METHOD FOR COLOR CORRECTION OF A DIGITAL PRINTER

Description

[0001] The present invention relates to a method for color correction of a digital printer.

[0002] An apparatus for carrying out the method and a use of the method are disclosed but not claimed.

[0003] Color correction methods for digital printers are well known. These methods identify deviations from the expected print result and take them into account during printing so that the print more closely matches the expected print result.

[0004] A major problem with digital image output is the color and density differences caused by printing artifacts across the print width of a printer, which often become visible as banding in the print direction, especially with the same color ("solid color"). There are many reasons for this. For example, the print dot size (droplet size in inkjet printing) is never exactly the same across the entire width of a print head and from print head to print head. Furthermore, the positioning accuracy of each print dot is subject to varying tolerances, thus altering the tonal value originally desired by ripping. Furthermore, especially in inkjet printing, spray mist settling on the substrate can alter the desired color and density values.In inkjet printing in particular, varying flow behavior, especially on non-absorbent materials, due to different print head positions in the direction of travel and their distance from the pinning or final drying stages, can adversely affect print density. Furthermore, especially in inkjet printing, print dropouts (nozzle errors) can negatively impact the visual appearance of the print result.

[0005] To determine the position and intensity of these printing artifacts, test images are printed and analyzed. The information obtained can then be used for correction in a variety of ways. In this context, published patent application DE 10 2016 224 303 A1 discloses a nozzle test pattern for an inkjet printing machine, which, in addition to a first element, contains a second element with stripes of varying area coverage.

[0006] However, one problem with this type of correction data determination is that the results achieved are often insufficient. In particular, the homogeneity achieved by the correction in the individual colors is sometimes not achieved to the same extent when printing together. This poses a major problem, especially when printing essentially solid-color images, because any remaining deviations are particularly noticeable and lead to clearly visible banding in the printing direction.

[0007] Color correction methods for digital printers therefore still offer potential for improvement. This potential can be seen particularly in color correction for essentially solid-color prints and in reducing banding in the print direction.

[0008] It is therefore the object of the present invention to provide an improved method for color correction of digital printers.

[0009] This object is achieved by the method for color correction of a digital printer according to claim 1.

[0010] Preferred embodiments of the invention are specified in the subclaims.

[0011] Aspects of the invention relate to a method for color correction of a digital printer across a print width of the digital printer, wherein the digital printer is provided for outputting a predetermined digital image, the method comprising the steps of: a) Providing the predetermined digital image, wherein the digital image has at least one color channel image, wherein each color channel image is assigned to a printing ink channel of the digital printer; b) Determining at least one test color of the predetermined digital image; c) Creating a digital test image, wherein the digital test image is provided with at least one solid-color test strip which is intended to be printed across the printing width of the digital printer, wherein each solid-color test strip is defined by a print density of at least one printing ink channel of the digital printer according to the following steps: i) Determining a print density intended for printing the test color from at least one printing ink channel of the digital printer, and ii) Determining the print density determined in step i) as the print density of the solid-color test strip; d) Printing the digital test image with the digital printer;e) detecting the colour values ​​of the printed test image as a function of their position in the direction of the print width using an optical colour measuring device; f) creating correction data for the digital printer based on the detected colour values; and g) applying the correction data to the digital printer and / or the specified digital image.

[0012] For the purposes of the present invention, a digital printer is understood to mean, in particular, a device that can output colored printing dots on a substrate that form the corresponding image.

[0013] For the purposes of the present invention, a digital image is understood to mean, in particular, a digitally storable image whose image information is determined by pixels, each of which has a color value with respect to a color system. A predefined digital image, for the purposes of the present invention, is a digital image intended for printing.

[0014] In step a) of the method, the predetermined digital image is provided, wherein the digital image has at least one color channel image, wherein each color channel image is assigned to a printing ink channel of the digital printer.

[0015] For the purposes of the present invention, a color channel image is understood to mean, in particular, a part of the digital image that contains only the information relating to one color channel of the color system in which the digital image is stored. For example, the digital image can be defined using color values ​​in the CMYK color system, and a color channel image, for example, contains only the color values ​​of the C color channel.

[0016] For the purposes of the present invention, a printing ink channel is understood to mean, in particular, a color channel in which the printer can print. For example, the printer can be designed for printing in the CMYK color system, and a printing ink channel can be the C color channel.

[0017] In other words, it is particularly provided that the digital image is composed of color channel images that correspond to the print color channels of the digital printer. For example, it can be provided that the digital image in the CMYK color system is determined via the color channel images of the C color channel and the M color channel, and the printer is a printer that can print in the CMYK color system. Thus, the print color channels C and M are respectively assigned to the color channel images C and M of the digital image.

[0018] In step b) of the method, at least one test color of the given digital image is determined.

[0019] For the purposes of the present invention, a test color of the given digital image is understood to be a color of the given digital image or a color that is similar to a color used for the method according to the invention. In particular, a test color of the given digital image for the purposes of the present invention is understood to be a color value that occurs in the digital image or is similar to a color value of the given digital image. For the purposes of the present invention, a similar color or a similar color value is understood to be a color or a color value that does not exceed a certain Delta E value compared to the color or color value to which it is supposed to be similar, i.e. does not exceed a certain color difference.

[0020] Preferably, it can be provided that the test color determined in step b) is a main color of the given digital image.

[0021] For the purposes of the present invention, a main color of the given digital image is to be understood as meaning, in particular, a color value that has a significant proportion in the digital image.

[0022] Further in step c), a digital test image is created, wherein the digital test image is provided with at least one plain-coloured test strip which is intended to be printed across the print width of the digital printer, wherein each plain-coloured test strip is defined by a print density of at least one print ink channel of the digital printer according to the following steps: i) determining a print density intended for printing the test color from at least one print color channel of the digital printer, and ii) determining the print density determined in step i) as the print density of the solid-color test strip.

[0023] For the purposes of the present invention, a digital test image is understood to mean a digital image.

[0024] For the purposes of the present invention, a single-color test strip is understood to mean, in particular, an area of ​​the digital test image that has a single color value and extends transversely to the printing direction of the digital printer.

[0025] For the purposes of the present invention, the fact that each solid-color test strip is determined via a print density of at least one print ink channel of the digital printer means, in particular, that the solid-color test strip has a color value that, like the specified digital image, is defined via the color channels that correspond to the print ink channels of the digital printer. Accordingly, the test strip can be defined at least via one color channel that corresponds to a print ink channel of the digital printer and, at most, via all color channels that correspond to the print ink channels of the digital printer.

[0026] For the purposes of the present invention, print density is understood to be the combination of print dot density and print dot size. For the purposes of the present invention, print density can be perceived as color saturation.

[0027] For the purposes of the present invention, the print density can also correspond to a color value in a printed image and can be measured analogously. For example, the print density can be measured with a spectrophotometer. Alternatively, the print density can be measured with a scanner, for example, an RGB scanner. In this case, it can preferably be provided that the print density is determined via the value of a measured complementary color. Advantages thus arise from the combination of an RGB scanner with a CMYK printer and the solid-color test strips created according to the invention.

[0028] In particular, the print density intended for printing the test color is determined, with the print density being determined by at least one print ink channel of the digital printer. This print density is then determined as the print density of the solid-color test strip.

[0029] Thus, for example, it can be provided that the test color is defined via three color channels, for example, via CMY color channels, whereby the printer has the CMYK printing color channels, and the print density of the C color channel of the test color is determined in step i) and defined as the print density of the solid-color test strip in step ii). Alternatively, for example, the print density of the C and M color channels of the test color can be determined and defined as the print density of the solid-color test strip.

[0030] In step d) the digital test image is then printed with the digital printer.

[0031] In step e), the color values ​​of the printed test image are recorded with an optical colorimeter depending on their position in the direction of the print width.

[0032] In the context of the present invention, this is to be understood in particular as meaning that the optical color measuring device detects the color of the printed test image across the print width and assigns a color value measured at that point to each position across the print width.

[0033] In step f), correction data for the digital printer is created based on the recorded color values.

[0034] In step g), the correction data is applied to the digital printer and / or the specified digital image.

[0035] This means, in particular, that correction data are created by determining deviations from the color values ​​determined by means of the optical colorimeter to the expected color values ​​of the digital test image depending on their position in the direction of the printing width, and when the correction data is applied, the specified digital image and / or the digital printer are modified accordingly in order to counteract the determined deviations.

[0036] The method described above makes it possible to achieve a particularly effective reduction of printing artifacts for the given digital image, particularly banding in the printing direction in digital images with a high proportion of solid colors. This makes it possible, in particular, to print large-area decorations, such as stone decorations, with particularly high precision. Compared to known methods for color correction in digital printers, the method described above also makes it possible to reduce banding caused by deviations in the print dot size (droplet size in inkjets) across the width of a print head and between print heads.Furthermore, the method described above can be used to reduce artifacts that arise, in particular, in inkjet printing due to spray mist settling on the substrate or due to different flow behavior, especially on non-absorbent materials, due to different positions of print heads in the direction of travel and their distance from the pinning or final drying.

[0037] Preferably, it can be provided that the printing of the digital test image with the digital printer in step d) takes place on a printing substrate which is the same printing substrate on which the predetermined digital image is to be printed.

[0038] This makes it possible to correct effects caused by the substrate in particular through color correction.

[0039] According to the invention, that at least one plain-colored test strip is defined by the print density of all the print ink channels of the digital printer, wherein in step i) the print density of all the print ink channels of the digital printer intended for printing the test color is determined; and / or at least one plain-colored test strip is defined by the print density of an individual print ink channel of the digital printer, wherein in step i) the print density of an individual print ink channel of the digital printer intended for printing the test color is determined; and / or at least one plain-colored test strip is defined by the print density of more than one and less than all the print ink channels of the digital printer, wherein in step i) the print density of more than one and less than all the print ink channels of the digital printer intended for printing the test color is determined.

[0040] In a preferred embodiment, it can therefore be provided that at least one solid-coloured test strip is defined by the print density of all print ink channels of the digital printer, wherein in step i) the print density of all print ink channels of the digital printer intended for printing the test colour is determined.

[0041] This means in particular that the plain-colored test strip has the same color value as the test color.

[0042] This advantageously allows color correction to be performed by printing all the colors used for the test color across the entire print width. This can, in particular, reduce artifacts that arise in inkjet printing due to overspray settling on the substrate or due to varying flow behavior, especially on non-absorbent materials, due to different print head positions in the direction of travel and their distance from the pinning or final drying stages.

[0043] Alternatively or additionally, in a preferred embodiment, it can be provided that at least one solid-colored test strip is defined by the print density of an individual print ink channel of the digital printer, wherein in step i) the print density intended for printing the test color is determined by an individual print ink channel of the digital printer.

[0044] This advantageously reduces artifacts caused by variations in dot size (droplet size in inkjet) across the width of a printhead and between printheads. In particular, artifacts attributable to a single ink channel can be reliably identified and corrected.

[0045] Further alternatively or additionally, in a preferred embodiment, it can be provided that at least one solid-colored test strip is defined by the print density of more than one and less than all print ink channels of the digital printer, wherein in step i) the print density intended for printing the test color is determined by more than one and less than all print ink channels of the digital printer.

[0046] This advantageously ensures that artifacts resulting from the combined printing of fewer than all ink channels can be reliably identified and corrected.

[0047] In a preferred embodiment, the digital test image can be provided with at least one of the aforementioned solid-color test strips. This can advantageously ensure that the correction is particularly successful. Without being bound by any theory, it is assumed that the combination of these test strips allows the source of the printing artifacts to be identified with particular certainty, thus enabling a color correction that delivers particularly good and stable results.

[0048] Preferably, it can be provided that in step b) more than one test color is determined and the digital test image is provided with at least one solid-colored test strip for each specific test color.

[0049] This makes it possible to reduce banding in multi-coloured digital images even in areas of different colour values.

[0050] Preferably, it can be provided that the digital test image for at least one test color of the predetermined digital image is provided with at least two solid-color test strips and preferably the number of solid-color test strips for the at least one test color of the predetermined digital image is less than or equal to the number of color channels of the digital printer, wherein preferably for the at least one test color a solid-color test strip is defined via the print density of a single print color channel of the digital printer, a solid-color test strip is defined via the print density of all print color channels of the digital printer, and the optionally remaining solid-color test strips are defined via the print density of more than one and less than all print color channels of the digital printer.

[0051] This makes it possible to keep the number of test strips low, which makes it easier to calculate the correction data and at the same time covers a sufficient number of color combinations to achieve very good results for color correction across the print width.

[0052] Preferably, it can be provided that the color channels of the digital printer have a printing sequence, wherein the solid-color test strip, which is defined by the print density of an individual printing color channel of the digital printer, is defined by the print density of the printing color channel to be printed first according to the printing sequence.

[0053] This makes it possible to start the color correction with the first color to be printed, which, without being bound to a theory, simplifies further correction in particular, as overlapping of different effects when applying the correction is avoided.

[0054] Preferably, it can be provided that the single-coloured test strips, which are defined by the print density of more than one and less than all print colour channels of the digital printer, are selected such that a first of these plain-coloured test strips is defined by the print density of the printing ink channel to be printed first in the printing sequence and additionally by the print density of the printing ink channel to be printed next in the printing sequence, and optionally each further of these plain-coloured test strips is defined by the print density of the respective previous plain-coloured test strip and additionally by the print density of the printing ink channel to be printed next in the printing sequence.

[0055] This makes it possible to combine printing ink channels in the test strips in such a way that only one printing ink channel is added from a first to a second test strip, so that the color correction can be calculated particularly easily and reliably.

[0056] For example, it can be particularly preferably provided that four printing ink channels are provided for printing a test color, for example CMYK, wherein the printing ink channels are printed in the order C, M, Y and K. The digital test image can then particularly preferably have four solid-color test strips, wherein the first solid-color test strip is defined by the print density of the C printing ink channel provided for printing the test color, the second solid-color test strip is defined by the print density of the C and M printing ink channels provided for printing the test color, the third solid-color test strip is defined by the print density of the C, M and Y printing ink channels provided for printing the test color, and the fourth solid-color test strip is defined by the print density of all CMYK printing ink channels provided for printing the test color.In particular, it can be provided, for example, that several test colors of the given digital image have been determined and the previously described plain-colored test strips are determined for each test color.

[0057] This allows color correction to compensate for artifacts caused by individual print head rows as well as artifacts caused by printing multiple colors together, using a particularly small number of test strips. In particular, this ensures that color correction reliably and accurately accounts for these artifacts without the need for complex calculation methods to separate the effects.

[0058] According to the invention, the test colors are selected from the colors that occur most frequently in the given digital image, with a minimum distance in the color space optionally being maintained between several test colors.

[0059] This allows for reliable color correction with just a few test colors. Minimum color space differences can be determined, for example, using a Delta E value or a histogram.

[0060] Preferably, it can be provided that steps d) to g) are carried out iteratively several times in succession.

[0061] This allows the color correction to achieve a particularly homogeneous print result. It is understood that in an iterative process, where step g) involves applying the correction data to the specified digital image, the correction data are applied accordingly to the digital test image.

[0062] Particularly preferably, steps d) to g) can be performed iteratively until the correction result is sufficiently good. In particular, steps d) to g) can be performed until the color values ​​acquired in step e) are sufficiently homogeneous across the print width or the correction values ​​determined in step f) are sufficiently small.

[0063] Optionally, the success of the process can be checked by printing the specified digital image with the appropriate correction data applied.

[0064] Preferably, it can be provided that the optical color measuring device is selected from the group consisting of a color sensor, a colorimeter, a spectrophotometer, a digital camera or a spectrodensitometer, wherein the optical color measuring device is preferably based on the same color model as the digital printer.

[0065] In a preferred embodiment, it can be provided that the color measuring device only measures relative color deviations across the print width and / or the correction data for the digital printer only takes into account relative color deviations across the print width.

[0066] In other words, the color correction can be configured not to measure the deviation of the printed solid-color test strips from the expected color, but only to measure color fluctuations of the printed solid-color test strips across the print width. This allows the color correction to compensate for printing artifacts particularly efficiently without being limited by the color fidelity of the print itself.

[0067] Preferably, it can be provided that step e) is optionally carried out several times in succession with different settings of the optical color measuring device, in particular under different lighting conditions and / or exposure times.

[0068] This ensures that even very small variations in the color of the printed test strips can be detected.

[0069] In a preferred embodiment, the test image can be provided with positioning aids. This allows the detection of the color values ​​in step e) to be correlated particularly precisely with the print width, thereby enabling the color correction to be carried out particularly accurately.

[0070] It can be provided that the test strips have different thicknesses in the printing direction, whereby the thicknesses can be practically selected so that the test strips can be easily detected by the optical color measuring device used. Furthermore, it can be provided that the test strips run across the entire printing width of the digital printer. This allows, in particular, color correction across the entire printing width. Alternatively, the test strips can also be provided only for sections of the printing width, for example, for sections across the width of the optical color measuring device or the width of individual print heads. This allows the method to be adapted to the specific conditions of the printer and the color measuring device.

[0071] Preferably, it can be provided that in step g) the correction data are applied to the printer, wherein in particular the correction is carried out by adapting the print head electronics.

[0072] Preferably, it can be provided that in step g) the correction data are applied to the predetermined digital image, wherein in particular the correction is carried out by adjusting printing points of the color channel images of the predetermined digital image.

[0073] By applying the correction data to the given digital image, it can advantageously be achieved that the optimal operating point of the print heads does not have to be changed. This can ensure that the application of the correction data does not cause any other disadvantages in the printing process. By performing the correction by adjusting the respective color channel images, it can advantageously be achieved that, in comparison to applying the correction data to the given digital image as such, no correction artifacts occur between color channels. This makes it possible to achieve particularly true color correction. In addition, by adjusting the printing points, it can be achieved in particular that the correction is equally good for areas with low and high correction, whereby a particularly homogeneous correction can be achieved.

[0074] Preferably, it can be provided that when the correction data is applied to the given digital image, correction data are applied to the individual color channel images of the given digital image, wherein in particular correction data are only applied if the respective raster method provides a printing dot at the respective image location of the color channel image. If the color channel image for a color print channel does not provide a printing dot at a point, no correction of this color channel is applied to this point. Preferably, it can be provided that the correction is carried out by adjusting the printing dots of the color channel images of the given digital image, during the creation of the printing dots, or after the printing dots have been created.

[0075] Preferably, it can be provided that the color model of the intended digital image is selected from RGB, CMY and CMYK, wherein the color model is in particular CMYK.

[0076] Furthermore, a device is proposed, comprising a data memory, a computing unit, a digital printer for outputting a predetermined digital image and an optical color measuring device, wherein the device is configured to carry out the method described above.

[0077] Furthermore, a use of the method or device described above is proposed, wherein the method or device is used for color correction for the printing of decorations, in particular for the printing of decorations with a low color variety, for example for wood and / or stone decorations.

[0078] Surprisingly, it was shown that the method described above is particularly well suited for color correction in such applications. In particular, stripes can be detected particularly well in such decors, so particularly good color correction is necessary for high-quality prints.

[0079] Further advantages and advantageous embodiments of the method according to the invention, the device according to the invention, and the use according to the invention are illustrated by the figures and explained in the following description. It should be noted that the figures are for descriptive purposes only and are not intended to limit the invention in any way.

[0080] It shows Fig. 1 schematically shows the sequence of the method according to the invention according to a preferred embodiment, and Fig. 2 schematically shows a test image as it is created or printed as a digital test image in one embodiment of the method according to the invention.

[0081] Fig. 1 shows a schematic of the sequence of the method according to the invention according to a preferred embodiment. In step a), a predetermined digital image is first provided, which is intended to be printed on a digital printer. For example, the digital printer is an inkjet printer with the four CMYK printing ink channels, which are printed in the order Y, M, C and K. The predetermined digital image is, for example, a stone decor, which is intended to be printed on a decorative panel. The digital image is accordingly composed of four color channel images, which are assigned to the four CMYK printing ink channels of the digital printer.

[0082] In step b), at least one test color from the given digital image is determined. For example, two test colors are determined by arranging the color values ​​occurring in the digital image in a histogram according to frequency. The two most common colors are determined as test colors, ensuring that the colors have a certain minimum distance in the color space. For example, one test color consists of 5% cyan, 7% magenta, 4% yellow, and 16% black, and a second test color consists of 8% cyan, 3% magenta, 5% yellow, and 12% black.

[0083] In step c), a digital test image 100 is now created, with an exemplary test image being shown schematically in Fig. 2is shown. For this purpose, the digital test image 100 is provided with at least one solid-color test strip 101, 102, 103, 104, 110. For example, the test image 100 for the first test color is provided with a total of four solid-color test strips 101, 102, 103, 104, i.e. with as many test strips as there are printing ink channels. For the first test color, for example, in step i) for the first solid-color test strip 101, the print density intended for printing the test color is determined from a printing ink channel of the digital printer. For example, the printing ink channel to be printed first according to the printing sequence is used. According to the present example, the print density of the Y printing ink channel of the first test color, i.e. 4% yellow, is determined and determined in step ii) as the print density of the first solid-color test strip 101.For the second solid-color test strip of the first test color 102, for example, the print density intended for printing the test color of the printing ink channels to be printed first and second in the printing sequence is determined in step i) and determined as the print density of the solid-color test strip in step ii). In other words, according to the present example, the print density of the Y printing ink channel and the M printing ink channel of the first test color, i.e., 4% yellow and 7% magenta, is determined as the print density of the second solid-color test strip 102. For the third solid-color test strip of the first test color 103, for example, the print density intended for printing the test color of the printing ink channels to be printed first, second, and third in the printing sequence is determined in step i) and determined as the print density of the solid-color test strip in step ii).In other words, according to the present example, the print density of the Y printing ink channel, the M printing ink channel, and the C printing ink channel of the first test color, i.e., 4% yellow, 7% magenta, and 5% cyan, is determined as the print density of the third solid-color test strip 103. For the fourth solid-color test strip of the first test color 104, for example, the print density of all printing ink channels intended for printing the test color is determined in step i) and determined as the print density of the solid-color test strip in step ii). In other words, according to the present example, the print density of the test color consisting of 5% cyan, 7% magenta, 4% yellow, and 16% black is determined as the print density of the fourth solid-color test strip 104.

[0084] Furthermore, in step c), the digital test image 100 can also be provided with solid-color test strips for additional test colors. For example, the digital test image 100 can have a fifth solid-color test strip 110, wherein, for the fifth solid-color test strip 110, the print density of all printing ink channels intended for printing the second test color is determined in step i), for example, and is defined in step ii) as the print density of the fifth solid-color test strip 110. In other words, according to the present example, the print density of the fifth test strip 110 is determined as 8% cyan, 3% magenta, 5% yellow, and 12% black.

[0085] In step d), the digital test image 100 is now printed with the digital printer. For example, the digital test image 100 is printed on a panel of the type that will later be used for printing the decor.

[0086] In step e), the color values ​​of the printed test image 100 are now recorded with an optical colorimeter depending on their position along the print width. For example, the colorimeter is scanned across the printed test image 100 and color variations in the solid-color test stripes along the print width are determined.

[0087] In step f), correction data for the digital printer is created based on the color values ​​and then applied to the digital printer and / or the specified digital image in step g). For example, correction data is created that specifies that a higher print density of a specific ink channel must be provided at specific locations along the print width for specific printing inks. This data can then be applied, for example, by adjusting the print heads along the print width or by modifying the specified digital image.

[0088] After an optional iterative application of process steps d) to g), the correction data is applied to the digital printer and / or the specified digital image, and the specified digital image can be printed with the color correction. As a result, the print exhibits reduced banding in the printing direction, particularly with solid-colored decors such as stone decors.

Claims

1. Method for color correcting a digital printer over a printing width of the digital printer, wherein the digital printer is provided for outputting a specified digital image, wherein the method comprises the steps of: a) providing the specified digital image, wherein the digital image comprises at least one color channel pattern, wherein each color channel pattern is associated with a print color channel of the digital printer; b) determining at least one test color of the specified digital image, where the test color is selected from the most frequently occurring colors in the given digital image, optionally maintaining a minimum distance in the color space between several test colors; c) creating a digital test pattern, wherein the digital test pattern is provided with at least one single-colored test stripe which extents crosswise to the printing direction of the digital printer and is printed over the printing width of the digital printer, wherein each single-colored test stripe is defined by a print density of at least one print color channel of the digital printer according to the following steps: i) determining a print density of at least one print color channel of the digital printer intended for printing the test color; and ii) specifying the print density determined in step i) as the print density of the single-colored test stripe; d) printing the digital test pattern by use of the digital printer; e) detecting the color values of the printed test image as a function of their position in the direction of the printing width by use of an optical color measuring device; f) creating correction data for the digital printer based on the detected color values; and g) applying the correction data to the digital printer and / or the specified digital image, characterized in that at least one single-colored test stripe is defined by the print density of all print color channels of the digital printer, wherein in step i) the print density of all print color channels of the digital printer intended for printing the test color is determined, and / or at least one single-colored test stripe is defined by the print density of a single print color channel of the digital printer, wherein in step i) the print density intended for printing the test color is determined from a single print color channel of the digital printer, and / or at least one single-colored test stripe is defined by the print density of more than one and less than all print color channels of the digital printer, wherein the print density of more than one and less than all print color channels of the digital printer intended for printing the test color is determined in step i).

2. Method according to claim 1, wherein in step b) more than one test color is determined and the digital test pattern is provided with at least one single-colored test stripe for each determined test color.

3. Method according to any one of claims 1 or 2, wherein the digital test pattern for at least one test color of the specified digital image is provided with at least two single-colored test stripes and preferably the number of single-colored test stripes for the at least one test color of the specified digital image is less than or equal to the number of color channels of the digital printer, wherein preferably for the at least one test color one single-colored test stripe is defined by the print density from a single print color channel of the digital printer, one single-colored test stripe is defined by the print density of all print color channels of the digital printer, and the optionally remaining single-colored test stripes are defined by the print density of more than one and less than all print color channels of the digital printer.

4. Method according to claim 3, wherein the color channels of the digital printer have a printing sequence, wherein the single-colored test stripe defined by the print density of a single print color channel of the digital printer is defined by the print density of the print color channel to be printed first according to the printing sequence.

5. Method according to claim 4, wherein the single-colored test stripes defined by the print density of more than one and less than all of the print color channels of the digital printer are selected such that a first of said single-colored test stripes is defined by the print density of the print color channel to be printed first according to the printing sequence and is additionally defined by the print density of the print color channel to be printed subsequently according to the printing sequence; and optionally each further of said single-colored test stripes is defined by the print density of the respective previous single-colored test stripe and additionally by the print density of the print color channel to be printed subsequently according to the printing sequence.

6. Method according to any one of claims 1 to 5, wherein steps d) to g) are carried out iteratively several times in succession.

7. Method according to any one of claims 1 to 6, wherein the optical color measuring device is selected from the group consisting of a color sensor, a colorimeter, a spectrophotometer, a digital camera and a spectral densitometer, wherein the optical color measuring device is preferably based on the same color model as the digital printer.

8. Method according to any one of claims 1 to 7, wherein step e) is optionally carried out several times in succession with different settings of the optical color measuring device, in particular under different lighting conditions and / or exposure times.

9. Method according to any one of claims 1 to 8, wherein in step g) the correction data are applied to the printer, wherein in particular the correction is carried out by adjusting the print head electronics.

10. Method according to any one of claims 1 to 9, wherein in step g) the correction data are applied to the specified digital image, wherein in particular the correction is made by adjusting print dots of the color channel patterns of the specified digital image.

11. Method according to any one of claims 1 to 10, wherein the color model of the intended digital image is selected from RGB, CMY and CMYK, wherein the color model is in particular CMYK.