Color management for machine-readable optical codes on printed products

Abstract

The invention relates to a method for printing a printed image comprising at least one machine-readable optical code by means of a printing press. During color conversion of the digital print data of the print image, the digital print data of the at least one machine-readable optical code is converted according to a different means than the digital print data of the remaining print image, the number of print colors of the at least one machine-readable optical code being reduced during the color conversion.

Description

Technical Field

[0001] The invention relates to a method for printing a printed image comprising at least one machine-readable optical code. Background Art

[0002] In the printing industry, various printing methods are known, such as offset printing, flexographic printing, screen printing, inkjet printing and many other methods. The print job data for such printing methods are usually in digital form and include, among other information, information about the desired color reproduction of the printed image. However, the color reproduction data of the printed image cannot usually be realized by the printing press without conversion, because the printing press has a different color space, such as cyan, magenta, yellow, black (CMYK), than the digital data of the printed image. In the prior art, the conversion of color information (also called color conversion) is usually carried out in the prepress stage (Druckvorstufe) by means of ICC profiles.

[0003] Especially when printing product packaging with barcodes or QR codes, the problem arises that the quality of the barcodes and QR codes is affected after the color conversion. After that, these barcodes and QR codes can no longer be read well by the cash register system. In label printing and packaging printing, spot colors (Sonderfarben) that need to be color managed are often used. This often leads to color mixtures that are particularly sensitive to register fluctuations (Passerschwankung) in printing. If the color mixture is adjusted by a relatively open halftone, the color will not be able to be changed. If the barcode is composed of a single pixel, additional edge blurring caused by the printed dots will occur. This further reduces the readability of the barcode and QR code. Simply replacing the color of the barcode or QR code with a high-contrast color (such as black) is not always possible or desirable.

[0004] DE 10 2018 201 669 A1 discloses a method for maintaining the black structure of an object. This document describes a method including a color space conversion, by means of which black image objects (such as barcodes) can be printed on a spot color without negatively affecting the print quality. However, this document does not describe a specific color conversion of the image data of a barcode while reducing the number of its printed colors. Summary of the invention

[0005] The object of the present invention is to provide a method by means of which printed images containing machine-readable optical codes can be printed on a printing press, wherein these codes can subsequently be read optically in an improved manner.

[0006] It has been found that a particularly machine-readable optical code can be obtained on a printing material by color-converting the digital print data of the code according to different measures compared to the digital print data of the remaining print image, wherein the number of printed colors of the code is reduced during the color conversion.

[0007] The method according to the invention is associated with a number of advantages. The color of the code can be used to improve the contour accuracy, thereby improving the readability of the code. The edge of the code can be made clear. At the same time, the primary color can be reduced. Use of The code obtained by the method according to the invention can be optically recognized and read by a machine with an improved error rate.

[0008] Therefore, the present invention relates to a method for printing a printed image comprising at least one machine-readable optical code by means of a printing press, wherein digital printing data of the printed image are provided, wherein the digital printing data of the printed image include digital printing data of at least one machine-readable optical code and digital printing data of the remaining printed image (remaining part of the printed image), the digital printing data of the printed image are subjected to color conversion, and this color conversion includes converting the color of the printed image into the printing color of the printing press, wherein the color-converted digital printing data of the printed image are transmitted to the printing press, and the printed image is printed by means of the printing press using these color-converted digital printing data, wherein, when the digital printing data of the printed image are subjected to color conversion, the digital printing data of at least one machine-readable optical code are converted according to a different method than the digital printing data of the remaining printed image, and the number of printing colors of at least one machine-readable optical code is reduced in the digital printing data of at least one machine-readable optical code.

[0009] A machine-readable optical code is understood to be a printed image on a substrate in printed form, wherein information is encoded in the printed image, which information can be optically captured with the aid of a machine optical device (preferably an electronic scanner, such as a cash register scanner, an electronic handheld scanner or a smartphone) and read with the aid of a computer. In a preferred embodiment, the at least one machine-readable optical code is selected from a barcode and a QR code.

[0010] According to the invention, the digital data of the residual printed image are to be understood as image data which, although color-converted, do not include any image data of a machine-readable optical code. This therefore involves a graphic representation of the content to be printed on the printing material by means of the printing press, but without the graphic representation of one or more machine-readable optical codes present in the original printed image.

[0011] In the method according to the invention, when color conversion is performed on the digital print data of the print image, the digital print data of at least one machine-readable optical code are converted according to a different means than the digital print data of the remaining print image. Accordingly, the digital print data of the at least one machine-readable optical code are subjected to a color conversion different from the color conversion to which the digital print data of the remaining print image are subjected. In particular, the digital print data of the remaining print image are not subjected to a color conversion that reduces the number of print colors of the remaining print image.

[0012] In principle, all types of printing presses are suitable for the method according to the invention. The printing press is preferably selected from offset printing presses, flexographic printing presses, screen printing presses and inkjet printing presses. These printing presses can be configured differently and therefore have different target color spaces. For the method according to the invention, preferably a printing press containing CMYK colors and, if necessary, at least one spot color is used. A spot color is understood to be a color that cannot be obtained by any mixing of CMYK colors. At least one spot color can be, for example, a metallic color.

[0013] According to the method of the invention, in principle, all printing materials known to those skilled in the art for processing in a printing press can be used as printing materials. These printing materials can be in the form of sheets or webs. These printing materials are preferably selected from paper, cardboard and foil.

[0014] In a preferred embodiment, the digital printing data of the at least one machine-readable optical code are distinguished from the digital printing data of the remaining print image by at least one digital marking within the digital printing data of the print image before the color conversion.

[0015] In another preferred embodiment, the color conversion is performed using an ICC profile in the color management module of the prepress stage. In a particularly preferred embodiment, the transformation rules for the color conversion are calculated before the color conversion is performed, the transformation rules are stored in at least one pre-calculated ICC profile, and the color conversion is performed using the at least one pre-calculated ICC profile. In another particularly preferred embodiment, the transformation rules for the color conversion are calculated during the color conversion, the transformation rules are stored in at least one ICC profile, and the color conversion is performed using the at least one ICC profile calculated during the color conversion.

[0016] According to the invention, during the color conversion of the digital print data of the printed image, the digital print data of the at least one machine-readable optical code are converted according to a method in which the number of print colors assigned to the at least one machine-readable optical code in the digital print data is reduced. In a preferred embodiment of the method according to the invention, the number of print colors is reduced to only one color.

[0017] In a preferred embodiment, the digital printing data of at least one machine-readable optical code are converted according to a method in which at least one digital printing data of the machine-readable optical code is assigned at least one area coverage having an increased area coverage. In this context, a printing color with increased surface coverage is understood to be one whose surface coverage is increased compared to a pre-set printing color that has not been color-converted according to the invention. By targeting the use of as few printing colors as possible from the existing color supply of the printing press for at least one machine-readable optical code and at the same time using at least one color with high surface coverage, a particularly good outline reproduction of the machine-readable optical code is achieved, thereby achieving a particularly good readability.

[0018] In another preferred embodiment, the digital printing data of the at least one machine-readable optical code are converted according to such a method: at least one printing color with increased contrast is assigned to the digital printing data of the at least one machine-readable optical code. In this case, a printing color with increased contrast is to be understood as a printing color whose contrast is increased compared to a predetermined printing color that has not been color-converted according to the invention.

[0019] In another preferred embodiment, during the color conversion of the digital print data of the print image, the color impression of the at least one machine-readable optical code is brought as close as possible to the color impression of the remaining print image. For example, when printing a package with a barcode, such a package can have large areas of the same color tone (for example, green tone) in the remaining print image. The barcode itself should then be printed as much as possible in the same green tone, but according to the invention using a reduced number of print colors. Thus, during the color conversion of the print data of the barcode, a color combination with a reduced number of print colors is selected, which color combination corresponds to the color impression of the green-toned surface in the remaining print image as far as possible when mixing the colors.

[0020] The printed image obtained according to the method of the present invention can be printed on different substrates to make different printed products. In a preferred embodiment, the printed image is selected from a printed image for a commodity package (preferably a commodity package for food, cosmetics or other consumer goods) with one or more bar codes.

[0021] In a preferred embodiment, the method according to the invention can be carried out as follows. The digital printing data of the printed image are passed to a color management module (Color Management Module, CMM) in the prepress stage together with a digital mark of the digital printing data of at least one machine-readable optical code. Based on this digital mark, a special color management is carried out, in which: i) a minimum number of printing colors are used for the color construction of the code, and ii) care is taken to use sufficiently high-contrast colors with a high area content as base colors ( Farbe). This high area share can be related to the dot It can also be related to dot gain or increased tonal value. Because in printing, this area or region It should be largely a solid area with slight edge modulation. And iii) if necessary, the permissible color deviations can be adjusted as required in order to better achieve the goals set according to points i) and ii), since the machine-readable optical code is individual and therefore not large-area, so direct color calibration for the human eye is limited.

[0022] In another preferred embodiment, the method according to the invention can be carried out as follows. In the document preparation at the prepress stage, the machine-readable optical code or the color used for the machine-readable optical code is marked and transferred to the color management module (CMM) with the help of corresponding tags. The color to be reproduced is processed in the color management specifically for the readability of the machine-readable optical code, wherein sufficiently high-contrast primary colors are used as base colors with a sufficiently high area share and the number of additional primary colors used is reduced to a minimum without falling below a certain quality limit in terms of color difference. For elements marked as machine-readable optical codes, the color management module performs a special color conversion, which can deviate from the color separation rules defined in the ICC profile. For this purpose, the printing process characteristics given by A2Bx in the ICC profile are used. Therefore, the color recipe is optimized for the color impression to be reproduced of the element, wherein, in addition to the chromatic distance between input and print, the color separation characteristics related to the machine readability of the element are also taken into account. Unlike the general color separation rules of the ICC profile, strong changes in the color separation for two similar input color positions are allowed here, because gradients are not to be treated. Color separation is performed so that the best color separation can be used for each input color position independently of the environment. In the method described here, the above-mentioned special color separation (Separation) for the input color position of an element can be calculated directly at the initialization of the color conversion of the print job. Therefore, the optimization of the color separation is only performed for one input color position used in the element. Alternatively, in a preparation phase that can occur directly when generating an ICC profile for the output process, the special color separation is calculated in a tabular manner for the entire input color space. The table can be stored as another conversion rule together with the generated ICC profile. The special color separation rules can also be stored in a second ICC profile as a color separation tag, wherein the second profile should only be used for the color separation of elements marked as machine-readable optical codes. When using tabular conversion rules for marked machine-readable elements, the color management module is placed in a special interpolation mode, in which the color separation of exactly one grid point (Gitterpunkt) of the table is used for each input color position to be interpolated. By means of this interpolation mode, it can be ensured that even at input color positions that do not coincide with the grid points of the table, no color separation with unfavorable characteristics is produced by combining two optimized color separations. With the aid of the unmodified ICC profile of the output process and the color separation rules optimized for machine-readable elements, a device link profile can be calculated. By applying this device link profile, a color separation optimized for machine readability can be generated from ordinary color separations. Even when applying this device link profile, the color management module preferably uses such an interpolation mode: in this interpolation mode, the color separation is output to exactly one grid point. Alternatively, such a device link profile can be generated, which has a high-resolution stepped input lookup table (LUT), so that each CMYK tuple (Tupel) consisting of 8-bit values ​​falls on exactly one grid point of the 4-dimensional CLUT after applying the input LUT. The described method can be expanded with an evaluation unit in a workflow system. The evaluation unit simulates the output of a machine-readable element and evaluates the machine readability of the element based on a soft proof, for example according to the specifications of the ISO 15415 standard. This can be done before the print job is output, so that the printer can decide whether adjustments are needed before output based on this information. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The flow chart of a preferred embodiment of the method according to the present invention is shown schematically. DETAILED DESCRIPTION

[0024] Figure 1The process of a preferred embodiment of the method according to the invention is schematically shown. The printing data of the entire printed image (1) are present in digital form in the prepress stage. The printing data of the entire printed image (1) include digital printing data of a machine-readable optical code (3) and printing data of the remaining printed image (2) without the code. The printing data of the code (3) are color-converted (5) in the color management module of the prepress stage using an ICC profile calculated directly during the color conversion, wherein the number of printing colors used by the code is reduced. Alternatively, the ICC profile for the color conversion is precalculated in an intermediate step (6), and then the color conversion of the code is performed (7) using the precalculated ICC profile, wherein the number of printing colors used by the code is reduced. The printing data of the remaining printed image (2) are subjected to a conventional color conversion (4). The printing data obtained after the color conversion is stored in a file (8), which contains all data for a print job of a printing press. The document (8) is transferred to a printing press and a complete printed image (1) is printed (9), which includes the printing data of the code (3) and the printing data of the remaining printed image (2). As a result, a printed printed page (10) is obtained with a printed code (12) and a printed remaining printed image (11). Due to the special color conversion of the code (3), the code can be read optically in a particularly advantageous manner.

[0025] Reference numerals list

[0026] 1Digital printing data of printed images

[0027] 2 Digital printing data of the remaining printed image

[0028] 3Digital printing of data in machine-readable optical codes

[0029] 4Color conversion of the digital print data of the remaining print image with the help of ICC profiles

[0030] 5Color conversion of digital printed data of machine-readable optical codes with the aid of ICC profiles calculated during color conversion

[0031] 6 Pre-computed ICC profiles for color conversion of machine-readable optical codes

[0032] 7Color conversion of digital printed data of machine-readable optical codes with the help of pre-calculated ICC profiles

[0033] 8. Printing job files

[0034] 9 Printing printing jobs with the help of printing press

[0035] 10 printed pages

[0036] 11 Remaining printed images

[0037] 12Printed machine-readable optical code

Claims

1. A method for printing a printed image comprising at least one machine-readable optical code by means of a printing press, wherein: Providing digital printing data of the printing image (1), wherein the digital printing data of the printing image (1) includes digital printing data of the at least one machine-readable optical code (3) and digital printing data of the remaining printing image (2), performing color conversion on the digital printing data of the printing image (1), wherein the color conversion includes converting the color of the printing image into the printing color of the printing press, wherein the color-converted digital printing data of the printing image (1) is transmitted to the printing press, and the printing image is printed with the color-converted digital printing data by means of the printing press, It is characterized in that When the digital printing data of the printed image (1) is subjected to color conversion, the digital printing data of the at least one machine-readable optical code (3) is converted by a method different from that of the digital printing data of the remaining printed image (2), and the number of printing colors of the at least one machine-readable optical code (3) is reduced in the digital printing data of the at least one machine-readable optical code (3).

2. The method according to claim 1, wherein: The at least one machine-readable optical code is selected from a barcode and a QR code.

3. The method according to any one of the preceding claims, wherein: Prior to the color conversion, the digital printing data of the at least one machine-readable optical code (3) are distinguished within the digital printing data of the print image (1) from the digital printing data of the remaining print image (2) by at least one digital marking.

4. The method according to any one of the preceding claims, wherein: When using ICC profiles, color conversion is performed in the color management module in the prepress stage.

5. The method according to claim 4, wherein: A conversion rule for color conversion is calculated before color conversion is performed, the conversion rule is stored in at least one ICC profile, and color conversion is performed using the at least one ICC profile calculated in advance.

6. The method according to claim 4, wherein: A conversion rule for color conversion is calculated during execution of color conversion, the conversion rule is stored in at least one ICC profile, and color conversion is performed using the at least one ICC profile calculated during color conversion.

7. The method according to any one of the preceding claims, wherein: When color conversion is performed on the digital printing data of the printed image (1), the digital printing data of the at least one machine-readable optical code (3) is converted according to the following means: in this means, at least one printing color is assigned to the digital printing data of the at least one machine-readable optical code (3), and the at least one printing color has an increased surface coverage.

8. The method according to any one of the preceding claims, wherein: When color conversion is performed on the digital printing data of the printed image (1), the digital printing data of the at least one machine-readable optical code (3) is converted according to the following means: in this means, at least one printing color is assigned to the digital printing data of the at least one machine-readable optical code (3), and the at least one printing color has an increased contrast.

9. The method according to any one of the preceding claims, wherein: When color conversion is performed on the digital printing data of the printed image (1), the digital printing data of the at least one machine-readable optical code (3) are converted according to the following means: in this means, at least one printing color is assigned to the digital printing data of the at least one machine-readable optical code (3), and the color impression of the at least one machine-readable optical code is made to be as close as possible to the color impression of the remaining printed image by means of the at least one printing color.

10. The method according to any of the preceding claims, wherein: The printed image is selected from printed images used for commercial product packaging having one or more bar codes.

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