JP2995105B2 - Method and apparatus for detecting color unevenness in printed matter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for automatically detecting color unevenness of a printed material, such as an offset color printed material.

[0002]

2. Description of the Related Art For example, in a color printed matter printed by an offset printing machine, a plurality of identical patterns are simultaneously printed on one sheet of paper, and each pattern is separated and independent by cutting performed after printing. Adjustment of the color density in offset color printing is performed by adjusting the amount of ink protrusion, and the greater the amount of ink protrusion (in other words, the amount of ink adhesion), the darker the color becomes. It is known that the lower the amount, the lighter the color. Therefore, in offset printing, color unevenness occurs due to the difference in the amount of ink protrusion between the ink pumps arranged side by side, and even with the same ink pump, color unevenness occurs due to the temporal change in the amount of ink protrusion. It is known that color unevenness is conspicuously noticeable in the same color portion (so-called solid portion) having a large area.

Therefore, conventionally, a skilled worker periodically visually checks the printed surface of a printed product to detect whether or not color unevenness has occurred, and adjusts the necessary amount of ink protrusion based on the detection. You are.

However, in color unevenness detection by visual observation, it is easy to recognize the color difference between adjacent identical color portions, but it is difficult to understand the color difference between identical color portions located apart from each other. And the printed matter tends to be uneven in color. Moreover, it is impossible to visually detect color unevenness in a state where the printed matter is moving, so that in-line color unevenness cannot be detected.

As a method of detecting color unevenness without visual observation, a printed matter printed in an appropriate darkness color is used as a master, and the printed matter is scanned in the width direction by a television camera having a CCD linear array image sensor as a light receiving portion. After a signal including an allowable value of variation in a video signal (analog signal) from the camera is stored in a memory as a reference signal, the inspected print is scanned by the camera while moving, and an image for each scan is scanned. There is a method of detecting color unevenness over the entire surface of the printed matter by comparing the signal with a reference signal stored in the memory.

[0006]

However, as described above, in the color nonuniformity detection method using the change amount of the analog video signal, a portion where color nonuniformity is not conspicuous other than a so-called solid portion is also detected. Therefore, there is a problem that there is much waste in the detection operation and the processing time is long. In addition, even if color unevenness is detected, since the information is for a local area on one scanning line, the spot-like detection information cannot be fully relied on, and the reliability of detection cannot be improved. Lack. In addition, since the detection is performed in a spot-like manner as described above, the occurrence position of the color unevenness cannot be specified. Therefore, even if the occurrence of the color unevenness is detected, it is not possible to take an after-action. . Further, the printed material has a different drying speed depending on the difference in the amount of ink adhered, and undulations occur accordingly (the thinner the paper, the more likely it is). There is a problem that reliability is poor.

An object of the present invention is to be able to shorten the processing time in spite of detecting color unevenness by digital processing, to specify a color in which color unevenness has occurred, and to improve the reliability of color unevenness detection. An object of the present invention is to provide a method for detecting color unevenness of a printed matter. Another object of the present invention is to provide an apparatus for detecting color unevenness of a printed matter, which can easily perform the method for detecting color unevenness.

[0008]

In order to achieve the above object, a method for detecting color unevenness of a printed matter according to the present invention comprises:
Variations in the average value of the brightness of a specific area in the solid portion of the same color in a plurality of patterns located apart from each other among the same pattern of the reference printed matter on which a plurality of the same patterns including the solid portion of the same color are printed The value including the allowable value is stored in the reference value memory as a reference value, and the printing surface of the test print printed with the same print pattern as the reference print is moved in a direction orthogonal to the moving direction of the test print. An image is picked up by a television camera having a linear array image sensor to be scanned as a light receiving unit, and the video signal from the television camera is subjected to A / D conversion to obtain image data, and this image data is synchronized with the moving speed of the test print. The image data stored in this memory is displayed on a monitor TV as a still image, and the same pattern is displayed on the monitor TV screen. The solid fabric part of Chi said reference printed matter
A specific area in the image memory corresponding to a specific area in
Is specified on the screen, an average value of the video levels for the image data of the specified specific area is calculated, and the average value is compared with the reference value.

According to another aspect of the present invention, there is provided an apparatus for detecting color unevenness of a printed matter, comprising: printing a printed surface on which a plurality of identical patterns including a solid background portion of the same color are printed; A television camera having a light receiving section composed of a linear array image sensor that scans in a direction perpendicular to the moving direction of the printed matter, and an A / D converter that A / D converts a video signal from the television camera into image data A speed sensor for detecting a moving speed of the printed matter; an image connected to the speed sensor and an output terminal of the A / D converter, for sequentially writing and storing the image data in synchronization with the moving speed of the printed matter; A memory, a monitor television on which the image data stored in the memory is displayed as a still image, and the same picture displayed on the monitor television screen. Before the plurality of pattern positioned Te
A control unit that specifies a specific area in the image memory corresponding to a specific area in the solid portion of the same color on the screen;
An arithmetic unit connected to the control unit and the image memory, for calculating an average value of video levels for image data of the specific area in the image memory specified by the control unit; and an output terminal of the arithmetic unit. A connected changeover switch, a reference value memory connected to one of the changeover terminals of the switch, and storing, as a reference value, a value including the average value and an allowable value of variation; and a reference value memory and the changeover switch. A comparator connected to the other switching terminal, for comparing the average value calculated by the arithmetic unit with the reference value stored in the reference value memory.

[0010]

In the configuration of the first aspect, first, the reference value is stored in the reference value memory. The reference value includes an allowable value of variation in an average value of lightness of a specific area in a solid background portion of the same color in a plurality of patterns located apart from each other among the same patterns of a reference print on which a plurality of the same patterns are printed. Value. After the storage, the printing surface of the test print being moved by the television camera using the linear array image sensor as the light receiving unit is scanned in a direction orthogonal to the direction of movement of the print.
By this scanning, the sensor outputs a voltage (analog video signal) corresponding to the brightness of the printing surface. Therefore,
Color unevenness on the printed surface can be recognized as a change in the voltage value of the video signal. Next, the video signal is A / D converted. This A /
The voltage value of the video signal, which is an analog amount, is converted into a digital signal as image data by the D conversion. Therefore, for example, if the A / D converter has an 8-bit conversion function, a digital output of 256 stages can be obtained, and the video signal is a digital signal of any of the 256 stages. (Image data). The image data obtained in this manner is sequentially written and stored in an image memory in synchronization with the moving speed of the test print,
The stored image data is displayed as a still image on the monitor television. Thereafter, of the same pattern displayed on the screen of the monitor television, the solid color of the same color of the reference print is used.
A specific area in the image memory corresponding to the specific area in the ground portion is designated on the screen of the monitor television, and the designated area is designated.
The average value of the video level for the image data of the specified specific area is calculated. Finally, the average value is compared with the reference value. Thus, automatic detection of color unevenness is performed.

According to such a method for detecting color unevenness, despite the fact that digital processing, which is generally slower than analog processing, is performed, it is not necessary to compare the entire surface of a printed material to be inspected. So-called identical
Since the detection operation is performed by specifying the solid color portion, the processing time can be shortened. Then, since the detection location is specified in advance as described above, the color of this specific portion is also known in advance, so that it is possible to take measures after detecting the color unevenness, and the practicality as the color unevenness detection is improved. high. Moreover, the same color is applied to the reference print and the test print.
Color unevenness is detected for a specific area in the covered ground portion . That is, unlike the method of detecting color unevenness based on data on a local area on one scan line, the color unevenness is detected by comparing with the average value of the brightness of a predetermined area. In addition to being able to reduce, the comparison data can be stabilized, and therefore, the reliability of color unevenness detection can be improved. Moreover, while watching the still image on the monitor TV,
By specifying on the screen, the specific area can be easily specified.
Can be.

[0012] In the configuration of the second aspect, the television camera scans the printing surface of the moving reference printed material and the inspected printed material in a direction orthogonal to the moving direction of these printed materials. By this scanning, the video signal output from the linear array image sensor at a voltage value corresponding to the brightness is A / D
It is converted into a digital signal as image data by the converter,
The image data is sequentially written and stored in the image memory in synchronization with the moving speed of the printed matter detected by the speed sensor. The image data stored in the image memory is displayed on the monitor television as a still image, and the control unit controls the same color pattern in a plurality of patterns among the same patterns in the still image.
A specific area in the image memory corresponding to the specific area in the ground portion is designated. The calculation unit calculates an average value of video levels of the image data of the specific area in the image memory designated by the control unit. First, the changeover switch causes the average value of the video level obtained by the above processing for the image data of the specific area in the solid portion of the same color of the reference print to be input to the reference value memory. Then, the reference value memory stores, as the reference value, a value including the average value and the allowable value of the variation, and inputs the reference value to the comparator. After this, the changeover switch performs the changeover operation,
The output of the arithmetic unit obtained by the above processing for the inspected printed material, that is, the output on the monitor TV screen
The average value of the video level of the image data of the specific area in the image memory designated by the control unit is input to the comparator. The comparator compares the reference value input thereto with the average value of the printed material to be inspected to determine whether there is color unevenness in the specific area.

Therefore, in this color unevenness detecting apparatus, a configuration is employed in which the average value of a specific area in a solid background portion of the same color is inspected for a printed material to be inspected.
Since the reference value can be stored in the reference value memory, there is no need for a device and trouble for finding the reference value , and further, the finger of the specific area is not required
Settings can easily be specified on the monitor TV screen.
I can.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a plan view of an offset color sheet-fed printed material A according to the embodiment, and a plurality of identical patterns C are printed on the printing surface B. For convenience of explanation, the portions D of the patterns C which are hatched in FIG.
In a large area, that is, a so-called solid area
is there. In FIG. 2, a two-dot chain line E indicates a portion to be cut, and when the printed matter A is a non-defective product, the pictures C are separated from each other along the chain line E and are separated and independent. .

FIG. 1 is a block diagram showing a configuration of an uneven color detecting apparatus according to one embodiment of the present invention. In FIG. 1, the printed matter A is moved in the front and back directions on the paper of FIG. At an inspection position arbitrarily determined with respect to the movement path of the printed matter A, for example, a camera unit 2 having four television cameras 1 is arranged, and an illumination device 3 for illuminating the field of view of the unit 2 is provided. Are located. In FIG. 1, reference numeral 4 denotes a speed sensor provided so as to be in contact with the edge of the printed material A to be moved, which is formed by, for example, a pulse generator, and detects a moving speed of the printed material A.

Each television camera 1 uses a CCD linear image sensor 1a as a light receiving section.
The cameras 1 are arranged along a direction orthogonal to the moving direction of the printed matter A, and the sensor 1a scans the printing surface B in a direction orthogonal to the moving direction of the printed matter A. An amplifier 5 is connected to an output terminal of each television camera 1. The amplifier 5 is used to amplify a video signal output from the television camera 1.

An A / D converter 6 having an 8-bit conversion function is connected to the amplifier 5, for example. This converter 6 is used for converting a voltage value of a video signal output from the image sensor 1a, which is an analog amount, into a numerical value by an A / D conversion thereby to obtain a digital signal as image data. Thus, 256 digital outputs are obtained by the 8-bit conversion function. Therefore,
Assuming that the range of the voltage value of the video signal is 0 V to 1 V, the resolution of the A / D converter 6 having the 8-bit conversion function is about 0.004 V.

The output terminal of the speed sensor 4 and the output terminal of the A / D converter 6 are connected to an image memory 7, respectively. In the memory 7, image data output from the A / D converter 6 is sequentially written and stored in synchronization with the moving speed of the printed material A for one printed material A as a whole. In this writing, when the fields of view of the respective television cameras 1 overlap as in the present embodiment, the image data from one of the television cameras in the overlapping portion is canceled.
The image data stored in the image memory 7 is updated each time the television camera 1 captures a new print.

A monitor TV 9 is connected to the image memory 7 via a CRT interface 8, and a control unit 10 is connected via the interface 8. The monitor television 9 displays the image data of the entire printed matter A stored in the image memory 7 as a still image. The control unit 10 controls the entire detection operation of the color nonuniformity detection device, and is formed by a CPU (central processing unit).

A designation input for designating a window of a specific area is input to the control unit 10. This designation input is performed using input means (not shown) such as a light pen, a keyboard, or a mouse. Upon receiving the designation input, the control unit 10 controls the specific area F in the solid portion D of the same color in the plurality of patterns C located apart from each other among the same patterns C displayed on the monitor television 9.
A specific area in the image memory 7 corresponding to (see FIG. 2) is designated. The same pattern C to be specified, preferably in the farthest pattern C in the moving direction of the printed material A (FIG. 2 in the direction) as shown in FIG. 2, the moving direction of the printed matter on the other orthogonal It is preferable to designate one picture C located at one end in the direction in which the picture C is drawn. And like this
While watching the still image displayed on the NITTER TV 9, the screen
The specific area F can be specified by specifying the window above
Thus, the designation operation can be easily performed.

An arithmetic unit 11 is connected to the control unit 10, and the arithmetic unit 11 is connected to the image memory 7. The calculation unit 11 calculates an average value of the video levels of the image data of the specific area in the image memory 7 specified by the control unit 10. This operation unit 1
A changeover switch 12 is connected to one output terminal.

One switching terminal 1 of the changeover switch 12
2a is connected to the reference value memory 13, and the other switching terminal 12b is connected to one input terminal of the comparator 14. The reference value memory 13 stores, as a reference value, a value including the average value calculated by the calculation unit 11 and an allowable value of variation. The reference value stored in the reference value memory 13 is updated when a new reference value is input through the switching terminal 12a. The reference value memory 13 is connected to the other input terminal of the comparator 14. The comparator 14 determines the color unevenness by comparing the reference value and the average value input to the comparator 14, and has an output terminal connected to a notifier such as a buzzer or a recording device (not shown).

Next, an operation of automatically detecting color nonuniformity using the color nonuniformity detecting device of the embodiment will be described. First, one sheet of reference printed matter, which has already been printed and has been judged to be proper without any color unevenness by visual inspection or the like, is prepared, and is subjected to a color unevenness detection device to obtain a reference for color unevenness detection. This reference value setting operation is shown in the flowchart of FIG.

That is, with the output end of the operation unit 11 connected to the reference value memory 13, the television camera 1 takes a monochrome image of the printing surface of the moving reference print. This imaging is performed by scanning of the linear array image sensor 1a along a direction orthogonal to the moving direction, and the linear array image sensor 1a outputs a video signal having a voltage value corresponding to the brightness of the picture on the printing surface. This video signal is an analog signal, and after being amplified by the amplifier 5, is supplied to an A / D converter 6 having an 8-bit conversion function.
Is converted into a digital signal as image data by A / D conversion. This digital signal corresponds to the voltage value corresponding to the brightness of the picture and is converted into a digital output of any one of 256 stages. In other words, A / D
The converter 6 converts the brightness information of the picture optically captured as a brightness difference into digitized image data.

This image data is sequentially written and stored in the image memory 7 in synchronization with the moving speed of the reference printed material detected by the speed sensor 4 for one entire reference printed material. The image data of the entire reference printed matter stored in the memory 7 is displayed as a still image on the monitor television 9 via the CRT interface 8.

On the basis of this screen display, the operator designates a window at several places where color unevenness is to be detected, for example, by displaying a cursor operated using a mouse. That is, the input operation to the control unit 10 causes the control unit 1 to operate.
0 is an image memory corresponding to a specific area F in a solid background portion D of the same color in a plurality of patterns C which are located apart from each other among the same patterns in a reference print having a configuration as shown in FIG. 7 is designated through the CRT interface 8.

The information for specifying the window is also supplied to the calculation unit 11. Receiving this supply, the arithmetic unit 11 reads the image data of the specific area in the image memory 7 designated as the window into the arithmetic unit 11 and performs an arithmetic operation. By this calculation, the average value A of the video levels for the image data of the specific area F read from the image memory 7 is calculated.

Then, since the changeover switch 12 has closed the changeover terminal 12a at this stage, the operation unit 11
(That is, the average value A of the video levels obtained for the specific area D of the reference print) is stored in the reference value memory 1.
3 is supplied. Therefore, the reference value memory 13 stores, as the reference value S, a value including the average value A and the allowable value (± α) of the variation, and stores the reference value S in the comparator 1.
Enter 4 That is, by the processing operations as described above, it is possible to obtain a reference for detecting color unevenness without requiring a special color difference meter.

Thereafter, the changeover switch 12 is changed over to open the changeover terminal 12a and change over the changeover terminal 1
After closing 2b, a specific area of the printing surface (this area corresponds to the specific area F of the reference printed material) while the detected printed material, which has been subjected to offset color printing with the same print pattern as the reference printed material, is moving in the printing line. ) Is periodically obtained and compared with the reference value to detect the presence or absence of color unevenness each time. This comparison operation is shown in the flowchart of FIG.

The process of storing image data of a predetermined length in the image memory 7 performed in the comparison operation is the same as the procedure performed for the reference printed material. That is, in brief, a monochrome image of the print surface of the test print by the TV camera 1, amplification of the video signal from the camera 1, and a video signal of a voltage value corresponding to the brightness of the pattern of the test print are A / 25 corresponding to the voltage value by the D converter 6
The digital data (image data) of one of the six stages is converted into digital signals (image data), and the image data thus obtained is sequentially stored in the image memory 7 in synchronization with the moving speed of the inspected print for the entire reference print. It is implemented by writing and storing.

The processing for calculating the average value B of the video levels of the designated image data, which is performed after this processing, is the same as the procedure performed for the reference printed matter. That is, to put it simply, image data of one entire reference print stored in the image memory 7 is displayed on the monitor television 9 as a still image, and several places where color unevenness is to be detected in this image, that is, the same picture A specific area in the image memory 7 corresponding to the specific area F in the solid portion D of the same color in a plurality of patterns C located apart from each other (this part is designated in the reference print. The window is designated by the operator, and the calculation unit 11
The calculation is performed by calculating the image data of the specific area read from the image memory 7 designated by the window and calculating the average value B of the video level for the data.

The average value B is supplied to the comparator 14 through the changeover terminal 12b of the changeover switch 12. Therefore, the comparator 14 compares whether the average value B is included in the reference value S stored in the reference value memory 13.

If it is determined that the average value B is within the range of the reference value S and the result of the comparison is YES, it is determined that there is no color unevenness, and the comparison operation ends. When the average value B is out of the range of the reference value S and a determination of NO is made, a determination is made that there is color unevenness, and this determination result is reported by a buzzer or the like, and the comparison is made. The operation ends.

Therefore, based on the notification of the detection of the color unevenness, the operator can adjust the protrusion amount of the ink pump that emits the color including the specific region so that the color unevenness does not occur.

The present invention is not limited to the above embodiment. For example, in the color unevenness detection method of the present invention, the reference value is stored in the reference value memory by measuring a predetermined color with a color difference meter, converting the value into a digital value, and externally inputting the value to the reference value memory. The information may be input and stored using a device (keyboard). Therefore, in this case, the color nonuniformity detection device omits the changeover switch of the one embodiment and directly connects the output terminal of the calculation unit to the comparator.
An external input device is connected to a reference value memory connected to the comparator, and the other configuration is a color nonuniformity detection device having the same configuration as that of the above-described embodiment.

Further, when the color unevenness is detected, knowing how much the average value B of the inspected printed matter is different from the average value A of the reference value S (the degree of the color unevenness) is based on the average. Since the values A and B can be determined by comparing the values, the correlation between the degree of color unevenness and the amount of ink protrusion from the ink pump is known experimentally in advance, so that feedback to the ink pump is made in accordance with the degree of color unevenness. , The amount of protrusion of the ink pump is automatically adjusted to prevent color unevenness. In addition, the present invention is not limited to sheet-fed printed matter, and can be applied to color unevenness detection of a continuous long printed matter.

[0037]

According to the configuration of the present invention described in detail above, the following effects can be obtained.

In the method for detecting color unevenness of a printed matter according to the first aspect, although the color unevenness is detected by digital processing, the detection operation is performed by specifying a so-called solid portion where the color unevenness is conspicuous. Processing time can be shortened. Then, since the detection location is specified in advance, the color of this specific area can be known in advance, and therefore, measures can be taken after detecting the color unevenness. High in nature. Moreover, color unevenness is not detected based on data on a local area on one scanning line, but is detected by comparing the average value of the brightness of a predetermined area, so that the comparison data is stable. In addition, the influence of the undulation of the printed matter can be reduced, and therefore, the reliability of the uneven color detection can be improved. In addition, monitor TV
While viewing a still image, specify
The area can be easily specified and the usability is good.

In the apparatus for detecting color unevenness of a printed matter according to the second aspect, not only can the above-described detection method be implemented, but also a configuration for performing processing for obtaining an average value of a specific area of a printed matter to be inspected can be used as a reference. Since the values can be stored in the reference value memory, there is no need for a device or trouble for finding the reference value, and the designation of the specific area is easy, and therefore, the implementation is easy .

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an uneven color detection device according to one embodiment of the present invention.

FIG. 2 is a plan view schematically showing a print pattern example of an offset color sheet-fed print according to the embodiment.

FIG. 3 is a flowchart showing a reference value setting operation in the embodiment.

FIG. 4 is a flowchart showing a comparison operation in the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... TV camera, 1a ... Linear array image sensor, 4 ... Speed sensor, 6 ... A / D converter, 7 ... Image memory, 9 ... Monitor television, 10 ... Control part, 11 ... Operation part, 12 ... Changeover switch, 13: Reference value memory, 14
... Comparator.

Claims (2)

(57) [Claims] 1. A solid fabric part of the same color in a plurality of the picture which is located remote from each other of the same picture of the same color reference prints multiple identical pattern is printed which includes a solid land portion
The value including the average value of the brightness of the specific area in the average value including the allowable value of the variation is stored in the reference value memory as a reference value, and the printing surface of the test print printed with the same print pattern as the reference print is An image is picked up by a television camera having a light-receiving unit as a light-receiving unit using a linear array image sensor that scans in a direction orthogonal to the moving direction of the print to be inspected, and a video signal from the television camera is A / D converted to obtain image data. The data is sequentially written and stored in an image memory in synchronization with the moving speed of the test print, the image data stored in the memory is displayed as a still image on a monitor television, and the same picture displayed on the screen of the monitor television is displayed. Specifying a specific area in the image memory corresponding to a specific area in the solid portion of the reference printed matter on the screen
And calculating an average value of video levels of the image data of the specified specific area , and comparing the average value with the reference value. 2. A solid portion of the same color of a printed material to be moved.
, A television camera having a light receiving section composed of a linear array image sensor that scans a printing surface on which a plurality of the same patterns are printed in a direction orthogonal to the moving direction of the printed matter, and outputs a video signal from the television camera to an A / An A / D converter that converts the image data into D-converted image data; a speed sensor that detects a moving speed of the printed material; a speed sensor that is connected to an output terminal of the A / D converter; An image memory that sequentially writes and stores the image data in synchronization with the moving speed of the monitor, a monitor television on which the image data stored in the memory is displayed as a still image, and a monitor separated from the same picture displayed on the screen of the monitor television. Of the same color in a plurality of pictures
A control unit that specifies a specific area in the image memory corresponding to a specific area in the solid background portion on the screen; and a control unit that is connected to the control unit and the image memory and that is specified by the control unit. An arithmetic unit for calculating an average value of the video level for the image data of the specific area, a changeover switch connected to an output terminal of the arithmetic unit, and a switch connected to one of the switch terminals of the switch. A reference value memory for storing a value including an allowable value of variation as a reference value; and a reference value memory connected to the reference value memory and the other switching terminal of the changeover switch, the average value calculated by the operation unit, and the reference value memory. And a comparator for comparing with a reference value stored in the printer.