Image processing device and image reading device

Abstract

Even when the reading resolution in the main scanning direction and the reading resolution in the sub-scanning direction differ, this prevents a decrease in the correction accuracy of the scanned image (original image) due to skew correction. [Solution] In an image reading device (image processing device), the edge detection unit detects the edges of the original document image in the first direction and the edges of the original document image in the second direction (main scanning direction) perpendicular to the first direction within the read image obtained by reading the original document being transported in the first direction. The reference position calculation unit and the reference position correction unit calculate the corner position of the original document image within the read image based on the detection result by the edge detection unit, the first resolution (sub-scanning resolution) which is the reading resolution in the first direction of the original document reading, and the second resolution (sub-scanning resolution) which is the reading resolution in the second direction of the original document reading, thereby determining a reference position for skew correction of the read image. The skew correction unit performs skew correction on the read image based on the determined reference position.

Description

Technical Field

[0001] The present invention relates to an image processing apparatus and an image reading apparatus.

Background Art

[0002] In an image reading apparatus (document reading apparatus) provided with an automatic document feeder (ADF), the document may be conveyed obliquely. When an obliquity occurs in the document, for example, the obliquity correction of the document is performed by a conveyance mechanism. Alternatively, obliquity correction is performed by image processing on a read image obtained by reading the document by an image reading unit.

[0003] In the obliquity correction of a document by image processing, rotational correction for rotating a read image is performed using a reference position determined based on the read image as a reference (rotation center). Patent Document 1 discloses a method of determining, as a reference position for rotational correction, an intersection point when a linear expression (straight line) representing the inclination of the leading end of a document image in a read image and an end portion in the main scanning direction of the read image are connected by a normal line. Thereby, even when deterioration such as folding or breakage occurs at the corner of the document to be read, it becomes possible to estimate the corner position of the document image and determine the reference position.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, if the scanning resolution in the main scanning direction differs from that in the sub-scanning direction, the original document image in the scanned image may become distorted into a parallelogram shape instead of a rectangle. In this case, the method described above will result in a discrepancy between the estimated reference position used for skew correction (rotation correction) of the scanned image and the actual corner position of the original document. This can lead to missing parts or margins in the original document image after skew correction.

[0006] Therefore, the present invention aims to provide a technology that prevents a decrease in the correction accuracy of the scanned image (original image) due to skew correction, even when the scanning resolution in the main scanning direction and the scanning resolution in the sub-scanning direction are different. [Means for solving the problem]

[0007] An image processing apparatus according to one aspect of the present invention includes: detection means for detecting the edges of the original document image in a first direction and the edges of the original document image in a second direction perpendicular to the first direction within a read image obtained by reading an original document being transported in a first direction; calculation means for determining a reference position for skew correction of the read image by calculating the corner position of the original document image within the read image based on the detection result by the detection means, a first resolution which is the reading resolution in the first direction for reading the original document, and a second resolution which is the reading resolution in the second direction for reading the original document; and correction means for performing the skew correction on the read image with respect to the reference position. [Effects of the Invention]

[0008] According to the present invention, even when the reading resolution in the main scanning direction and the reading resolution in the sub-scanning direction are different, it is possible to prevent a decrease in the correction accuracy of the scanned image (original image) due to skew correction. [Brief explanation of the drawing]

[0009] [Figure 1] A cross-sectional view showing an example configuration of the image reading device 100. [Figure 2] A block diagram showing an example configuration of controller 200. [Figure 3] Diagram illustrating the edge detection range of the edge detection unit 205. [Figure 4] An explanatory diagram of the edge detection results of the edge detection unit 205. [Figure 5] Diagram illustrating the valid data range of the slope calculation unit 208. [Figure 6] Diagram illustrating the processing performed by the reference position calculation unit 209. [Figure 7] An explanatory diagram for skew correction applied to scanned images. [Figure 8] A diagram showing an example of obtaining the reference position O. [Figure 9] A diagram showing an example of the results of skew correction. [Figure 10] Diagram illustrating the processing performed by the reference position correction unit 210. [Figure 11] Diagram illustrating the processing performed by the skew correction unit 211. [Figure 12] A flowchart illustrating an example of the processing procedure performed by an image reading device. [Figure 13] A flowchart (modified version) showing an example of the processing procedure by an image reading device. [Figure 14] Diagram illustrating the processing performed by the skew correction unit 211. [Figure 15] A diagram showing an example of an output image from the skew correction unit 211. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0011] [First Embodiment] <Image reading device> FIG. 1 is a cross-sectional view showing a configuration example of an image reading apparatus 100 having a document conveyance mechanism according to the first embodiment. The image reading apparatus 100 includes a document tray 101, a document conveyance motor 105, an image reading unit 106, and a paper discharge tray 108. One or more rectangular documents 102 are placed on the document tray 101. Along the conveyance path 120 of the document 102, a paper feed roller 121, a conveyance roller 122, and a discharge roller 123 are provided. The paper feed roller 121, the conveyance roller 122, and the discharge roller 123 are driven by the document conveyance motor 105.

[0012] The document tray 101 includes two document guides 103 arranged side by side in a direction orthogonal to the conveyance direction of the document 102. In this specification, the direction orthogonal to the conveyance direction of the document 102 may be referred to as the main scanning direction or the width direction of the document 102, and the conveyance direction of the document 102 may be referred to as the sub-scanning direction of the document 102. The two document guides 103 are slidable in the width direction of the document 102 and sandwich and align the document 102 placed on the document tray 101. The document tray 101 further includes a document detection sensor 124 for detecting the document 102 placed on the document tray 101.

[0013] The paper feed roller 121 takes in the documents 102 placed on the document tray 101 one by one into the conveyance path 120. The conveyance roller 122 conveys the document 102 taken into the conveyance path 120 by the paper feed roller 121 toward the image reading unit 106. A document background plate 109 is provided at a position facing the image reading unit 106 across the conveyance path 120. The image reading unit 106 forms a reading position 107 between itself and the document background plate 109. The image reading unit 106 reads the document 102 when the document 102 conveyed along the conveyance path 120 by the conveyance roller 122 passes through the reading position 107. The document 102 read by the image reading unit 106 is discharged from the reading position 107 to the paper discharge tray 108 by the discharge roller 123.

[0014] <Configuration of the Controller> Figure 2 is a block diagram showing an example configuration of a controller 200 that controls the operation of the image reading device 100. The image reading device 100 has a built-in controller 200. The controller 200 includes a central processing unit (CPU) 201. The CPU 201 controls the operation of the entire image reading device 100 by controlling the operation of each device within the controller 200. In this embodiment, the controller 200 may be configured as an image processing device that performs image processing on the scanned image obtained by scanning the document (by the image reading unit 106).

[0015] The controller 200 further comprises an A / D conversion unit 203, a shading correction unit 204, an edge detection unit 205, and a memory 207. It may also have multiple processors or CPU cores. The memory 207 is a storage device including read-only memory (ROM), random access memory (RAM), a solid-state drive (SSD), and a hard disk drive (HDD). The controller 200 further comprises a tilt calculation unit 208, a reference position calculation unit 209, a reference position correction unit 210, and a skew correction unit 211, which are used to correct the skew of the original document.

[0016] The controller 200 is connected to the document transport motor 105 and the image reading unit 106. The controller 200 controls the transport of the document 102 by the document transport motor 105 and the reading of the document image by the image reading unit 106. The controller 200 is configured to acquire analog image data representing the scanned image obtained by reading the document 102 from the image reading unit 106 and generate image data after image processing such as skew correction and shading correction. The image data generated by the controller 200 can be used for copying, facsimile transmission, transmission to a personal computer, etc.

[0017] The controller 200 is further connected to a volume resistor 104 and detects the resistance value of the volume resistor 104. The volume resistor 104 is configured so that its resistance value changes according to the distance between the two document guides 103 provided on the document tray 101. The controller 200 (CPU 201) detects the distance between the two document guides 103 based on the resistance value of the volume resistor 104. By detecting the distance between the two document guides 103, the controller 200 (CPU 201) detects the widthwise size (in the direction perpendicular to the transport direction) of the document 102 placed on the document tray 101. In this specification, the widthwise size of the document 102 is also referred to as the "document width".

[0018] The controller 200 is connected to the operation unit 130. The operation unit 130 has a display device (e.g., a liquid crystal display) that outputs information to the user and an input device (e.g., a touch panel sensor) that receives instructions from the user. The input device receives instructions from the user, such as instructions to start image reading processing, specifying the document size, and specifying the reading mode, and transmits input information indicating the received input to the controller 200. The display device displays messages or operation screens, etc., according to the control of the controller 200.

[0019] In this embodiment, the CPU 201 determines the resolution (reading resolution) for the main scanning direction and the sub-scanning direction, as instructed by the user as settings for reading the document. This determination result is used by the reference position correction unit 210 and the skew correction unit 211, which will be described later. Based on the user's instructions input from the operation unit 130, the CPU 201 performs image reading processing using the image reading unit 106.

[0020] The A / D conversion unit 203 converts the analog image data representing the read image output from the image reading unit 106 into digital image data and outputs it. The shading correction unit 204 performs shading correction on the image data of the read image output from the A / D conversion unit 203. Shading correction is a process that corrects for the non-uniformity of the light intensity of the LED light source in the image reading unit 106 and the influence of the pixel sensitivity of the CCD line sensor in the image reading unit 106.

[0021] The edge detection unit 205 detects edge portions within the scanned image (of the original image) based on the shading-corrected image data output from the shading correction unit 204, and generates edge information representing those edge portions. The edge detection unit 205 stores the generated edge information in the memory 207. The edge detection unit 205 detects two edge portions in the main scanning direction (width direction) of the original image within the scanned image as the left main scanning edge position and the right main scanning edge position, and inputs them to the CPU 201. The left main scanning edge position corresponds to the left edge (left side) of the original image with respect to the transport direction of the original 102, and the right main scanning edge position corresponds to the right edge (right side) of the original image with respect to the transport direction. The edge detection unit 205 may also detect edge portions within the scanned image based on thresholds instructed by the CPU 201. Details of the processing performed by the edge detection unit 205 will be described later.

[0022] The tilt calculation unit 208 calculates a linear equation representing the tilt of the original image in the scanned image based on the left main scan edge position or the right main scan edge position detected by the edge detection unit 205. As will be described later, the calculation is performed using the pixel group included in the set valid data range within the scanned image.

[0023] The reference position calculation unit 209 calculates one of the two front corner positions (corner positions) of the document 102 in the transport direction as the reference position for correcting the skew of the scanned image, and inputs this to the CPU 201. As described later, the reference position calculation unit 209 performs estimation calculations using the left main scan edge position and sub-scan edge position of the document image and a linear equation obtained by the tilt calculation unit 208, so that the reference position can be calculated even if the edges of the document 102 are deteriorated due to bending or the like.

[0024] The reference position correction unit 210 calculates a correction amount for the discrepancy between the reference position (corner position) estimated by the reference position calculation unit 209 and the actual corner position of the original image, and inputs it to the CPU 201. As will be described later, the original image in the scanned image is distorted into a parallelogram shape when the scanning resolution in the main scanning direction (hereinafter also referred to as "main scanning resolution") and the scanning resolution in the sub-scanning direction (hereinafter also referred to as "sub-scanning resolution") during scanning of the original 102 are different. The corner position of the original image estimated by the reference position calculation unit 209 will deviate from the actual corner position if the original image is distorted into a parallelogram shape. In such cases, the reference position correction unit 210 performs a correction calculation to determine a correction amount for correcting the reference position for skew correction using the method described later. As will be described later, the reference position correction unit 210 may output a correction amount of 0 or not perform a correction calculation if the main scanning resolution and the sub-scanning resolution are the same.

[0025] The skew correction unit 211 performs skew correction on the scanned image by image processing of the scanned image data. The skew correction unit 211 uses the skew angle (amount of skew) of the original image with respect to the main scanning direction and the correction amount of the reference position to perform skew correction on the scanned image and outputs the corrected image. Details of the skew correction performed by the skew correction unit 211 will be described later.

[0026] Each of the above-mentioned units included in the controller 200 may be implemented by hardware circuits such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and image processors. Alternatively, at least some of the above-mentioned units may be implemented as part of the functions of the CPU 201.

[0027] The following describes in detail the processing performed by the edge detection unit 205, the tilt calculation unit 208, the reference position calculation unit 209, the reference position correction unit 210, and the skew correction unit 211.

[0028] <Edge detection unit> The edge detection unit 205 detects the edge portions (edges) of the original image within the scanned image by performing edge detection processing on the image data after shading correction. The edge detection unit 205 detects the edge portions of the original image from the scanned image within a range set by the CPU 201 in the main scanning direction and sub-scanning direction. The edge detection unit 205 can also detect the edge portions of the original image using known methods such as first derivative, second derivative, and Hough transform. The edge detection unit 205 stores information indicating the detection result of the edge portions of the original image (edge ​​information) in the memory 207.

[0029] Figures 3 and 4 are explanatory diagrams of the edge detection process that detects the main scanning edge and sub-scanning edge of the original image from the scanned image. In the edge detection process, two edge portions (left edge and right edge) in the main scanning direction (width direction) of the original image are detected as the left main scanning edge position and the right main scanning edge position. The edge portion at the leading edge of the original is detected as the sub-scanning edge position.

[0030] In Figures 3 and 4, the left-right direction (horizontal direction) corresponds to the main scanning direction (width direction), and the up-down direction (vertical direction) corresponds to the sub-scanning direction (transport direction). Also, (as indicated by the arrow in Figure 3) in each figure, the upward direction corresponds to the transport direction of the original document 102. For explanatory purposes, in each figure, the leftmost pixel is designated as the 1st pixel, and the rightmost pixel is designated as the 36th pixel.

[0031] As shown in Figure 3, in this embodiment, the edge detection range by the edge detection unit 205 is determined by the edge detection range H in the main scanning direction and the edge detection range V in the sub-scanning direction. In the examples of Figures 3 and 4, the edge detection range H in the main scanning direction is 36 pixels and the edge detection range in the sub-scanning direction is 4 pixels. The edge detection range V in the sub-scanning direction is set so that the edge portion of the original image in the scanned image can be detected even when the original document 102 is tilted relative to the transport direction and read by the image reading unit 106.

[0032] The edge detection unit 205 detects the edge portion of the original image within a set edge detection range. Figure 4(A) shows an example of the detection result by the edge detection unit 205. In the main scanning direction or sub-scanning direction, the edge detection unit 205 detects pixels in the scanned image where the color has changed from the background color to another color, for example, as edge portions. The edge detection unit 205 generates an image (detection image) as the detection result by binarizing the image, with pixels detected as edge portions set to "1" and pixels not detected as edge portions set to "0".

[0033] ● Detection of the main scanning edge The edge detection unit 205 performs a logical OR operation on the pixel values ​​across multiple pixels arranged in the sub-scanning direction for each position (main scan position) in the detection image shown in Figure 4(A). As a result, as shown in Figure 4(B), a calculation result is obtained indicating the presence or absence of an edge portion of the original image for each position (pixel) in the main scan direction. Pixels in which an edge portion is detected are represented as "1", and pixels in which an edge portion is not detected are represented as "0". For each position (pixel) in the main scan direction, if any of the multiple pixels arranged in the sub-scanning direction are "1", the result of the logical OR operation is "1", and if all of the multiple pixels are "0", the result of the logical OR operation is "0". In this example, the edge detection unit 205 detects that the left main scan edge position is at the 10th pixel position in the main scan direction, and the right main scan edge position is at the 27th pixel position in the main scan direction.

[0034] ● Detection of sub-scanning edges The edge detection unit 205, within the detection image in Figure 4(A), for each main scan position, refers to the pixel value of each pixel in the sub-scan direction and detects the position (pixel) of the edge portion where the pixel value changes from "0" to "1" as the sub-scan edge position. Figure 4(C) shows an example of the detection result of the sub-scan edge at each main scan position. As shown in Figure 4(C), based on the detection image in Figure 4(A), the sub-scan edge position at the 10th pixel in the main scan direction is detected as the position of the 2nd pixel in the sub-scan direction. Also, the sub-scan edge position at the 27th pixel in the main scan direction is detected as the position of the 3rd pixel in the sub-scan direction. For main scan positions where no edge portion is detected in the sub-scan direction, the sub-scan edge position is represented as the position of the V-th pixel (V=4 in this example).

[0035] The edge detection unit 205 outputs the information obtained in this manner regarding the left main scan edge position, the right main scan edge position, and the sub-scan edge position to the CPU 201. In this embodiment, the left main scan edge position and the right main scan edge position are represented by the position information of a single pixel in the edge portion in the main scan direction of the document image, and the sub-scan edge position is represented by the position information of a group of pixels that constitute the edge of the leading edge of the document.

[0036] <Slope Calculation Unit> To correct for skew in the scanned image, information indicating the tilt of the leading edge of the document (document image) relative to the main scanning direction (width direction) is required. The tilt of the corresponding line at the leading edge of the document is used as the correction amount when performing rotational correction on the scanned image to correct for skew. Furthermore, the intercept of this line is used to determine the corner position (reference point) of the document.

[0037] The tilt calculation unit 208 obtains the main scan edge position and sub scan edge position detected by the edge detection unit 205 from the CPU 201 and performs calculations to determine a linear equation (slope and intercept) that represents the straight line corresponding to the leading edge of the document. This linear equation (slope and intercept) is obtained by applying a general least squares method or Hough transform to the pixel group representing the leading edge of the document.

[0038] To accurately determine the tilt of the leading edge of a document, it is desirable that the pixels constituting the pixel group representing the leading edge of the document are arranged in a straight line. If the corners of the document to be scanned are damaged, for example, due to tears or folds, the positions of pixels around the corners of the document may deviate from the straight line corresponding to the leading edge of the document. In such cases, if pixels around the corners of the document are used in the calculation to determine the tilt of the leading edge, the error between the calculated tilt and the actual tilt of the leading edge of the document may become large. Therefore, when calculating the tilt of the leading edge of a document, it is necessary to set the range excluding the area around the corners of the document as the effective data range for acquiring data to be used in the calculation, and then perform the calculation.

[0039] Figure 5 shows an example of determining the effective data range as described above. The tilt calculation unit 208 determines the central position and image length of the original image in the main scanning direction as follows, based on the left main scanning edge position and the right main scanning edge position detected by the edge detection unit 205. Center position = (Left primary scan edge position) + (Right primary scan edge position) / 2 Image length = ((Right main scan edge position) - (Main scan edge position))

[0040] The tilt calculation unit 208 obtains the values ​​of a predetermined number of pixels centered on the central position within the image length range (between the right main scan edge position and the left main scan edge position) in the main scan direction from the edge detection results. The range of a predetermined number of pixels centered on the central position in the main scan direction corresponds to the effective data range shown in Figure 5.

[0041] In the example in Figure 5, the number of pixels in the main scanning direction is 7200, with the leftmost pixel being the 1st pixel and the rightmost pixel being the 7200th pixel. The edge detection unit 205 detects that the left main scanning edge position is at the 100th pixel position and the right main scanning edge position is at the 5060th pixel position. In this case, the center position of the document image in the main scanning direction is at the 2580th pixel position, and the image length in the main scanning direction is 4960 pixels. In the example in Figure 5, the effective data range is set to a range of 2048 pixels (1557th to 3604th pixels) in the main scanning direction, centered on the center position of the document image (2580th pixel position).

[0042] The tilt calculation unit 208 calculates a linear equation (with its parameters, tilt a and intercept C) representing the straight line corresponding to the leading edge of the document, based on the sub-scan edge position within the valid data range detected by the edge detection unit 205. This linear equation is expressed as (y=ax+C). Tilt a corresponds to the tilt angle (skew angle) of the document 102 with respect to the main scanning direction. The calculation result of the parameters of the straight line corresponding to the leading edge of the document is output to the CPU 201. The skew angle may also be referred to as the amount of skew.

[0043] <Reference position calculation section> Next, the processing performed by the reference position calculation unit 209 will be described. The reference position calculation unit 209 calculates one of the two corner positions (corner positions) on the front side in the transport direction of the original image within the scanned image as the reference position for skew correction of the scanned image. Below, an example will be described in which the left corner position of the two corner positions on the front side in the transport direction of the original image is used as the reference position. Note that the reference position calculation unit 209 may also calculate using one of the two corner positions as the reference position according to the instructions of the CPU 201.

[0044] If the edges of the original document 102 are deteriorated due to bending or other reasons, it is difficult to correctly determine the corner position of the original image from the edge detection result of the edge detection unit 205. For this reason, the reference position calculation unit 209 determines the corner position of the original image by estimation calculation using the left main scan edge position and sub-scan edge position of the original image detected by the edge detection unit 205 and a linear equation obtained by the tilt calculation unit 208.

[0045] Figure 6 shows an example of the calculation process for the reference position. In this example, the document is scanned at a main scan resolution of 600 dpi and a sub-scan resolution of 600 dpi. In Figure 6, position L(xL, yL) is the left main scan edge position detected by the edge detection unit 205, where xL represents the x-coordinate and yL represents the y-coordinate. The x-axis direction corresponds to the main scan direction, and the y-axis direction corresponds to the sub-scan direction. Line A corresponds to a linear equation obtained by the slope calculation unit 208 and is a line with a slope a and an intercept C. Line B is a normal that passes through the left main scan edge position L and is perpendicular to line A. The linear equation representing line B is obtained based on the left main scan edge position L and the slope a of line A. The intersection point of line A and line B corresponds to the corner position of the document image and is used as the reference position O for correcting the skew of the scanned document.

[0046] If the x-coordinate of the reference position O is x0 and the y-coordinate is y0, the reference position O(x0,y0) shown in Figure 6 can be found using the following equations (1) and (2). TIFF2026060574000002.tif25147

[0047] According to equations (1) and (2), the reference position O(x0,y0) is determined using the slope a and intercept C of the line A determined by the slope calculation unit 208, and the left main scan edge position L(xL,yL) detected by the edge detection unit 205. In this way, even if the edges of the original document 102 are degraded, the corner position of the original image can be used as the reference position for calculation based on the edge position detected by the edge detection unit 205 and the parameters of the line A representing the leading edge of the original document, determined by the slope calculation unit 208.

[0048] <Effect of error in reference position> Next, we will explain the error that occurs in the reference position calculated by the reference position calculation unit 209 and its effects.

[0049] Figure 7(A) shows an example of skew correction for the original document image (scanned image) when the main scan resolution and sub scan resolution are equal during scanning of the original document 102. In the example in Figure 7(A), the original document image in the scanned image obtained when scanning an original document with skew does not exhibit the distortion described later. Therefore, skew correction for the original document image is possible by performing rotation correction of the original document image (scanned image) by the angle of inclination (skew angle) Θ of the original document image with respect to the main scan direction.

[0050] Figures 7(B) and (C) show examples of skew correction for the original document image (scanned image) when the main scan resolution and sub scan resolution are different during the scanning of the original document 102. Figure 7(B) shows the case where the main scan resolution is smaller than the sub scan resolution, and Figure 7(C) shows the case where the main scan resolution is larger than the sub scan resolution. In the examples of Figures 7(B) and (C), when a skewed original document is scanned, the original image in the resulting scanned image will be distorted into a parallelogram shape due to the difference between the main scan resolution and the sub scan resolution. In this case, unlike the example in Figure 7(A), simply performing rotational correction of the tilt angle (skew angle) Θ of the original image (scanned image) is not enough to correct it into a rectangular original image (scanned image). To convert a parallelogram-shaped image into a rectangular image, shear correction is required for the tilt angle Θ' of the parallelogram.

[0051] Thus, when scanning a document that has become skewed with different scanning resolutions for the main and sub-scanning settings, it becomes necessary to perform not only rotational correction but also shear correction on the document image (scanned image). Generally, both such rotational and shear corrections can be performed using affine transformations based on the reference position shown in Figures 7(A) to (C).

[0052] Next, using Figures 8 and 9, we will explain an example of obtaining the reference position O using calculations with equations (1) and (2) when the main scan resolution and sub-scan resolution are different.

[0053] Figure 8(A) shows the reference position O obtained (calculated) from the scanned image when the document is scanned at a main scan resolution of 300 dpi and a sub-scan resolution of 600 dpi. In this case, because the main scan resolution is smaller than the sub-scan resolution, the document image in the scanned image has the shape of a parallelogram. When the reference position O is calculated from this scanned image, as shown in Figure 8(A), a position different from the corner position P of the document image is obtained as the reference position O.

[0054] Figure 9(A) shows the correction results when rotation correction and shear correction are applied to the scanned image, with the reference position O shown in Figure 8(A) as the reference (center of rotation). If there is a deviation (error) from the corner position P of the original image at the reference position O, the controller 200 (CPU 201) mistakenly identifies the reference position O as the corner position of the original image within the scanned image. As a result, the area indicated by the shaded lines in Figure 9(A) is determined to be an invalid pixel area, resulting in loss of pixels in the final acquired original image.

[0055] Figure 8(B) shows the reference position O obtained (calculated) from the scanned image when the document is scanned with a main scan resolution of 600 dpi and a sub-scan resolution of 300 dpi. In this case, since the sub-scan resolution is smaller than the main scan resolution, the document image in the scanned image will have the shape of a parallelogram, similar to the example in Figure 8(A). When the reference position O is calculated from this scanned image, a position different from the corner position P of the document image is obtained as the reference position O, as shown in Figure 8(B).

[0056] Figure 9(B) shows the correction results when rotation correction and shear correction are applied to the scanned image, with the reference position O shown in Figure 8(B) as the reference (center of rotation). If there is a deviation (error) from the corner position P of the original image at the reference position O, the controller 200 (CPU 201) mistakenly identifies the reference position O as the corner position of the original image within the scanned image. As a result, the margin area shown by the diagonal lines in Figure 9(B) is also determined to be part of the original image, resulting in a margin appearing in the final acquired original image.

[0057] Thus, when the main scanning resolution and the sub-scanning resolution are different, if the reference position O is obtained by calculation using equations (1) and (2), the reference position O will be shifted from the actual corner position P of the original image. As a result, an original image (scanned image corresponding to the original) with missing or marginal parts will be obtained. For this reason, in this embodiment, as described below, the reference position O is corrected by the reference position correction unit 210 so that the reference position for rotation correction and shear correction for the scanned image is set to the corner position P of the original image.

[0058] <Reference position correction section> Figure 10 shows an example of obtaining correction amounts (dxP, dyP) to correct the reference position O acquired by the reference position calculation unit 209. Figure 10 shows the area around the left corner of the leading edge of the document. In this example, as in the example in Figure 8(A), it is assumed that the document was scanned with a main scan resolution of 300 dpi and a sub-scan resolution of 600 dpi.

[0059] In Figure 10, position O represents the reference position obtained (calculated) by the reference position calculation unit 209, and position P represents the expected angular position in the actual original image. The reference position correction unit 210 determines the amount of displacement between position O and position P obtained by the reference position calculation unit 209, and uses this displacement amount as the correction amount for the reference position. Therefore, the amount of displacement between position O and position P is obtained by setting position O as the origin and determining the coordinates (dxP, dyP) of position P.

[0060] As shown in Figure 10, the coordinates of position P with position O as the origin are determined as the coordinates of the intersection of the line A' corresponding to the leading edge of the document and the line B' corresponding to the left edge of the document. Since line A' passes through the origin (position O), the linear equation representing line A' is expressed using only the slope a obtained by the slope calculation unit 208, and the intercept C is not used. If the slope angle of line A' with respect to the main scanning direction (x-axis direction) is Θ (skew angle of the document image), then the skew angle Θ is determined by setting a = tanΘ. Θ = tan -1 (a) (3)

[0061] The position L shown in Figure 10 represents the left main scan edge position of the original image. If the x-coordinate of position L is dxL, then the coordinates of position L are expressed as L(dxL, dxL / tanΘ). Since the value of dxL is relative to coordinate O, dxL can be calculated as the difference between the x-coordinate of the reference position O obtained by the reference position calculation unit 209 and the x-coordinate of the left main scan edge coordinate L detected by the edge detection unit 205, as shown in the following equation. dxL = x0 - xL (4) It can be calculated using this method.

[0062] The angle Θ' shown in Figure 10 represents the angle of the edge (left edge) of the document image in the main scanning direction within the scanned image, relative to the sub-scanning direction (the transport direction of the document 102). The angle Θ' is obtained by multiplying the skew angle Θ by the skew correction coefficient N, so Θ' = Θ·N. The skew correction coefficient N is calculated based on the main scanning resolution and the sub-scanning resolution using the following formula. N = (Main scan resolution / Sub scan resolution) 2 (5) As can be seen from equation (5), when the main scan resolution and the sub scan resolution are equal, N=1 and Θ'=Θ.

[0063] As shown in Figure 10, the linear equation representing line B' is obtained as a linear equation representing a line with a slope of 1 / tanΘ' that passes through position L. The coordinates (dxP, dyP) of the intersection point P of line A' and line B' are: Assuming the filename is TIFF2026060574000003.tif19147, it can be calculated using the following formula. TIFF2026060574000004.tif23147

[0064] According to equations (6) and (7), the correction amount (dxP, dyP) relative to the reference position O is determined based on the left main scan edge position L (x-coordinate dxL), the skew angle Θ of the original image, and the skew correction coefficient N determined based on the main scan resolution and sub-scan resolution.

[0065] <Skew correction section> The skew correction unit 211 performs skew correction on the read image by image processing of the image data of the read image, in accordance with the instructions of the CPU 201. The skew correction unit 211 performs skew correction on the read image using the reference position O (first reference position) acquired by the reference position calculation unit 209, the skew angle Θ of the original image with respect to the main scanning direction, and the correction amount of the reference position (dxP, dyP), which are acquired by the reference position correction unit 210.

[0066] As described above, when scanning a document that is skewed using a scanning setting where the main scanning resolution and sub-scanning resolution are different, the scanned image (document image) will be distorted into a parallelogram shape due to the difference in main scanning resolution and sub-scanning resolution. To compensate for such distortion, it is necessary to perform not only rotational correction but also shear correction on the scanned image (document image).

[0067] In this embodiment, affine transformation is used for rotation correction and shear correction processing. Figure 11(A) shows the reading result of the original document 102 (original document image within the scanned image) when an original document with skewness is read using reading settings where the main scanning resolution and sub-scanning resolution are different. The coordinate transformation of each pixel in the original document image due to the rotation correction processing on the original document image shown in Figure 11(A) is expressed by the following equation. TIFF2026060574000005.tif15147 Here, each parameter in equation (8) is defined as follows: x: Pixel position before rotation correction (main scanning direction) y: Pixel position before rotation correction (sub-scan direction) x': Pixel position after rotation correction (main scanning direction) y': Pixel position after rotation correction (sub-scan direction) Θ: Oblique angle of the leading edge of the document relative to the main scanning direction.

[0068] Figure 11(B) shows the result of applying rotation correction to the original image shown in Figure 11(A). Since the original image after rotation correction exhibits distortion that deforms it into a parallelogram shape, it is necessary to compensate for this distortion by shear correction processing. The coordinate transformation of each pixel in the original image due to the shear correction processing applied to the original image shown in Figure 11(B) is expressed by the following equation. TIFF2026060574000006.tif14147 Here, each parameter in equation (9) is defined as follows: x: Pixel position before shear correction (main scanning direction) y: Pixel position before shear correction (sub-scan direction) x': Pixel position after shear correction (main scanning direction) y': Pixel position after shear correction (sub-scan direction) Θ'': The oblique angle of the parallelogram shown in the original image after rotation correction. As shown in Figure 11(B), the skew angle Θ'' is determined by the skew angle Θ of the leading edge of the document with respect to the main scanning direction and the skew correction coefficient N, so Θ'' = Θ(N-1).

[0069] Figure 11(C) shows the result of shear correction applied to the original image shown in Figure 11(B). The original image after shear correction has a rectangular shape, indicating that the distortion described above has been compensated for. In this way, by applying the coordinate transformations of equations (8) and (9) to the scanned image (original image), it is possible to correct the skew of the scanned image while compensating for the distortion that occurs in the scanned image due to the difference between the main scan resolution and the sub-scan resolution.

[0070] The oblique correction, which involves rotational correction according to equation (8) and shear correction according to equation (9), is expressed by the following equation. TIFF2026060574000007.tif13147 Here, each parameter in equation (10) is defined as follows: x: Pixel position before correction (main scanning direction) y: Pixel position before correction (sub-scan direction) x': Corrected pixel position (main scanning direction) y': Corrected pixel position (sub-scan direction) Θ: Oblique angle of the leading edge of the document relative to the main scanning direction. N: Skew correction coefficient dxP: Correction amount for the reference position (main scanning direction) dyP: Correction amount for the reference position (sub-scan direction)

[0071] In this way, the skew correction unit 211 acquires the skew angle Θ of the leading edge of the document, the skew correction coefficient N, the reference position O, and the correction amount (dxP, dyP) of the reference position, and applies these to equation (10) to perform skew correction on the scanned image (document image). This makes it possible to correct the skew while correcting the reference position O for skew correction, and also correct the rotation and shear of the scanned image.

[0072] <Processing Procedure> Figure 12 is a flowchart showing an example of the procedure for processing performed by the image reading device 100 of this embodiment. This process includes an image reading process that reads a document and generates image data of the read image, and a skew correction process for the read image, and is performed by the CPU 201.

[0073] In step S101, the CPU 201 determines whether or not a document 102 is present on the document tray 101. If it determines that a document 102 is present, it proceeds to step S102. This determination is made based on the detection value output from the document detection sensor 124. For example, the document detection sensor 124 outputs a detection value of "0" when it does not detect a document 102 on the document tray 101, and outputs a detection value of "1" when it detects a document 102. The CPU 201 determines that there is no document if the detection value is "0", and that there is a document if the detection value is "1".

[0074] In S102, the CPU 201 obtains the reading resolution (main scan resolution and sub scan resolution) settings based on the settings entered by the user from the operation unit 130. Then, in S103, if the CPU 201 determines that it has received an instruction to start the image reading process by pressing the start button on the operation unit 130, it proceeds to S104.

[0075] In S104, the CPU 201 controls the document transport motor 105 and the image reading unit 106 to start the transport of the document 102 and the reading of the document 102 by the image reading unit 106. As a result, each time the document 102 is transported to the reading position 107 of the image reading unit 106, a scanned image corresponding to the document 102 is generated. In S105, the CPU 201 uses the edge detection unit 205 and the tilt calculation unit 208 to obtain the left main scan edge position L(xL, yL) and the parameter values ​​of a linear equation (slope a and intercept C) corresponding to the leading edge (end in the transport direction) of the document image within the scanned image.

[0076] Next, in S106, the CPU 201 uses the reference position calculation unit 209 to perform an estimation calculation of the reference position O(xO,yO) based on the information acquired in S105. Once the estimation result of the reference position O(xO,yO) is obtained, the CPU 201 uses the reference position correction unit 210 in S107 to perform a calculation (correction calculation) to obtain a correction amount (dxP,dyP) to correct the error in the reference position O that occurs when the main scan resolution and sub scan resolution are different. As described above, the calculation by the reference position correction unit 210 uses the left main scan edge position L, the skew angle Θ of the original image, and the skew correction coefficient N determined based on the main scan resolution and sub scan resolution. The calculation result by the reference position correction unit 210 is output from the reference position correction unit 210 to the skew correction unit 211. In S108, the CPU 201 performs skew correction on the image data of the read image (image data after shading correction) using equation (10) with the skew correction unit 211.

[0077] Subsequently, in S109, the CPU 201 determines whether or not there is the next document 102 on the document tray 101 based on the detection value output from the document detection sensor 124. If there is the next document, the process returns to S104. If there is no next document, the CPU 201 terminates the process according to the procedure in Figure 12.

[0078] <Variation> The processing procedure described above can be modified in various ways. For example, in the processing procedure described above, the correction calculation (S107) performed by the reference position correction unit 210 to obtain the correction amount (dxP, dyP) for the reference position O may only be performed when the main scan resolution and the sub-scan resolution are different. Figure 13 shows an example of the processing procedure in such a case. In the processing procedure in Figure 13, the processing from S101 to S106 is the same as in Figure 12. In this example, when the estimation result of the reference position O(xO, yO) is obtained in S106, the CPU 201 proceeds to S201.

[0079] In S201, the CPU 201 compares the main scan resolution and sub-scan resolution acquired in S102. If they match, it proceeds to S108, skipping the correction calculation in S107. In this case, in S108, skew correction is performed with the correction amount (dxP, dyP) = (0, 0). On the other hand, only if the main scan resolution and sub-scan resolution are different, the CPU 201 proceeds from S201 to S107, where the correction calculation is performed by the reference position correction unit 210 to obtain the correction amount (dxP, dyP).

[0080] As described above, in the image reading device (image processing device) of this embodiment, the image reading unit 106 reads a document being transported in a first direction (transport direction) and generates a read image. The edge detection unit 205 detects the edges of the document image in the first direction and the edges of the document image in a second direction (main scanning direction) perpendicular to the first direction within the read image obtained by reading the document being transported in the first direction. The reference position calculation unit 209 and the reference position correction unit 210 calculate the corner position of the document image within the read image based on the detection result by the edge detection unit 205, the first resolution (sub-scan resolution) which is the reading resolution in the first direction of document reading, and the second resolution (sub-scan resolution) which is the reading resolution in the second direction of document reading, thereby determining a reference position for skew correction of the read image. The skew correction unit 211 performs skew correction on the read image based on the determined reference position.

[0081] According to this embodiment, even when the main scan resolution and sub-scan resolution differ during reading by the image reading unit 106, it is possible to appropriately determine the reference position for skew correction, thereby preventing a decrease in the correction accuracy of the original image due to skew correction. Therefore, it becomes possible to provide high-quality original images.

[0082] [Second Embodiment] In the second embodiment, an example is described in which the skew correction unit 211 included in the controller 200 within the image reading device 100 performs a different skew correction process for the read image than in the first embodiment. In the following, the explanation of parts common to the first embodiment is omitted.

[0083] The skew correction unit 211 of this embodiment performs skew correction processing on the read image without performing the rotation correction processing and shear correction processing described in the first embodiment. Specifically, the skew correction unit 211 obtains a corrected reference position O' based on the reference position O obtained by the reference position calculation unit 209 and the correction amount (dxP, dyP) obtained by the reference position correction unit 210. The skew correction unit 211 further generates a skew-corrected image by reading each pixel from the read image and rearranging it so that the parallelogram-shaped image is converted into a rectangular-shaped image, using this reference position O' as a reference.

[0084] Referring to Figures 14 and 15, an example of a method for determining the pixel positions of pixels read from a scanned image will be described. Figure 14 shows an example of a scanned image obtained when a document is scanned at a main scanning resolution of 300 dpi and a sub-scanning resolution of 600 dpi. Figure 15 shows an example of a skew-corrected image obtained by reading the pixels constituting the document image in the scanned image shown in Figure 14 with reference to reference position O' and rearranging them to form a rectangular image.

[0085] In the example in Figure 14, the horizontal axis (x-axis) shows the pixel number in the main scanning direction, and the vertical axis (y-axis) shows the pixel number in the sub-scanning direction. The example shows the case where the reference position O' is corrected to coordinate (9,6) using correction amounts (dxP, dyP). The pixel at reference position O' corresponds to the pixel at coordinate (1,1) in Figure 15.

[0086] In the example in Figure 14, when the reference position O' is taken as the origin, the linear equation representing the straight line A corresponding to the leading edge of the document is expressed by the following equation, using the parameter (slope a) of the linear equation obtained by the slope calculation unit 208. A: y=a·x (11) On the other hand, the linear equation representing the line B corresponding to the left edge of the manuscript can be expressed by solving for the horizontal axis (x axis) as follows. Note that N is the skew correction coefficient N obtained by the reference position correction unit 210. B: x = tan{tan -1 (a)·N}·y (12)

[0087] ● Identifying the pixel position on the left edge line of the original document The skew correction unit 211 first identifies the pixel position on the document left edge line, which indicates the left edge of the document image within the scanned image. This document left edge line corresponds to the document left edge line in Figure 15 (the line of the first pixel in the main scanning direction, which is aligned with the sub-scanning direction). In the scanned image, the first pixel on the document left edge line is the pixel at reference position O' (the pixel at coordinates (9,6) in Figure 14, and the pixel at coordinates (1,1) in Figure 15).

[0088] The skew correction unit 211 determines the pixel positions on the left edge line of the document, starting from the first pixel on the left edge line, within the scanned image. Other pixel positions on the left edge line of the document (i.e., pixel positions corresponding to coordinates (1,2) to (1,34) in Figure 15) can be determined using equation (12). For example, let's consider the case where the slope of line B is -1 / 16, and we determine the position of the 32nd pixel in the y-axis direction (sub-scanning direction) from the reference position O' (i.e., the pixel position corresponding to coordinate (1,32) in Figure 15). Substituting y=32 into equation (12), we get y=-32 / 16=-2. That is, the x-coordinate of the determined pixel is shifted by -2 pixels from the reference position O'. In absolute coordinates, this means that the pixel at coordinate (7,37) in Figure 14 corresponds to the pixel at coordinate (1,32) in Figure 15.

[0089] The skew correction unit 211 can determine the position of pixels in one column of the left edge line of the original document (the pixel positions corresponding to coordinates (1,1) to (1,34) in Figure 15) through such calculations.

[0090] ● Regarding the identification of pixel positions on the main scanning line The skew correction unit 211 then identifies the pixel positions on each main scan line, starting from the pixel on the left edge line of the original document (the first pixel in the main scan direction) determined as described above. For example, in the case of the 32nd main scan line, the pixel position on each main scan line refers to the pixel position corresponding to the coordinates (2,32) to (19,32) in Figure 15.

[0091] The starting point (first pixel) of each main scanning line is the pixel position on the left edge line of the document. For example, in the case of the 32nd main scanning line, it is the pixel position of the 32nd pixel on the left edge line of the document, which is the pixel position (7,37) on the left edge line of the document in Figure 14. To find the other pixel positions on each main scanning line, substitute the difference in the x-axis direction from the first pixel on the main scanning line into equation (11) to find the y-coordinate of the main scanning line for the x-coordinate of any pixel position in the x-axis direction.

[0092] For example, let's consider the case where the slope of line A is 1 / 2, and we want to find the position of the 10th pixel from the left edge on the 32nd main scan line (corresponding to the pixel with coordinates (10,32) in Figure 15). In this case, in Figure 14, we use the 32nd pixel position on the left edge line of the original document as the starting point (1st pixel) and find the y-coordinate of the 10th pixel in the x-axis direction on the 32nd main scan line. Specifically, by substituting x=10 into equation (11), we can obtain y=5. This indicates that, in the original image, the position of the 10th pixel from the left edge on the 32nd main scan line is shifted 10 pixels in the x-axis direction and 5 pixels in the y-axis direction, starting from the 1st pixel on the 32nd main scan line. That is, when expressed in absolute coordinates, the coordinates (17,42) in Figure 14 represent the position of the 10th pixel on the 32nd main scan line.

[0093] The skew correction unit 211 can determine the position of a pixel on each main scanning line in the original image (the pixel position corresponding to coordinates (1,1) to (1,34) in Figure 15) through such calculations.

[0094] The skew correction unit 211 ultimately reads out the pixel data at the identified pixel positions within the read image and rearranges it into a rectangular shape as shown in Figure 15 to form an image. This generates a corrected image in which skew correction (rotation correction and shear correction) has been applied to the read image.

[0095] In the example described above, the sub-scanning direction (y-axis direction) range for determining the pixel position on the left edge line of the document is set to 49 pixels, and the second range for determining the pixel position on the main scanning line is set to 36 pixels in the main scanning direction (x-axis direction). These sub-scanning and main scanning direction ranges may be predetermined, or they may be determined by detecting the length of the main scanning direction and the sub-scanning direction of the document image within the scanned image based on the edge detection result of the edge detection unit 205.

[0096] As described above, in the image reading device (image processing device) of this embodiment, the skew correction unit 211 identifies the position of each pixel constituting the original image in the read image with respect to the reference position O', and generates a skew-corrected image by rearranging each identified pixel in the read image. This makes it possible to perform skew correction processing without performing rotation correction processing and shear correction processing (affine transformation).

[0097] The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0098] The disclosures herein include the following image processing apparatus and image reading apparatus. (Item 1) An image processing device, A detection means for detecting, within a scanned image obtained by reading a document being transported in a first direction, the edge of the document image in the first direction and the edge of the document image in a second direction perpendicular to the first direction, A calculation means that determines a reference position for skew correction for the read image by calculating the corner position of the document image within the read image based on the detection result by the detection means, the first resolution which is the reading resolution in the first direction in reading the document, and the second resolution which is the reading resolution in the second direction in reading the document. Correction means for performing the skew correction on the read image with respect to the aforementioned reference position, An image processing device equipped with the following features. (Item 2) The aforementioned calculation means is A first calculation means for determining a first reference position by performing a first calculation based on the edge position of the end of the original image in the second direction, obtained from the detection result, and a parameter representing a first straight line corresponding to the end of the original image in the first direction; A second calculation means determines a correction amount for the first reference position by performing a second calculation based on the edge position, the skew angle of the original image in the second direction determined from the parameters, the first resolution and the second resolution, and determines a second reference position as the reference position for the skew correction by correcting the first reference position with the correction amount. The image processing apparatus described in item 1, including the image processing apparatus described in item 1. (Item 3) The aforementioned calculation means is If the first resolution and the second resolution are equal, the first reference position is determined as the reference position. If the first resolution and the second resolution are different, the second reference position is determined as the reference position. The image processing device described in item 2. (Item 4) If the first resolution and the second resolution are equal, the calculation means performs only the calculation by the first calculation means without performing the calculation by the second calculation means. An image processing apparatus as described in item 2 or 3. (Item 5) The second calculation means determines the correction amount to 0 without performing the second calculation if the first resolution and the second resolution are equal. The image processing device described in item 2. (Item 6) The first calculation means calculates the intersection point of the normal to the first straight line, which passes through the edge position, with the first straight line, using the intersection point as the first reference position. An image processing device as described in any one of items 2 through 5. (Item 7) The second calculation means determines the position of the intersection point between the first line and the second line corresponding to the end of the original image in the second direction, and determines the correction amount based on the difference between the intersection point and the first reference position. An image processing device as described in any one of items 2 through 6. (Item 8) The second straight line passes through the edge position and has an angle obtained by multiplying the oblique angle by a correction coefficient determined from the first and second resolutions with respect to the first direction. The image processing device described in item 7. (Item 9) The second calculation means determines the position of the intersection point by performing calculations based on the edge position, the oblique angle, and a correction coefficient obtained from the first and second resolutions. Image processing apparatus as described in item 7 or 8. (Item 10) The correction means performs rotation correction, which rotates the read image with respect to the reference position, and shear correction, which converts the parallelogram-shaped image into a rectangular-shaped image, on the read image after the rotation correction. An image processing device as described in any one of items 1 through 9. (Item 11) The correction means is Based on the aforementioned reference position, the position of each pixel constituting the original image within the read image is identified, and the identified pixels within the read image are rearranged to generate the image with the skew correction applied. An image processing device as described in any one of items 1 through 9. (Item 12) An image processing device described in any one of items 1 to 11, A reading means that reads a document being transported in the first direction and generates the read image, An image reading device equipped with [a specific feature].

[0099] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of Symbols]

[0100] 100: Image reading device, 106: Image reading unit, 200: Controller, 205: Edge detection unit, 209: Reference position calculation unit, 210: Reference position correction unit, 211: Skew correction unit

Claims

1. An image processing device, A detection means for detecting, within a scanned image obtained by reading a document being transported in a first direction, the edge of the document image in the first direction and the edge of the document image in a second direction perpendicular to the first direction, A calculation means that determines a reference position for skew correction for the read image by calculating the corner position of the original image within the read image based on the detection result by the detection means, the first resolution which is the reading resolution in the first direction in the reading of the original, and the second resolution which is the reading resolution in the second direction in the reading of the original. Correction means for performing the skew correction on the read image with respect to the aforementioned reference position, An image processing device equipped with the following features.

2. The aforementioned calculation means A first calculation means for determining a first reference position by performing a first calculation based on the edge position of the end of the original image in the second direction, obtained from the detection result, and a parameter representing a first straight line corresponding to the end of the original image in the first direction; A second calculation means determines a correction amount for the first reference position by performing a second calculation based on the edge position, the skew angle of the original image in the second direction determined from the parameters, the first resolution and the second resolution, and determines a second reference position as the reference position for the skew correction by correcting the first reference position with the correction amount. The image processing apparatus according to claim 1, including the following:

3. The aforementioned calculation means If the first resolution and the second resolution are equal, the first reference position is determined as the reference position. If the first resolution and the second resolution are different, the second reference position is determined as the reference position. The image processing apparatus according to claim 2.

4. If the first resolution and the second resolution are equal, the calculation means performs only the calculation by the first calculation means without performing the calculation by the second calculation means. The image processing apparatus according to claim 2.

5. The second calculation means determines the correction amount to 0 without performing the second calculation if the first resolution and the second resolution are equal. The image processing apparatus according to claim 2.

6. The first calculation means calculates the intersection point of the normal to the first straight line, which passes through the edge position, with the first straight line, using the intersection point as the first reference position. The image processing apparatus according to claim 2.

7. The second calculation means determines the position of the intersection point between the first line and the second line corresponding to the end of the original image in the second direction, and determines the correction amount based on the difference between the intersection point and the first reference position. The image processing apparatus according to claim 2.

8. The second straight line passes through the edge position and has an angle obtained by multiplying the oblique angle by a correction coefficient determined from the first and second resolutions with respect to the first direction. The image processing apparatus according to claim 7.

9. The second calculation means determines the position of the intersection point by performing calculations based on the edge position, the oblique angle, and a correction coefficient obtained from the first and second resolutions. The image processing apparatus according to claim 7.

10. The correction means performs rotation correction, which rotates the read image with respect to the reference position, and shear correction, which converts the parallelogram-shaped image into a rectangular-shaped image, on the read image after the rotation correction. The image processing apparatus according to claim 1.

11. The correction means is Based on the aforementioned reference position, the position of each pixel constituting the original image within the read image is identified, and the identified pixels within the read image are rearranged to generate the image with the skew correction applied. The image processing apparatus according to claim 1.

12. An image processing apparatus according to any one of claims 1 to 11, A reading means that reads a document being transported in the first direction and generates the read image, An image reading device equipped with [a specific feature].

Images