JPH0696216A - Threshold value deciding device and image inspection device - Google Patents

Abstract

PURPOSE:To improve the accuracy or reliability of comparative inspection by rationally calculating a threshold used for this comparative inspection of density between a reference image and an image to be inspected at every corresponding pixel unit. CONSTITUTION:A critical value calculating means 20 estimates allowable fluctuation range B of the density of the image to be inspected at every pixel unit basing on a reference image A. An inspection threshold value calculating means 22 calculates the inspection threshold value C of the image to be inspected at every pixel unit according to the allowable fluctuation range. Concerning the inspection threshold value used for the comparative inspection between the reference image and the image to be inspected at every corresponding pixel unit, an optimum value is rationally calculated at every picture element. Thus, the accuracy or reliability of comparative inspection is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a threshold value determination device for image inspection, which performs a density comparison inspection between a reference image and an inspection image for each corresponding pixel unit, or a correspondence between the reference image and the inspection image. For each pixel unit, the present invention relates to an image inspection apparatus that performs a density comparison inspection, in particular, a reference image and an image to be inspected, for each corresponding pixel unit, a rational determination of the threshold value used for the density comparison inspection, Accordingly, the present invention relates to a threshold value determination device or an image inspection device that can improve the accuracy and reliability of the comparison inspection.

[0002]

2. Description of the Related Art Defects in printed matter include stains on printing paper,
There are various things such as printing defects. Even if the defective portion is minute, it may cause a problem in the quality of the printed matter. Furthermore, when printed matter such as a rotary printing machine is continuously running at high speed, it is necessary to inspect each printed matter at high speed.

Conventionally, printed matter inspection has been performed manually by various methods. For example, depending on the printing machine and the type of printed matter, the printed matter after printing has been appropriately extracted and visually inspected. Alternatively, in the case of a printed matter that continuously travels at a constant speed, a strobe emits light in synchronization with the traveling speed to visually inspect the printed matter.

In recent years, various techniques for automatically inspecting printed matter have been disclosed.

For example, Japanese Examined Patent Publication No. 1-47823 includes a memory capable of storing image data read from a design of a traveling printed matter at a predetermined time, and the image data read from the memory is used as reference data, and the remaining portion of the traveling printed matter. There is disclosed a technique relating to a printed matter inspection apparatus of a system in which image data read from a pattern is used as inspection data, and whether the printing is good or bad is determined based on a comparison between the reference data and the inspection data. This technique uses a first feature extraction / comparison / determination means for performing a print quality determination by extracting and comparing the features of the reference data and the features of the inspection data for each corresponding pixel unit, and A second characteristic extraction / comparison / determination unit that determines the quality of printing by extracting and comparing the characteristic and the characteristic of the inspection data as the total sum of the pixels in a predetermined range within the same pattern is further used. Third characteristic extraction / comparison / determination means for performing a quality judgment of printing by extracting and comparing the characteristics and the characteristics of the inspection data as the total sum of the pixels arranged on the same straight line in the running direction of the printed matter in the same pattern. Is also used to make a comprehensive determination of the determination results of the first to third feature extraction comparison / determination means to make a final pass / fail determination of the printed matter. Further, in this technique, the comparison means for comparing the difference between the traveling speed of the traveling printed matter at a predetermined time point and the traveling speed of the traveling printed matter at the time of reading the inspection data with a predetermined value is used, and based on the result of the comparison, There is also provided means for newly rewriting the inspection data read from the pattern of the running printed matter at this time as the reference data. According to the technique disclosed in this Japanese Patent Publication No. 1-47823, the accuracy of the quality judgment in the case where the density change such as the pattern of the printed matter is wide range is improved, and the masking function is provided to change the state of the printed matter. It is possible to always obtain a stable operation.

Further, in Japanese Patent Publication No. 1-20477, sample data detected by decomposing a sample pattern of a printed matter into a pixel matrix is compared with sampled data preliminarily extracted from a sampled printed matter and recorded in a memory, pixel by pixel, A technique relating to a pattern inspection method for a printed matter, which determines whether a pattern is good or bad, is disclosed. In this technique, one of the sample data and the sample data is displaced by one pixel in the lateral direction of the printed matter and compared with the other of the two data, and when the two data are closest to each other This is a technique in which the sample data or the sample data is corrected in position in the lateral direction of the printed matter according to the amount of position deviation and then compared with the sample data. According to the technique disclosed in Japanese Patent Publication No. 1-20477, the pattern inspection can be performed with high accuracy by a relatively inexpensive device even if the printed material conveying system is misaligned.

Further, in Japanese Patent Laid-Open No. 62-11152, a detection means for extracting pixel data in a state where the visual fields overlap each other in the direction perpendicular to the running direction of the printed matter and the images overlap each other is used. Then, the data to be inspected is taken in and compared with the reference data. In this comparison, each pixel is compared and then the addition data are compared with each other. According to the technique disclosed in Japanese Patent Laid-Open No. 62-11152, accurate inspection can be performed without being affected by positional displacement, which is inevitable in a printed matter that is running.

[0008]

However, in the past,
As a threshold value used for the density comparison inspection for each corresponding pixel unit between the reference image and the inspection image, a single value is usually used for all the pixels of the reference image and all the pixels of the inspection image. It was For this reason, it is difficult to determine an appropriate threshold value, and there is a problem in the accuracy and reliability of the comparison inspection.

Conventionally, some specific pixels are masked according to the reference image and the image to be inspected and excluded from the inspection object. This is because accurate inspection cannot be performed if there is a positional deviation between the reference image and the image to be inspected. In particular, in a portion of the reference image or the image of the inspected image in which the density changes drastically, even if the positional deviation is about 1 pixel, the adverse effect thereof becomes extremely large. Therefore, by applying a mask as described above, such a problem regarding the positional deviation is solved.
However, when the mask is applied in this manner, there is a problem that a portion that is not an inspection target is generated.

As described above, the reference image and the inspection image are
Conventionally, there have been various problems in determining the value of the threshold value used for the density comparison inspection for each corresponding pixel unit.

The present invention has been made to solve the above-mentioned conventional problems, and more rationalizes the threshold value used for the density comparison inspection for each corresponding pixel unit of the reference image and the inspection image. It is an object of the present invention to provide a threshold value determination device and an image inspection device that can improve the accuracy and reliability of the comparison inspection.

[0012]

The threshold value determining device of the first invention of the present application is a threshold value determining device for image inspection, which performs a comparative inspection of the densities of corresponding pixel units of a reference image and an image to be inspected. Then, based on the reference image, a limit value calculating means for estimating an allowable variation range of density for each pixel unit of the inspection image, and for each pixel unit of the inspection image according to the allowable variation range The above object is achieved by including an inspection threshold value calculation unit for obtaining an inspection threshold value.

The image inspection apparatus of the second invention of the present application is an image inspection apparatus for performing a comparative inspection of the density of a reference image and an image to be inspected for each corresponding pixel unit, based on the reference image. Limit value calculating means for estimating an allowable variation range of the density of each pixel unit of the inspection image, and inspection threshold calculating means for obtaining an inspection threshold value of each pixel unit of the inspection image according to the allowable variation range, A threshold value memory that stores the inspection threshold value for each pixel unit of the image to be inspected, a density difference value for each pixel unit corresponding to the reference image and the image to be inspected, and the pixel unit From the inspection threshold,
The above object is achieved by including the comparison inspection means for inspecting the image to be inspected.

[0014]

If the threshold value used for the density comparison inspection for each corresponding pixel unit between the reference image and the image to be inspected is too large, it may be overlooked despite the difference between these images. Will end up. On the other hand, if the threshold value is too small,
Due to misalignment of the reference image and the image to be inspected,
Even if these images are the same, it is determined that they are different. As described above, the threshold value used in the comparative inspection has a great influence on the accuracy and reliability of the comparative inspection.

In the present invention, the threshold value whose value affects the accuracy and reliability of the inspection result is set for each pixel of the reference image and the inspection image. For example, the threshold value is increased in a portion where the positional deviation between the reference image and the inspected image has a large adverse effect and the density of the patterns of these images changes drastically. On the other hand, the threshold value of the portion where the density change is small is reduced.
As a result, the overall accuracy and reliability of the comparison inspection can be improved.

Further, in the present invention, the complicated and time-consuming setting of setting such a large number of threshold values for each pixel is more rationally determined.

FIG. 1 is a block diagram showing the gist of the present invention.

As shown in FIG. 1, the characteristic parts of the present invention are the limit value calculating means 20 and the inspection threshold value calculating means 22.
Has become.

The limit value calculating means 20 is means for estimating the permissible variation range of the density of each pixel unit of the inspection image based on the reference image. The present invention does not specifically limit the permissible fluctuation range of the density for each pixel unit, but for example, up to a portion (means) for performing a comparative inspection as in an embodiment described later. It may be estimated from the noise level expected in the input system, or may be estimated from the maximum positional deviation amount between the reference image and the inspection image in the horizontal direction or the vertical direction.

The inspection threshold value calculating means 22 is responsive to the allowable variation range calculated by the limit value calculating means 20.
It is means for obtaining an inspection threshold value for each pixel unit of the image to be inspected. Although the present invention does not specifically limit the method of obtaining the inspection threshold value for each pixel unit, for example, in the first example of the threshold value determination unit of the embodiment described later, one threshold value T (x, y
). Further, for example, in the second example of the threshold value determining unit of the embodiment described later, the upper limit allowable threshold value T _H (x,
y) and the lower limit allowable threshold T _L (x, y).

The inspection threshold value for each pixel thus obtained is, for example, the threshold value memory 2 shown in FIG.
Written to 4. The threshold memory 24 has a storage capacity capable of storing the inspection threshold value for each pixel.

As described above, according to the present invention, not only can the accuracy and reliability of the comparison inspection be improved by obtaining the inspection threshold value for each pixel, but also such a threshold value for each pixel can be obtained efficiently. It is possible.

[0023]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing the construction of a printing machine and a printed matter concentrated inspection apparatus to which the present invention is applied.

FIG. 2 shows a printed matter centralized inspection apparatus main body 80 for inspecting a plurality of printing machines including a printing machine (not shown) at one location. In the printing machine 10 shown in FIG. 1, the strip-shaped printed matter 1 sent from the final printing unit 12 is wound into a roll shape by the feed roll 14 and the winding portion 16. Also, the printing machine 10
From the above, a printing state signal indicating whether or not the printing machine is in operation and the like, and a pulse signal according to the traveling of the printed material 1 are output by the rotary encoder 18 attached to the printing unit 12. When the perimeter of the plate cylinder of the printing unit included in the printing machine 10 such as the printing unit 12 is longer than one pattern to be printed (hereinafter, also referred to as one surface),
Plate cylinder-Several pictures are printed by rotation. In order to detect such a surface position, the rotary encoder 18 is
A pulse signal is output every predetermined rotation.

In the printing machine 10 shown in FIG. 2, a detection unit 30 for photographing the surface state of the printed material during traveling and outputting a predetermined image signal is provided between the printing unit 12 and the feed roll 14. It is arranged. Further, the printing state signal and the pulse signal from the rotary encoder 18 are input to the repeater 40, and the detecting unit 3
0 is connected. As with the three repeaters 40 shown in the figure, other repeaters not shown also
It is provided corresponding to another printing machine (not shown). These relays 40 are respectively provided in the centralized inspection apparatus body 80.
It is connected to the inside determination unit 100.

FIG. 3 is a side view of the detection section of the printed matter concentration inspection apparatus as seen from the printed matter running direction.

In FIG. 3, the printed matter 1 is running from the front side to the other side. Further, the detection unit 30 mainly includes a light source 32b housed in the lamp house 32a and an optical fiber 33 that guides light from the light source 32b to a light guide 34, and a slit provided in the light guide 34 The printed matter 1 is illuminated. A heat radiation fan (not shown) is built in the lamp house 32a to radiate heat generated by the light source 32b. A discharge light source such as a halogen lamp or a xenon lamp is used as the light source 32b. Further, the detection unit 30 has a plurality of line sensor cameras 36 arranged orthogonally to the traveling direction of the printed matter 1. The one-dimensional line-shaped imaged portions on the printed matter 1 photographed by the individual line sensor cameras 36 are also orthogonal to the traveling direction of the printed matter 1. Further, the visual fields of the plurality of line sensor cameras 36 overlap with the visual fields of other adjacent line sensor cameras 36. The electric circuit 38 obtains one one-dimensional line-shaped image signal over substantially the entire width of the printed matter 1 from the image signal of the one-dimensional line-shaped image from the plurality of line sensor cameras 36, and Processing for transmitting this to the repeater 40 is performed.

FIG. 4 is an electric circuit diagram of a detection part electric circuit of the printed matter concentration inspection apparatus.

As shown in FIG. 4, the detection section electric circuit 38 for outputting the image signals obtained from the plurality of line sensor cameras 36 to the repeater 40 mainly includes A / D conversion. Part 38a, frame memory 38b,
The image compression circuit 38c, the optical communication unit 38d, and the driver 3
And 8e.

The A / D converter 38a converts an image analog signal from each of the plurality of line sensor cameras 36 into an image digital signal by the A / D converter 38g. Further, the A / D converter 38a integrates the images of the adjacent line sensor cameras 36 to generate a continuous one-dimensional linear digital image over substantially the entire width of the printed matter 1. Further, the generated digital images are sequentially written in the frame memory 38b in synchronization with the traveling of the printed matter 1. As a result, it is possible to obtain an image of a two-dimensional frame scanned by the plurality of line sensor cameras 36 in synchronization with the traveling of the printed matter 1.

1 written in the frame memory 38b
The digital image for the screen (one frame) is data-compressed by the image compression circuit 38c, and the optical communication unit 38d
Is output to. The data compression performed by the image compression circuit 38c is a JPEG (joint photographic coding exp) which has been used recently in still image coding.
ert group) encoding is used. The data compression performed by the image compression circuit 38c is for improving the transmission efficiency such as shortening the transmission time of the image digital signal.
Other data compression methods may be used. For example, conventionally known entropy coding, Huffman coding, run length coding, etc. may be used singly. The image digital signal from the image compression circuit 38c is optically modulated in the optical communication unit 38d and transmitted to the repeater 40.

On the other hand, the timing signal transmitted from the repeater 40 in synchronism with the traveling of the printed matter 1, that is, the signal of the timing of photographing the printed matter 1 in a one-dimensional line form while scanning by the traveling is the above-mentioned. It is output to each of the plurality of line sensor cameras 36 by the driver 38e. Also, from the repeater 40, a timing signal for each surface corresponding to the pattern to be printed is also sent,
The signal is used for detecting the start of one frame when the A / D converter 38a writes a digital image in the frame memory 38b.

FIG. 5 is a block diagram showing a hardware configuration of a repeater of the printed matter concentration inspection apparatus.

As shown in FIG. 5, the repeater 40 installed close to each one of the printing machines mainly
CPU (central processing unit) 40a and ROM
(Read only menory) 40b and RAM (random acces
40 c, a parallel input / output circuit 40 d, a counter 40 e, an O / E (optical to electrical) converter 40 f, a serial converter 40 g, and a serial converter 4
0h and E / O (electrical to optical) converter 40
i and a bus 40j.

The CPU 40a uses the bus 4 according to a program previously written in the ROM 40b.
The RAM 40c, the parallel input / output circuit 40d, the serial converter 40g, and the serial converter 40h are accessed via 0j to perform a predetermined process. For example, the CPU 40a is configured to generate a timing signal to the detection unit 30 mainly according to a signal from the printing machine 10 according to a program written in advance in the ROM 40b, and an image digital signal from the detection unit 30. Is relayed to the determination unit 100.

The RAM 40c is used not only for temporary storage of data when the CPU 40a executes a program, but also for buffering the image digital signal when the image digital signal is relayed from the detection unit 30 to the determination unit 100. Also used as memory. The parallel input / output circuit 4
0d indicates the input / output for each of the printing machine 10 and the detection unit 30 in a bit unit or every predetermined number of bits,
U40a and the bus 40j are processed with a bit number width which is a processing unit. The counter 40e determines an absolute traveling position of the printed matter 1 from an encoder signal sent from the rotary encoder 18 and relatively corresponding to the traveling position of the printed matter 1. The O / E converter 40f demodulates the light-modulated image digital signal sent from the detection unit using an optical fiber, and the serial converter 4f
Output to 0g. The serial converter 40g has the O
The serial image digital signal output by the / E converter 40f is converted into parallel data having a predetermined number of bits width that can be accessed by the CPU 40a. The serial converter 4
0h serially converts the image digital signal of a predetermined bit number width written by the CPU 40a and outputs it to the E / O converter 40i. The E / O converter 40i
Optically modulates the serial image digital signals sequentially sent from the serial converter 40h and sends them to the determination unit 100 via an optical fiber.

FIG. 6 is a block diagram showing the functional arrangement of the repeater.

As shown in FIG. 6, the repeater 4
The main function of 0 is composed of an image timing control section 40m, an image signal relay section 40p, and a memory 40n.

The image timing control section 40m is a timing signal used by the detection section 30, for example, the camera start signal or the read enable signal, according to a signal from the rotary encoder 18 of the printing press 10, for example, the A phase signal. To generate. At this time, the image timing control unit 40m also uses the imposition information previously input by the operator from the keyboard 62 described later. This imposition information is information relating to the printing contents of the plate cylinder of the printing machine 10 and is, for example, information such as the number of pages to be printed.

The image signal relay section 40p receives the image digital signal sent from the detection section electric circuit 38 through the optical fiber and stores it in the memory 40n. Further, the image signal relay section 40p sends the digital image stored in the memory 40n to the judging section 100 as an image digital signal in response to a request from the judging section 100 of the centralized inspection apparatus body 80. Output via. A plurality of frames of digital images can be stored in the memory 40n. A plurality of repeaters 40 (40a to 40c) are connected to the determination unit 100,
Thus, the image signal relay unit 40p and the memory 40
By performing the relay process of the relay device 40 using n, it is possible to sequentially perform the printed matter inspection of each printing press corresponding to each relay device 40.

FIG. 7 is a block diagram showing the hardware structure of the main body of the printed matter concentration inspection apparatus.

As shown in FIG. 7, the printed matter centralized inspection apparatus main body 80 mainly includes a CPU (central pr).
cessing unit) 50, main storage device 52, hard disk device 54, floppy disk device 58, input / output device 60, O / E converter 60a, and keyboard 62.
And a CRT (cathode ray tube) controller 64a, and C
The RT 64b, a network control device 66, a printer device 68, and a system bus 70.

The CPU 50 executes a program module or the like read from the hard disk device 54 into the main storage device 52, such as one related to a printed matter inspection process. The hard disk device 54 stores program modules, data, etc. according to the present embodiment,
The data is read out to the main storage device 52 as needed. The floppy disk device 58 is used for exchanging various program modules and data with other computer systems. The input / output device 60 is used to connect to another digital processing device. For example, it is connected to the plurality of relays 40 (40a to 40c) via the plurality of O / E converters 60a, and image digital signals relating to the printed matter inspection of each printing machine are input.

The keyboard 62 is used together with the CRT control device 64a and the CRT 64b when the operator operates the centralized inspection device body 80.
The keyboard 62 is also used when setting various data. Also, the CRT controller 64a and the CRT
The reference numeral 64b is used for transmitting the printed matter inspection result in the centralized inspection apparatus main body 80 and the abnormality detection based on the result to the operator.

The network control device 66 is used to connect the centralized inspection device main body 80 online to another computer system. For example, data and printed matter inspection results that can be collected by the centralized inspection apparatus main body 80, further self-diagnosis results of the centralized inspection apparatus main body 80, devices and devices connected to the centralized inspection apparatus main body 80, for example, The repeater 40 and the detector 30
Also, the result of abnormality diagnosis of the printing machine 10 can be centrally monitored by another computer system.
The printer device 68 prints a printed matter inspection result in the centralized inspection device main body 80, information relating to the result, and the like.

The system bus 70 is connected to the CP
U50 is the main storage device 52, the hard disk device 54, the floppy disk device 58, the input / output device 60, the keyboard 62, the CRT control device 64a, the network control device 66, the It is used when accessing the printer device 68. The system bus 70 includes an address bus used for selecting devices connected to the system bus 70 and the CPU 50.
And a data bus used for data transfer at the time of access.

FIG. 8 is a block diagram showing the functional arrangement of the main body of the printed matter concentration inspection apparatus.

As shown in FIG. 8, the printed matter concentrated inspection apparatus main body 80 mainly includes a determination unit 100, a defective image storage unit 82, a defective display unit 84, a data totaling unit 86, and a network connection unit. And 88. or,
Keyboard 62, CRT controller 64a, CRT 64b
A printer 68 and the like are used. These determination unit 1
00 and the processing and operations performed in the defective image storage unit 82,
This is performed for a plurality of printing machines 10 connected to the centralized inspection apparatus body 80. The data such as the printed matter inspection result is shared among the printing machines 10.

The judging section 100 demodulates the image digital signal optically modulated and transmitted from the repeater 40 by an optical fiber, and restores the data compression performed by the image compression circuit 38c of the detection section electric circuit 38. Then, the printed matter is inspected according to the resulting digital image.

The defective image storage section 82 is provided in the judging section 1
When a defect of the printed matter is detected at 00, the digital image of the corresponding frame is data-compressed and stored in the hard disk device 54 together with the defect occurrence location information and the like. The defect occurrence location information is information indicating the frame number in which the defect of the printed matter is detected and the location of the defective portion in the frame.

The defect display section 84 is the keyboard 6
The image stored in the defective image storage section 82, the defect occurrence location information related to the image, and the like are displayed by an operator's operation of the CRT control device 64a, the CRT 64b, or the CRT 64b, or automatically when a print defect occurs. At this time, the defective display section 84 restores the stored digital image of the compressed data to be displayed.

As described above, in this embodiment, when a defective printed matter occurs, the image of the frame and the defective location information relating to the frame are stored, so that the operator can grasp the state of the defective printed matter at any time. You can observe it. When a print defect is visually detected on a rotary printing machine, labels have been inserted and marking has been performed in the past.To observe the defective part or defective part, rewind the wound print product. There was a problem that had to be. However, according to this embodiment,
At any time, it is possible to grasp and inspect defects in printed matter.

The data aggregating unit 86 includes the determining unit 10
The number of print defects detected at 0 is totaled, and the result is stored. Further, the totalized result can be output by being displayed on the CRT 64b or printed on the printer device 68 by an operation of the operator from the keyboard 62 or the like.

The network connection unit 88 is provided with an abnormality such as a failure of the centralized inspection apparatus main body, a device or a device connected to the centralized inspection apparatus main body 80, such as the detection unit 30, the relay 40 or the printing. An abnormality such as a failure of the machine 10 is detected and transmitted to another computer system online.

FIG. 9 is a block diagram showing the functional arrangement of the determination unit of the main body of the printed matter inspection apparatus.

As shown in FIG. 9, the judging unit 1
00 is mainly the light receiving unit 102 and the image restoration unit 104.
And a temporary image memory 106, a comparison / determination unit 110, and a recording unit 118. These configurations are provided for each of the detectors 30 of the printing machine 10. Alternatively, one set of these configurations is provided, and the print defect determination for each of the detectors 30 is sequentially performed.

The optical receiving section 102 demodulates the image digital signal optically modulated and transmitted from the repeater 40 via the optical fiber. The image decompression unit 104 decompresses the digital image data-compressed by the image compression circuit 38c in the detection unit electric circuit 38.

The temporary image memory 106 temporarily stores an image for one screen (one frame) until the process performed by the comparison / determination unit 110 or the recording unit 118 is completed. The comparison / determination unit 110 compares the image to be inspected stored in the temporary image memory 106 with a reference image previously stored in the comparison / determination unit 110, and determines a difference between these images. The determination result is the recording unit 11
8 is output. When the print defect is input from the comparison / determination unit 110, the recording unit 118 reads out the digital image of the temporary image memory 106 corresponding to the print defect, together with various information such as the defect occurrence time and the defect occurrence location. , And temporarily stores it as print defect information. At this time, the recording unit 118 also performs data compression of the digital image. In addition, the temporarily stored various information is output in response to a request from the defective image storage unit 82 or the data totaling unit 86.

FIG. 10 is a block diagram showing the configuration of the comparison / determination unit of the determination unit.

As shown in FIG. 10, the comparison / determination unit 11 of the determination unit 100 described with reference to FIG. 9 is used.
0 has a total of four image layering circuits 120, a total of five comparison inspection circuits 130, and an inspection result determination circuit 170.

The digital image stored in the temporary image memory 106 is input to one of the image layering circuits 120. Further, the output of the one image layering circuit 120 is input to one of the other image layering circuits 120, and the input output of the image layering circuit 120 is the next image layering circuit 120. Input to one of the. The other remaining image layering circuit 120 is similarly connected. In this way, these four image hierarchization circuits 12 in total are included.
0 is a daisy chain connection in which the digital image input portion and the digital image output portion are sequentially connected.

Further, these four image hierarchization circuits 12 in total are included.
0 for each other output, that is, for these image layering circuits 1
Each of the 20 extracted image outputs is input to the comparison inspection circuit 130. The digital image output from the fourth image layering circuit 120 is input to the fifth comparison inspection circuit 130.

All the temporary judgment results output from each of the five comparison inspection circuits 130 are input to the inspection result determination circuit 170.

The image layering circuit 120 has an image frequency component filter, that is, a low-pass circuit 122 and a high-pass circuit 126 which will be described later. By extracting the frequency components of the image to be inspected, a total of two characteristics are obtained. Get different output images. That is, the image layering circuit 120 obtains the output of the digital image and the output of the extracted image having different characteristics. Therefore, by connecting the image layering circuit 120 as shown in FIG. 10, a total of five output images having different characteristics can be obtained. In the present embodiment, these total 4
The image layering circuit 120 constitutes an image layering unit of the present invention.

The image hierarchizing means of the present invention is not limited to the above-described daisy chain connection of the plurality of image diffraction circuits 120. However, the daisy chain connection may be adopted. If 1
By designing the two image layering circuits 120,
It is possible to design various image layering means with different numbers of output images.

The comparison inspection circuit 130 compares the extracted image output from the image layering circuit 120 with a reference image corresponding to the extracted image and stored in advance in the comparison inspection circuit 130 to determine a predetermined value. Get the test result of. The inspection result determination circuit 170 obtains an overall determination result based on the temporary determination results input from each of the five comparison inspection circuits 130 in total. The inspection result determination circuit 170 determines that the comprehensive determination result is defective if any one of the input temporary determination results is defective. Specifically, a 5-input OR circuit is used. Has been.

FIG. 11 is a block diagram showing the configuration of a first example of the image layering circuit of the judging section.

As shown in FIG. 11, the image layering circuit 12 used in the judging section 100.
0, that is, one of the image layering circuits 120 of FIG. 10 is mainly composed of a low-pass circuit 122 and an image thinning circuit 1.
24 and. The low pass circuit 122 is a low pass filter having a predetermined cutoff frequency FC. The low-pass circuit 122 uses the input digital image to
An image spatial frequency component lower than the cutoff frequency FC is extracted and output. The image thinning circuit 124 reduces the number of pixels of the digital image (pixel image) output from the low pass circuit 122. The low-pass circuit 122 and the image thinning circuit 124 may be combined.

As described above, in the first example of the image layering circuit, the input digital image is output as it is as the extracted image, and at the same time, it is passed through the low-pass circuit 122 and the image thinning-out circuit 124 to be predetermined. Output a digital image of. In this way, the first example of the image layering circuit 120 has two different characteristics based on the input digital image.
Get two output images.

FIG. 12 shows the configuration of a second example of the image layering circuit 120 used in the comparison / determination unit 110, that is, the image layering circuit 120 shown in FIG. The image layering circuit 1 shown in FIG.
20 is mainly composed of a low-pass circuit 122, an image thinning circuit 124, and a high-pass circuit 126. The low-pass circuit 122 and the image thinning circuit 124
Is the same as that in the first example of the image layering circuit 120 having the same reference numeral.

The high pass circuit 126 is a high pass filter having a predetermined cutoff frequency FC, and extracts and outputs an image spatial frequency component higher than the cutoff frequency FC of the input digital image. The high pass circuit 12
The output of 6 is the output of the extracted image of the image layering circuit 120.

As described above, in the second example of the image layering circuit of the present embodiment, in addition to the low pass circuit 122, the high pass circuit 126 having the same cutoff frequency FC as the low pass circuit 122 is provided. And outputs two output images with different characteristics, that is, an extracted image and a digital image.

The low-pass circuit 122 and the high-pass circuit 126 used in the first and second examples of the image layering circuit are the digital signal processor (DSP) and the ordinary CPU (central CPU). processing unit
), Or a predetermined arithmetic logic operation circuit or the like. Further, the image thinning circuit 124 can be similarly configured.

FIG. 13 is a diagram showing the relationship between the image hierarchy and the total number of pixels in this embodiment.

As shown in FIG. 13, in this embodiment, the 0th layer digital image V ₀ having a total number of pixels of 256 × 256 pixels has its low frequency image spatial frequency component extracted, and the total number of pixels is thinned out. And sequentially, the first layer digital image V ₁
~ The fourth layer digital image V ₄ is obtained. These 0th
The thinning out of the total number of pixels from the hierarchical digital image V ₀ to the fourth hierarchical digital image V ₄ is that the total number of pixels sequentially becomes 1/4, and that four adjacent pixels are sequentially integrated. It is a thing. Therefore, the total number of pixels of the digital image of each layer is as follows.

Total number of pixels of the 0th layer digital image V ₀ : 2
56 × 256 = 65536 pixels Total number of pixels of the first layer digital image V ₁ : 128 × 128
= 16384 pixels Total number of pixels of second layer digital image V ₂ : 64 × 64 = 4
096 pixels total number of pixels of the third hierarchy digital image V _3: 32 × 32 = 1
024 pixels total number of pixels of the fourth hierarchy digital image V _4: 16 × 16 = 2
56 pixels

FIG. 14 is a diagram showing the relationship between the image layering and the image spatial frequency distribution in this embodiment.

As shown in FIG. 14, as shown in FIG.
The cutoff frequencies FC _{1 to} FC ₄ of the _four image layering circuits 120 shown in FIG. 10 become lower as they go downward in FIG. Further, when the first example of the image layering circuit 120 is used in this embodiment,
The output of the extracted image of the image layering circuit 120 is, in order, the 0th layer digital image V ₀ , the first layer digital image V ₁ ,
Second layer digital image V ₂ and third layer digital image V ₃
And the fourth layer digital image V ₄ . On the other hand, particularly when the second example of the image layering circuit 120 is used in the present embodiment, the output of the extracted images output from the four image layering circuits 120 in total is high frequency in order. The component image O ₀ , the high frequency component image O ₁ , the high frequency component image O ₂ , the high frequency component image O _3, and the fourth hierarchical digital image V ₄ are obtained.

15 to 24, the 0th layer digital image V ₀ to the 4th layer digital image V ₄ , the high frequency component images O _{0 to} O ₃ , and the 4th layer digital are respectively shown. of the second example of the image V _4, it is an image diagram illustrating an example of each image.

That is, FIG. 15 shows the 0th layer digitizer.
Le image V₀It is an image figure which shows an example. In FIG. 16,
The high frequency component image O₀It is an image diagram showing an example of
It FIG. 17 shows the first layer digital image V₁One
It is an image figure which shows an example. 18 is the high frequency component
Minute image O₁It is an image figure which shows an example. FIG. 19 shows
The second layer digital image V₂It is an image diagram showing an example of
It 20 is the high frequency component image O₂An example of
It is an image figure to show. FIG. 21 shows the third-layer digitizer.
Le image V₃It is an image figure which shows an example. 22 is the front
High frequency component image O₃It is an image figure which shows an example.
FIG. 23 shows the fourth layer digital image V_FourFirst example of
It is an image figure which shows. FIG. 24 shows the fourth layer digital
Tar image V _FourIt is an image figure which shows the 2nd example of.

The operation of the comparison / determination unit 110 using the second example of the image layering circuit 120 will be described below using mathematical expressions.

In FIG. 12, the nth layer digital image V _n (x, y) input to the image layering circuit 120 is input.
), A low pass filter (that is, an image spatial frequency filter) realized in the low pass circuit 122.
The process using K _L (i, j) can be expressed as the following equation when the thinning process is performed simultaneously.

V _{n + 1} (x, y) = K _L (i, j) * V _n (2x, 2 y) ... (1)

Further, in the processing using the low-pass filter K _L (i, j), when the thinning processing is separately performed, first,
The processing shown by the following equation is performed (filter processing).

V _n ′ (x, y) = K _L (i, j) * V _n (x, y) ... (2)

After that, the processing represented by the following equation is performed as the thinning processing (thinning processing).

V _{n + 1} (x, y) = V _n ′ (2x, 2y) ... (3)

Here, "*" represents a convolution operation. As the low pass filter K _L , the following formula is usually used.

1/9 1/9 1/9 1/9 1/9 1/9 1/9 1/9 1/9 (4)

In the equation (2), an example of the low-pass filter K _L of 3 × 3 pixels is shown, but it may be applied to 5 × 5 pixels or 7 × 7 pixels. It goes without saying that the cutoff characteristic of the spatial filter can be improved as the number of pixels of the filter is increased.

Subsequently, a high-pass filter (image spatial frequency filter) K _H (i, j) realized in the high-pass circuit 126 is used, and the extracted image obtained from the high-pass circuit 126 is set to a high-pass frequency. When component image O _n, processing performed by the high-pass circuit 126 can be expressed by the following equation.

O _n (x, y) = K _H (i, j) * V _n (x, y) ... (5)

The high pass filter K _H (i, j
), As an example, the one represented by the following equation of 3 × 3 pixels can be used.

-1 -1 -1 -1 -1 8 -1 -1 -1 -1 (6)

The high-pass filter K _H (x, y) shown in the equation (4) is a filter known as 8-direction Laplacian.

FIG. 25 is a block diagram showing the configuration of the comparison inspection circuit of the comparison / determination unit.

In FIG. 25, there is shown one configuration of the total of five comparison / inspection circuits 130 of the comparison / determination unit 110 shown in FIG. This Figure 2
As shown in FIG. 5, the comparison inspection circuit 130 used in this embodiment mainly includes a switch 132, a reference image memory 134, an inspection image memory 136, and a threshold value determining unit 1.
38, a threshold memory 140, and a comparison inspection means 142.

The switch 132 switches the extracted image output from the image layering circuit 120 to the reference image memory 134 or the inspected image memory 136. When the contact point a and the contact point c are turned on, the switch 132 outputs the extracted image to the inspected image memory 136.
Written in. On the other hand, when the contact b and the contact c are turned on, the extracted image is written in the reference image memory 134.

In the image inspection apparatus of this embodiment, when starting a predetermined image inspection, first, the switch 132 is switched to the contact b, so that a non-defective digital image is first written in the reference image memory 134. Also, during the subsequent image inspection, the switching device is switched to the contact a, and the signals are sequentially sent from the detection unit 30 and the relay device 40, the image restoration unit 104 and the temporary image memory 106, and if necessary. Accordingly, the extracted images input through some of the image layering circuits 120 are written to the inspected image memory 136.

The threshold value determining section 138 uses a predetermined threshold value T (x
, Y). The obtained threshold value T (x, y) is
It is stored in the threshold memory 140. The threshold memory 14
0 has a storage capacity capable of storing a plurality of threshold values T (x, y) as many as the total number of pixels of the extracted image input to the comparison inspection circuit 130.

When the threshold value determining unit 138 and the threshold value memory 140 shown in FIG. 26 are used, the comparison inspection means 142 calculates the inspection result G (x, y
) Is obtained for each pixel of the extracted image.

G (x, y) = NG: | S (x, y) -I (x, y) |> T (x, y) GOOD: | S (x, y) -I (x, y) | ≤T (x, y) (7)

Note that (x, y) is the position of each pixel of the extracted image, the reference image stored in the reference image memory 134, or the inspection image stored in the inspection image memory 136. , S (x
, Y) is each pixel of the reference image, and I (x, y)
Is each pixel of the inspection image. Further, “NG” indicates that the inspection result is defective, and “GOOD” indicates that the inspection result is good.

As described above, in this embodiment, the image to be inspected is inspected for each pixel, and the permissible threshold value at this time is set for each pixel. If there is a positional deviation between the reference image and the image to be inspected, the comparison inspection means 142.
Therefore, it becomes impossible to carry out an accurate inspection. In particular, in a portion of the reference image or the image of the inspected image in which the density changes drastically, even if the positional deviation is less than one pixel, the adverse effect thereof becomes extremely large. However, in the present embodiment, the threshold value of the portion where the density changes drastically can be set to a large value automatically, and it is possible to reduce erroneous inspection.

FIG. 26 is a block diagram showing the configuration of a first example of the threshold value determining unit of the comparison inspection circuit.

In FIG. 26, the configuration of the threshold value determining unit 138 of FIG. 25 is shown.

The threshold value determining section 138 is mainly composed of a maximum value calculating circuit 150, a minimum value calculating circuit 152, a difference circuit 154 and an arithmetic circuit 156.
The threshold value determining unit 138 calculates the maximum positional deviation amount between the reference image and the inspection image in the horizontal direction or the vertical direction,
That is, it is provided in order to allow the maximum misalignment amount MX in the horizontal direction (X-axis direction), the maximum misalignment amount MY in the vertical direction (Y-axis direction), and noise expected in the input system up to the comparison inspection means. The allowable value NMIN and the threshold value T
(X, y) is required.

T (x, y) = Max [NMIN, Max {S (x + i, y + j)}-Min {S (x + i, y + j)}] ... (8)

Here, Max (A, B ...) is A, B.
, Which is the function that returns the maximum value of Min (A, B
...) is a function that returns the minimum value of A, B, .... Also, i is a variable that changes from -MX to MX, and j is a variable that changes from -MY to MY. or,
In the equation (6), “Max {S (x + i, y + j
)} ”Is performed in the maximum value calculation circuit 150, and is to obtain the maximum density value in the range of i from −MX to MX and j from −MY to MY. "Min {S (x + i, y + j)}" is an operation performed by the minimum value calculation circuit 152, where i is -MX.
To MX, j is the minimum density value in the range of -MY to MY. Therefore, the above (6)
The expression is based on the difference between the maximum density value and the minimum density value when the positional deviation occurs within the allowable range, considering the noise expected in the input system, and the allowable threshold value T (x
, Y).

In the equation (6), when the maximum positional deviation amount is smaller than one pixel in both the horizontal and vertical directions, it can be transformed into the following equation.

T (x, y) = Max (NMIN, [Max {S (x + i, y + j)}-Min {S (x + i, y + j)}] × r%) (9)

Where i and j are in the range of ± 1, and r
Is a numerical value of 0% or more and 100% or less.

FIG. 27 is a block diagram showing the configuration of a second example of the threshold value determining unit of the comparison inspection circuit.

The threshold value determining unit 138 shown in FIG.
Is mainly composed of a maximum value calculation circuit 160, a minimum value calculation circuit 162, and a calculation unit 164. In the threshold value determining unit 138, the upper limit allowable threshold value T _H (x, y)
And the lower limit allowable threshold T _L (x, y) are obtained, and these allowable thresholds are respectively written in the upper limit threshold memory 140a or the lower limit threshold memory 140b in the threshold memory 140.

In the threshold value determining unit 138, the calculation shown in the following equation is performed.

[0117] _{T H (x, y) =} Min [MXV, Max {S (x + i, y + j)} + NMIN] ... (10)

T _L (x, y) = Max [0, Min {S (x + i, y + j)}-NMIN] (11)

Here, MXV is the threshold value determining unit 138.
And the maximum value that can be represented by the threshold memory 140 and the like. Further, the equations (8) and (9) can be modified in the same manner as the equation (7) when the maximum positional deviation amount is less than one pixel.

When the threshold value determining unit 138 is the second example described later, the comparison inspection means 142 obtains the inspection result G (x, y) by the following equation.

G (x, y) = OVER: I (x, y)> _TH (x, y) UNDER: I (x, y) < _TL (x, y) GOOD: otherwise (12)

As described above, the second value of the threshold value determining unit 138 is
When the example is used, it is possible to more finely judge the inspection failure by the comparison inspection means 142. That is, it is possible to distinguish whether the defect is above the allowable range or is below the allowable range. When the second example of the threshold value determining unit 138 is used,
The storage capacity of the threshold memory 140 is 2 compared to the first example.
However, since the reference image memory 134 is not used at the time of inspection, it may be diverted. Therefore, when the second example is used, it is possible to distinguish whether the defect is due to lack of color or addition of color, and
It is possible to reduce the problem of uneven light source and speed up the inspection process by not performing the absolute value conversion process.

[0123]

As described above, according to the present invention, the threshold value used for the comparative inspection of the density of the reference image and the image to be inspected for each corresponding pixel unit is more rationally obtained, and the An excellent effect that the accuracy and reliability of the comparison inspection can be improved can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the gist of the present invention.

FIG. 2 is a block diagram showing a configuration of a printing machine and a printed matter concentrated inspection apparatus to which the present invention is applied.

FIG. 3 is a side view of the detection unit of the printed matter concentration inspection apparatus as seen from the printed matter running direction.

FIG. 4 is a block diagram of a detection unit electric circuit of the detection unit.

FIG. 5 is a block diagram showing a hardware configuration of a repeater of the printed matter concentrated inspection apparatus.

FIG. 6 is a block diagram showing a functional configuration of the repeater.

FIG. 7 is a block diagram showing a hardware configuration of a main body of the printed matter concentrated inspection apparatus.

FIG. 8 is a block diagram showing the functional configuration of the main body of the print concentrated inspection apparatus.

FIG. 9 is a block diagram showing a functional configuration of a determination unit of the printed matter concentrated inspection apparatus main body.

FIG. 10 is a block diagram showing a configuration of a comparison / determination unit of the determination unit.

FIG. 11 is a block diagram showing a configuration of a first example of an image layering circuit of the comparison / determination unit.

FIG. 12 is a block diagram showing a configuration of a second example of an image layering circuit of the comparison / determination unit.

FIG. 13 is a diagram showing the relationship between the image layering and the total number of pixels in the embodiment.

FIG. 14 is a diagram showing a relationship between image layering and spatial frequency distribution in the embodiment.

FIG. 15 is an image diagram showing an example of a 0th layer digital image targeted by the embodiment.

FIG. 16 is an image diagram showing an example of a high frequency component image of the 0th layer which is a target of the embodiment.

FIG. 17 is an image diagram showing an example of a first layer digital image targeted by the embodiment.

FIG. 18 is an image diagram showing an example of a first layer high frequency component image targeted by the embodiment.

FIG. 19 is an image diagram showing an example of an image to be inspected in the second layer, which is a target of the embodiment.

FIG. 20 is an image diagram showing an example of a second-layer high-frequency component image targeted by the embodiment.

FIG. 21 is an image diagram showing an example of a third layer digital image targeted by the embodiment.

FIG. 22 is an image diagram showing an example of a third-layer high-frequency component image targeted by the embodiment.

FIG. 23 is an image diagram showing a first example of a fourth hierarchical digital image targeted by the embodiment.

FIG. 24 is an image diagram showing a second example of the fourth-layer digital image targeted by the embodiment.

FIG. 25 is a block diagram showing a configuration of a comparison inspection circuit of the comparison determination unit.

FIG. 26 is a block diagram showing a configuration of a first example of a threshold value determining unit of the comparison inspection circuit.

FIG. 27 is a block diagram showing the configuration of a second example of the threshold value determining unit of the comparison inspection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Printed matter 10 ... Printing machine 12 ... Printing unit 14 ... Feed roll 16 ... Winding top 18 ... Rotary encoder 20 ... Limit value calculation means 22 ... Inspection threshold value calculation means 24 ... Threshold memory 30 ... Detection part 32a ... Lamp house 32b ... Light source 33 ... Optical fiber 34 ... Light guide 34a ... Slit 34b ... Casing 34c ... Glass rod 34d ... Paint 36 ... Line sensor camera 38 ... Detection part electric circuit 38a ... A / D conversion part 38b ... Frame memory 38c ... Image compression circuit 38d ... Optical communication unit 38e ... Driver 38g ... A / D converter 40 ... Repeater 40a ... CPU 40b ... ROM 40c ... RAM 40d ... Parallel input / output circuit 40e ... Counter 40f ... O / E converter 40g, 40h ... Serial converter 40i ... E / O converter 40j ... Bus 40m ... Image timing control unit 4 n ... Memory 40p ... Image signal relay unit 50 ... CPU 52 ... Main storage device 54 ... Hard disk device 58 ... Floppy disk device 60 ... Input / output device 60a ... O / E converter 62 ... Keyboard 64a ... CRT control device 64b ... CRT 66 ... network control device 68 ... printer device 80 ... printed matter centralized inspection device main body 82 ... defective image storage portion 84 ... defective display portion 86 ... data totaling portion 88 ... network connection portion 100 ... determination portion 102 ... optical receiving portion 104 ... image restoration portion 106 ... Temporary image memory 110 ... Comparison determination unit 118 ... Recording unit 120 ... Image hierarchy circuit 122 ... Low pass circuit 124 ... Image thinning circuit 126 ... High pass circuit 130 ... Comparison inspection circuit 132 ... Switcher 134 ... Standard Image memory 136 ... Image memory to be inspected 138 ... Threshold determination unit 140 ... Threshold memo 142 ... comparison inspection unit 150 ... maximum value calculation circuit 152 ... minimum value calculating circuit 154 ... difference circuit 156 ... arithmetic circuit 160 ... maximum value calculation circuit 162 ... minimum value calculating circuit 164 ... arithmetic unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Hashimoto 1-1-1, Ichigayaka-cho, Shinjuku-ku, Tokyo Dai Nippon Printing Co., Ltd.

Claims (2)

[Claims] 1. A threshold value determining device for image inspection, which performs a density comparison inspection for each corresponding pixel unit of a reference image and an inspection image, wherein the inspection image of the inspection image is based on the reference image. A limit value calculating means for estimating an allowable variation range of density for each pixel unit, and an inspection threshold value calculating means for obtaining an inspection threshold value for each pixel unit of the inspection image according to the allowable variation range are provided. And a threshold value determining device. 2. An image inspection apparatus for performing a density comparison inspection between a reference image and an image to be inspected for each corresponding pixel unit, wherein the density of each pixel unit of the image to be inspected is based on the reference image. Limit value calculating means for estimating an allowable variation range of the inspection image, inspection threshold calculating means for obtaining an inspection threshold value for each pixel unit of the inspection image according to the allowable variation range, and the inspection threshold value for each inspection image of the inspection image. An inspection image is inspected from a threshold value memory that stores each pixel unit, a density difference value corresponding to each pixel unit between the reference image and the inspection image, and the inspection threshold value corresponding to the pixel unit. An image inspection apparatus, comprising: