Image inspection apparatus, image forming apparatus, image inspection method, and computer program product

Abstract

This invention provides an image inspection apparatus, an image forming apparatus, an image inspection method, and a computer program product, improving the accuracy of positional offset detection. The image forming apparatus (image inspection apparatus) compares a readout image generated by reading a recording medium on which an image has been formed with a reference image, and detects a positional offset of the image forming position in the recording medium. The control unit of the image forming apparatus aligns the image contained in the readout image with the image contained in the reference image. While aligned, it detects the positional offset of the image forming position based on the offset between the reference position in the readout image and the reference position in the reference image. The control unit selects a reference position for detecting the positional offset from the reference positions contained in the readout image and the reference image, based on the position of the area on the recording medium where the image is formed.

Description

Technical Field

[0001] This invention relates to an image inspection apparatus, an image forming apparatus, an image inspection method, and a computer program product. Background Technology

[0002] In image forming apparatus (printing press), the process of adjusting the medium so that an image can be formed at a predetermined position on the recording medium is called registration. In registration, crosshairs (register marks) are used as registration marks, so registration is also called register line alignment. Registration requires the formation of register lines at predetermined positions on the recording medium, and the offset of the actual position where the register lines are formed is measured. Besides register lines, quadrilaterals, circles, etc., are also used as registration marks.

[0003] Patent Document 1 discloses a technique that detects positional offsets between a watermark pattern and a printed pattern by reading the positions of the registration marks on the watermark pattern and the registration marks on the printed pattern. According to this technique, it is unnecessary for a person to visually confirm the correctness of the printed pattern's position. Furthermore, the detected offset is used to automatically control the position of the printed pattern, eliminating the need for manual adjustments.

[0004] However, for operations where alignment marks cannot be formed, position offset detection methods using alignment marks (images for position detection) cannot be utilized. Furthermore, attaching alignment marks to images is laborious. Additionally, the alignment marks used in position offset detection eventually need to be cropped and removed, resulting in waste of recording media.

[0005] To address this problem, consider the following method: compare the image of the object to be inspected formed on the recording medium with a pre-registered reference image to detect positional offsets without using alignment marks. In this method, for example, for a readout image generated by reading the recording medium containing the image of the object to be inspected and a reference image, corresponding regions in the actual image areas are identified, and image alignment is performed.

[0006] Existing technical documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2001-270086 Summary of the Invention

[0008] However, when there is a large blank area in the recording medium where the image is not present, there is a problem of decreased alignment accuracy. For example, as... Figure 15As shown, consider the case where the printed area 111 that actually forms the image exists only in the upper part of the recording medium 110. In this case, if the read image and the reference image are aligned using the printed area 111 in the upper part where the image exists as a reference, the deviation at the lower corners T13 and T14 where the image does not exist becomes larger compared to the upper corners T11 and T12. As a result, sometimes the offset at the lower corners T13 and T14 is greater than the threshold used in determining the positional offset, and the detection accuracy of the positional offset may be reduced.

[0009] The present invention was made in view of the problems in the prior art described above, and its objective is to improve the accuracy of position offset detection.

[0010] To address the aforementioned issues, technical solution 1 describes an image inspection apparatus that compares a read image generated by reading a recording medium containing an image with a reference image, and detects a positional offset of the image formation position in the recording medium. The image inspection apparatus includes a control unit that aligns an image contained in the read image with an image contained in the reference image. In this aligned state, based on the offset between a reference position in the read image and a reference position in the reference image, the control unit selects a reference position for detecting the positional offset from reference positions contained in the read image and the reference image.

[0011] In the image inspection apparatus described in technical solution 1, the reference positions in technical solution 2 are the four corners of the recording medium.

[0012] In the image inspection apparatus described in technical solution 2, the control unit calculates the positions of the four corners of the recording medium based on the edge information of the recording medium.

[0013] In the image inspection apparatus described in technical solution 2, if the distance from the region where the image is formed to the end of the recording medium in the predetermined direction is greater than a preset threshold, the control unit excludes the reference position of the end side of the recording medium from the reference positions used to detect the position offset.

[0014] In the image inspection apparatus described in technical solution 2, the control unit excludes reference positions used for detecting position offsets from a reference position that is at a distance of more than a preset threshold from the region where the image is formed.

[0015] In the image inspection apparatus described in technical solution 5, the distance from the region where the image is formed to the reference position is the distance between the closest position in the region where the image is formed and the reference position.

[0016] In the image inspection apparatus described in technical solution 2, the control unit selects at least two of the four corners of the recording medium as reference positions for detecting the positional shift.

[0017] The invention described in technical solution 8 is an image forming apparatus comprising: an image inspection device described in any one of technical solutions 1 to 7; an image forming unit for forming an image onto the recording medium; and a reading unit for reading the recording medium on which the image is formed to generate a read image.

[0018] Technical solution 9 describes an image inspection method that compares a read image generated by reading a recording medium in which an image is formed with a reference image, and detects a positional offset of the image formation position in the recording medium. The image inspection method includes: an alignment step, aligning an image contained in the read image with an image contained in the reference image; and a detection step, in the aligned state, detecting a positional offset of the image formation position based on the offset between a reference position in the read image and a reference position in the reference image. The image inspection method further includes a selection step, in which a reference position for detecting the positional offset is selected from reference positions contained in the read image and the reference image, based on the position of the region in which the image is formed on the recording medium.

[0019] In the image inspection method described in technical solution 9, the reference position in technical solution 10 is the four corners of the recording medium.

[0020] The invention described in technical solution 11, in the image inspection method described in technical solution 10, further includes a calculation step of calculating the positions of the four corners of the recording medium based on the edge information of the recording medium.

[0021] In the image inspection method described in technical solution 10, the invention described in technical solution 12 excludes the reference position of the end side of the recording medium from the reference positions used to detect the position offset when the distance from the area where the image is formed to the end of the recording medium in the predetermined direction is greater than a preset threshold in the selection step.

[0022] In the image inspection method described in technical solution 10, the invention described in technical solution 13 excludes reference positions used for detecting position offset from the reference positions that are at a distance of more than a predetermined threshold from the region where the image is formed during the selection process.

[0023] In the image inspection method described in technical solution 13, the distance from the region forming the image to the reference position is the distance between the closest position in the region forming the image and the reference position.

[0024] In the image inspection method described in technical solution 10, the invention described in technical solution 15, in the selection step, selects at least two of the four corners of the recording medium as reference positions for detecting the positional offset.

[0025] The invention described in technical solution 16 is a computer program product used to enable a computer as a control unit to function as a control unit for detecting positional offset of an image formation position in a recording medium by comparing a read image generated by reading an image formed on a recording medium with a reference image. The control unit aligns an image contained in the read image with an image contained in the reference image. In this aligned state, it detects the positional offset of the image formation position based on the offset between a reference position in the read image and a reference position in the reference image. The control unit selects a reference position for detecting the positional offset from reference positions contained in the read image and the reference image, based on the position of the region forming the image on the recording medium.

[0026] In the invention described in technical solution 17, in the computer program product described in technical solution 16, the reference position is the four corners of the recording medium.

[0027] In the computer program product described in technical solution 17, the control unit calculates the positions of the four corners of the recording medium based on the edge information of the recording medium.

[0028] In the computer program product described in technical solution 17, the invention described in technical solution 19, when the distance from the area where the image is formed to the end of the recording medium in the predetermined direction is greater than a preset threshold, excludes the reference position of the end side of the recording medium from the reference positions used to detect the position offset.

[0029] In the computer program product described in technical solution 17, the control unit excludes a reference position that is at a distance of more than a preset threshold from the reference position used to detect the position offset from the reference position that is located from the region where the image is formed.

[0030] In the computer program product described in technical solution 20, the distance from the region forming the image to the reference position is the distance between the closest position in the region forming the image and the reference position.

[0031] In the computer program product described in technical solution 17, the control unit selects at least two of the four corners of the recording medium as reference positions for detecting the position offset.

[0032] According to the present invention, the accuracy in detecting positional offset can be improved. Attached Figure Description

[0033] Figure 1 This is a schematic structural diagram of the image forming apparatus according to an embodiment of the present invention.

[0034] Figure 2 This is a block diagram showing the functional structure of the image forming apparatus.

[0035] Figure 3 This is a flowchart illustrating the position offset detection process performed in the image forming apparatus.

[0036] Figure 4 It is a diagram used to illustrate the image location that serves as the reference image and the reference for image matching in the image reading.

[0037] Figure 5 This diagram illustrates a method for detecting the four corners of a recording medium based on a aligned reference image and a read image.

[0038] Figure 6 It is a diagram that compares the points at the four corners of the recording medium in the aligned reference image with the points at the four corners of the recording medium in the read image.

[0039] Figure 7 This is a flowchart representing the reference position selection process performed in the image forming apparatus.

[0040] Figure 8 This is a flowchart representing the reference position selection process performed in the image forming apparatus.

[0041] Figure 9 This is a flowchart representing the reference position selection process performed in the image forming apparatus.

[0042] Figure 10 This is an example of an image used to illustrate the position of the printed area relative to the recording medium.

[0043] Figure 11 This is an example of an image used to illustrate the position of the printed area relative to the recording medium.

[0044] Figure 12 This is an example of an image used to illustrate the position of the printed area relative to the recording medium.

[0045] Figure 13 This is an example of an image used to illustrate the position of the printed area relative to the recording medium.

[0046] Figure 14 This is an example of an image used to illustrate the position of the printed area relative to the recording medium.

[0047] Figure 15 This diagram is used to illustrate the problem when the printed area exists only at the top of the recording medium. Detailed Implementation

[0048] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The advantages and features provided by these embodiments will be understood from the following detailed description and the accompanying drawings. However, the scope of the present invention is not limited to the embodiments disclosed below or the examples in the drawings.

[0049] Figure 1 This is a schematic structural diagram of the image inspection apparatus and the image forming apparatus 100, which is an image forming apparatus, according to this embodiment. The image forming apparatus 100 forms a color image onto a recording medium such as paper using an electrophotographic method. The image forming apparatus 100 forms an image based on image data obtained from reading an image from an original document or image data received from an external device. The image forming apparatus 100 includes an operation unit 10, a display unit 20, an original document reading unit 30, an image forming unit 40, a supply unit 50, a post-processing unit 60, and an image reading unit 70, etc.

[0050] Operation unit 10 outputs operation signals based on user operations to control unit 81 (see reference). Figure 2 The operation unit 10 is equipped with various operation keys and a touch screen. The operation keys accept various user commands. The touch screen is formed to cover the display screen of the display unit 20. The touch screen accepts touch operations on the display screen and detects the touch location.

[0051] The display unit 20 is composed of an LCD (Liquid Crystal Display). The display unit 20 displays various images according to the display signals input from the control unit 81.

[0052] The original document reading unit 30 includes an ADF (Automatic Document Feeder), a scanner, etc. The original document reading unit 30 outputs the image data obtained by reading the image of the original document to the control unit 81.

[0053] The image forming unit 40 forms an image from the recording medium supplied from the supply unit 50. The image forming unit 40 includes photosensitive drums 41Y, 41M, 41C, and 41K corresponding to yellow, magenta, cyan, and black colors, respectively. The image forming unit 40 also includes an intermediate transfer belt 42, a secondary transfer roller 43, a fixing unit 44, and a flipping mechanism 45.

[0054] After uniformly charging the photosensitive drum 41Y, the image forming unit 40 scans and exposes the image data using a laser beam to form an electrostatic latent image. Next, the image forming unit 40 attaches yellow toner to the electrostatic latent image on the photosensitive drum 41Y and develops the electrostatic latent image.

[0055] The photosensitive drums 41M, 41C, and 41K are the same as the photosensitive drum 41Y, except for the different colors they process, so descriptions are omitted.

[0056] The image forming unit 40 sequentially transfers the toner images of each color formed on the photosensitive drums 41Y, 41M, 41C, and 41K onto the rotating intermediate transfer belt 42 (first transfer). That is, a color toner image formed by overlapping the four toner images is formed on the intermediate transfer belt 42. The image forming unit 40 then transfers the color toner image on the intermediate transfer belt 42 onto the recording medium via the secondary transfer roller 43 (secondary transfer).

[0057] The fixing unit 44 fixes the color toner image onto the recording medium by heating and pressurizing.

[0058] The flipping mechanism 45 flips the surface of the recording medium when images are formed on both sides of the recording medium.

[0059] The supply unit 50 has supply trays 51-53 for supplying recording media to the image forming unit 40. Each supply tray 51-53 contains recording media of a predetermined paper type and size.

[0060] The post-processing unit 60 performs post-processing on the recording medium after the image is formed by the image forming unit 40, as needed. For example, post-processing includes cutting, sorting, binding, punching, folding, and stapled processing. The post-processing unit 60 discharges the recording medium after image formation to discharge trays 61 and 62. Alternatively, the post-processing unit 60 stores the recording medium after image formation in a high-capacity stacker 63.

[0061] Image reading unit 70 (reading unit) in the transport direction of the recording medium ( Figure 1 The image reading unit 70 is positioned downstream of the image forming unit 40 in the Y-direction (as shown). The image reading unit 70 reads the transported recording medium and generates a read image (image data). The image reading unit 70 outputs the generated read image to the control unit 81. The image reading unit 70 is a color sensor that uses a light-receiving element to receive light emitted from a light source and reflected from the surface of the recording medium, and outputs a signal corresponding to the intensity of the light. The image reading unit 70 is positioned in a direction orthogonal to the transport direction (Y-direction) of the recording medium (as shown). Figure 1 It is a line sensor composed of multiple light-receiving elements arranged at predetermined intervals in the X direction (as shown). For example, the image reading unit 70 reads the image formed by the image forming unit 40 on the recording medium and is used when checking the position, color, stains, etc. of the image.

[0062] Figure 2 This is a block diagram showing the functional structure of the image forming apparatus 100. For example... Figure 2 As shown, the image forming apparatus 100 includes an operation unit 10, a display unit 20, a document reading unit 30, an image forming unit 40, a supply unit 50, a post-processing unit 60, an image reading unit 70, a control unit 81, a storage unit 82, a communication unit 83, and a transport unit 84. Furthermore, descriptions of the already explained functional units are omitted.

[0063] The control unit 81 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU reads various processing programs stored in the ROM based on operation signals input from the operation unit 10 or instruction signals received from the communication unit 83, and expands the read programs into the RAM. The CPU centrally controls the operation of each part of the image forming apparatus 100 according to the expanded programs.

[0064] The storage unit 82 is composed of non-volatile storage devices such as hard disks and flash memory, and stores various types of data. For example, a reference value V is pre-stored in the storage unit 82.

[0065] The communication unit 83 transmits and receives data with external devices connected to communication networks such as LANs (Local Area Networks).

[0066] The conveying unit 84 is equipped with conveying rollers for conveying recording media. The conveying unit 84 conveys recording media within the image forming apparatus 100. For example, the conveying unit 84 conveys recording media stored in supply trays 51-53 of the supply unit 50 to the image forming unit 40. The conveying unit 84 conveys recording media from which images are formed by the image forming unit 40. The conveying unit 84 conveys recording media from which images are read by the image reading unit 70. The conveying unit 84 conveys the image-formed recording media to discharge trays 61, 62 or a high-capacity stacker 63.

[0067] The control unit 81 acquires the read image generated by the image reading unit 70 reading the recording medium in which the image is formed by the image forming unit 40.

[0068] The control unit 81 compares the read image generated by reading the recording medium on which the image is formed with the reference image, and detects the positional offset of the image formation position in the recording medium.

[0069] The reference image is pre-registered in the storage unit 82. The reference image can be either a RIP image (RIP data) or an image generated by reading an image formed on the recording medium (an image without positional offset or abnormality).

[0070] Positional offsets include offsets from the position where the image should be formed on the recording medium, offsets on the back of the printing plate when printing on both sides, color offsets, etc.

[0071] The control unit 81 aligns the image included in the read image with the image included in the reference image. While aligned, the control unit 81 detects the positional offset of the image formation position based on the offset between the reference position in the read image and the reference position in the reference image.

[0072] The reference position is a point (position) within a reference image used to detect positional offset of the image formation location by comparing the read image with a reference image. In this embodiment, the four corners of the recording medium are used as the reference position.

[0073] Based on the position of the area forming the image on the recording medium, the control unit 81 selects a reference position for detecting positional offset from the reference positions contained in the read image and the reference image.

[0074] The control unit 81 calculates the positions of the four corners of the recording medium based on the edge information of the recording medium. This edge information includes the position and direction of the edge. For example, the control unit 81 detects the boundary line (edge) between the recording medium area and the background area from the read image. The recording medium area is the area corresponding to the recording medium within the image. The background area is the area corresponding to the outer edge of the recording medium within the image. Specifically, the control unit 81 determines a threshold for separating the brightness values ​​corresponding to the recording medium area from the brightness values ​​corresponding to the background area based on the distribution (histogram, etc.) of the brightness values ​​in the read image. The control unit 81 uses this threshold to detect the edges of the recording medium in the read image. Typically, since the recording medium is rectangular, the control unit 81 detects four straight lines from the read image as the edges of the recording medium. The control unit 81 obtains the positions of four points as the intersection points of the four straight lines and sets these four points as the positions of the four corners of the recording medium.

[0075] The control unit 81 determines whether the distance from the area where the image is formed to the end of the recording medium in a predetermined direction is greater than a preset threshold. If the distance from the area where the image is formed to the end of the recording medium in the predetermined direction is greater than the threshold, the control unit 81 excludes the reference position at the end of the recording medium from the reference positions used to detect position offset. The predetermined direction is, for example, the transport direction of the recording medium (sub-scanning direction). Alternatively, the predetermined direction may be a width direction orthogonal to the transport direction of the recording medium (main scan direction). Furthermore, when either the transport direction or the width direction of the recording medium is used as the predetermined direction, it is preferable to set the direction along the long side of the recording medium as the predetermined direction.

[0076] The control unit 81 selects a reference position that is relatively close to the region from which the image is formed as the reference position for detecting positional shift. The control unit 81 excludes reference positions that are relatively far from the region from which positional shift is detected. Here, the distance from the "region from which the image is formed" to a certain reference position is the distance between the closest position in the "region from which the image is formed" and the reference position.

[0077] The control unit 81 selects at least two of the four corners of the recording medium as reference positions for detecting position offset.

[0078] The control unit 81 calculates the offset from the target position for the image formed on the recording medium, thereby determining whether there is a positional shift in the image forming position of the image forming unit 40. For example, the control unit 81 detects the positional shift of the back side during double-sided printing based on the offset.

[0079] Next, the operation of the image forming apparatus 100 will be explained.

[0080] Figure 3 This is a flowchart illustrating the position offset detection process performed in the image forming apparatus 100. In the position offset detection process, the position offset is detected by comparing the image with a reference image without using alignment marks such as guide lines (position detection image). This process is implemented through software processing based on the cooperation of the CPU of the control unit 81 and a program stored in ROM.

[0081] Figure 4 The left figure shows an example of a reference image A1. The reference image A1 includes a recording medium area 121 and a background area 122. Furthermore, even when the reference image A1 is a RIP image, a background area 122 corresponding to the outer side of the recording medium area 121 is virtually appended to the reference image A1.

[0082] also, Figure 4 The X direction shown is orthogonal to the transport direction of the recording medium (main scan direction). Figure 4 The Y-direction shown is the transport direction of the recording medium (sub-scan direction). Regarding... Figure 5 The same applies to the X and Y directions shown.

[0083] First, the control unit 81 searches for image formation positions in the reference image A1 and obtains image positions O1 to O4, which serve as reference (model points) for image matching (step S1). Then, the control unit 81 obtains images surrounding image positions O1 to O4 as template images. The image formation position is the area where an image is actually formed. Image positions O1 to O4 are preferably located near the four corners of the recording medium within the area where the image is formed. When image positions O1 to O4 are near the four corners of the recording medium, the detection accuracy of positional offset increases. Furthermore, the template image is preferably an image suitable for template matching.

[0084] Next, the control unit 81 controls the image forming unit 40 to form an image of the object to be inspected on the recording medium (step S2). The image of the object to be inspected is an image corresponding to the reference image A1, and is an image inspected based on the reference image A1.

[0085] Next, the control unit 81 controls the image reading unit 70 to read the recording medium on which the image of the object to be inspected has been formed by the image forming unit 40, generating a readout image B1. The control unit 81 controls the transport unit 84 to transport the recording medium while simultaneously causing the image reading unit 70 to read the recording medium. The control unit 81 obtains the readout image B1 generated by reading the recording medium on which the image of the object to be inspected is formed from the image reading unit 70 (step S3). Figure 4The right figure shows an example of reading image B1. Reading image B1 includes a recording medium area 131 and a background area 132.

[0086] Next, the control unit 81 performs template matching on the read image B1, using image positions O1-O4 as a reference, to obtain image positions P1-P4 of the read image B1 (step S4). Specifically, the control unit 81 uses the template image obtained from the reference image A1 and image positions O1-O4 to find the part in the read image B1 that has the highest similarity to the template image. The control unit 81 sets the points corresponding to image positions O1-O4 of the parts found in the read image B1 as image positions P1-P4.

[0087] Next, based on the information of image positions O1-O4 and image positions P1-P4, the control unit 81 aligns the reference image A1 with the read image B1 (step S5). Specifically, the control unit 81 rotates and moves the reference image A1 in a manner that overlaps each of the image positions O1-O4 in the reference image A1 with the image positions P1-P4 in the read image B1, including the edges of the recording medium. In this way, the control unit 81 aligns the images contained in the reference image A1 with the images contained in the read image B1. Figure 5 The left image shows the aligned reference image A2.

[0088] Next, as Figure 5 As shown in the left figure, the control unit 81 determines the coordinates of points Q1 to Q4 at the four corners of the recording medium (recording medium area 121) based on the aligned reference image A2 (step S6). Specifically, the control unit 81 detects four straight lines from the aligned reference image A2 as the edges of the recording medium area 121. The control unit 81 obtains the positions of the four points as the intersection points of the four straight lines, and uses these four points as the positions of the four corners of the recording medium area 121 (points Q1 to Q4). Points Q1 to Q4 are reference positions in the aligned reference image A2.

[0089] Next, as Figure 5 As shown in the right figure, the control unit 81 determines the coordinates of points R1~R4 at the four corners of the recording medium (recording medium area 131) based on the read image B1 (step S7). Specifically, the control unit 81 detects four straight lines from the read image B1 as the edges of the recording medium area 131. The control unit 81 obtains the positions of the four points as the intersection points of the four straight lines, and sets the positions of these four points as the positions of the four corners of the recording medium area 131 (points R1~R4). Points R1~R4 are the reference positions in the read image B1.

[0090] Next, the control unit 81 calculates the distance between points Q1~Q4 in the aligned reference image A2 and points R1~R4 in the read image B1 as offsets D1~D4 (step S8). The control unit 81 calculates the offsets D1~D4 based on the differences between points Q1~Q4 and points R1~R4 in each of the X and Y directions.

[0091] Figure 6 The image comparing point Q1 and point R1 is shown. The distance between point Q1 and point R1 is called the offset D1.

[0092] Next, the control unit 81 determines whether at least one of the offsets D1 to D4 is greater than or equal to a preset reference value V (step S9). If all offsets D1 to D4 are less than the reference value V (step S9: "No"), the control unit 81 determines that there is no positional offset (step S10).

[0093] In step S9, if at least one of the offsets D1 to D4 is above the reference value V (step S9: "Yes"), the control unit 81 determines that there is a position offset (step S11).

[0094] After step S10 or step S11, the position offset detection process ends.

[0095] In the above position offset detection process, the use of all four corners of the recording medium as reference positions for detecting position offset is explained. Next, the determination of which point among the four corners of the recording medium is selected as the reference position for detecting position offset, and which point is excluded from the reference positions for detecting position offset, is explained.

[0096] Figures 7-9 This is a flowchart illustrating a reference position selection process performed in the image forming apparatus 100. The reference position selection process is performed after the position offset detection process (see reference...). Figure 3 The previous processing. The reference position selection processing is achieved through software processing based on the cooperation of the CPU of the control unit 81 and the program stored in ROM.

[0097] First, the control unit 81 obtains the area (printing area) from the object image that forms an image on the recording medium (step S21). Specifically, the control unit 81 performs binarization processing on the recording medium area of ​​the reference image using a predetermined threshold, and extracts the pixels on which the image is formed. The control unit 81 obtains the smallest rectangle that surrounds the pixels on which the image is formed as the printing area. Here, the obtained printing area is a rectangular area surrounded by straight lines along the transport direction and width direction of the recording medium.

[0098] Figures 10 to 14Examples of images (reference images) showing different positions of the printed area 91 on the recording medium 90 are shown. The transport direction of the recording medium 90 (in...) Figures 10-14 The distance between the printing area 91 (vertical direction) and the upper end of the recording medium 90 is defined as L1, and the distance between the printing area 91 and the lower end of the recording medium 90 in the transport direction of the recording medium 90 is defined as L2. Additionally, the distance in the width direction (orthogonal to the transport direction of the recording medium 90) is defined as L2. Figures 10-14 The distance between the printing area 91 (in the horizontal direction) and the left end of the recording medium 90 is set as W1, and the distance between the printing area 91 and the right end of the recording medium 90 in the width direction is set as W2. Additionally, the length of the recording medium 90 in the transport direction is set as H, and the length of the recording medium 90 in the width direction is set as W.

[0099] Additionally, let 'a' be the distance between the top left vertex of the printing area 91 (rectangle) and the top left corner T1 of the recording medium 90. Let 'b' be the distance between the top right vertex of the printing area 91 and the top right corner T2 of the recording medium 90. Let 'c' be the distance between the bottom left vertex of the printing area 91 and the bottom left corner T3 of the recording medium 90. Let 'd' be the distance between the bottom right vertex of the printing area 91 and the bottom right corner T4 of the recording medium 90.

[0100] The control unit 81 calculates the distance L1 between the printing area 91 and the upper end of the recording medium 90 in the transport direction of the recording medium 90, and the distance L2 between the printing area 91 and the lower end of the recording medium 90 (step S22). Additionally, the control unit 81 calculates the distance W1 between the printing area 91 and the left end of the recording medium 90 in the width direction of the recording medium 90, and the distance W2 between the printing area 91 and the right end of the recording medium 90 (step S22).

[0101] Next, the control unit 81 calculates the distances a, b, c, and d from the printing area 91 to the four corners T1 to T4 of the recording medium 90 (step S23).

[0102] Next, the control unit 81 determines whether the distance L1 between the printing area 91 and the upper end of the recording medium 90 in the transport direction is greater than half of the length H of the recording medium 90 in the transport direction (step S24). If L1 is greater than H / 2, the control unit 81 determines that there is no image in the upper half region of the recording medium 90, and if L1 is less than H / 2, the control unit 81 determines that there is an image in the upper half region of the recording medium 90.

[0103] If L1 is greater than H / 2 (step S24: "Yes"), the process proceeds to step S25. In step S25, the control unit 81 determines whether the distance W1 between the printed area 91 in the width direction of the recording medium 90 and the left end of the recording medium 90 is greater than half of the length W in the width direction of the recording medium 90. If W1 is greater than W / 2, the control unit 81 determines that there is no image in the left half region of the recording medium 90; if W1 is less than W / 2, the control unit 81 determines that there is an image in the left half region of the recording medium 90.

[0104] If W1 is greater than W / 2 (step S25: "Yes"), the control unit 81 uses the lower right corner T4 and point 1 or above as the points closest to the printing area 91 among the four corners T1 to T4 of the recording medium 90 for position offset determination (step S26). The control unit 81 selects the lower right corner T4 and point 1 or above as the reference position for detecting position offset.

[0105] In step S25, when W1 is less than or equal to W / 2 (step S25: "No"), the control unit 81 determines whether the distance W2 between the printing area 91 in the width direction of the recording medium 90 and the right end of the recording medium 90 is greater than W / 2 (step S27). If W2 is greater than W / 2, the control unit 81 determines that there is no image in the right half region of the recording medium 90; if W2 is less than W / 2, the control unit 81 determines that there is an image in the right half region of the recording medium 90.

[0106] If W2 is greater than W / 2 (step S27: "Yes"), the control unit 81 uses the lower left corner T3 and point 1 or above as the points closest to the printing area 91 among the four corners T1 to T4 of the recording medium 90 for position offset determination (step S28). The control unit 81 selects the lower left corner T3 and point 1 or above as the reference position for detecting position offset.

[0107] In step S27, if W2 is less than or equal to W / 2 (step S27: "No"), the control unit 81 uses the lower left corner T3 and the lower right corner T4 as points closest to the printing area 91 among the four corners T1 to T4 of the recording medium 90 for position offset determination (step S29). The control unit 81 selects the lower left corner T3 and the lower right corner T4 as reference positions for detecting position offset.

[0108] In step S24, if L1 is less than or equal to H / 2 (step S24: "No"), the process is transferred to... Figure 8Step S30. In step S30, the control unit 81 determines whether the distance L2 between the printing area 91 and the lower end of the recording medium 90 in the transport direction of the recording medium 90 is greater than H / 2. If L2 is greater than H / 2, the control unit 81 determines that there is no image in the lower half region of the recording medium 90, and if L2 is less than H / 2, the control unit 81 determines that there is an image in the lower half region of the recording medium 90.

[0109] If L2 is greater than H / 2 (step S30: yes), then the control unit 81 determines whether the distance W1 between the printing area 91 in the width direction of the recording medium 90 and the left end of the recording medium 90 is greater than W / 2 (step S31).

[0110] If W1 is greater than W / 2 (step S31: "Yes"), the control unit 81 uses the upper right corner T2 and point 1 or above as the points closest to the printing area 91 among the four corners T1 to T4 of the recording medium 90 for position offset determination (step S32). The control unit 81 selects the upper right corner T2 and point 1 or above as the reference position for detecting position offset.

[0111] Figure 11 This is an example of the image corresponding to step S32. In Figure 11 In the example shown, L2 is greater than H / 2, and W1 is greater than W / 2. That is, there is no image in the lower half of the recording medium 90 and no image in the left half of the recording medium 90. The printing area 91 is located slightly to the right relative to the recording medium 90. First, the control unit 81 selects the upper right corner T2 as the reference position. Next, the control unit 81 compares the distance a from the printing area 91 to the upper left corner T1 and the distance d from the printing area 91 to the lower right corner T4, and selects the shorter distance, the lower right corner T4, as the reference position. Thus, the control unit 81 uses the upper right corner T2 and the lower right corner T4 as reference positions for detecting positional offset.

[0112] Figure 12 This is an example of the image corresponding to step S32. In Figure 12 In the example shown, L2 is greater than H / 2, and W1 is greater than W / 2. That is, there is no image in the lower half of the recording medium 90 and no image in the left half of the recording medium 90. The printing area 91 is located slightly to the right relative to the recording medium 90. First, the control unit 81 selects the upper right corner T2 as the reference position. Next, the control unit 81 compares the distance a from the printing area 91 to the upper left corner T1 with the distance d from the printing area 91 to the lower right corner T4. Since distance a and distance d are the same, the upper left corner T1 and the lower right corner T4 are selected. Thus, the control unit 81 uses the upper left corner T1, the upper right corner T2, and the lower right corner T4 as reference positions for detecting positional offset.

[0113] In step S31, when W1 is less than or equal to W / 2 (step S31: "No"), the control unit 81 determines whether the distance W2 between the printing area 91 in the width direction of the recording medium 90 and the right end of the recording medium 90 is greater than W / 2 (step S33).

[0114] If W2 is greater than W / 2 (step S33: "Yes"), the control unit 81 uses the upper left corner T1 and above as the points closest to the printing area 91 among the four corners T1 to T4 of the recording medium 90 for position offset determination (step S34). The control unit 81 selects the upper left corner T1 and above as the reference position for detecting position offset.

[0115] In step S33, if W2 is less than or equal to W / 2 (step S33: "No"), the control unit 81 uses the upper left corner T1 and the upper right corner T2 as points closest to the printing area 91 among the four corners T1 to T4 of the recording medium 90 for position offset determination (step S35). The control unit 81 selects the upper left corner T1 and the upper right corner T2 as reference positions for detecting position offset.

[0116] Figure 10 This is an example of the image corresponding to step S35. In Figure 10 In one example shown, L2 is greater than H / 2, and no image exists in the lower half of the recording medium 90. Additionally, W1 is less than or equal to W / 2, and W2 is less than or equal to W / 2. The control unit 81 excludes the two corner points T3 and T4 on the lower side, which are determined to have no image, from the reference positions used for detecting position shift. The control unit 81 uses the two corner points T1 and T2 on the upper side of the four corners of the recording medium 90 as the reference positions for detecting position shift.

[0117] Alternatively, the control unit 81 may select the corners T1 and T2 on the upper side based on the reason that the distances a and b between the four corners T1 to T4 of the printing area 91 and the recording medium 90 are the shortest.

[0118] In step S30, if L2 is less than or equal to H / 2 (step S30: "No"), the process is transferred to... Figure 9 Step S36. In step S36, the control unit 81 determines whether the distance W1 between the printing area 91 in the width direction of the recording medium 90 and the left end of the recording medium 90 is greater than W / 2.

[0119] If W1 is greater than W / 2 (step S36: "Yes"), the control unit 81 selects either the upper right corner T2 or the lower right corner T4 and a point above as the points closest to the printing area 91 among the four corners T1 to T4 of the recording medium 90 for position offset determination (step S37). The control unit 81 selects either the upper right corner T2 or the lower right corner T4 and a point above as the reference position for detecting position offset.

[0120] Figure 13 This is an example of the image corresponding to step S37. In Figure 13 In the example shown, L1 is less than or equal to H / 2, L2 is less than or equal to H / 2, and W1 is greater than or equal to W / 2. That is, there is no image in the left half of the recording medium 90. The printing area 91 is located slightly to the right relative to the recording medium 90. First, the control unit 81 compares the distance b from the printing area 91 to the upper right corner T2 with the distance d from the printing area 91 to the lower right corner T4, and selects the corner with the shorter distance as the reference position. Next, the control unit 81 selects the corner with the shortest distance from the printing area 91 among the remaining three corners as the reference position. Figure 13 In the example shown, since distance b and distance d are the same, the control unit 81 selects the upper right corner T2 and the lower right corner T4. Thus, the control unit 81 uses the upper right corner T2 and the lower right corner T4 as reference positions for detecting position offset.

[0121] In addition, the control unit 81 may select the two corners T2 and T4 on the right side based on the reason that the distances b and d among the distances a to d between the printing area 91 and the four corners T1 to T4 of the recording medium are the shortest.

[0122] In step S36, if W1 is less than W / 2 (step S36: "No"), the control unit 81 determines whether the distance W2 between the printing area 91 in the width direction of the recording medium 90 and the right end of the recording medium 90 is greater than W / 2 (step S38).

[0123] If W2 is greater than W / 2 (step S38: "Yes"), the control unit 81 selects the upper left corner T1 or the lower left corner T3 and a point above as the points closest to the printing area 91 among the four corners T1 to T4 of the recording medium 90 for position offset determination (step S39). The control unit 81 selects the upper left corner T1 or the lower left corner T3 and a point above as the reference position for detecting position offset.

[0124] In step S38, if W2 is less than or equal to W / 2 (step S38: "No"), the control unit 81 uses the four corners T1 to T4 of the recording medium 90 for position offset determination (step S40). The control unit 81 selects all four corners T1 to T4 as reference positions for detecting position offset.

[0125] Figure 14 This is an example of the image corresponding to step S40. In Figure 14 In the example shown, L1 is less than H / 2, L2 is less than H / 2, W1 is less than W / 2, and W2 is less than W / 2. Since there is a printing area 91 near the center of the recording medium 90, the control unit 81 uses the corners T1 to T4 at four locations as reference positions for detecting position offset.

[0126] After steps S26, S28, S29, S32, S34, S35, S37, S39 or S40, the reference position selection process ends.

[0127] Control unit 81 uses at least two of the reference positions (top left, top right, bottom left, and bottom right) selected in the reference position selection process to perform position offset detection processing. Figure 3 ).

[0128] Specifically, in step S6, the control unit 81 determines the selected reference positions from the four corner points Q1 to Q4 of the recording medium only from the aligned reference image A2.

[0129] In step S7, the control unit 81 reads the image B1 and determines the selected reference positions from the four corner points R1 to R4 of the recording medium.

[0130] In step S8, the control unit 81 calculates the distance between two points of the corresponding reference positions obtained from the aligned reference image A2 and the reference position obtained from the read image B1 as an offset. Thus, the control unit 81 calculates the offset for each reference position selected in the reference position selection process.

[0131] In step S9, the control unit 81 determines whether at least one of the calculated offsets is greater than or equal to a preset reference value V. If all offsets are less than the reference value V (step S9: "No"), the control unit 81 determines that there is no positional offset (step S10). If at least one offset is greater than or equal to the reference value V (step S9: "Yes"), the control unit 81 determines that there is a positional offset (step S11).

[0132] Furthermore, the control unit 81 can also control the image formation position in the image forming unit 40 based on the offset calculated in step S8. Specifically, the control unit 81 corrects the image formation position in the image forming unit 40 to eliminate positional offset in the image forming unit 40. The control unit 81 feeds back the offset to an adjustment value used to correct the positional offset.

[0133] Furthermore, the control unit 81 can also check for abnormalities in the read image B1 based on the aligned reference image A2 and the read image B1. Here, the control unit 81 considers abnormalities other than positional offset as inspection targets. Abnormalities in the read image B1 include image color, stains, etc. For example, the control unit 81 generates a difference image between the aligned reference image A2 and the read image B1. The control unit 81 calculates the difference in pixel values ​​(brightness values, RGB values, etc.) of each pixel in the two images to generate the difference image. The control unit 81 checks for abnormalities in the read image B1 based on whether each pixel in the difference image exceeds a predetermined threshold. Thus, the control unit 81 can perform normal product inspection operations while detecting positional offset.

[0134] Furthermore, if an abnormality is found in the image B1 being read, the control unit 81 can also control the transport unit 84 to discharge the recording medium with the abnormality to a discharge tray different from the discharge tray for normally discharged recording media. The abnormality in the image B1 can be either a positional shift or an abnormality other than a positional shift.

[0135] As explained above, according to this embodiment, the control unit 81 of the image forming apparatus 100 selects a reference position for detecting positional shift from reference positions included in the read image and the reference image, based on the position of the area (printed area) where the image is formed on the recording medium. The control unit 81 selects or discards reference positions for detecting positional shift based on the position of the printed area in the recording medium, and determines the positional shift accordingly, thereby enabling stable positional shift determination. Therefore, the control unit 81 can improve the accuracy of positional shift detection.

[0136] The control unit 81 uses the four corners of the recording medium as reference positions, and thus can detect position offset based on information about the recording medium area, which is the largest usable area.

[0137] The control unit 81 calculates the positions of the four corners of the recording medium based on the edge information of the recording medium. As a result, the control unit 81 can obtain the positions of the four corners of the recording medium with high accuracy even when the four corners of the recording medium are not included in the image being read due to angles or other reasons.

[0138] If, in a predetermined direction of the recording medium, the distance from the area where the image is formed (printed area) to the end of the recording medium in the predetermined direction is greater than a threshold, the control unit 81 excludes the reference position on the end side of the recording medium from the reference positions used to detect position offset.

[0139] At positions far from the printing area, the misalignment after alignment is large. By excluding reference positions far from the printing area, the control unit 81 can improve the accuracy of position offset detection. In addition, by using the distance from the printing area to the end of the recording medium in a predetermined direction, the control unit 81 can determine whether the printing area is separated from the reference position through a simpler process.

[0140] exist Figure 10 In the example shown, in the transport direction of the recording medium 90, the distance L2 from the printing area 91 to the lower end of the recording medium 90 is greater than the threshold H / 2. Therefore, the control unit 81 excludes the corners T3 and T4 on the lower end side of the recording medium 90 from the reference positions used for detecting position offset.

[0141] The control unit 81 excludes reference positions that are relatively far from the area where the image is formed (printed area) from the reference positions used for detecting positional shifts. By excluding reference positions that are far from the printed area, the control unit 81 can improve the accuracy of positional shift detection.

[0142] exist Figure 11 In the example shown, when comparing the distances a to d from the printing area 91 to the four corners T1 to T4 of the recording medium 90, the distances from the largest to the smallest are c, a, d, and b. Therefore, the control unit 81 excludes the lower left corner T3 and the upper left corner T1, which are farther from the printing area 91, from the reference positions used to detect position offset.

[0143] The control unit 81 selects at least two of the four corners of the recording medium as reference positions for detecting position offset. Therefore, the control unit 81 can improve the accuracy of position offset detection.

[0144] Furthermore, the embodiments described above are examples of the image inspection apparatus, image forming apparatus, image inspection method, and computer program product of the present invention, and are not limited thereto. The detailed structure and operation of each part constituting the apparatus can be appropriately modified without departing from the spirit of the present invention.

[0145] For example, in the above embodiment, the image forming apparatus 100 (image inspection apparatus) is described as including an image forming unit 40 and an image reading unit 70. Alternatively, the image inspection apparatus may acquire a readout image generated by reading an image formed by an external image forming unit (image forming apparatus) from a recording medium by an external image reading unit (image reading device), and use it as the object of inspection. Furthermore, in the above embodiment, the various processes performed by the image forming apparatus 100 may be performed collaboratively by multiple devices.

[0146] Additionally, in the position offset detection processing (refer to...) Figure 3 In the case where the reference image is a RIP image, a background area corresponding to the outer edge of the recording medium area is virtually added to the reference image. Alternatively, if the reference image is a RIP image, no background area may be added to the reference image. In this case, the control unit 81 can treat the end of the image data of the reference image as a position corresponding to the edge of the recording medium.

[0147] Furthermore, when the control unit 81 selects reference positions for detecting positional shifts from the four corners of the recording medium, a simpler method can be used. For example, the control unit 81 can exclude reference positions whose distance from the image-forming area (printing area) is greater than or equal to a preset threshold from the reference positions used for detecting positional shifts. Here, the distance from the printing area to a certain reference position is the distance between the closest position in the printing area to that reference position and the reference position itself. By excluding reference positions that are away from the printing area, the control unit 81 can improve the accuracy of positional shift detection.

[0148] Furthermore, in the above embodiment, the control unit 81 obtains the area where the image is formed (the printing area) as a rectangular area, but it is not limited to this. As the area where the image is formed, the control unit 81 only needs to be able to identify the approximate range of the image to be formed.

[0149] In addition, processing is selected at the reference position (refer to...) Figures 7-9 The document describes setting the threshold in the transport direction of the recording medium to H / 2 and the threshold in the width direction of the recording medium to W / 2, but the thresholds in each direction can be changed appropriately. Alternatively, thresholds can be set for each dimension of the recording medium in each direction.

[0150] Additionally, select processing at the reference position (refer to...) Figures 7-9 The document describes the following scenario: using a reference image as the object image, determining the region (printing area) that forms the image, and selecting a reference position for detecting positional offset. Alternatively, if sufficient processing time is available, the control unit 81 can also use the read image as the object image, determine the region that forms the image, and select a reference position for detecting positional offset.

[0151] In addition, if the control unit 81 is unable to select more than two reference positions from the read image or reference image for some reason, it can also use other thresholds different from the preset thresholds (H / 2, W / 2, etc.) to select reference positions.

[0152] In addition, if the control unit 81 is unable to select more than two reference positions from the read image or reference image for some reason, it may also refrain from checking for abnormalities in the read image (image of the object to be inspected).

[0153] The computer-readable medium for storing programs used to execute various processes is not limited to the examples mentioned above. Additionally, a carrier wave can also be used as a medium for providing program data via a communication line.

[0154] The embodiments disclosed above are for illustrative and exemplary purposes only, and are not intended to be limiting. The scope of the present invention should be interpreted through the description in the claims.

[0155] [Explanation of Symbols]

[0156] 40: Image forming unit; 50: Supply unit; 70: Image reading unit; 81: Control unit; 82: Storage unit; 84: Transfer unit; 90: Recording medium; 91: Printing area; 100: Image forming apparatus.

Claims

1. An image inspection apparatus, comprising comparing a read image generated by reading a recording medium on which an image has been formed with a reference image, and detecting a positional offset of the image formation position in the recording medium, wherein, The image inspection apparatus includes a control unit that aligns an image contained in the read image with an image contained in the reference image. In this aligned state, based on the offset between the reference position in the read image and the reference position in the reference image, the control unit detects a positional offset of the image formation position. The control unit selects a reference position for detecting the positional offset from reference positions contained in the read image and the reference image, based on the position of the region forming the image for the recording medium.

2. The image inspection apparatus according to claim 1, wherein, The reference positions are the four corners of the recording medium.

3. The image inspection apparatus according to claim 2, wherein, The control unit calculates the positions of the four corners of the recording medium based on the edge information of the recording medium.

4. The image inspection apparatus according to claim 2, wherein, If, in a predetermined direction of the recording medium, the distance from the region where the image is formed to the end of the recording medium in the predetermined direction is greater than a preset threshold, the control unit excludes the reference position of the end side of the recording medium from the reference positions used to detect the position offset.

5. The image inspection apparatus according to claim 2, wherein, The control unit excludes reference positions that are at a distance of more than a preset threshold from the region where the image is formed from the reference positions used to detect the positional offset.

6. The image inspection apparatus according to claim 5, wherein, The distance from the region forming the image to the reference position is the distance between the closest position in the region forming the image and the reference position.

7. The image inspection apparatus according to claim 2, wherein, The control unit selects at least two of the four corners of the recording medium as reference positions for detecting the positional offset.

8. An image forming apparatus comprising: The image inspection apparatus according to any one of claims 1 to 7; The image forming unit forms an image onto the recording medium; and The reading unit reads the recording medium on which the image is formed and generates a read image.

9. An image inspection method, comprising comparing a read image generated by reading a recording medium on which an image has been formed with a reference image, and detecting a positional offset of the image formation position in the recording medium, the image inspection method comprising: The alignment process involves aligning the image contained in the read image with the image contained in the reference image. as well as In the detection process, under the aligned state, based on the offset between the reference position in the read image and the reference position in the reference image, the positional offset of the image formation position is detected. The image inspection method further includes a selection step in which a reference position for detecting the positional offset is selected from reference positions contained in the read image and the reference image, based on the position of the region for which the image is formed on the recording medium.

10. The image inspection method according to claim 9, wherein, The reference positions are the four corners of the recording medium.

11. The image inspection method according to claim 10, wherein, The image inspection method further includes a calculation step of calculating the positions of the four corners of the recording medium based on the edge information of the recording medium.

12. The image inspection method according to claim 10, wherein, In the selection process, if the distance from the region where the image is formed to the end of the recording medium in the predetermined direction is greater than a preset threshold, the reference position of the end side of the recording medium is excluded from the reference positions used to detect the position offset.

13. The image inspection method according to claim 10, wherein, In the selection process, reference positions that are at a distance of more than a preset threshold from the region where the image is formed are excluded from the reference positions used to detect the positional offset.

14. The image inspection method according to claim 13, wherein, The distance from the region forming the image to the reference position is the distance between the closest position in the region forming the image and the reference position.

15. The image inspection method according to claim 10, wherein, In the selection process, at least two of the four corners of the recording medium are selected as reference positions for detecting the positional offset.

16. A computer program product for enabling a computer that detects a positional offset of an image formation position in a recording medium by comparing a read image generated by reading an image formed on a recording medium with a reference image to function as a control unit, wherein, The control unit aligns the image contained in the read image with the image contained in the reference image. In this aligned state, based on the offset between the reference position in the read image and the reference position in the reference image, it detects the positional offset of the image formation position. The control unit selects a reference position for detecting the positional offset from reference positions contained in the read image and the reference image, based on the position of the region forming the image for the recording medium.

17. The computer program product according to claim 16, wherein, The reference positions are the four corners of the recording medium.

18. The computer program product according to claim 17, wherein, The control unit calculates the positions of the four corners of the recording medium based on the edge information of the recording medium.

19. The computer program product according to claim 17, wherein, If, in a predetermined direction of the recording medium, the distance from the region where the image is formed to the end of the recording medium in the predetermined direction is greater than a preset threshold, the control unit excludes the reference position of the end side of the recording medium from the reference positions used to detect the position offset.

20. The computer program product according to claim 17, wherein, The control unit excludes reference positions that are at a distance of more than a preset threshold from the region where the image is formed from the reference positions used to detect the positional offset.

21. The computer program product according to claim 20, wherein, The distance from the region forming the image to the reference position is the distance between the closest position in the region forming the image and the reference position.

22. The computer program product according to claim 17, wherein, The control unit selects at least two of the four corners of the recording medium as reference positions for detecting the positional offset.

Images