JPH09193361A - Measuring point regulating method for scanning of printing image for controlling or adjusting inking in printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for automatically find out a measuring point for scanning of a printing image for controlling or adjusting an inking in a printer. SOLUTION: In this method, a coordinate of a measuring color value and a measuring point is derived from an image data for reproducing all printing images and a measuring point for scanning of the printing images for controlling or adjusting an inking in a printer is decided. By using a model which expresses a relationship between the color measuring value and an adjusting quantity of an adjusting element which influences the inking, a measuring point which exceeds a critical value whose change in measuring color value is designated by simulation of a predetermined change of adjusting quantity is automatically selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining measuring points for scanning a printed image for controlling or adjusting inking of a printing press.

[0002]

2. Description of the Related Art Inking of printed products depends on various factors such as the thickness of ink printed by an offset printing machine and the proportion of dampening water in an emulsion of ink and dampening water. Depends on. From the scanning signal at a given measuring point, the actual value of the physical quantity that allows a determination as to the actual state of inking should be derived. These actual values are compared with the target value of each physical quantity. From these comparison values, the control signals for the control elements are derived, which control signals influence the ink application in the desired manner. Especially when scanning a printed image at a high printing speed, it is necessary to limit the number of measuring points to a reasonable number because of the large amount of information to be processed by the control device.

PCT patent application publication specification WO 95/0
0336A2 already describes a method which makes it possible to automatically find suitable measuring points from an image signal. An image signal obtained in forming a print image in a pre-printing stage or an image signal obtained by an image capturing device provided in a printing machine during printing can be used. These image signals are
It is sent to a computer system containing a program that automatically selects the relevant measurement points. With this program, the printed image is analyzed according to the relevant parameters. For example, in a printed image, a place where gray tone is dominant or a place where color is almost independent is obtained. Further, an appropriate measurement point is found in a place where the contrast and the colorimetric value are drastically changed in the printed image.

However, the method of determining the measurement point in this way causes a dynamic adjustment characteristic peculiar to the printing press, for example, an adjustment characteristic curve or a frequency characteristic of an adjusting element arranged at the rear stage of the controller, or an abnormality. It does not take into account the dynamic behavior of the regulator or the regulatory element when. In other words, the measuring points selected exclusively according to the printed image are not always optimal for the adjustment of the particular ink or the adjustment of the watering.

[0005]

SUMMARY OF THE INVENTION The object of the invention is to automatically find a measuring point suitable for adjusting the ink deposit. When determining the measurement points, the dynamic adjustment characteristics specific to the printing press should be taken into account. Further, the present invention should allow for rapid adjustment and improved print quality.

[0006]

According to the invention, the above problem is solved by a method as characterized in claim 1.

The present invention is a model that expresses the relationship between a colorimetric value and an adjustment amount for an adjustment element that affects inking, and is based on simulating a change in a predetermined adjustment value. For each physical quantity to be controlled or adjusted, a model is used which incorporates the adjusting characteristics specific to the printing press. The adjusting characteristics can then be adapted to the conditions that actually prevail on the printing press. For example, temperature,
Air humidity and ink viscosity can be measured and these measured signals can be used for model formation. By doing so, it is guaranteed that each model is almost perfectly matched to the actual press or the actual printing conditions.

The present invention is advantageous in that the measurement points are already selected before printing. There is no need to manually enter measurement points or perform test runs during the test printing stage. The measuring point is optimal for the physical quantity to be controlled or adjusted in each case.

A variant of the invention has the method feature as claimed in claim 2. By specifying a limit value for the resulting change in the colorimetric value, only those measuring points which give the optimum actual value signal for the physical quantity to be controlled or adjusted are selected. Measuring points that show only a slight sensitivity to certain physical quantities are not taken into account during the printing process.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

The diagram of FIG. 1 shows an offset printing press 1 for producing multicolor printing. In order to achieve the desired printed image, the individual printing units 2, 3, 4 are equipped with an ink adjusting device 5, 6, 7, for the ink thickness S, a fountain solution in an emulsion consisting of ink and fountain solution. The adjusting elements 8, 9, 10 and the registration devices 11, 12, 13 for the quantity of the are provided, which are all associated with the machine control device 14. At the exit of the offset printing machine 1, an image-taking device 15 is arranged which completely captures the surface of the printing-completed sheet 16 on the cylinder 17. Image capturing device 1
5 and the offset printing machine 1 are also connected. The machine control device 14 includes a circuit configuration for processing an image signal of the image capturing device 15 and a computer equipped with a storage device and a program system. Can be defined from the signal.

The work steps required to define the measuring points will be described below with reference to the flow chart shown in FIG.

In the first stage 18, a mathematical model F = f (s) is defined in the machine controller 14. This model is a function f, indicating that within a certain band the colorimetric value F depends on the opening size s of the individual adjusting elements of the ink adjusting devices 5, 6, 7. It is assumed that the ink film thickness S can be adjusted in the printing units 2, 3, 4 or in the zone on the sheet 16 as realized in a general offset printing machine 1. The colorimetric value F can be converted as color coordinates (L, a, b) in the Lab color system. Using the image-taking device 15, the sheet 16 can be scanned over a large number of measuring points in one raster area. These raster elements can be square and one side can be, for example, 3.2 mm. The coordinates of the raster elements define the possible measuring points. As noted in step 19, for each raster element, the colorimetric values are defined as color coordinates in the Lab color system.

In this embodiment, the image signal for reproducing the print image is taken out from the image photographing device 15. These image signals can be obtained from a device that generates a print image in a pre-printing stage or an original drawing scanner arranged outside the offset printing machine 1.

In the next step 20, the partial derivative dF / ds of the colorimetric value F according to the size s of the aperture is calculated for each raster element and each of the inks C, M and Y used. Partial derivative dL / (ds.C, ds.M, d
s. Y), da / (ds.C, ds.M, ds.Y) and db / (ds.C, ds.M, ds.Y) are obtained.

This embodiment is limited to the three color inks C, M and Y. However, this method can also be applied in principle to printing using three or more colors.

In step 21, a weighting factor G is assigned to each raster element according to the color coordinates. For example, a raster element whose color coordinates are in the critical range, eg red, gets a greater weighting than a raster element whose color coordinates are in the non-critical range, eg yellow. The critical range or the non-critical range means a hue whose change is perceived by the human eye very quickly or slowly.

In the next step 22, the weighting factor G is modified according to the position of the raster element. For example, raster elements in the center of a band are weighted more strongly than raster elements at the edges of a band.

Further modification of the weighting factor G is performed in step 23 depending on the contrast around each raster element. At this stage 23, raster elements with very non-uniform perimeters are weaker weighted.

The weighting G can also be subject to another modification. Examples include corrections depending on the dynamics or disturbing factors of the colorimetric values in an area.

In a further step 24, the partial derivative F'multiplied by the weighting factor G is compared with the limit value _F'Grenz . If the respective weighted partial derivative F ′ exceeds the limit value F ′ _Grenz , then in step 25 the coordinates of the raster element are stored as measurement points. For the inquiry in step 26, the above method steps apply to all raster elements. Once this procedure has been carried out for all raster elements, in the final step 27 the parameter image containing all the coordinates of the raster element is stored and these coordinates are used for actual control or adjustment of inking during production. You will get the colorimetric value of.

By this method, selection is made from a large number of possible measurement points. By doing so, it is ensured that only particularly useful colorimetric values are obtained at such measuring points. By reducing the number of measuring points, the speed of inking control or adjustment is increased without compromising the adjustment accuracy.

In this embodiment, the ink adjusting devices 5, 6, 7 are used.
2 shows the definition of the measurement points from which the processed signal is obtained. This method can be applied to control or adjust any physical quantity that affects inking.

Examples include adjusting the amount of dampening water using the adjusting elements 8, 9, 10 and registering using the registering devices 11, 12, 13. In this case, independent mathematical models can be defined in step 18.

Another embodiment will be described with reference to the flowchart shown in FIG.

In the first step 28 the mathematical model F = f
After (s) has been defined, the following step 29 is the partial derivative F'for all inks C, M, Y involved.
= DF / ds is calculated. In the next step 30, the colorimetric values F are classified according to the size of the partial derivative F ′ and the table LUT
Stored in. As already explained in the previous example,
In step 31, the colorimetric value is La for each raster element.
b Defined as color coordinates in color system, steps 32, 3
3, 34 are weighted depending on the color coordinates, the position of each raster element within the band and the contrast around the raster element. In step 35, for each ink C, M, Y and each band, have the maximum weight,
Alternatively, the coordinates of the raster element that exceed the values in the table specified for each ink are stored as measurement points. By doing so, in the ideal case, for each ink and area there will be exactly one measuring point for the physical quantity to be adjusted. These measuring points are stored as parameter images in step 36 and are used in the final printing.

[Brief description of the drawings]

FIG. 1 is a diagram showing an arrangement for processing measured values.

FIG. 2 is a float chart showing the procedure of the method of the present invention.

FIG. 3 is a float chart showing the procedure of a modified example of the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printing machine 2, 3, 4 Printing unit 5, 6, 7 Ink adjusting device 8, 9, 10 Adjusting element 11, 12, 13 Registration device 14 Machine control device 15 Image capturing device 16 Sheet paper 17 Body

Continuation of the front page (71) Applicant 390009232 Kurfuersten-Anlage 52-60, Heidelberg, Fedé ral Republish of Germany (72) Inventor Harald Bucher, Germany 74927 Eschelbronn Finkenwerk Vener 5 (72) Inventor Germany 69231 Lauenberg Dambach-La-Willestraße 2d (72) Inventor Bernd Kistler Germany 75031 Eppingen Kartenbergstraße 46

Claims (2)

[Claims] 1. A measurement point for scanning a print image for controlling or adjusting inking of a printing machine by deriving a colorimetric value and coordinates of the measurement point from image data that reproduces the entire print image. In the method, a model expressing the relationship between the colorimetric value and the adjustment amount for the adjustment element that affects the ink deposit is used to determine the limit value for which the change in the colorimetric value is specified in the simulation of the change in the predetermined adjustment amount. A method characterized by automatically selecting measurement points that exceed. 2. A colorimetric value that exceeds a limit value for a change in the colorimetric value is determined as a threshold value for each of the adjustment elements that affect the inking, by a simulation of a change in a predetermined adjustment amount. The derived colorimetric value is compared with the colorimetric value derived from the print image, and if the derived colorimetric value is around the specified colorimetric value, the measurement point of the derived colorimetric value is measured. The method according to claim 1, wherein is set as a measuring point for obtaining the actual value of the physical quantity to be controlled or adjusted.