JP2021197605A - Image reading device, skew angle determination method, and program - Google Patents

Abstract

To prevent an image from being deteriorated by skew correction when a part of the edge of a document is curled.SOLUTION: An image reading device 2 includes: a document transport unit 3 that automatically transports a document; and an image reading unit 20 that reads an image when the document transported by the document transport unit 3 passes through a predetermined reading position. The image reading device 2 further includes: a shadow detection unit 61 that detects a shadow appearing near the edge of the document in the image read by the image reading unit 20; a skew angle detection unit 62 that detects the skew angle of the image on the basis of the shadow; and a skew angle determination unit 65 that determines the suitability of the skew angle on the basis of the shape of the shadow, and when a part of the edge of the document is curled, determines that the skew angle detected from the image is inappropriate.SELECTED DRAWING: Figure 5

Description

The present invention relates to an image reader, a skew angle determination method and a program, and more particularly to a technique for processing an image read when a conveyed document passes a predetermined position.

An image processing device such as an MFP (Multifunction Peripherals) having a copy function, a scan function, and a print function is provided with an image reading device on the upper part of the device body. The image reader optically scans an image in the main scanning direction of the document when the document carrier section automatically transports the documents set by the user one by one and the document automatically transported by the document carrier section passes through a predetermined position. It is provided with an image reading unit to be read, and by operating the document conveying unit and the image reading unit in synchronization with each other, the image of the entire document is read and image data is generated.

In this type of image reading device, there is known one that performs skew correction on an image read by an image reading unit from an automatically conveyed original (for example, Patent Document 1). In order to properly perform skew correction, it is important to detect, for example, a skew angle indicating how much the image is tilted with respect to the main scanning direction read by the image reading unit. The prior art of Patent Document 1 is configured to detect the skew angle by detecting a shadow generated near the tip of the original in the image read by the image reading unit.

JP-A-2018-157417

By the way, when the original to be read by the image reading device is exposed to a low humidity environment, the moisture inside the original may evaporate and curl may occur at the end of the original. When this curl occurs on one side in the main scanning direction at the tip of the document, the shadow width gradually decreases from the curled part toward the uncurled part, and the boundary between the background area and the shadow area (shadow). It is possible that the edge) is not parallel to the edge of the tip of the document. In such a case, if the skew angle is detected based on the shadow generated near the tip of the document, an angle different from the skew angle of the actual image will be erroneously detected. Therefore, when a part of the edge of the original is curled, there is a problem that the image is deteriorated if the conventional skew correction is performed.

The present invention has been made to solve the above problem, and by determining the suitability of the skew angle based on the shadow detected near the edge of the document, a part of the edge of the document is curled. It is an object of the present invention to provide an image reading device, a skew angle determination method, and a program capable of preventing the image from being deteriorated by skew correction in such a case.

In order to achieve the above object, the invention according to claim 1 is an image reading device, in which a document transporting means for automatically transporting a document and a document transported by the document transporting means pass through a predetermined reading position. An image reading means for reading an image, a shadow detecting means for detecting a shadow appearing near the edge of a document in the image, and a skew angle detecting means for detecting the skew angle of the image based on the shadow. The configuration is characterized by comprising a skew angle determining means for determining the suitability of the skew angle based on the shape of the shadow.

The invention according to claim 2 is characterized in that, in the image reading device of claim 1, the skew angle determining means determines that the skew angle is unsuitable when the shape of the shadow is a substantially triangular shape. It is a composition.

The invention according to claim 3 is characterized in that, in the image reading device of claim 1 or 2, the skew angle determining means determines that the skew angle is appropriate when the shape of the shadow is not a substantially triangular shape. It is a configuration to do.

The invention according to claim 4 is the image based on the skew angle when the skew angle determining means determines that the skew angle is appropriate in the image reading device according to any one of claims 1 to 3. The configuration is characterized in that an image correction means for performing skew correction is further provided.

The invention according to claim 5 is the image reading apparatus according to any one of claims 1 to 4, wherein the document transporting means is between the image reading means and a background plate arranged so as to face the image reading means. The skew angle detecting means detects the skew angle by detecting the first boundary between the shadow and the background plate in the image.

The invention according to claim 6 is the image reading device according to claim 5, wherein the skew angle detecting means approximates the first boundary with a straight line, and the straight line is read by the image reading means in the main scanning direction or the sub. The configuration is characterized in that the angle formed with respect to the scanning direction is detected as the skew angle.

The invention according to claim 7 is the image reading device according to claim 5, wherein the skew angle determining means specifies the shape of the shadow based on the first boundary. ..

The invention according to claim 8 further includes, in the image reading device according to any one of claims 5 to 7, a document edge detecting means for detecting a second boundary between the shadow and the edge of the document in the image. The skew angle determining means is characterized in that the shape of the shadow is specified based on the first boundary and the second boundary.

According to a ninth aspect of the present invention, in the image reading device of the eighth aspect, the skew angle determining means has a substantially triangular shape of the shadow when the first boundary and the second boundary intersect. It is a configuration characterized by specifying that it is.

According to a tenth aspect of the present invention, in the image reading device of the ninth aspect, the skew angle determining means calculates a distance from each of a plurality of positions on the first boundary to the second boundary. The configuration is characterized in that when the distance is monotonically decreasing toward the center of the second boundary, it is determined that the first boundary intersects with the second boundary.

The invention according to claim 11 comprises a gradation value acquisition means for acquiring a gradation value for each pixel along a straight line that approximates the first boundary in the image reading device according to any one of claims 5 to 10. Further, a region determination means for determining which region of the background region, the shadow region, and the original region the straight line belongs to based on the gradation value for each pixel acquired by the gradation value acquisition means is provided. The skew angle determining means is configured to specify that the shape of the shadow is a substantially triangular shape when at least a part of the straight line is determined to belong to the original region by the area determining means. ..

According to a twelfth aspect of the present invention, in the image reading device according to the eleventh aspect, in the skew angle determining means, the straight line belongs to two shadow regions by the area determining means, and between the two shadow regions. When it is determined that the portion of the shadow belongs to the background region, the configuration is characterized in that it is specified that the shape of the shadow is not a substantially triangular shape.

According to a thirteenth aspect of the present invention, in the image reading device according to claim 11, when the area determination means equals the gradation value acquired by the gradation value acquisition means to the original gradation value specified in advance. The configuration is characterized in that the pixel on the straight line is discriminated as a document area.

The invention according to claim 14 is the image reading apparatus according to claim 11, wherein the area determination means equals the background plate gradation value to which the gradation value acquired by the gradation value acquisition means is set in advance. In this case, the configuration is characterized in that the pixel on the straight line is determined as a background region.

The invention according to claim 15 states that in the image reading device according to any one of claims 1 to 14, the skew angle is unsuitable when the skew angle determining means determines that the skew angle is unsuitable. The configuration is characterized by further including a notification means for notifying.

The invention according to claim 16 includes an image reading means for automatically transporting a document and an image reading means for reading an image when the document transported by the document transporting means passes through a predetermined reading position. A skew angle determination method for determining the suitability of the skew angle of an image read from a document in the apparatus, based on a shadow detection step of detecting a shadow appearing near the edge of the document in the image and the shadow. The configuration is characterized by having a skew angle detecting step for detecting the skew angle of the image and a skew angle determining step for determining the suitability of the skew angle based on the shape of the shadow.

The invention according to claim 17 comprises an image reading means for automatically transporting a document and an image reading means for reading an image when the document transported by the document transporting means passes through a predetermined reading position. A program executed by the device, the image reading device detects a shadow detecting step for detecting a shadow appearing near the edge of a document in the image, and a skew angle of the image based on the shadow. The configuration is characterized in that a skew angle detection step and a skew angle determination step for determining the suitability of the skew angle based on the shape of the shadow are executed.

According to the present invention, it is possible to determine whether or not a part of the document edge is curled based on the shadow detected near the edge of the document, and the part of the document edge is curled. If this is the case, it is possible to prevent the image from being deteriorated by the skew correction when a part of the edge of the document is curled by determining that the skew angle is inappropriate.

It is a figure which shows one configuration example of the image processing apparatus equipped with an image reading apparatus. It is sectional drawing which shows the internal structure of an image reader. It is a block diagram which shows an example of the control mechanism of an image processing apparatus. It is a block diagram which shows the control mechanism of an image reader. It is a block diagram which shows the structural example of the image processing part for performing skew correction. It is a figure which shows the example which the 1st image reading unit reads an image of a document. It is a figure which shows an example of the image read by a reading sensor. It is a figure which shows the example which detects the inclination of a straight line with respect to the main scanning direction as a skew angle. It is a figure which illustrates the mode of reading the document which the edge is curled. It is a figure which shows the image which read the original which curled on one side of the tip part. It is a figure which shows an example of the process which detects the edge of a document. It is a figure which shows an example of the processing concept which determines the shape of a shadow. It is a flowchart which shows an example of the processing procedure performed in an image reader. It is a flowchart which shows an example of the detailed processing procedure of the skew angle determination processing. It is a figure which shows the example of a different shadow when a manuscript is curled. It is a block diagram which shows the structural example of the image processing part in 2nd Embodiment. It is a figure which shows the example of the pixel which the gradation value acquisition part acquires a gradation value. It is a figure which shows an example of the gradation value acquired from the pixel on a straight line. It is a figure which shows the example which curl occurs on both sides of the document edge. It is a figure which shows the image which read the original which has two even curls on both sides of the original edge.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the embodiments described below, the elements common to each other are designated by the same reference numerals, and duplicate description thereof will be omitted.

(First Embodiment)
FIG. 1 is a diagram showing a configuration example of an image processing device 1 equipped with an image reading device 2 according to an embodiment of the present invention. The XYZ three-dimensional coordinate system shown in FIG. 1 is a coordinate system having an XY plane as a horizontal plane and a Z direction as a vertical direction, and is a coordinate system common to the coordinate system shown in FIG.

The image processing device 1 is a device configured as an MFP having a scan function, a copy function, and a print function, and executes a scan job, a copy job, a print job, and the like.

The image processing device 1 includes an image reading device 2 on the upper part of the device main body. The image reading device 2 is a device that automatically conveys the originals set by the user one by one and reads the image of the originals. The image reading device 2 includes a document transporting unit 3 and a scanner unit 4 arranged below the document transporting unit 3. The document transport unit 3 is, for example, a device called an ADF (Auto Document Feeder), which takes out documents set by the user one by one and automatically transports them. The scanner unit 4 optically scans the image of the document when the document automatically conveyed by the document transfer unit 3 passes through a predetermined reading position. For example, when the document passes through the scanning position, the scanner unit 4 illuminates the surface to be scanned of the document and receives the reflected light from the surface to be scanned of the document to read the image in the main scanning direction of the document. Then, the scanner unit 4 repeatedly reads the image in the sub-scanning direction orthogonal to the main scanning direction by continuously performing the operation of reading the image in the main scanning direction of the document in synchronization with the transport operation of the document. That is, the scanner unit 4 reads the image of the entire document by performing a scanning operation synchronized with the document transporting operation.

Further, the image processing device 1 includes a printer unit 5 below the image reading device 2. The printer unit 5 is a device that prints and outputs an image on a sheet such as printing paper based on the image data to be printed. For example, the printer unit 5 takes out sheets one by one from a sheet bundle composed of a plurality of sheets to be accommodated in advance, feeds them, and prints an image based on image data when the sheets pass through a predetermined position. The printer unit 5 outputs the sheet on which the image is printed to the output tray 5a provided on the upper part of the printer unit 5.

Further, the image processing apparatus 1 is provided with an operation panel 6 serving as a user interface on the front side of the apparatus main body. The operation panel 6 displays an operation screen that can be operated by the user, and accepts operations by the user. The image processing device 1 sets a job based on an operation by the user, and when the user instructs to execute the job, the image reading device 2 and the printer unit 5 are operated to operate the job specified by the user. To execute.

The user may select the type of the original to be read by the image reading device 2 and specify the reflectance of the original by performing an operation on the operation panel 6. If the reflectance of the document is known, the scanner unit 4 can specify the gradation value of the document when the document is read.

FIG. 2 is a cross-sectional view showing the internal structure of the image reading device 2. The scanner unit 4 includes a first image reading unit 20 that reads an image of the first surface (for example, the surface) of the document in the internal space 33 of the housing. The first image reading unit 20 includes a reading head 21 extending in the main scanning direction so as to read an image in the main scanning direction (X direction) of the document.

The reading head 21 includes a light source 22, a lens 23, and a reading sensor 24, and can move in the sub-scanning direction (Y direction) along the guide rail 34. The light source 22 is for illuminating the first surface of a document to be read, and is, for example, a line light source composed of an LED array in which a plurality of LEDs (Light Emitting Diodes) are arranged in the main scanning direction. The reading sensor 24 has a plurality of image reading elements arranged in the main scanning direction, and can read an image in the main scanning direction of the document. The lens 23 is a lens array arranged in the main scanning direction, and images the reflected light from the document on each of the plurality of image reading elements of the reading sensor 24.

The scanner unit 4 can move the first image reading unit 20 in the sub-scanning direction by a drive mechanism (not shown). On the upper surface side of the housing of the scanner unit 4, a contact glass 31 elongated in the main scanning direction and a substantially rectangular platen glass 32 are arranged at positions adjacent to each other in the sub-scanning direction. When the scanner unit 4 reads a document automatically conveyed by the document transfer unit 3, the scanner unit 4 arranges the scanning head 21 at a position below the contact glass 31 as shown in FIG. 2, and the document is placed on the upper surface side of the contact glass 31. Allows the first image reader 20 to read the image on the first surface of the document as it passes. In this case, the first image reading unit 20 is in a state of being stopped at a lower position of the contact glass 31 until the reading operation of all the documents is completed. Further, the scanner unit 4 can also read the image of the document placed on the platen glass 32 by the user. In this case, the first image reading unit 20 moves in the sub-scanning direction along the guide rail 34 while reading the image in the main scanning direction of the document, thereby moving the entire document placed on the platen glass 32 in the sub-scanning direction. Read the image of.

The document transport unit 3 has a document placing table 10 on which an image to be read is placed, and a paper ejection tray 16 for ejecting the document from which the image has been read. The tip portion 10a of the document mounting table 10 is rotatable around the rotation shaft 10b, and when the job execution start is instructed while the document is placed, the tip portion 10a of the document mounting table 10 is turned on. By lifting, the tip of the document is brought into contact with the pickup roller 11.

The pickup roller 11 is a roller that sends out the document at the top of the plurality of documents placed on the document mounting table 10 toward the document transport path 13. A paper feed roller 12 is provided on the downstream side of the pickup roller 11. The paper feed roller 12 is a roller that, when two or more originals are sent out by the pickup roller 11, only one original document at the top is sent out to the downstream original transfer path 13.

The document transport path 13 is a path for guiding documents from the document mounting table 10 toward the paper output tray 16. A plurality of transport rollers 14 are provided in the document transport path 13. Further, the document transport path 13 is provided with a paper ejection roller 15 at a position near the paper ejection tray 16 for ejecting the original paper toward the paper ejection tray 16. Further, the document transport path 13 is provided with a background plate 17 at a position facing the contact glass 31 of the scanner unit 4. The background plate 17 reflects the light of the light source 22 provided in the first image reading unit 20 with a high reflectance. For example, the reflectance of the background plate 17 is set to a value higher than the reflectance of the document transported through the document transport path 13. When the document conveyed through the document transfer path 13 passes through the position between the contact glass 31 and the background plate 17, the image of the first surface (for example, the surface) of the document is read by the first image reading unit 20. A gap is formed between the contact glass 31 and the background plate 17 so that the original can be passed through the gap, and a relatively thick original such as thick paper or embossed paper can be passed through the gap without any problem. Set to interval.

Further, the document transport path 13 is provided with a second image reading unit 26 at a predetermined position further downstream of the background plate 17. For example, assuming that the first image reading unit 20 is provided at the first position of the document transport path 13, the second image reading unit 26 is provided at a second position on the downstream side of the first position. ing. The second image reading unit 26 is for reading an image of the second surface (for example, the back surface) of the document transported through the document transport path 13. The second image reading unit 26 includes a light source 22, a lens 23, and a reading sensor 24, similarly to the first image reading unit 20. Further, a background plate 18 is provided at a position facing the second image reading unit 26 across the document transport path 13. Like the background plate 17, the background plate 18 has a reflectance higher than that of the original. When the document conveyed through the document transfer path 13 passes through the position between the second image reading unit 26 and the background plate 18, the second image reading unit 26 displays an image of the second surface (for example, the back surface) of the document by the second image reading unit 26. Read.

As described above, the image reading device 2 of the present embodiment has a configuration capable of reading both the front and back sides of the original while the original is conveyed once along the original conveying path 13. However, the present invention is not limited to this, and the image reading device 2 may include only the first image reading unit 20. In that case, the image reading device 2 may be provided with a reversing path for inverting the front and back of the document in the document transport path 13 in order to read the back surface of the document. By providing the inversion path in the document transport path 13, the first image reading unit 20 can read both the front and back surfaces of the document.

Next, the control mechanism of the image processing device 1 will be described. FIG. 3 is a block diagram showing an example of the control mechanism of the image processing device 1. The image processing device 1 includes a system controller 40, a network interface 41, and an image memory 42 in addition to the image reading device 2, the printer unit 5, and the operation panel 6 described above. The system controller 40 is for controlling the overall operation of the image processing device 1. The network interface 41 is for connecting the image processing device 1 to a network such as a LAN and communicating with an external device. The image memory 42 is a memory for storing image data generated by executing a job and image data to be executed by the job. The system controller 40 controls the execution of a job designated by the user by comprehensively controlling each of the network interface 41, the operation panel 6, the image reading device 2, the image memory 42, and the printer unit 5.

Next, FIG. 4 is a block diagram showing a control mechanism of the image reading device 2. The image reading device 2 includes a control unit 45, an input / output interface 46, a transport driving unit 47, a first image reading unit 20, and a second image reading unit 26.

The control unit 45 controls the operation of each unit. The control unit 45 includes a CPU 48 and a memory 49. The CPU 48 is a hardware processor that reads out and executes a program 50 stored in the memory 49. The memory 49 is a non-volatile storage device composed of, for example, a semiconductor memory, and stores the program 50.

The input / output interface 46 inputs / outputs data to / from the system controller 40 and the image memory 42. The control unit 45 can receive the document reading instruction output from the system controller 40 via the input / output interface 46, and starts the image reading operation of the document when the document reading instruction is received. Further, the control unit 45 can output image data via the input / output interface 46 and store it in the image memory 42.

The transport drive unit 47 drives various rollers such as the transport roller 14 provided in the document transport unit 3, takes out the documents set on the document mounting table 10 one by one, and automatically transports the documents along the document transport path 13. do. For example, the transport drive unit 47 transports the document at a constant speed along the document transport path 13.

Each of the first image reading unit 20 and the second image reading unit 26 includes an AD conversion unit 29 in addition to the light source 22 and the reading sensor 24 described above. The AD conversion unit 29 converts the analog signal output from the reading sensor 24 into a digital signal. The first image reading unit 20 and the second image reading unit 26 output the image data converted into a digital signal by the AD conversion unit 29 to the control unit 45.

By executing the program 50, the CPU 48 of the control unit 45 functions as a transfer control unit 51, a read control unit 52, an image acquisition unit 53, and an image processing unit 54. The transport control unit 51 controls the automatic transport of the documents set on the document mounting table 10 by driving the transport drive unit 47. The reading control unit 52 drives the light source 22 and the reading sensor 24 provided in each of the first image reading unit 20 and the second image reading unit 26 in synchronization with the document transport operation by the transport control unit 51. , Control the reading operation of the document. When reading only the first surface of the document, the reading control unit 52 may operate only the first image reading unit 20.

The image acquisition unit 53 acquires image data output from each of the first image reading unit 20 and the second image reading unit 26.

The image processing unit 54 performs image processing on the image data as the image acquisition unit 53 acquires the image data. For example, the image processing unit 54 performs skew correction on the images read by each of the first image reading unit 20 and the second image reading unit 26 on the automatically conveyed original. Skew correction is a process for correcting the inclination of an image read from a document when it is inclined in the main scanning direction or the sub-scanning direction. In addition to skew correction, the image processing unit 54 can perform various image processing such as background adjustment processing.

FIG. 5 is a block diagram showing a configuration example of the image processing unit 54 for performing skew correction. As shown in FIG. 5, the image processing unit 54 includes a shadow detection unit 61, a skew angle detection unit 62, an image correction unit 63, a document edge detection unit 64, a skew angle determination unit 65, and a notification unit 68. And have. In the following, in order to simplify the explanation, the processing when the first image reading unit 20 reads the image of the original is illustrated.

The shadow detection unit 61 detects shadows appearing near the edge of the document in the image read by the first image reading unit 20. This will be explained in detail.

FIG. 6 is a diagram showing an example in which the first image reading unit 20 reads an image of a document. As shown in FIG. 6A, the document 9 conveyed in the direction of arrow F1 by the document transfer unit 3 passes through the gap 8 between the background plate 17 and the contact glass 31, and the first image reading unit 20 Read by. At this time, the document 9 normally passes through the reading reference position Pz at the center of the gap 8.

The first image reading unit 20 includes a first light source 22a arranged on the upstream side of the reading sensor 24 and a second light source 22b arranged on the downstream side of the reading sensor 24 as a light source 22 for illuminating the document 9. ing. The first light source 22a has a higher illuminance than the second light source 22b and is configured to illuminate the document brightly. As shown in FIG. 6A, when the document 9 does not reach between the background plate 17 and the contact glass 31, the light emitted from each of the first light source 22a and the second light source 22b is the background plate 17. The reflected light is incident on the reading sensor 24.

When the tip of the document 9 enters between the background plate 17 and the contact glass 31, as shown in FIG. 6B, the tip of the document 9 is conveyed because it blocks the light emitted from the first light source 22a. A shadow 28 is formed on the downstream side of the direction F1. Therefore, the image read by the reading sensor 24 is an image in which the shadow 28 is reflected on the tip end portion of the document 9.

FIG. 7 is a diagram showing an example of an image read by the reading sensor 24. As shown in FIG. 6B, when the reading sensor 24 reads a normal document 9 having no curl at the tip of the document 9, the image obtained thereby is an image as shown in FIG. 7A. It becomes. That is, the image is an image in which the shadow 28 of the light emitted from the first light source 22 is reflected on the tip of the document 9.

The shadow detection unit 61 detects the shadow 28 reflected in the image by analyzing the image obtained from the reading sensor 24. Before the tip of the document 9 enters the gap 8 between the background plate 17 and the contact glass 31, the reading sensor 24 receives the reflected light from the background plate 17, so that each pixel read by the reading sensor 24. The gradation value of is relatively high. On the other hand, when the tip portion of the document 9 enters the gap 8 between the background plate 17 and the contact glass 31 and the reading sensor 24 begins to receive light on the shadow 28 portion, the gradation value of each pixel gradually decreases. It will become. The shadow detection unit 61 detects the shadow 28 by extracting the portion of the tip of the document 9 whose gradation value is lowered as described above.

For example, since the gradation value of the background plate 17 is unique to the image reading device 2, it can be stored in advance in a memory 49 or the like. In that case, the shadow detection unit 61 compares the background plate gradation value stored in the memory 49 with the gradation value of each pixel, and the difference between the gradation value of each pixel and the background plate gradation value is predetermined. When it becomes more than a value, it can be determined that it is a shadow 28.

When the shadow 28 is detected by the shadow detection unit 61, the skew angle detection unit 62 functions. The skew angle detection unit 62 detects the skew angle of the image read by the reading sensor 24. Specifically, the skew angle detection unit 62 detects the skew angle of the image based on the shadow 28 detected by the shadow detection unit 61. This will be explained in detail.

When the shadow 28 is detected from the image read by the reading sensor 24 as shown in FIG. 7A, the skew angle detection unit 62 first detects the boundary between the shadow 28 and the background plate 17 as the first boundary. do. For example, the skew angle detection unit 62 specifies pixels located at the boundary between the shadow 28 and the background plate 17 in the sub-scanning direction (horizontal direction) of the image shown in FIG. 7A in order in the main scanning direction (vertical direction). Then, the positions of the plurality of pixels are detected as the first boundary. The first boundary detected in this way varies from pixel to pixel and may not be aligned on a straight line. Therefore, as shown in FIG. 7B, the skew angle detection unit 62 calculates a straight line L1 that approximates the first boundary. If the plurality of pixels detected as the first boundary are located on the straight line L1 without being close to each other, the skew angle detection unit 62 may specify the straight line L1.

When the skew angle detection unit 62 obtains a straight line L1 corresponding to the first boundary between the shadow 28 and the background plate 17, the reading sensor 24 reads an image in the main scanning direction (X direction) or the sub scanning direction (Y). The slope of the straight line L1 with respect to the direction) is calculated, and the slope is detected as the skew angle. FIG. 8 is a diagram showing an example of detecting the inclination of the straight line L1 with respect to the main scanning direction as the skew angle θ. As shown in FIG. 8, the skew angle detection unit 62 calculates the inclination of the straight line L1 with respect to the main scanning direction (X direction), and detects the inclination as the skew angle θ. However, the present invention is not limited to this, and the skew angle detection unit 62 may calculate the inclination of the straight line L1 with respect to the sub-scanning direction (Y direction) and detect the inclination as the skew angle θ. When the skew angle detection unit 62 detects the skew angle θ, the skew angle detection unit 62 outputs the skew angle θ to the image correction unit 63.

The image correction unit 63 performs skew correction on the image in which the original is read, based on the skew angle θ detected by the skew angle detection unit 62. For example, in the case of an image as shown in FIG. 8, the image correction unit 63 corrects the straight line L1 so as to be parallel to the main scanning direction by rotating the image clockwise based on the skew angle θ. Further, when the skew angle detection unit 62 calculates the inclination of the straight line L1 with respect to the sub-scanning direction (Y direction) and detects the skew angle θ, the image correction unit 63 rotates the image so that the straight line L1 is in the sub-scanning direction. Correct so that it is parallel to. By such skew correction, the image obtained by scanning the document 9 becomes an image without tilt.

When no curl is generated at the tip of the document 9 in this way, the shadow 28 appearing at the tip of the document 9 has a substantially rectangular shape. Therefore, if the first boundary between the shadow 28 and the background plate 17 is detected and the skew angle θ is obtained, the skew angle θ is the same as the inclination of the tip portion of the document 9. Therefore, the image correction unit 63 can appropriately perform skew correction on the image.

Next, FIG. 9 is a diagram illustrating an embodiment of reading a document 9 having a curled end. For example, as shown in FIG. 9A, it is assumed that the curl 9a is generated on one side of the tip end portion of the document 9 in the transport direction F1. When the manuscript 9 enters between the background plate 17 and the contact glass 31 with the curl 9a facing downward, the tip of the curl 9a approaches the reading sensor 24 and the surface of the contact glass 31 is as shown in FIG. 9B. At the same time, the bent portion of the curl 9a pushes up the uncurled portion upward, so that the uncurled portion is in a state close to the background plate 17. That is, in this case, most of the document 9 does not pass through the reading reference position Pz, the tip of the curl 9a passes through a position close to the reading sensor 24, and the portion other than the curl 9a passes through a position far from the reading sensor 24. When the document 9 is illuminated by the light source 22a, a shadow 28 is generated only at the tip of the document 9 where the curl 9a is generated.

FIG. 10 is a diagram showing an image obtained by scanning a document 9 having a curl 9a on one side of the tip portion. When the curl 9a is generated on one side of the tip portion of the document 9, the shadow 28 is reflected only on one side of the tip portion of the document 9 in the scanned image as shown in FIG. 10 (a). Similar to the above, when the first boundary between the background plate 17 and the shadow 28 is detected for such an image and the straight line L1 that approximates the first boundary is obtained, it is as shown in FIG. 10 (b). Obtain a straight line L1. However, since the straight line L1 is clearly not parallel to the edge of the tip of the document 9, if the skew angle is detected based on the straight line L1, appropriate skew correction cannot be performed.

Therefore, as shown in FIG. 5, the image reading device 2 of the present embodiment includes a document edge detecting unit 64 and a skew angle determining unit 65, and the edge of the document 9 to be read is curled. I am trying to determine whether or not it is.

The document edge detection unit 64 is a processing unit that detects the edge of the document 9. For example, the document edge detection unit 64 detects the edge of the document 9 by detecting the second boundary between the shadow 28 and the document 9 in the image read by the reading sensor 24. FIG. 11 is a diagram showing an example of a process for detecting an end portion of a document 9. First, as shown in FIG. 11A, the document edge detection unit 64 predicts the position where the tip of the document 9 is located in the sub-scanning direction, and is within a predetermined range in the sub-scanning direction including the predicted position ( For example, the range from the position Y1 to the position Y2) is set as the document edge search area. The document edge detection unit 64 selects one position Xp in the main scanning direction in the document edge search area, and examines the gradation value change in the sub-scanning direction at that position Xp. FIG. 11B is a diagram showing a change in gradation value in the line segment Lp shown in FIG. 11A. The position Y1 in the sub-scanning direction is a position where the background plate 17 is reflected, and the gradation value thereof shows the highest value (background plate gradation value). As the shadow 28 appears in the image from the position Y1 to the position Y2, the gradation value gradually starts to decrease. This shadow 28 is darkest in the vicinity of the edge of the document 9. Then, in the area where the document 9 is reflected, the gradation value becomes higher than that of the shadow 28 portion. The document edge detection unit 64 detects the edge of the document 9 by detecting the rising portion H that switches from the shadow 28 to the document 9. That is, the pixel at the position of the rising portion H is specified as the end portion of the document 9. In other words, the document edge detection unit 64 can identify whether each pixel on the line segment Lp belongs to the background region, the shadow region R2, or the document region R3, and the shadow region R2 can be identified. The second boundary between the document and the document area R4 is detected as the end of the document 9. When the sub-scanning direction position of the end of the document 9 is detected at one position Xp in the main scanning direction as described above, the document edge detecting unit 64 switches the position Xp in the main scanning direction to another position and similarly. Is processed. By repeating this, the document edge detection unit 64 can detect the edge 9e of the document 9 as shown in FIG. 11 (c).

When the edge of the document 9 is detected by the document edge detection unit 64, the skew angle determination unit 65 functions. The skew angle determination unit 65 determines the suitability of the skew angle θ detected by the skew angle detection unit 62. That is, when the curl 9a is generated at the end of the document 9, the skew angle θ detected by the skew angle determination unit 65 is different from the edge of the end of the document 9, so that such skew is achieved. If skew correction is performed based on the angle θ, the image will be deteriorated. In order to prevent this, the skew angle determination unit 65 determines whether or not the skew angle θ detected by the skew angle detection unit 62 is an appropriate angle as the angle used for the skew correction.

As shown in FIG. 10A, when the curl 9a is generated on one side of the end of the document 9, the shadow 28 appearing at the end of the document 9 does not have a substantially rectangular shape but a substantially triangular shape. .. Therefore, the skew angle determination unit 65 determines the suitability of the skew angle θ based on the shape of the shadow 28 detected by the shadow detection unit 61. For example, when the shape of the shadow 28 detected by the shadow detection unit 61 is substantially triangular, the skew angle determination unit 65 determines that the skew angle θ detected by the skew angle detection unit 62 is inappropriate.

FIG. 12 is a diagram showing an example of a processing concept for determining the shape of the shadow 28 in the skew angle determination unit 65. The skew angle determination unit 65 includes a straight line L1 indicating a first boundary between the shadow 28 detected by the skew angle detection unit 62 and the background plate 17, and a second shadow 28 and the document 9 by the document edge detection unit 64. The shape of the shadow 28 is specified based on the end portion 9e of the document 9 detected as the boundary of the shadow 28. For example, when the straight line L1 and the end portion 9e of the document 9 intersect with each other, the skew angle determination unit 65 can specify that the shadow 28 is a substantially triangular shape.

For example, as shown in FIG. 12, the skew angle determination unit 65 has distances D1, D2, D3, ... From each of the plurality of positions P1, P2, P3, ... , Dn is calculated. These distances D1, D2, D3, ..., Dn may be calculated by counting the number of pixels. Then, the skew angle determination unit 65 monotonically decreases the distances D1, D2, D3, ..., Pn toward the substantially center position of the end portion 9e of the document 9, and the straight line L1 and the end portion of the document 9. It is determined that 9e and 9e intersect with each other.

Further, in addition to the directions for calculating the distances D1, D2, D3, ..., Dn as described above, for example, the skew angle determination unit 65 has the inclination of the end portion 9e of the document 9 and the inclination of the straight line L1 (skew). It may be determined that the shadow 28 is a substantially triangular shape by comparing with the angle θ) and when the difference in inclination is equal to or larger than a predetermined value.

When the skew angle determination unit 65 determines that the shape of the shadow 28 is substantially triangular and the skew angle θ is inappropriate, the determination result is output to the image correction unit 63. When the skew angle determination unit 65 determines that the skew angle θ is inappropriate, the image correction unit 63 does not perform skew correction based on the skew angle θ. This makes it possible to prevent the image output from the image reading device 2 from deteriorating.

Further, when the skew angle determination unit 65 determines that the shape of the shadow 28 is substantially triangular and the skew angle θ is inappropriate, the skew angle determination unit 65 causes the notification unit 68 to function. The notification unit 68 displays a notification screen on the operation panel 6 via, for example, the system controller 40, and notifies the user instructed to execute the job that normal skew correction has not been performed. At this time, the notification unit 68 may notify that the end portion of the document 9 is curled. With such a notification, the user can know that normal skew correction has not been performed, and in order to obtain a high-quality image, the edges of the document 9 are corrected to be uncurled. You can understand that you should execute the job again.

FIG. 13 is a flowchart showing an example of a processing procedure performed in the image reading device 2 having the above configuration. This process is performed by the CPU 48 of the control unit 45 executing the program 50. Note that FIG. 13 illustrates, as an example, a case where the first image reading unit 20 reads an image on the first surface of the document 9.

When the image reading device 2 detects a job execution start instruction by the user, the image reading device 2 drives the transport driving unit 47 to start transporting the document 9 (step S10). Then, the image reading device 2 drives the first image reading unit 20 when the document 9 transported along the document transport path 13 passes through the reading position between the background plate 17 and the contact glass 31, and the document 9 is driven. The image reading of the first surface of the above surface is started (step S11).

When the image reading device 2 starts reading an image by the first image reading unit 20, the shadow detecting unit 61 is made to function. Then, the image reading device 2 performs a shadow detecting process for detecting the shadow 28 included in the image output from the first image reading unit 20 (step S12). Next, the image reading device 2 makes the skew angle detection unit 62 function, and detects the skew angle θ of the image based on the shadow 28 detected from the image (step S13). That is, the skew angle detection unit 62 detects the first boundary between the background plate 17 and the shadow 28 in the image acquired from the first image reading unit 20, approximates the first boundary with a straight line L1, and skews the image. The angle θ is detected.

Then, the image reading device 2 executes the skew angle determination process (step S14). FIG. 14 is a flowchart showing an example of a detailed processing procedure of the skew angle determination processing (step S14). When the skew angle determination process is started, the image reading device 2 makes the document edge detection unit 64 function and performs the document edge detection process (step S20). That is, the document edge detection unit 64 detects the edge of the document 9 by detecting the second boundary between the document 9 and the shadow 28 in the image acquired from the first image reading unit 20.

Next, the image reading device 2 causes the skew angle determination unit 65 to function. The skew angle determination unit 65 specifies the shape of the shadow based on the first boundary between the background plate 17 and the shadow 28 and the second boundary between the document 9 and the shadow 28 (step S21). Then, the skew angle determination unit 65 determines whether or not the shape of the shadow 28 appearing near the end portion of the document 9 is a substantially triangular shape (step S22). As a result, when the shape of the shadow 28 is substantially triangular (YES in step S22), the skew angle determination unit 65 determines that the skew angle θ detected in step S13 is inappropriate (step S23). On the other hand, when the shape of the shadow 28 is not substantially triangular (NO in step S22), the skew angle determination unit 65 determines that the skew angle θ detected in step S13 is appropriate (step S24). This completes the skew angle determination process.

Returning to the flowchart of FIG. 13, the image reading device 2 then determines whether or not the skew angle θ is determined to be appropriate in the skew angle determination process (step S15). When it is determined that the skew angle θ is appropriate (YES in step S15), the image reading device 2 causes the image correction unit 63 to function, and skew correction processing of the image is performed based on the skew angle θ detected in step S13. Is executed (step S16). Then, the image reading device 2 outputs the skew-corrected image (step S17).

On the other hand, when it is determined that the skew angle θ is inappropriate (NO in step S15), the image reading device 2 outputs the image without performing skew correction on the image (step S18). Then, the image reading device 2 makes the notification unit 68 function, and notifies that the skew angle θ detected for skew correction is inappropriate (step S19). This completes the processing by the image reading device 2. When continuously reading a plurality of originals 9, the image reading device 2 repeatedly performs the above processing to determine whether the skew angle θ is appropriate one by one. ..

Further, in the above, the process when the first image reading unit 20 reads the image on the first surface of the document 9 is illustrated, but the second image reading unit 26 reads the image on the second surface of the document 9. In this case, the same processing as above can be applied.

As described above, the image reading device 2 of the present embodiment can read the image of the document 9 when the document 9 conveyed by the document conveying unit 3 passes through a predetermined reading position, and the document 9 can read the image. A shadow 28 appearing near the end of the original 9 in the image scanned when passing through a predetermined scanning position is detected, and the skew angle θ of the image is detected based on the shadow 28 to perform skew correction of the image. It is configured as follows. The image reading device 2 is provided with a configuration for determining whether or not the skew angle θ detected for skew correction is appropriate based on the shape of the shadow 28 appearing near the end of the document 9. There is. According to such a configuration, when the curl 9a is generated on one side of the tip portion of the document 9, it is possible to determine that the skew angle θ detected for skew correction is inappropriate. .. That is, the image reading device 2 of the present embodiment can determine erroneous detection of the skew angle θ when the document 9 is curled, and prevents the image from being deteriorated by skew correction. It is configured to be able to.

In the above description, when the skew angle θ is inappropriate, the image reading device 2 outputs an image without performing skew correction on the image, but the present invention is not limited to this, and the skew angle is not limited to this. Even if θ is inappropriate, the image may be output after skew correction is performed on the image. Further, when the skew angle θ is inappropriate, the image reading device 2 may output two images, an image without skew correction and an image with skew correction.

Further, in the above, the case where the shadow 28 appears in the vicinity of the edge of the document 9 along the sub-scanning direction of the edge of the document 9 is illustrated. However, depending on the arrangement mode of the light source 22, a shadow 28 may appear along the main scanning direction of the end portion of the document 9, for example, as shown in FIG. Even if a shadow 28 appears in the main scanning direction at the end of the document 9 as shown in FIG. 15, the skew angle θ can be detected by applying the same processing as the above processing. By performing the same processing as above, it is possible to determine the suitability of the skew angle θ.

(Second Embodiment)
Next, the second embodiment of the present invention will be described. In the present embodiment, a process different from that of the first embodiment will be described as a process for determining the suitability of the skew angle θ. In the following, the parts different from the first embodiment will be described.

FIG. 16 is a block diagram showing a configuration example of the image processing unit 54 in the second embodiment. As shown in FIG. 5, the image processing unit 54 includes a shadow detection unit 61, a skew angle detection unit 62, an image correction unit 63, a skew angle determination unit 65, a gradation value acquisition unit 66, and an area determination unit. 67 and a notification unit 68 are provided. Of these, each of the shadow detection unit 61, the skew angle detection unit 62, the image correction unit 63, and the notification unit 68 is the same as that described in the first embodiment. In the following, in order to simplify the explanation, a case where the first image reading unit 20 reads the image of the original is illustrated.

The shadow detection unit 61 detects the shadow 28 appearing at the end of the image read by the reading sensor 24, as in the first embodiment. The skew angle detection unit 62 identifies the first boundary between the background plate 17 and the shadow 28 in the image read by the reading sensor 24, and obtains a straight line L1 that approximates the first boundary. Then, the skew angle detection unit 62 detects the skew angle θ of the image based on the inclination of the straight line L1.

When the skew angle detection unit 62 obtains the straight line L1 corresponding to the first boundary between the background plate 17 and the shadow 28, the gradation value acquisition unit 66 acquires the gradation values of the pixels located on the straight line L1. do. FIG. 17 is a diagram showing an example of pixels in which the gradation value acquisition unit 66 acquires gradation values. The gradation value acquisition unit 66 specifies pixels P1, P2, P3, P4, ..., Pm, ..., Pn located on a straight line L1 that approximates the first boundary between the background plate 17 and the shadow 28 in order. Then, the gradation values of the specified images P1, P2, P3, P4, ..., Pm, ..., Pn are acquired.

The area determination unit 67 determines the area to which each pixel on the straight line L1 belongs based on the gradation value acquired by the gradation value acquisition unit 66. FIG. 18 is a diagram showing an example of gradation values acquired from pixels on the straight line L1. As shown in FIG. 18, the straight line L1 is any one of three areas: a background area R1 in which the background plate 17 is reflected, a shadow area R2 in which the shadow 28 is reflected, and a document area R3 in which the document 9 is reflected. Belongs to. The area determination unit 67 determines which area each pixel belongs to by analyzing the gradation value of each pixel on the straight line L1.

For example, the area determination unit 67 acquires the background plate gradation value V1 stored in the memory 49, and the background area R1 is a pixel whose difference from the background plate gradation value V1 is less than a predetermined value. Specify as.

Further, the area determination unit 67 acquires a preset shadow determination threshold value Vth, and identifies pixels having a gradation value less than the shadow determination threshold value Vth as the shadow area R2.

Further, the area determination unit 67 acquires, for example, a document gradation value V2 designated in advance by the user, and identifies pixels having a gradation value equal to the document gradation value V2 as the document area R3. The document gradation value V2 is specified by the user according to the type of the document 9, for example, when the user performs a scan job setting operation. Further, the original gradation value V2 may be automatically detected by the area discrimination unit 67. For example, the area discrimination unit 67 cuts out an image of a portion of the image read by the reading sensor 24 in which the document 9 is shown, and creates a histogram based on the gradation value of each pixel included in the cut out image. .. Then, the area discrimination unit 67 may acquire the gradation value indicating the frequency peak in the histogram as the original gradation value V2.

As described above, the area determination unit 67 determines whether each pixel on the straight line L1 belongs to the background area R1, the shadow area R2, or the document area R3. Then, the area discrimination unit 67 outputs the discrimination result to the skew angle determination unit 65.

The skew angle determination unit 65 determines the suitability of the skew angle θ detected by the skew angle detection unit 62 by specifying the shape of the shadow 28 based on the region including the straight line L1. For example, when at least a part of the straight line L1 belongs to the document area R3, the straight line L1 intersects the document area R3. Therefore, the skew angle determination unit 65 identifies that the shape of the shadow 28 is a substantially triangular shape when at least a part of the straight line L1 belongs to the document region R3, and determines that the skew angle θ is inappropriate. If it is determined that the skew angle θ is inappropriate, the skew angle determination unit 65 outputs the determination result to the image correction unit 63. Further, the skew angle determination unit 65 causes the notification unit 68 to function to perform a process of notifying the user that normal skew correction has not been performed.

As described above, the image reading device 2 of the present embodiment is composed of a gradation value acquisition unit 66 that acquires a gradation value for each pixel along a straight line L1 that approximates the first boundary, and a gradation value acquisition unit 66. A region determination unit 67 for determining which region of the background region R1, the shadow region R2, and the original region R3 the straight line L1 belongs to based on the acquired gradation value for each pixel is provided, and the skew angle determination is determined. When the region 65 determines that at least a part of the straight line L1 belongs to the document region R3 by the region discrimination unit 67, it is specified that the shape of the shadow 28 is a substantially triangular shape, and it is determined that the skew angle θ is inappropriate. do. Even with such a configuration, when the curl 9a is generated on one side of the tip portion of the document 9, the skew angle θ detected for skew correction is inappropriate, as in the first embodiment. It is possible to reliably determine that. That is, even in the image reading device 2 of the present embodiment, it is possible to determine erroneous detection of the skew angle θ when the document 9 is curled, and it is possible to prevent the image from being deteriorated by the skew correction. It is possible.

The points other than those described above in the present embodiment are the same as those described in the first embodiment.

(Modification example)
Although the embodiments relating to the present invention have been described above, the present invention is not limited to the contents described in the above embodiments, and various modifications can be applied.

For example, in the above embodiment, when the curl 9a is generated on one side of the tip of the document 9, it is detected to determine that the skew angle θ detected based on the shadow 28 is inappropriate. explained. On the other hand, as shown in FIG. 19, curls 9a and 9b may occur on both sides of the tip of the original document 9. As shown in FIG. 19, when curls 9a and 9b are generated on both sides of the tip of the document 9, if the two curls 9a and 9b are evenly curled with each other, the image of the document 9 in the image read by the reading sensor 24 Two even shadows 28 appear at the tip. FIG. 20 is a diagram showing a scanned image of a document 9 in which two even curls 9a and 9b are generated at the tip portion. As shown in FIG. 20A, two shadows 28 are reflected in the image read by the reading sensor 24 in the vicinity of the end portion of the document 9. In this case, the shadow detection unit 61 detects two shadows 28 in the vicinity of the end portion of the document 9. When a plurality of shadows 28 are detected near the end of the document 9, the skew angle detection unit 62 specifies the tip positions of the plurality of shadows 28 and approximates the straight line L1 connecting the tip positions. As a result, a straight line L1 as shown in FIG. 20 (b) can be obtained. That is, when a plurality of shadows 28 are detected near the edge of the document 9, the skew angle detection unit 62 is a straight line that approximates the first boundary between the shadow 28 and the background plate 17 as described in the above embodiment. Instead of finding, the straight line L1 connecting the tip positions of the plurality of shadows 28 is found. The straight line L1 thus obtained is in a state substantially parallel to the edge of the end portion of the document 9. In this case, the skew angle determination unit 65 may determine the suitability of the skew angle θ based on the straight line L1 shown in FIG. 20 (b). For example, as described in the second embodiment, when the suitability of the skew angle θ is determined by the skew angle determination unit 65 based on the region to which the straight line L1 belongs, the straight line L1 shown in FIG. 20B has two lines. It is specified that it belongs to the shadow region R2 and the portion between the two shadow regions R2 belongs to the background region R1. Therefore, in the skew angle determination unit 65, when the straight line L1 belongs to the two shadow regions R2 and the portion between the two shadow regions R2 belongs to the background region R1, the shape of the shadow 28 is substantially triangular. It should be judged that it is not. As a result, the image correction unit 63 performs skew correction on the image.

If the two curls 9a and 9b generated on both sides of the tip of the document 9 are not equal to each other, the substantially triangle of one shadow 28 becomes larger than the substantially triangle of the other shadow 28, and the two shadows 28 The straight line L1 connecting the tip positions is not substantially parallel to the edge of the end portion of the document 9. Therefore, the skew angle determination unit 65 determines whether or not the sizes of the two shadows 28 are equal, and the straight line L1 connecting the tip positions of the two shadows 28 is parallel to the edge of the tip portion of the document 9. If it is not parallel, it may be determined that the skew angle θ is inappropriate.

Further, in the above embodiment, the skew correction when the first image reading unit 20 mainly reads the document 9 has been described. However, the above-mentioned skew correction is not applicable only when the first image reading unit 20 reads the first surface of the document 9, and the second image reading unit 26 reads the second surface of the document 9. Of course, it can also be applied to cases.

Further, in the above embodiment, the light sources 22a and 22b are arranged on both the upstream side and the downstream side of the document reading position as the light source 22 for illuminating the document 9 in the first image reading unit 20 and the second image reading unit 26. A configuration example has been described. However, in order to make the shadow 28 having a substantially triangular shape appear when the tip of the document 9 is curled, it is sufficient that at least the light source 22a on the upstream side of the document reading position is provided, and the light source 22b on the downstream side is provided. Is not required.

Further, in the above embodiment, the case where the image reading device 2 is mounted on the image processing device 1 is exemplified. However, the present invention is not limited to this, and the above-mentioned image reading device 2 may be configured by itself.

Further, in the above embodiment, the case where the program 50 executed by the CPU 48 is stored in the memory 49 in advance is illustrated. However, the program 50 may be installed in the image reader 2 after the fact. In this case, the program 50 may be provided in a manner that can be installed in the image reading device 2 via a network or the like, or is recorded on a computer-readable recording medium such as a CD-ROM or a USB memory. It may be provided in the same state as before.

1 Image processing device 2 Image reader 3 Document transfer unit (document transfer means)
4 Scanner unit 20 First image reading unit (image reading means)
26 Second image reading unit (image reading means)
50 Program 61 Shadow detection unit (shadow detection means)
62 Skew angle detection unit (skew angle detection means)
63 Image correction unit (image correction means)
64 Manuscript edge detection unit (manuscript edge detection means)
65 Skew angle determination unit (skew angle determination means)
66 Gradation value acquisition unit (gradation value acquisition means)
67 Area discrimination unit (area discrimination means)
68 Notification unit (notification means)

Claims (17)

Document transport means for automatic document transport and
An image reading means that reads an image when the document conveyed by the document conveying means passes through a predetermined reading position.
A shadow detecting means for detecting a shadow appearing near the edge of the document in the image, and a shadow detecting means.
A skew angle detecting means for detecting the skew angle of the image based on the shadow, and
A skew angle determining means for determining the suitability of the skew angle based on the shape of the shadow, and
An image reading device comprising. The image reading device according to claim 1, wherein the skew angle determining means determines that the skew angle is unsuitable when the shape of the shadow is a substantially triangular shape. The image reading device according to claim 1 or 2, wherein the skew angle determining means determines that the skew angle is appropriate when the shape of the shadow is not a substantially triangular shape. An image correction means that performs skew correction on the image based on the skew angle when the skew angle determining means determines that the skew angle is appropriate.
The image reading device according to any one of claims 1 to 3, further comprising. The document transporting means passes a document between the image reading means and a background plate arranged so as to face the image reading means.
The image according to any one of claims 1 to 4, wherein the skew angle detecting means detects the skew angle by detecting a first boundary between the shadow and the background plate in the image. Reader. The skew angle detecting means is characterized in that the first boundary is approximated by a straight line, and the angle formed by the straight line with respect to the main scanning direction or the sub-scanning direction read by the image reading means is detected as the skew angle. The image reading device according to claim 5. The image reading device according to claim 5 or 6, wherein the skew angle determining means identifies the shape of the shadow based on the first boundary. A document edge detecting means for detecting a second boundary between the shadow and the edge of the document in the image,
Further prepare
The image reading device according to any one of claims 5 to 7, wherein the skew angle determining means identifies the shape of the shadow based on the first boundary and the second boundary. The eighth aspect of the present invention is characterized in that the skew angle determining means specifies that the shape of the shadow is a substantially triangular shape when the first boundary and the second boundary intersect. Image reader. The skew angle determining means calculates the distance from each of the plurality of positions on the first boundary to the second boundary, and the distance is monotonically decreasing toward the center of the second boundary. The image reading device according to claim 9, wherein it is determined that the first boundary intersects with the second boundary in some cases. A gradation value acquisition means for acquiring a gradation value for each pixel along a straight line that approximates the first boundary,
An area determination means for determining whether the straight line belongs to a background area, a shadow area, or a document area based on the gradation value for each pixel acquired by the gradation value acquisition means.
Further prepare
5. The skew angle determining means is characterized in that when it is determined by the area determining means that at least a part of the straight line belongs to the original area, the shape of the shadow is substantially triangular. The image reading device according to any one of 10. When the area determination means determines that the straight line belongs to two shadow areas and the portion between the two shadow areas belongs to the background area, the skew angle determining means determines that the shadow belongs to the background area. The image reading device according to claim 11, wherein the shape of the image is not substantially triangular. The area determination means is characterized in that when the gradation value acquired by the gradation value acquisition means is equal to a predetermined document gradation value, the pixel on the straight line is determined as the document area. Item 12. The image reading device according to Item 11. The area discrimination means is characterized in that when the gradation value acquired by the gradation value acquisition means is equal to a preset background plate gradation value, the pixel on the straight line is discriminated as a background region. The image reading device according to claim 11 or 12. A notification means for notifying that the skew angle is unsuitable when the skew angle determining means determines that the skew angle is unsuitable.
The image reading device according to any one of claims 1 to 14, further comprising. A document transporting means that automatically transports documents and
An image reading means that reads an image when the document conveyed by the document conveying means passes through a predetermined reading position.
It is a skew angle determination method for determining the suitability of the skew angle of an image read from a document in an image reading device including the above.
A shadow detection step for detecting a shadow appearing near the edge of the document in the image, and a shadow detection step.
A skew angle detection step that detects the skew angle of the image based on the shadow,
A skew angle determination step for determining the suitability of the skew angle based on the shape of the shadow, and
A skew angle determination method comprising. Document transport means for automatic document transport and
An image reading means that reads an image when the document conveyed by the document conveying means passes through a predetermined reading position.
A program executed in an image reading device comprising the above-mentioned image reading device.
A shadow detection step for detecting a shadow appearing near the edge of the document in the image, and a shadow detection step.
A skew angle detection step that detects the skew angle of the image based on the shadow,
A skew angle determination step for determining the suitability of the skew angle based on the shape of the shadow, and
A program characterized by executing.

Images