EP0668164B1 - 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 the digital prepress regardless of output devices and materials become. The colors are therefore in one by the Commission Internationale de l'Eclairage (CIE) standardized colorimetric coordinate system, such as XYZ, CIELAB or CIELUV. If the output is defined in this way multicolored images on paper over a in the sense of color management calibrated system, this ensures that the color appearance of the Outputs 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 production,
• random deviations suppressed or corrected and
• systematic deviations can be compensated.

For monitoring and controlling the coloring in multi-color offset printing numerous solutions are known today.

EP 0 196 431 B1, for example, describes a method and a device to achieve a uniform print result on an autotype Multi-color offset printing machine. Measuring is characteristic of this solution of ink layer thicknesses (solid ink densities) and screen dot sizes (Area coverage) on measuring fields, for each printing ink in each Inking zone of the printing machine. Based on these the color guide actuators on the Printing machine set automatically.

There is a need to print several measuring fields in each color setting zone has led to the fact that the mentioned method has so far only Commercial offset printing was used. In commercial offset printing, they can Measuring fields namely outside the type area, i.e. printed on a border which will be cut away at the end. This requirement is in Newspaper offset not fulfilled. No edge is cut off here, if necessary the measuring fields printed on them must be housed within the type area and take up space that is otherwise available through advertisements or editorial Contributions could be used. The newspaper publishers therefore accept that Measuring fields reluctant.

Another obstacle to using the above method in newspaper offset is to see in the high equipment and manpower involved in the Measuring the measuring fields arises. If the web offset measurement is to be carried out online, i.e. happen automatically on the running web, so there is one for each web page optical measuring head with automatic positioning necessary. Would Instead, measure with a commercially available handheld densitometer or Hand-held spectrophotometer, so considering the large Number of measuring fields and the time required for manual Measuring device positioning especially for the purpose of quality data acquisition additional staff can be hired. A systematically carried out Quality data acquisition cannot work in newspaper offset print runs prevail as long as they have high investment costs or large additional Personnel requirements are connected.

The method described in EP 0 196 431 B1 has another disadvantageous one Property by using the solid and halftone densities of the individual colors Characteristics are measured which have no direct relation to the color Have appearance of the printed product. This deficiency can be caused by this be met that so-called combination measuring fields, i.e. Measuring fields in which the basic colors involved in the printing are shown in a grid tone are printed on top of each other, provided and measured colorimetrically.

Colorimetric measurement values obtained in this way can refer to the other Sensitivity function of the average human eye XYZ color space or according to the sensation derived from the XYZ system equally spaced color spaces CIELUV or CIELAB, which are all characterized by the CIE (Commission Internationale de l'Eclairage) have been standardized.

The colorimetric measurement on combination measuring fields has the advantage that it a statement about the interaction of all on a multi-color print colors involved. The colorimetric measurements say immediately something about how the combination measuring field or the printed product human viewer appears in color. Another advantage is that the combination measuring fields, if necessary, by imaging with a suitable one Image composition can be replaced. In contrast to densitometric methods The colorimetric measurement methods have the disadvantage that they do not provide direct information on process control. A deviation of the color location leaves For example, no conclusion about how the color guide on the Printing press needs to be corrected to reduce the deviation.

Methods have been developed with the help of which deviations of the Color loci in variations in layer thickness or Densities of the individual colors involved in printing can be converted. So EP 0 321 402 A1 and EP 0 408 507 A1 describe linear transformations for converting variations of full tone or screen densities into variations the color location of combination measuring fields in the CIELUV or CIELAB.

These transformations make it possible, for example from a deviation the color location of a combination measuring field on a sample sheet the change to calculate the solid color densities of single color measuring fields, which is necessary to compensate for the deviation of the color location in the combination measuring field. The The strategy pursued is therefore to avoid undesirable deviations from the Color locations of combination measuring fields only by suitable Changes in the ink layer thickness of the colors involved in the printing process correct.

The restriction to changes in the color layer thicknesses in EP 0 408 507 A1 appears somewhat arbitrary. Basically, the correction of Color location deviations also about a suitable change of To achieve area coverage of the individual printing inks. This can for example in digital prepress when the color separations be calculated. This option is particularly interesting if it is for a certain combination measuring field observed color location deviations to a essential part systematic, i.e. are not exclusively random in nature. Another advantage is that a change in Coverage levels of the printing inks often when calculating the color separations is easier to control than changing the press guided layer thicknesses. The idea of individual printing characteristics of individual Taking inking units into account when calculating the color separations is already out known from DE 42 09 165 A1. However, there is no reference to colorimetric Measured values produced at combination measuring fields or image points.

A measuring field group known from EP 0 421 003 A1 for acquiring color data of a The printed product comprises a first combination measuring field, in which the basic colors are printed with their nominal area coverage and single-color grids in the primary colors, which in their respective primary colors have an area coverage have that of the same color in the first combination measuring field. The The measuring field group can be optically scanned onto a printed product or to be checked a calibration print is printed on and optically scanned after the printing process. The evaluation The remitted light is used to control the color control of an offset printing press.

In "Sonderdruck der Offsetpraxis, 2nd edition 1990, test forms and print control strips for offset printing and offset copy, "W. Walensky" is the GATF gray balance scale listed and shown on the accompanying printed sheet. The GATF gray balance scale includes, among other things, single-color grids for each primary color, the primary colors have a nominal area coverage in the first single-color grid fields and in the second individual color grid fields, the respective primary color in each case opposite one another the nominal area coverage has varied area coverage. The There are variations in the nominal area coverage in the single-color grids unequal signs. The GATF gray balance scale also includes a combination measuring field, in which the basic colors with their nominal area coverage are printed on top of each other and additional combination measuring fields in which the basic colors with their nominal or in relation to the nominal area coverage varied degrees of area coverage are printed one above the other, with each primary color at least once with their varied compared to the nominal area coverage Area coverage and at least one in each additional combination measuring field different base color with its nominal coverage varied area coverage is printed.

a) Die notwendige Anzahl der Messfelder sollte reduziert werden, damit die Messfelder im Satzspiegel der Zeitung weniger Platz beanspruchen.

b) Der gerätemässige und personelle Aufwand zum Ausmessen der Messfelder soll verkleinert werden.

c) 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.

d) Das Messen an Bildstellen mit einem geeigneten Bildaufbau soll das Mitdrucken und Ausmessen von speziellen Messfeldern so weit wie möglich unnötig machen.

e) 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.

For use in newspaper offset production, it is desirable to improve the objective processes discussed above, in particular in the following respects:

a) 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.

b) The device-related and personnel expenditure for measuring the measuring fields should be reduced.

c) 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.

d) Measuring at image points with a suitable image structure should make the printing and measuring of special measuring fields as unnecessary as possible.

e) 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 create a method for quality data acquisition, especially for statistical quality data acquisition in web offset print run, the at least the requirements a) and b) and preferably all of the above Demands are enough. The process is also intended to be used in newspaper offset production runs his.

This object is solved by the subject matter of claim 1. The solution is characterized by the special requirements of newspaper printing, but this includes one beneficial application in other areas, such as the role commercial offset, in no way out.

• 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 Abtastung 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 Abtastungen.
• 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 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 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 colors are printed one above the other in halftone or full tones, the combined effect of the printing colors involved is recorded by a single optical scanning.
• 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 panel 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 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, for example, this results in at least ten optical scans.
• 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 screen 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 values at combination measuring fields and variations in the screen density of the individual colors is empirically determined on calibration prints for given paper, colored material, a specific printing machine and a working point. The working 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 originals 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 in the screen density in the individual color screen fields into variations in 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, are measuring fields and / or serving as measuring fields Image areas 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 , F _g1 ).

The calibration print or prints additionally have combination measurement fields in which the primary colors with the nominal area coverage F _c2 = F _c1 + ΔF _c , F _m1 , F _g1 ), (F _c1 , F _m3 = F _m1 + ΔF _m , F _g1 ), (F _c1 , F _m1 , F _g4 = F _g1 + ΔF _g ) are printed on top of each other. In each of these additional combination measuring fields, at least one other basic color is varied, for example the first basic color by the value ΔF _c in the second, the second basic color by the value ΔF _m in the third and the third basic color by the value ΔF _g 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 grid fields in the basic colors for each basic color, one in each color having an area coverage that corresponds to that of the same color in the first combination measuring field. 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 grids thus have the area coverage F _c1 , F _c2 , F _m1 , F _m3 , F _g1 and F _g4 . The calibration print or prints can be printed separately or also in the printed product.

On these calibration prints, the color locus vectors R ₁ , R ₂ , R ₃ and R _{4 are determined} in a selected colorimetric coordinate system 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 , D _g1 and D _{g4 are} determined by densitometric measurement with a filter characteristic corresponding to the individual field.

der Rastertondichten in den Einzelfarbenrasterfeldern mit den nominellen Flächendekkungsgraden F_c1, F_m1, F_g1 in Farbortsvektordifferenzen ΔR _E des ersten Kombinationsmessfelds mit den nominellen Flächendeckungsgraden F_c1, F_m1, F_g1 umrechnet.The color locus vectors and the halftone density values of one or more calibration prints are used according to the invention to determine a transformation function L , which is a difference

converted the screen density in the individual color grids with the nominal area coverage degrees F _c1 , F _m1 , F _g1 into color locus vector differences ΔR _{E of} the first combination measuring area with the nominal area coverage levels F _c1 , F _m1 , F _g1 .

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

Finally, the deviation of the color locus vector ΔR _D = R ₁₁ - R ₀ determined on the printed product, based on a predetermined target color locus vector R ₀ , can be reversed by transforming the transformation function L into a difference ΔD _{D of} the halftone densities in existing or imagined single color grid areas with the nominal area coverage degrees F _c1 , F _m1 , F _{g1 can be} converted.

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 quality data acquisition in web offset production printing, has several measuring fields, which can be optically scanned on a printed product to be checked or on a calibration print are printed.

A first combination measuring field, in which the Primary colors with their nominal area coverage are printed on top of each other, additional combination measuring fields in which the basic colors with different nominal Coverage levels are printed on top of each other, each basic color at least once and varies at least one other basic color in each additional combination measuring field is and further additional single-color grids in the primary colors, the first Individual grid color fields in their respective primary color have a degree of area coverage, which corresponds to that of the same color in the first combination measuring field and the second Individual grid color fields in their respective primary color have a degree of area coverage, of the varied area coverage of the same color in the additional Combination measuring fields corresponds.

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

• 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 (F_c2 = F_c1 + ΔF_c, F_m1, F_g1), (F_c1, F_m3 = F_m1 + ΔF_m, F_g1) und (F_c1, F_m1, F_g4 = F_g1 + ΔF_g). 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_c, in Kombinationsmessfeld 3 derjenige von Magenta um ΔF_m3 und in Kombinationsmessfeld 4 derjenige von Gelb um ΔF_g, ΔF_c, ΔF_m und ΔF_g 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 Flächendeckungsgraden F_g1 und F_g4.

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 , 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 (F _c2 = F _c1 + ΔF _c , F _m1 , F _g1 ), (F _c1 , F _m3 = F _m1 + ΔF _m , F _g1 ) and (F _c1 , F _m1 , F _g4 = F _g1 + ΔF _g ). 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 _c , in combination measuring field 3 that of magenta by ΔF _m3 and in combination measuring field 4 that of yellow ΔF _g , ΔF _c , ΔF _m and ΔF _g 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 Area coverage F _g1 and F _g4 .

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 particularly in relation to the color material, the Ink layer thickness and dot gain, i.e. the enlargement of the Area coverage from the film template or the printing plate to printing, below standardized conditions printed. These conditions were for the Edition printing, for example by UGRA in Switzerland or FOGRA in Germany set. It does not matter for the basic functionality Role whether the inventive method in the newspaper or in Commercial web offset is applied. The only essential thing is that the calibration print 40 according to the same standard as the edition, i.e. that too controlling and optimizing printed matter.

A further condition must be met when producing the calibration pressure 40. Besides the measuring field blocks, the calibration pressure has to be with all others Primary colors have printed areas so that at the location of the measuring field block in A sufficient amount of ink is guaranteed. The design this area is free. Analogous considerations apply with regard to the color acceptance for the printed product 50.

With the help of the calibration pressure 40, the relationship between variations of the Screen density of cyan, magenta and yellow and the color appearance of the Combination measuring field 1 can be determined quantitatively.

When determining the dependence of the color appearance of the Combination measuring field 1 of the grid densities of the primary colors is good to determine a transformation function L which is a variation of the Screen density in the resulting variation in the color location of the Combination measuring field converted.

In the general case, the transformation function L is non-linear. Since we have it in the Printing practice mostly with relatively small variations around a standardized one Operating point, it is permissible to linearize the relationships. in the In the following, the inventive method is of interest for clarity explained using a linearized model.

• 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 R ₁ für Messfeld 1, R ₂ für Messfeld 2, R ₃ für Messfeld 3 und R ₄ 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, D_g1 für Messfeld 10 und D_g4 für Messfeld 13.
• Mit den Definitionen ΔR E = [R 2 - R 1   R 3 - R 1   R 4 - R 1] und
  
  lassen sich die linearisierten Zusammenhänge zwischen den gemessenen Grössen durch die folgende Gleichung darstellen: ΔR E = L ΔD E
• 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: L = ΔR E ΔD E -1

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 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 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, D _g1 for measuring field 10 and D _g4 for measuring field 13.
• With the definitions ΔR E = [ R 2nd - R 1 R 3rd - R 1 R 4th - R 1 ] and
  
  the linearized relationships between the measured quantities can be represented by the following equation: ΔR E = L ΔD E
• 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 : L = ΔR E ΔD E -1

By evaluating the calibration pressure 40 we now have the quantitative relationship between variations in the density of the basic colors on one side and Variations of the color locus vector in combination measuring field 1 are determined.

According to the method just described, the matrix L is calculated on the basis of the matrices ΔR _E and ΔD _E. ΔR _E and ΔD _E 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 gained from calibration printing can now be useful be used when the quality of production prints is to be monitored. The prerequisite for this is that the combination measuring field 1 in the printed product 50 the same nominal area coverage for cyan, magenta and yellow is also printed as in calibration print 40.

The color locus vector R ₁₁ 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. By referring to a predetermined target color locus vector R ₀ , the color locus deviation ΔR _D = R ₁₁ - R ₀ is then calculated. The target color locus vector can either be a measurement 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: ΔD D = L -1 ΔR D By reversing the transformation function L , the differences associated with the color locus deviation ΔR _{D can}

the screen density of the basic colors cyan, magenta and yellow can be calculated on the printed product 50: ΔD D = L -1 ΔR D

• 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 a quantitative Criterion is checked, which says something directly to the customer of the print shop, like the average human viewer the color appearance of the Perceives printed matter.

The method according to the invention allows instead of the combination measuring field 1 to use an image location with a suitable image structure on the printed product 50. This allows the space occupied by the combination measuring field 1 on the Print product can be saved.

Another sensible application of the method according to the invention is that in the printed product 50 the complete measuring field block of the calibration print 40 is also printed, so that the actual calibration printing is dispensed with and an as good-looking calibration copy of the printed product in place of the calibration print can kick. It is easily possible to determine the transformation function L for example, the first good copy of the edition instead of the calibration print 40 use.

If a larger number of calibration prints are evaluated to determine the matrix L than is necessary for a mathematically clear solution, the resulting over-determined system of equations can be solved using the methods of the compensation or regression calculation.

It does not matter what type of Measuring devices the measurement data are collected. For example, it is in principle open whether densitometric values using a densitometer, a spectrophotometer, one Video camera or any other suitable device become. Analogue are colorimetric measurements with spectrophotometers, Three-area color measuring devices, video cameras or other suitable devices possible without breaking the invention. Furthermore, it is irrelevant with which aids the further processing of the measurement data is concerned with.

The inventive method can also be in the direction of the four-color Extend superimposed pressure by using the combination measuring fields on the Verification printing 40 and the printed product 50 also a portion of the printing ink black is allowed. The only condition is that the nominal area coverage von Schwarz is the same on 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 printing, but especially in newspaper offset printing, to systematically and routinely record quality data on the print 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, suddenly occurring changes in material properties, and to take countermeasures.
• The possibility of numerically documenting the print quality produced vis-à-vis the customers of a printing company gives them 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 (9)

1. A method for quality data acquisition, in particular for statistical quality data acquisition in rotary offset production printing, in which

   a) at least two single-colour halftone fields (8, 11; 9, 12; 10, 13) are printed on at least one calibration print (40) for each primary colour, in particular for the three primary colours cyan, magenta and yellow, first single-colour halftone fields (8, 9, 10) possessing in the respective primary colour in each case a nominal dot percentage (P_c1, P_m1, P_y1), and second single-colour halftone fields (11, 12, 13) possessing in the respective primary colour in each case a dot percentage varied with respect to the respective nominal dot percentage (P_c2 = P_c1 + ΔP_c, P_m3 = P_m1 + ΔP_m, P_y4 = P_y1 + ΔP_y),

   b) a first combination measuring field (1), in which the primary colours are overprinted with their nominal dot percentages (P_c1, P_m1, P_y1), is printed in each case on a printed product (50) to be checked and the at least one calibration print (40),

   c) additional combination measuring fields (2, 3, 4), in which the primary colours are overprinted with their nominal dot percentages or their dot percentages varied with respect to the nominal dot percentages (P_c2, P_m1, P_y1), (P_c1, P_m3, P_y1), (P_c1, P_m1, P_y4), are printed on the at least one calibration print (40), each primary colour being printed at least once with its dot percentage varied with respect to the nominal dot percentage and in each additional combination measuring field at least one other primary colour being printed with its dot percentage varied with respect to the respective nominal dot percentage,

   d) in each case a colour location vector (R ₁₁, R ₁) in a chosen colorimetric coordinate system (X, Y, Z) is determined by colorimetric measurement on the first combination measuring field of the printed product (50) and the at least one calibration print (40),

   e) in each case an additional colour location vector (R ₂, R ₃, R ₄) in the chosen colorimetric coordinate system is determined by colorimetric measurement on the additional combination measuring fields (2, 3, 4) of the at least one calibration print (40), and

   f) the respective halftone density values (D_c1, D_c2, D_m1, D_m3, D_y1, D_y4) are determined by densitometric measurement on the single-colour halftone fields (8, 11; 9, 12; 10, 13).
2. A method according to Claim 1, characterised in that the colour location vector (R ₁) of the at least one calibration print, the additional colour location vectors (R ₂, R ₃, R ₄) and the halftone density values (D_c1, D_c2, D_m1, D_m3, D_y1, D_y4) are used to determine a transformation function (L) which converts a difference (ΔR _ε) in each case of the colour location vector of the combination measuring field from the additional colour location vectors into a difference ( ΔD _ε) of the halftone densities of the first single-colour halftone fields from the halftone densities of the second single-colour halftone fields for each primary colour according to the following relations: ΔR ε = L ΔD ε where ΔR ε = [R 2 - R 1   R 3 - R 1   R 4 - R 1] and

   
3. A method according to Claim 2, characterised in that the deviation (ΔR _D), in relation to a preset desired colour location vector (R ₀), of the colour vector (R ₁₁) determined on the first combination measuring field of the printed product is converted, by inverting the transformation function (L), into a difference (ΔD _D) of the halftone densities in existing or imaginary single-colour halftone fields on the printed product with the nominal dot percentages (P_c1, P_m1, P_y1) according to the following relations: ΔD D = L -1 ΔR D where ΔR D = R 11 - R 0.
4. A method according to one of Claims 1 to 3, characterised in that the first combination measuring field of the printed product is an image area.
5. A method according to one of Claims 1 to 4, characterised in that the first combination measuring field of the at least one calibration print and of the printed product and also the additional combination measuring fields are also printed with a halftone in black, the nominal dot percentage of black being the same in all the combination measuring fields.
6. A method according to one of Claims 1 to 5, characterised in that a spectrophotometer is used for the colorimetric measurements.
7. A method according to one of Claims 1 to 5, characterised in that a three-colour colorimeter is used for the colorimetric measurements.
8. A method according to one of Claims 1 to 7, characterised in that a spectrophotometer is used for the densitometric measurement.
9. A method according to one of Claims 1 to 7, characterised in that a densitometer is used for the densitometric measurement.

Images