EP0196431A2 - Method, control device and auxiliary means for obtaining uniform printing results from a multicolour half-tone offset printing machine - Google Patents

Abstract

The invention relates to a method, a control device and aids for achieving a uniform printing result on an autotypically operating multicolor printing machine. In addition to full-tone densities and / or halftone dot sizes, selected relationships of solid-ink densities and / or halftone dot sizes of different printing inks to one another are also determined on measuring fields printed within the ink zones. If the tolerance ranges assigned to them fall out, the printing process is corrected by actuating the actuators of the inking units. In order to regulate the inking units, instead of conventional single-color measuring fields, combination measuring fields are now provided as a first aid, which result from the overprinting of single-color measuring fields. Since the measured values obtained on combination measuring fields do not correspond to the measured values obtained on single-color measuring fields, they are corrected accordingly before they are processed into control signals for the actuators of the inking units. A second aid consists of a device for determining the color balance in the printing result.

Description

The invention relates to a method, a control device and aids for achieving a uniform printing result on a multi-color offset printing press that works in an autotypical manner according to the preambles of claims 1, 13, 14 and 18.

Multi-color originals are today mostly reproduced by four-color printing, using four primary colors, mostly cyan, magenta, yellow and black. The originals are first broken down into so-called color separations, which are then converted into printing forms. These consist, for example, of offset printing plates produced with the aid of raster films.

The brightness or tonal value levels of a printed color are obtained in multi-color autotypical printing in that the original is represented on the printing form of each color separation by a large number of printing halftone dots which have a different size or area coverage per unit area. Each area coverage corresponds to a brightness level, and the sum of all brightness levels gives the tonal value scale, which on the dark side is covered by 100% of the halftone dots, corresponding to a uniform area covered with printing ink, and on the light side is covered by 0% of the mostly white area Color of the printing material (e.g. paper) is limited. In contrast, the so-called color nuances are obtained when the rasterized color separations of the original are precisely printed on top of each other, due to a so-called autotypical color mix, which is a combination of additive and subtractive color mix, since the raster dots partly lie on top of each other and partly next to each other on the substrate. By adhering to the recommended and partially standardized angles at which the halftone dots are printed one above the other in the halftones of the various printing plates, it is achieved that no significant color fluctuations can be caused by changing proportions of halftone dots lying next to and on top of one another.

In modern multicolor offset printing machines, the printing inks are printed on the substrate in rapid succession, with a separate printing unit being provided for each printing ink. If, for example, 10 brightness levels are provided for each printing ink, 1000 different color shades can be obtained with three printing inks. The reproduction of a color shade essentially depends on two factors, namely on the one hand on the layer thickness of the printing inks on the printing material and on the other hand on the mentioned surface coverage of the halftone dots. In order to influence these factors, the inking units of the printing units of the multicolour offset printing press are each provided with an ink fountain, which extends across the width of the printing material, and a large number of actuators in the form of so-called zone screws, by means of which the ink supply to adjacent ink zones (or longitudinal strips) of the printing plates or the Printing material can be adjusted individually. An increase in the ink supply is usually associated with a vertically directed increase in the ink layer thickness as well as with a horizontally oriented widening or increase in the area coverage of the halftone dots, while a decrease in the ink supply leads to a corresponding reduction in the ink layer thickness and the area coverage of the halftone dots.

Three tools are used to control printing processes. The first tool is to use optical or automatic Densjtometem optical density measurements on preselected Measuring fields in the form of grid fields and / or full fields, that is to say areas completely covered with printing ink. The raster and full fields can be parts of the printed image itself or can be generated by attaching special sections to the printing form. The densiometric evaluation of a full field leads to a value hereinafter referred to as full tone density, whereas the densiometric evaluation of a grid field leads to a value hereinafter referred to as grid density. The density values allow statements about changes in the ink layer thickness or the area coverage of the halftone dots. The second tool is to provide the printing forms with special control elements, which consist of differently sized halftone dots and differently sized microelements, which disappear or are preserved during printing and thereby allow an immediate quantitative statement about the change in the halftone dots or their area coverage. Special density measurements are not necessary, but can also be carried out. The control elements, like the measuring fields, are preferably attached to the upper or lower edge of the printing form or the printing result, expediently each actuator of the inking units and thus each color zone of the printed image and also each color separation in particular. Control elements or measuring fields can be assigned. The third aid is finally the use of semi or fully automatic control devices, especially in connection with multi-color offset printing machines. These regulating devices are based on the principle of using manually operated or automatically operating densitometers to determine the screen and / or solid tone densities of printed screen and / or full fields, to compare the density values obtained with predetermined target values or tolerance ranges and, if there are deviations, to determine the determined ones Density values from the target values or tolerance ranges to actuate the actuators of the inking units so that the measured density values again reach their target values or fall within the tolerance ranges. In Ge In contrast to the other two tools, which are primarily aimed at checking the printing result, the third tool is also aimed at changing the printing result when the measured values deviate from the target values. In automatic control devices, this is done by forwarding the density values determined with densitometers to an electronic data processing system equipped with microprocessors, comparing them with preselected setpoints or tolerance ranges and, in the event of deviations that are no longer tolerable, used to calculate an actuating signal that is used to automatically adjust the associated actuator , for example a zone screw rotatable with a stepper motor.

• Der Drucker beginnt zunächst, mit geringer Farbzuführung zu drucken, um die z.B. vier Druckfarben im Zusammendruck so aufeinander abzustimmen, daß ein einwandfreier Passer entsteht, welcher für die Schärfe des gedruckten Bildes von Bedeutung ist. Sodann versucht der Drucker, das fertige Druckresultat durch Steuerung des Zuflusses der Druckfarben zu den Farbzonen mit Hilfe der Stellglieder so zu beeinflussen, daß es sich möglichst gut an das ihm vorliegende Original angleicht, das ein Probedruck, welcher-in der Fachsprache Andruck genannt wird, oder auch die Vorlage selbst sein kann, welche zur Herstellung der Farbauszüge diente. Die Angleichung des Druckresultats an das Original geschieht dabei vorwiegend gefühlsmäßig und auf der Basis des visuellen Vergleichens von Original und Druckresultat, d.h. nach subjektiven Kriterien. Durch ständiges Korrigieren an den Stellgliedern der Farbwerke wird außerdem versucht, immer näher an das Original heranzukommen bzw. das erzielte Druckresultat über die gesamte Dauer des Druckvorgangs konstant zu halten. Eine vollständige visuelle Übereinstimmung von Druckresultat und Original wird in der Regel ebenso wenig erreicht wie ein gleichförmiges Druckergebnis über eine lange Zeitspanne. Welche Farb- und Tonwertunterschiede bestehen bleiben, unterliegt in starkem Maße dem subjektiven Empfinden des Druckers oder dem Kunden, der manchmal beim Beginn einer Druckauflage dabei ist. Die Kontrolle des Druckresultats ist daher zeitaufwendig und ungenau.

When printing a multi-color print, the printer can essentially do the following:

• The printer first begins to print with a small amount of ink in order to match the four printing colors together so that a perfect register is created, which is important for the sharpness of the printed image. The printer then tries to influence the finished print result by controlling the inflow of the printing inks to the ink zones with the help of the actuators in such a way that it matches as closely as possible to the original that is available to him, which is a test print, which is called pressure in technical terms. or can also be the template itself, which was used to produce the color separations. The adjustment of the print result to the original happens primarily emotionally and on the basis of the visual comparison of original and print result, ie according to subjective criteria. By constantly correcting the actuators of the inking units, an attempt is also made to get ever closer to the original or to keep the print result constant over the entire duration of the printing process. A complete visual correspondence between the print result and the original is generally not achieved, just like a uniform printer result over a long period of time. Which color and tonal value differences remain depends to a large extent on the subjective feeling of the printer or the customer, who is sometimes present at the beginning of a print run. Checking the print result is therefore time consuming and inaccurate.

To switch off subjective impressions obtained by visually checking the print result, the printer can use the measurement fields and control elements mentioned and evaluate them continuously. Alternatively, the printer can provide a semi-automatic or fully automatic control device and can only intervene to assist if the control device can no longer maintain a match between the original and the printing result.

All of these measures and aids for achieving a uniform printing result are liable for three. fundamental disadvantages.

First, for corrective intervention in the printing process, for practical reasons only the inking units of the multicolor printing machine or the sum of the actuators determining the ink supply are available. Therefore, the ink layer thicknesses and area coverage of the halftone dots can only ever be changed together, but not independently of each other, since a change in the position of a zone screw or the like, in addition to a change in the ink layer thickness, always results in a change in the area coverage of the halftone dots in the respective ink zones . The result of this is that both the measured values for the solid ink densities and the measured values for the screen densities change when the printing process is corrected.

Secondly, there is no clear and also no constant relationship between changes in the ink layer thickness and changes in the area coverage, since the correlations between Constantly change changes in screen densities and changes in solid densities in the course of a printing process. It should be noted that changes in the ink layer thickness have a strong influence on the brightness levels within a given printing ink and a slight influence on the color nuances formed by the interaction of several printing inks and thus on the color balance, while the reverse applies to changes in the area coverage of the halftone dots. A reasonably fixed relationship or correlation between these changes has so far only been found for periods to be measured after minutes, ie for the short-term range. In contrast, for the long-term area, which is measured after hours and is particularly important for the production run, considerable changes in the correlations between changes in the solid and screen densities are found. The reason for this is to be seen in the rheology of the printing inks and thus in their tendency to form halftone dots of different sizes under the influence of temperature and fountain solution supply. Oxidation processes and other phenomena also affect the correlations. This can go so far that in a border area of a long-term printing process, for example, even through very strong changes in the supply of printing ink, combined with a large change in the ink layer thickness, only comparatively small changes in the area coverage of the halftone dots can be brought about, while in another Border area of the same long-term printing process with small changes in the ink supply or the ink layer thickness, large changes in the area coverage of the halftone dots can be achieved. In these cases, the most important size to be observed during the printing process, namely the color balance, is changed or influenced accordingly. It follows that the effect of the aids mentioned, in particular also of the control methods and devices, although these already provide considerable help to the printer because they work according to objective criteria, is actually based on one of two previously possible compromises, namely either to define narrow or comparatively large tolerance ranges for the screen and / or solid densities. When defining narrow tolerance ranges, the color balance can be kept at a sufficiently constant value in the short-term range. However, the printing process often has to be interrupted because changes in the correlations between the screen and solid densities in the long-term range quickly leave the tolerance ranges or the control device becomes uncontrollable because adjustments to the actuators no longer allow the changes in the area coverage of the screen dots required to maintain the color balance . If, on the other hand, large tolerance ranges are specified, there is practically no regulation of the color balance, because the human eye is very sensitive to changes in color shades due to changes in the area coverage of the halftone dots and therefore, according to previous knowledge, the grid densities or area coverage should remain as unchanged as possible. Overall, therefore, the achievement of a uniform printing result still has many shortcomings.

Third, there are considerable problems with the shape, arrangement, number and size of the measuring fields. The actuators of conventional printing presses have widths between 30 mm and 40 mm, so that ink zones of corresponding width are created, a large number of actuators and ink zones being strung together seamlessly. It follows that all measuring fields must be accommodated within a width of 30 mm to 40 mm, provided that each individual color zone is to be examined, evaluated and regulated independently of adjacent color zones, as is desirable in modern printing machines.

The size and arrangement of the measuring fields are subject to two restrictions in practice. On the one hand, they must have a certain minimum size so that the measuring spot of a densitometer can lie completely within each measuring field for at least a time, even if the measurements are carried out on a printing material that is transported at high speed (web offset) instead of on a stationary sheet (sheet offset). On the other hand, the areas of the printing material carrying the measuring fields are cut off after the printing process has ended, so that they represent waste which must be kept as small as possible for economic reasons.

In normal four-color printing with three colorful printing inks (magenta, cyan, yellow) and a achromatic printing ink (black), if both measuring fields in the form of grid fields and measuring fields in the form of full fields are to be used, at least six measuring fields for each of the color zones colored printing inks, but preferably eight measuring fields are provided so that the achromatic printing ink can also be regulated. In addition, there should be further control elements in the form of microline fields, balance fields, trapping fields or the like, which are not required for the control but are useful for the pressure analysis. At least 10 measuring fields and control elements would be desirable per color zone.

On high-speed web printing presses, the measuring fields should have a width of 6 mm to 8 mm so that a reliable measurement result is obtained. If ten measuring fields were used, this would require a space requirement of 60 mm to 80 mm in width, which is about twice the actual width of a color zone. If the ten measuring fields were arranged in a double row, the amount of waste would almost double, which is undesirable for economic reasons alone. So far, the printing result has therefore been regulated either only with raster fields or only with full fields, so that only a total of six measuring fields are required per color zone and all measuring fields can be accommodated in a single row.

The invention has for its object to develop a new strategy with a view to achieving uniform printing results and to design the method and the control device of the genera described in such a way that they are flexible, but subject to tolerances in terms of color balance but subject to tight control and control of the printing process.

A further object of the invention is to propose an aid for the constant control and monitoring of the printing result in the form of a single-color strip set for regulating multicolor offset printing machines in such a way that there are no space problems in the printed control strip and there is little waste on the printed sheet, even if the regulation takes place both with the help of grid fields and with the help of full fields. In addition, it should be possible to provide further measuring fields or control elements without the evaluation of the measuring fields intended for regulating the printing result being impaired thereby.

Finally, it is an object of the invention to propose a further aid for the control of a multicolor printing machine in the form of a device which enables the color balance in the printing result to be determined visually. This device is also intended to help the printer to provide the degree of difficulty of an image to be printed and, depending on the respective economic and technical possibilities, to establish meaningful tolerance ranges for the solid densities and / or screen dot sizes and / or selected relationships.

The method, the control device and the aids according to claims 1, 13, 14 and 18 serve to achieve this object.

The invention is based on the knowledge that the color balance differs not only from the absolute values of the ink layer thicknesses and the area coverage of the halftone dots, but also from the relationships between those in a color zone Liche colors measured area coverage and / or ink layer thicknesses or the resulting screen and / or solid color densities depends on each other. In other words, a color shade formed, for example, from cyan and magenta will change only slightly if the halftone dots of both the cyan and magenta are changed in the same direction within the relevant screen step due to changed printing conditions and, for example, from 50% area coverage to 55% area coverage for Cyan or grow from 40% to 45% magenta. In such a case, the brightness of the color shade should change, but not the color shade itself. On the other hand, the color shade will change itself if the area coverage or screen density of the screen dots are changed in different directions and, for example, the area coverage of cyan is increased from 50% to 55%, but at the same time the area coverage for magenta is reduced from 40% to 35% becomes. The new strategy for achieving a uniform print result therefore first takes into account that selected relationships of the screen densities and / or solid densities of the screen dots are to be kept within preselected, narrow tolerance ranges, in order to largely tolerate changes in the printing inks that are involved in the formation of a color zone to keep changes moving in opposite directions within narrow limits. Since the human eye can only distinguish about 50 different brightness levels of a given color shade, but about 1 million different color shades, an associated change in the brightness of the color shades is less critical than a change in the color shade itself. Apart from this, the new strategy has the significant advantage that the tolerance ranges for the absolute values of the full tone or screen densities can be significantly increased compared to the previous methods. Limiting these absolute values only serves the purpose of increasing the contrast in the print result right to maintain. For if the human eye on H _el - ligkeitsschwankungen less sensitive than react to variations in color, the brightness variations are still not completely negligible because the overall contrast of the solid densities and the color is determined the printing material, while limiting the absolute values of the screen densities or the size of the halftone dots is desirable because it determines the color nuances within the print result. Since the halftone dot changes in halftone image printing take place according to largely known laws, it is usually sufficient, however, to measure a single halftone level, for example at 50%, per printing ink and possibly per ink zone and to define a tolerance range for this. Finally, when using the special relationships obtained from measurement values obtained in combination measuring fields, there is the surprising advantage that their deviations from the values determined on basic colors are considerably smaller than when the absolute values of the halftone dots or solid densities are considered. Therefore, approximation formulas or comparative studies in connection with the selected relationships lead to corrected measured values, which are excellent as a basis for a control process.

The single-color stripe set according to the invention has the advantage that, when three colored printing inks are present per color zone, only a single combination measuring field is required in order to obtain information about the solid densities or screen dot sizes of all the printing inks involved by densitometric evaluation. Even if each combination measuring field has a width of approx. 8 mm and a combination measuring field in the form of a full field as well as in the form of a grid field is provided, only a space with a width of approx. 16 mm within each color zone ne needed to get all information about the solid densities and screen dot sizes of all colored printing inks. There is therefore always enough space to accommodate additional measuring fields and control elements in each color zone. Alternatively, it can also be provided that only two single-color measurement fields are printed one above the other to form a combination measurement field, so that a total of four combination measurement fields appear in each color zone, for which purpose a width of approximately 32 mm is required in the example above.

The densitometric scanning of the combination measuring elements according to the invention leads to relatively imprecise measured values in comparison with those measured values which are obtained on single-color measuring fields. As a result, experts have hitherto avoided the information from combination measuring fields required for controlling a multicolour offset printing press, i.e. so-called mixed colors to win. One reason for the incorrect measured values is that densitometers are not colorimeters and are not suitable for colorimetric determinations. Densitometers are designed to measure color densities of primary colors that are printed separately. A suitable complementary filter is assigned to each basic color, although there are no international agreements regarding the choice of these color filters. If, on the other hand, mixed colors, which are produced by overprinting several primary colors, are densitometrically scanned using such color filters, the result is that the measured values obtained only very poorly match those measured values which are obtained in the same way from separately printed primary colors. This poor correspondence is attributed to so-called secondary color adsorption and other causes and has generally prevented the use of combination measuring fields for control purposes.

In contrast, the invention is based on the surprising finding that the deviations obtained by using combination measuring fields are generally subject to certain laws. It is therefore possible to develop approximation formulas by means of which the erroneous measurement values can be converted into corrected measurement values which correspond fairly exactly to the measurement values obtained on single-color measurement fields. Apart from this, it is possible to produce color tables or color tables with corresponding mixed colors which, in addition to the measured values determined on combination measuring fields, have the correct measured values determined on single-color measuring fields, so that it is easy to compare the incorrect measured values obtained during printing with the color tables or color tables the corrected measured values relevant to the control process can be obtained. Such comparisons can, for example, be carried out automatically by means of a data processing system.

The device for determining the color balance in the printing result has the advantage that the printer, the gray, brown or other mixed tones of the combination measuring fields of the print control strip can be visually assigned directly to a corresponding control element of the device. With an orderly structure of the device, it is then easily possible to estimate or read the deviations from a defined zero point that occurred in the course of the printing process and to adjust the inking units of the printing press accordingly to eliminate these deviations.

According to a further feature of the invention, the actuators are actuated as a function of the current correlation between the changes in the screen and / or solid density. This takes into account the fact that these correlations can change in the course of the printing process NEN, ie a given change in the color layer thickness can be associated with different changes in the area coverage. Another major advantage of the strategy according to the invention for maintaining a uniform printing result is thus that the control process is made more flexible and can be kept controllable over long periods of time by constant adaptation to the changing correlations.

Further advantageous features of the invention emerge from the subclaims.

• Fig. 1 eine schematische Seitenansicht eines einzelnen Druckwerks einer Offsetdruckmaschine;
• Fig. 2 die schematische Seitenansicht einer Vierfarben-Offsetdruckmaschine;
• Fig. 3schematisch eine Draufsicht auf ein Druckwerk einer Offsetdruckmaschine mit einem dieses verlassenden, bedruckten Bogen;
• Fig. 4 den schematischen Aufbau eines Densitometers;
• Fig. 5 schematisch eine erfindungsgemäße Regelvorrichtung;
• Fig. 6 weitere Einzelheiten der Regelvorrichtung nach Fig. 5;
• Fig. 7 schematisch die Wirkungsweise der Regelvorrichtung nach Fig. 5;
• Fig. 8 und 9 zwei Ausführungsbeispiele des erfindungsgemäßen Einzelfarbenstreifen-Satzes;
• Fig. 10 bis 13 schematisch vier Auszüge aus Farbtabellen.
• Fig. 14 eine Vorrichtung zur Ermittlung der Farbbalance im Druckresultat einer Offsetdruckmaschine;
• Fig. 15 ein Koordinatensystem für die Vorrichtung nach Fig. 14;

• Muster A eine farbige Darstellung der Vorrichtung nach Fig. 14; und
• Muster B bis D Farbbilder zur Erläuterung der Vorrichtung nach Fig. 14 in Verbindung mit Farbkontrastklassen.

The invention is explained in more detail in connection with the accompanying drawing and the attached color samples of exemplary embodiments. Show it:

• Figure 1 is a schematic side view of an individual printing unit of an offset printing press.
• 2 shows the schematic side view of a four-color offset printing machine;
• 3 shows a schematic plan view of a printing unit of an offset printing press with a printed sheet leaving it;
• 4 shows the schematic structure of a densitometer;
• 5 schematically shows a control device according to the invention;
• FIG. 6 further details of the control device according to FIG. 5;
• Fig. 7 shows schematically the operation of the control device according to Fig. 5;
• 8 and 9 show two exemplary embodiments of the single-color strip set according to the invention;
• 10 to 13 schematically four extracts from color tables.
• 14 shows a device for determining the color balance in the printing result of an offset printing machine;
• 15 shows a coordinate system for the device according to FIG. 14;

• Sample A is a colored representation of the device according to FIG. 14; and
• Patterns B to D color images to explain the device of FIG. 14 in connection with color contrast classes.

1, a conventional multi-color offset printing machine contains a plurality of printing units, each with a dampening unit 1, an inking unit 2, a plate cylinder 3, around which a printing form 4 carrying the image to be printed, e.g. an aluminum pressure plate is tensioned, a rubber cylinder 5 and a pressure cylinder 6.

The dampening unit 1 is used to first coat the printing formes with 86431 nem thin, uniform water film, and for this purpose has a reservoir 7 from which water is transported to two application rollers 9 by means of rubber rollers 8 covered with fabric, which are applied with light pressure Apply to the printing plate 4 and keep it constantly moist.

The inking unit 2 has the task of constantly supplying the printing form 4 with the required amount of ink. For this purpose, it has an ink fountain 10 which serves as a memory for a printing ink 11 and to which a large number of actuators 12 are attached in the form of zone screws. These actuators 12 are distributed over the entire width of the ink fountain 10 at regular intervals and control the outflow of the printing ink 11 from the ink fountain 10 in such a way that the amount of ink flowing out can be individually adjusted zone by zone over the entire printing width. The ink 11 flowing out of the ink fountain 10 passes via a ductor 13 and a lifter 14 to a number of distribution rollers 15, which have different diameters and are partially axially movably mounted, in order to split and distribute the ink film several times. The printing ink is finally taken over by application rollers 16 which are in contact with the printing form 4 and cover it with a thin ink film.

The printing form 4 carries the image to be printed, the areas which are to be printed being receptive to the printing ink 11 and at the same time water-repellent (hydrophobic), while the areas which are not to be printed are receptive to water (hydrophilic) and do not accept any printing ink 11. Therefore, only the hydrophobic areas of the printing plate 4 are coated with ink by the inking unit 2, while the hydrophilic areas remain free of ink.

The ink is now transferred from the ink-bearing areas of the printing form 4 to the rubber cylinder 5, which lies against the plate cylinder 3 with slight pressure. From the rubber roller 5 the printing ink 4 is finally transferred to a printing material 17 which passes through the gap between the blanket cylinder 5 and the printing cylinder 6. For this purpose, the printing cylinder 6 has a gripper system (not shown in more detail) which has a multiplicity of grippers 18 which are distributed at short intervals over the entire width of the printing cylinder 6 and hold the individual sheets of the printing material while the printing cylinder 6 is rotating.

2 shows the diagram of a four-color offset printing press with four printing units I to IV, printing unit I being assigned to the color black, for example, while printing units II to IV are printing the colors cyan, magenta and yellow, for example. Each printing unit comprises a dampening unit 21, an inking unit 22, a plate cylinder 23, a rubber cylinder 24 and a printing cylinder 25 according to FIG. 1. A number of transfer cylinders 26 is provided in front of and behind the printing cylinder 25. Furthermore, the offset printing machine has at its entrance a storage container 27 for a stack 28 of individual, unprinted sheets 29 of the printing material and a feed table 30, while a storage container 31 for printed sheets 32 is provided at its outlet.

• Die unbedruckten Bögen 29 werden einzeln vom Stapel 28 getrennt und nacheinander auf dem Anlagetisch 30 exakt ausgerichtet. Darauf wird der auf dem Anlagetisch 30 befindliche Bogen 29 vom ersten Übergabezylinder 26 übernommen, der dazu wie der Druckzylinder 25 mit Greifern ausgestattet ist. Der Bogen 29 wird vom ersten Übergabezylinder 26 an den Druckzylinder 25 übergeben, worauf der eigentliche Druckvorgang stattfindet. Während der Drehung des Druckzylinders 25 läuft der Bogen 29 zwischen dem Druckzylinder 25 und dem Gummizylinder 24 durch und nimmt dabei die erste, z.B. schwarze, Druckfarbe auf. Nach dem Druckvorgang wird der Bogen 29 mittels der weiteren Übergabezylinder 26 dem zweiten Druckwerk II zugeführt. Dort wird der Bogen 29 vom entsprechenden Druckzylinder 25 paßgenau übernommene so daß das Druckbild der zweiten Farbe, z.B. Cyan, passgenau aufgedruckt wird. Entsprechend erfolgt der Druck in den Druckwerken III und IV. Nachdem alle vier Farbbilder in vier hintereinander angeordneten Druckwerken auf die Bogen 29 gedruckt sind, werden diese mittels eines Transportbandes 32 dem Vorratsbehälter 31 zugeführt und in diesem gestapelt. Mit modernen Offsetdruckmaschinen dieser Art können pro Stunde ca. 6000 bis 8000 Bogen vierfarbig bedruckt werden.

The operation of such an offset printing machine is as follows:

• The unprinted sheets 29 are individually separated from the stack 28 and exactly aligned one after the other on the feed table 30. The sheet 29 located on the system table 30 is then taken over by the first transfer cylinder 26, which, like the impression cylinder 25, is equipped with grippers for this purpose. The sheet 29 is transferred from the first transfer cylinder 26 to the printing cylinder 25, whereupon the actual printing process takes place. During the rotation of the printing cylinder 25, the sheet 29 runs between the printing cylinder 25 and the rubber cylinder 24 and takes up the first, for example black, printing ink. After the printing process, the sheet 29 is fed to the second printing unit II by means of the further transfer cylinders 26. There will the sheet 29 was transferred from the corresponding printing cylinder 25 with a precise fit, so that the printed image of the second color, for example cyan, is printed with a precise fit. The printing in printing units III and IV takes place accordingly. After all four color images have been printed on the sheets 29 in four printing units arranged one behind the other, these are fed to the storage container 31 by means of a conveyor belt 32 and stacked therein. With modern offset printing machines of this type, approximately 6000 to 8000 sheets can be printed in four colors per hour.

In the plan view according to FIG. 3 of a printing unit of an offset printing machine, only an ink fountain 36 with the actuators 37 also indicated in FIG. 2, a plate cylinder 38 carrying the printing form, a rubber cylinder 39 and a printing cylinder 40 are indicated, all of which are shown over the entire range Extend the printing width of the machine. A printed sheet 41 is still partially on the printing cylinder 40. Because of the actuators 37, the arc 41 is one of the number of actuators corresponding. Number of imaginary, parallel and adjacent color zones 42 printed, which consist of strips 41 extending in the transport direction (arrow v) of the sheet 41. In order to be able to check how thick the color layer applied to the sheet 41 is, measurement fields in the form of raster fields 43 and full fields 44 are also printed on the upper or lower edge of the sheet, expediently at least one raster and full area 43 for each color zone 42. 44 is provided, although each grid or full surface 43, 44 could also extend across the width of a plurality of color zones 42. The grid fields 43 consist of a plurality of grid points of the same size, which have a certain area coverage per unit area of the grid fields. The raster fields 43 are printed by corresponding sections formed in the printing form, which are attached in preselected raster steps with, for example, 25%, 50% or 75% area coverage. From the enlargement or reduction of the halftone dots in the halftone fields 43 with respect to the corresponding sections in the printing form, ge can therefore be taken conclude how the amount of ink set with any actuator has an effect on printing or what changes occur with regard to the area coverage of the halftone dots when the setting of the corresponding actuator 37 changes. The full fields 44, on the other hand, consist of fields that are completely covered with printing ink and are created by corresponding sections in the printing form. The full fields 44 therefore provide information in particular as to whether much or little printing ink has been supplied by means of an actuator 37, because in the full fields 44 only the layer thickness of the applied printing ink can change.

The grid and full fields 43, 44 are examined with the aid of known densitometers, preferably incident light densitometers, in order to achieve objective measurement results. These can be manually operated densitometers (e.g. Macbeth RD-918) or automatically operating densitometers (e.g. Macbeth PXD-981), which are manufactured by Kollmorgen-Macbeth or its subsidiary Process Measurements Inc. in Newburgh, N.Y. (USA) are manufactured and distributed. When using manual densitometers, a sheet 29 is removed from the stack of printed sheets and checked at preselected intervals. If the values determined on the print result differ from those of the original, the printer can try to adjust the measured values again to those of the original by adjusting the actuators. If an automatic densitometer 45 is used, it is expediently mounted on a slide 47 which can be controlled by means of controllable motors, e.g. Stepper motors can be moved back and forth on a rail 48 in the direction of a double arrow w across the width of the arc 41. 2, the rail 48 can be arranged at any point in the transport path of the sheet 29 between the storage containers 27, 31.

If only one measuring station is desired, the sections producing the measuring fields 43, 44 are applied to the printing form in such a way that after the sheets 29 have been completely printed, the associated measuring fields of all printing inks are printed one above the other.

In other words, the single-color measuring fields of all the printing inks used for printing are printed on top of one another with the aid of sections which are attached to the printing plates in the same locations everywhere, in such a way that a single combination measuring element of corresponding shape and size is produced, which is not due to the overprinting has only halftone dots or a solid surface of a single printing ink, but halftone dots or superimposed solid surfaces of all printing inks and therefore has a gray tone. Alternatively, it is also possible to combine the single-color measuring fields from fewer than all printing inks used for printing or, for example, only from two printing inks to form a combination measuring field. According to a preferred embodiment, only the colored printing colors (for example magenta, cyan and yellow) are used to form the combination measuring field, while achromatic colors (for example black) are assigned a single-color measuring field, if such is desired at all. The same procedure can be used for prints other than four-color. It is also possible to provide such combination measuring fields not in all color zones, but only in selected color zones, for example in every second, third, etc. color zone. In any case, the use of combination measuring fields has the essential advantage that fewer measuring fields are required within each selected color zone than printing inks, preferably colored printing inks, so that there is sufficient space in a row and within each color zone to accommodate measuring fields which provide all the information required for the regulation. If, for example, three single-color measuring fields with the basic colors magenta, cyan and yellow are combined to form a brown or gray combination measuring field, then only a third of the space that would be required if three single-color measuring fields were printed side by side. Therefore, if in each color zone there are two brown or gray combination measuring fields, which are used as grid or Full fields can be formed, are provided, of the available width of a color zone from 30 mm to 40 mm only about 16 mm are required for two 8 mm wide combination measuring fields, so that a number of further measuring fields or Control elements can be housed for the same or different purposes. Because wherever a combination measuring field is provided, the associated single-color measuring fields can be omitted.

When using combination measuring fields only, the densitometer 45 is arranged, for example, between the printing unit IV and the storage container 31. In this case, the densitometer 45 is either provided with a beam splitter, by means of which the incident light beam is divided into a plurality of light beams, which are evaluated simultaneously through a plurality of filters and separately from one another, or with a number of filters, in particular complementary filters, which are arranged one behind the other through the light beams one after the other. Other arrangements are also conceivable, provided that it is possible to obtain information about all the printing inks from each combination measuring field. Apart from this, if necessary, suitable and known measures for synchronization can be provided in order to precisely specify the times at which the densitometer takes a measurement.

Alternatively, further measuring stations can be provided between the individual printing units I to IV and the measuring fields of the individual printing inks can be arranged such that they lie next to one another after printing and therefore each printing ink is assigned to a separate measuring field and a separate densitometer to increase the accuracy. Otherwise, the densitometer 45 is expediently connected via a trailing cable 49 to an automatic evaluation station, an electronic data processing system 50 or the like.

A corresponding procedure can be used when using a roller offset machine. Alternatively, a single sheet removed from the machine can be scanned manually or by means of a densitometer that is automatically guided over the sheet.

4, the functioning of the densitometer 45 is shown schematically. From a light source 56, light beams are directed onto the sheet 29 by means of optics 57, e.g. on a raster or full field 43, 44 of a certain printing ink of the same. Part of the incident light rays is absorbed while the rest is reflected and directed onto a color filter 59 by optics 58. This color filter 59 has a color complementary to the measured printing ink (cyan-red, magenta-green, yellow-blue), as a result of which the colored light rays are converted into achromatic or gray light rays. The light rays arrive behind the color filter, a receiver 60, which consists of an opto-electronic converter and converts the light rays into electrical signals. These are then forwarded to an evaluation circuit 61 and processed in the latter. The measurement results obtained can be digitally displayed on a screen 62. The color filter 59 can be arranged together with other color filters within a swiveling or rotating device in such a way that a color filter assigned to the printing ink to be observed can optionally be swiveled into the light beams in order to make manual examinations possible in a simple manner.

The densitometer 45 measures the optical density D, ie the decimal logarithm of the reciprocal of the degree of reflection, which is the quotient of the reflected luminous flux and the incident luminous flux. If the optical density is determined on a raster field 43, the raster density D _{R is obtained} , while the density determined on a solid surface 44 is referred to as solid tone density D _V. From D _R and D _V the so-called optically effective area coverage of the grid points can be calculated in a known manner (Murray-Davies, Jule-Nielson) points are obtained with a microscope or the like. For the purposes of the invention, however, it is important that the screen density, like the optically effective or the mechanical surface coverage, is ultimately only a size that enables a statement about the size of the screen points. The same applies to the concept of halftone dot change, which provides information about the extent to which halftone dots are enlarged or reduced during printing. In the following description and also in the claims, these four terms are therefore summarized under the designation "screen dot size". Otherwise, the grid fields can be provided in different grid levels of, for example, 25%, 50% and 75%, based on their optically effective or mechanical area coverage. The sequence and frequency of the measurements depend primarily on the specific properties of the multicolour offset printing press used and the changes in the printing result that occur in the short or long term. Apart from this, manually operated densitometers are mainly used in the preparation phase in order to obtain the data required for the subsequent production print based on a sample or sample print, while fully automatic densitometers are mainly used for print production.

In addition to a measuring device for actual values in the form of the densitometer 45 (or more densitometers), the control device according to the invention (FIG. 2) includes an actuating device which consists of the sum of all actuators 37. The controlled system is the path of the ink from the ink fountains to the sheets to be printed. The controller of the control device consists of an electronic data processing system 65, to which the measured values measured by the densitometer 45 are fed via a line 66 and which emits the control signals to the actuators 37 via lines 67. % In addition, the data processing system 65 can be connected to a screen 68 on which measured values or the like can be made visible. The data processing system can also be programmed with previously determined control programs and then calculate a suggestion for actuating the actuators 37 according to these control programs based on the measured values either first made visible on the screen 68 or the like and then released by the printer at the command of the latter or, in the case of fully automatic operation, immediately sent to the actuators 37.

An exemplary embodiment of the control method according to the invention is explained below, it being assumed that all measuring fields consist of single-color measuring fields.

Grids 43 (FIG. 3), which are assigned to one or more color zones 42, are also printed from each colored printing ink, for example cyan, magenta and yellow, and possibly also from black. At the beginning of a printing process, a grid value in the form of a grid density or a mechanical or optically effective area coverage of the grid points is assigned to each grid field 43, which defines the desired grid point size in the respective grid field 43. If, as usual, the area coverage of the halftone dots in the section of the assigned printing form producing the halftone field 43 is known, the halftone dot size in the halftone fields 43 can also be defined by the halftone dot enlargement or halftone dot reduction with reference to the halftone dot size on the corresponding section of the printing plate. Each grid field 43 is also assigned a lower and / or upper limit for the grid point size, which define a tolerance range for the grid point size. Furthermore, selected relationships between the halftone fields of two or more printing inks can be defined, e.g. the differences or quotients of the halftone dot sizes to the color pairs cyan / magenta, cyan / yellow and magenta / yellow, whereby usually only the selected relationships for two Color pairs are required because the corresponding relationships of the third color pair result automatically. Here, as with the other sizes, the choice depends on whether the screen densities, the mechanical or the optically effective surface coverage or the screen dot changes are used to define the screen dot size, depending on the properties of the den used sitometer or other measuring devices, the data processing system used, the respective control program, the multi-color printing machine or the like used in individual cases. Then upper and / or lower limit values are also defined for the selected relationships, which define further tolerance ranges. It can be provided that the tolerance ranges for the halftone dot ize ^g during the entire printing process remain constant. However, it is also possible to use the program to specify the data processing system, to repeatedly recalculate the tolerance ranges during the printing process on the basis of the measured values supplied, for example in dependence on changing correlations between the ink layer thickness and the area coverage of the halftone dots.

In a corresponding manner, full fields 44 (FIG. 3) can be printed from each colored printing ink (or also from black), which are assigned to one or more color zones 42. For these full fields 44, guide values, upper and / or lower tolerance ranges defining limit values and, if necessary, selected relationships with associated tolerance ranges are defined in a corresponding manner or are repeatedly calculated using the control program.

If, in addition to the screen dot sizes, the solid color densities are also taken into account in the control program, the data processing system is also correlated between the screen dot sizes and the ink layer thicknesses, the ink layer thicknesses being expediently communicated in the form of the associated full surface densities, since these are representative of the respective ink layer thicknesses. Such a correlation can mean, for example, that an increase or decrease in the solid tone density in the range Dy = 1.20 to D _V = 1.40 by ΔD _V = 0.10 an increase or decrease in the screen density by ΔD _R = 0, 03 corresponds. Here too, the correlation between ink layer thickness or solid color density on the one hand and halftone dot change or halftone dot density on the other hand can be defined by other variables, for example the solid ink density and the associated halftone dot changes in percent the. Different correlations can exist for different printing inks and different areas of solid ink density. In addition, the computer can be informed via the control program that it repeatedly calculates the correlations that can be changed during the printing process from the supplied measured values and that it always uses the instantaneous correlations when calculating its suggestions for actuating the actuators 37.

Finally, the data processing system can be given preselected priorities which must be taken into account when calculating the suggestions for actuating the actuators 37. These priorities can, for example, require that 1) the screen dot sizes and / or solid ink densities must lie within the tolerance ranges assigned to them, 2) the selected relationships for the screen dot sizes and / or solid ink densities of different printing inks must be within the tolerance ranges assigned to them, and 3) the absolute values the dot sizes and solid densities are as close as possible to the specified guide values. The priorities must be set so that the data processing system can make a clear decision in any case. Alternatively, a priority could also be that the data processing system is informed of certain dominances, e.g. state that the calculation of a rule proposal must start with the color on which the greatest deviations in the course of the printing process have been identified, or which, viewed integrally, is most strongly represented in the relevant color zone.

• a) Cyan: D_R (Leitwert) = 0,55, Toleranzbereich + 0,05; D_V (Leitwert) = 1,30, Toleranzbereich ± 0,10;
• b) Magenta: D_R (Leitwert) = 0,45, Toleranzbereich + 0,05; D_V (Leitwert) = 1,30, Toleranzbereich + 0,10;
• c) Gelb: D_R (Leitwert) = 0,45, Toleranzbereich + 0,05; D_V (Leitwert) = 1,30, Toleranzbereich ± 0,10;
• d) ausgewählte Beziehungen:
  • D_R (Cyan) - D_R (Magenta) (Leitwert) = + 0,10, Toleranzbereich + 0,08 - + 0,12;
  • D_R (Cyan) - D_R (Gelb) (Leitwert) = + 0,10, Toleranzbereich + 0,03 - + 0,12;
  • D_R (Magenta) - D_R (Gelb) (Leitwert) = 0,00, Toleranzbereich - 0,02 - + 0,02;
• e) Korrelation zwischen Volltondichten und Rasterdichten: Eine Änderung der drei Volltondichten im Bereich D_V = 1,20 bis D_V = 1,40 um ΔD_V = 0,10 hat eine gleichgerichtete Änderung der Rasterdichte von ΔD_R = 0,03 zur Folge.
• f) Prioritäten:
  • 1) Die Toleranzbereiche für die Raster- und Volltondichten sollen nicht unter- oder überschritten werden. Ergibt die Messung Werte, die außerhalb der Toleranzbereiche liegen, soll ein Vorschlag für eine solche Betätigung der Stellglieder Nr. 24 errechnet werden, daß die Werte wieder in die Toleranzbereiche zurückgeführt werden und nach Möglichkeit auch die Bedingungen nach den Prioritäten 2) und 3) erfüllt sind.
  • 2) Die Toleranzbereiche für die ausgewählten Beziehungen nach d) sollen nicht verlassen werden. Ergibt die Messung Werte, die außerhalb der Toleranzbereiche liegen, soll ein Vorschlag für eine solche Betätigung der Stellglieder Nr. 24 errechnet werden, daß die Werte wieder in die Toleranzbereiche zurückgeführt werden. Dabei soll die Rechnung mit derjenigen Druckfarbe begonnen werden, welche hinsichtlich der Größe D_R am stärksten von ihrem Leitwert abweicht. Der errechnete Vorschlag muß die Bedingungen nach Priorität 1) erfüllen und soll die Bedingungen nach Priorität 3) erfüllen.
  • 3) Wenn die Bedingungen nach 1) und 2) erfüllt sind, aber die Vorschläge noch Alternativen offen lassen, sollen zuerst die Leitwerte der Rasterdichten und dann die Leitwerte der Volltondichten möglichst gut erreicht werden.
  • 4) Erkennt die Datenverarbeitungsanlage keine Regelmöglichkeit, um die Bedingungen nach 1) und 2) zu erfüllen, so wird ein diesbezügliches Fehlersignal abgegeben.

Below is a calculation example for the control of a four-color offset printing press, the inking units of which each have 32 actuators. The example relates to a single ink zone, for example ink zone No. 24, and to the associated actuators No. 24 of the inking units printing this ink zone. The inks cyan, magenta and yellow are considered. The printing forms for these printing inks have a share of 60% printing places for cyan and in the associated ink zone 50% each of the printing areas for magenta and yellow. In addition, the printing forms in this color zone have at least one grid and one full field 43, 44. The densitometer PX-981 from Macbeth is used for density measurement, which measures the measuring fields while the machine is running. The data processing system is informed of the following values for color zone 24:

• a) Cyan: D _R (conductance) = 0.55, tolerance range + 0.05; D _V (conductance) = 1.30, tolerance range ± 0.10;
• b) Magenta: D _R (conductance) = 0.45, tolerance range + 0.05; D _V (conductance) = 1.30, tolerance range + 0.10;
• c) Yellow: D _R (conductance) = 0.45, tolerance range + 0.05; D _V (conductance) = 1.30, tolerance range ± 0.10;
• d) selected relationships:
  • D _R (cyan) - D _R (magenta) (conductance) = + 0.10, tolerance range + 0.08 - + 0.12;
  • D _R (cyan) - D _R (yellow) (conductance) = + 0.10, tolerance range + 0.03 - + 0.12;
  • D _R (magenta) - D _R (yellow) (conductance) = 0.00, tolerance range - 0.02 - + 0.02;
• e) Correlation between full-tone densities and screen densities: A change in the three full-tone densities in the range D _V = 1.20 to D _V = 1.40 by ΔD _V = 0.10 results in a rectified change in the screen density of ΔD _R = 0.03 .
• f) Priorities:
  • 1) The tolerance ranges for the screen and solid densities should not be exceeded or fallen short of. If the measurement yields values that lie outside the tolerance ranges, a proposal for actuating actuators no. 24 should be calculated so that the values return to the tolerance ranges are reduced and, if possible, the conditions according to priorities 2) and 3) are met.
  • 2) The tolerance ranges for the selected relationships according to d) should not be left. If the measurement yields values that lie outside the tolerance ranges, a proposal for actuating actuators no. 24 should be calculated so that the values are returned to the tolerance ranges. The calculation should start with the printing ink that deviates the most from its conductivity in terms of size D _R. The calculated proposal must meet the requirements of priority 1) and should meet the requirements of priority 3).
  • 3) If the conditions according to 1) and 2) are met, but the suggestions still leave alternatives open, first the guide values of the screen densities and then the guide values of the solid densities should be achieved as well as possible.
  • 4) If the data processing system does not recognize a control option in order to meet the conditions according to 1) and 2), then an error signal is issued in this regard.

Bedingung nach Priorität 1) ist für alle-Farben erfüllt.

Bedingung nach Priorität 2) ist für zwei Differenzen nicht erfülltMeasurements in ink zone no. 24 now result in the following measured values, for example, during the print run:

Priority 1) condition is met for all colors.

Priority 2) condition is not met for two differences

The printing ink with the greatest deviation of the screen density from the conductance is magenta with ΔD _R = 0.05. Therefore, an attempt is first made to bring the screen density of magenta back to 0.45. Because of the correlation, however, this would mean that the solid tone density would decrease by approx. 0.167 to D _V = 1.133, so that the condition according to priority 1) would not be met. Even if the screen density was reduced from magenta to 0.46, the condition according to priority 1) would not be fulfilled with D _V = 1.167. If, on the other hand, the screen density of magenta is reduced from 0.50 to 0.47, the condition according to priority 1) with D _V = 1.20 for magenta is fulfilled. Accordingly, the conditions according to priority 1) could also be met by reducing the screen density from magenta to 0.48 and 0.49. However, since priority 3) prescribes that if there are several possible alternatives, the grid density should first be approximated as close as possible to the associated conductance, the value D _R = 0.47 is the best value that can be achieved according to the above control program. It can then be expected that the differences in the screen density will assume the following values in the further course:

The conditions according to priority 2) are all met.

As a result, after calculating all the alternatives, the data processing system suggests reducing the grid density of magenta from 0.50 to 0.47. In the case of off-line operation, this proposal is implemented by the printer using a table in a corresponding change in the actuator 37 for the ink zone no. 24 and the magenta printing inks. The amount to which the actuator has to be adjusted depends on the special printing press, ie it must always be determined beforehand what correlation there is between a change in the position of the actuators and the change in ink layer thickness or solid density achieved thereby. In the case of online operation, the printer only gives his consent by pressing an operating key, whereupon the associated actuator is automatically adjusted by means of a stepping or servo motor or the like.

If a full-tone density for magenta of D _V = 1.24 instead of D _V = 1.30 had been measured according to a variant of the above calculation example, reducing the screen density of magenta to values between 0.45 and 0.48 would result in full-tone densities that do not meet the conditions of priority 1). Only when D _{R is} reduced to 0.49 is the full-tone density with D _v = 1.207 in the required tolerance range, so that the data processing system would recommend reducing the screen density from magenta to 0.49, which would result in the following differences between the Grid densities can be expected:

These values are all within the tolerance ranges according to priority ₂ ).

The examples above show the superiority of the control strategy according to the invention compared to conventional control methods. In the calculation example, it was assumed that the screen densities important for maintaining the color balance had all changed. The change in magenta was relatively large and should have been outside a narrow tolerance range using conventional control devices. As a result of the grid falling out Density of magenta from the tolerance range would have been suggested by the data processing system to change the grid density of magenta to 0.45 or a closely adjacent value. If only the screen density was used as the control variable, it would not have been noticed that the proposed rule simultaneously causes an intolerable change in the solid color density. The same would result if only the full-tone density is regulated, since an increase in the full-tone density for yellow from 1.28 to the conductance of 1.30 at the same time a change in the associated screen density from 0.47 to 0.53 and thus an unnoticed falling out would have resulted in the associated tolerance range. If, on the other hand, both the full-tone densities and the screen densities are used as control variables, then the data processing system could not have calculated a reasonable rule proposal. When using the control strategy according to the invention, on the other hand, it is possible to a) define relatively large tolerance ranges for the absolute values of the solid and screen densities, nevertheless b) maintain the color balance by means of relatively narrow tolerances for the selected relationships, and c) develop reasonable rule proposals by taking the correlation into account . The "selected relationships" serve the purpose of tolerating such changes to one another in the screen densities and / or the solid densities of the printing inks involved that essentially go in the same direction, while largely eliminating changes running in opposite directions. The arithmetic mean of the screen dot sizes and / or solid ink densities of all the colorful and / or achromatic printing inks involved can only be mentioned as selected relationships, for example. Instead of the differences and quotients, other relationships could also be selected and these extended to the relationships between three or more printing inks to one another. The proposed differences and quotients for color pairs have the advantages, however, that on the one hand they can be easily implemented by electrical circuits and therefore can also be calculated automatically using inexpensive switching elements, while on the other hand, closely tolerated changes in the differences and quotients of the screen densities in the associated color cubes practically only result in changes in close to the room diagonals and therefore mainly changes in the brightness of a printed color, but hardly changes the color shade. In contrast to previous control methods and devices, the correlation not only enables a comparison of the absolute values of the screen and solid densities, but also an estimate of the changes caused by an intervention in the printing process with the actuators 37 both with regard to the solid density and also in terms of screen density can actually be achieved. In the case of constant new calculations in the long-term range, the correlation ultimately serves to automatically adapt the control strategy to the changing properties of the printing press.

Details of the process control system of the control device according to the invention are explained in more detail below with reference to FIGS. 5 to 7. The control device initially comprises a densitometer 71, e.g. Macbeth PXD-981, which scans a printed sheet and feeds the measurement data obtained to a measured value concentrator 72, which then forwards the data to a process control system 73. This essentially consists of a setpoint or conductance calculator 74, an actual value or measured value calculator 75 and a manipulated value calculator 76 which is connected via lines 77 to the actuators of ink fountains 78 of a multicolor printing press. The conductance calculator 74 is connected to a number of peripheral devices, e.g. with an operating console 80 having buttons 79, a memory 81 in the form of a magnetic tape, blister, perforated tape memory or the like, a printing unit 82 and a monitor 83, for example in the form of a screen.

The operation console 80 is used to enter commands, in particular those relating to the various guide values, tolerance ranges or the like, into the process control system 73. For example, all data relating to a specific edition, which has already led to a good printing result and in particular includes all the necessary settings for the ink boxes 78 are stored. The pressure Unit 82 can print out the data appearing on monitor 83 or a log of the printing process during a print run. The monitor 83 serves to visualize the respective operating states of the multicolour printing press, suggestions for a control process or the like calculated by the process control system 73. The master value computer 74 processes the data and commands received from the operation console 80 and from the memory 81, compares them with the data determined by the actual value computer 75, works out rule proposals and, if necessary, forwards them in the monitor 83 and after approval by the printer to the manipulated variable calculator 76. The latter then converts this data into corresponding electrical signals, by means of which the actuators of the actuating device, which consists of the ink fountains and their zone screws or the actuators controlling them, are controlled in the desired manner. The measured-value concentrator 72 is connected to the densitometer (s) 71 by means of trailing cables and takes up all the measured values determined by them with a large number of parallel lines 84 in very rapid succession. So that these measured values do not have to be forwarded via a corresponding plurality of lines to the process control system 73 _' , which is usually remote from the multicolour printing machine, the measured value concentrator 72 is arranged directly on the multicolour printing machine, so that it concentrates the measured data supplied and then via a few lines 85 can pass on in series to the process control system 73.

The densitometer 71 is guided over the printed sheet according to a program located in the memory 81, which is fed to it via the conductance calculator 74 and the measured value concentrator 72. The program contains data for the motor, for example, by means of which the densitometer 71 is moved over the printed sheet, as well as data relating to the times at which it is to deliver measurement data and, for this purpose, for example, throws a flash of light on the printed sheet. It can be provided that the densitometer 71 moves gradually from color zone 42 to color zone 42 (FIG. 3) and always after reaching a color zone is then triggered to deliver measured values when a raster or full field 43, 44 or some other measuring field of a printed sheet moves beneath it. In this case, for example, densitometers are used which, when a flash of light is emitted, the reflected light beam by means of a prism, by means of optical filters or the like are immediately broken down into the partial beams assigned to the existing printing inks, so that measured values for all printing inks are obtained per flash of light. According to FIG. 6, all data relating to a printing process can be entered into the conductance calculator 74 with the memory 81 or with the operation console 80. This data is allocated to them. Storage units of a conductance memory 86 are distributed, for example, with the terms "full tone densities", "screen dot sizes", "selected relationships" (what is meant here are their conductance values), "tolerance ranges V, R, B" for the solid density, the screen density and the selected relationships, "correlations", priorities ", color consumption", "color balance", "print type correction" and "color type correction".

For the values already explained above, data relating to the color consumption can thus first be entered. This means the total amount of used printing ink determined within a color zone, which can fluctuate between 0% and 100% for each color. The sensitivity or the response speed of the control process can be influenced via the color consumption. With high ink consumption in a color zone, the adjustment of an actuator will affect the print result faster than with low ink consumption. In the presence of a given difference between an actual or measured value and the desired guide or setpoint value, it may therefore be expedient to initially adjust the associated actuator more strongly with a low color consumption than would be required with a high color consumption, in order thereby to achieve a faster approximation to get the conductance. Apart from this, an adjustment of the actuators can also be made dependent on whether a printing ink is more or less intensive, ie with greater or smaller color layer thickness is applied. A correction value for the control signal supplied to the relevant actuator can thus be entered via the "color consumption" storage unit.

Further corrections for the control signals may prove necessary if there are extreme differences in color consumption and / or color intensity in two adjacent color zones in order to avoid visible changes in these transitions when adjusting the control elements. Finally, the values "printing type correction" and "color type correction" are to be used to generate correction values for the target signals which are required on account of the properties of the printing materials or printing inks used. In particular, it should be taken into account that printing substrates can take up a lot or little printing ink or that the printing inks are applied more or less strongly to the printing substrate due to their rheology under otherwise identical conditions. The actual value calculator 75 contains an actual value memory 87, in particular with storage units for the screen and solid densities measured by the densitometers 71. In addition, storage units can be provided, into which data relating to the "optically effective area coverage", the "mechanical area coverage", the "halftone dot changes" and the "ink layer thickness" are entered. Finally, storage units can be provided in which information is stored which relates to measurement programs, parameters of the raster areas 43 (for example their area coverage in%) or the like. These data are measured by the computer 75 repeatedly executes the grid and _'solid densities determined.

The manipulated value calculator 76 is used to compare the information calculated and supplied by the actual value calculator 75 at certain time intervals or continuously with the guide values or tolerance ranges specified by the conductance calculator 74, based on the priorities or control strategies communicated by the conductance calculator 74 for actuators 88 to be calculated and, if necessary, displayed on monitor 83 or di to be fed directly to the actuators 88, which consist of the zone screws, their servomotors or the like. Each inking unit of the multi-color printing press can have, for example, 32 such actuators. For this purpose, the manipulated value computer has a manipulated value memory 89 with storage units for the information supplied by the conductance computer 74. This information relates, for example, to the starting conditions of the ink ductors or actuators depending on the ink consumption or previously produced, identical or similar editions, as well as correction factors for the printing and / or ink types, compensation factors (e.g. if an ink zone is influenced by an adjacent ink zone, calculated from the Ink consumption), furthermore characterizations of the ink duct openings or the like with the aid of characteristic curves (for example on the basis of the relation ΔOpening / Δ color mass flow) or finally current control strategies, calculated on the basis of priorities or color dominances.

Finally, details of the process control system are shown schematically in FIG. 7. The actual value calculator 75 then contains a computing unit 91 for each color zone, the inputs 92 of which are supplied with the measured values of the screen densities of the available printing inks. These measured values are converted into suitable signals which correspond to the respective actual values and which appear in lines 93. Corresponding computing units 91 can be provided for the area coverage. The computing units 91 for the “selected relationships” between the grid point sizes additionally have difference, divider or other stages 94 in order to form the differences, quotients or the like from two or more measured values.

For each color zone, the master value calculator 74 contains computing units 95, the inputs 96 of which are supplied with the master values or the limit values of the tolerance ranges for the screen dot size and have the stages 97, which calculate the differences from the master and the actual values or only fixedly set whether the actual values lie within or outside the associated tolerance ranges. The data obtained are fed to a microprocessor 98 constructed from programmable matrices, with which the control strategies for the manipulated value computer 76 are calculated with the aid of the correlations and priorities.

For the full-tone densities, similarly constructed computer units 99 can be provided, the inputs 100 of which, for example, the measured and correspondingly converted actual values and the further inputs 101 of which are supplied with the guide values or the limit values of the tolerance ranges. The computer unit 99 has stages 102 which calculate the deviations between the guide and actual values or merely determine whether the full-tone densities are within or outside the tolerance ranges. The corresponding data are also fed to the microprocessor 98. Finally, the information contained in the "priorities" storage units (FIG. 6) is fed to the microprocessor 98 via a line 103. In the example in FIG. 7, it is provided, for example, that a comparator 104, which is also connected to the line 103, is connected in the connecting line between the arithmetic unit 99 and the microprocessor 98 and, for example, specifies as a priority that the microprocessor 98 first processes the data Data of the printing ink whose solid ink density deviates the most from the associated target or guide value should begin.

In the microprocessor 98, the data determined are processed in accordance with the program described above or some other predetermined program, for example stored in the memory 81 (FIG. 5). A proposal is then made for how the actuators should be operated so that all priorities are met. This suggestion is made visible in monitor 83 if necessary and evaluated by the printer. If necessary, 80 corrections can be made via the operating console. Finally, the data calculated by the microprocessor 98 becomes either direct (in the case of fully automatic operation). or after free Handing and possibly correction converted by the printer into control signals for the actuators and then not supplied to linear controllers 105, with a controller 105 being assigned to each actuator. The regulators 105 effect a specific adjustment of the actuators in dependence on the supplied control signals. In this case, further inputs of the controllers 105, for example via lines 106 and 107, can each be supplied with the correction values for the print type or color type correction stored in the corresponding memories of the setpoint computer 74 (FIG. 6). A further correction stage 108 is connected to the outputs of the controllers 105, which has the data of the memory for the color consumption (FIG. 6) via a line 109 and the data of the memory for the color balance with respect to the two adjacent color zones via lines 110 and 111 are fed. The output lines 112 of the correction stage 108 lead to the actuators. It should be noted that the correction stage 108 and the controller 105 _. one of the 32 available color zones and three printing colors, e.g. cyan, magenta and yellow, are assigned and corresponding correction levels and controls must be available for the other color zones.

The invention is not limited to the exemplary embodiments described, but can be modified in many ways. This applies in particular to the various circuits of the control device. With regard to the specified tolerance ranges, it should be noted that these should be chosen so closely that if a measured value falls out of the tolerance range assigned to it, the print result is still within the limits tolerated by the printer or the customer, and that there are also minor deteriorations that occur before full effect of the control device could not lead to the fact that the now printed sheets are unusable. In particular, further limit values could be entered into the process control system which lie outside the tolerance ranges mentioned and prescribe to the process control system that a printing process must be finally stopped if these limit values are reached or exceeded.

The number and frequency of the measurements with the densitometers is largely at the discretion of the person skilled in the art. To increase the measuring accuracy in each color zone, it is advisable to first take several measurements with regard to the solid density as well as the screen densities, for example by measuring five successive sheets and forming an average from the measured values obtained in this way. At most, a period of a few seconds is required for this, during which the properties of a multicolor printing machine generally do not change significantly. From the mean values obtained in this way, rule suggestions for the color zone in question are then calculated. After completing these measurements, the densitometer is set to the next color zone, where the same measurements are repeated on the next sheet passing through. By constantly moving the densitometer back and forth step by step or in cycles across the entire printing width, information about the printing process is continuously collected in this way and rule suggestions are calculated if necessary. In this case, a further memory of the setpoint computer can additionally be informed of the time periods after which, given, for example, the number of sheets passing through, a given control command must be converted into the desired change in the associated control variable. Finally, the changes then actually made to the actuators or the changes in the ink layer thicknesses resulting therefrom or screen densities based on the given control commands and continuously existing between these correlations are re-calculated to thereby system changes when ^- determine pressure and rule proposals always the to be able to use the last measured correlations.

8 shows an embodiment of a single-color stripe set 118 according to the invention, which consists of three single-color stripes 119, 120 and 121. The set or each individual color strip 119 to 121 preferably contains as many zones 122, 123 and 124 in a row and next to one another as color zones in the multi-color offset printing machine used are provided. The upper single color stripe 119 is assigned the color cyan, the middle single color stripe 120 the color magenta and the lower single color stripe 121 the color yellow. The individual color strips are, for example, positive films, which are transferred in a known manner to a designated location of the associated printing form in such a way that they are printed by the individual printing units in succession at the same location on the upper or lower edge of the image and there the so-called. Form pressure control strips.

The single color strip 119 contains a raster element 126 and a solid element 127 in the zone 122, so that corresponding measuring fields appear at the corresponding location of the printing material. The number and shape of the grid points appropriately correspond to a preselected grid. In offset machines today, depending on the type, a 54 or 60 screen is used. However, since it is possible based on the boundary zone theory to mathematically convert the values obtained with 60 rasters into the values that would result with a 54 raster (and vice versa), the same set of single-color strips can be used for both subtleties. Other screen finenesses are also conceivable, since the mathematical conversion is possible at least for screen finenesses that deviate by approximately 10% to 15% from the screen fineness used in printing. The size of the halftone dots, on the other hand, is preselected in accordance with a preselected gray value in such a way that those halftone dots of the individual color strip 119 which lead to areas to be printed on the printing form, e.g. have an area coverage of 50%. The full element 127 is formed so that it corresponds to a. large area with a defined solid color density.

The individual color strips 120 and 121 each have a raster element 128 or 130 and a full element 129 or 131 within zones 123 and 124. Shape and number of halftone dots in the Screen elements 128 and 130 again correspond to the selected screen fineness, whereas the size of the screen dots in these screen elements lead, for example, to area coverage of 41% each. The solid elements 129 and 131 are selected such that areas with a defined solid tone density result from them.

The raster elements 126, 128 and 130 are each arranged in a region of the zones 122, 123 and 124 in such a way that the corresponding sections of the printing forms print at the same location of the printing material. This means that instead of a set of three grid fields in one color per color zone, only a single, gray or brown grid field with a gray value appears, which is composed of the grid levels 50% cyan, 41% magenta and 41% yellow. In a corresponding manner, the three full-tone elements 127, 129 and 131 are also printed on top of one another on the printing material, so that there is also a single measuring field in gray or brown.

The zones 122, 123 and 124 shown in the right part of the single color strip set in FIG. 8 are designed accordingly. In addition, only two of, for example, 28 zones are drawn.

While only two measuring elements are shown in each zone in the set according to FIG. 8, FIG. 9 shows a set 133 of four individual color strips 134 to 137 which are assigned to the colors cyan, magenta, yellow and black. The set or each individual color strip in turn has a length corresponding to the width of the ink zones of the printing press and a correspondingly long zone 138 to 141 for each ink zone. Contrary to FIG. 8, the zone 138 of the single color strip 134 contains two raster elements 142 and 143 and two solid elements 144 and 145. The single color strip 135 contains a raster element. 146 and a full element 147 at the position corresponding to the raster element 142. The single color strip 136 contains at that point of the raster element 143 is a raster element 148 and at the location of the full element 145 Solid element 149. Finally, the single color strip 137 in the zone 141 contains a raster element 150. The arrangement is such that after the transfer of single color strips 134 to 137 to the assigned sections of the printing forms and during printing, the raster elements 142 and 146, furthermore the raster elements 143 and 148, furthermore the full elements 144 and 147 and finally the full elements 145 and 149 are each printed on top of one another, while the raster element 150 is not printed on top of one another with any other measuring element. As a result, measurement fields are obtained on the printing material which contain combined raster information about the colors cyan / magenta or cyan / yellow and combined full tone information about the colors cyan / magenta or cyan / yellow. In addition, a measuring field is obtained which only has information about the color black.

The illustrated embodiments can be modified in many ways. It is sufficient to save as much space in the selected color zones in which information about certain colors is to be obtained by printing at least two measuring elements of the individual color strips on top of one another as is necessary for attaching other measuring or control elements. It is not necessary to assign a corresponding zone on the single color strip set to each color zone. Rather, it is also possible to examine two or more adjacent color zones with a common zone of the single color strip set. Additional halftone and full fields, which are not printed on top of each other with any other halftone or full field, and which are expediently arranged over the entire length of the individual color strips, are used to continuously determine measured values from which the correlations between the halftone dot sizes and solid densities are calculated. These measured values are preferably first collected and then statistically evaluated in order to obtain an average. The computer programs for this are generally known.

If the measurements are carried out on combination measuring fields, the full-tone densities and / or screen dot sizes and / or selected relationships obtained therefrom often deviate from the corresponding values obtained with the aid of single-color measuring fields, which can be attributed to various causes can be performed. Surprisingly, however, it has been shown that the observed deviations are not only significantly smaller if, instead of the absolute full-tone densities and screen dot sizes, only the selected relationships between these, in particular differences, are determined, but are also made negligibly small by simple and schematic corrections to the measured values obtained can. This is particularly true if the deviations in the selected relationships fluctuate only during the printing within the relatively small tolerance ranges specified above, for example. It is therefore in principle sufficient to subsequently subject the measurement values obtained by scanning combination measurement fields to a correction.

In order to produce the desired accuracy in the correction, it is necessary to provide aids in order to bring the measured values obtained on combination measuring fields into agreement with the measured values obtained on single-color measuring fields. Such an aid consists, for example, in a set of mathematical approximation formulas for correcting the measured values.

Another aid is, for example, a color table or color table, which enables the determination of corrected measured values by means of a comparison. It is assumed that the combination measuring field is a grid and has arisen from the combination of the grid levels 50% cyan, 41% magenta and 41% yellow, the percentage values relating to the positive screen films of the single-color strip set which were used in the production of the printing forms (printing plates) are photographically transferred to them and may be subject to changes during this transfer, which, however, can be measured in a known manner.

When printing, e.g. During the production run, color and tonal fluctuations now arise, which should be kept within the desired limits by the control strategy described. The causes of these fluctuations are mainly changes in the sizes of the halftone dots of the individual printing inks, which are usually fluctuations of approximately + 10% with respect to the respective halftone level.

According to the invention, a precise color table is now produced, which comprises a color field which has arisen from the above-mentioned halftone levels 50% cyan, 41% magenta and 41% yellow and also forms the zero point of the printing process, and also a multiplicity of further color fields which consist of combinations of halftone levels in the Neighborhood of the zero point have arisen, e.g. the combinations 50% cyan, 41% magenta, 39% yellow or 50% cyan, 39% magenta, 41% yellow or 48% cyan, 41% magenta, 41% yellow etc., which corresponds to different shades of gray. This color chart is printed under the same or very similar conditions under which the edition to be regulated is printed.

The color table contains both combination measuring fields from two or all three colors as well as the corresponding single-color measuring fields. If the combination measuring fields are scanned with the same densitometer that is also used for printing, three measured values (a so-called number triplet) can be obtained for each of the above-mentioned screen step combinations, the falsified screen dot densities for the three printing colors cyan, magenta and Specify yellow. By correspondingly scanning the single-color measuring fields, a further, unadulterated number triplet can be obtained, which likewise shows the screen dot densities for the three colors, but in the event that the three printing colors have been scanned separately. The two number triplets differ from one another in accordance with those deviations which, according to the above description, are also obtained during printing due to the scanning of combination measuring fields. The color table or the color table can therefore be used to read what changes a number triplet obtained on single-color measuring fields undergoes when it is determined by scanning a combination measuring field or in what way the number triplets obtained on combination measuring fields have to be corrected, to get from them the values corresponding to the unadulterated triplets.

During printing and whenever a regulation of the printing process is required or desired, selected combination measuring fields, which are also printed on the edge of the substrate according to FIG. 8 or 9, are measured using the densitometer, whereby a falsified number triplet is also obtained in each case becomes. For this number triplet, the identical or closest number triplet of the color table obtained and therefore correspondingly falsified is sought. For the control process then but not this Zahlentri is lett ^p, but which is also apparent from the color table, used right, obtained in single-color measurement fields number triplet that meets the true and fair and that includes the here as "corrected values" values designated. From such a comparison, depending on the structure of the color table, not only the correct or corrected absolute values of the screen dot densities, but also all of the values that can be derived from these screen dot densities, such as the changes in the area of the screen dots during printing or compared to the original individual color stripes, the distances of the respective color shade from od a preselected zero, any selected relations like preserver _-.. are th.

The color tables or color tables are expediently produced under similar or the same conditions as for the production print. This means that similar printing materials (papers) and similar colors are used. The various papers can be divided into paper classes which comprise papers with largely similar behavior, so that usually a few, for example three, color charts corresponding to three occurring paper classes should suffice. With regard to the colors, if standardized or standardized printing inks are used, no additional color tables are required, but this could also prove expedient when using non-standardized colors. Reasons other than different papers and colors can also contribute to the fact that additional color charts are required. Corresponding color charts can also be produced with full fields if only or in addition a regulation with measured values of the solid color density is desired. Finally, special color tables or color tables can be provided that only include the values for the selected relationships.

A particular advantage of the color charts described is that by searching for the triplet of numbers obtained when scanning a combination measuring field, it can immediately be determined whether the specified tolerance ranges have to be observed during printing or whether corrective action has to be taken in the printing process. If such a visual-mechanical regulation by an operator is undesirable, the triplet of numbers of the color table can also be stored in a memory of a data processing system and the measurement results can be fed to it repeatedly. In this case, a computer program takes over the search for the corresponding number triplet of the picture plate, the correction of the number triplet and, if necessary, also the regulation or the development of a rule proposal. The correction could be carried out, for example, with the aid of the computing units 91 and 99 shown in FIG. 7, it being possible for a special memory to be provided for the color table or for the approximation formula to be contained in the program located in the memory 81 (FIGS. 5, 6).

An exemplary embodiment of how the corrected values can be obtained by comparison from the measured values determined on combination measuring fields is shown in FIGS. 10 to 13, which each represent small sections of color tables. 10 shows the halftone steps which have the positive halftone films which were used to produce the printing forms. In the top left corner, for example, a number triplet is arranged, which has the grid levels C = cyan = 48%, M = magenta = 38% and Y = yellow = 40%. Fig. 11 shows the same section of the color table, but the Screen densities measured on single-color grids for the number triplets. The number triplet in the upper left corner thus indicates that the number triplet 48/38/40 of FIG. 10 after printing to a number triplet with the screen densities 0.51, 0.40 and 0.42 for the three colored ones Leads inks. The number triplet 0.51 / 0.40 / 0.42 is thus called the correct number triplet. If necessary, the associated optically effective area coverings can be calculated from the values given in FIG. 11 using the Murray-Davies formula, which are shown in FIG. 12 in the same arrangement.

Finally, FIG. 13 shows, again in an appropriate arrangement, those measured values which are obtained after printing on combination measuring fields if the corresponding screen steps according to FIG. 10 are used again for the production of the printing forms. It can be seen from this that values of 0.57 / 0.59 / 0.64 are obtained for the number triplet in the upper left corner, which differ considerably from the corresponding values of FIG. 11 obtained on single-color measuring fields. Therefore, if correct control is to be carried out despite the use of combination measuring fields, then it is necessary to correct the measured values obtained from FIG. 13, for example by automatically replacing them with the assigned and correct values from FIG. 11 with the aid of a data processing system will. A comparison of FIGS. 11 and 13 shows, however, that the number triplets assigned to one another have quite unexpected differences, so that without the color tables it cannot always be clearly estimated how the values of FIG. 13 have to be corrected. For this reason, it is also difficult to find general approximation formulas for the correction of the measured values according to FIG. 13.

From FIGS. 10, 11 and 13 it can also be seen which errors would occur if the numerical triplets of FIG. 13 were used as the basis for the control process. If you compare, for example If the uppermost left with the uppermost right number triplet shows, then a change in density results from FIG. 11 only with respect to the color magenta, namely from 0.40 to 0.44. This is in good agreement with FIG. 10, since there is also a change in the raster level from 38% to 42% for the corresponding number triplets only for the color magenta. FIG. 13, on the other hand, shows that in the case of the corresponding triplet, not only has the color magenta changed from 0.59 to 0.64, that is to say a little more than FIG. 11, but also the color yellow has changed 0.64 to 0.66 is displayed. If the printer alone were to use the values of Fig. 13 for control, it would erroneously try to change the magenta value more than necessary and also change the yellow value, although there is no need to do so. A comparison with FIG. 11, however, indicates to the printer that only the value for the magenta color has to be changed and the change can be smaller than the two triplets of numbers selected in FIG. 13, for example. The color tables or other aids therefore make it possible to use the combination measuring fields, which are very advantageous for other reasons, also for a control process and to obtain the correct measuring values obtained from them so far, which until now could only be obtained by measuring individual barbel measuring fields.

Corresponding tables and comparisons can also be implemented for the selected relationships instead of for the absolute values of the screen or solid densities, for example for the differences in screen densities, by using the values according to FIGS. 11 and 13 for C - M, C - Y and M - G are calculated and compared. From such calculations and comparisons it follows that the deviations for the differences and other selected relationships are generally smaller compared to the application of the absolute values or at least show a certain regularity, so that approximate formulas can be developed in a relatively simple way, that make the use of the color charts or color tables superfluous.

If a number triplet is obtained by measuring on a combination measuring field, which does not appear in the color table, e.g. C = 0.569, M = 0.59 and Y = 0.635, then the number triplet is sought in the color table that the three with these measured values on best matching values. In the example above, this applies to the number triplet in the upper left corner. Apart from this, the color tables according to FIGS. 10 to 13 can of course be combined into a single table, which also contains other useful values _. can be included.

In colorimetry, the sensory, i.e. Assessment of color differences depending on the particular perception of the individual viewer using known formulas according to CIELAB, CIE-USC, Hunter or the like. The color difference is defined as the distance between two color points in the color space. In contrast, with regard to the sensitivity of images, the invention is based on the surprising finding that such assessments of color differences can only be used meaningfully if selected color nuances are compared with neighboring color nuances and no contrasts are effective. This is usually not the case when assessing an image, since images have more or less strong contrasts, which change the perceived assessment of color differences to a very great extent.

• Es wird zunächst ein Testbild ausgewählt, das in seinem Kontrast repräsentativ für eine Gruppe von Bildern mit gleichen oder ähnlichen Kontrastverhältnissen ist. Von diesem Testbild werden in bekannter Weise Reproduktionen und ein Probedruck (vgl. z.B. Muster B,Motiv "Place de la Concorde" oder Muster C, Motiv: Vasen, im beigefügten Farbprospekt "System Brunner PCP Picture Contrast Profile") angefertigt. Wird dieser Probedruck von einem durchschnftlichen Betrachter als farbrichtig, d.h. in der Farbe mit dem Testbild übereinstimmend bezeichnet, dann werden von diesem Testbild Varianten mit vorgewählten Farbabständen hergestellt. Diese Varianten sind dadurch gekennzeichnet, daß beispielsweise die Flächendeckungen der Rasterpunkte jeder Variante von den Flächendeckungen der Rasterpunkte des als farbrichtig bezeichneten Probedrucks in wenigstens einer Farbe um einen festgelegten Wert von beispielsweise 2 %, 4 % od. dgl. abweichen, wobei diese Abweichungen jeweils auf eine vorgewählte Rasterstufe, z.B. die 50%-Stufe, bezogen werden. Die Änderungen für die übrigen Stufen ergeben sich daraus auf bekannte Weise. Damit diese Varianten aussagekräftig sind, muß bei ihrer Herstellung eine große Genauigkeit eingehalten werden. Dazu werden beispielsweise die Flächendeckungen der Rasterpunkte von gerasterten Filmen im Kontaktverfahren fotografisch in vorgewählter Weise verändert und dabei in den Mitteltönen vorzugsweise Genauigkeiten von mindestens 0,5 % eingehalten. Auf diese Weise werden zweckmäßig für die einzelnen Farbauszüge der bunten Grundfarben Cyan, Magenta und Gelb mehrere Filme mit unterschiedlichen Farbabständen hergestellt, wobei die Abstufungen jeweils dort erfolgen sollten oder können, wo für den durchschnittlichen Betrachter eine kritische Akzeptanzgrenze vermutet wird. In den Mustern B und C ist jeweils das Bild in der linken oberen Ecke der farbrichtige Probedruck, die drei anderen Bilder sind Varianten davon.

Up to now it has not been possible to quantitatively assess the color differences of images in the presence of contrasts. However, in order to better define the tolerance range for the control technique described above or another control technique, it would be very useful to know which color differences are just perceived as acceptable for any image, taking into account the existing contrast. In this respect, the invention proposes the following procedure:

• First, a test image is selected that is representative in its contrast for a group of images with the same or similar contrast ratios. Reproductions and a test print (cf., for example, pattern B, motif "Place de la Concorde" or pattern C, motif: vases, in the attached color brochure "System Brunner PCP Picture Contrast Profile") are made in a known manner from this test image. If this sample print is termed color-correct by an average viewer, ie the color matches the test image, then variants with preselected color distances are produced from this test image. These variants are characterized in that, for example, the area coverage of the halftone dots of each variant deviate from the area coverage of the halftone dots of the sample print designated as color correct in at least one color by a fixed value of, for example, 2%, 4% or the like, these deviations in each case a preselected grid level, e.g. the 50% level, can be obtained. The changes for the other stages result from this in a known manner. In order for these variants to be meaningful, great precision must be maintained in their manufacture. For this purpose, for example, the area coverage of the halftone dots of rasterized films are changed photographically in a preselected manner using the contact method, and accuracy in the midtones is preferably maintained at least 0.5%. In this way, several films with different color distances are expediently produced for the individual color separations of the brightly colored primary colors cyan, magenta and yellow, the gradations should or can take place where a critical acceptance limit is suspected for the average viewer. In patterns B and C, the image in the upper left corner is the color-correct proof, the other three images are variants of it.

The variants obtained with the known color differences are now preferably presented to a plurality of viewers individually with the request to designate each variant which can still be accepted. An average is formed from the answers of the different viewers, which is then typical for an average viewer in the assessment of all images that have similar or identical contrast ratios as the associated test image. Since it is known which color distances are assigned to the individual variants, the desired values for the tolerance ranges can be derived directly from these.

Careful quantitative investigations with the aid of the described method have shown that in images which are characterized by strong contrasts, much stronger changes in the color distances are tolerable than was previously assumed, so that relatively large tolerance ranges can be assigned to such image types without these image types of perceived as unacceptable. In contrast, tolerance ranges should be provided for low-contrast images, which are up to three times smaller than those of high-contrast images.

In the case of very low-contrast images, which are predominantly composed of achromatic tones, color differences, which are caused by differences in the halftone dot changes in the three primary colors of the order of 3% to 4%, lead to color differences which the viewer considers to be at the limit of acceptance to be felt lying down. On the other hand, very high-contrast images, which are predominantly composed of pure, complementary, intensive colors, only become at the acceptance limit when color differences caused by differences in the halftone dot changes in the three basic colors are reached perceived lying.

In order to avoid having to produce a large number of variants with preselected color distances for a large number of test images, it is proposed according to the invention to divide a small number of carefully selected, typical test images into a number of image contrast classes, so that in each image contrast class a number of typical images with different subjects, but with the same or similar contrast ratios. Since the experts on the In the field of reproduction and printing technology because of their professional activity in classifying images with similar contrast ratios, they are also able to classify any other image to be reproduced or printed into one of the image contrast classes. The number of variants per test pattern can also be limited to a small number, for example three.

Finally, according to the invention, the individual image contrast classes are assigned tolerance ranges for the control method according to the invention described above. In this way, it is sufficient to divide an image to be reproduced or printed into one of the existing image contrast classes and to use the quantitative tolerance ranges assigned to the respective image contrast class for the control method monitoring the print.

The method described has the essential advantage that the person skilled in the art can use the test images and their variants to show the customer which color variations are possible during printing. Since the tolerance ranges to be observed during printing can be read from the image contrast class assigned to the image at the same time, the specialist can immediately make an offer to the customer about the costs to be expected for his print run, because these are largely determined by the size of the tolerance ranges to be observed. Finally, the customer can still require closer tolerances for images in which relatively large tolerance ranges can be permitted, or, in the knowledge of the higher costs, request narrow tolerances, or deviate from his original desire for the narrowest possible tolerance ranges because of the high costs to be expected and select an image contrast class with larger tolerance ranges. ,

14 and the attached sample A (cf. enclosed color brochure) show a device for determining the color balance in the printing result of a multicolor offset printing machine or for displaying the image contrast classes. The device consists of a hexagon 152, which is constructed from a multiplicity of small control elements 153 which are arranged around a central control element 154 which defines a zero point and is delimited by an outline 155. The control elements 153 preferably consist of hexagons of the same size, which adjoin one another with their side edges. A first group of six control elements 155 to 161 surrounds the central control element 154 in an approximately circular manner, this group being delimited on the outside by an outline 162. The first group is surrounded by control elements 153 of a second group which is delimited by an outline 163 and in turn is approximately circularly surrounded by the control elements 153 of a third group delimited by an outline 164.

The central control element 154 is produced by printing three individual color fields of the three printing colors cyan, magenta and yellow on top of one another. A certain combination of halftone levels is chosen, which should form the zero point of the gray balance or color balance during printing. For example, the 50% level for the color cyan and in each case the 41% level for the colors magenta and yellow are provided in the halftone film used for the production of the printing form.

The control elements 156 to 161 surrounding the control element 154 and representing selected color nuances, on the other hand, have grid levels which differ from those of the zero point in different but defined ways. For example, the upper control element 156 is characterized by a halftone dot enlargement in magenta of 2% and halftone dot reductions of 2% in cyan and yellow. The lower control element 159 is characterized by a 2% reduction in halftone dots in magenta and 2% halftone dot enlargements in cyan and yellow. The upper left control element 161 has a halftone dot reduction of 2% in yellow and halftone dot enlargements of 2% each in magenta and cyan, while the lower right control element 158 has an halftone dot enlargement of 2% in yellow and dot increases of 2% in magenta and cyan. Finally, the control elements 160 and 157 are distinguished by corresponding screen dot enlargements or reductions of 2% each in cyan and corresponding screen dot reductions or enlargements of 2% each in magenta and yellow. The control elements 156 to 161 of the first group are thus characterized in that the area coverage of the halftone dots in the halftone film differs from that of the central control element 154 by exactly + 2% or - 2%.

For the above-mentioned reasons, these deviations in the absolute values of the raster levels or the raster dot sizes are only of limited suitability for defining tolerance limits in the control of a multicolor printing machine, in particular multicolor offset printing press. In addition, a special hexagon 152 would have to be produced for each defined zero point, even if the halftone levels of the colors cyan, magenta and yellow forming the zero point were changed in the same direction and by the same amount and, for example, instead of the zero point defined above with the halftone levels 50%, 41 % and 41% would be a zero point with the screen steps 52%, 43% and 43% for the colors cyan, magenta and yellow.

According to the invention, the proposed control strategy, on the other hand, is based on the idea that a color shade changes only slightly if the screen levels of all the colors involved change in the same direction. This also applies accordingly to the respective zero point and in particular within certain limits. Therefore, the control elements 156 to 161 of the first group are not assigned the absolute values of the screen dot sizes, but rather the selected relationships derived from these, for example the differences which are preferably used, while the screen levels of the control element 154 receive the values "zero", so that instead of C = 50%, M = 41% and Y = 41% now gives C = 0%, M = 0% and Y = 0%. If the difference C - M is referred to as B1, the difference C - Y as B2 and the difference M - Y = B3, the following assignments result:

The differences B1, B2 and B3 for the control elements 159, 160 and 161 can be calculated accordingly. These assignments thus mean that the differences B1, B2 and B3 within the first group differ by a maximum of + 4% or - 4% from those of the central control element 154, for whose differences, by definition, B1 = B2 = B3 = regardless of their actual value 0 applies.

The first group, which contains the control elements 156 to 161, is now referred to as image contrast class X. At the same time, this means that the image contrast class X includes all those images in which the differences B1, B2 and B3 may not change by more than ± 4%, based on the selected zero point, during printing and therefore the tolerance ranges for the selected relationships are set to ± 4%.

In a corresponding manner, the control elements of the second group, which is delimited by the outline 163, can be produced by changing the area coverage of the grid points by + 4% in each case. Differences B1, B2 and B3 are now also assigned to the control elements obtained in this way. Furthermore, the second group is referred to as image contrast class Y, so that it belongs to all those images in which the Differences B1, B2 and B3 during printing may not change by more than + 8% in relation to the selected zero point and therefore the tolerance ranges for the selected relationships (here the differences B1, B2, B3) to + 8% can be set.

In the third group, delimited by the outline 164, the changes in the area coverings are respectively ± 6%, which leads to tolerance ranges for B1, B2 and B3 of + 12%. This group is called image contrast class Z.

Another advantage of the hexagon 152 is that its control elements, like the combination measuring fields in the print control strip (see FIGS. 8 and 9), can also be produced under the same conditions as these. Therefore, the printer can visually assign a combination measuring field of the print control strip to the control element best matching this in the hexagon 152 and from this directly estimate the distance of the combination measuring field from the defined zero point or recognize whether the printed combination measuring field is still within the tolerance range to be observed lies. The coordination system shown in FIG. 15 can serve him as a further aid. In this the lines between the letters M and C mean the values for B1, the lines between the letters C and Y the values for B2 and the lines between the letters Y and M the values for B3. If, for example, a combination measuring field of the print control strip corresponds to a control element 165 of the hexagon in terms of its color shade, it can be immediately read by placing the coordination system according to FIG. 15 on the hexagon 152 that the color shade has the values B1 = 0, B2 = 8 and B3 = 8 are assigned and must therefore be corrected in the printing process if an image is currently being printed that is assigned to image contrast class X. If the measured values C m + 4%, M = + 4% and Y = 0% are determined on a combination measuring field of the pressure control strip, the values B1 = 0, B2 = 4 and B3 = 4 result from this. With the help of the coordinate system it follows that the control element 161 is assigned to this combination measuring field. It can be seen from this that the tolerance range has not yet been left during printing, provided that it is an image that is assigned to image contrast class I. If one were to use the absolute values of the screen dot size instead of the selected relationships, the tolerance range would be erroneously displayed, because within the image contrast class X the deviations of the screen dot sizes compared to the zero point are a maximum of + 2%, but the measured deviations for cyan and magenta are + 4% .

Instead of the selected zero point with the levels 50%, 41% and 41%, zero points with any other level can be selected. Such a zero point can also be any control element 153 of the hexagon 152, since in such a case only the numerical values for the special relationships B1, B2 and B3 need to be changed, as can be easily determined by applying the coordinate system according to FIG. 15 if whose zero point is placed on some other control element instead of the central control element 154. Moreover, the coordinate system can be used to assign a unique triplet of numbers for the values B1, B2 and B3 to each individual control element of the hexagon 152. If the hexagon 152 is produced in other gradations, the coordinate system must be changed accordingly. The same can apply if instead of hexagons other shapes, e.g. Circles, or a completely different spatial arrangement is selected instead of the spatial arrangement of the control elements shown in FIG. 14.

In the enclosed samples B and C (cf. enclosed color brochure), the color-correct printed product is shown in the left upper corner. In the picture in the upper right The corner of magenta is increased by 4%, while the other two colors are reduced by 4% each. In the picture in the lower right corner, the percentage of yellow is increased by 4%, while the percentage of other colors is decreased by 4%. Finally, in the picture in the lower left corner, the cyan component is increased by 4%, while the magenta and yellow components are each reduced by 4%. In the Hexagon 152, the control elements 154, 167, 168 and 169 of the binding contrast class Y are assigned to these four images. The pattern D (cf. enclosed color brochure) finally shows an image in the center corresponding to the central control element 154 of the hexagon 152 and a further six images which are assigned to the control elements 156 to 161 and thus to the image contrast class X in the hexagon.

Studies with the patterns B, C and D have shown that an average viewer only accepts fluctuations in the pattern D (girl) which result from the narrow tolerance ranges of the image contrast class X. In contrast, the color fluctuations in pattern C (vases) are readily accepted. Even the color fluctuations of the image contrast class Z with their large tolerance ranges are still acceptable here. Finally, pattern B (Place de la Concorde) shows excessive variations in the variants and would only be accepted with the tolerance ranges assigned to image contrast class X. It follows that the patterns B and D represent subjects for the image contrast class X, while the pattern C is a subject for the image contrast class Z.

In addition, the tolerance ranges assigned to the image contrast classes can be freely selected and adapted to the respective needs. The class division described is only an example. In addition, more or less than three image contrast classes can be selected and the levels between the individual image contrast classes can be selected differently. Furthermore, the Hexagon 152 can be replaced by a device the one in which the control elements consist of overprinted full fields instead of grid fields. It would also be possible to assign other selected relationships to the individual control elements or to convert the differences in the grid point sizes into other values. Furthermore, it would be conceivable to produce devices of a similar type which are produced by the overprinting of more or less than three individual color fields.

Finally, the invention is not limited to the exemplary embodiments described, which can be modified in many ways.

Claims (21)

1) Method for achieving a uniform printing result on an autotypically working multicolor printing machine, in which the supply of the printing inks to adjacent ink zones of a printing material can be changed by means of actuators and in which, in order to regulate the printing process on measuring fields also printed within the ink zones, solid densities and / or screen dot sizes are repeatedly determined and if the same tolerance ranges fall out of them, corrective intervention in the printing process is carried out by actuating the actuators, characterized in that, in order to maintain the color balance during the printing process, repeatedly selected relationships of full-tone densities and / or screen dot sizes of different printing inks are also determined and also when the selected relationships drop out corrective intervention in the printing process from actuation of the control members is assigned to them. 2) Method according to claim 1, characterized in that measuring fields in the form of raster and / or full areas (43,44) are printed and, as selected relationships, the differences of the raster dot sizes determined on the raster and / or full areas of two different printing inks and / or solid densities can be used. 3) Method according to claim 1 or 2, characterized in that the actuators are operated depending on the correlation between changes in the thickness of the ink layer and the screen dot size. 4) Method according to claim 3, characterized in that the correlation is repeatedly determined during the printing process and the actuators are actuated on the basis of the correlation determined in this way. 5) Method according to claim 1, characterized in that the printing process is stopped when the screen dot size and / or solid density and / or the selected relationships fall out of the assigned tolerance ranges for a preselected time. 6) Method according to claim 3, characterized in that the actuators are operated depending on the correlation so that the screen dot size and / or solid density and / or the selected relationships come as close as possible to preselected guide values. 7) Method according to claim 1, characterized in that groups of tolerance ranges are provided at least for the selected relationships, each group comprising the tolerance ranges determined for a preselected quality of the print result, and that in each case a selected one of these groups of tolerance ranges is used for printing . 8) Method according to claim?, Characterized in that the selection of the group of tolerance ranges is made dependent on the contrast in the image to be printed. 9) Method according to claim 7 or 8, characterized in that a number of image contrast classes are provided with contrasts typical for multicolor images, each image contrast class is assigned one of the groups of tolerance ranges and that group of tolerance ranges is used for printing that corresponds to the image to be printed is assigned to the corresponding image contrast class. 10) Method according to claim 9, characterized in that for each image contrast class, a color-correct sample print of at least one test image with a contrast typical for the image contrast class and a number of variants of the sample print with precisely defined color distances are made by selecting the screen dot sizes and / or solid densities and / or selected relationships in the individual color separations accordingly in the production of the test prints and variants, and that the group of tolerance ranges assigned to the image contrast class is determined on the basis of the color differences. 11) Method according to claim 1, characterized in that measuring fields in the form of combination measuring fields are formed in selected color zones by individual color measuring fields of at least two different printing inks being printed on top of one another, that the combination measuring fields are scanned densitometrically and measurement values are thereby obtained that Corrected values for the solid densities and / or screen dot sizes and / or selected relationships can be obtained from these measured values in order to at least partially correct the errors resulting from the use of the combination measuring fields, and that control signals for the actuators are derived from the corrected values. 12) Method according to claim 12, characterized in that the corrected values are obtained with the aid of a data processing system by using approximate formulas. 13) Control device for achieving a uniform printing result on a multi-color printing machine which works in an autotypical manner and which has a printing form having sections for printing measuring fields for printing on a printing material and an inking unit assigned to a printing ink, which has a large number of actuators for transferring the assigned Printing ink on adjacent color zones of the associated printing form or Printing material is provided, with an actuator comprising the actuators and with a process control system that an actual value computer for processing the measured values repeatedly determined in the form of screen dot sizes and / or solid densities during a printing process, a master value computer for inputting the measured values assigned tolerance ranges and a manipulated value calculator for repeated comparison of the measured values and the tolerance ranges and for proposing actuating signals for the actuating device when the measured values fall out of the tolerance ranges, characterized in that the actual value calculator (75) has computing units (91) for the calculation of selected relationships between the actual values of different printing inks to one another and the conductance calculator (74), a conductance memory (86) for entering tolerance ranges for the selected relationships and microprocessors (98) for repeated comparison of the selected relationships gene and the assigned tolerance ranges and for proposing actuating signals for the actuating device when the selected relationships fall out of their tolerance ranges. 14) Single-color strip set for obtaining information for the control of the inking units of a multicolor offset printing machine printing in a plurality of adjacent color zones, the printing forms of which are provided with sections for printing a print control strip, consisting of a number of single-color strips corresponding to at least the number of colored printing inks used in printing which have single-color elements in selected zones assigned to the color zones, characterized in that these single-color elements (126 to 131 or 142 to 149) are arranged in such a way that in each selected zone of the set (118, 133) at least two , different single-color strips (119 to 121 or 134 to 136) assigned single-color elements by overlaying to form a combination measuring field in the print control strip. 15) set of single color strips according to claim 14, characterized in that the elements leading to combination measuring fields consist of raster and / or solid elements. 16) set of single color strips according to claim 14 or 15, characterized in that grid and solid elements are provided in each zone of the set in such a way that at least one combination grid and at least one full combination field are created in each color zone of the print control strip. 17) set of single color strips according to claim 15, characterized in that the full elements consist of grids near the 100% level. 18) Device for determining the color balance in the printing result of a multicolor printing machine, characterized in that it has a first control element (154), defined as a zero point and preselected by overprinting individual color fields, which is formed by at least a first group of further, by overprinting individual color fields control elements (156 to 161) formed by the same printing inks, the individual color fields which form the first control element (154) having preselected, zero point-defining screen dot sizes and / or solid densities and / or selected relationships, while the individual color fields of the other control elements (156 to 161) of the group of halftone dot sizes and / or solid densities and / or selected relationships which differ from the halftone dot sizes and / or solid ink densities and / or selected relationships of the individual color fields which form the first control element (154) Distinguish preselected but different values and set the limits for tolerable changes in the screen dot size and / or solid density and / or the selected relationships during printing. 19) Device according to claim 18, characterized in that the control element (154) and the other control elements (156 to 161) consist of hexagon of the same size. 20) Device according to claim 19, characterized in that the first group of six control elements (156 to 161) is surrounded by a second group of twelve correspondingly large hexagonal control elements (153) and all control elements are combined to form a hexagon (152). 21) Device according to claim 20, characterized in that all control elements (153, 154, 156 to 161) are formed from single-color elements of the colors cyan, magenta and yellow and that along the three main axes intersecting the center of the first control element (154) and running perpendicular to the side edges thereof respectively, the dot sizes and / or solid densities and / or selected relationships of one of the colors increase in one direction, but decrease in the opposite direction, while at the same time the dot sizes and / or solid densities and / or selected relationships of the other colors decrease in one direction and in increase in the opposite direction or remain unchanged in both directions.

Images