JP2017228165A - Image processing apparatus, image forming system, and image processing program - Google Patents

Abstract

An object of the present invention is to suppress the influence of scanner orthogonal distortion by at least one scan on each of the front and back sides of a front / back adjustment chart, and perform adjustment by correct front / back registration. Surface measurement data and back surface measurement data including information on the shape of a sheet on which a front / back adjustment chart is formed and information on the position of a pattern included in the front / back adjustment chart are input, and an image processing unit , One of the surface measurement data and the back surface measurement data is reversed and superimposed, and the surface measurement data and the back surface measurement data are deformed so that the shapes match each other. Refer to the measurement data to find the pattern misalignment. For the misalignment, extract the rotational misalignment component in the direction in which the pattern rotates and the orthogonal misalignment component in which the orthogonal part of the pattern is deformed. Skew correction is performed on the orthogonal deviation component so as to match the averaged state in the front surface measurement data and the back surface measurement data. [Selection] Figure 1

Description

  The present invention relates to an image processing apparatus, an image forming system, and an image processing program, and more particularly to a technique for easily correcting the inclination of an image in a printed material.

2. Description of the Related Art There is known a technique for adjusting an image position so that characters and images (hereinafter referred to as “images”) are printed on a sheet to generate a printed matter so that the printed position is printed at the correct position on the sheet.
The technology for adjusting the image position includes a method of mechanically adjusting the position of the paper and the print head, the paper transport speed and the rotation speed of the polygon mirror to adjust the main scanning printing speed and the density in the sub-scanning direction. There is a method to adjust.

  In recent years, in addition to this, there is a case where a method of adjusting the image position and the inclination by deforming the image information before printing in a direction to cancel the image position shift and image distortion at the time of printing may be used. For example, when double-sided printing, if the image has an inclination (skew) on the front and back of the paper, the image can be easily adjusted by changing the position so that the image is inclined in the opposite direction. is there.

  Related techniques are described in prior art documents such as Patent Documents 1 to 4 below.

Japanese Patent Laid-Open No. 2004-314567 Japanese Patent Laid-Open No. 3-27946 Japanese Patent No. 3143709 JP 2012-165220 JP

The contents described in the prior art documents and their problems will be described below.
Patent Document 1:
The front and back sides of the double-sided printed product with the register mark printed on both sides are converted into digital data by the image input device, and the position of the register mark on the front side and the position of the register mark on the back side are detected from both data and detected. It has been proposed as a registration adjustment method for a double-sided sheet-fed printing press to obtain a registration adjustment amount between the front and back sides from the positions of register marks on both the front side and the back side. However, this adjustment method is not a positioning method that takes into account orthogonal deviation components and rotational deviation components, or a method that corresponds to the distortion of the measurement apparatus. In addition, in this method, when the front and back are registered based only on the information read by the scanner, the position accuracy of the scanner itself needs to be sufficiently high. However, a normal scanner has a problem that some distortion remains.

Patent Document 2:
The first reference mark printed on the front side of the paper and the second reference mark printed on the back side of the paper are respectively imaged from the front side and the back side of the paper by the first and second imaging means. The first and second image data resulting from the positional error of the first and second imaging means when calculating the shift amount between the first and second reference marks by comparing the obtained first and second video data This is a proposal of a registration amount calculation in the second video data calibration apparatus. Here, the film has two linear sides extending in the vertical direction, which is the direction in which the paper is transported in the printing machine, and the horizontal direction, which is a direction perpendicular to the vertical direction, so that the film can be seen at the same position on the front and back sides. A calibration mark formed on a flat plate such as a first imaging means for imaging the calibration mark from the surface side of the flat plate to form first video data representing the calibration mark, and the calibration mark The second imaging means for forming the second video data representing the calibration mark by imaging from the back side of the flat plate, the first imaging means and the second imaging data by comparing the first and second video data 2. Calculates the relative deviation amounts in the vertical direction and the left-right direction of the two imaging means, and calibrates the relative deviation amounts of the marks taken by the first and second imaging means based on these relative deviation amounts. Have a department It has been proposed. However, this method has a big problem that a highly accurate calibration chart is required to correct the measurement distortion. Actually, the environment used by the user may not have a highly accurate calibration chart.

Patent Document 3:
Read the calibration chart with the scanner to be evaluated, compare the calibration data with the actual read data from the actually read calibration chart, create an error correction table by this comparison, and store it in the memory. It has been proposed to read a manuscript original with a scanner, perform correction using the error correction table stored in the memory, and obtain image information of the manuscript with the error corrected. However, this method has a big problem that a highly accurate calibration chart is required to correct the measurement distortion. Actually, the environment used by the user may not have a highly accurate calibration chart.

Patent Document 4:
By changing the direction of the correction chart on which the correction pattern is formed on the paper with respect to the reading area, the correction chart is read at a plurality of different positions in the reading area to read a plurality of images. Get the data. A correction pattern is extracted from a plurality of acquired image data, the extracted same correction patterns are compared, a reading distortion amount corresponding to each reading position in the reading area is calculated, and each calculated reading There has been proposed a method for correcting the reading distortion of image data based on the reading distortion amount corresponding to the position.

In this case, it is necessary to scan the same chart a plurality of times in order to measure the measurement distortion. In particular, for correcting orthogonal distortion, a 90-degree rotation scan of the chart is required. That is, there is a problem that the measurement method is greatly restricted and burdens the user.
Conventional issues:
As in the above Patent Document 1, when the front and back are registered based only on the information read by the scanner, the positional accuracy of the scanner itself needs to be sufficiently high. However, in a normal scanner, a slight orthogonal distortion remains due to an attachment error of the reading unit. For this reason, there is a problem that the accuracy of scanning is lowered.

In other words, even when the chart is scanned, there is a problem that accurate correction processing cannot be performed because it cannot be distinguished from the reading result whether it is distortion caused by image formation or distortion caused by the scanner. doing.
As a solution to this problem, a means for calibrating scanner distortion is required. For example, there is a method of reading a calibration chart with high accuracy as in Patent Document 2 and Patent Document 3 described above. However, special calibration is required, and there is a problem that labor and cost increase. In addition, there is a problem that adjustment is not possible when there is no highly accurate calibration chart.

  Further, for example, as in Patent Document 4, a mechanism is known in which the same chart is scanned a plurality of times at different positions, and self-calibration is performed during actual work based on the relationship of the same pattern in each image. However, in order to detect the orthogonal distortion of the scanner, it is necessary to read the same chart a plurality of times by rotating each other by 90 degrees, which causes a problem in workability, leading to an increase in user burden and a complicated mechanism.

  The present invention has been made in view of such a situation, and realizes correct front-to-back registration in a state where the influence of the orthogonal distortion of the scanner is reduced by at least one scan on each side of the front-back adjustment chart. An object is to realize an image processing apparatus, an image forming system, and an image processing program that can be adjusted.

That is, in order to solve the above-described problems, an image processing apparatus, an image forming system, and an image processing program that reflect one aspect of the present invention are described below.
(1) This image processing apparatus performs image processing including skew correction that deforms the image in advance so that distortion generated in the image formed on the paper is canceled when images are formed on both sides of the paper. The image processing apparatus includes an image processing unit to be executed, and front and back measurement data including front surface measurement data and back surface measurement data obtained by reading both surfaces of a front and back surface adjustment chart on which double-sided images are formed is input to the image processing unit. In the front and back measurement data, each of the front surface measurement data and the back surface measurement data includes information on the shape of the paper on which the front and back adjustment chart is formed, and information on the position of the pattern included in the front and back adjustment chart. And the image processing unit inverts and superimposes one of the front surface measurement data and the back surface measurement data to form each other's shape. The front surface measurement data and the back surface measurement data are deformed so as to coincide with each other, the surface measurement data and the back surface measurement data in a state of being overlapped and deformed are referred to, the positional deviation of the pattern is obtained, and the positional deviation is performed. In the state where the rotational deviation component in the direction in which the pattern rotates and the orthogonal deviation component in which the orthogonal part of the pattern is deformed are extracted and averaged in the surface measurement data and the back surface measurement data in a state of being superimposed and deformed The skew correction is performed on the orthogonal deviation component so as to match the above.

  In addition, this image forming system preliminarily adjusts the distortion generated in the image formed on the sheet and the reading apparatus that acquires the front and back measurement data by reading the pattern of the sheet formed on both sides by the front and back adjustment chart. The image processing apparatus that executes image processing including skew correction that deforms the image, and the image forming apparatus that forms an image on the paper based on image data image-processed by the image processing unit. It is characterized by that.

  In addition, this image processing program inputs front and back measurement data consisting of front and back measurement data obtained by reading both sides of a front and back adjustment chart on which double-sided images are formed, and forms an image on both sides of a sheet. An image processing program for executing image processing including skew correction for deforming the image in advance so that distortion generated in the image formed on the sheet is canceled out, wherein the front and back measurement data includes When each of the front surface measurement data and the back surface measurement data includes information on the shape of the paper on which the front and back adjustment chart is formed and information on the position of the pattern included in the front and back adjustment chart, The front surface measurement data and the back surface measurement data are reversed and overlapped so that the shapes match each other. The front surface measurement data and the back surface measurement data are deformed, and the surface measurement data and the back surface measurement data in a state of being overlapped and deformed are referred to determine the positional deviation of the pattern. The rotational deviation component in the rotating direction and the orthogonal deviation component in which the orthogonal part of the pattern is deformed are extracted, and the surface measurement data and the back surface measurement data in a state of being superposed and deformed are matched with the averaged state. The computer of the image processing apparatus is caused to function so as to execute the skew correction on the orthogonal shift component.

(2) In the above (1), the shift direction of the orthogonal shift component is determined to be orthogonal to the shift direction of the rotational shift component.
(3) In the above (1) to (2), when the image processing unit executes the skew correction for the rotation deviation component, the image processing unit performs predetermined processing of the sheet in each of the front surface measurement data and the back surface measurement data. Either one of the above-mentioned parts is matched with a reference, or one of them is matched with the averaged state in the surface measurement data and the back-surface measurement data in a state of being overlapped and deformed. .

  (4) In the above (3), when the image processing unit executes the skew correction for the rotational deviation component, the line segment constituting the pattern in each of the front surface measurement data and the back surface measurement data. In the front surface measurement data and the back surface measurement data in a state of being overlapped and deformed with reference to the information on the intersection position where the two intersect, the skew of the rotation deviation component is adjusted to match the average position of the intersection position. Correction is performed.

(5) In the above (3), the image processing unit selects whether the outer shape of the paper or a specific paper edge common to the front and back of the paper when performing the skew correction for the rotational deviation component It is characterized in that either one of them is used as a reference.
(6) In the above (1) to (5), the orthogonal deviation component performs the skew correction in an application range different from the rotational deviation component.

  (7) In the above (1) to (6), in the case where a parallelogram shift in which a rectangle is deformed into a parallelogram is generated by the orthogonal shift component, the surface measurement in a state of being superimposed and deformed In the data and the back surface measurement data, the skew correction is performed on the parallelogram deviation by matching the front and back parallelograms with an averaged state.

  (8) In the above (1) to (7), in the case where a trapezoidal deviation in which a rectangle is deformed into a trapezoid is generated by the orthogonal deviation component, the surface measurement data and the back surface in a state of being superimposed and deformed In the measurement data, the skew correction is performed on the trapezoidal deviation so as to match the trapezoids on the front and back sides with an averaged state.

In the image processing apparatus, the image forming system, and the image processing program reflecting one aspect of the present invention, the following effects can be obtained.
(1) After reversing and superimposing one of the surface measurement data and the back surface measurement data and deforming the surface measurement data and the back surface measurement data so that their shapes coincide with each other, the surface measurement data and the back surface data Refer to the measurement data to find the pattern misalignment. For the misalignment, extract the rotational misalignment component in the direction in which the pattern rotates and the orthogonal misalignment component in which the orthogonal part of the pattern is deformed. Skew correction is performed on the orthogonal shift component so as to match the averaged state in the front surface measurement data and the back surface measurement data. Accordingly, it is possible to perform correct front-to-back registration in a state where the influence of the orthogonal distortion of the scanner is reduced by performing at least one scan on each side of the front-back adjustment chart.

  (2) In the above (1), by determining the shift direction of the orthogonal shift component to be orthogonal to the shift direction of the rotational shift component, each component can be obtained independently while suppressing the mutual influence. Therefore, each shift component can be handled appropriately, and processing by a certain simple algorithm becomes possible.

  (3) In the above (1) to (2), when skew correction is executed for the rotational deviation component, whether a predetermined part of the sheet is matched with the reference in each of the front surface measurement data and the back surface measurement data, Appropriate correction in accordance with the measurement method can be performed by matching either the averaged state of the surface measurement data and the back surface measurement data in the state of being overlapped and deformed, or by executing one of them.

  (4) In the above (3), with reference to the information on the intersection position where the line segments constituting the pattern intersect in each of the surface measurement data and the back surface measurement data, In the back surface measurement data, the skew correction is performed on the rotational deviation component so as to match the intersection position with the averaged state, thereby making it possible to appropriately correct the rotational deviation component.

(5) In the above (3), when skew correction is performed for the rotational deviation component, the outer shape of the paper, the specific paper edge common to the front and back of the paper, or the selected one is used as a reference. This makes it possible to correct the rotational deviation component with high accuracy.
(6) In the above (1) to (5), the orthogonal deviation component is used when a double-sided image is formed by one image forming apparatus by executing skew correction in an application range different from the rotational deviation component, Corrections for orthogonal blur components obtained under certain conditions in various application ranges, such as when forming images on both sides by forming images one side at a time with two image forming apparatuses, or when forming images on long paper that cannot be printed on both sides Efficient and appropriate correction is possible by using the value under other conditions.

  (7) In the above (1) to (6), in the surface measurement data and the back surface measurement data in the state of being overlapped and deformed, the parallelogram deviation is made so as to match the parallelogram on the front and back sides with the averaged state. By executing the skew correction for the case, it is possible to perform appropriate correction even when a parallelogram shift occurs due to the orthogonal shift component.

  (8) In the above (1) to (7), in the surface measurement data and the back surface measurement data in a superposed and deformed state, the front and back trapezoids are matched to the averaged state, and skew correction is performed for trapezoidal deviation. By executing, proper correction can be performed even when a trapezoidal deviation occurs due to the orthogonal deviation component.

It is a block diagram which shows the structure of embodiment of this invention. It is a block diagram which shows the structure of embodiment of this invention. It is a block diagram which shows the structure of embodiment of this invention. It is a block diagram which shows the structure of embodiment of this invention. It is a block diagram which shows the other structure of embodiment of this invention. It is a block diagram which shows the other structure of embodiment of this invention. It is explanatory drawing which shows the mode of the image processing of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is a flowchart which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention.

Hereinafter, embodiments of an image processing apparatus, an image forming system, and an image processing program capable of performing appropriate skew correction corresponding to various distortions that occur during image formation will be described in detail with reference to the drawings. .
[Configuration Example of Image Processing Apparatus, Image Forming Apparatus, and Image Forming System (1)]
A first configuration example of an image forming apparatus constituting the image forming system will be described in detail with reference to FIGS. FIG. 1 is a functional block diagram showing the function of each part, and FIG. 2 is an explanatory diagram showing the mechanical components of each part.

  The image forming apparatus 100 includes a control unit 101, a communication unit 102, an operation display unit 103, a storage unit 104, a paper feeding unit 105, a transport unit 107, a document reading unit 110, and an image data storage unit 130. The image processing unit 140, the image forming unit 150, the fixing unit 160, and the output product reading unit 190 are configured.

  Here, the control unit 101 controls each unit in the image forming apparatus 100. The communication unit 102 communicates with other connected devices. The storage unit 104 stores various settings. The operation display unit 103 performs an operation input by the user and a status display of the image forming apparatus 100. The paper feed unit 105 feeds the paper stored in the paper feed tray. The transport unit 107 transports paper in the apparatus. Further, the transport unit 107 has a function of reversing and transporting the front and back of the paper so that the image forming unit 150 can perform double-sided printing, but is not illustrated here. The conveyance unit 107R can convey the sheet in reverse, and supply the sheet to an output object reading unit 190 described later so that printing on a specific surface can be read by a specific reading sensor. The document reading unit 110 reads a document. The image data storage unit 130 stores image data and various data used when forming an image. The image processing unit 140 executes various image processes necessary for image formation. The image forming unit 150 forms an image on a sheet based on an image forming command and image data. The fixing unit 160 stabilizes an image formed by toner formed on a sheet with heat and pressure. The output material reading unit 190 reads an image formed on a sheet during conveyance.

  As shown in FIG. 2, the image forming unit 150 develops the electrostatic latent image formed on the charged image carrier to become a toner image, and the toner images of the respective colors are superimposed on the intermediate transfer member. This is a so-called electrophotographic image forming unit that is transferred to a sheet afterwards. However, the specific configuration of the image forming unit 150 is not limited to that shown in FIG.

  The output product reading unit 190 reads an image formed on a sheet, and can be used for various adjustments and measurements using the read image as image data. The image forming unit 150 and the fixing unit It is arranged on the downstream side of 160, and is configured to read an image during paper conveyance. Note that the output product reading unit 190 may be disposed in an intermediate processing device or a post-processing device at the subsequent stage of the image forming apparatus 100. The output object reading unit 190 includes an output object reading unit 190a that reads an image on one side of a sheet and an output object reading unit 190b that reads an image on the other side of the sheet. Further, an image processing apparatus can be used for a part excluding the image forming unit 150 and the fixing unit 160 from the image forming apparatus 100.

Further, the document reading unit 110 can read the printed matter output from the image forming apparatus 100 and can be used for measurement of the printed matter in the configuration of the image forming apparatus 100 without the output matter reading unit 190.
[Configuration Example of Image Processing Apparatus, Image Forming Apparatus, and Image Forming System (2)]
A second configuration example of the image forming apparatus constituting the image forming system will be described with reference to FIG. FIG. 3 is an explanatory diagram showing mechanical components of each part.

  Here, the internal configuration of the image forming apparatus 100 is the same as that shown in FIGS. 1 and 2 except that the output material reading unit 190 does not exist. For this reason, redundant description is omitted. Further, the reading device 200 is connected to the downstream side of the image forming apparatus 100 in the paper conveyance direction. Here, the reading device 200 is configured to include an output product reading unit 290 for reading an image formed on a sheet during conveyance. The read image data obtained by the output material reading unit 290 is transmitted to the control unit 101 via a communication unit or the like.

[Configuration Example of Image Processing Apparatus, Image Forming Apparatus, and Image Forming System (3)]
A third configuration example of the image forming apparatus constituting the image forming system will be described with reference to FIG. FIG. 4 is an explanatory diagram showing mechanical components of each part.
Here, an image forming apparatus 100A and an image forming apparatus 100B similar to the image forming apparatus 100 described above are connected in series along the paper transport direction. For this reason, image formation on the front side of the paper is executed by the image forming apparatus 100A, and subsequently, image formation on the back side of the paper is executed by the image forming apparatus 100B, thereby enabling high-speed image formation.

  In this case, the output product reading unit as shown in FIG. 2 may be incorporated in both the image forming apparatus 100A and the image forming apparatus 100B, or as shown in FIG. 4, on the downstream side in the sheet conveying direction of the image forming apparatus 100B. The reading device 200 may be connected. Here, the reading device 200 is configured to include an output product reading unit 290 for reading an image formed on a sheet during conveyance. The read image data obtained by the output material reading unit 290 is transmitted to the control unit 101 via a communication unit or the like.

[Configuration Example of Image Processing Apparatus, Image Forming Apparatus, and Image Forming System (4)]
FIG. 5 shows a fourth configuration example of the image forming apparatus constituting the image forming system. Here, a total of n image forming apparatuses 100-1 to 100-n are connected to the network 10. In addition, an image reading apparatus 200 is connected to the network 10. In this case, the scan result in the image reading apparatus 200 is supplied to the image forming apparatus 100-1 to the image forming apparatus 100-n via the network 10.

[Configuration Example of Image Processing Apparatus, Image Forming Apparatus, and Image Forming System (5)]
FIG. 6 shows a fifth configuration example of the image forming apparatus constituting the image forming system. Here, a total of n image forming apparatuses 100-1 to 100-n are connected to the network 10. In addition, an image reading device 200 and an image processing control device 300 are connected to the network 10. In this case, the image processing parameters calculated by the image processing control apparatus 300 according to the scan result in the image reading apparatus 200 are transmitted from the image processing control apparatus 300 to the image forming apparatuses 100-1 to 100-1 through the network 10. -N.

[Principle of image distortion and image processing]
FIG. 7A1 shows an image obtained when an image is formed in an ideal state without distortion based on image data for forming a rectangular image. In FIG. 7, the distortion itself is greatly exaggerated as an explanation of the distortion.

Here, in the image forming apparatus 100, the sheet shape, the sheet conveyance characteristics, the optical system characteristics at the time of image formation, the image transfer characteristics from the image carrier of the image forming unit 150 to the sheet, the image fixing characteristics on the sheet, etc. As a cause, distortion (FIG. 7 (a2)) occurs.
As a result, an image having distortion as shown in FIG. Here, a state in which a rotational deviation component and an orthogonal deviation component are generated as distortion is shown. In FIG. 7 and related drawings, the rotation component is mainly shown for the sake of brevity.

  Here, the “rotational deviation component” is a component of deviation (distortion) in the direction in which the image rotates on the paper. The “orthogonal deviation component” is a component of deviation (distortion) in the direction in which the orthogonal part (such as the corners of the corner) of the image is deformed on the paper. In other words, for example, the lattice image shown in FIG. The vertical line and the horizontal line that are supposed to intersect at right angles are components of deviation (distortion) that do not intersect at right angles.

  FIG. 7 (a4) schematically shows a state in which the user sees an image formed with distortion on both sides of the paper. That is, when the image having the distortion as described above is formed on both sides of the paper and the user sees the paper through the watermark, when the paper front image is indicated by a solid line and the paper back image is indicated by a broken line, for example, FIG. )become that way. Here, the paper front image and the paper back image are distorted in opposite directions when the paper is viewed through.

  Then, the image (FIG. 7 (b1) = FIG. 7 (a3)) of the image-formed paper is read by the document reading unit 110 or the output material reading unit 190 (output material reading unit 290), and read image data is generated. In this case, distortion (FIG. 7 (b2)) occurs due to an attachment error of the reading optical system (mirror or reading element). In this case, due to the mounting error of the reading optical system, in the read image data, in addition to the distortion at the time of image formation described above (FIG. 7 (a2)), the distortion of the orthogonal shift component (FIG. 7 (b2)). Is further included (FIG. 7B3). Note that, due to the influence of distortion at the time of reading, the read image data includes a quadrature shift component including the paper outer shape.

Here, in the case of using the image forming apparatus 100 that generates distortion at the time of image formation as described above, in order to obtain an output product in an appropriate state without distortion by image formation, distortion in image formation (FIG. 7 (a2)). It is possible to eliminate this by performing image processing in the opposite direction in advance.
In the read image data obtained by the output product reading unit 190, distortion in image formation (FIG. 7 (a2)) in the image forming apparatus 100 and distortion in image reading (FIG. 7 (b2)) are mixed. (FIG. 7 (b3)). For this reason, it is difficult to extract only the distortion (FIG. 7 (a2)) in image formation excluding the distortion during image reading (FIG. 7 (b2)).

  Therefore, in this embodiment, as will be described later, skew correction is performed by extracting only the distortion (FIG. 7 (a2)) in image formation while reducing the influence of the distortion during image reading (FIG. 7 (b2)). When executed (FIGS. 7 (c2) and (c3)) and image formation in a distorted state (FIG. 7 (c4)) is executed, an output product in an appropriate state without distortion is obtained (FIG. 7 (c5)). , (C6)). That is, at the stage of image data for image formation, the image is deformed in advance so that the angle and direction are opposite to those at the time of image formation (FIG. 7 (a2)). As a result, distortion generated in image formation is canceled out, and an original image without distortion is formed as shown in FIG. 7 (c5). FIG. 7C6 schematically shows a state in which the user sees an image formed on the both sides of the paper in a state where the distortion is eliminated.

[Example of images to be formed on paper, front and back adjustment chart]
Hereinafter, the output form of the printed matter will be described with reference to FIG. FIG. 8A shows a state in which the image IMG is printed on the entire sheet P and the sheet P is used as it is. In FIG. 8B, registration marks Mk1 to Mk4 as cutting marks are attached to the periphery of the paper P, and the image IMG is printed inside the registration marks Mk1 to Mk4. Cutting is performed at the positions of the register marks Mk1 to Mk4 as post-processing after printing. In addition, as the register marks Mk1 to Mk4 as cutting marks, not only a cross shape but also a combination of various line segments can be used. In this case, the register marks Mk1 to Mk as cutting marks can be used as the front / back adjustment chart.

  In FIG. 8C, the measurement reference lines LnH1 to LnH2 in the main scanning direction and the measurement reference lines LnV1 to LnV2 in the sub-scanning direction are printed on the entire sheet P and output as a front / back adjustment chart. These measurement reference lines form a predetermined pattern and are formed on the periphery of the sheet. Further, the measurement reference lines constituting these predetermined patterns intersect each other at an angle of 90 degrees, and the intersections of the measurement reference lines are formed at the four corners of the sheet.

The front / back adjustment chart is read by the document reading unit 110, the output product reading unit 190, and the image reading apparatus 200, and distortion of an image to be printed is detected from the read result. The measurement reference line is not limited to the specific example shown here, and various modes are possible.
In addition to reading the front / back adjustment chart by the document reading unit 110 or the like, the user can also measure the result visually and input the measurement result (numerical value) to the operation display unit 103. This front / back adjustment chart will be described in detail later.

[Image processing procedure]
Hereinafter, the image processing procedure in the image forming apparatus 100 according to the present embodiment will be described in detail with reference to the flowchart of FIG. In this case, the control unit 101 and the image processing unit 140 that has received an instruction from the control unit 101 execute processing of the following steps.

  When the power of the image forming apparatus 100 is turned on, the control unit 101 performs initial setting for each part of the entire image forming apparatus 100 (step S101 in FIG. 9). Here, the control unit 101 determines whether or not it is time to execute the distortion correction in consideration of the usage status of the image forming apparatus 100 (number of images formed and image formation execution time) (step S102 in FIG. 9). .

  Here, various setting methods can be considered as the timing to be implemented, and are not specified in the present embodiment. For example, it may be when the measurement mode is selected by a user instruction, when the paper in the paper supply unit 105 is replaced, or when the temperature and humidity inside the apparatus is measured and an environmental change is detected. The determination may be made according to the cumulative number of prints since the last correction.

If it is not time to execute the distortion correction (NO in step S102 in FIG. 9), the process proceeds to an image forming process (step S112 in FIG. 9) as will be described later.
On the other hand, if it is time to execute distortion correction (YES in step S102 in FIG. 9), the control unit 101 uses a front / back adjustment chart (see FIGS. 7 and 8) in which a predetermined pattern is formed on the front and back. A double-sided image is formed and output (step S103 in FIG. 9). In the front / back correction chart output in this way, distortions (rotational deviation component, orthogonal deviation component, main scanning direction positional deviation component, sub-scanning direction positional deviation component, magnification error component) in image formation at this time point are included. include.

  Further, it is desirable that the control unit 101 displays the contents of each process and the processing procedure on the operation screen displayed on the operation display unit 103 when executing the front / back correction processing of the present embodiment. In the operation display unit 103, the user can set a maximum amount that can be corrected for the orthogonal shift component and the rotation shift component, and the maximum amount that can be corrected may be stored in the storage unit 104 as a set value.

  If the front / back correction chart formed in this way can be read during image formation, the output reading unit 190 (290) reads the image during the image formation and reads the front / back measurement data (front surface measurement data and back surface data). Measurement data) is generated (step S105 in FIG. 9). Each of the front surface measurement data and the back surface measurement data includes information on the shape of the paper on which the front / back adjustment chart is formed and information on the positions of the patterns included in the front / back adjustment chart.

  Note that, as described above, when the output product reading unit 190 reads an image, it is necessary to acquire information on the shape of the paper. For this purpose, it is necessary to accurately read the paper edge position. Therefore, if the reading area is set larger than the paper size and the background color is black, for example, the paper edge can be detected accurately. Become. Alternatively, a specific texture may be used as the background, or when printing on a color paper, it may be automatically changed to a background color that provides a large brightness difference with the paper.

Alternatively, when the front / back adjustment chart is read by the document reading unit 110, the operator executes a reading operation based on the display of the operation display unit 103 to generate front / back measurement data (front surface measurement data and back surface measurement data) ( Step S105 in FIG. 9).
In this case, since the information on the paper shape of the front / back correction chart is also required, when placing the measurement paper on the platen of the document reading unit 110, a background member such as black paper is applied to the background of the front / back correction chart to correct the front / back side. It is desirable to read larger than the size of the front / back correction chart so that the paper outline (outer shape) of the chart can be detected in the black background. In this case as well, as described above, background paper having a specific texture may be used instead of black paper, and when printing on color paper, a background color that provides a large brightness difference with the paper is used. May be.

  If the paper size including the black background does not fit in the maximum reading size of the original reading unit 110, first the half of the front and back correction chart surface is read, and then the front and back correction chart surface is rotated 180 degrees. Read the other half. Further, the back half of the front / back correction chart is read, and then the back half of the front / back correction chart is rotated 180 degrees to read the other half. In this way, the front and back correction chart is read in a plurality of times, and the read image is combined into one large image, which is used as the front and back measurement data of the read result.

  When executing such reading, it is desirable to display the sheet reading method on the operation screen displayed on the operation display unit 103. Also, on the front and back correction chart, a mark that can detect the orientation and operation procedure is formed, the mark is detected from the read image, and the chart placement, direction, and procedure can be automatically confirmed, When there is an operation mistake, a message or a drawing for notifying the user of the mistake and the correct procedure may be displayed on the operation display unit 103.

  When the front and back measurement data composed of the front surface measurement data and the back surface measurement data is created, the image processing unit 140 receiving the instruction from the control unit 101 inverts one of the front surface measurement data and the back surface measurement data and then superimposes them. At the same time, the front surface measurement data and the back surface measurement data are deformed so as to match each other's shape (step S106 in FIG. 9).

One of the surface measurement data and the back surface measurement data is inverted and then overlapped, and the surface measurement data and the back surface measurement data are deformed so that their shapes coincide with each other (step S106 in FIG. 9).
Hereinafter, the processing in step S106 will be described in detail with reference to FIGS.

  FIG. 10 (a1) shows a case where the chart is image-formed on the surface of the paper based on the image data for forming a rectangular chart, without distortion at the time of image formation in an ideal state without distortion. The chart (thin line) and paper outline (thick line) obtained are shown in FIG. Then, the image (FIG. 10A1) of the image-formed paper surface is read by the document reading unit 110 or the output product reading unit 190 (output product reading unit 290) and read image data (FIG. 10) as surface measurement data. (B1)) is generated. At the time of reading, distortion due to the orthogonal deviation component is included due to the mounting error of the reading optical system. In this case, the orthogonal deviation component acts in the same direction on both the paper outer shape and the chart on the paper.

  FIG. 10A2 shows that the chart is image-formed on the back side of the paper based on the image data for forming a rectangular chart without any distortion at the time of image formation in an ideal state without distortion. A chart (thin line) and a sheet outline (thick line) obtained in the case of printing are shown. Then, the image on the back side of the sheet on which the image has been formed (FIG. 10A2) is read by the document reading unit 110 or the output matter reading unit 190 (the output matter reading unit 290), and read image data as back side measurement data (FIG. 10). (B2)) is generated. At the time of reading, distortion due to the orthogonal deviation component is included due to the mounting error of the reading optical system. In this case, the orthogonal deviation component acts in the same direction on both the paper outer shape and the chart on the paper.

Here, FIG. 10C shows a state in which one of the read surface measurement data and back surface measurement data is inverted and then overlapped. For example, the solid line is the surface measurement data, and the broken line is the back surface measurement data.
Then, in a state where either one of the surface measurement data and the back surface measurement data is inverted and then superimposed, the front surface measurement data and the back surface measurement data are deformed so that the shapes of each other match. Specifically, for example, the projective transformation is performed so that the feature points (generally, four corners) of the paper outer shape come to the prescribed coordinates. As a result, as shown in FIG. 10D, the difference between the front and the back of the orthogonal deviation component caused by reading is eliminated. In the case of this figure, since the chart on which the image is formed is not distorted, the images on the front and back charts overlap.

FIG. 11A1 is a chart (thin line) obtained when a chart is image-formed on the surface of a sheet based on image data for forming a rectangular chart in a state where distortion during image formation has occurred. And the paper outline (thick line). Then, the image (FIG. 11 (a1)) on the surface of the sheet on which the image has been formed is read by the document reading unit 110 or the output product reading unit 190 (output product reading unit 290) and read image data (FIG. 11) as the surface measurement data. (B1)) is generated.
At the time of reading, distortion of the orthogonal deviation component due to mounting error of the reading optical system and lens distortion is included. In this state, the distortion caused by image formation and the distortion caused by reading are integrated and are difficult to discriminate.

  FIG. 11A2 is a chart obtained when an image of a chart is formed on the back side of the paper based on image data for forming a rectangular chart in a state where distortion occurs during image formation. A thin line) and a paper outline (thick line) are shown. Then, the image on the back side of the sheet on which the image has been formed (FIG. 11 (a2)) is read by the original reading unit 110 or the output matter reading unit 190 (output matter reading unit 290), and read image data as back side measurement data (FIG. 11). (B2)) is generated. At the time of reading, distortion of the orthogonal deviation component due to mounting error of the reading optical system and lens distortion is included. In this state, the distortion caused by image formation and the distortion caused by reading are integrated and are difficult to discriminate.

Here, FIG. 11C shows a state in which one of the read surface measurement data and back surface measurement data is inverted and then overlapped. For example, the solid line is the surface measurement data, and the broken line is the back surface measurement data.
Then, in such a state that either one of the surface measurement data and the back surface measurement data is mirror-inverted and then superposed (one reverse superposition state), the front surface measurement data and the back surface data are matched to each other. Transform measurement data. At this time, the chart portion is similarly deformed in accordance with the deformation of the paper outer shape. As a result, as shown in FIG. 10D, only the distortion at the time of image formation is extracted in a state in which the orthogonal shift component generated due to reading is eliminated.

  As described above, the orthogonal deviation component caused by the reading included in the front and back measurement data including the front surface measurement data and the back surface measurement data is removed. In the above description, it is assumed that the orthogonal deviation component is included at the time of image formation. However, when the rotational deviation component is included, the orthogonal deviation component caused by reading is removed or reduced in the same way, A rotational deviation component is extracted. Even if an orthogonal shift component and a rotational shift component are included during image formation, the orthogonal shift component caused by reading is similarly removed or reduced, and the orthogonal shift component and the rotational shift component during image formation are extracted. Become so.

  The direction of superposition is determined according to the paper reversing mechanism of the printing press, so that the positional relationship between the front and back paper edges matches (the front and back positional relationship of the printed image was observed through the actual printed matter. To be the same as the case). Hereinafter, the superimposed state refers to the above state.

  In addition, in the processing described later, when correction is performed using an angle formed by a measurement reference line constituting the chart and a sheet side close to the measurement reference line, distortion caused by reading at the time of calculating the angle is performed. Is almost canceled out, so the processing in step S106 can be omitted.

  When the processing for removing or reducing the orthogonal deviation component due to reading is completed as described above, the image processing unit 140 that has received an instruction from the control unit 101 is included in the front / back adjustment chart in the front surface measurement data and the back surface measurement data. For the pattern, the image magnification error is corrected by a known method, and the shift (main scanning direction positional deviation, sub-scanning direction positional deviation) is known for the pattern included in the front / back adjustment chart in the front surface measurement data and the back surface measurement data. (Step S107 in FIG. 9). That is, when there is a pattern magnification error caused by contraction at the time of fixing the paper, a pattern shift caused by a paper transport deviation, etc., correction is performed using a known arbitrary correction method.

  Here, FIG. 12 shows a state in which one of the read surface measurement data and back surface measurement data is reversed after being inverted. For example, the solid line is the surface measurement data, and the broken line is the back surface measurement data. It is assumed that the orthogonal deviation component resulting from the above reading is already corrected.

  In this shift and magnification error correction, it is desirable to execute shift correction and magnification error correction so as to match the vicinity of the midpoint of the measurement reference line constituting the pattern (FIG. 12D). Shift correction and magnification error correction are not limited to specific methods. For example, when scanning exposure is performed with a polygon mirror, the rotation speed of the polygon mirror with respect to the paper conveyance speed, the synchronous clock frequency for scanning exposure control, and drawing What is necessary is just to implement suitably by known methods, such as timing adjustment of a start trigger, and the position shift and zooming of image information itself. In this way, when the orthogonal deviation component is generated (FIGS. 12 (a) and 12 (b)) and when the rotational deviation component is generated (FIG. 12 (c)), both are for measurement constituting the pattern. Since the position near the midpoint of the reference line does not change and the positional deviation of the pattern near the four corners of the paper tends to increase, each deviation amount can be clearly identified and measured, and each measured value can be easily measured. It is preferable because it can be calculated.

  When the processing for removing or reducing the orthogonal deviation component resulting from reading and the shift / magnification correction are completed as described above, the image processing unit 140 that has received an instruction from the control unit 101 receives the rotation deviation component of the pattern and the pattern deviation. An orthogonal shift component is extracted (step S108 in FIG. 9). Subsequently, the image processing unit 140 that has received an instruction from the control unit 101 calculates a correction amount between the rotational shift component and the orthogonal shift component of the pattern (steps S109 and S110 in FIG. 9).

  Here, with reference to FIG. 13, the main skew table: HsF, the main skew back: HsR, the secondary skew table: VsF, and the secondary skew back: VsR are defined as deviation amounts due to the inclination of the measurement reference line. deep. FIG. 13 shows that the positional relationship between the front and back paper edges matches after either one of the read front surface measurement data and back surface measurement data (in this example, the front surface side) is reversed in the mirror image direction (printed). The image shows the state observed from the back side (superimposed) so that the relationship between the front and back positions of the images is the same as when viewed through an actual printed material. In FIG. 13, the solid line is the surface measurement data for the pattern, the broken line is the back surface measurement data for the pattern, and the alternate long and short dash line is the ideal state of the pattern when there is no rotational deviation component and orthogonal deviation component.

  In FIG. 13, the amount of deviation from the appropriate state of the measurement reference line on the front surface of the paper that is substantially parallel to the front end of the paper from the appropriate state at the left end of the paper is VsF, The amount of deviation from the appropriate state at the left edge of the sheet is defined as VsR. In addition, regarding the amount of deviation due to the inclination, when viewed from the back side, the sign of the deviation in the clockwise direction is defined as positive and the sign of the deviation in the counterclockwise direction is defined as negative.

In addition, regarding the unit at the time of execution of the processing of the present embodiment, either the mm or the number of dots at the time of image processing may be appropriately specified for the deviation amount, the length, or the like.
Similarly, in FIG. 13, HsF is the amount of deviation from the appropriate state at the leading edge of the measurement reference line on the front surface of the paper that is substantially parallel to the left edge of the paper, and is measured on the back of the paper that is substantially parallel to the left edge of the paper. The amount of deviation of the reference line from the proper state at the leading edge of the paper is defined as HsR. In addition, regarding the amount of deviation due to the inclination, when viewed from the back side, the sign of the deviation in the clockwise direction is defined as positive and the sign of the deviation in the counterclockwise direction is defined as negative.

  In FIG. 13, the deviation amounts VsF, VsR, HsF, and HsR due to the inclination of the measurement reference line in the leading edge direction and the left edge portion of the sheet are calculated, but similarly measured using the other three locations, Averaging is also desirable from the viewpoint of accuracy. Furthermore, since the paper outer shape is not always a correct rectangle, it is also desirable from the viewpoint of suppressing the influence of the paper shape error to measure and average in the same manner using the other three locations.

  As described above, since the pattern position shift and the magnification shift in the main scanning direction and the sub-scanning direction are adjusted, the front and back measurement charts intersect at the center of the sheet side as shown in the figure. When the shift and magnification deviation remain, the positions where the charts on the front and back cross are displaced, and as a result, values corresponding to HsR, HsF, VsR, and VsF in the figure (because measurement is possible at each paper corner). 4 measurement values are obtained), but the average values at the four locations are in a direction that cancels out the changes in the respective measurement values. It becomes a constant value, and stable tilt deviation measurement is possible. Therefore, in addition to the above-described one place shown in the figure, the other three places are measured in the same manner, and the method of averaging can perform stable measurement even in the case where the shift and the magnification deviation remain. Therefore, it is preferable.

Here, the main skew front / back difference: HsFR and the sub skew front / back difference: VsFR will be described. Similarly to the above, the sign of the inclination is defined as positive when the back surface measurement data is inclined clockwise with respect to the front surface measurement data when viewed from the back surface side. Therefore,
HsFR = HsR−HsF,
VsFR = VsR−VsF,
It can be expressed. In FIG. 13 (in the case of FIG. 13 viewed from the back side), the dotted line that is the back surface pattern rotates counterclockwise with respect to the solid line that is the front surface pattern. Is also a negative value.

Here, referring to FIG. 14, the cross mark at the intersection of the measurement reference line (intersection where the line segments constituting the pattern intersect) is a registration mark or a cross hair, and it is caused by the inclination by referring to the information on the position of the intersection. A case where the deviation amount is measured will be described.
Note that FIG. 14 also shows a state in which one of the read surface measurement data and back surface measurement data is inverted and then superimposed (one inverted overlap state). In FIG. 14, the gray cross marks indicate the intersections of the above-described measurement reference lines for the front surface measurement data, and the black cross marks indicate the intersections of the above-described measurement reference lines for the back surface measurement data. Here, the paper transport direction is defined as the y direction, and the direction orthogonal to the y direction is defined as the x direction. In addition, identification marks Mk1 to Mk4 are attached to the cross marks at the four corners of the paper, and the front and back differences of the cross mark positions at the position of Mk1 (here, as viewed from the back side, the marks printed on the front side are marked on the back side. The x direction (horizontal direction) of the printed mark position difference is defined as Δx1, and the y direction (vertical direction) as Δy1. The x direction (horizontal direction) of the front / back difference of the cross mark position at the position of Mk2 is Δx2, and the y direction (vertical direction) is Δy2. The x direction (horizontal direction) of the front / back difference of the cross mark position at the position of Mk3 is Δx3, and the y direction (vertical direction) is Δy3. The x direction (horizontal direction) of the front / back difference of the cross mark position at the position of Mk4 is Δx4, and the y direction (vertical direction) is Δy4.

In the case of FIG. 14, the main skew front / back difference: HsFR and the secondary skew front / back difference: VsFR are as follows, and both HsFR and VsFR have negative values.
HsFR = {(Δx3 + Δx4) / 2− (Δx1 + Δx2) / 2} * (paper sub-scanning length / distance between registration marks),
VsFR = {(Δy2 + Δy4) / 2− (Δy1 + Δy3) / 2} * (paper main scanning length / distance between registration marks),
Main skew front / back difference: HsFR and sub-skew front / back difference are each converted into a slope.

(Front / back difference main scanning gradient) = HsFR / (paper sub-scanning length),
(Front / back difference sub-scanning gradient) = VsFR / (paper main scanning length),
Further, this is divided into a rotational deviation component and a quadrature component (front-back difference rotation gradient) = {(front-back difference main scanning gradient) + (front-back difference sub-scanning gradient)} / 2.
(Front-back difference orthogonal gradient) = {(Front-back difference sub-scanning gradient) − (Front-back difference main scanning gradient)} / 2
It can be expressed.

Here, first, only the rotational deviation component is extracted as the inclination of the surface pattern with respect to the sheet. The orthogonal deviation component is withheld because paper distortion and image output distortion cannot be identified.
That is, the main skew table: HsF and the sub skew table: VsF for the sheet surface are converted into gradients, and the average of the main and sub gradients is defined as the rotation gradient of the sheet surface.

(Main scanning gradient) = HsF / (paper sub-scanning length),
(Sub-scanning gradient) = VsF / (paper main scanning length),
(Rotational gradient) = {(Main scanning gradient) + (Sub scanning gradient)} / 2
It can be expressed.

Further, a front rotation deviation gradient, a front orthogonal deviation gradient, a reverse rotation deviation gradient, and a reverse orthogonal deviation gradient are calculated as the respective deviation gradients of the sheet.
In this example, the rotational deviation component is corrected to match the front sheet, and the orthogonal deviation component is corrected to match the average of the front and back surfaces in the reverse overlapping state.

(Table / rotational gradient) = (rotational gradient),
(Front / Orthogonal Deviation Gradient) = (Front / Back Difference Orthogonal Gradient) / 2
(Back / Rotation Gradient) = (Front / Back Difference Gradient)-(Rotational Gradient),
(Back / Orthogonal Deviation Gradient) = (Front / Back Difference Orthogonal Gradient) / 2
It can be expressed.

It should be noted that when both the rotational deviation component and the orthogonal deviation component are corrected so as to match the average of the front and back in the one-sided overlapping state, the following is performed. For example, this method is preferable when the value of each part in FIG. 14 is measured by the user.
(Front / Rotational Gradient) = (Front / Back Differential Gradient) / 2
(Front / Orthogonal Deviation Gradient) = (Front / Back Difference Orthogonal Gradient) / 2
(Back / Rotation Gradient) = (Front / Back Difference Gradient) / 2
(Back / Orthogonal Deviation Gradient) = (Front / Back Difference Orthogonal Gradient) / 2
It can be expressed.

  Furthermore, each of the above-mentioned deviation gradients (front rotation deviation gradient, front orthogonal deviation gradient, reverse rotation deviation gradient, reverse orthogonal deviation gradient) is treated as a skew which is a concept of deviation integrating rotation and orthogonality, and the main skew on the front and back sides. Convert to deviation / sub-skew deviation. Here, the skew direction in which the position is sequentially shifted in the image processing progress direction is defined as “positive”.

(Table / main skew deviation amount) = {− {(table rotation deviation gradient) − (table orthogonal deviation gradient)} * (paper sub-scanning length) / 2,
(Front / sub skew deviation amount) = {(front rotation deviation gradient) + (front orthogonal deviation gradient)} * (sheet main scanning length) / 2
(Back / Main skew deviation amount) = {− {(Back rotation deviation gradient) − (Back orthogonal deviation gradient)} * (Paper sub-scanning length) / 2
(Back / sub skew deviation amount) = {(Back rotation deviation gradient) + (Back orthogonal deviation gradient)} * (Paper main scanning length) / 2. Here, [/ 2] in the equation is a coefficient for calculating the deviation amount with the center of the sheet as a fulcrum.

  Then, the image processing unit 140 that has received an instruction from the control unit 101 determines a specific front / back correction amount (front / main skew correction) from the shift amount (main skew shift amount / sub-skew shift amount) calculated as described above. Amount, front / sub skew correction amount, back / main skew correction amount, back / sub skew correction amount) (step S111 in FIG. 9).

Specifically, the sign of the deviation amount is reversed to obtain the correction amount. Further, when the correction amount is displayed on the screen of the operation display unit 103, for example, when the correction amount 0.01 mm is displayed as 1 on the screen, the correction amount is converted into a unit for the display.
(Table / main skew correction amount) = − (table / main skew deviation amount) * (unit conversion coefficient),
(Table / sub skew correction amount) =-(table / sub skew deviation amount) * (unit conversion coefficient),
(Back / main skew correction amount) =-(Back / main skew deviation amount) * (unit conversion coefficient),
(Back / sub skew correction amount) =-(Back / sub skew deviation amount) * (unit conversion coefficient),
Here, as a unit conversion coefficient, for example, if the unit at the time of deviation amount calculation is a pixel, the pixel density is 600 dpi, and 0.01 mm is expressed as 1, unit conversion coefficient = (25.4 / 600 ) /0.01=4.233.

  Further, the image processing unit 140 that has received an instruction from the control unit 101 displays the correction amount calculated by treating it as a skew, which is a concept of deviation integrating rotation and orthogonality as described above, on the screen of the operation display unit 103. Are converted into “rotational deviation correction amount” and “orthogonal deviation correction amount”. Hereinafter, FIG. 15 and FIG. 16 are also referred to.

  Here, in FIGS. 15 and 16, the dashed-dotted line rectangle is an image before correction, and the solid line rectangle is an image after deformation by correction. The paper transport direction is the sub-scanning (= Y) direction, and the direction orthogonal to the paper transport direction is the main scanning (= X) direction. The paper size in the X direction is size_x, and the paper size in the Y direction is size_y.

Further, in FIG. 15, the shift amount in the x direction for correcting the rotational shift component is expressed as rot_X using the abbreviation rot for rotation, and the shift amount in the y direction for correcting the rotational shift component is set as rot_Y. To do.
Further, in FIG. 16, the shift amount in the x direction for correcting the orthogonal shift component is set to ortho_X, and the shift amount in the y direction for correcting the orthogonal shift component is set to ortho_Y, using the abbreviation orth of ortholog (orthogonal). . Note that, as described above, a value obtained by inverting the sign of the shift amount corresponds to the correction amount (shift amount).

  For each of the front and back sides of the paper, the rotational deviation correction amount and the orthogonal deviation correction amount are calculated by the following formula using the main skew correction amount and the sub skew correction amount described above. In the following expression, a numerical value with ^ 2 means the square of the numerical value, and SQRT means a square root. In the drawing, the sheet conveyance direction is synonymous with the sub-scanning direction in the present invention, and the main scanning direction is a direction orthogonal to the sub-scanning direction.

here,
Constant Const = size_X / size_Y,
ortho_Y = ((main skew correction amount) * Const + (sub skew correction amount)) / (1 + Const ^ 2),
orth_X = Const * orth_Y,
rot_Y = (sub skew correction amount) −orth_Y,
rot_X = −rot_Y / Const,
And calculate sequentially.

With these,
(Rotation deviation correction amount) = SQRT (rot_Y ^ 2 + rot_X ^ 2),
(Orthogonal deviation correction amount) = SQRT (orth_Y ^ 2 + orth_X ^ 2) is obtained.
However, if the result of this equation remains (rotation correction amount), (orthogonal deviation correction amount) always takes a positive value. Therefore, if the following conditions are met, a negative sign is added with a minus sign.

Rotation correction amount: When rot_X is negative, a negative value is set.
Orthogonal deviation correction amount: When ort_X is negative, it is a negative value.
The image processing unit 140 applies these rot_X, rot_Y, ortho_X, and ortho_Y as parameters to the image processing.

  The “rotational deviation correction amount” and the “orthogonal deviation correction amount” obtained as described above are used to calculate the “rotational deviation correction amount” and the “orthogonal deviation correction amount” before being updated by the image processing unit 140. Each parameter is added to the parameters, and the updated "rotational deviation correction amount" and "orthogonal deviation correction amount" parameters are obtained and stored in the storage unit 104 in a designated array or memory (based on separate specifications) (step in FIG. 9). S111).

That is,
(After update: Rotational deviation correction amount) = (Previous: Rotational deviation correction amount) + (Calculation: Rotational deviation correction amount),
(After update: Orthogonal deviation correction amount) = (Previous: Orthogonal deviation correction amount) + (Calculation: Orthogonal deviation correction amount),
And

  It should be noted that a predetermined threshold is set in advance for the updated “absolute value of (rotational deviation correction amount)” + “(absolute value of (orthogonal deviation correction amount)”) so that it is within the range of the threshold. In addition, it is preferable to limit the values in the order of the orthogonal deviation correction amount and the rotation correction amount from the viewpoint of preventing malfunction of image processing and stable operation. Further, when the value is limited, the instruction display unit may display the fact that the value is limited to notify the user. Further, the limitation of the value by the threshold value may be applied to each of the main scanning tilt correction amount and the sub-scanning tilt correction amount in the later stage (described later).

Furthermore, by transforming the above equation,
rot_X = SQRT ((rotational deviation correction amount) ^ 2 / (1 + Const ^ 2)),
rot_Y = (− 1) * rot_X * Const,
ortho_Y = SQRT ((orthogonal deviation correction amount ^ 2) / (1 + Const ^ 2)),
orth_X = orth_Y * Const,
The inverse transformation formula is obtained.

Further, (after update: rotational deviation correction amount) and (after update: orthogonal deviation correction amount) are converted by the inverse conversion formula obtained by the above formula, and the main scan (X direction described above) and sub scan ( In the above Y direction), each inclination correction amount is calculated and set as a parameter applied to the image processing unit 140. That is,
Main scanning tilt correction amount = rot_X + orth_X,
Sub-scanning tilt correction amount = rot_Y + orth_Y.

  When the parameters to be applied by the image processing unit 140 are prepared as described above, the control unit 101 determines whether it is time for the image forming apparatus 100 to execute image formation (step S112 in FIG. 9). . If it is not time to execute image formation (NO in step S112 in FIG. 9), the process ends (end in FIG. 9).

  On the other hand, if it is time to execute image formation (YES in step S112 in FIG. 9), the image processing unit 140 executes image processing by applying the parameters described above according to an instruction from the control unit 101 (FIG. 9). Step S113), the image forming unit 150 executes image formation based on the image processed image data (Step S114 in FIG. 9).

The above image processing (step S113 in FIG. 9) and image formation (step S114 in FIG. 9) are repeated until image formation is completed for all image data of the job to be executed.
When the image formation is completed for all the image data of the job to be executed (YES in step S115 in FIG. 9), each unit ends the processing (end in FIG. 9) according to an instruction from the control unit 101.

[Specific example of image shift handled in this embodiment]
Examples of image shifts that can be processed by the image processing described above are shown in FIGS. 17A to 17D. In addition, what is shown here is a typical specific example, and does not indicate all the image shifts that can be processed by the image processing of the present embodiment. Also, those shown in FIGS. 17A to 17D are typical basic components of the shift component.

  In FIGS. 17A to 17D, a thick rectangular frame indicates the outer shape of the paper P, the dashed-dotted rectangle indicates an ideal image G in which no shift occurs, and the solid line square indicates an image G ′ after the shift has occurred. Show. In addition, the paper conveyance direction (sub-scanning direction) during image formation is indicated by an arrow. The direction perpendicular to the sub-scanning direction is the main scanning direction.

  FIG. 17A shows a state where the image G ′ has a shift of the rotational shift component with respect to the ideal image G. The rotation displacement component is a component of displacement (distortion) in the direction in which the image rotates on the paper. In this case, the shape of the image G ′ remains rectangular and the angles of the four corners remain at right angles, but are not parallel to the peripheral edge of the paper P.

  FIG. 17B shows that the image G ′ has a shift of an orthogonal shift component with respect to the ideal image G, the shape of the image G ′ is deformed from a rectangle to a parallelogram, and the angles of the four corners are not at right angles. It has changed. Here, the diagonal angles are the same. The orthogonal deviation component is a component of deviation (distortion) in a direction in which an orthogonal part (such as four corners) of an image is deformed on a sheet. Further, although the side in the sub-scanning direction of the image G ′ is parallel to the end in the sub-scanning direction around the paper P, the side in the main scanning direction of the image G ′ is the end in the main scanning direction around the paper P. Is not parallel to However, the sides in the main scanning direction of the image G ′ are in a parallel state. In addition to the above, the deformed state of the parallelogram is not limited to the above, although the side in the main scanning direction of the image G ′ is parallel to the edge in the main scanning direction around the paper P, but in the sub-scanning direction of the image G ′. In some cases, the side is not parallel to the edge in the sub-scanning direction around the paper P.

  In FIG. 17C, the image G ′ has a shift of an orthogonal shift component with respect to the ideal image G, the shape of the image G ′ is changed from a rectangle to a trapezoid, and the angles of the four corners are changed to angles other than a right angle. ing. In the image G ′, since the sides in the main scanning direction are parallel to each other, this is called a main trapezoid (or main trapezoidal deviation). This image G ′ is also a component of deviation (distortion) in the direction in which the orthogonal part (the corners of the four corners) of the image is deformed, and has an orthogonal deviation component. In addition, the side in the main scanning direction of the image G ′ is parallel to the edge in the main scanning direction around the paper P, but the side in the sub scanning direction of the image G ′ is the edge in the sub scanning direction around the paper P. Is not parallel to Further, the sides of the image G ′ in the sub-scanning direction are not parallel to each other.

  FIG. 17D shows that the image G ′ has a shift of an orthogonal shift component with respect to the ideal image G, the shape of the image G ′ is changed from a rectangle to a trapezoid, and the angles of the four corners are changed to an angle other than a right angle. ing. In the image G ′, since the sides in the sub-scanning direction are parallel to each other, this is called a sub-trapezoid (or sub-trapezoid shift). This image G ′ is also a component of deviation (distortion) in the direction in which the orthogonal part (the corners of the four corners) of the image is deformed, and has an orthogonal deviation component. Further, although the side in the sub-scanning direction of the image G ′ is parallel to the end in the sub-scanning direction around the paper P, the side in the main scanning direction of the image G ′ is the end in the main scanning direction around the paper P. Is not parallel to Further, the sides in the main scanning direction of the image G ′ are not parallel to each other.

[Description of keystone deviation]
A description will be given of front and back misalignment in double-sided image formation when trapezoidal misalignment occurs due to the above-described orthogonal misalignment component when images are formed on both sides of a sheet.
In FIG. 18A, in the image formation on the paper surface, the upper end is the front end in the transport direction, and the main trapezoidal deviation occurs. In FIG. 18B, in the image formation on the back side of the paper, the upper end is the front end in the transport direction, and the main trapezoidal deviation occurs. FIG. 18C schematically shows a state in which the user sees a double-sided image formed with a main trapezoidal deviation. In FIGS. 18A, 18B, and 18C, the thick line portions indicate the same end portions of the paper. That is, the front end in the transport direction in the paper front surface image formation is positioned at the rear end in the transport direction in the paper back surface image formation. As a result, when the image having the main trapezoidal deviation as described above is formed on both sides of the paper and the user sees the paper through the watermark, if the paper front image is indicated by a solid line and the paper backside image is indicated by a broken line, the main trapezoidal deviation will occur. The short side and the long side of the are opposite to each other.

In FIG. 19A, in the image formation on the paper surface, the upper end is the front end in the transport direction, and a sub trapezoidal deviation occurs. In FIG. 19B, in the image formation on the back side of the sheet, the sheet is reversed during conveyance, the upper end is the leading end in the conveyance direction, and a sub trapezoidal deviation occurs. FIG. 19C schematically shows a state in which the user sees a double-sided image formed with a main trapezoidal deviation. In FIGS. 19A, 19B, and 19C, the thick line portion indicates the same end portion of the sheet. That is, the front end in the transport direction in the paper front surface image formation is positioned at the rear end in the transport direction in the paper back surface image formation. As a result, the image having the sub trapezoidal deviation as described above is formed on both sides of the paper, and when the user sees the paper through the watermark, when the paper front image is indicated by a solid line and the paper back image is indicated by a broken line,
The short side and long side of the sub trapezoidal deviation are in agreement with each other.

  In FIG. 20A, in the image formation on the paper surface, the upper end is the front end in the transport direction, and the main trapezoidal deviation occurs. In FIG. 20B, in the image formation on the back side of the sheet, the sheet is reversed during conveyance, the upper end is the leading end in the conveyance direction, and a main trapezoidal deviation occurs. FIG. 20 (c) schematically shows a state where the user sees the image formed on both sides with the main trapezoidal deviation occurring. In FIGS. 20A, 20B, and 20C, the thick line portion indicates the same end portion of the sheet. That is, the left end in the paper front surface image formation is positioned at the right end in the paper back surface image formation. As a result, when the image having the main trapezoidal deviation as described above is formed on both sides of the paper and the user sees the paper through the watermark, if the paper front image is indicated by a solid line and the paper backside image is indicated by a broken line, the main trapezoidal deviation will occur. The short side and the long side of are in a state of matching each other.

  In FIG. 21A, in the image formation on the paper surface, the upper end is the front end in the transport direction, and a sub trapezoidal deviation occurs. In FIG. 21B, in the image formation on the back side of the sheet, the sheet is reversed during conveyance, the upper end is the leading end in the conveyance direction, and a sub trapezoidal deviation occurs. FIG. 21 (c) schematically shows a state where the user sees through the image formed on both sides with the sub trapezoidal deviation. In FIGS. 21A, 21B, and 21C, the thick line portion indicates the same end portion of the sheet. That is, the left end in the paper front surface image formation is positioned at the right end in the paper back surface image formation. As a result, when the image having the sub trapezoidal deviation as described above is formed on both sides of the paper, and the user sees the paper through the watermark, the front surface image of the paper is indicated by a solid line and the back side image of the paper is indicated by a broken line. The short side and long side of the shift are in the opposite state. In the present embodiment, the front and back misalignment measurement and correction targets are FIGS. 18 and 21 in which front and back image position misalignment occurs.

Hereinafter, correction of main trapezoidal deviation will be described with reference to FIG. 22, and correction of sub-trapezoidal deviation will be described with reference to FIG. Basically, trapezoidal deviation can be considered as a modification of orthogonal deviation.
Here, FIG. 22 and FIG. 23 show a state in which one of the read front surface measurement data and back surface measurement data is reversed and then overlapped. For example, the solid line indicates the surface measurement data, the broken line indicates the back surface measurement data, and the alternate long and short dash line indicates the image in the ideal state.

That is, FIG. 22 schematically shows a state in which the user sees a double-sided image formed with a main trapezoidal deviation. FIG. 23 schematically shows a state in which the user sees a double-sided image formed with a sub-trapezoidal deviation.
The magnitudes of the main / sub and front / back position shift amounts are directly HsFR and VsFR as the illustrated position shift amounts.
Since HsFR and VsFR are present at four locations, four measurement values are obtained. However, as described above, after correcting the positional deviation, the magnification deviation, the rotation deviation, and the orthogonal deviation (excluding the trapezoid deviation), only the illustrated trapezoid formation remains. For this reason, in that case, the measured values at the four locations are substantially equal to HsFR and VsFR. Although HsFR and VsFR are measured at the edge of the paper, they may be measured at a location where the measurement reference line intersects.

Here, as already explained,
(Front / back difference main scanning gradient) = HsFR / size_Y,
(Front / back difference sub-scanning gradient) = VsFR / size_X,
If the above-described processing is performed, the amount of deviation between the front and back sides is calculated, and the sign is reversed to obtain a correction amount, and parameters are set in the image processing unit 140 so that image deformation corresponding to the correction amount can be performed. good. In the present embodiment, the image deformation process performed by the image processing unit 140 is not limited. Using the well-known projective transformation and other methods, the deformation process according to (main / secondary) skew deformation and (main / secondary) trapezoidal deformation, for example, set to the above parameters is sequentially performed on the same image. Alternatively, the above parameters may be integrated and the transformation process may be performed by one projective transformation.

  For the actual correction value calculation, the measurement pattern and “angles” θ1 to θ4 between the paper sides substantially parallel to the measurement pattern are used. If the measurement pattern is observed from the back side and tilted clockwise with respect to the paper edge, it is defined as a positive direction. In FIG. 22, θ1 is positive, θ2 is negative, θ3 is negative, and θ4 is positive. . In FIG. 23, θ1 is positive, θ2 is negative, θ3 is negative, and θ4 is positive. In the case of a trapezoidal shift during image formation, the correction amount may be determined so that the front and back distortion directions are aligned with the respective center positions.

  That is, if the back surface is corrected by {(θ1−θ2) − (θ3−θ4)} / 2 (this is assumed to be a trapezoidal amount Tr), the front and back sides will match if the front surface is corrected in the same amount and in the reverse direction. Will do. This is the same in the case of the main trapezoid in FIG. 22 and in the case of the sub trapezoid in FIG. 23. If these overlap, they may be obtained for each. Actually, when superimposing the main / sub, the position shift occurs due to each superimposing action, but since it is a very small value, it can be ignored.

  Since the correction amount has been obtained as described above, in the actual image processing, in the case of the main trapezoidal image in FIG. 22, the writing position of the leading edge of the image (the left side) is advanced by HsFR / 2, and the size of the writing image is set. Start drawing so that the image size in the main scanning direction is increased by HsFR, shifting the leading edge writing position by {(θ1−θ2) − (θ3−θ4)} / 2, and changing the main scanning image size to − {(θ1−θ2) Appropriate trapezoidal correction can be performed by sequentially reducing the image by − (θ3−θ4)} or by forming an image after performing image deformation on the original image in advance so that the same change occurs.

[Applying orthogonal deviation correction to long paper]
When the orthogonal deviation occurs due to the print engine of the image forming unit 150, it is highly likely that the deviation occurs on any paper. And if the main scanning direction size is the same, even if the sub scanning direction size is different, there is a high possibility that the amount of orthogonal deviation is the same.

Therefore, as shown in FIG. 24A, the orthogonal deviation component may be obtained on a standard sheet on which double-sided image formation is possible, and the orthogonal deviation component correction parameter may be applied to a long sheet on which double-sided image formation is not possible.
[Other Embodiments]
In the above description, the front / back measurement data including the front surface measurement data and the back surface measurement data is obtained by measuring the front / back adjustment chart on which the image is formed when the paper is reversed and the double-sided image is formed in one image forming apparatus. It is what was done. This embodiment is particularly preferable in this case.

  However, in a tandem image forming system composed of a plurality of image forming apparatuses (for example, two image forming apparatuses are responsible for image formation on the front and back surfaces), double-sided image formation is performed for each image forming apparatus. It is most desirable to perform correction of the surface in charge at the time of image formation, but it is most desirable to execute correction for the sheet on which the image is formed on each side and formed on both sides in one image forming apparatus. It is also possible to apply a form.

The front / back adjustment chart is an image formed by using the previously calculated correction value, and the correction value obtained from the correction value is added to the previously calculated correction value to obtain a new adjustment value. .
The correction value is measured and calculated with the image position and the image magnification adjusted in the main scanning direction and the sub-scanning direction, respectively, or the image position and the image magnification are adjusted simultaneously. It is possible to calculate the correction values of the rotation and the orthogonal deviation component after predicting the state where the image position and the image magnification are adjusted.

  In the above embodiment, when the edge of the paper is used as a reference, the use of the leading edge during image formation facilitates real-time position adjustment by the leading edge sensor, and the use of the edge in the sub-scanning direction during image formation enables large paper. Can be easily processed when it is in the longitudinal direction, and if it is the edge in the longitudinal direction of the paper at the time of image formation, it is aligned with a direction that is easily noticeable by the user, so that the confirmation work becomes easy. Further, a plurality of options as described above may be configured so that the user can select as appropriate.

DESCRIPTION OF SYMBOLS 100 Image processing apparatus 101 Control part 102 Communication part 103 Operation display part 110 Document reading part 130 Image data storage part 140 Image generation part 150 Image formation part 160 Fixing part 190 Output thing reading part

Claims (10)

An image processing unit that executes image processing including skew correction that deforms the image in advance so that distortion generated in the image formed on the paper is offset when forming images on both sides of the paper;
An image processing apparatus in which front and back measurement data consisting of surface measurement data and back surface measurement data obtained by reading both sides of a front and back adjustment chart on which double-sided images are formed is input to the image processing unit,
In the front and back measurement data, each of the front surface measurement data and the back surface measurement data includes information on the shape of the paper on which the front and back adjustment chart is formed and information on the position of the pattern included in the front and back adjustment chart. And
The image processing unit
Inverting and superimposing one of the front surface measurement data and the back surface measurement data, deforming the front surface measurement data and the back surface measurement data so that their shapes match each other,
Refer to the front surface measurement data and the back surface measurement data in a state of being overlapped and deformed, and determine the positional deviation of the pattern,
For the positional deviation, extract a rotational deviation component in a direction in which the pattern rotates and an orthogonal deviation component in which an orthogonal part of the pattern is deformed,
Performing the skew correction on the orthogonal deviation component so as to match the averaged state in the front surface measurement data and the back surface measurement data in a state of being overlapped and deformed,
An image processing apparatus. The shift direction of the orthogonal shift component is determined to be orthogonal to the shift direction of the rotational shift component.
The image processing apparatus according to claim 1. The image processing unit
When performing the skew correction for the rotational deviation component,
In each of the front surface measurement data and the back surface measurement data, a predetermined part of the paper is matched with a reference,
Whether to match the averaged state in the surface measurement data and the back surface measurement data in a state of being superimposed and deformed,
Run either one,
The image processing apparatus according to any one of claims 1 and 2. The image processing unit
When performing the skew correction for the rotational deviation component,
With reference to the information of the intersection position where the line segments constituting the pattern intersect in each of the front surface measurement data and the back surface measurement data,
In the surface measurement data and the back surface measurement data in a state of being overlapped and deformed, the skew correction is performed on the rotational deviation component so as to match the state of the intersection point.
The image processing apparatus according to claim 3. When the skew correction is performed on the rotational deviation component, the image processing unit is based on either the outer shape of the paper, a specific paper edge common to the front and back of the paper, or a selected one. ,
The image processing apparatus according to claim 3. The orthogonal deviation component performs the skew correction in an application range different from the rotational deviation component.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. In the case where a parallelogram shift in which a rectangle is transformed into a parallelogram by the orthogonal shift component occurs,
In the surface measurement data and the back surface measurement data in a state of being overlapped and deformed, the skew correction is performed on the parallelogram deviation so that the parallelograms on the front and back surfaces are averaged.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. In the case where a trapezoidal deviation in which a rectangle is deformed into a trapezoid due to the orthogonal deviation component occurs,
In the surface measurement data and the back surface measurement data in a state of being overlapped and deformed, the skew correction is performed on the trapezoidal deviation so as to match the front and back trapezoids with an averaged state.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. A reading device that reads the pattern of the paper on which the front and back adjustment chart is imaged on both sides to acquire front and back measurement data;
9. The image processing unit according to claim 1, further comprising an image processing unit that executes image processing including skew correction that deforms the image in advance so as to cancel distortion generated in the image formed on the paper. The described image processing apparatus;
An image forming apparatus that forms an image on the paper based on the image data image-processed by the image processing unit;
An image forming system comprising: Front and back measurement data consisting of front and back measurement data obtained by reading both sides of the front and back adjustment chart on which the double-sided image is formed is input, and the image formed on the paper when the image is formed on both sides of the paper An image processing program in which an image processing apparatus executes image processing including skew correction for deforming the image in advance so as to cancel distortion generated in the image,
In the front and back measurement data, each of the front surface measurement data and the back surface measurement data includes information on the shape of the paper on which the front and back adjustment chart is formed and information on the position of the pattern included in the front and back adjustment chart. If you are
Inverting and superimposing one of the front surface measurement data and the back surface measurement data, deforming the front surface measurement data and the back surface measurement data so that their shapes match each other,
Refer to the front surface measurement data and the back surface measurement data in a state of being overlapped and deformed, and determine the positional deviation of the pattern,
For the positional deviation, extract a rotational deviation component in a direction in which the pattern rotates and an orthogonal deviation component in which an orthogonal part of the pattern is deformed,
Performing the skew correction on the orthogonal deviation component so as to match the averaged state in the front surface measurement data and the back surface measurement data in a state of being overlapped and deformed,
An image processing program for causing a computer of the image processing apparatus to function as described above.