JP7021144B2 - Printed matter inspection methods and programs, printed matter inspection equipment, printing systems - Google Patents

Description

The present invention relates to a printed matter inspection method and program, a printed matter inspection device, and a printing system, and particularly relates to a technique for identifying a candidate for a streak-like defect from a printed matter.

In a single-pass inkjet recording device, streak-like defects are likely to occur due to nozzle non-ejection or ejection defect. On the other hand, there is known a method of performing a streak inspection by comparing an inspection image obtained by reading a printed matter with a reading device and a reference image serving as an inspection reference of the printed matter by a method based on a difference.

In Patent Document 1, streak defect candidates are extracted from the high-pass inspection image showing the difference between the inspection image obtained by reading the printed matter and the inspection image subjected to the smoothing treatment, and the reference image from which the printed matter is generated and the smoothing treatment are described. Described is an inspection device that extracts a streak-like pattern from a high-pass reference image showing a difference from the applied reference image, collates the streak defect candidate with the streak-like pattern, and detects a streak-like defect. In this inspection device, the "overlap degree" using the streak length and the collation range is collated.

However, in the inspection device described in Patent Document 1, the degree of overlap cannot be accurately obtained depending on the provisions of the method for comparing the intensities and the difference intensities of the high-pass inspection image and the high-pass reference image, and there is no streak-like defect. Detection and false positives occur. In particular, when the reference image is digital data from which the printed matter is generated, it is difficult to accurately determine the degree of overlap because the microstructures of the inspection image and the image are different.

Further, in contrast to the detection method based on a simple difference between the high-pass inspection image and the high-pass reference image, the degree of overlap tends to be relatively small with a weak signal difference, so that weak streak-like defects are likely to be undetected.

Furthermore, since the high-pass inspection image is created from the difference between the inspection image and the smoothed image of the inspection image, the smoothing is not sufficiently performed in the part containing a strong streak-like defect, and the streak information remains even after the smoothing. Often ends up. As a result, most of the streak information is drowned out by the difference, so that streak-like defects may not be detected.

Japanese Unexamined Patent Publication No. 2017-53673

In printed matter printed by a single-pass inkjet recording device, streak-like defects occur only in a certain direction. For this reason, inspection data was acquired by making each inspection section of the inspection image in which the printed matter was imaged one-dimensional by averaging or integration in the direction of the streaks, and reference data was acquired from the reference image as the inspection standard. In the above, it is determined whether the streak portion has a streak-like defect or the non-streak portion without the streak-like defect by the signal strength difference of the difference data between the inspection data and the reference data. However, it has been found that the following problems occur when such an inspection is carried out.

The reading value of the streak portion in the inspection data is observed as a very weak signal value when the streak-like defect is weak. Even such a weak defect needs to be detected in order to be visually conspicuous when the spatial frequency occurs on a low frequency background. In this case, since the signal strength difference between the inspection data and the reference data in the streak portion is small, it is necessary to perform threshold processing so that even a small signal strength difference can be determined as the streak portion.

On the other hand, in a place where the spatial frequency of the background is high, each signal of the inspection data and the reference data is easily affected by noise at high frequency, and a signal intensity difference due to noise occurs in the difference data. This noise-induced signal strength difference may be greater than or equal to the signal strength difference of the weak streaks that occur on a low-frequency background, and if a threshold value is used to determine that even a small signal strength difference is a streak, Despite the non-streak part, there is a problem that it is erroneously detected as a streak part due to noise.

Therefore, for example, it is conceivable to analyze the frequency of the reference data so that if the frequency is high, it is determined not to be a streak portion. However, in this case, there is a problem that the high-frequency background streaks are not detected. Since the intermediate gradation is expressed by the presence or absence of ink dots in the printed matter, the spatial frequency distribution is often microscopically high in the intermediate gradation, and it is not preferable that the high frequency background streaks are not detected. ..

As described above, conventionally, it is difficult to satisfy all three points of positive detection of weak streaks in low frequency part, avoidance of false detection of streak-like part in high frequency part, and positive detection of streak part in high frequency part. rice field.

The present invention has been made in view of such circumstances, and is an inspection method and program for printed matter, an inspection device for printed matter, and printing for appropriately identifying candidates for streak-like defects contained in printed matter regardless of the spatial frequency of the printed matter. The purpose is to provide a system.

One aspect of the printed matter inspection method for achieving the above object is an inspection data acquisition step of acquiring inspection data based on an inspection image of the printed matter to be inspected by an image pickup device, and an inspection standard of the printed matter. A reference data acquisition process for acquiring reference data based on the reference image, and a base level data acquisition process for acquiring smoothed base level data based on at least one of the data based on the inspection image and the data based on the reference image. , A streak candidate specifying step for identifying streak candidates that are candidates for streak-like defects contained in printed matter based on inspection data, reference data, and base level data, and the streak candidate specifying step is an inspection at a specific position. When the first difference strength between the data and the reference data has a certain value, the smaller the second difference strength between the reference data and the base level data at the specific position, the higher the probability that there is a streak-like defect at the specific position. A method for inspecting printed matter, comprising: a streak degree index calculation step for calculating a streak degree index which is an index for quantifying characteristics, and a first threshold value processing step for subjecting the calculated streak degree index to a threshold value according to a first threshold value. Is.

According to this aspect, when the first difference strength between the inspection data and the reference data at the specific position has a constant value, the smaller the second difference strength between the reference data and the base level data at the specific position, the more the specific position. The streak degree index, which is an index that quantifies the characteristic that the probability of having streak-like defects increases, is calculated, and the calculated streak degree index is subjected to the threshold processing by the first threshold value, so that the spatial frequency of the printed matter is applied. Regardless of this, candidates for streak-like defects contained in printed matter can be appropriately identified.

The streak degree index is an index that quantifies the characteristic that when the second difference intensity at a specific position has a certain value, the probability that there is a streak-like defect at a specific position increases as the first difference intensity at the specific position increases. Is preferable. This makes it possible to appropriately identify candidates for streak-like defects contained in the printed matter regardless of the spatial frequency of the printed matter.

The streak degree index is preferably an index using the ratio of the first value including the first difference strength and the second value including the second difference strength. This makes it possible to appropriately calculate the streak degree index.

Assuming that the first difference strength of the streak candidate position specified in the streak candidate specifying step is ΔS and the second difference strength of the streak candidate position specified in the streak candidate specifying step is ΔR, it is 0 when ΔS> 0. It is preferable to satisfy ΔS / (ΔS + ΔR)> ε for ε which is 1 or more and 0.9 or less. This makes it possible to appropriately identify candidates for streak-like defects contained in the printed matter regardless of the spatial frequency of the printed matter.

Assuming that the first difference intensity at a specific position is ΔS, the second difference intensity at a specific position is ΔR, and the streak degree index at a specific position is P, the streak degree index P is represented by P = ΔS / (ΔS + ΔR). Is preferable. This makes it possible to appropriately calculate the streak degree index.

Assuming that the first threshold value is ε which is 0.1 or more and 0.9 or less, the streak candidate specifying step may specify a specific position as a streak candidate position when ΔS> 0 and P> ε is satisfied. preferable. This makes it possible to appropriately identify candidates for streak-like defects contained in the printed matter regardless of the spatial frequency of the printed matter.

The base level data is preferably obtained by smoothing the data based on the reference image. Further, the base level data may be obtained by smoothing the reference data. As a result, the base level data can be appropriately acquired.

The base level data is preferably obtained by smoothing the data based on the inspection image and the data based on the reference image. Further, the base level data may be acquired by smoothing the inspection data and the reference data. As a result, the base level data can be appropriately acquired.

The reference data is preferably acquired based on the reference image captured by the image pickup apparatus. As a result, the reference data can be appropriately acquired.

The reference data is preferably acquired based on the halftone-processed digital data used when the printed matter was printed. Further, the reference data may be acquired by simulating a print dot image produced by printing by a printing apparatus with respect to digital data that has undergone halftone processing. As a result, the reference data can be appropriately acquired.

It is preferable that at least one of the reference data and the difference data between the reference data and the base level data is provided with a filtering step of performing a filtering process by a filter that expands at least in the spatial direction. This makes it possible to absorb the positional deviation between the inspection data and the reference data.

The filter is preferably a maximum value filter. As a result, the positional deviation between the inspection data and the reference data can be appropriately absorbed.

It is preferable to include a second threshold value processing step in which the value based on the first difference intensity is subjected to the threshold value processing by the second threshold value. As a result, it is possible to prevent false detection as a streak candidate even though a streak-like defect has not occurred.

This aspect also includes a program for causing a computer to execute a method for inspecting printed matter.

One aspect of the printed matter inspection device for achieving the above object is an inspection data acquisition unit that acquires inspection data based on an inspection image of the printed matter to be inspected by the image pickup device, and an inspection standard for the printed matter. A reference data acquisition unit that acquires reference data based on the reference image, and a base level data acquisition unit that acquires smoothed base level data based on at least one of the data based on the inspection image and the data based on the reference image. , A streak candidate identification unit that identifies streak candidates that are candidates for streak-like defects contained in printed matter based on inspection data, reference data, and base level data, and the streak candidate identification unit is inspected at a specific position. When the first difference strength between the data and the reference data has a certain value, the smaller the second difference strength between the reference data and the base level data at the specific position, the higher the probability that there is a streak-like defect at the specific position. A printed matter inspection device including a streak degree index calculation unit that calculates a streak degree index that is an index that quantifies characteristics, and a first threshold value processing unit that performs threshold processing by a first threshold on the calculated streak degree index. Is.

According to this aspect, when the first difference strength between the inspection data and the reference data at the specific position has a constant value, the smaller the second difference strength between the reference data and the base level data at the specific position, the more the specific position. The streak degree index, which is an index that quantifies the characteristic that the probability of having streak-like defects increases, is calculated, and the calculated streak degree index is subjected to the threshold processing by the first threshold value, so that the spatial frequency of the printed matter is applied. Regardless of this, candidates for streak-like defects contained in printed matter can be appropriately identified.

One aspect of the printing system for achieving the above object includes a printing device that prints a printed matter based on digital data, an imaging device that captures an image of the printed matter and acquires an inspection image, and the above-mentioned inspection device. It is a printing system.

According to this aspect, the printed matter is printed based on the digital data, the printed matter is imaged, the inspection image is acquired, and the printed matter is inspected. Can identify defect candidates appropriately.

According to the present invention, candidates for streak-like defects contained in a printed matter can be appropriately identified regardless of the spatial frequency of the printed matter.

Graph showing the intensity distribution of a relatively low frequency background image A diagram showing the distribution of ink dots and their intensity distribution A diagram showing the distribution of ink dots and their intensity distribution Diagram showing the definition of each value Overall configuration diagram showing the overall schematic configuration of an inkjet printing system Block diagram showing the internal configuration of an inkjet printing system Block diagram showing the internal configuration of the inspection device Flowchart showing the processing of the printing method

<Streak degree index>
[Specific example of the problem of streak detection]
First, a defect inspection of a printed matter for detecting a streak-like defect (hereinafter, simply referred to as a streak) contained in the printed matter will be described. The defect inspection of the printed matter is performed by comparing the inspection data based on the inspection image obtained by capturing the printed matter with the image pickup apparatus and the reference data based on the reference image which is the inspection reference of the printed matter.

FIG. 1 is a graph showing the intensity distribution of a background image having a relatively low frequency. In FIG. 1, the horizontal axis indicates the position of the image in the X direction, and the vertical axis indicates the intensity value that becomes larger as the brightness of the image is larger (brighter). The solid line in FIG. 1 is the inspection data in which the inspection image is one-dimensionalized in the Y direction orthogonal to the X direction, and shows the intensity distribution of the inspection data when weak streaks, which are low-contrast streaks, occur in the Y direction. Shows. Further, the dotted line in FIG. 1 shows the intensity distribution of the reference data in which the reference image is one-dimensionalized in the Y direction. The broken line in FIG. 1 will be described later.

In the example shown in FIG. ₁ , since _a weak streak is generated at the position X1 in the X direction, the intensity value of the inspection data at the position X1 is relatively large. Therefore, when the difference strength, which is the difference between the inspection data and the reference data, is calculated, the difference strength is relatively large at the position X1 which is the streak portion as compared with the _other positions. Therefore, it can be seen that the streak portion can be positively detected by extracting the difference strength between the inspection data and the reference data, setting a threshold value that does not extract the difference strength other than the streak portion, and performing the threshold value processing.

FIG. 2 is a diagram showing the distribution of ink dots in the inspection image and the intensity distribution thereof. F2A shown in FIG. 2 is the distribution of ink dots in the intermediate gradation of the inspection image. F2B shown in FIG. 2 is a graph showing the intensity distribution of the inspection data of the inspection image shown in F2A and the reference data of the reference image. In F2B, as in FIG. 1, the horizontal axis indicates the position of the image in the X direction, and the vertical axis indicates the intensity value. The solid line in FIG. 2B shows the inspection data one-dimensionalized in the Y direction, and the dotted line shows the reference data one-dimensionalized in the Y direction. The broken line in FIG. 2B will be described later.

In the example shown in FIG. 2, no streaks are generated, but since the gradation is intermediate, both the inspection data and the reference data are high-frequency signals. Further, since the frequency is high, the inspection data and the reference data are easily affected by noise. For example, at the position X2 in the X direction, a certain degree of strength difference occurs between the inspection data and the reference data even though no streaks _are generated, and the streaks are similar to the streaks.

Therefore, when the difference strength between the inspection data and the reference data shown in FIG. 2 is threshold-processed using the threshold value for positively detecting the weak streaks shown in FIG. There is a problem of false detection.

As a method of solving such a problem, for example, there is a method of performing frequency analysis of reference data and not detecting a streak portion in a relatively high frequency part.

FIG. 3 is a diagram showing the distribution of ink dots in the inspection image and the intensity distribution thereof. F3A shown in FIG. 3 is the distribution of ink dots in the intermediate gradation of the inspection image. The reference image of this inspection image is the same as the reference image of the inspection image shown in FIG. F3A shows an example in which dots are removed and streaks _are generated at the position X3 in the X direction because some of the nozzles in charge of dot formation are non-ejection.

F3B shown in FIG. 3 is a graph showing the intensity distribution of the inspection data of the inspection image shown in F3A and the reference data of the reference image. In F3B, similarly to F2B, the horizontal axis indicates the position in the X direction of the image, and the vertical axis indicates the intensity value. The solid line in FIG. 3B shows the inspection data one-dimensionalized in the Y direction, and the dotted line shows the reference data one-dimensionalized in the Y direction. The broken line of F3B will be described later.

Since the dots _are missing at the position X3 in the X direction _, the intensity of the inspection data is relatively large at the position X3 as shown in F3B. In the example of the inspection image shown in F3A, streaks are generated, so we want to detect them correctly. However, if control is performed so that the streak portion is not detected at a relatively high frequency portion, the streak portion will not be detected.

As described above, it is difficult to satisfy all three points of positive detection of the weak streak portion of the low frequency portion, avoidance of false detection of the streak-like portion of the high frequency portion, and positive detection of the streak portion of the high frequency portion. As a result of diligent studies, the inventor of the present application has found a solution that satisfies these three points.

〔solution〕
In the graphs showing the intensity distributions of FIGS. 1, 2, and 3, the broken line indicates the base level data one-dimensionalized in the Y direction. The base level data is obtained by smoothing at least one of the data based on the reference image and the data based on the inspection image by some means. The base level data shown in FIGS. 1, 2, and 3 are obtained by smoothing the reference data in which the reference image is one-dimensionalized in the Y direction.

Comparing the graphs of FIGS. 1 and 2, the first difference strength, which is the difference between the inspection data and the reference data at the position X1 in the X direction shown in the graph of FIG. ₁ , and the position in the X direction shown in the graph of FIG. The first difference intensity, which is the difference between the inspection data and the reference data in X ₂ , is the same constant value. Then, when the first difference strength has the same value, it can be seen that the smaller the second difference strength, which is the difference between the reference data and the base level data, the higher the possibility that there is a streak at that position. By utilizing this characteristic, it is possible to satisfy three points: positive detection of a weak streak portion in a low frequency portion, avoidance of false detection of a streak-like portion in a high frequency portion, and positive detection of a streak portion in a high frequency portion.

The details will be described. FIG. 4 is a diagram showing the definition of each value. The solid line in FIG. 4 shows the inspection data one-dimensionalized in the Y direction, the dotted line shows the reference data one-dimensionalized in the Y direction, and the broken line shows the base level data one-dimensionalized in the Y direction. As shown in FIG. ₄ , the position in the X direction is T for the strength of the inspection data at a specific position (here, position X4), R for the strength of the reference data, B for the strength of the base level data, and T for the inspection data. The first difference intensity, which is the difference (TR) from the data R, is defined as ΔS, and the second difference intensity, which is the difference (RB) between the reference data R and the base level data B, is defined as ΔR.

Here, using ΔS and ΔR, the streak degree index P can be defined as follows (Equation 1).

P = ΔS / (ΔS + ΔR)… (Equation 1)
As shown in Equation 1, when the first difference strength ΔS and the second difference strength ΔR are both 0 or more, the streak degree index P approaches 0 as the second difference strength ΔR increases, and the second difference strength The smaller ΔR, the closer to 1. That is, under the condition that both the first difference intensity ΔS and the second difference intensity ΔR are 0 or more, the streak degree index P has a range of 0 to 1, and the larger the streak degree index P is, the more the streak degree index P is located at a specific position. The probability of having a streak-like defect is high, and the smaller the streak degree index P is, the lower the probability of having a streak-like defect at a specific position. As described above, the streak degree index P has a characteristic that when the first differential intensity at a specific position has a constant value, the smaller the second differential intensity at the specific position, the higher the probability that there is a streak-like defect at the specific position. Is a quantified index.

Further, the streak degree index P is an index that quantifies the characteristic that when the second difference strength ΔR has a constant value, the larger the first difference strength ΔS is, the higher the probability that there is a streak-like defect at a specific position. be. That is, the larger the first difference intensity ΔS, the smaller the calculation contribution of the second difference intensity ΔR. By utilizing this characteristic, the three points of positive detection of weak streaks in the low frequency part, avoidance of false detection of streak-like parts in the high frequency part, and positive detection of streaks in the high frequency part are satisfied. Shows that it can be done.

The streak degree index P calculated in this way is subjected to threshold processing with the threshold value ε. can do.

For example, when the threshold value ε is set to “0.5”, the position X1 in the X direction in FIG. ₁ is a streak candidate, the position X2 in the X direction in FIG. ₂ is a non-streak part _, and the position X3 in the X direction in FIG. Is judged to be a streak candidate.

If the first difference strength ΔS is less than 0, there is no streak strength in the first place, so it may be determined that the streak portion is not. Further, when the first difference intensity ΔS is 0 or more and the second difference intensity ΔR is less than 0, the streak degree index P becomes larger than 1, but in this case, it is highly possible that the streak is streak. Therefore, there is no failure in the definition of the streak degree index P that the larger the value, the higher the probability of streaks.

In addition, the word "streak candidate" is used, but the reason for this is that there are multiple judgment criteria for the streak part and the non-streak part, and the multiple criteria may be combined and finally judged as a streak. Is. For example, with respect to the position of the streak candidate specified by the above method, when the first difference intensity ΔS exceeds the second threshold value α, it may be finally determined as the streak portion. By doing so, when both the first difference strength ΔS and the second difference strength ΔR are small, it is possible to prevent the non-streak portion from being erroneously detected as the streak portion.

[Magnitude of threshold value ε]
The larger the value of the threshold value ε, the lower the false positive rate, while the higher the undetected rate, the lower the positive detection rate. In order to secure the minimum false positive rate, it is desirable that the threshold value ε is 0.1 or more. Further, in order to secure the minimum positive detection rate, it is desirable that the threshold value ε is 0.9 or less.

[Deformation of streak degree index P]
As shown in FIG. 4, there is a relationship of ΔS = TR and ΔR = RB. Therefore, using this relationship, (Equation 1) may be used in a modified state. Further, if the difference (TB) between the inspection data T and the base level data B is defined as ΔT, it can be seen that ΔT = ΔS + ΔR. Therefore, the streak degree index P may be defined as the following (Equation 2).

P = ΔS / ΔT ... (Equation 2)
Further, the determination may be made by reversing the relationship between the magnitude of the threshold setting, such as ε'= 1-ε.

All of these modifications are included in the scope of (Equation 1). That is, the streak degree index P includes a value using the ratio of the first value including the first difference intensity and the second value including the second difference intensity.

[Countermeasures against peak position deviation]
Depending on the noise generation situation, the peak position in the X direction of the inspection data and the peak position in the X direction of the reference data may deviate from each other. For example, in F2B of FIG. 2, the peak position of the inspection data is located at the position X ₂₁ in the X direction, and the peak position of the reference data is located at the position X ₂₂ in the X direction. However, the peak position of the inspection data and the peak position of the reference data should originally exist at the same position in the X direction. When such a deviation occurs, a place where the value of the first difference strength ΔS is calculated unreasonably large occurs, which causes erroneous detection or non-detection. In defect inspection of printed matter, we often dislike the occurrence of false positives. Therefore, in order to suppress the occurrence of false positives, it is desirable to filter at least one of the reference data and the difference data between the reference data and the base level data by a filter that expands at least in the spatial direction. The filter that expands in the spatial direction is preferably a maximum value filter. The spatial direction here refers to the X direction. As will be described later, when the inspection is performed on a two-dimensional image without making it one-dimensional, the spatial direction includes at least the X direction.

[Reference image]
The reference data is acquired based on the reference image which is the inspection standard of the printed matter. The reference data may be acquired based on the reference image captured by the image pickup apparatus for the printed matter without streaks, or may be acquired based on the digital data used when the printed matter is printed.

[How to get base level data]
In this embodiment, the base level data is acquired by smoothing the reference data. The base level data may not be sufficiently smoothed if there are streaks in the image, and in such a case, the difference may drown out much of the streak information, leading to undetection. Therefore, the base level data should be created based on the reference data. However, the base level data may be acquired by smoothing the inspection data. Alternatively, the base level data may be acquired by smoothing the reference data and the inspection data.

When the reference image is digital data, the image structure of the reference data and the image structure of the inspection data are different. Therefore, the base level data for the reference data is obtained by smoothing the reference data, and the base level for the inspection data. The data is obtained by smoothing the inspection data and two base level data may be used in each calculation. For example, if the base level data for inspection data is BT and the base level data for reference data is BR, even if it is calculated as ΔT = T-BT, ΔR = R-BR, ΔS = ΔT-ΔR, etc. good.

However, under the condition that the image structures of the digital data and the inspection data are similar, it is preferable to create the base level data based on the reference data. As an example of the condition where the image structure is similar, there is a case where halftone processed digital data (including both binarization of single ink droplet size and multi-valued of multiple ink droplet sizes) is used as digital data. .. A simulation processing unit that simulates a print dot image produced by printing by a printing apparatus that actually prints halftone-processed digital data may be provided, and the image structure may be further brought closer. Examples of the simulation include a method of simulating a physical dot gain such as an ink droplet size and an ink droplet shape, and a method of simulating an optical dot gain due to light scattering of a print medium. Of course, other simulations may be performed.

[Method not to make it one-dimensional]
The inspection data, the reference data, and the base level data of the present embodiment are data that have been made one-dimensional in the direction of the streaks in advance, but the present embodiment can be applied even if the two-dimensional image is used as it is. That is, an inspection image obtained by capturing a printed matter with an imaging device is used as inspection data, a reference image serving as an inspection standard for printed matter is used as reference data, and a base level image obtained by smoothing at least one of a reference image and an inspection image as base level data. By using, it is possible to detect streak candidates in the same way.

<Inkjet printing system>
An inkjet printing system to which an inspection device for printed matter using the above streak degree index is applied will be described.

[Structure of inkjet printing system]
FIG. 5 is an overall configuration diagram showing an overall schematic configuration of the inkjet printing system 100. The inkjet printing system 100 prints a color image by ejecting four color inks of cyan (C), magenta (M), yellow (Y), and black (K) onto sheet-fed paper 1 which is a printing medium. Includes printing equipment.

General-purpose printing paper is used as the paper 1. The general-purpose printing paper is not a so-called inkjet-only paper, but a paper mainly composed of cellulose such as coated paper used for general offset printing. Further, water-based ink is used as the ink. The water-based ink refers to an ink in which a coloring material such as a dye or a pigment is dissolved or dispersed in water or a solvent soluble in water.

As shown in FIG. 5, the inkjet printing system 100 includes a transport unit 110, a printing unit 120, an image pickup unit 130, a drying unit 140, a sorting unit 150, a paper ejection unit 160, and the like. Of these, at least the transport unit 110 and the printing unit 120 constitute the printing apparatus.

[Transport section]
The transport unit 110 transports the paper 1 fed from the paper feed unit (not shown) in the transport direction (Y direction). The transport unit 110 includes an upstream pulley 112, a downstream pulley 114, and a transport belt 116.

The upstream pulley 112 has a rotation axis (not shown) extending in the horizontal direction, and the rotation axis is rotatably supported. The downstream pulley 114 has a rotation axis (not shown) parallel to the rotation axis of the upstream pulley 112, and the rotation axis is rotatably supported.

The conveyor belt 116 is a stainless steel endless belt. The transport belt 116 is bridged over the upstream pulley 112 and the downstream pulley 114. By using the stainless steel conveyor belt 116, the flatness of the paper 1 can be kept good.

The downstream pulley 114 has a motor (not shown) as a driving means. When the motor is driven, the downstream pulley 114 rotates counterclockwise in FIG. The upstream pulley 112 rotates counterclockwise in FIG. 5 in accordance with the rotation of the downstream pulley 114. Due to the rotation of the upstream pulley 112 and the downstream pulley 114, the transport belt 116 travels between the upstream pulley 112 and the downstream pulley 114 along the traveling path.

Paper 1 supplied from a paper feeding unit (not shown) is placed on the transport surface of the transport belt 116. The transport unit 110 transports the paper 1 placed on the transport belt 116 along the transport path from the upstream pulley 112 to the downstream pulley 114, and delivers the paper 1 to the paper discharge unit 160. The paper 1 is conveyed while the printing surface is held horizontally at positions facing the printing unit 120, the imaging unit 130, the drying unit 140, and the sorting unit 150 on this transfer path.

By providing a plurality of suction holes (not shown) in the transport belt 116 and sucking the suction holes of the transport belt 116 with a pump (not shown), the paper 1 placed on the transport surface of the transport belt 116 is sucked and held on the transport surface. You may.

[Printing section]
The printing unit 120 forms (prints) an image on the paper 1. The printing unit 120 includes inkjet heads 122C, 122M, 122Y, and 122K. The inkjet head 122C ejects cyan (C) ink droplets by an inkjet method. Similarly, the inkjet heads 122M, 122Y, and 122K eject magenta (M), yellow (Y), and black (K) ink droplets by an inkjet method, respectively. The ejected ink droplets form ink dots on the printing surface of the paper 1.

The inkjet heads 122C, 122M, 122Y, and 122K are arranged at regular intervals along the transport path of the paper 1 by the transport belt 116. The inkjet heads 122C, 122M, 122Y, and 122K are line heads in which a plurality of nozzles (not shown) for ejecting ink droplets are arranged over a length equal to or larger than the X-direction width of the paper 1. The line head may be configured by connecting a plurality of head modules (not shown).

The inkjet heads 122C, 122M, 122Y, and 122K are arranged so that the nozzle surfaces provided with a plurality of nozzles (not shown) face the conveyor belt 116. The inkjet heads 122C, 122M, 122Y and 122K are single on the printing surface of the paper 1 by ejecting ink droplets from the nozzle formed on the nozzle surface toward the paper 1 conveyed in the Y direction by the conveying belt 116. An image with ink dots is formed by the pass method. Therefore, for example, when a non-ejection nozzle in which ink droplets are not ejected is generated, white streaks in the Y direction are generated in the formed image.

[Image pickup unit]
The image pickup unit 130 is an image pickup device that acquires an image obtained by capturing an image of the printed surface of paper 1 which is a printed matter. The image pickup unit 130 is arranged on the downstream side of the printing unit 120 with respect to the transport direction of the paper 1. The image pickup unit 130 includes a scanner 132.

The scanner 132 is a device that optically reads an image formed on the paper 1 using the inkjet heads 122C, 122M, 122Y, and 122K, and generates image data indicating the read image. The scanner 132 includes an image pickup device that captures an image printed on paper 1 and converts it into an electric signal. A color CCD (Charge Coupled Device) linear image sensor can be used as the image pickup device. A color CMOS (Complementary Metal Oxide Semiconductor) linear image sensor can also be used instead of the color CCD linear image sensor.

In addition to the image pickup device, the scanner 132 may include an illumination optical system that illuminates the reading target and a signal processing circuit that processes signals obtained from the image pickup device to generate digital image data.

[Dry part]
The drying unit 140 dries the ink on the paper 1. The drying unit 140 is arranged on the downstream side of the image pickup unit 130 with respect to the transport direction of the paper 1.

The drying unit 140 includes a heater 142. As the heater 142, for example, at least one of a halogen heater and an infrared heater is used. The heater 142 heats the printing surface of the paper 1 to dry the ink on the paper 1. The drying unit 140 may include a blowing means such as a fan or a blower.

[Sort section]
The sorting unit 150 sorts the printed matter according to the quality determination regarding the paper 1 conveyed by the conveying belt 116. The sorting unit 150 is arranged on the downstream side of the drying unit 140 with respect to the transport direction of the paper 1. The sorting unit 150 includes a stamper 152.

The stamper 152 performs a stamping process for adhering ink to the tip edge of the paper 1 determined to be a defective printed matter, according to the quality determination of the paper 1 conveyed by the transport belt 116.

[Paper ejection section]
The paper ejection unit 160 collects the dried paper 1 (printed matter) on which an image is formed. The paper ejection unit 160 is located on the downstream side of the sorting unit 150 with respect to the transport direction of the paper 1, and is arranged at the end point of the transport path of the transport unit 110. The paper ejection unit 160 includes a paper ejection table 162.

The paper ejection table 162 stacks and collects the paper 1 conveyed by the conveying belt 116. The paper ejection table 162 is provided with a front paper pad, a rear paper pad, and a horizontal paper pad (not shown), and the paper 1 is stacked in an orderly manner.

Further, the paper discharge table 162 is provided so as to be able to move up and down by an elevating device (not shown). The drive of the elevating device is controlled in conjunction with the increase / decrease of the paper 1 stacked on the output table 162. As a result, the paper 1 located at the highest position among the paper 1 stacked on the paper ejection table 162 always has a constant height.

[Control system of inkjet printing system]
FIG. 6 is a block diagram showing an internal configuration of the inkjet printing system 100. The inkjet printing system 100 includes a transport unit 110, a printing unit 120, an imaging unit 130, a drying unit 140, a sorting unit 150, and a paper ejection unit 160, as well as an inspection device 10, a user interface 170, a storage unit 172, and a general control unit 174. , A transport control unit 176, a print control unit 178, an image pickup control unit 180, a drying control unit 182, a sorting control unit 184, and a paper ejection control unit 186.

The user interface 170 includes an input unit (not shown) and a display unit (not shown) for the user to operate the inkjet printing system 100. The input unit is, for example, an operation panel that receives input from a user. The display unit is, for example, a display that displays image data and various types of information. The user can have the inkjet printing system 100 print a desired image by operating the user interface 170.

The storage unit 172 stores a program for controlling the inkjet printing system 100 and information necessary for executing the program. The storage unit 172 is composed of a hard disk (not shown) or a non-temporary recording medium such as various semiconductor memories. A volatile memory such as a RAM (Random Access Memory) (not shown) for temporarily storing a reference image or the like may be provided.

The integrated control unit 174 performs various processes according to the program stored in the storage unit 172, and controls the overall operation of the inkjet printing system 100 in an integrated manner.

The transport control unit 176 controls a motor (not shown) of the transport unit 110 to transport the paper 1 in the transport direction by the transport unit 110. As a result, the paper 1 supplied from the paper feeding unit (not shown) passes through the positions facing the printing unit 120, the imaging unit 130, the drying unit 140, and the sorting unit 150, and finally is discharged to the paper ejection unit 160. Will be done.

The print control unit 178 controls the ejection of ink by the inkjet heads 122C, 122M, 122Y, and 122K. The print control unit 178 uses the inkjet heads 122C, 122M, 122Y, and 122K to transfer cyan, magenta, yellow, and black ink droplets to the paper 1 at the timing when the paper 1 passes through the positions facing the nozzle surfaces. Discharge toward. As a result, a color image is formed on the printed surface of the paper 1, and the paper 1 becomes a “printed matter”.

The image pickup control unit 180 controls the image pickup by the scanner 132, so that the image pickup unit 130 captures an image of the paper 1 (printed matter). The image pickup control unit 180 causes the scanner 132 to read the image formed on the paper 1 at the timing when the paper 1 passes through the position facing the scanner 132. As a result, the scanner 132 acquires the inspection image.

The drying control unit 182 controls the heating by the heater 142, so that the drying unit 140 dries the paper 1. The drying control unit 182 heats the paper 1 by the heater 142 when the paper 1 passes through the position facing the heater 142.

The sorting control unit 184 controls the stamping process by the stamper 152 based on the inspection result of the inspection device 10, so that the sorting unit 150 sorts the paper 1. When the paper 1 passing through the position facing the stamper 152 is the paper 1 determined to be a defective printed matter, the sorting control unit 184 performs stamp processing by the stamper 152.

The paper ejection control unit 186 controls the loading of the paper 1 by the paper ejection table 162. The paper 1 is discharged to the paper ejection table 162 and stacked. Ink adheres to the tip edge of the defective printed matter paper 1. Therefore, the user can identify the defective printed matter from the paper 1 loaded on the output table 162.

The inspection device 10 (an example of an inspection device for a printed matter) inspects the paper 1 (an example of a printed matter to be inspected) for the presence or absence of streak-like defects, and determines a good product or a defective product of the printed matter. The inspection device 10 may perform an inspection other than the presence or absence of streaky defects.

FIG. 7 is a block diagram showing an internal configuration of the inspection device 10. As shown in FIG. 7, the inspection device 10 includes an inspection data acquisition unit 12, a reference data acquisition unit 14, a base level data acquisition unit 16, a streak degree index calculation unit 18, a threshold value processing unit 20, and a quality determination unit 22. ..

The inspection data acquisition unit 12 acquires inspection data based on an inspection image of a printed matter to be inspected by the image pickup unit 130. For example, the inspection data acquisition unit 12 acquires an inspection image from the scanner 132, integrates the acquired inspection images in the Y direction, and acquires one-dimensional inspection data.

The reference data acquisition unit 14 acquires reference data based on a reference image that serves as an inspection standard for printed matter. For example, the reference data acquisition unit 14 acquires reference data obtained by imaging a printed matter without streaks in advance and making the reference image one-dimensional in the Y direction. The reference data acquisition unit 14 may acquire digital data that has undergone halftone processing and may acquire reference data by simulating an actual print dot image.

The base level data acquisition unit 16 acquires smoothed base level data based on at least one of the data based on the inspection image and the data based on the reference image. The base level data acquisition unit 16 may acquire the base level data smoothed by the smoothing means based on at least one of the inspection data and the reference data. The base level data acquisition unit 16 may acquire the data based on the inspection image and the data based on the reference image by smoothing them by the smoothing means, or the inspection data and the reference data may be smoothed and acquired by the smoothing means. You may. Further, the base level data acquisition unit 16 may acquire the data based on the inspection image and the reference data by smoothing by the smoothing means, or the inspection data and the data based on the reference image are smoothed by the smoothing means. You may get it. Here, the base level data acquisition unit 16 smoothes the reference data by a smoothing means and acquires the base level data. The base level data acquisition unit 16 may acquire base level data by making an image in which at least one of the data based on the inspection image and the data based on the reference image smoothed at least in the X direction by a smoothing means into one dimension. ..

The smoothing means is not particularly limited, and examples thereof include smoothing filters such as a Gaussian filter, a median filter, and a moving average filter.

In addition, the terms "based" and "based" are expressions that include the use of themselves. For example, the "reference data based on the reference image" includes the reference image itself and also includes data obtained by processing the reference image by some means.

The streak degree index calculation unit 18 and the threshold value processing unit 20 constitute a streak candidate identification unit. The streak candidate identification unit identifies streak candidates that are candidates for streak-like defects based on inspection data, reference data, and base level data.

When the streak degree index calculation unit 18 has a constant value for the first difference strength between the inspection data at the specific position and the reference data, the smaller the second difference strength between the reference data at the specific position and the base level data, the smaller the difference strength. The streak degree index, which is an index that quantifies the characteristic that the probability of having a streak-like defect at a specific position increases, is calculated. The streak degree index is an index that quantifies the characteristic that when the second difference intensity at a specific position has a certain value, the probability that there is a streak-like defect at a specific position increases as the first difference intensity at the specific position increases. Is preferable. The streak degree index may be any one using the ratio of the first value including the first difference intensity and the second value including the second difference intensity. The streak degree index calculation unit 18 calculates the streak degree index P using, for example, (Equation 1).

The threshold value processing unit 20 performs threshold value processing according to the first threshold value on the calculated streak degree index. The first threshold value is, for example, the above-mentioned ε. Further, the threshold value processing unit 20 may perform threshold value processing based on the second threshold value on the first difference intensity.

The quality determination unit 22 determines the quality of the printed matter, which is the source of the inspection data, based on the threshold value processing result of the threshold value processing unit 20. The determination result of the pass / fail determination unit 22 is output to the sorting control unit 184 as the inspection result of the inspection device 10.

[Printing method]
The printing method in the inkjet printing system 100 will be described. FIG. 8 is a flowchart showing the processing of the printing method. As shown in FIG. 8, the printing method includes a reference data acquisition process (step S1), a base level data acquisition process (step S2), a printing process (step S3), an inspection data acquisition process (step S4), and a streak degree index calculation. It includes a step (step S5), a first threshold processing step (step S6), a second threshold processing step (step S7), a pass / fail determination step (step S8), and a stamp processing step (step S9). Of these, at least a reference data acquisition step (step S1), a base level data acquisition step (step S2), an inspection data acquisition step (step S4), a streak degree index calculation step (step S5), and a first threshold processing step (step). S6) constitutes an inspection method for printed matter. The printed matter inspection method may include a second threshold value processing step (step S7) and a quality determination step (step S8).

In step S1, the reference data acquisition unit 14 acquires reference data based on a reference image that serves as an inspection reference for printed matter. Here, it is assumed that the reference image created by photographing the printed matter without streaks in advance by the image pickup unit 130 is stored in the storage unit 172. The reference data acquisition unit 14 acquires a reference image from the storage unit 172, and acquires reference data in which the acquired reference image is one-dimensionalized in the Y direction. The reference image stored in the storage unit 172 may be created by imaging a printed matter without streaks in advance with an image pickup device different from that of the image pickup unit 130.

The reference data acquisition unit 14 may acquire digital data for printing as reference data. Further, the reference data acquisition unit 14 may acquire the digital data that has undergone halftone processing and may acquire the reference data by simulating an actual print dot image. Further, the reference data may be stored in the storage unit 172 in advance.

In step S2, the base level data acquisition unit 16 acquires smoothed base level data based on at least one of the inspection image and the reference image. Here, the base level data obtained by smoothing the reference data acquired in step S1 is acquired.

In step S3, the inkjet printing system 100 prints on paper 1. That is, the transport control unit 176 transports the paper 1 in the Y direction by the transport unit 110, and the print control unit 178 controls the inkjet heads 122C, 122M, 122Y, and 122K based on the digital data for printing, and transports the paper 1. Ink droplets are ejected onto the paper 1 to be printed. The digital data for printing is the same data as the digital data when the printed matter without streaks, which is the source of the reference image, is printed.

In step S4, the image pickup control unit 180 causes the scanner 132 to take an image of the paper 1 printed by the printing unit 120 and conveyed by the conveying unit 110 to a position facing the imaging unit 130. As a result, the inspection image is acquired. The inspection data acquisition unit 12 acquires inspection data in which the acquired inspection image is one-dimensionalized in the Y direction.

The streak candidate identification process is configured by steps S5 to S7. The streak candidate identification step extracts streak candidates that are candidates for streak-like defects in the printed matter of the inspected matter.

In step S5, the streak degree index calculation unit 18 calculates the streak degree index P using (Equation 1) for each position in the X direction using the reference data, the inspection data, and the base level data. Prior to step S5, the streak degree index calculation unit 18 performs a filter process on the reference data or the difference data between the reference data and the base level data by a filter such as a maximum value filter that expands in the spatial direction. An example of the filtering step) is preferable.

In step S6, the threshold value processing unit 20 (an example of the first threshold value processing unit) performs threshold value processing according to the first threshold value on the streak degree index of each position in the X direction calculated in step S5. Here, the threshold value processing unit 20 is a position in the X direction in which the streak degree index P calculated by (Equation 1) exceeds the threshold value ε (an example of the first threshold value) of 0.1 or more and 0.9 or less. Is specified as the position of the streak candidate.

In step S7, the threshold value processing unit 20 (an example of the second threshold value processing unit) performs threshold value processing according to the second threshold value with respect to the positions of the streak candidates extracted in step S6, and extracts the final streak unit. Here, the threshold value processing unit 20 compares the first difference intensity ΔS with the second threshold value α, and when the first difference intensity ΔS exceeds the second threshold value α, finally determines that it is a streak unit. The threshold value processing unit 20 may perform threshold value processing according to the second threshold value not only at the position of the streak candidate but also at each position in the X direction.

The order of step S6 and step S7 may be reversed. That is, the threshold processing unit 20 performs threshold processing according to the second threshold value at each position in the X direction to extract streak candidates, and performs threshold processing according to the first threshold value on the streak candidates to extract the final streak part. You may.

In step S8, the quality determination unit 22 determines the quality of the printed matter, which is the source of the inspection data, based on the result of step S7. For example, the quality determination unit 22 determines in step S7 that the printed matter is a defective printed matter when the streaks are present, and determines that the printed matter is a non-defective printed matter when the streaks are not present. The quality determination unit 22 may determine that the printed matter is a defective product when the number of streaks is larger than the third threshold value. The pass / fail determination unit 22 may have a pass / fail determination criterion other than the result of step S7. The determination result of the pass / fail determination unit 22 is output to the sorting control unit 184 as the inspection result of the inspection device 10.

In step S8, the quality determination unit 22 may determine the quality of the printed matter from the processing result of step S6. In this case, step S7 can be omitted.

In step S9, the sorting control unit 184 determines whether or not the paper 1 (printed matter) transported to the position facing the sorting unit 150 by the transporting unit 110 is a non-defective printed matter based on the inspection result of the inspection device 10. do. If it is a non-defective printed matter, the process proceeds to step S11. If it is not a non-defective printed matter, that is, if it is a defective printed matter, the process proceeds to step S10.

In step S10, the sorting control unit 184 causes the paper 1 determined by the stamper 152 to be a defective printed matter to be stamped.

In step S11, the overall control unit 174 determines whether or not printing of all the sheets 1 has been completed. When the printing of all the papers 1 is completed, the processing of this flowchart is completed. If there is paper 1 to be printed, the process returns to step S3 and the same process is repeated.

As described above, according to the printing method and the printed matter inspection method according to the present embodiment, when the first difference strength between the inspection data at the specific position and the reference data has a constant value, the reference data at the specific position is obtained. The smaller the second difference intensity between the data and the base level data, the higher the probability that there is a streak-like defect at a specific position. Therefore, candidates for streak-like defects can be appropriately identified regardless of the spatial frequency of the printed matter.

The printing method and the inspection method of the printed matter according to the present embodiment are not necessarily limited to sequentially performing each step. For example, while the processes of steps S4 to S9 are being performed on a certain sheet 1, the processes of step S3 may be started on the next sheet to be conveyed, and the processes may be performed in parallel.

<Others>
Here, the detection of so-called white streaks (bright streaks) in which the brightness is larger than that in the places where streaks do not occur has been described, but the detection of so-called black streaks (dark streaks) in which the brightness is smaller than in the places where streaks do not occur. It is also applicable to. When applied to black streaks (dark streaks), for example, when calculating the first difference intensity ΔS and the second difference intensity ΔR, “reverse what is supposed to be the difference” may be performed (example: AB). To BA). Alternatively, the captured image (the higher the brightness, the higher the value) may be converted in advance without reversing at the time of difference, and the image may be made into an image in which the higher the brightness, the lower the value. In addition, another means for obtaining the same effect may be used.

An inspection program that causes a computer to execute an inspection method for printed matter may be provided by storing it in a non-temporary storage medium that can be read by the computer. Further, the inspection program may be provided as an application that can be downloaded from an external server.

In the embodiments described so far, for example, the hardware-like structure of the processing unit that executes various processes of the inspection device 10 is various processors as shown below. The various processors include a CPU (Central Processing Unit), which is a general-purpose processor that executes software (programs) and functions as various processing units, and a GPU (Graphics Processing Unit), which is a processor specialized in image processing. Dedicated to execute specific processing such as programmable logic device (PLD), ASIC (Application Specific Integrated Circuit), which is a processor whose circuit configuration can be changed after manufacturing FPGA (Field Programmable Gate Array), etc. A dedicated electric circuit or the like, which is a processor having a designed circuit configuration, is included.

One processing unit may be composed of one of these various processors, or may be composed of two or more processors of the same type or different types (for example, a plurality of FPGAs, or a combination of a CPU and an FPGA, or a CPU and a processing unit. It may be composed of a combination of GPUs). Further, a plurality of processing units may be configured by one processor. As an example of configuring a plurality of processing units with one processor, first, one processor is configured by a combination of one or more CPUs and software, as represented by a computer such as a server and a client. There is a form in which the processor functions as a plurality of processing units. Secondly, as typified by System On Chip (SoC), there is a form of using a processor that realizes the functions of the entire system including a plurality of processing units with one IC (Integrated Circuit) chip. be. As described above, the various processing units are configured by using one or more various processors as a hardware-like structure.

Further, the hardware-like structure of these various processors is, more specifically, an electric circuit (circuitry) in which circuit elements such as semiconductor elements are combined.

The technical scope of the present invention is not limited to the scope described in the above embodiments. The configurations and the like in each embodiment can be appropriately combined between the embodiments without departing from the spirit of the present invention.

1 ... Paper 10 ... Inspection device 12 ... Inspection data acquisition unit 14 ... Reference data acquisition unit 16 ... Base level data acquisition unit 18 ... Streak degree index calculation unit 20 ... Threshold processing unit 22 ... Good / bad judgment unit 100 ... Inkjet printing system 110 ... Conveying unit 112 ... Upstream pulley 114 ... Downstream pulley 116 ... Conveying belt 120 ... Printing unit 122C ... Inkjet head 122K ... Inkjet head 122M ... Inkjet head 122Y ... Inkjet head 130 ... Imaging unit 132 ... Scanner 140 ... Drying unit 142 ... Heater 150 ... Sorting unit 152 ... Stamper 160 ... Paper ejection unit 162 ... Paper ejection stand 170 ... User interface 172 ... Storage unit 174 ... General control unit 176 ... Transfer control unit 178 ... Printing control unit 180 ... Imaging control unit 182 ... Drying control unit 184 ... Sorting control unit 186 ... Paper ejection control unit

Claims (19)

An inspection data acquisition process for acquiring inspection data based on an inspection image of a printed matter to be inspected with an image pickup device, and an inspection data acquisition process.
A standard data acquisition process for acquiring standard data based on a standard image that serves as an inspection standard for printed matter, and a standard data acquisition process.
A base level data acquisition step of acquiring smoothed base level data based on at least one of the data based on the inspection image and the data based on the reference image, and
A streak candidate specifying step for identifying streak candidates that are candidates for streak-like defects contained in the printed matter based on the inspection data, the reference data, and the base level data.
Equipped with
The streak candidate identification step is
When the first difference intensity between the inspection data and the reference data at a specific position has a constant value, the smaller the second difference intensity between the reference data and the base level data at the specific position, the more the specific position. The streak degree index calculation step for calculating the streak degree index, which is an index for quantifying the characteristic that the probability of having the streak-like defect is increased,
The first threshold value processing step of performing the threshold value processing by the first threshold value on the calculated streak degree index, and
A method of inspecting printed matter. In the streak degree index, when the second differential intensity at the specific position has a constant value, the larger the first differential intensity at the specific position, the higher the probability that the specific position has the streak-like defect. The method for inspecting a printed matter according to claim 1, which is an index quantifying the enhanced characteristics. The method for inspecting printed matter according to claim 1 or 2, wherein the streak degree index is an index using the ratio of the first value including the first difference strength and the second value including the second difference strength. The first difference intensity at the position of the streak candidate specified in the streak candidate specifying step is ΔS,
The second difference intensity at the position of the streak candidate specified in the streak candidate specifying step is ΔR,
Then, when ΔS> 0, for ε which is 0.1 or more and 0.9 or less,
ΔS / (ΔS + ΔR)> ε
The method for inspecting printed matter according to any one of claims 1 to 3. The first difference intensity at the specific position is ΔS,
The second difference intensity at the specific position is ΔR,
The streak degree index of the specific position is P,
Then
The streak degree index P is
P = ΔS / (ΔS + ΔR)
The method for inspecting printed matter according to any one of claims 1 to 3 represented by. Assuming that the first threshold value is ε which is 0.1 or more and 0.9 or less.
When ΔS> 0, the streak candidate identification step is performed.
P> ε
The method for inspecting a printed matter according to claim 5, wherein the specific position is specified as the position of the streak candidate when the condition is satisfied. The method for inspecting printed matter according to any one of claims 1 to 6, wherein the base level data is obtained by smoothing the data based on the reference image. The method for inspecting printed matter according to any one of claims 1 to 6, wherein the base level data is obtained by smoothing the reference data. The method for inspecting printed matter according to any one of claims 1 to 6, wherein the base level data is obtained by smoothing the data based on the inspection image and the data based on the reference image. The method for inspecting printed matter according to any one of claims 1 to 6, wherein the base level data is obtained by smoothing the inspection data and the reference data. The method for inspecting a printed matter according to any one of claims 1 to 10, wherein the reference data is acquired based on a reference image captured by the image pickup apparatus. The method for inspecting a printed matter according to any one of claims 1 to 10, wherein the reference data is acquired based on the halftone-processed digital data used when the printed matter is printed. The method for inspecting printed matter according to claim 12, wherein the reference data is obtained by simulating a print dot image produced by printing by a printing apparatus with respect to the digital data that has undergone halftone processing. 1 The method for inspecting printed matter described in the section. The method for inspecting printed matter according to claim 14, wherein the filter is a maximum value filter. The method for inspecting a printed matter according to any one of claims 1 to 15, further comprising a second threshold value processing step of performing a threshold value process according to a second threshold value on a value based on the first difference strength. A program for causing a computer to execute the method for inspecting printed matter according to any one of claims 1 to 16. An inspection data acquisition unit that acquires inspection data based on an inspection image of a printed matter to be inspected with an image pickup device, and an inspection data acquisition unit.
A reference data acquisition unit that acquires reference data based on a reference image that serves as an inspection standard for printed matter, and a reference data acquisition unit.
A base level data acquisition unit that acquires smoothed base level data based on at least one of the data based on the inspection image and the data based on the reference image, and
A streak candidate specifying unit that identifies streak candidates that are candidates for streak-like defects contained in the printed matter based on the inspection data, the reference data, and the base level data.
Equipped with
The streak candidate identification part is
When the first difference intensity between the inspection data and the reference data at a specific position has a constant value, the smaller the second difference intensity between the reference data and the base level data at the specific position, the more the specific position. The streak degree index calculation unit that calculates the streak degree index, which is an index that quantifies the characteristics that increase the probability of having the streak-like defect,
A first threshold value processing unit that performs threshold value processing by the first threshold value on the calculated streak degree index, and
A printed matter inspection device. A printing device that prints printed matter based on digital data,
An image pickup device that captures an image of the printed matter and acquires an inspection image,
The inspection device according to claim 18,
Printing system with.

Images