Printing quality inspecting method and printing quality inspecting device

Abstract

To provide a printing quality inspecting technique that can determine whether a printing quality such as dot-gain concerning ink is good or not, with high efficiency and in detail.SOLUTION: An image of a region including a prescribed halftone-dot region constituted of dots of a single ink color and a back ground printed on a sheet is photographed. A straight line passing through at least one of the dots and included in the photographed image of the halftone-dot region is set. A color density level is measured along the straight line so as to obtain a color density profile along the straight line of the dot. It is determined whether a printing quality including a dot format concerning ink of an ink color of the dot is good or not, on the basis of the color density profile.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a print quality inspection method and a print quality inspection device for inspecting print quality such as dot gain of a printed matter. [Background technology]

[0002] One known print quality issue is dot gain, whereby the dots in a printed image become thicker, making the color of the printed image appear darker than the original ink color. A print quality inspection method that can determine dot gain involves shining light of the three primary colors onto the printed image, determining print density and color values based on the reflected light, and converting these values into dot gain values to determine quality (see Patent Document 1).

[0003] However, the inspection method of Patent Document 1 does not provide details of how to determine whether a dot gain phenomenon has occurred. Even if it were possible to determine the possibility of dot gain overall, it would be impossible to determine in more detail what caused the dot gain, such as whether it was due to poor ink adjustment or poor transfer pressure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-349739 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above, the present invention aims to provide a print quality inspection technique that can determine the quality of ink print quality, such as dot gain, with high efficiency and in more detail. [Means for solving the problem]

[0006] That is, the present invention includes the following inventions. (1) A print quality inspection method characterized by capturing an image of an area including a predetermined halftone dot area consisting of dots of a single ink color printed on a sheet and a background, setting a straight line passing through at least one of the dots included in the image of the captured halftone dot area, measuring the color density level along the straight line, obtaining a color density profile of the dot along the straight line, and judging the quality of the print, including the dot shape of the ink of the ink color of the dot, based on the color density profile.

[0007] (2) A print quality inspection method as described in (1), in which the length L1 of the area where ink is substantially applied, where the color density level falls within the range from the minimum value to a predetermined value, is calculated from the color density profile of the dot, and the print quality of the ink is judged based on these L1 values.

[0008] (3) A print quality inspection method according to (2), in which the print quality of the ink is judged to be good by comparing a value calculated by a predetermined calculation formula using L1 and the total area length L2 of the dot along the straight line with a reference value.

[0009] (4) A print quality inspection method according to (1) or (2), in which the difference H1 between the minimum and maximum color density levels is calculated from the color density profile of the dot, and the print quality of the ink is judged to be good by comparing this H1 value with a reference value.

[0010] (5) A print quality inspection method according to any one of (1) to (4), which includes setting two lines that intersect within the dot, obtaining two color density profiles along each line of the dot, and determining from each density profile the position T1 of the minimum color density level on each line of the dot, and the positions E1 and E2 of both ends of the area on each line of the dot, and judging the bias direction of the ink that constitutes the dot, among the print quality related to the ink, based on T1, E1, and E2 of each of these lines.

[0011] (6) A print quality inspection method as described in (5), in which the position of the center of the dot to be used as a reference is identified from E1 and E2 of each of the straight lines, and the position of the actual ink center of the dot is identified from T1 of each of the straight lines, and the direction of ink bias is determined from the positional relationship between these two.

[0012] (7) A print quality inspection device characterized by comprising: an imaging means for imaging an area including a predetermined halftone dot area consisting of dots of a single ink color printed on a sheet and a background; a color density acquisition means for setting a straight line passing through at least one of the dots included in the image of the predetermined halftone dot area imaged by the imaging means and measuring the color density level along the straight line to acquire a color density profile of the dot along the straight line; and a judgment means for judging the quality of the print, including the dot shape related to the ink of the ink color of the dot, based on the color density profile acquired by the color density acquisition means.

[0013] (8) A print quality inspection device as described in (7), wherein the judgment means includes a substantial ink area length calculation unit that calculates an area length L1 within the range of color density levels from the minimum value to a predetermined value from the color density profile of the dot acquired by the color density acquisition means, and a judgment processing unit that judges whether the print quality of the ink is good or bad based on the value of L1.

[0014] (9) A print quality inspection device as described in (8) that includes a dot area length calculation unit that calculates the total area length L2 along the straight line of the dot, and the judgment processing unit judges whether the print quality of the ink is good or bad based on each of the values of L1 and L2.

[0015] (10) A print quality inspection device as described in (9), wherein the judgment processing unit judges whether the print quality of the ink is good by comparing the value obtained by a predetermined calculation formula using L1 and L2 with a reference value.

[0016] (11) A print quality inspection device as described in (7), wherein the judgment means comprises an ink density calculation unit that calculates the difference H1 between the minimum and maximum color density levels from the color density profile of the dot acquired by the color density acquisition means, and a judgment processing unit that judges whether the print quality of the ink is good by comparing the value of H1 with a reference value. [Effects of the Invention]

[0017] According to the present invention, the quality of ink-related prints, such as dot gain, can be determined with high efficiency and in more detail. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is an explanatory diagram showing a printing line incorporating a print quality inspection device according to the present invention; [Figure 2] (a) is an explanatory diagram showing an inspection mark printed in the corner of a printed material, and (b) is an enlarged view of the area where the mark is printed. [Figure 3] 1 is a block diagram showing the configuration of a print quality inspection device according to the present invention; [Figure 4] FIG. [Figure 5] 10A and 10B are explanatory diagrams showing an image of a predetermined halftone dot area cut out from a mark, and how a color density profile is obtained by following a straight line through a specific dot. [Figure 6] FIG. 10 is an explanatory diagram showing an example of a color density profile of a specific dot range. [Figure 7] FIG. 10 is an explanatory diagram showing an example of a color density profile of a specific dot range. [Figure 8] FIG. 10 is an explanatory diagram showing an example of a color density profile of a specific dot range. [Figure 9] FIG. 10 is an explanatory diagram illustrating registration using marks. [Figure 10] FIG. 10 is an explanatory diagram illustrating a modified example of the registration. DETAILED DESCRIPTION OF THE INVENTION

[0019] Next, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0020] As shown in Fig. 1, the print quality inspection device 1 of the present invention includes an imaging means 2 that captures an image of the printing surface 9 of a printed material W being conveyed, an illumination means 3 that illuminates the imaged surface captured by the imaging means 2, and a judgment means 41c that judges the print quality of the printing surface 9 based on image information obtained by the imaging means 2. Reference numerals 11A, 11B, 11C, and 11D in Fig. 1 each represent a printing device that prints ink of a different color. The number of printing devices is not limited. The printing devices 11A, 11B, 11C, and 11D are, for example, offset printing machines, but the present invention can also be applied to various other printing devices such as flexographic printing machines and gravure printing machines.

[0021] Although the printed matter W, which is the subject of inspection in the present invention, is illustrated as a cut sheet in the figure, the present invention can be applied to a continuous strip of sheet instead of a cut sheet. Furthermore, the material of the printed matter W includes various materials in addition to paper, such as synthetic resin film and aluminum foil. The printed surface of the printed matter W includes at least a predetermined dot area consisting of halftone dot printing consisting of a single ink color printed on the sheet and a background. This area is imaged by the imaging means 2.

[0022] The halftone dot area imaged by the imaging means 2 is preferably an area consisting of inspection marks printed in a single ink color on the edge of the paper or the like and having a fixed shape so as to have a fixed color density distribution. For example, as shown in Figures 2(a) and 2(b), such inspection marks correspond to four marks M1, M2, M3, and M4 printed in each ink color (for example, each of the ink colors Y / M / C / K) on the edge area other than the image P1.

[0023] In this example, as shown in the enlarged view of FIG. 4 (the enlarged view of mark M1), each is a "field" - shaped mark, and these marks also serve as alignment marks. More specifically, it is composed of a first area r1 filled with ink of the color of the mark in the center, a second area r2 halftone - printed with ink of that color in the surrounding area, and a white background area r3. By providing the first area r1 filled in the center like this, the color density inspection described later can be carried out with high efficiency and high precision.

[0024] By analyzing the marks (M1 - M4) printed for each of these inks, it is possible to determine not only the quality of printing quality such as dot gain and color density but also the presence or absence of alignment deviation based on the position information of the inspection marks. For example, as shown in FIG. 9, when an alignment deviation occurs, taking the line connecting the centers of marks M1 of the same color (for example, K (black)) as a reference line, the deviation amount of each of the marks M2 - M4 with respect to this can be measured to detect the alignment deviation.

[0025] The shape of the mark is not limited to the "field" - shape as in this example, and other shapes may be used. Also, such inspection marks are not essential. It is of course possible to omit the printing of the inspection marks and inspect a specific area of only one color in the pattern P1 as the above - mentioned halftone area.

[0026] The imaging means 2 can widely apply a known imaging device used in a conventional printed matter inspection apparatus. For example, a line - sensor camera composed of a plurality of line sensors arranged in parallel in the horizontal direction orthogonal to the conveyance direction, each having an imaging element such as a CCD or a CMOS, is provided. The illumination means 3 can also widely apply a known illumination device used in a conventional printed matter inspection apparatus.

[0027] As shown in FIG. 1, the determination means 41c is provided in the processing device 41 that constitutes the computer. Reference numeral 42 is a storage means connected to the processing device 41. The processing device 41 is mainly composed of a CPU such as a microprocessor, and transmits and receives various information to and from the imaging means 2, the illumination means 3, and the storage means 42 through an input / output unit and a bus line.

[0028] The storage means 42 is composed of storage memories such as RAM and ROM inside and outside the processing device 41, a hard disk, etc., and stores programs and processing data that define the procedures of various processing operations in the processing device 41. Figure 3 shows the configuration of the processing device 41 and storage means 42 of this embodiment.

[0029] 3, the processing device 41 functionally comprises at least an area image acquisition processing unit 41a that stores an image of a predetermined halftone dot area captured by the imaging means in an area image storage unit 42a of the storage means 42, a color density acquisition processing unit 41b that sets a straight line passing through at least one dot included in the image of the halftone dot area and measures the color density level along the straight line to acquire a color density profile of the dot along the straight line and stores the acquired color density profile in a color density profile storage unit 42b of the storage means 42, and a judgment processing unit serving as judgment means 41c that judges the quality of the print, including the dot shape related to the ink of the ink color of the dot, based on the acquired color density profile. These functions are realized by the above-mentioned program.

[0030] The area image acquisition processing unit 41a first acquires images of areas R01 to R04, which include the inspection marks M1, M2, M3, and M4 shown in Fig. 2(b), using the imaging means 2, and stores these images in the area image storage unit 42a. Next, from among the marks M1 to M4 included in each of the areas R01 to R04, images of predetermined halftone dot areas R11 to R14, which are made up of single-color dots, are cut out and stored in the area image storage unit 42a as halftone dot areas for acquiring a color density profile.

[0031] More specifically, images of the areas of the marks M1 to M4 can be cut out and stored from an image of the entire or part of the printed surface obtained by the imaging means 2, and then halftone dot areas R11 to R14 at predetermined positions that are previously identified as areas that make up the marks M1 to M4 can be cut out and stored.

[0032] The color density acquisition processing unit 41b is a processing unit that constitutes the color density acquisition means, and sets a straight line passing through at least one dot included in each image of the halftone dot areas R11 to R14, and measures the color density level along the straight line. Figure 5 shows an image of the halftone dot area R11 cut out from the area R01 of the mark M1. As shown in the figure, the image of R11 is a halftone dot image made up of a plurality of dots.

[0033] The color density acquisition processing unit 41b identifies one dot for each of the halftone dot areas R11 to R14. The dot d11 can be identified using known shape recognition techniques (such as those that identify and recognize feature points or those that use artificial intelligence). Then, a straight line passing through the approximate center of the dot is set, and a color density profile is acquired along the straight line.

[0034] To give a specific example of mark M1, as shown in Figure 5, one dot d11 is identified from among the multiple dots included in halftone dot area R11, and two perpendicular straight lines x1, y1 that pass approximately through the center of dot d11 are set. Then, R / G / B color density profiles 510, 511, 512, 520, 521, and 522 are obtained along each of the straight lines x1 and y1. In this example, because the background color is white, the color density profiles have large values for the color density of the background and small values for the color density of the dots.

[0035] While this example shows an example in which a color density profile is acquired for a specified dot along two directions, x1 and y1, the present invention is not limited to this, and only one straight line may be set and a density profile acquired in only one direction. Also, while this example shows an example in which three density profiles of R / G / B are acquired along a straight line, the present invention is not limited to this, and for example, a color density profile of any of R / G / B appropriate for the ink color may be acquired.

[0036] 6 is an example of a color density profile 512 for "B" out of R / G / B along x1 in the range of the above-mentioned dot d11. Each dot typically has an area with a lot of moisture around the ink area that gradually becomes lighter towards the periphery, and in this example, the color density profile 512 shows that the color density value in the ink area of dot d11 is small, and the color density value gradually increases from the outer periphery to the background.

[0037] As shown in Figure 3, the judgment processing unit serving as the judgment means 41c includes a substantial ink area length calculation unit 410 that calculates the length L1 of the area that is essentially made up of ink and whose color density level falls within the range from the minimum value to a predetermined value based on the color density profile of the obtained dot for each halftone dot area R11 to R14, a dot area length calculation unit 411 that calculates the length L2 of the entire area along the straight line as the size of the dot, a dot shape analysis unit 412 that analyzes the shape of the dot based on the values of L1 and L2, and a judgment unit 413 that judges the quality of the ink print based on the analysis results.

[0038] The "predetermined value" used by the actual ink area length calculation unit 410 to calculate L1 is preferably a predetermined percentage value at which the color density becomes smaller due to the presence of ink, with the numerical range from the lowest value to the highest value being 100%, for example, a predetermined percentage value of about 5 to 30%, such as 10%. Alternatively, the predetermined value may be determined based on the shape of the profile curve, such as an inflection point. Using the example of Figure 6, two points 61 and 62 on the line x1 where the color density level becomes a predetermined value are identified, and the distance L1 between them is calculated.

[0039] The dot region length calculation unit 411 can set in advance the color density at the boundary position between the dot and the background, and calculate the distance between the boundary positions (positions 71 and 72 in the example of FIG. 6) as L2. Alternatively, L2 can be calculated by determining the boundary position based on the results of shape recognition when the dot is identified.

[0040] For example, if the calculated L1 is greater than the maximum value (reference value) predetermined as the normal range of L1 for the dot (d11 in the example of FIG. 6), the dot shape analysis unit 412 can analyze that there is too much ink, and if it is less than the minimum value (reference value), it can analyze that there is not enough ink.Furthermore, if the calculated L2 is greater than the maximum value (reference value) predetermined as the normal range of L2 for the dot, it can analyze that there is dot gain, where the dot is crushed, and if it is less than the minimum value (reference value), it can analyze that the dot is missing.

[0041] Also, for example, if the calculated difference between L1 and L2 is greater than the maximum value (reference value) predetermined as the normal range of the difference between L1 and L2 for the dot in the image (d11 in the example of Figure 6), it can be analyzed as having too much moisture.In addition to the difference, it is also possible to analyze the ratio or other values found by a predetermined formula using the calculated L1 and L2, by comparing them with a reference range.

[0042] The dot shape analysis unit 412 also calculates the distance L31 between positions 61 and 71 and the distance L32 between positions 62 and 72 at both ends of the dot (d11 in the example of Figure 6) along the line x1, and if the difference between the two (L31 and L32) is within a predetermined range of normal values, it analyzes that there is no ink bias, but if it is greater than the maximum value (reference value) of that range, it analyzes that the ink is biased toward the position with the smaller distance value. Figure 6 shows an example of no ink bias, but if there is ink bias, as in the dot shown in Figure 7, the difference between L31 and L32 will be large, and if it is greater than the maximum value, it can be analyzed that the ink is biased toward the position with the smaller distance, i.e., L32 in the example of Figure 7.

[0043] In this example, in addition to the line x1, the distance L33 between similar positions 63 and 73 and the distance L34 between positions 64 and 74 along the line y1 can also be determined, thereby making it possible to more accurately determine the direction of ink distribution. For example, using the dot example in FIG. 7 , the dot shape analysis unit 412 identifies, from each color density profile along the lines x1 and y1, point m1 on the line x1 and point m2 on the line y1, where the color density is lowest within the range of dot d11, as shown in FIG. 8 . These are then set as the centers of the effective ink projected onto x1 and y1, respectively. Then, point c11 on a two-dimensional plane, identified by the x and y coordinates of the centers m1 and m2, is set as the actual center of the effective ink. The direction and amount of ink distribution can be more accurately determined from vector B11 starting from center point c10 of dot d11.

[0044] Furthermore, an ink density calculation unit is provided that calculates the difference H1 between the minimum and maximum color density levels from the color density profile of the dot acquired by the color density acquisition means, and the dot shape analysis unit 412 can analyze the presence or absence of dot blurring or dot gain by comparing the H1 value with a predetermined reference range (reference value: minimum value / maximum value) as the normal value of H1 for the dot of the image (d11 in the examples of Figures 6 and 7).

[0045] In a preferred example, the judgment processing unit has a machine learning mechanism, stores color density profiles for various cases, including color density profiles for abnormal cases, as training data, and performs analysis and judgment by referring to the learning results of the machine learning mechanism. The learning method of the machine learning mechanism can be any method, such as deep learning using a neural network.

[0046] It is also preferable that the judgment processing unit (judgment means 41c) further judges the moisture content and adjustment amount of each ink. For example, in the abnormal state shown in Figure 7, it is also preferable to judge the moisture content of the ink, the necessary moisture and other adjustment amounts, etc. based on the degree of the abnormality, i.e., the amount of ink unevenness and the amount of deviation of dot gain from the normal value.

[0047] In the case of blurring, the water content is high and the ink is in an over-emulsified state, and in the case of dot gain that appears darker than the ink color, the water content is low, and if the necessary adjustment amounts for each are known, it will be possible to automatically adjust and control the water content of the ink (for example, temperature, ink viscosity, etc. in addition to water content).Here too, it is a preferable example to determine the adjustment amount for water content, etc. by referring to the learning results of a machine learning mechanism.

[0048] The above example of the judgment processing unit is an example of the color density profile 512 of "B" out of R / G / B, but other color density profiles can also be processed in the same way to analyze and judge in more detail. It is also possible to determine the average value.

[0049] The processing device 41 further includes a misregistration inspection unit 41d, a color density inspection unit 41e, and an output processing unit 41f. The misregistration inspection unit 41d calculates the amount of misregistration from the relative positions of the inspection marks captured by the imaging unit 2, and determines that misregistration has occurred if the calculated amount exceeds a preset threshold. For example, as shown in Fig. 9, the presence or absence of misregistration can be determined by calculating the vertical and horizontal deviations of the other marks M2 to M4 (x1 to x3, y1 to y3 in the figure) relative to mark M1.

[0050] The reference line L1 for x1 to x3 and the reference line L2 for y1 to y3 can be formed by providing a reference mark M1 at each end and printing M2 to M4 between them so that the marks are aligned in a row, so that the line connecting the centers of M1 at both ends can be used as the reference line L1, and L2 can be a line that passes through the center of one of M1 and is perpendicular to L1.

[0051] Another method of detecting misregistration is to determine the positions of regions R01 to R04 on the printed material in advance, as shown in Figure 10, and analyze the color density of each pixel of the image of each mark M1 to M4 within the acquired region.Then, based on the pixel-by-pixel position information, it is possible to analyze how the ink color and background color are biased vertically and horizontally from the center of the region and determine the degree of misregistration.

[0052] The color density inspection unit 41e analyzes the color density of the first region r1 where the marks of the above-mentioned regions R01 to R04 are printed solidly, compares it with a color density level that is a preset normal reference, and determines whether or not there is an abnormality.

[0053] The output processing unit 41f generates the judgment results (results such as blurred dots, dot gain occurrence, necessary adjustment amount of ink moisture, etc., misregistration, abnormal color density, etc.) by the above-mentioned judgment processing unit (41c), misregistration inspection unit 41d, and color density inspection unit 41e as output information, and displays this on a display or transmits it to an operator terminal along with audible and visual warnings and cautions.

[0054] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and it goes without saying that the present invention can be embodied in various forms without departing from the spirit of the present invention. [Explanation of symbols]

[0055] 1. Print quality inspection device 2. Imaging Method 3 Lighting means 9 Printing surface 11A,11B,11C,11D Printing device 41 Processing equipment 41a Area image acquisition processing unit 41b Color density acquisition processing unit 41c Judgment processing unit 41d Misregistration Inspection Department 41e Color Density Inspection Unit 41f Output processing section 42 Memory means 42a Area image storage unit 42b Color density profile storage section 410 Actual ink area length calculation unit 411 Dot area length calculation unit 412 Dot Morphology Analysis Unit 413 Judgment section 510, 511, 512 color density profiles M1~M4 marks P1 Picture R01~R04 area R11~R14 halftone dot area W printed matter d11 dot

Claims

1. An image of an area including a predetermined halftone dot area consisting of dots of a single ink color printed on a sheet and a background is captured; A straight line passing through at least one of the dots included in the captured image of the halftone dot region is set; measuring color density levels along the straight line to obtain a color density profile of the dot along the straight line; The print quality inspection method is characterized in that the print quality, including the dot shape of the ink of the ink color of the dot, is judged based on the color density profile.

2. From the color density profile of the dot, a region length L1 of a region where ink is substantially applied and the color density level falls within a range from the minimum value to a predetermined value is calculated, 2. The print quality inspection method according to claim 1, wherein the print quality of the ink is judged based on the value of L1.

3. 3. The print quality inspection method according to claim 2, wherein the print quality of the ink is determined by comparing a value calculated by a predetermined calculation formula using L1 and the total area length L2 of the dot along the straight line with a reference value.

4. 2. A print quality inspection method according to claim 1, further comprising the steps of: determining a difference H1 between the minimum and maximum color density levels from the color density profile of the dots; and comparing this H1 value with a reference value to determine whether the print quality of the ink is acceptable.

5. Setting two of the straight lines to intersect within the dot, Obtain two color density profiles along each line of the dots; From each density profile, a position T1 of the minimum color density level on each straight line of the dots and positions E1 and E2 of both ends of the area on each straight line of the dots are obtained, 2. The print quality inspection method according to claim 1, wherein the direction of ink bias constituting the dots is determined based on the straight lines T1, E1, and E2.

6. 6. A print quality inspection method according to claim 5, wherein the position of the center of the dot to be used as a reference is identified from E1 and E2 of each of the straight lines, and the position of the actual ink center of the dot is identified from T1 of each of the straight lines, and the direction of ink bias is determined from the positional relationship between these two.

7. an imaging means for imaging an area including a predetermined halftone dot area composed of dots of a single ink color printed on a sheet and a background; a color density acquisition means for setting a straight line passing through at least one of the dots included in the image of the halftone dot area captured by the imaging means, and measuring a color density level along the straight line to acquire a color density profile of the dot along the straight line; a determining means for determining whether or not the print quality, including the dot shape, of the ink of the ink color of the dot is good or bad, based on the color density profile acquired by the color density acquiring means; A print quality inspection device comprising:

8. The determination means a substantial ink area length calculation unit that calculates an area length L1 where the color density level falls within a range from a minimum value to a predetermined value from the color density profile of the dot acquired by the color density acquisition unit; a determination processing unit that determines whether the print quality of the ink is good or bad based on the value of L1; The print quality inspection device of claim 7 , comprising:

9. a dot area length calculation unit for calculating a total area length L2 of the dot along the straight line, 9. The print quality inspection device according to claim 8, wherein the judgment processing unit judges whether the print quality of the ink is good or bad based on the values of L1 and L2.

10. 10. The print quality inspection device according to claim 9, wherein the judgment processing unit judges whether the print quality of the ink is good by comparing a value obtained by a predetermined calculation formula using L1 and L2 with a reference value.

11. The determination means an ink density calculation unit that calculates a difference H1 between a minimum value and a maximum value of a color density level from the color density profile of the dot acquired by the color density acquisition unit; a judgment processing unit that judges whether the print quality of the ink is good by comparing the value of H1 with a reference value; The print quality inspection device of claim 7 , comprising:

Images