Method for the color control of a printing machine

Abstract

The invention relates to a method for color control of a printing press by means of a computer, in which spectral data of a printing material is determined using a color measuring device, the spectral data of the printing material being determined both in the form of polarization spectral data and in the form of non-polarization spectral data, and the computer performs color control of the printing machine based on the polarization spectral data and the non-polarization spectral data.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for color control of a printing press by means of a computer, wherein the color control is based on polarized and non-polarized spectral data of a color measuring device. BACKGROUND

[0002] In the printing industry, various printing methods are known, such as offset printing, flexographic printing and screen printing. When performing a printing job, it is often not possible to achieve an acceptable printing quality from the beginning. It is generally necessary to perform several printing processes and to discard some pages or web segments as debugging waste before the desired printing quality is achieved. In order to reduce waste as much as possible, it is desirable to achieve an acceptable printing quality as quickly as possible. At this point, the optimal setting of the color control of the printing press plays a central role. A common method for controlling the quality of the printed product during a printing job is to use color measuring devices for measurements, which can be arranged inside or outside the printing press. For example, the color measuring devices can be compact devices that can be carried by the operator.

[0003] DE 102 57 981 A1 describes a method and a measuring device for color control of a printing press based on spectral reflection values of a printing surface element.

[0004] EP 1 154 247 A2 describes a color measuring device that can simultaneously collect polarized and non-polarized measurement data.

[0005] DE 10 2010 004 417 A1 describes a method for color control of a printing press, in which color measurement values are measured with and without spectral filters. The method is used to compensate for the influence of optical brighteners in the substrate.

[0006] In the printing industry, there is still a need for methods that can improve the color control of a printing press, in particular to reduce or avoid debugging waste. SUMMARY

[0007] Surprisingly, it has now been found that improved control of the color of a printing press can be achieved by analyzing unprinted substrate material using a color measuring device, while collecting the determined spectral data in polarized and non-polarized form, and setting the color control of the printing press based on both types of measurement data.

[0008] By means of the described measuring method, conclusions can be drawn about the surface parameters of the printing material, such as roughness, texture and ink absorption. In particular, the surface roughness can be determined therefrom, which has a decisive influence on the optimum setting of the color control. The reason for this is that light scattered at the printing material surface and entering the measuring optical system of the color measuring device provides different measurement values depending on the roughness of the printing material surface. By comparing the measurement values of the light entering the measuring optical system without a polarizing filter with the measurement values obtained with a polarizing filter, conclusions can be drawn relatively simply about the roughness of the printing material surface measured.

[0009] If necessary, additional camera images of the printing material can also be taken and by evaluating the pixels thereof using statistical methods, additional conclusions can be drawn about the roughness of the printing material surface and the acquired spectral data can be additionally taken into account in the color control.

[0010] The acquisition of the spectral data can be simple. For this purpose, it is possible to use, preferably, commercially available color measuring devices, such as handheld measuring devices, which usually also have a camera function for taking images of the printing material.

[0011] By means of the method according to the application, the operator can correctly classify the printing material used from the beginning of the printing job and optimize the adjustment of the color control of the printing press with the aid of the computer. Thereby, it is possible to reduce or completely avoid the adjustment waste.

[0012] Accordingly, the application relates to a method for color control of a printing press with the aid of a computer, wherein spectral data of a printing material are determined using a color measuring device, characterized in that the spectral data of the printing material are determined not only in the form of polarized spectral data but also in the form of non-polarized spectral data and the color control of the printing press is carried out by the computer on the basis of the polarized spectral data and the non-polarized spectral data.

[0013] According to the application, the color control of the printing press is carried out by the computer. In other words, the computer influences the color control of the printing press and adjusts the color control parameters of one or more printing units. The aim is to set and, if necessary, to readjust the color control in order to achieve the best printing quality on the printing material and thus to produce no waste. As an important parameter of the color control adjusted according to the application, it is possible to mention, for example, the ink quantity.

[0014] In a preferred embodiment, the computer calculates correlation parameters on the basis of the polarized spectral data and the non-polarized spectral data and performs the color control of the printing press on the basis of the correlation parameters. These correlation parameters establish a link between the polarized and non-polarized spectral data. In a particularly preferred embodiment, the computer calculates characteristic curves for one or more color pre-settings of a printing unit of the printing press on the basis of the correlation parameters and performs the color control of the printing press on the basis of these characteristic curves. In a very particularly preferred embodiment, the computer compares these characteristic curves with values in a database and performs the color control of the printing press on the basis of the comparison with the values in the database. The values in the database are preferably determined beforehand by comparative measurements.

[0015] In a preferred embodiment, the color measurement device is a color measurement device for acquiring spectral reflectance values. Such a measurement device is known, for example, from the above-mentioned EP 1 154 247 A2. The spectral data acquired according to the application are therefore preferably spectral reflectance values.

[0016] In another preferred embodiment, the color measurement device is a mobile color measurement device, also referred to as a handheld measurement device. The operator can use it, for example, to examine a printed sample taken from a running printing process at the printing press console.

[0017] In another preferred embodiment, the polarized spectral data are determined by the color measurement device with the use of at least one polarizing filter and the non-polarized spectral data are determined by the color measurement device without the use of a polarizing filter.

[0018] In another preferred embodiment, the polarized spectral data and the non-polarized spectral data are determined at the same location on the printing material.

[0019] In another preferred embodiment, the polarized spectral data and the non-polarized spectral data are determined at an unprinted location on the printing material. In a particularly preferred embodiment, the polarized spectral data and the non-polarized spectral data are determined at the same unprinted location on the printing material.

[0020] In another preferred embodiment, the printing material is a printing material having a high surface roughness, particularly preferably paper. In a very particularly preferred embodiment of the application, the printing material is recycled paper.

[0021] In another preferred embodiment, the color measurement device additionally takes a camera image of the printing material, evaluates the taken camera image and takes the evaluation of the taken camera image into account in the color control of the printing press. The evaluation can be carried out according to the principles of statistical image evaluation known in the art, in particular the evaluation of grayscale images.

[0022] In another preferred embodiment, the roughness of the printing material is determined when evaluating the taken camera image. In a particularly preferred embodiment, the roughness of the printing material is determined by a statistical method for analyzing the camera image pixels. Here, image analysis methods known in principle from the art can be used.

[0023] In another preferred embodiment, the printing press in which the color control is carried out is selected from the group consisting of offset printing presses, flexographic printing presses and screen printing presses. In a particularly preferred embodiment, the printing press is selected from the group consisting of offset printing presses. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A preferred embodiment of the inventive method is schematically shown.

[0025] Figure 2 A flowchart of a preferred embodiment of the inventive method is schematically shown. DETAILED DESCRIPTION

[0026] Figure 1 A preferred embodiment of the inventive method is schematically shown. The printing material 3 is measured by a color measuring device 4, wherein non-polarized spectral data 6, polarized spectral data 5 obtained using a polarization filter 7 and a camera image 9 are captured and transmitted to a computer 2. The computer 2 is connected to a database 8 in which reference values are stored. The computer 2 takes into account the non-polarized spectral data 6, the polarized spectral data 5, the camera image 9 and the reference values in the connected database 8 and optimally sets the color control of the printing press 1 on this basis. Thereby, little waste or no waste at all is produced when a print job is started in the printing press.

[0027] Figure 2 A flowchart of a preferred embodiment of the inventive method is schematically shown. In step I, the printing material is prepared, in steps II, III and IV, non-polarized and polarized spectral data are captured by a color measuring device, and a camera image of the printing material is also captured by the color measuring device. Subsequently, in step V, the data are transmitted to a computer, which optimally sets the color control in the printing unit of the printing press on the basis of the obtained measurement data and camera image.

[0028] LIST OF REFERENCE SIGNS

[0029] 1 printing press

[0030] 2 computer

[0031] 3 printing material

[0032] 4 color measuring device

[0033] 5 polarized spectral data

[0034] 6 non-polarized spectral data

[0035] 7 polarization filter

[0036] 8 database

[0037] 9 camera image

Claims

1. A method for color control of a printing press (1) using a computer (2), wherein a color measuring device (4) is used to determine the spectral data of the printing substrate (3), characterized in that, The spectral data of the printing substrate (3) is determined not only in the form of polarized spectral data (5) but also in the form of non-polarized spectral data (6), and the computer (2) performs color control of the printing press (1) based on the polarized spectral data (5) and the non-polarized spectral data (6).

2. The method according to claim 1, wherein, The computer (2) calculates relevant parameters based on the polarization spectral data (5) and the non-polarization spectral data (6), and performs color control of the printing press (1) based on the relevant parameters.

3. The method according to claim 2, wherein, The computer (2) calculates a feature curve for color presetting of one or more printing units of the printing press (1) based on the relevant parameters, and performs color control of the printing press (1) based on the feature curve.

4. The method according to claim 3, wherein, The computer (2) compares the feature curve with the values ​​existing in the database (8) and performs color control of the printing press (1) based on the comparison with the values ​​existing in the database (8).

5. The method according to any one of the preceding claims, wherein, The color measurement device (4) is a color measurement device used to collect spectral reflectance values.

6. The method according to any one of the preceding claims, wherein, The color measurement device (4) is a mobile color measurement device.

7. The method according to any one of the preceding claims, wherein, Polarized spectral data (5) is determined by color measurement device (4) using at least one polarization filter (7), and unpolarized spectral data (6) is determined by color measurement device (4) without using polarization filter (7).

8. The method according to any one of the preceding claims, wherein, Polarized spectral data (5) and non-polarized spectral data (6) are determined at the same location on the printing material (3).

9. The method according to any one of the preceding claims, wherein, Polarization spectral data (5) and non-polarization spectral data (6) are determined at the unprinted positions on the substrate (3).

10. The method according to any one of the preceding claims, wherein, The printing material (3) is a printing material with high surface roughness.

11. The method according to any one of the preceding claims, wherein, The camera image (9) of the printing substrate (3) is additionally captured using a color measurement device (4), the captured camera image (9) is evaluated, and the evaluation result of the captured camera image (9) is taken into account in the color control of the printing press (1).

12. The method according to claim 11, wherein, Camera images were captured in grayscale format (9).

13. The method according to any one of claims 11 or 12, wherein, When evaluating the captured camera image (9), the roughness of the substrate (3) is determined by a statistical method used to analyze the pixels of the camera image (9).

14. The method according to any one of the preceding claims, wherein, The printing press (1) is selected from offset printing press, flexographic printing press and screen printing press.

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