Method for evaluating a property of a paper sample

Abstract

The invention relates to a method for determining a property of paper, the method comprising the steps of: printing a paper sample (1) with at least one measurement field (A, B, C, D, E, F); analysing the at least one measurement field (A) on the paper sample (1) using an image analysis device; and determining a property of the paper sample (1) based on the analysis of the at least one measurement field (A, B, C, D, E, F) on the paper sample (1). The invention also relates to a computer program product comprising program instructions in order to carry out and / or control the method according to the invention when the program is executed on a processor, and to a computer-readable storage medium (41, 42, 43, 44, 45, 46) comprising the computer program product according to the invention.

Description

[0001]May 7, 2024 Method for Evaluating a Property of a Paper Sample Technical Field The invention relates to a method for evaluating a property of a paper sample. Furthermore, the invention relates to a computer program product comprising program instructions for executing and / or controlling the method according to the invention when the program is executed on a processor, as well as to a computer-readable storage medium comprising the computer program product according to the invention. Background The gravure printing process is still the dominant printing process in decorative printing today. The center of a gravure printing press is the printing unit, which essentially comprises an ink tray containing printing ink, a forme cylinder that receives the printing ink from the ink tray, a doctor blade for wiping excess printing ink from the forme cylinder, a printing cylinder, and a drying system.In rotogravure printing, depressions on the outside of the forme cylinder, called cells, are filled with printing ink. Excess ink on the forme cylinder is scraped off the surface using a doctor blade before printing. The ink is then transferred from the cells to the paper. Strong pressure and the suction power of the paper transfer the ink to the printing medium. The printing cylinder's job is to press the substrate against the forme cylinder so that it makes contact with the ink and draws it out of the cells. Creative templates are created for decorative printing. The layout is engraved directly into the surface of the forme cylinder, for example, electromechanically or by laser engraving. Gravure printing enables high quality thanks to the fine cells that are carefully engraved into the cylinder. The dimensions of the cells determine the ink distribution.Both the width and height precisely define how much printing ink the cylinder absorbs at which points. This precision affects the tones, halftones, and color nuances. Color gradations can thus be realistically reproduced. However, with decorative printing, the problem arises that papers of the same type can have different printability properties, even if the specified specifications for paper production have been adhered to. For example, the ink absorption of the paper can vary greatly; despite the same base paper color, significant color and density differences can be observed after printing. Decorative printers then have to laboriously adjust the ink formulation for printing. Longer adjustment times can occur, especially at the start of a printing process and / or when using paper rolls from different production lines. This is also associated with increased waste.One method for determining a paper property is the Bekk smoothness measurement. Here, the paper's smoothness is not determined directly, but rather related to an air flow along the paper surface. It should be noted, however, that the smoothness can be at least partially reversible. In particular, moisture absorption from the air reduces the smoothness value, as the paper fibers partially reswell. Ink acceptance is currently monitored, for example, by visual assessment of laboratory proofs. While these visual inspections allow a rudimentary assessment of the print results, they are subjective and not precise or repeatable. The object of the present invention is therefore to provide a method with which the properties of a paper sample can be determined objectively and reliably.In particular, the aim is to produce printing base papers with great economic efficiency that have optimal runability and printability properties. H / SH 230482WO May 7, 2024 ErfindungAccording to a first aspect of the present invention, the object is achieved by a method for determining a property of a paper sample, the method comprising the steps of: printing the paper sample with at least one measurement field, analyzing the at least one measurement field on the paper sample using an image analysis device, and determining a property of the paper sample based on the analysis of the measurement field on the paper sample. The paper sample is, in particular, decorative paper. The paper can, for example, have a weight of 20 to 350 g / m², in particular 20 to 210 g / m², preferably 40 to 100 g / m². For printing the paper sample, black or brown printing ink, for example, can be used. In particular, dark printing ink can be used for printing light paper samples. For printing dark paper samples, in particular dark gray or black paper samples, light printing ink, for example, white, can be used.The paper sample is printed with at least one measurement field, in particular, using gravure printing. Printing the paper sample can, for example, involve a proof. The paper sample is, for example, mounted on a roller and rolled at a specific pressure over a printing plate wetted with ink. The printing plate can comprise individual fields with different cell depths. For example, it is conceivable that the printing plate has a cell depth of 51 µm for printing a 100% measurement field E, a cell depth of 38 µm for printing a 75% measurement field D, a cell depth of 25.5 µm for printing a 50% measurement field C, a cell depth of 12.75 µm for printing a 25% measurement field B, and a cell depth of 5.1 µm for printing a 12.5% ​​measurement field A. The cells can be arranged in a grid, for example, with 60 x 60 cells per cm2. One or more measurement fields can be applied to the paper sample in this way.The roller pressure, the blade pressure, and / or the unwinding speed can be adjustable, although these are generally kept constant. It is also conceivable that at least one measuring field can be controlled by means of a S. H / SH 230482WOMay 7, 2024. This is particularly advantageous when the paper sample is printed inline with other process steps, for example, inline with paper production. The paper sample can also be printed parallel to the production process. The measuring field can be designed to determine at least one property of the paper sample. The at least one measuring field can be, for example, a solid or halftone field. Preferably, different measuring fields are printed on the paper sample. Different amounts of ink can be applied to individual measuring fields, for example. Within the scope of an inline process, the at least one measuring field can be applied to a paper layer outside the actual printing area. In particular, the measuring field is applied in an edge area, also known as the technical edge.The method can comprise analyzing the at least one measurement field on the paper sample using an image analysis device. Analyzing the at least one measurement field can comprise analyzing at least a section of the measurement field. For example, it is conceivable that a measurement area is defined as a region of interest. The measurement area can be analyzed within the scope of the method. Analyzing the at least one measurement field using the image analysis device comprises, for example, analyzing an image of the at least one measurement field. The printed paper sample can be digitized, for example, using an image capture device. For analyzing the measurement field using the image analysis device, the printed paper sample can be scanned, for example, using a scanning device. A PC-controlled scanner, for example, serves as the scanning device.Using the scanning device, a section of the paper sample comprising the measurement field can be captured as an image, for example, as a grayscale image. In particular, a bitmap image can be created from a digitized image. For example, paper weights from 20 to 350 g / m², in particular 20 to 210 g / m², preferably 40 to 100 g / m², can be scanned. H / SH 230482WOMay 7, 2024. Furthermore, the method may comprise determining a property of the paper sample based on the analysis of the measurement field on the paper sample. In particular, the method comprises determining the printability, in particular a printability property, of the paper sample. For example, the method comprises determining the ink acceptance behavior of the paper sample. It is conceivable that the method comprises determining the quality of the paper sample. In particular, the method comprises evaluating the paper sample based on the analysis of the measurement field. Determining at least one property of the paper sample may further comprise determining comparability or identity with at least one property of another paper, for example, at least one reference paper sample.Determining at least one property of the paper sample can comprise comparing the at least one property of the paper sample with at least one property of at least one reference paper sample. Determining a property of the paper sample based on the analysis of the measurement field on the paper sample can be carried out using at least one device, for example, also using the image analysis device. It has been recognized that the method for determining a property of a paper sample can provide an objective measurement method with which the properties of the paper sample can be determined quantitatively and comprehensibly. In particular, the method allows a reliable prediction of the printability of decorative papers, in particular the provision of paper with consistent and reproducible ink acceptance behavior for problem-free ink matching with the shortest possible color matching times.The method allows conclusions to be drawn about the behavior of decorative paper in industrial printing and can therefore be used as an important tool for quality assurance. dienen. According to a second aspect of the present invention, the object is achieved by a computer program product comprising program instructions to H / SH 230482WOMay 7, 2024 To carry out and / or control the method according to the first aspect when the program is executed on a processor. According to a third aspect of the present invention, the object is also achieved by a computer-readable storage medium comprising a computer program product according to the second aspect. A computer-readable storage medium can be designed, for example, as a magnetic, electrical, electromagnetic, optical, and / or other type of storage medium. Such a computer-readable storage medium is preferably tangible (i.e., "tangible"), for example, it is designed as a data storage device. Such a data storage device is, for example, portable or permanently installed in a device. Examples of such a data storage device are volatile or non-volatile random access memories (RAM), such asNOR flash memory or with sequential access such as NAND flash memory and / or read-only memory (ROM) or random access memory. Computer-readable should be understood, for example, to mean that the storage medium can be read and / or written to by a computer or data processing system, for example, by a processor. It is also conceivable that the computer program product is comprised by a cloud-based system, in particular a cloud server. Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below. According to a first advantageous embodiment of the invention, analyzing the at least one measurement field on the paper sample with the aid of the image analysis device comprises quantitatively determining a measurement variable based on the at least one measurement field on the paper sample. For example, the color density can be determined based on the measurement field.Compared to a visual subjective assessment, the method can be used to quantify the properties of a paper sample. H / SH 230482WO May 7, 2024. According to a further advantageous embodiment of the invention, analyzing the at least one measuring field on the paper sample with the aid of the image analysis device comprises: determining an actual value of the measured variable based on the at least one measuring field on the paper sample, and comparing the determined actual value of the measured variable with a target value range. In particular, the method comprises checking whether the determined actual value of the measured variable lies within the target value range. liegt.According to a further advantageous embodiment of the invention, the target value range is determined based on at least one reference paper sample. In particular, the target value range is determined based on a plurality of reference paper samples. For example, the limit value for each paper type is determined on a plurality of reference paper samples. A plurality of reference paper samples means, for example, at least two reference paper samples. For example, a plurality means at least five, at least ten, at least 15, at least 20, or at least 50 reference paper samples. A target value of a measured variable is determined, for example, based on the mean value of the measured variables of a plurality of reference paper samples. It is conceivable, for example, that absolute values ​​are determined for the reference paper samples, e.g., absolute values ​​for the density and the unprinted area, and the mean value is determined based on the absolute values.The target value range is determined, for example, based on the standard deviation of the measured values ​​of the plurality of reference paper samples. It is conceivable, for example, that the target value range is determined based on 3-sigma limits. It is also conceivable that the target value range is defined as a percentage tolerance range around the mean value, for example, ± 5% or ± 3% of the mean value. The limits of the target value range can be adjusted, for example, based on defined requirements, particularly customer-specific, e.g., by a printer customer. H / SH 230482WO May 7, 2024. According to a further advantageous embodiment of the invention, the measuring field on the paper sample is designed to determine the color density. Color density refers in particular to the amount of color per unit area. Based on a measuring field for determining the color density, in particular a 75% measuring field, the mean gray value gMean of the pixels in the measuring area can be used, for example: 100 The darker the pixels in the analyzed print area, the higher the average print density DMean. The measurement field can be particularly suitable for determining color density, area coverage, and / or a color value. A 75% measurement field can be understood as a measurement field in which 75% of the area is expected to be printed. While a 100% measurement field, for example, is understood to be a measurement field that should be completely covered with printing ink, i.e., a solid color field, the desired target value for a 75% measurement field is 75% printed area. According to a further advantageous embodiment of the invention, the measurement field on the paper sample is designed to determine area coverage. Based on a measurement field for determining area coverage, in particular a 25% measurement field, the proportion of the unprinted area UF relative to the measurement area AROI can be analyzed, for example: Based on the measured values ​​of ink density and unprinted area, the printability of the paper sample can be assessed. A 25% measurement patch can be understood as a patch where 25% of the area is expected to be printed. Color defects are identified as missing dots, for example, during the analysis of the patch. H / SH 230482WOMay 7, 2024. According to a further advantageous embodiment of the invention, analyzing the at least one measurement field on the paper sample with the aid of the image analysis device comprises a missing dot, an ink acceptance, and / or an ink level analysis. In the missing dot analysis, the measurement field on the paper sample is examined for missing printing dots. If ink remains in a cell, an ink defect, a missing dot, forms on the paper. The missing dot count is the number of printing dots that are missing to complete a grid of existing printing dots specified by the printing form. The measurement field of the printed paper sample is examined for missing printing dots as part of the missing dot analysis. The 25% field is particularly suitable for the missing dot analysis. Ink acceptance indicates how well a printing ink, especially wet printing ink, is transferred to the paper.The ink should penetrate the paper slightly, but not too deeply, as this would weaken the printed image. Likewise, the ink should not remain too high on the paper, as this would create the risk of uneven color placement (mottling). This can be analyzed using a color balance analysis. According to a further advantageous embodiment of the invention, analyzing the at least one measurement field on the paper sample with the aid of the image analysis device comprises determining a threshold value for differentiating between a printed and an unprinted area on the paper sample. In particular, in an image, all pixels that are recognized as darker than the referenced threshold value can be considered a printed area. All pixels that are recognized as brighter than or equal to the threshold value can be considered an unprinted area.It is also conceivable that the method comprises determining the proportion of the unprinted area in at least one measuring field on the paper sample depending on the determined limit value.S. H / SH 230482WOMay 7, 2024 To determine the limit value for differentiating between the printed and unprinted areas on the paper sample, an unprinted reference measurement area is preferably provided on the paper sample. The determined color value of the reference measurement area can serve as a limit value to distinguish between the printed and unprinted areas in the printing areas to be analyzed. The reference measurement area serves, in particular, to take into account the influence of the unprinted paper. The reference measurement area can, in particular, serve to define the unprinted area. An image of at least one measurement field is measured, in particular, against the specific background. Depending on the color of the unprinted paper, for example, the measured color density of a 75% measurement field differs. Using the reference measurement area, the influence of the paper can preferably be calculated out.The threshold value for differentiating between the printed and unprinted areas on the paper sample is preferably determined depending on the paper type and / or paper color. The color difference between the printing ink and the paper must be clear to achieve good results. Therefore, for example, a dark brown printing ink is selected for the generally light-colored papers. This allows most paper colors for printing base papers to be covered, and the contrast is still good even with darker gray or brown. For black paper samples, white printing ink can be used, for example. The reliability of the analysis of the at least one measuring field on the paper sample depends significantly on the quality of the printing on the paper sample or the printing device for printing on the paper sample, in particular the printing plate or printing roller. The method can therefore further comprise checking the printing device for printing on the paper sample.Checking the printing device can, for example, be carried out at regular intervals. To check the printing device, the method can include: printing a calibration paper sample with the at least one measurement field, and analyzing the at least one measurement field on the calibration paper sample with S. H / SH 230482WOMay 7, 2024, with the aid of the image analysis device, wherein the analysis comprises comparing the actual value of a measured variable of the measuring field on the calibration paper sample with a target value range of the measured variable, wherein the target value range is determined based on at least one reference calibration paper sample, in particular a plurality of reference calibration paper samples. Depending on the comparison of the actual value of the measured variable of the measuring field on the calibration paper sample with the target value range, the printing device can, for example, be cleaned and / or wearing parts of the printing device can be replaced. Regularly checking the wear of the printing device serves to preventively replace the wear parts and thus exclude any influence on the print. This eliminates the need for subsequent consideration in the calculation.According to a further advantageous embodiment of the invention, the method further comprises: selective further processing of the paper depending on the determined property of the paper sample. Based on the determined property of the paper sample, selective further processing of the paper can take place. Determining the at least one property of the paper sample can be used, for example, for an evaluation, in particular sorting, of the paper, in particular the paper rolls from which the paper sample originates. In particular, based on the at least one determined property of the paper sample, it can be determined whether the paper meets certain requirements in order to be further processed accordingly with other papers. Consistent printability properties enable, for example, the mixing of paper rolls from different production runs.By using printing base papers with consistent printability properties, homogeneity within a print job can be ensured. In particular, the process ensures a consistent influence of the paper on the print result and reproducible quality. This can advantageously lead to increased printer productivity, particularly by reducing inking times and waste. H / SH 230482WOMay 7, 2024 According to a further advantageous embodiment of the invention, the method further comprises: controlling or regulating paper production depending on the specific property of the paper sample. With the aid of the method, for example, a statement can be made about at least one property of the paper sample, and in the event of an inadequate property, quality-relevant paper production parameters can be readjusted. In particular, the method comprises controlling or regulating a paper machine device, in particular a paper machine device for smoothing the paper, depending on the specific property of the paper sample. It has been recognized that, in particular, the setting of the paper machine device, in particular a calender, influences the printability properties of the paper. The key influencing factors are the calender pressure and the moisture content. Refining can also influence the paper properties.Refining increases the fiber surface area, resulting in a denser paper structure and thus reducing air permeability. Mechanical compaction during calendering also reduces air permeability. Due to the compaction of the paper, the ink cannot penetrate deeply and remains on the surface, resulting in higher ink density. The features and embodiments of the invention described above can equally relate to the various aspects of the present invention. The exemplary embodiments of the present invention described above in this description are also to be understood as disclosed in all combinations with one another. Rather, it is understood that the representation of embodiments of the invention is merely exemplary and non-limiting.Detailed DescriptionFurther advantageous exemplary embodiments of the invention can be found in the following detailed description of some exemplary embodiments of the present invention, in particular in conjunction with the figures.S. H / SH 230482WOMay 7, 2024. However, the figures are intended only for the purpose of illustration, not to determine the scope of the invention. The figures are not to scale and are intended merely to reflect the general concept of the present invention by way of example. In particular, features contained in the figures should in no way be considered a necessary component of the present invention. The drawing shows, in Fig. 1, a schematic representation of an apparatus for printing a paper sample; Fig. 2, a schematic representation of a paper sample printed with the measurement fields; Fig. 3, a schematic representation of a computer program for image-analytical evaluation of measurement fields of a paper sample; and Fig. 4, a schematic representation of exemplary embodiments of the computer-readable storage medium according to the third aspect. Fig. 1 shows an apparatus 10 for printing a paper sample 1.The device 10 for printing the paper sample 1 comprises a printing plate 11 with a plurality of engraved printing fields a, b, c, d, e, f, wherein the individual printing fields a, b, c, d, e, f have a different cell depth. For example, the print field e for printing a 100% measurement field E can have a cell depth of 51 µm, the print field d for printing a 75% measurement field D can have a cell depth of 38 µm, the print field c for printing a 50% measurement field C can have a cell depth of 25.5 µm, the print field b for printing a 25% measurement field B can have a cell depth of 12.75 µm, and the print field a for printing a 12.5% ​​measurement field A can have a cell depth of 5.1 µm. Furthermore, the device 10 comprises a S. H / SH 230482WOMay 7, 2024 Roller 12, which is moved at a constant speed over the printing plate 11. The paper sample 1 is mounted on the roller 12, and this is rolled with a specific pressure over the printing plate 11, which is wetted with printing ink. In this way, the printing ink applied to the printing fields a, b, c, d, e, f of the printing plate 11 can be transferred to the paper sample 1, and the paper sample 1 is printed with measuring fields (not shown) of different ink quantities. The paper sample 1 printed with the measuring fields A, B, C, D, E is shown in Fig. 2. A dark brown color has been chosen as the printing ink. In order to ensure that the printing ink is evenly distributed in the printing fields a, b, c, d, e, f of the printing plate 11 before printing and that there is no excess printing ink, the device 10 also comprises a blade 13 for distributing and scraping off the printing ink.The roller pressure, blade pressure, and unwind speed are adjustable, although these are generally kept constant. To check the printing device or the wear condition of the squeegee and printing plate, a calibration print can be performed using a stabilized paper, a calibration paper sample. The paper sample 1 printed with the measurement fields A, B, C, D, and E is scanned using a scanning device (not shown), and an image 2 of the paper sample 1 printed with the measurement fields A, B, C, D, and E is made available in a computer program for image analysis of the paper sample 1, as shown in Fig. 3. Based on image 2, the measurement field B of the paper sample 1, which is designed to determine the area coverage, and the measurement field D of the paper sample 1, which is designed to determine the ink density, are analyzed using an image analysis device. For this purpose, sections of the measurement fields B and D, the measurement areas B' and D', are analyzed.First, a limit value is determined to differentiate between a printed and an unprinted area on paper sample 1. For this purpose, an unprinted reference measuring area R is provided on paper sample 1. UnderS. H / SH 230482WO May 7, 2024 Taking into account the reference measurement area R, the limit value for differentiating between the printed and unprinted area on paper sample 1 is determined depending on the color of paper sample 1. Based on the reference measurement area R, an average gray value of paper sample 1 is determined. To determine the properties of paper sample 1, the proportion of the unprinted area UF relative to the measurement area AROI is analyzed based on the 25% measurement field B to determine the area coverage: A missing dot analysis is also performed based on the 25% measurement field B. Based on the 75% measurement field D, the mean gray value gMean of the pixels in the measurement area D' is used to determine the color density: 100The darker the pixels in the analyzed print area, the higher the average print density DMean. In contrast to the 75% measurement field D, the 100% measurement field E is "overfilled" with ink, which would falsify the results. The results are graphically visualized in a dashboard 3. Analyzing the measurement fields B and D using the image analysis device involves quantitatively determining the measured variables based on the measurement fields. The determined actual values ​​of the measured variables are not used absolutely to determine the properties of paper sample 1, but are compared with a target value range, whereby the upper and lower limits of the target value range were determined through statistical tests for reference paper samples of the respective paper type. Dashboard 3 shows that both the actual value of 1.6 for the area coverage and the actual value of -4.6 for the ink density are within the specified target range of -2.5S. H / SH 230482WOMay 7, 2024 to 2.5 for the area coverage or from -7.0 to 7.0 for the color density. Based on this analysis, it can be determined, for example, that the printability properties of paper sample 1 sufficiently match the properties of the reference paper samples. Accordingly, the paper from which paper sample 1 originates can be further processed in the same way. In the event of deviations, corrective measures can be taken instead. If, for example, the actual values ​​lie outside the target value range, the paper production process, in particular a paper machine device for smoothing the paper, could be controlled or regulated. Fig. 4 shows exemplary embodiments of a computer-readable storage medium comprising an embodiment of a computer program product according to the invention. The storage medium can, for example, be a magnetic, electrical, optical, and / or other type of storage medium.The storage medium can, for example, be part of a processor, for example a (non-volatile or volatile) program memory of the processor or a part thereof. Exemplary embodiments of a storage medium are a flash memory 41, an SSD hard drive 42, a magnetic hard drive 43, a memory card 44, a memory stick 45 (e.g., a USB stick), a CD-ROM or DVD 46, or a floppy disk 47. The exemplary embodiments of the present invention described in this specification are also to be understood as disclosed in all combinations with one another. In particular, the description of a feature encompassed by an embodiment—unless explicitly stated otherwise—should not be understood to imply that the feature is essential or essential for the function of the exemplary embodiment.Terms used in the patent claims such as "comprise," "comprise," "include," "contain," and the like do not exclude further elements or steps. The phrase "at least partially" includes both "partially" and "completely." The phrase "and / or" is intended to be used in conjunction with the above-mentioned phrase. H / SH 230482WO May 7, 2024, should be understood to mean that both the alternative and the combination are intended to be disclosed, thus "A and / or B" means "(A) or (B) or (A and B)." A plurality of units, persons, or the like, in the context of this specification, means several units, persons, or the like. The use of the indefinite article does not exclude a plurality. A single device can perform the functions of several units or devices recited in the claims. Reference symbols recited in the claims are not to be considered limitations on the means and steps employed. H / SH 230482WO May 7, 2024

Claims

7 May 2024Patent Claims1. Method for determining a paper property, the method comprising Schritte:- printing a paper sample (1) with at least one measurement field (A, B, C, D, E, F), - analyzing the at least one measurement field (A, B, C, D, E, F) on the paper sample (1) using an image analysis device, and - determining a property of the paper sample (1) based on the analysis of the at least one measurement field (A, B, C, D, E, F) on the paper sample (1).

2. The method according to claim 1, wherein analyzing the at least one measurement field (A, B, C, D, E, F) on the paper sample (1) using the image analysis device comprises quantitatively determining a measured variable based on the at least one measurement field (A, B, C, D, E, F) on the paper sample (1). 3.Method according to claim 2, wherein analyzing the at least one measuring field (A, B, C, D, E, F) on the paper sample (1) with the aid of the image analysis device comprises: - determining an actual value of the measured variable based on the at least one measuring field (A, B, C, D, E, F) on the paper sample (1), and - comparing the determined actual value of the measured variable with a target value range.

4. Method according to claim 3, wherein the target value range is determined based on at least one reference paper sample, in particular a plurality of reference paper samples.

5. Method according to one of claims 1 to 4, wherein the measuring field (D) on the paper sample (1) is designed to determine the color density. - 2 -6. Method according to one of claims 1 to 5, wherein the measuring field (B) on the paper sample (1) is designed to determine the area coverage.

7. Method according to one of claims 1 to 6, wherein the analysis of the at least one measuring field (B) on the paper sample (1) with the aid of the image analysis device comprises a missing dot, a color acceptance and / or a color level analysis.

8. Method according to claim 6 or 7, wherein the analysis of the at least one measuring field (B) on the paper sample (1) with the aid of the image analysis device umfasst:- Determining a limit value for differentiating between a printed and an unprinted area on the paper sample (1).

9. Method according to claim 8, wherein an unprinted reference measuring area (R) is provided on the paper sample (1) to determine the limit value for differentiating between the printed and the unprinted area on the paper sample (1).

10. Method according to claim 8 or 9, wherein the limit value for differentiating between the printed and the unprinted area on the paper sample (1) is determined depending on the paper type and / or the paper color.

11. Method according to one of claims 1 to 10, wherein the method further umfasst: -selective further processing of the paper depending on the specific property of the paper sample (1).

12. Method according to one of claims 1 to 11, wherein the method further mfasst: S H / SH 230482WO May 7, 2024 - 3 - - Controlling or regulating paper production, in particular a paper machine device for smoothing the paper, depending on the determined property of the paper sample (1).

13. A computer program product comprising program instructions for executing and / or controlling the method according to any one of claims 1 to 10 when the program is executed on a processor.

14. A computer-readable storage medium (41, 42, 43, 44, 45, 46) comprising a computer program product according to claim 13. H / SH 230482WO May 7, 2024

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