 printed on top of each other with the nominal area coverage (F _c2 = F _c1 + ΔF _c2 , F _m1 , Fgi), (F _c1 , F _m3 = F _m1 + ΔF _m3 , F _g1 ) and (F _c1 , F _m1 , Fg ₄ = F _g1 + AFg ₄ ). 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 DF _c2 , in combination measuring field 3 that by magenta by AF _m3 and in combination measuring field 4 that by yellow AFg ₄ , ΔF _c2 , AF _m3 and AFg ₄ may have both positive and negative signs.
• - Six single-color fields are printed with halftone tones, namely fields 8 and 11 in cyan with the nominal area coverage F _c1 and F _c2 , fields 9 and 12 in magenta with the nominal area coverage F _m1 and F _m3 as well as field 10 and 13 in yellow with the nominal area coverage Fg _l and Fg ₄ .

The printed product 50 to be checked 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 40 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 40 according to the same standard as the edition, i.e. the printed product to be checked and optimized is produced.

A further condition must be met when producing the calibration pressure 40. In addition to the measuring field blocks, the calibration print must also have additional 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 to ink acceptance for the printed product 50.

With the help of the calibration print 40, the relationship between variations in the screen density of cyan, magenta and yellow and the color appearance of the combination measuring field 1 can now be determined quantitatively.

When determining the dependence of the color appearance of the combination measuring field 1 on the screen density of the primary colors, it is a matter of determining a transformation function L which converts a variation of the screen density into the resulting variation in the color location of the combination measuring field.

In the general case, the transformation function L is 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 not detract from the generalization of claims 3 to 8 to linear and nonlinear systems.

• - 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 40 werden die Normfarbwerte XYZ gemessen. Es resultieren vier Farbortsvektoren
  
  und zwar R1 für Messfeld 1, R₂ für Messfeld 2, R₃ für Messfeld 3 und R₄ für Messfeld 4.
• - An den Einzelfarbenfeldern 8 bis 13 von Eichdruck 40 werden Farbdichten gemessen. Es resultieren dabei sechs Rastertondichtewerte, und zwar D_c1 für Messfeld 8, D_c2 für Messfeld 11, D_m1 für Messfeld 9, D_m3 für Messfeld 12, Dg₁ für Messfeld 10 und Dg₄ für Messfeld 13.
• - Mit den Definitionen
  
  und
  
  lassen sich die linearisierten Zusammenhänge zwischen den gemessenen Grössen durch die folgende Gleichung darstellen:
  
• - Hier steht die 3x3-Matrix L für die gesucht Transformationsfunktion L. Um zu der Transformationsfunktion zu gelangen, müssen wir also die letzte Gleichung nur noch nach L auflösen:
  

The transformation function can be determined, for example, as follows:

• - 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 40. Four color locus vectors result
  
  namely R1 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 8 to 13 of calibration print 40. This results in six grid density values, namely D _c1 for measuring field 8, D _c2 for measuring field 11, D _m1 for measuring field 9, D _m3 for measuring field 12, Dg ₁ for measuring field 10 and Dg ₄ for measuring field 13.
• - With the definitions
  
  and
  
  the linearized relationships between the measured quantities can be represented by the following equation:
  
• - Here the 3x3 matrix L stands for the sought transformation function L. To get to the transformation function, we only have to solve the last equation for L:
  

By evaluating the calibration print 40, we have now determined the quantitative relationship between variations in the screen density of the primary colors on the one hand and variations in the color locus vector in the combination measuring field 1.

berechnet.

sind dabei durch Messwerte definiert, welche allein vom Eichdruck 40 stammen. Das bedeutet, dass die Matrix L vollständig aufgrund eines einzigen Eichdrucks bestimmt werden kann.According to the method just described, the matrix L is based on the matrices

calculated.

are defined by measured values which originate from calibration pressure 40 alone. This means that the matrix L can be determined completely on the basis of a single calibration pressure.

The transformation function obtained from calibration printing can now be used to advantage if the quality of production prints is to be monitored. The prerequisite for this is that the combination measuring field 1 is also printed in the printed product 50 with the same nominal area coverage for cyan, magenta and yellow as in the calibration print 40.

The color locus vector Rn in the combination measuring field 1 is measured on samples of the printed product 50 taken by sampling by measurement with a color measuring device. The color locus deviation ΔR ₁₁ = R ₁₁ - Ro is then calculated by referring to a predefined target color locus vector Ro. The target color locus vector can either be a measured value originating from a given template or come directly from the digital prepress.

der Rastertondichte der Grundfarben Cyan, Magenta und Gelb auf dem Druckerzeugnis 50 berechnet werden:

By reversing the transformation function L, the variations associated with the color locus deviation ΔR _{11 can}

the screen density of the basic colors cyan, magenta and yellow can be calculated on the printed product 50:

• - Auf dem Druckerzeugnis sind weniger Messfelder notwendig, d.h. Ein Kombinationsmessfeld in Cyan, Magenta und Gelb anstelle von drei Einzelfarbenrasterfeldern und drei Rasterfeldern im zweifarbigen Übereinanderdruck.
• - Die Anzahl der am Druckerzeugnis durchzuführenden Messungen reduziert sich von mindestens sechs auf eins.

With the application of the method according to the invention that has just been described, it has been shown that variations in the color guidance on the printed product 50 in the three bright primary colors can be determined by a single colorimetric measurement. In this way, information about the behavior of the individual colors and their interaction can be obtained in a very efficient manner. The effort for this is reduced in two ways compared to conventional processes:

• - Fewer measuring fields are required on the printed product, ie one combination measuring field in cyan, magenta and yellow instead of three single-color grid fields and three grid fields in two-color overprinting.
• - The number of measurements to be carried out on the printed product is reduced from at least six to one.

Another advantage of the method is that the colorimetric measurement on the combination measuring field 1 of the printed product 50 checks a quantitative criterion that directly tells the print shop customer how the average human viewer perceives the color appearance of the printed product.

The method according to the invention makes it possible to use an image location with a suitable image structure instead of the combination measurement field 1 on the printed product 50. The space occupied by the combination measuring field 1 on the printed product can thereby be saved.

Another sensible application of the method according to the invention is that the complete measurement field block of the calibration print 40 is also printed in the print product 50, so that the actual calibration print is dispensed with and a calibration copy of the print product that is found to be good can take the place of the calibration print. It is easily possible to use the first good copy of the edition instead of the calibration print 40 to determine the transformation function L.

• - Alle Eichdrucke enthalten zumindest das Kombinationsmessfeld 1 und die Einzelfarbenmessfelder 8, 9 und 10.
• - Die Eichdrucke werden mit variierenden Farbschichtdicken in allen Grundfarben hergestellt, so dass die Mittelwerte der Farbschichtdicken über die Eichexemplare immer noch genügend genau dem Druckstandard entsprechen.

Under these circumstances, there may be too little space on the printed product to print each of the calibration fields 2, 3, 4, 8, 9, 10, 11, 12 and 13. In such a case, the method according to the invention can nevertheless be used if, in addition to a first calibration print, several additional calibration copies are printed if the following conditions are met:

• - All calibration prints contain at least the combination measuring field 1 and the single color measuring fields 8, 9 and 10.
• - The calibration prints are produced with varying ink layer thicknesses in all primary colors, so that the mean values of the ink layer thicknesses across the calibration copies still correspond sufficiently precisely to the printing standard.

wobei die Mtrizen

als Glieder allerdings Differenzbeträge enthalten, welche nicht durch unterschiedliche nominelle Flächenbedeckungen der Messfelder sondern durch unterschiedliche Farbschichtdicken zwischen den einzelnen Eichdrucken entstehen. Werden zur Bestimmung der Matrix L eine grössere Anzahl von Eichdrucken ausgewertet als für eine mathematisch eindeutige Lösung notwendig ist, so kann das dadurch entstehende überbestimmte Gleichungssystem nach den Methoden der Ausgleichs- bzw. der Regressionsrechnung aufgelöst werden.It is then possible to determine the transformation L on the basis of a comparison of the fluctuations in the color locus vector R, in the combination measuring field 1 and the fluctuations in the density values D _e1 , D _mi , Dg ₁ in the individual color measuring fields 8, 9, 10. The equation still applies to the determination of the matrix L.

being the mtrices

as links, however, contain differences that do not result from different nominal area coverings of the measuring fields but from different ink layer thicknesses between the individual calibration prints. If a larger number of calibration prints are evaluated to determine the matrix L than is necessary for a mathematically unambiguous solution, the resulting over-determined system of equations can be calculated using the methods of the compensation or regression calculation be resolved.

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 expanded 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 print 40 and the printed product 50. The only condition is that the nominal area coverage of black is the same in all four combination measuring fields.

• - Durch gezielte statistische Erhebungen kann das Druckunternehmen nun mit vertretbarem Aufwand repräsentative Daten über das von seiner Produktion eingehaltene Qualitätsniveau gewinnen. Dabei ist es in farbzonenorientiert arbeitenden Druckmaschinen keinesfalls notwendig, für jede druckende Farbzone ein separates Kombinationsmessfeld auf dem Druckerzeugnis mitzudrucken und auszumessen. Es genügen einige wenige Stellen mit Messfeldern für eine Produktion.
• - Weiter wird es möglich, Störungen im Druckprozess, beispielsweise unvermittelt auftretende Änderungen von Materialeigenschaften, früher zu erkennen und Gegenmassnahmen zu treffen.
• - Die Möglichkeit, die produzierte Druckqualität gegenüber den Kunden eines Druckunternehmens zahlenmässig zu dokumentieren, verschafft diesem einen Wettbewerbsvorsprung vor Konkurrenten, welche nicht über diese Möglichkeit verfügen. Dieser Aspekt wird in Zukunft noch an Bedeutung gewinnen, da heute ein starker Trend erkennbar ist, das Qualitätssicherungssystem von Druckereibetrieben nach der Norm ISO 9000 zu zertifizieren.

The savings that the presented method brings to the necessary measuring fields and the measuring effort make it possible for the first time in web offset, but especially in newspaper offset on-page printing, to systematically and routinely record quality data on the printed product.

• - Through targeted statistical surveys, the printing company can now obtain representative data on the quality level maintained by its production with reasonable effort. In printing machines that work in an ink zone-oriented manner, it is by no means necessary to also print and measure a separate combination measuring field for each printing ink zone. A few places with measuring fields are sufficient for a production.
• - Furthermore, it becomes possible to recognize faults in the printing process, for example, sudden changes in material properties, and to take countermeasures.
• - The ability to document the print quality produced vis-à-vis the customers of a printing company gives the printing company a competitive advantage over competitors who do not have this option. This aspect will become even more important in the future, since today there is a strong trend to certify the quality assurance system of printing companies according to the ISO 9000 standard.

Claims (14)

1. measuring field group for recording color data of a printed product, in particular for quality data recording in web offset print run, with several measuring fields that are optically scanned printed on a printed product to be checked or a calibration print,
marked by a) a first combination measuring field (1), in which the basic colors, in particular the three colors cyan, magenta and yellow, with their nominal area coverage (F _c1 , F _m1 , Fg _i ) are overprinted and b) additional single-color grids (8, 9, 10), in the primary colors, the single-color grids (8, 9, 10) in their respective primary colors having an area coverage F _c1 , F _mi , Fg ₁ that corresponds to that of the same color in the first combination measurement area (1) corresponds. 2. measuring field group according to claim 1,
characterized in that a) the measuring field group contains additional combination measuring fields (2, 3, 4), in which the basic colors with different nominal area coverage (F _c2 = F _c1 + ΔF _c2 , F _mi , F _g1 ), (F _c1 , F _m3 = F _m1 ⁺ AF _m3 , Fg _i ) and (F _c1 , F _m1 , Fg ₄ = Fg ₁ + ΔF _g4 ) are printed on top of each other, whereby each basic color is varied at least once and in each additional combination measuring field (2, 3, 4) and b) the measuring field group has additional individual color grids (11, 12, 13) in which the basic colors have an area coverage F _c2 , F _m3 , Fg ₄ , which corresponds to the varied area coverage of the same color in the additional combination measuring areas (2, 3, 4) . 3. Process for quality data acquisition, in particular for statistical quality data acquisition in web offset print run, in which a) measuring fields and / or image points serving as measuring fields are also printed and b) are optically scanned after the printing process and c) the remitted light is evaluated,
characterized in that d) a measuring field group according to claim 1 or 2 is used. 4. Process for quality data acquisition, in particular for statistical quality data acquisition in web offset print run, in which a) measuring fields and / or image points serving as measuring fields are also printed and b) are optically scanned after the printing process and c) the remitted light is evaluated,
characterized in that d) a first combination measuring field (1) is applied to the printed product (50) to be checked and one or more calibration prints (40), in which the basic colors, in particular the three colors cyan, magenta and yellow, with nominal degrees of area coverage (F _c1 , F _m1 , Fg _i ) are printed on top of each other and e) additional single-color grids (8, 9, 10) in the basic colors are applied to the calibration prints (40), the single-color grids (8, 9, 10) having an area coverage F _c1 , F _m1 , Fg ₁ in their respective basic colors, which corresponds to that of the same color in the first combination measuring field (1). 5. Process for quality data acquisition, in particular for statistical quality data acquisition in web offset print run, in which a) measuring fields and / or image points serving as measuring fields are also printed and b) are optically scanned after the printing process and c) the remitted light is evaluated,
characterized in that d) a first combination measuring field (1) is applied to the printed product (50) to be checked and one or more calibration prints (40), in which the basic colors, in particular the three colors cyan, magenta and yellow, with nominal degrees of area coverage (F _c1 , F _m1 , F _g1 ) are _{printed on} top of each other and e) additional single-color grids (8, 9, 10) in the basic colors are applied to the calibration prints (40), the single-color grids (8, 9, 10) having an area coverage F _c1 , F _m1 , Fg ₁ in their respective basic colors, which corresponds to the same color in the first combination measuring field (1), f) the calibration prints (40) contain additional combination measuring fields (2, 3, 4), in which the basic colors with varying nominal area coverage (F _c2 = F _c1 + ΔF _c2 , F _m1 , F _g1 ), (F _c1 , F _m3 = F _m1 ⁺ AF _m3 , F _g1 ) and (F _c1 , F _m1 , Fg ₄ = Fg ₁ + ΔF _g4 ) are printed on top of each other, with each basic color at least once and in each additional combination measuring field (2, 3, 4) at least one different basic color is varied and g) the calibration prints (40) have additional single-color grids (11, 12, 13) in which the basic colors have an area coverage F _c2 , F _m3 , Fg ₄ , which corresponds to the varied area coverage of the same color in the additional combination measurement areas (2, 3, 4) corresponds. 6. The method according to any one of claims 3 to 5
characterized in that a) on the calibration prints (40) by measurement with a color measuring device on the combination measuring fields (1, 2, 3, 4), if available, the corresponding color locus vectors R ₁ , R ₂ , R ₃ and R ₄ in a selected colorimetric coordinate system be determined and b) by means of densitometric measurement on the individual color fields, if they exist, with a filter characteristic corresponding to the individual color fields, the respective screen density values D _c1 , D _c2 , D _m1 , D _m3 , Dg ₁ and Dg _{4 are} measured. 7. The method according to claim 6, characterized in that the color locus vectors R ₁ , R ₂ , R ₃ and R ₄ and the screen density values D _c1 , D _c2 , D _m1 , D _m3 , Dg ₁ and Dg _{4 of} one or more calibration prints (40 ), to the extent that the corresponding measurement fields were present on the calibration prints, can be used to determine a transformation function L which
a variation

converted the screen density in the individual color grids (8, 9, 10) with the nominal area coverage F _c1 , F _ml , Fg _l in variations of the color locus vector ΔR of the first combination measuring area with the nominal area coverage (F _c1 , F _m1 , Fg _i ). 8. The method according to claim 7,
characterized in that a) the color locus vector R _{11 is} determined repeatedly in the selected colorimetric coordinate system on the printed product (50) to be checked by measurement with a color measuring device on the first combination measuring field (1) and b) the deviation of the color locus vector ΔR ₁₁ = R ₁₁ - R ₀ determined on the printed product based on a predefined target color locus vector Ro by reversing the transformation function L into a variation

the grid density in existing or imagined single-color grids is converted with the nominal area coverage F _c1 , F _m1 , and Fg ₁ . 9. The method according to claim 8, characterized in that the transformation function L is linear, ie characterized by a 3x3 matrix L and that the relationships

respectively.

be valid. 10. The method according to any one of claims 8 or 9, characterized in that the combination measuring field on the printed product is an image point. 11. The method according to any one of claims 8 to 10, characterized in that the combination measuring fields on the calibration prints and the printed product in addition to cyan, magenta and yellow are also printed with a raster tone in the sword, the nominal area coverage of the sword being the same in all combination measuring fields . 12. The method according to any one of claims 8 to 11, characterized in that the colorimetric and / or densitometric measurements are carried out with a spectrophotometer. 13. The method according to any one of claims 8 to 11, characterized in that the densitometric measurements are carried out with a densitometer. 14. The method according to any one of claims 8 to 11, characterized in that the colorimetric measurements are carried out with a three-area color measuring device.

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