JP7259635B2 - Image reading device, image forming device and program - Google Patents

Description

The present invention relates to an image reading apparatus provided with an automatic document feeder (ADF), an image forming apparatus provided with this image reading apparatus, and a program.

In the following description, the automatic document feeder may also be referred to as ADF.

2. Description of the Related Art An image forming apparatus such as a copier or a multi-function digital composite machine called an MFP (Multi Function Peripheral) is generally equipped with an image reading device having an ADF.

A recent image reading apparatus equipped with an ADF is often equipped with an electronic skew detection and correction function that detects and corrects the inclination (skew) of a document during reading. The advantage of this is that since the document is read while it is tilted and the angle is detected/corrected electronically, it can be corrected with higher precision than the conventional mechanical deskew.

The electronic skew detection method uses a mirror member for the background plate and detects the boundary (edge) between the document and the background plate based on the difference in reflectance between the document and the mirror member. A plate is used to detect the boundary portion based on the shadow generated between the background plate and the document, and the detected boundary portion is used to calculate the skew angle (inclination angle) of the document.

Specifically, in order to detect the boundary between the document S and the background plate 700, as shown in the left diagram of FIG. The diffusely reflected light 703 is incident on the light receiving sensor 702. As for the background plate 700, as shown in the left diagram of FIG. By extremely reducing the amount of light incident on 702, it is possible to create a clear boundary between the background plate (black) and plain paper (white), as shown in the left diagram of FIG. 16(C). Become.

In addition, as shown in the right diagram of FIG. light is totally reflected according to Further, as shown in the right diagram of FIG. 16B, the background plate 700 totally reflects the light from the light source 701 to extremely reduce the amount of light incident on the light receiving sensor 702 . Therefore, as a result of reading the thin paper, the amount of light incident on the light receiving sensor 702 is reduced, the gradation difference between the background plate 700 and the document S is reduced, and as shown in the right diagram of FIG. detection becomes difficult.

Normally, it is not recommended to read a document S made of thin paper or the like with the ADF. If so, it is quite conceivable that the user can stack thin sheets of paper without worrying about the characteristics of the sheets.

When detecting the shadow generated between the document S and the background plate 700 to detect the boundary between the background plate 700 and the document, as shown in the left diagram of FIG. A shadow 710 clearly appeared between the background plate 700 and the plain paper document S because the paper firmly blocked the light from 701 . As shown in the right figure of (D), the shadow becomes less conspicuous and difficult to detect.

In the above example, the number of detection elements at the boundary during skew detection decreases, making it impossible to detect the boundary. When a document S having a torn leading edge or a document S having a folded or torn leading edge as shown in the right diagram of FIG. Therefore, there are cases where the skew angle is erroneously detected.

In general, when a document that is not suitable for electronic skew detection, such as thin paper, is input, it is conceivable to correct it according to the default skew amount set by the service person, but the habit of placing the document depends on the user. For example, the tightening of the regulation plate that regulates both ends of the document is sloppy, and there are various types such as the type that tightens it tightly, so correcting with the default setting will cause an error in the input document. There is a high possibility that you will have to make corrections.

Japanese Patent Application Laid-Open No. 2002-200000 discloses a technique for switching from electronic skew correction to mechanical correction when a document such as thin paper that is not suitable for electronic skew detection is input.

JP 2012-244383 A

However, although the electronic skew correction has the advantage of being able to be configured at a low cost compared to the mechanical correction, in Patent Document 1, it is necessary to provide a mechanical correction function in addition to the electronic skew correction. However, there is a problem that the effectiveness of electronic skew correction, which can be configured in a simple manner, is lost.

The present invention has been made in view of such a technical background. To provide an image reading device, an image forming device, and a program capable of specifying a document that is not skewed, performing electronic skew correction at a level that does not make a user feel uncomfortable, and requiring no mechanical correction mechanism.

The above objects are achieved by the following means.
(1) an automatic document feeder, reading means for reading an image of one or more sheets of document conveyed to a reading position by the automatic document feeder at the reading position to obtain image data, and the document; When it is determined that the boundary between the document and the background is reliable by the boundary reliability determining means for determining whether or not the boundary between the document and the background is reliable for each document, and by the boundary reliability determining means, The first skew angle detection means for detecting the first skew angle of the document, the accumulation means for accumulating the first skew angle, and the boundary reliability judgment means determine that the boundary between the document and the background is unreliable. a convergence degree determining means for reading out the first skew angles accumulated for the originals of the same job from the storing means and determining the degree of convergence of the first skew angles; saving means for saving the image data when it is determined to be lower than a threshold; a second skew angle determining means for determining a second skew angle of the document; and the first skew angle detected by the first skew angle detecting means or the second skew angle determined by the second skew angle determining means and correction means for correcting the inclination of the image data of each of the originals.
(2) The boundary reliability determining means has a sensor for detecting the transmittance of the document, and determines that the boundary is unreliable when the transmittance detected by the sensor is equal to or greater than a predetermined value. The described image reader.
(3) The boundary reliability determination means includes a plurality of sensors for detecting the start or end of passage of the document in the main scanning direction, and detects the boundary when the timing of the output values of the plurality of sensors deviates by a predetermined value or more. 3. The image reading device according to the preceding item 1 or 2, which is determined to be unreliable.
(4) The boundary reliability determination means includes boundary detection means for electronically detecting the boundary between the original and the background, and counting means for counting the number of detected boundaries between the original and the background. 4. The image reading apparatus according to the preceding item 1 or 3, wherein the reliability of the boundary is determined to be unreliable when the number of detections of the boundary between the scanned original and the background is equal to or less than a predetermined value.
(5) The boundary reliability determination means includes boundary detection means for electronically detecting boundary coordinates between the document and the background, and third skew angle detection for electronically detecting a third skew angle based on the detected boundary coordinates. means for calculating a linear expression based on the third skew angle and an arbitrary point of the boundary coordinates, and calculating the main scanning coordinate position or the sub-scanning coordinate position in the boundary coordinates and the linear expression corresponding to the boundary coordinates any of the preceding paragraphs 1, 2, and 4, in which the error between the main scanning coordinate position or the sub-scanning coordinate position is checked, and if an error of a predetermined value or more has occurred, it is determined that the boundary is unreliable The image reading device according to .
(6) The convergence degree determination means includes histogram creation means for creating a histogram for the first skew angle, and calculation means for calculating a peak value from the created histogram. 6. The image reading apparatus according to any one of the preceding items 1 to 5, wherein the degree of convergence is determined to be high when the ratio of the frequency to the total frequency is equal to or greater than a predetermined value.
(7) The image reading apparatus according to (6) above, wherein the second skew angle determining means determines the peak value of the histogram as the second skew angle.
(8) The convergence degree determination means determines that the convergence degree is high when the number of documents read by the reading means and determined to have boundary reliability is equal to or greater than a predetermined number. 1. The image reading device according to claim 1.
(9) the second skew angle determination means calculates a linear expression obtained by using at least two or more of the elements, with the reading order of the document by the reading means and the skew detection angle at that time as one element; 9. The image reading apparatus according to 8 above, wherein the skew detection angle corresponding to the reading order of the originals whose boundaries are unreliable is obtained from the linear expression, and the obtained skew detection angle is determined as the second skew angle.
(10) In addition to the first skew angle, the accumulating means accumulates job data including one or more of the user who uses the document, the paper type of the document, and the number of sheets, and the degree of convergence. Among the accumulated data accumulated in a plurality of jobs executed in , if the degree of convergence of the second job is judged to be low as a result of the judgment by the degree of convergence judging means, the second skew angle deciding means determines based on the first skew angle of the first job: 10. The image reading apparatus according to any one of 1 to 9, wherein the second skew angle is determined in the second job.
(11) The saving means checks the occupancy of the save destination of the saved image data, and if there is image data equal to or greater than a predetermined value, the convergence degree determining means determines the first 11. The image reading device according to any one of the preceding items 1 to 10, wherein the threshold for determining the degree of skew angle convergence is lowered.
(12) An image forming apparatus provided with the image reading apparatus according to any one of (1) to (11) above.
(13) A computer of an image reading apparatus equipped with an automatic document feeder reads an image of one or more sheets of document conveyed to a reading position by the automatic document feeder at the reading position to obtain image data. a reading step for acquiring; a boundary reliability determining step for determining whether or not the boundary between the document and the background is reliable for each document; and the boundary reliability determining step, so that the boundary between the document and the background is reliable is determined, the first skew angle detection step of detecting the first skew angle of the document, the step of storing the first skew angle in the storage means, and the boundary reliability determination step are carried out to determine the relationship between the document and the background. a convergence degree determination step of reading the first skew angle accumulated for the original of the same job from the accumulation means and determining the degree of convergence of the first skew angle when it is determined that the boundary between and is unreliable; a saving step of saving the image data when the convergence degree is determined to be lower than the threshold value by the convergence degree determination step; a second skew angle determining step of determining a second skew angle of the document from the read first skew angle; and determining the first skew angle detected by the first skew angle detecting step or the second skew angle. and a correcting step of correcting the inclination of the image data of each document according to the second skew angle determined by the step.

According to the invention described in the preceding item (1), when it is determined that the boundary between the document and the background is reliable, the first skew angle of the document is detected, and the inclination of the image data is detected according to the first skew angle. is corrected. If it is determined that the boundary between the document and the background is unreliable, the first skew angle in the same job stored in the storage means is read, and the degree of convergence of the first skew angle is determined. If the degree of convergence is determined to be low, the image data is saved in a saving means. The tilt of the image data is corrected according to the second skew angle thus obtained.

In this way, a document with an unreliable boundary between the document and the background, in other words, a document unsuitable for electronic skew detection, such as a thin paper document, is identified. If the degree of convergence is high, the tilt of the image data is corrected according to the second skew angle determined based on the first skew angle. Therefore, even if the document is not suitable for electronic skew detection, electronic skew correction can be performed at a level that does not make the user feel uncomfortable. Moreover, since no mechanical correction mechanism is required, the effectiveness of the electronic skew correction that can be constructed at low cost is not lost.

According to the invention described in the preceding item (2), a sensor for detecting the transmittance of the document is provided, and when the transmittance detected by the sensor is equal to or higher than a predetermined value, the boundary is determined to be unreliable. For example, it is possible to accurately determine whether or not the document is not suitable for electronic skew detection, such as thin paper.

According to the invention described in the preceding item (3), when the timing of the output values of the plurality of sensors in the main scanning direction for detecting the start or end of passage of the document is deviated by a predetermined value or more, it is determined that the boundary is unreliable. Therefore, it is possible to accurately determine whether or not the document is unsuitable for electronic skew detection, such as a document with a folded leading edge, a tear at the leading edge of the document, or a document torn from a loose leaf.

According to the invention described in the preceding item (4), when the number of electronically detected boundaries between the original and the background is less than a predetermined value, it is determined that the boundaries are unreliable. Therefore, it is possible to accurately determine whether or not the document is not suitable for electronic skew detection.

According to the invention described in the preceding item (5), the third skew angle is electronically detected based on the electronically detected boundary coordinates between the document and the background, and the third skew angle and boundary coordinates are arbitrary. A linear expression is calculated based on the points of Then, the error between the main scanning coordinate position or sub-scanning coordinate position on the boundary coordinates and the main scanning coordinate position or sub-scanning coordinate position on the linear expression corresponding to the boundary coordinates is checked, and an error of a predetermined value or more occurs. If so, the boundary is judged to be unreliable. Therefore, it is possible to accurately determine whether or not the document is unsuitable for electronic skew detection, such as a document with a folded leading edge, a tear at the leading edge of the document, or a document torn from a loose leaf.

According to the invention described in the preceding item (6), the frequency and the total frequency within a predetermined range are acquired from the peak value of the histogram for the first skew angle, and if the ratio is equal to or greater than the predetermined value, it is determined that the convergence degree is high. is determined, and the skew of the image data is corrected according to the second skew angle.

According to the invention described in (7) above, the peak value of the histogram for the first skew angle is determined as the second skew angle.

According to the invention described in the preceding item (8), when the number of documents read by the reading means and determined to have boundary reliability is equal to or greater than a predetermined number, it is determined that the degree of convergence is high, and the second skew angle is determined. The tilt of the image data is corrected in accordance with .

According to the invention described in the preceding item (9), the reading order of the document by the reading means and the skew detection angle at that time are regarded as one element, and a linear expression obtained by using at least two elements is calculated to determine the boundary. The skew detection angle corresponding to the reading order of the unreliable document is obtained from the linear expression, and the obtained skew detection angle is determined as the second skew angle.

According to the invention described in the preceding item (10), in addition to the first skew angle, the accumulating means accumulates job data including one or more of the user, the paper type of the original, the number of sheets, and the degree of convergence, For example, if it is determined that the degree of convergence is low for a second job consisting of only one document, out of the accumulated data accumulated in a plurality of jobs executed before the second job is executed, Since the second skew angle is determined based on the first skew angle in a job having conditions similar to the job data of the second job, even if the job consists of only one sheet of unreliable document, for example, the second skew angle A skew angle can be determined.

According to the invention described in the preceding item (11), the amount of image data occupied in the save destination of the image data is checked, and if image data having a predetermined value or more exists, the first skew angle read from the storage means converges. Since the degree judgment threshold is lowered, the possibility that the degree of convergence is judged to be low is reduced, the saving of image data is suppressed, and the saved image data prevents the capacity of the storage device from becoming tight. can.

According to the invention described in the preceding item (12), an image forming apparatus equipped with an image reading device capable of performing electronic skew correction at a level that does not cause a user to feel discomfort even if the document is not suitable for electronic skew detection. become a device.

According to the invention described in the preceding item (13), the computer of the image reading apparatus is caused to perform electronic skew correction at a level that does not make the user feel uncomfortable even if the document is not suitable for electronic skew detection. be able to.

1 is a perspective view showing the overall configuration of an image forming apparatus 100 equipped with an image reading device according to an embodiment of the invention; FIG. 2 is a block diagram showing the electrical configuration of the image forming apparatus; FIG. 2 is a block diagram showing the configuration of an imaging unit; FIG. 2 is a cross-sectional view of an imaging unit and an automatic document feeder; FIG. 4 is a flowchart showing electronic skew correction processing performed by the image forming apparatus; 3 is a block diagram showing a functional configuration example of an input image processing unit; FIG. FIG. 9 is an explanatory diagram of an example of detection processing of a first skew angle; 4 is a block diagram showing a configuration example of a boundary reliability determination unit; FIG. FIG. 9 is a block diagram showing another configuration example of the boundary reliability determination unit; (A) and (B) are diagrams for explaining an example of boundary reliability determination processing. FIG. 10 is a diagram for explaining an example of processing for determining the degree of convergence of a first skew angle and determining a second skew angle; 8A and 8B are diagrams for explaining another example of the process of determining the degree of convergence of the first skew angle and determining the second skew angle; FIG. FIG. 11 is a diagram for explaining a processing example of determining a second skew angle of a current job from a first skew angle of a past job; FIG. 11 is a block diagram showing a configuration example of a saving unit that saves image data when there is no document boundary reliability and the degree of convergence of the first skew angle is low; FIG. 11 is a table for explaining a case where a determination threshold for the degree of convergence of the first skew angle is lowered; FIG. (A) to (E) are diagrams for explaining problems of the conventional technology.

Embodiments of the present invention will be described below with reference to the drawings.
[Overall Configuration of Image Forming Apparatus]
FIG. 1 is a perspective view showing the overall configuration of an image forming apparatus 100 equipped with an image reading device according to one embodiment of the invention. In this embodiment, as a typical example of the image forming apparatus 100, a multi-function peripheral (MFP) equipped with multiple functions such as a scan function, a copy function, a facsimile function, a network function, and a BOX function is illustrated. In the following description, the image forming apparatus is also referred to as MFP.

As shown in FIG. 1, the MFP 100 includes an operation panel 1 arranged on the front side (the side facing the user) of the upper surface of the main body, and an imaging section (scanner section) for optically reading a document and obtaining image data. 3, a printer engine 6 for printing an image on paper based on image data, and a tray 8 for discharging the paper on which an image is formed by the printer engine 6. FIG. An automatic document feeder (ADF) 4 for feeding documents to an imaging unit 3 is arranged on the upper surface of the main body of the MFP 100, and a plurality of paper feeding units 9 for supplying paper to a printer engine 6 are arranged below. . An image reading device is configured including the imaging unit 3 and the ADF 4 .

Operation panel 1 is a device for operating MFP 100, and includes a plurality of keys for accepting operations such as various instructions from a user, inputs such as numbers, letters, and symbols, and a display device. As this display device, a touch panel is used for the input function, and various information in response to user operations and/or menu screens for accepting various operations are displayed to the user, and the position touched by the user is displayed. and acquire input information corresponding to the acquired position.
[Electrical Configuration of Image Forming Apparatus]
FIG. 2 is a block diagram showing the electrical configuration of MFP 100. As shown in FIG.

Referring to FIG. 2, MFP 100 includes system controller 101, memory 102, network interface (network I/F) 103, output image processing unit 105, storage device 106, input image processing unit 500, It includes the operation panel 1 described above, the imaging unit 3, the ADF 4, the printer engine 6, and the like.

Memory 102, network I/F 103, printer engine 6, output image processing unit 105, storage device 106, imaging unit 3, ADF 4, input image processing unit 500, and operation panel 1 are connected to system controller 101. .

A system controller 101 controls the entire MFP 100 for various jobs such as scan jobs, copy jobs, mail transmission jobs, and print jobs. The system controller 101 includes a CPU (Central Processing Unit) 121, a ROM 122 (Read Only Memory), and the like. The CPU 121 executes control programs stored in the ROM 122 .

ROM 122 stores various programs for operating MFP 100 and various fixed data. The system controller 101 reads data from the memory 102 and writes data to the memory 102 by performing predetermined processing.

The memory 102 is a RAM (Random Access Memory), and is used for temporarily storing data and image data required when the CPU 121 executes the control program.

A network I/F 103 communicates with external devices via a network according to instructions from the system controller 101 .

The printer engine 6 performs print processing on paper or the like based on the print data processed by the output image processing unit 105 . In particular, when the MFP 100 operates as a printer, the printer engine 6 prints images, and when the MFP 100 operates as a copier, the printer engine 6 prints images read by the imaging unit 3 .

The output image processing unit 105 performs conversion processing for converting the format of image data into print data when printing an image.

Storage device 106 is, for example, an HDD (Hard Disk Drive), and stores various data related to the operation of MFP 100 . Further, storage device 106 stores image data of screens displayed on operation panel 1 of MFP 100 .

The imaging unit 3 reads an image of a document. The input image processing unit 500 performs conversion processing for converting the format of image data when an image is read by the imaging unit 3, detects an electronic skew angle, determines a skew angle for a thin paper document or the like, and processes image data. electronic skew correction, etc.
[Configuration of imaging unit 3]
FIG. 3 is a block diagram showing the configuration of the imaging section 3. As shown in FIG. The imaging unit 3 includes a light emitting unit 310, a document reading sensor 320, an A/D converting unit 330, a driving unit 340, and the like. light is incident on the document.

The reflected light from the document is read by the document reading sensor 320, and the output analog data is converted into digital data by the A/D conversion unit 330, and then processed by the input image processing unit 108 or the like. there is

FIG. 4 is a cross-sectional view of the imaging unit 3, which is arranged below the ADF 4. As shown in FIG. Although the imaging unit 3 and the ADF 4 are actually close to each other, they are drawn apart in the example of FIG.

A contact glass 301 closing a slit opened in the upper surface of the imaging unit 3 faces a portion of the document transport path exposed on the bottom surface of the ADF 4 . The imaging unit 3 irradiates the surface of the document passing through part of the transport path with light through the contact glass 301 and detects the reflected light. The platen glass 302 on the upper surface of the imaging unit 3 also closes an opening different from the slit closed by the contact glass 301 . The imaging unit 3 irradiates the surface of the document placed thereon with light through the platen glass 302 and detects the reflected light.

A slider 343 connected to a wire 346 moves from directly under the contact glass 301 to the end of the platen glass 302 by rotating a motor 341 that constitutes a drive unit 340 inside the imaging unit 3 in the a direction or the b direction. It is installed so that it can reciprocate between them. The slider 343 irradiates the surface of the document with the light from the linear light source 310 through the contact glass 301 or the platen glass 302 from its upper surface. Further, the slider 343 reflects the light that is reflected by the surface of the document and is incident from the upper surface toward the pair of mirrors 345 and the lens 321 by the mirror 344 . These optical elements 345 and 321 converge this reflected light, and the line sensor (corresponding to reading means) 323 detects the amount of light. Since this amount of light changes according to the color of the surface of the document (more precisely, the light reflectance), the electric signal output from the line sensor 323 in response to the detection of this amount of light is used to reproduce the image displayed on the surface of the document. show. This electrical signal is converted into image data by the A/D converter 330 and output to a printer or an external electronic device.
[Skew correction processing]
FIG. 5 is a flowchart showing electronic skew correction processing executed by the MFP 100 for electrically correcting the skew of the read image data in accordance with the skew angle, which is the skew angle of the document when the document is read by the ADF 4. . This process is executed by CPU 121 of MFP 100 operating according to an operation program stored in a recording medium such as ROM 122 .

In step S01, a document is input from the ADF 4 to the imaging unit 3, and the image of the document is read by the line sensor 323 to obtain image data.

In step S02, the reliability of the boundary between the document and the background is calculated, and in step S03, it is determined whether or not the boundary is reliable. Whether or not the boundary is reliable will be described later. If there is reliability (YES in step S03), the process proceeds to step S09 to detect the skew angle (first skew angle). Next, in step S10, after correcting the inclination of the image data according to the detected first skew angle, in step S11, the detected first skew angle is saved in the memory 102, and the process ends. When a plurality of documents are read in one job, the processing from step S01 is performed for each document, and if the boundary between the document and the background is reliable for each document, the first skew angle is calculated for each document. detected. Then, the inclination of the image data of each document is corrected according to the detected first skew angle, and the first skew angle is stored in the storage device 106 or the like.

If the boundary between the original and the background is unreliable in step S03 (NO in step S03), then in step S04 the first skew angle accumulated in step S11 for the same job is read from the memory 102. After that, in step S05, it is determined whether or not the degree of convergence of the read first skew angle is high. The degree of convergence of the first skew angle will be described later.

If the degree of convergence of the first skew angle is high (YES in step S05), in step S06, based on the first skew angle, the skew angle (second skew angle) for the document without boundary reliability is estimated and determined. After that, in step S08, the inclination of the image data is corrected according to the determined second skew angle. As a result, electronic skew correction can be performed even on a thin sheet of paper or an unreliable document with no linearity at the leading edge of the document.

If the degree of convergence of the first skew angle is low in step S05 (NO in step S05), the process is terminated after saving the image data in step S07. Saving of image data will be described later.

5 is executed under the control of the CPU 121 in the input image processing unit 500 in FIG. The functional configuration of the input image processing unit 500 is shown in the block diagram of FIG.

The input image processing unit 500 includes a document input unit 510 for inputting document image data from the imaging unit (scanner) 3, a boundary reliability determination unit 520 for determining whether the boundary between the document and the background is reliable, a first skew A first skew angle detection unit 530 for detecting an angle, an angle accumulation unit 550 for accumulating the detected first skew angle, an accumulated angle reading unit 560 for reading out the first skew angle accumulated in the angle accumulation unit 550, and a read result If the convergence degree determination unit 570 determines the degree of convergence of the first skew angle from the second skew angle , the first skew angle detected by the first skew angle detection unit 530, and the second skew angle determined by the second skew angle determination unit 580, image It comprises a skew correction unit 540 that corrects the inclination of data, an image output unit 511 that outputs image data after skew correction, and an image data saving unit 590 that saves the image data.
[Detection of first skew angle]
Next, detection of the first skew angle performed by the first skew angle detection unit 530 of FIG. 6 will be described.

As shown in FIG. 7, the first skew angle detection unit 530 detects the X-coordinates (X1 . . . Xn) and Y-coordinates (X1 . Y1 . . . Yn) are obtained. Then, based on the obtained coordinates of the n points, a straight line Y=aX+b is calculated by the method of least squares. The obtained slope a of the approximation formula becomes the first skew angle to be detected. The X and Y coordinates up to the n-th point of each detection point 11 may be obtained by reading image data obtained by the line sensor 323, as will be described later, or by using a plurality of original detection sensors in the main scanning direction. It may be arranged and acquired based on the output of the document detection sensor.
[Boundary Reliability Judgment]
A method for determining whether or not the boundary between the document and the background is reliable by the boundary reliability determination unit 520 in FIG. 6 will be described.

As shown in FIG. 8, the boundary reliability determination unit 520 has one or more transmittance sensors 521 for detecting the transmittance of the document S, and determines the transmittance of the document S based on the output of the transmittance sensor 521. A transmittance determination unit 522 for determination is provided. The transmittance sensor 521 detects the transmittance by measuring the amount of light transmitted through the document S. FIG. If the transmittance detected by the transmittance sensor 521 is equal to or greater than a predetermined value, the document S is thin, so it is determined that the boundary is unreliable. If the transmittance detected by the transmittance sensor 521 is less than a predetermined value, it is determined that the document S is plain paper, not thin paper, and that the boundary is reliable.

Further, as shown in FIG. 9, the boundary reliability determination unit 520 detects the start or end of passage of the document S by detecting the leading edge or the trailing edge of the document S instead of the transmittance sensor 521. A sensor 523 may be provided in the main scanning direction, and a timing deviation determination section 524 may be provided. The timing deviation determination unit 524 compares the timings of the output values of the plurality of sheet passing sensors 523, and if the timings of the output values deviate by a predetermined value or more, that is, if the amount of deviation is greater than a threshold value, the folded edge of the document is detected. It may be determined that there is a break or breakage, and that the boundary is unreliable.

Alternatively, without using the transmittance sensor 521, the boundary between the document S and the background may be electronically detected from the image data to determine whether the paper is thin and to determine whether the boundary is reliable. That is, in the case of a normal plain paper document S, there is a clear boundary such as a shadow between the background plate and the document S, and the boundary detection points 11 are located as indicated by the circles in the left diagram of FIG. 10(A). the number increases. However, as shown in the right diagram of FIG. 10A, in the case of a thin paper document S, the gradation difference between the background plate and the document S is reduced, making it difficult to detect the boundary. The number of detection points 11 is reduced. Therefore, the number of boundary detection points 11 is counted, and it is checked whether or not the number of boundary detection points 11 is equal to or less than the threshold. Conversely, if the number of boundary detection points 11 is not equal to or less than the threshold value, it is determined that the paper is plain paper, not thin paper, and that the boundary is reliable. The method of determining the threshold value at this time depends on the method of electronic skew detection to be performed later, but considering variations in the detection of boundary points (such as shifts in the sub-scanning direction), the detection point 11 that can absorb the variations in detection is determined. If the number of is secured, it may be judged as plain paper or the like.

In addition, it is electronically determined from the image data whether the document edge is folded or torn, without using the paper passing sensor 523 for detecting the start or end of passage of the document S, and the presence or absence of reliability of the boundary is determined. You can

That is, there is a clear boundary such as a shadow between the background plate and the document S, and this is defined as the boundary detection point 11 as indicated by the circle in the left diagram of FIG. 10(B). Detect (boundary coordinates). Further, a skew angle (corresponding to a third skew angle) is electronically detected based on the detected boundary coordinates. Then, a linear expression is calculated based on the detected skew angle and an arbitrary point of the boundary coordinates. A straight line L1 in the left diagram of FIG. 10B indicates the calculated linear expression.

In the case of ordinary plain paper with no damage such as folds or tears at the edges of the document, as shown in the left diagram of FIG. do not have.

On the other hand, in the case of a document S with folds or tears, it is pulled at the angle formed by the folds or tears, and the skew angle shows a different angle from the original inclination. For this reason, as shown in the right diagram of FIG. 10(B), the linear line L2 calculated based on the skew angle and arbitrary point of the boundary coordinates does not overlap well with the boundary detection point 11, and there is an error between them. occurs. That is, the error between the main scanning coordinate position or sub-scanning coordinate position in the boundary coordinates of each boundary detection point 11 and the main scanning coordinate position or sub-scanning coordinate position on the linear expression corresponding to each boundary coordinate is examined, and a predetermined If an error equal to or greater than the threshold has occurred, it is determined that the boundary is unreliable. The error may be the integrated amount of the absolute values of the errors obtained for each boundary coordinate, or may be the maximum value of the errors obtained for each boundary coordinate. The threshold at this time may be set to "the number of detection points×absolute value of variation=threshold", taking into consideration the detection variation of the detected boundary detection points (such as deviation in the sub-scanning direction).
[Convergence Determination of First Skew Angle and Determination of Second Skew Angle]
Next, the convergence degree determination process of the first skew angle (step S05 in the flowchart of FIG. 5), and when it is determined that the convergence degree is higher than the threshold value, a plurality of first skew angles read from the memory 102 are An example of the process of determining the second skew angle of the document S (step S06 in the flowchart of FIG. 5) will be described.

As a first example, as shown in FIG. 11, a histogram is created for a plurality of first skew angles and the peak value of the histogram is detected. Then, with the peak value as the starting point, the frequency and the total frequency existing within a predetermined detection angle w on both sides of the peak value are acquired, and the ratio of the frequency existing within the detection angle w on both sides of the peak value to the total frequency is given. If it is equal to or greater than the value, it is determined that the degree of convergence of the first skew angle is high. Then, the detected peak value is determined as the second skew angle.

However, as shown in FIG. 12A, if the paper feed roller 41 in the ADF 4 is slightly skewed, the bundle of paper placed on the ADF 4 will be read while being skewed each time paper is fed. , the histogram does not converge because it is read with a different skew angle each time.

Therefore, as a second example of determination of convergence, when the number of documents S input from the ADF 4 to the imaging unit 3, read by the line sensor 323, and determined to have boundary reliability is equal to or greater than a predetermined number, It may be determined that the degree of convergence is high. For example, when there are two or more such documents S, it may be determined that the degree of convergence is high.

When it is determined that the degree of convergence is high, the second skew angle for the unreliable document S is determined from the plurality of first skew angles read from the memory 102 as follows.

That is, as shown in the graph of FIG. 12B, X: reading order of document S (sheet), Y: detection angle (first skew angle) of read document S (X, Y ) is one element, and two or more of these elements are used to create a first-order approximation formula. Assuming that the linear expression is Y(°)=αX (sheet)+β, for example, if it is determined that the fifth document S is thin and unreliable, the approximate angle Y5 for the fifth sheet is Y5=α× It can be calculated by 5+β. Then, the calculated Y5 is determined as the second skew angle.

In this way, the degree of convergence of the first skew angle is determined, and when the degree of convergence is determined to be high, the second skew angle is estimated and determined for the document S having no boundary reliability. Then, the tilt of the image data is corrected according to the determined second skew angle. Therefore, even if the document is not suitable for electronic skew detection, for example, thin paper or a document with torn or folded edges, electronic skew correction can be performed at a level that does not make the user feel uncomfortable. Moreover, since no mechanical correction mechanism is required, the effectiveness of the electronic skew correction that can be constructed at low cost is not lost.

By the way, if the document S is unreliable and the degree of convergence of the first skew angle read from the memory 102 is low, the second skew angle may not be determined. For example, this is the case of a job consisting only of unreliable thin paper originals S. FIG. Even in such a case, the second skew angle can be determined as follows.

That is, the MFP 100 accumulates the first skew angle and its convergence degree for each job executed in the past (corresponding to the first job), as shown in the upper table of FIG. name is stored. In the upper table of FIG. 13, three jobs, job 1 to job 3, are accumulated. The "skew angle" item in the table may be the average value of the first skew angles of a plurality of originals S, for example. Further, the item of "degree of convergence" may be, for example, the ratio of the frequency within a predetermined range with the peak value as the starting point in the histogram graph of FIG. 16 to the total frequency.

Further, as shown in the lower table of FIG. 13, Mr. Yamada is the user of the current job (corresponding to the second job), the document S in the current job is unreliable, and the current job is unreliable. If the first skew angle is not accumulated, the user who is using the current job is searched as a search word from among the previously accumulated jobs (Job 1 to Job 3), and the skew is determined based on the search result. Read out the angle and degree of convergence. In the example of FIG. 13, job 1 is searched.

Then, the degree of convergence in the retrieved job 1 is determined. Since the degree of convergence is 90%, it is determined that the degree of convergence is high, and the first skew angle of job 1 is the skew angle of the current job (second skew angle).

In the above example, the user name is stored together with the first skew angle and convergence degree of the first job. A job that matches the current job in at least one of the number of sheets may be retrieved as the first job, and the skew angle of the job may be determined as the skew angle (second skew angle) of the current job.
[Processing when document S is saved]
If the document S has no boundary reliability and the degree of convergence of the first skew angle is also low, the image data is saved in the saving unit 590 (step S07 in the flowchart of FIG. 6). This saving process will be described.

As shown in FIG. 14, the saving unit 590 has a storage unit 591 as a save destination for storing image data, a capacity determination unit 592 for monitoring and determining the capacity of the storage unit 591, and an image data reading unit 593. there is

As a result of monitoring by the capacity determination unit 592, when image data of a predetermined value or more has been saved in the storage unit 591, the accumulated first skew angle is read from the angle accumulation unit 550 via the accumulated angle reading unit 560. is read out, and the degree of convergence of the first skew angle is determined by the degree-of-convergence determination unit 570 . At this time, the convergence degree is judged by lowering the judgment threshold of the convergence degree.

For example, as shown in the table of FIG. 15, in job 4, 10 documents S are read, only the 5th document is a thin sheet with no boundary reliability, and the other 9 documents S are boundary unreliable. It is assumed that the paper is plain paper with good properties. Four first skew angles are detected at the stage of reading the 1st to 4th sheets of the document S, and the inclination of the image data of each of the 1st to 4th sheets of the document S is corrected by the detected first skew angles. and the detected first skew angle is stored in the memory 102 .

Here, when there are four or more accumulated first skew angles, in other words, when the number of documents S determined to have boundary reliability is four or more, the convergence degree determination unit 570 converges. shall be judged to be high. For the fifth sheet of thin paper, it is determined that there is no boundary reliability, and the degree of convergence of the first skew angle is determined. It determines that it is high, and notifies the image data reading unit 593 of the determination result. The image data reading unit 593 reads the image data from the storage unit 591, and the second skew angle determination unit 580 in FIG. is determined, and the skew correction unit 540 corrects the inclination of the image data according to the determined second skew angle.

In job 5 of FIG. 15, the document S is only one sheet of thin paper. Based on the first skew angle in the job, the second skew angle for one sheet of thin paper is determined, and the skew correction unit 540 corrects the inclination of the image data according to the determined second skew angle.

In job 6 of FIG. 15, it is assumed that the first and second sheets of the document S are plain paper, the third to eighth sheets of the document S are thin paper, and the ninth and tenth sheets are plain paper. Here, when reading the third sheet of thin paper, it was determined that there was no boundary reliability. If the threshold is used for determining that the degree of convergence is high, the degree of convergence is determined to be low because it is less than the threshold. Therefore, the image data for thin paper is saved in the storage unit 591 . Accordingly, in job 6, a total of six image data read for the third to eighth sheets of the thin paper document S are saved in the storage unit 591. FIG.

Assuming that the capacity of the storage unit 591 is only for five pieces of image data, the capacity of the storage unit 591 will be full at the time when the eighth sheet of the thin paper document S is read. When the capacity determination unit 592 determines that the capacity is already occupied, the convergence degree determination unit 570 lowers the reference threshold value of the first skew angle for determining that the degree of convergence is present, for example, from four to two. Therefore, for the third to eighth thin paper documents S, the two first skew angles for the first and second documents S have already been accumulated. judged to be high. The second skew angle determination unit 580 determines the second skew angles for the third to eighth sheets of the thin paper document S based on the two first skew angles, and the skew correction unit 540 corrects the determined second skew angles. Inclination correction of image data is performed according to the skew angle.

In this way, the amount of image data occupied in the storage device 591 in which the image data is saved is checked, and if there is image data of a predetermined value or more, the degree of convergence of the first skew angle read from the angle accumulation unit 550 is determined. Since the threshold is lowered, the possibility that the degree of convergence is judged to be low can be reduced, saving image data can be suppressed, and the capacity of the storage device 591 can be prevented from becoming tight due to the saving of image data.

If the convergence degree of the first skew angle is not determined to be high even if the threshold value for determining the degree of convergence of the first skew angle is lowered, the fact that the tilt cannot be corrected is displayed on the operation panel 200 via the CPU 121 .

1 operation panel 3 imaging unit 4 automatic document feeder (ADF)
6 printer engine 11 boundary detection point 100 image forming apparatus 101 system controller 102 memory 106 storage device 121 CPU
122 ROMs
500 Input image processing unit 510 Document input unit 520 Boundary reliability determination unit 530 First skew angle detection unit 540 Skew correction unit 550 Angle storage unit 560 Accumulated angle readout unit 570 Convergence degree determination unit 580 Second skew angle determination unit 590 Image data Retraction section S Document

Claims (13)

an automatic document feeder;
reading means for obtaining image data by reading, at the reading position, an image of one or more documents conveyed to the reading position by the automatic document feeder;
boundary reliability determination means for determining whether or not the boundary between the document and the background is reliable for each document;
a first skew angle detection means for detecting a first skew angle of the document when the boundary reliability determination means determines that the boundary between the document and the background is reliable;
accumulating means for accumulating the first skew angle;
When the boundary reliability determination means determines that the boundary between the document and the background is unreliable, the first skew angle accumulated for the document of the same job is read out from the accumulation means, and the first skew angle is determined. convergence determination means for determining the convergence of
saving means for saving the image data when the convergence degree determining means determines that the degree of convergence is lower than a threshold value;
a second skew angle determining means for determining a second skew angle of the document from the read first skew angle when the convergence degree determining means determines that the degree of convergence is higher than a threshold;
correcting means for correcting the inclination of the image data of each document according to the first skew angle detected by the first skew angle detecting means or the second skew angle determined by the second skew angle determining means; ,
An image reading device comprising: 2. The boundary reliability judging means according to claim 1, wherein said boundary reliability judging means comprises a sensor for detecting the transmittance of the document, and judges that the boundary is unreliable when the transmittance detected by said sensor is equal to or greater than a predetermined value. Image reader. The boundary reliability determination means includes a plurality of sensors in the main scanning direction for detecting the start or end of passage of the document, and determines the reliability of the boundary when the timing of the output values of the plurality of sensors deviates by a predetermined value or more. 3. The image reading apparatus according to claim 1, wherein the image reading apparatus determines that there is no The boundary reliability determination means includes:
Boundary detection means for electronically detecting the boundary between the document and the background, and counting means for counting the number of detections of the detected boundary between the document and the background,
4. The image reading apparatus according to claim 1, wherein the reliability of the boundary is determined to be unreliable when the number of detections of the boundary between the document and the background counted by the counting means is equal to or less than a predetermined value. The boundary reliability determination means includes:
a boundary detection means for electronically detecting boundary coordinates between the document and the background; and a third skew angle detection means for electronically detecting a third skew angle based on the detected boundary coordinates,
A linear expression is calculated based on the third skew angle and an arbitrary point on the boundary coordinates, and a main scanning coordinate position or a sub-scanning coordinate position on the boundary coordinates and the main scanning coordinates on the linear expression corresponding to the boundary coordinates 5. The method according to any one of claims 1, 2, and 4, wherein an error between the position and the sub-scanning coordinate position is checked, and if an error of a predetermined value or more has occurred, it is determined that the boundary is unreliable. Image reader. The convergence degree determination means is
histogram creating means for creating a histogram for the first skew angle;
a calculating means for calculating a peak value from the created histogram;
with
6. The image reading apparatus according to claim 1, wherein it is determined that the degree of convergence is high if the ratio of the frequency within a predetermined range from the peak value to the total frequency is greater than or equal to a predetermined value. 7. The image reading apparatus according to claim 6, wherein said second skew angle determining means determines the peak value of said histogram as said second skew angle. 8. The convergence degree judging means judges that the convergence degree is high when the number of documents read by the reading means and judged to have boundary reliability is equal to or greater than a predetermined number. The described image reader. The second skew angle determining means calculates a linear expression obtained by using at least two or more of the reading order of the document by the reading means and the skew detection angle at that time as one element, and calculates the boundary reliability. 9. The image reading apparatus according to claim 8, wherein the skew detection angle corresponding to the reading order of the document having no skew is obtained from the linear expression, and the obtained skew detection angle is determined as the second skew angle. The accumulating means accumulates, in addition to the first skew angle, job data including one or more of the user, the paper type of the document, and the number of sheets, and the degree of convergence;
A job that has data whose conditions are close to those of the second job and whose degree of convergence is equal to or higher than the threshold, among the accumulated data accumulated in a plurality of jobs executed before the execution of the second job. is the first job, and as a result of the judgment by the convergence degree judging means, if it is judged that the degree of convergence is low for the second job, the second skew angle determining means determines the first job 10. The image reading apparatus according to any one of claims 1 to 9, wherein the second skew angle for the second job is determined based on the first skew angle for the job. The saving means checks the occupancy of the save destination of the saved image data, and if image data having a predetermined value or more exists, the convergence degree determining means determines the first skew angle read from the storing means. 11. The image reading apparatus according to any one of claims 1 to 10, wherein a judgment threshold for the degree of convergence is lowered. An image forming apparatus comprising the image reading apparatus according to any one of claims 1 to 11. In the computer of the image reader equipped with the automatic document feeder,
a reading step of reading, at the reading position, an image of one or more documents conveyed to the reading position by the automatic document feeder to obtain image data;
a boundary reliability determination step of determining whether or not the boundary between the document and the background is reliable for each document;
a first skew angle detection step of detecting a first skew angle of the document when the boundary reliability determination step determines that the boundary between the document and the background is reliable;
accumulating said first skew angle in an accumulating means;
If the boundary reliability determining step determines that the boundary between the document and the background is unreliable, the first skew angle accumulated for the document of the same job is read out from the accumulation means, and the first skew angle is obtained. a convergence determination step for determining the convergence of
a saving step of saving the image data when the convergence degree is determined to be lower than a threshold value by the convergence degree determining step;
a second skew angle determination step of determining a second skew angle of the document from the read first skew angle when the convergence degree is determined to be high at a threshold value or more in the convergence degree determination step;
a correction step of correcting the inclination of the image data of each document according to the first skew angle detected by the first skew angle detection step or the second skew angle determined by the second skew angle determination step; ,
program to run the

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