JPH0811399A - Print quality inspection method - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] The present invention relates to a print quality inspection method, and conventionally, is to quantitatively inspect a deviation in reciprocal printing that causes a variation in results because it relies on visual inspection of work. A system comprising a storage unit for storing numerical data representing light and darkness of an image, a drawing unit for extracting the numerical data, a conveying unit for the numerical data, and an arithmetic processing unit for the numerical data is configured, and forward printing is performed. The dot arrangement in the column direction at the time and the dot arrangement in the column direction at the time of the backward pass are regarded as two parallel lines, and the print quality is inspected by measuring the interval between the parallel lines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prints by reciprocally moving a print head having a printing element, for example, an ink ejection timing of a printing element in a forward path by using a pattern printed on a paper in an ink jet printer or a wire dot printer. In order to evaluate whether the ink ejection timing in the return path is appropriate or not, the dot array in the row direction printed in the forward path and the dot in the row direction printed in the return path, which should originally be aligned, should be evaluated. The present invention relates to a print inspection method that measures the amount of misalignment in the row direction of a row and determines whether it is appropriate or not.

[0002]

2. Description of the Related Art Conventionally, the amount of deviation between the dot arrangement on the forward path and the dot arrangement on the return path has been measured and inspected visually by an operator using a magnifier and a scale such as a loupe.

[0003]

Conventionally, an operator has visually read the size of dots and the distance between dots from the scale of a scale by using a magnifier such as a magnifying glass. And there was a difference in the results.

An object of the present invention is to quantitatively measure the amount of horizontal displacement of the dot array.

[0005]

The above-described object is achieved by using a camera for image input and a frame memory to arithmetically process an image of dots on the frame memory.
Specifically, using the numerical data that represents the light-dark level of the dots in the frame memory, the dot array in the column direction during forward printing and the dot array in the column direction during backward printing are recognized as straight lines that are parallel to each other. Then, it is achieved by measuring the distance between the parallel lines.

[0006]

With the above arrangement, the deviation between the forward printing and the backward printing can be quantitatively measured.

[0007]

Embodiments of the present invention will now be specifically described with reference to the drawings.

FIG. 1 is a block diagram of an apparatus for carrying out the evaluation method according to the present invention. The keyboard 7 is operated to drive the device, the image processing program stored in the image processing program memory 3 is executed from the CPU 5, and the dot arrangement on the printed material photographed by the image input CCD camera 1 is used as a video signal A It is taken into the / D converter 2. A /
The D conversion unit 2 converts this video signal into numerical data representing a light-dark level, and the numerical data is sent via the CPU 5 to the frame memory 4 in which the memory is allocated to one pixel for each ground.
Remember on top. The CPU 5 uses the numerical data representing the brightness level read from the frame memory 4 and the image processing program and calculation memory in the image processing program memory 3 to calculate the line width, the center position of the line, and the like. The calculation result is output from the output device 6.

FIG. 14 shows a printed matter in which dots in the column direction are printed on the forward path and the backward path of a printing element (not shown).

In the present invention, the apparatus is used to arrange the dots 8 ', 9', 10 ', 11' in the column direction printed on the printed matter in the forward path of the printing element on the printed matter shown in FIG. 14 and the row printed in the backward path. The dots 12 ', 13', 14 ', 15' in the direction are photographed by the image input camera 1, and the video signal is A
Numerical data representing a light / dark level is converted by the / D converter 2, for example, the brightest part is converted into a numerical value such as 255 and the darkest part is converted into a numerical value such as 0 and stored in the frame memory 4. Calculate the line width, the center position of the line, and the like.

FIG. 2 is a conceptual diagram of the frame memory 4 for storing numerical data representing the brightness level of an image. Each of the memories forming the frame memory 4 corresponds to one pixel of the screen imaged by the image input camera 1, and stores numerical data representing the light / dark level of each pixel. Hereinafter, the memory for each address on the frame memory 4 will be referred to as a pixel.

Although the addresses of the frame memory are originally assigned one-dimensional continuous values, since the object to be inspected is a planar figure in this embodiment, the addresses of each memory are assigned two-dimensional XY coordinate values ( Express in the 4th quadrant). Therefore, the address of the pixel G at the origin in the frame memory 4 is (0,
0). Numerical data representing the brightness level immediately after being stored in the frame memory 4 through the image input camera 1 is defined as numerical data representing the brightness level of the original image. For example, in the case where numerical data representing the lightness level of a printed portion of a printed matter in which dots other than white such as black and magenta are printed on a white background paper is stored in the frame memory 4 by the apparatus of FIG. The numerical data indicating the light-dark level stored in each pixel is smaller than the pixel of the portion where the white background is photographed for the pixel of the dot portion. Therefore, in order to extract the pixels corresponding to the dots in the frame memory 4 from the numerical data representing the brightness level of the original image, the threshold value is determined and the frame memory 4 is determined.
Numerical data representing the brightness level of each pixel above is compared with a threshold value, and when the numerical data representing the brightness level of the pixel is greater than or equal to the threshold value, the numerical data representing the brightness level of the pixel is the brightest value, for example, Change to 255. When the numerical data representing the light / dark level of the pixel is smaller than the threshold value, the numerical data representing the light / dark level on the pixel is changed to the darkest value, for example, 0. In the area where dots are printed by this binarization processing, numerical data indicating lightness and darkness in the frame memory 4 is represented by a group of pixels having the darkest value.

In FIG. 3, a printed matter 53 printed by an ink jet printer or the like is photographed by the image input camera 1, a video signal is converted by the A / D conversion unit 2 into numerical data indicating light and dark, and stored in the frame memory 4. The state after performing the said binarization process is shown. Dots 8, 9, 10, 1
1 corresponds to dots 8 ', 9', 10 ', 11' printed on the forward path of the printing element of the inkjet printer of FIG. 14, and dots 12, 13, 14, 15 are printed on the backward path of the printing element. Dots 12 ', 13', 14 ', 1
It corresponds to 5 '.

As a result of the binarization processing, the numerical data indicating the lightness and darkness of the group of pixels forming the dot has the darkest value, and the other background pixels have the numerical data indicating the lightness and darkness. It is the brightest value. Usually, in printers, dots 9, 10, 11, 12,
Ideally, 13, 14, and 15 are arranged in a straight line in the column direction, but in FIG. 3, the dots 8, 9, 10, 11 in the forward direction of the dots 8, 9, 10, 11 due to the deviation of the ink ejection timing of the printing element of the inkjet printer are shown in FIG. It shows a state in which the dots 12, 13, 14, 15 in the column direction on the return path and the shift δ in the row direction are generated. In this embodiment, the procedure of measuring the distance between the forward straight line and the backward straight line by treating the arrangement of the dots printed in the paper feed direction in the forward and backward passes by the horizontal movement of the printing element as the straight line in the column direction, respectively. Will be described below with reference to FIGS. 4 to 13.

In FIG. 4, the circular dot 16 has a pixel on the frame memory 4 for which the numerical value indicating lightness and darkness has the minimum value, and a pixel for which the numerical value data indicating the lightness and darkness has the maximum value is white.
The dots 16 are represented by an image of values, and the dots 16 are represented by a group of pixels having minimum values of numerical data indicating lightness and darkness. Each dot 8, 9, 10, 11, 12, 1 in FIG.
3, 14, and 15 are also represented by a dot 16. In the embodiment of the present invention, the coordinate value of the pixel corresponding to the center position of each dot represented by the binarized pixel on the frame memory 4 is acquired as the pre-processing for recognizing the dot arrangement as a straight line. .

In FIG. 5, numerical data indicating the lightness and darkness is examined in pixel units along the X-axis tracing direction 17 from the pixel G at the origin of the frame memory 4 in FIG. 4, and the pixel whose minimum value is detected first is shown. The recognition of the outer shape of the dot is started from 18, the pixels in the vicinity of 8 shown in FIG. 6 are examined counterclockwise, and when the color changes from white to black, the pixel that becomes black is used as the next reference. By repeating this procedure, the pixels on the outer peripheral portion of the dot 16 are traced, and as shown by the locus 19 on the outer peripheral edge, the pixel 18 is returned to. When returning to the start pixel 18, the shape surrounded by the pixels of each outer peripheral portion is recognized as one dot, and the address on the frame memory 4 of each pixel of the outer peripheral portion is stored as a coordinate value.

In FIG. 7, a dot number is assigned to a group of pixels recognized as one dot by the above procedure, and X, Y on the frame memory 4 of each pixel on the outer periphery traced by the processing of FIG.
The data type for registering coordinate values is shown.

After registering one dot in the data type shown in FIG. 7, a black pixel is searched to search for another dot. If the searched pixel is not included in the registered dot, the dot is registered by tracing the outer peripheral portion of the dot in the same manner as the procedure shown in FIGS. By repeating this procedure, all the dots on the binarized image are searched, the dot numbers that are the serial numbers in the search order are added, and the X and Y coordinate values of the pixels in the outer peripheral portion are registered.

FIG. 8 is a flow chart of a process for obtaining the central pixel of a certain detected dot. In the flowchart, in steps 26 to 29, the coordinate values of the pixels at both ends in the row direction of the dot and the coordinate values of both ends in the column direction of the dot are acquired, and the pixel corresponding to the position where each average is calculated is defined as the center of the dot. To do. The method of assuming the center of the dot in the present invention is not limited to the above method. For example,
About M pixels that make up one dot

[0020]

[Equation 1]

Is a coordinate value indicating the center of gravity of the dot, and the pixel at the center of gravity may be the central pixel of the dot shape.

9 and 10 show the dots 8 shown in FIG.
Up to 9, 10, 11 and dots 12, 13, 14, 15
Are treated as groups representing different straight lines, and therefore, a flow chart showing a process for setting and limiting the limit value εX of the distance in the row direction and the limit value εY of the distance in the column direction between the pixels at the center of each dot. is there. FIG. 9 shows a process of extracting dot candidates that form the same straight line by performing a neighborhood check in the row direction, and FIG. 10 shows adjacent dots in the column direction based on the result of the neighborhood check in the row direction shown in FIG. This shows a process of checking whether the distance between the central pixels of the dots is within the vicinity εY and completing the grouping of dots representing the same straight line.

The dots 8, 9, 10, 11, 12, in FIG.
The dots 13, 14, and 15 are sequentially recognized from the dot 8 at the top of the frame memory to the dot 15 at the bottom of the frame memory by executing the recognition of each dot in accordance with the procedure shown in FIGS. 4, 5, and 6. Then, for example, serial numbers from 1 to 8 are added and registered in the data type shown in FIG. In FIG. 9, the coordinate values of the central pixel obtained by the procedure of FIG.

[0024]

[Equation 2]

In the case of, the X coordinate value X of the center of the dot 8
By calculating the distance from the X coordinate value of the pixel at the center of another dot based on mid (1) in step 33, it is checked whether it is within the limit value εX of the dot distance in the row direction. For the time being, it is possible to determine whether or not the dot 8 and the other dots satisfy the condition of forming a group of dots forming the same straight line in the row direction. In each element of the array P in step 35, the dot number of a dot that may be in the same group as the dot 8 is registered. The serial number of the dot 8 itself is also registered in advance in step 32.

In this embodiment, the dot numbers of dots 9, 10, and 11 are registered in the array P by the neighborhood εX between the central pixels in the row direction, and dots 12 and 1 are registered.
For 3, dots 14, and dots 15, in step 36, dot numbers are registered in the array Q as a group representing a straight line different from the straight line represented by the dot 8. Step 38
When it is determined that the check has been completed for all the dots, the check of the distance between pixels at the center in the row direction is ended.

Continuing with FIG. 10, the array P in which the serial numbers of the dots that may be in the same group as the dot 8 are stored by the processing of FIG. 9 is used, and in step 41, the centers of the dots adjacent to each other in the row direction are set. The distance between pixels is calculated, and it is checked whether the distance is within the limit value εY of the distance in the column direction. If it is within εY, in step 42 the dot numbers of the same group are stored according to the data type shown in FIG. If it is not within εY, the group number is incremented in step 43, and the dot number is sequentially stored as a new group by the data type shown in FIG.

The dots 8, 9, 10, and 11 are recognized as the same group by a series of processes shown in FIGS. In the process of FIG. 9, for the dots determined not to be in the same group as the dot 8, the dot having the smallest dot number stored in the array Q is used as a reference for the dot 8 and the array Q is used. The neighborhood check in the row direction and the column direction is executed again in the range of dots registered in. By repeating this procedure, the dots on the frame memory 4 can be completely grouped. In the case of FIG. 3 of the present embodiment, the dots 8, 9, 10,
11 and dots 12, 13, 14, and 15 are divided into two groups.

FIG. 12 shows the X-axis and the Y-axis which are the coordinate system on the frame memory 4 for the groups of dots 8, 9, 10, 11 and the groups of dots 12, 13, 14, 15.
Rectangle 4 circumscribing with each line parallel to the axis
FIG. 6 is a distribution diagram in the row direction of the sum of numerical data indicating the brightness of each pixel in the column direction inside the rectangle 47.

In this case, since the numerical data indicating the lightness and darkness is the minimum value for the pixels forming the dots, the smaller the sum of the numerical value data indicating the lightness and darkness in the group of dots representing the straight line in the column direction, the closer to the column. It can be determined that the percentage of hanging dots is high. Therefore, it is determined that the X coordinate value of the pixel in which the sum of the numerical values indicating light and dark in the column direction is the minimum is the center of the width of the straight line represented by the dot group.

FIG. 13 is a flow chart showing the program processing for detecting the center of the line width by the distribution in the row direction of the sum of the numerical data in the column direction shown in FIG. Are compared, and the X coordinate value of the position where the sum of the numerical data changes from decrease to increase is detected, and the center of the line width is determined in step 51.

In the present embodiment, in the case of dots arranged in the column direction in the coordinate system shown in FIG. 12, the center coordinate value of each grouped dot

[0033]

(Equation 3)

Of these, the average value of the X coordinate values for each group can be used as the center of the line width represented by the dot row.

By the above method, the center of the line width of each straight line indicated by the group of dots shown in FIG. 12 is obtained to measure the line distance, and the ink of the ink jet printer is ejected from the printing element at an appropriate timing. You can know whether it is done or not.

[0036]

According to the present invention, the printer can be easily maintained and adjusted because it is possible to automatically and quantitatively measure and inspect the displacement, which has been visually performed using a measuring instrument such as a magnifying glass. You can

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus for carrying out an evaluation method according to the present invention.

FIG. 2 is a conceptual diagram of a frame memory that stores numerical data indicating the brightness of an image.

FIG. 3 Array of dots in the column direction binarized by a threshold value

FIG. 4 State of dots on frame memory

FIG. 5: Flowchart of dot perimeter tracking

FIG. 6 Check directions in the vicinity of 8 pixels

FIG. 7 is a data type that stores dot numbers and coordinate values of pixels around the dots.

FIG. 7 is a flowchart of processing assuming a central pixel of a dot.

FIG. 9 is a flowchart of a grouping process in the row direction of a dot array.

FIG. 10 is a flowchart of column-wise grouping processing of dot arrangement.

FIG. 11 is a data type in which dots are registered for each group representing the same straight line.

FIG. 12 is a distribution diagram showing, in the row direction, the sum of numerical data indicating the lightness and darkness of each pixel in the column direction inside a rectangle inscribed by groups of dots representing the same straight line.

FIG. 13 is a flowchart showing a process for detecting the center of a line width of a straight line expressed by a group of dots representing the same straight line.

FIG. 14: Printed matter in which dots are printed in the column direction in each of the forward and backward passes

[Explanation of symbols]

1 is an image input camera, 2 is an A / D converter, 3 is an image processing program memory, 4 is a frame memory, 5 is a CP
U, 6 is an output device, 7 is a keyboard, 8 to 16 are dots, 17 is a check direction of numerical data indicating the brightness of one pixel unit, 18 is a start pixel of the outer periphery tracking of the dot 16, 19
Is a trace of the outer circumference of the dot 16, 20 to 22 are steps, 23 is the pixel of the dot outer circumference tracking key, 24 is the check direction near 8 of the pixel 23 of the key, 25 is the pixel, 26
~ 45 is a step, 46 is a circumscribed dot group and X
A rectangle whose one side is a line segment parallel to each of the axes and the Y-axis, 47 is a rectangle circumscribing the dot group and one side is a line segment parallel to each of the X-axis and the Y-axis, and 48 to 52 are steps.

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[Procedure amendment]

[Submission date] October 28, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus for carrying out an evaluation method according to the present invention.

FIG. 2 is a conceptual diagram of a frame memory that stores numerical data indicating the brightness of an image.

FIG. 3 Array of dots in the column direction binarized by a threshold value

FIG. 4 State of dots on frame memory

FIG. 5: Flowchart of dot perimeter tracking

FIG. 6 Check directions in the vicinity of 8 pixels

FIG. 7 is a data type that stores dot numbers and coordinate values of pixels around the dots.

FIG. 8 is a flowchart of processing assuming a central pixel of a dot.

FIG. 9 is a flowchart of a grouping process in the row direction of a dot array.

FIG. 10 is a flowchart of column-wise grouping processing of dot arrangement.

FIG. 11 is a data type in which dots are registered for each group representing the same straight line.

FIG. 12 is a distribution diagram showing, in the row direction, the sum of numerical data indicating the lightness and darkness of each pixel in the column direction inside a rectangle inscribed by groups of dots representing the same straight line.

FIG. 13 is a flowchart showing a process for detecting the center of a line width of a straight line expressed by a group of dots representing the same straight line.

FIG. 14: Printed matter in which dots are printed in the column direction in each of the forward and backward passes

[Description of Reference Signs] 1 is an image input camera, 2 is an A / D converter, 3 is an image processing program memory, 4 is a frame memory, 5 is a CP
U, 6 is an output device, 7 is a keyboard, 8 to 16 are dots, 17 is a check direction of numerical data indicating the brightness of one pixel unit, 18 is a start pixel of the outer periphery tracking of the dot 16, 19
Is a trace of the outer circumference of the dot 16, 20 to 22 are steps, 23 is the pixel of the dot outer circumference tracking key, 24 is the check direction near 8 of the pixel 23 of the key, 25 is the pixel, 26
~ 45 is a step, 46 is a circumscribed dot group and X
A rectangle whose one side is a line segment parallel to each of the axes and the Y-axis, 47 is a rectangle circumscribing the dot group and one side is a line segment parallel to each of the X-axis and the Y-axis, and 48 to 52 are steps.

Claims (2)

[Claims] 1. An image processing apparatus comprising an image input camera and an image analysis part, wherein a center position of each of a plurality of dots arranged in a print paper feed direction, that is, in a column direction in a read printed matter to be inspected. The dot rows in which the distances between the centers of the dots arranged next to each other in the row direction are within a predetermined range are regarded as one group, and the dot rows constituting the group are regarded as one straight line, A print quality inspection method characterized by measuring and evaluating width and line spacing. 2. A printing paper feed direction, that is, a column direction, has N printing elements which are ink ejection sources, and the printing elements are reciprocally moved along a row direction of the printing paper, and in the process of movement. A method for inspecting print quality of a printing device that prints N dots along a column direction, in which two dots are printed on a printing paper.
Images of at least one CCD element are picked up and the bright and dark states thereof are stored in a frame memory, the center position of each dot is obtained using the coordinate value of the pixel forming each dot on the frame memory, and the X between these center positions is calculated. It is determined that each dot in which the difference between the distances in the Y direction and the Y direction is within a predetermined range is a set of dots forming the same straight line, and each dot set has one pixel in the column direction on the frame memory. The sum of the numerical data representing the unit brightness level is calculated, the column position where the sum is minimized is obtained, and the column position is regarded as the center of the straight line formed by this set of dots, and the N dots are formed. A printing quality inspection method, wherein the figure to be treated is regarded as the straight line.