JP6607019B2 - Document inclination amount detection apparatus and image processing apparatus - Google Patents

Description

  The present invention relates to an apparatus for detecting a tilt amount of a sheet-like document.

  2. Description of the Related Art Conventionally, an image processing apparatus that reads an image from a document and processes it, such as a copying machine or an MFP (Multi-functional Peripheral), has been provided with an automatic document feeder. The automatic document feeder automatically conveys a plurality of set documents one by one to a reading position in order.

  When the document is conveyed by the automatic document feeder, the document may be inclined (skew) depending on the state of the document or the set state thereof. As a method for correcting the inclination of the document, a method of making the document abut against the registration roller and bending it is well known. However, when this method is used, there is a problem in that the noise generated by the collision between the registration roller and the document is lost.

  Thus, in recent years, attention has been paid to a technique for generating an image having no inclination by image processing in which an image is read from a tilted original and the read image is rotated without correcting the inclination of the original.

  In order to correct the tilt by image processing, it is necessary to detect the tilt amount of the document prior to the correction. As prior art for detecting the amount of inclination of a document, there are technologies described in Patent Documents 1 to 5.

  Patent Document 1 discloses that when reading a document image, a shadow due to the thickness of the document is also read, and the inclination angle of the edge of the document is detected based on the position of the black pixel due to the shadow. Yes. Patent Document 2 describes that a shadow portion in a read image is sharpened by density conversion, and Patent Document 3 sharpens a shadow portion by filtering using a Laplacian filter. Is described.

  Patent Documents 4 and 5 disclose that an edge in an image is specified by Hough transformation. By specifying the edge, the inclination of the edge can be known.

JP 2003-259089 A JP 2003-259090 A JP 2003-319160 A JP 2009-042814 A JP 2002-199179 A

  By detecting the amount of inclination of the document by image processing, it is possible to detect the amount of inclination with higher accuracy than by using a sensor that detects the presence or absence of the document. In addition, since no sensor is used, the component cost can be reduced.

  However, in the detection of the inclination amount of the document by image processing, there is a problem of how accurately the boundary between the document and the background is detected based on the gradation value of each pixel of the image.

  When detecting the inclination amount of the shadow of the document in the image as in Patent Documents 1 to 3, it is difficult to distinguish the document from the shadow when the background color of the document is dark. In addition, when the width of the shadow is wide due to a thick original or the entire edge is raised, and when the width of the shadow is uneven because the edge of the original is partially lifted The tilt amount cannot be detected or the error is large even if it can be detected. That is, there is a problem that the detection accuracy depends on the original.

  In addition, when the sides are specified by Hough transform as in Patent Documents 4 and 5, there is a problem that it takes a long time to perform image processing for detecting the inclination.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to detect the amount of inclination of a document with accuracy that does not depend on the document and in a shorter time than the prior art.

  An apparatus for detecting an amount of inclination of a document according to an embodiment of the present invention is an apparatus that detects the amount of inclination of a sheet-like document that is disposed on or passes through a surface of a background plate, and a light source that irradiates the document; Image reading means for acquiring an input image by reading a rectangular area including at least one edge of the document by a reflected light from the document by the light source in a main scanning direction and a sub-scanning direction perpendicular thereto; and Boundary point detection means for detecting boundary points between the original and the background plate from a change in gradation value in the sub-scanning direction in the input image, and a plurality of the boundary points detected along the main scanning direction, An inclination amount detecting means for detecting an inclination amount of two points on the boundary point and separated by a set distance between the two points, and shifting the two points for each set distance along the main scanning direction Pair on one edge A tilt amount group acquiring unit that acquires a tilt amount group including a plurality of tilt amounts, and a document tilt amount determining unit that determines the tilt amount of the one edge as the tilt amount of the document based on the tilt amount group. And having.

  The background plate is white or glossy, for example.

Before Symbol boundary point detection means, among the pixels of the input image, present in the vicinity of the sub-scanning direction with respect to the background plate, and the gradation value of the brightness information is equal to or less than the first threshold value A pixel having a difference with respect to the gradation value of the brightness information of the background plate is detected as the boundary point. For example, when a plurality of boundary points are detected, a boundary point existing at a position closest to the background plate in the sub-scanning direction may be selected.

  For example, the inclination amount determination unit determines the inclination amount having the highest frequency among the inclination amounts included in the inclination amount group as the inclination amount of the document.

  According to the present invention, it is possible to detect the amount of inclination of an original with a precision that does not depend on the original and in a shorter time than the prior art.

1 is a diagram illustrating a schematic configuration of an image processing apparatus according to an embodiment of the present invention. It is a figure which shows the hardware constitutions of an image processing apparatus and its control part. It is a figure which shows the structure of an automatic document feeder and a scanner. It is a figure which shows an example of a mode that the original and the background board were seen from the bottom, and the input image corresponding to it. It is a figure which shows the example of the change of the gradation value in the subscanning direction of an input image. It is a figure which shows the example of a functional structure of an image processing apparatus. It is a figure which shows the example of the shift of 2 points | pieces for acquiring the amount of inclination groups. FIG. 6 is a diagram illustrating an example of determination of a document inclination amount. FIG. 6 is a diagram illustrating an example of determination of a document inclination amount. It is a figure which shows the example of the setting of the distance between 2 points | pieces, and the shift amount of 2 points | pieces. 3 is a flowchart illustrating an example of the overall processing flow in the image processing apparatus 1.

  FIG. 1 shows a schematic configuration of an image processing apparatus 1 according to an embodiment of the present invention, and FIG. 2 shows a hardware configuration of the image processing apparatus 1 and its control unit 100.

  The image processing apparatus 1 is an MFP that integrates functions such as a copier, a printer, and a facsimile machine. When the image processing apparatus 1 executes a job for reading an image from a sheet-like document 8 and processing the image data, such as copying, image data conversion (scanning), and facsimile transmission, the document 8 is processed. It operates as a tilt amount detection device that detects the tilt amount of the.

  The image processing apparatus 1 includes an automatic document feeder (ADF) 10, a scanner 20, a printer unit 30, a paper feeding unit 35, a paper feeding cabinet 40, an automatic duplex unit 50, an operation panel 60, a facsimile unit 70, communication. An interface 75, a control unit 100, and an auxiliary storage device 120 are provided.

  The automatic document feeder 10 includes a paper feed tray 11 and a paper discharge tray 16, and conveys one or a plurality of originals 8 set on the paper feed tray 11 to the paper discharge tray 16. During conveyance, the image of the document 8 is read by the scanner 20. The paper feed tray 11 has a sensor that detects the presence or absence of the document 8.

  The automatic document feeder 10 is configured as a cover that covers the platen glass 21 of the scanner 20 and can be opened and closed by rotating around a back-side axis. The user of the image processing apparatus 1 can lift the front end of the automatic document feeder 10 to expose the platen glass 21 and place the document on the platen glass 21.

  The scanner 20 optically reads an image recorded on the original 8 conveyed by the automatic original feeder 10 or the original 8 placed on the platen glass 21 by the user. The scanner 20 sends image data representing the gradation value of each pixel of the read image to the control unit 100.

  The configurations of the automatic document feeder 10 and the scanner 20 will be described in more detail later.

  The printer unit 30 prints an image on a sheet by electrophotography. Photosensitive drums 31a, 31b, 31c and 31d and exposure scanning units 32a, 32b, 32c and 32d for forming toner images of yellow, magenta, cyan and black are provided. Four toner images having different colors are transferred onto the transfer belt 33 so that the overlapped toner images are transferred onto the sheet conveyed from the paper feeding unit 35.

  The paper feed unit 35 includes paper feed cassettes 36 and 38 for storing paper, and pickup rollers 37 and 39 for feeding paper from the paper feed cassettes 36 and 38, and supplies paper to the printer unit 30. To do.

  The paper feed cabinet 40 includes paper feed cassettes 41 and 43, and pickup rollers 42 and 44 for feeding paper from the paper feed cassettes 41 and 43, similarly to the paper feed unit 35. The paper fed out by the pickup rollers 42 and 44 is supplied to the printer unit 30 via the paper transport path of the paper feed unit 35.

  The automatic duplex unit 50 is a unit for enabling duplex printing, takes in a sheet of paper on which an image is printed on one side from the printer unit 30, reverses the front and back, and returns the sheet to the printer unit 30.

  The operation panel 60 includes a touch panel display 61 that displays a screen for an input operation by a user and a key input unit 62 in which hard keys are arranged, and sends a signal corresponding to the input operation to the control unit 100.

  The facsimile unit 70 exchanges image data with an external facsimile terminal using a protocol such as G3.

  The communication interface 75 is an interface for communicating with devices such as a personal computer, a smartphone, and a USB memory that can be attached to and detached from the image processing apparatus 1 via a communication line. As the communication line, a local area network line (LAN line), the Internet, a near field communication line, or the like is used.

  The control unit 100 is a main controller that is responsible for overall control of the image processing apparatus 1. As illustrated in FIG. 2, the control unit 100 includes a central processing unit (CPU) 101, a random access memory (RAM) 102, a read only memory (ROM) 103, and an image processing unit 104.

  The ROM 103 stores a program for controlling the automatic document feeder 10, the scanner 20, the printer unit 30, and the like so that the image processing apparatus 1 operates as a copier, a facsimile machine, an image reader, and the like. Further, a tilt correction program for controlling the image processing unit 104 to detect the tilt amount SV of the document 8 and correct the tilt of the read image is stored. These programs are loaded into the RAM 102 as necessary and executed by the CPU 101.

  The image processing unit 104 performs processing related to the characteristics of the reading optical system, such as shading correction and chromatic aberration correction, on the image data received from the scanner 20. Further, the image processing unit 104 is responsible for part or all of the processing for detecting the tilt amount SV of the document 8 and part or all of the tilt correction processing for correcting the image data based on the detected tilt amount SV. . The image processing unit 104 is configured to include hardware for performing the detection of the tilt amount SV at a higher speed than in the case where the detection is performed only by software.

  The auxiliary storage device 120 stores image data sent from the control unit 100. As the auxiliary storage device 120, a hard disk drive or an SSD (Solid State Drive) is used.

  FIG. 3 shows the configuration of the automatic document feeder 10 and the scanner 20.

  The automatic document feeder 10 includes a paper feed tray 11, a pickup roller 12a, a separating roller pair 12b, a plurality of feeding roller pairs 12c, 12d, 12e, 12f, 12g, and 12h, a conveyance path 13, background plates 14 and 15, and a discharger. It has a paper tray 16 and the like.

  The pickup roller 12 a takes out the uppermost document 8 from the paper feed tray 11. The roller pair 12b is wound by rotation so that only one sheet is allowed to pass when a plurality of documents 8 are taken out in a superimposed manner.

  The feed roller pairs 12c, 12d, 12e, 12f, 12g, and 12h are arranged at intervals along the transport path 13, and transport the document 8 taken out from the paper feed tray 11 and pass it through the reading position. After that, the paper is discharged to the paper discharge tray 16.

  When the document 8 passes between the feed roller pair 12e and the next feed roller pair 12f in the conveyance path 13, the image on the lower surface of the document 8 is image sensor 27 through the light source unit 22 in a stationary state at the reading position. Read by. That is, the document 8 is scanned in the main scanning direction by moving the document 8 from the front end side to the rear end side on the reading position on the surface of the background plate 14.

  The background plates 14 and 15 are members that appear as the background of the document 8 on the imaging surface read by the scanner 20. The background plate 14 is disposed so as to be a part of the wall surface forming the conveyance path 13, and becomes the background of the document 8 when the automatic document feeder 10 reads the image while conveying the document 8. The background plate 15 is disposed opposite to the platen glass 21 when the automatic document feeder 10 that supports the background plate 15 is closed, and the document is read when an image is read from the stationary document 8 placed on the upper surface of the platen glass 21. 8 background.

  The background plates 14 and 15 are made of resin, metal, or a composite material combining these, and the surface thereof is white or has a gloss. The materials of both the background plates 14 and 15 may be the same or different.

  The scanner 20 is a flat head type and includes a light source unit 22, a mirror unit 23, an imaging lens 26, and an image sensor 27. The light source unit 22 includes a light source 24 that irradiates the document 8 and a mirror 25 a that guides reflected light from the document 8 to the mirror unit 23. The light source 24 is, for example, an LED array, and can irradiate the document 8 over the entire length in a direction orthogonal to the conveyance direction. The mirror unit 23 includes mirrors 25 b and 25 c that return light incident from the light source unit 22 and enter the image sensor 27. The light source unit 22 and the mirror unit 23 are configured to be movable in parallel with the platen glass 21.

  When the image is read while the document 8 is conveyed by the automatic document feeder 10, the light source unit 22 and the mirror unit 23 do not move. The light source unit 22 remains stationary at a position below the background plate 14. The light source 24 irradiates, for example, white light through the platen glass 21 from the rear side in the traveling direction of the document 8 toward the lower surface of the document 8 passing through the surface of the background plate 14. This light is reflected by the document 8 and the background plate 14 and enters the image sensor 27 through the mirrors 25 a, 25 b, 25 c and the imaging lens 26. As a result, images of the irradiated portions of the document 8 and the background plate 14 are formed on the imaging surface of the image sensor 27. The image sensor 27 reads the formed image as a row of pixels arranged in a row. Main scanning is performed by driving the image sensor 27, and sub-scanning is performed by conveying the document 8. The image of the document 8 is read line-sequentially together with the background plate 14 by main scanning and sub-scanning.

  On the other hand, when reading an image from the stationary document 8 placed on the platen glass 21, the light source unit 22 moves at a constant speed, and the mirror unit 23 has a constant light path length so that the optical path length is constant. Move at half the speed. In this case, sub-scanning is performed by moving the light source unit 22 and the mirror unit 23. Main scanning is performed by driving the image sensor 27.

  Hereinafter, the function of detecting the amount of inclination of the document 8 will be described by taking as an example the case of reading an image while conveying the document 8 using the automatic document feeder 10. However, even when an image is read from the stationary document 8 placed on the surface of the background plate 15, the inclination amount of the document 8 can be detected.

  FIG. 4 shows an example of a bottom view of the original 8 and the background plate 14 and an input image G10 corresponding to the original. That is, FIG. 4 is a diagram showing the background plate 14 in FIG. 3 and the document 8 passing through the surface as viewed from the light source unit 22 side.

  In FIG. 4, main scanning is periodically performed at a predetermined density during a period in which the document 8 is conveyed in the sub-scanning direction M2 and passes the surface of the background plate 14. As shown in FIG. 4A, the main scanning direction M1 is a direction perpendicular to the sub-scanning direction M2. An area 200 read by main scanning and sub-scanning is a rectangular area having a size that encompasses the entire document 8.

  While the vicinity of the front end 8 a of the document 8 is being irradiated by the light source 24, a band-like shadow 9 is generated on the front side of the document 8. The shadow 9 extends over the entire length of the document 8 in the main scanning direction M1, and has a width corresponding to the thickness of the document 8. The shadow 9 is imaged by the image sensor 27 together with the document 8 and the background plate 14.

  That is, as shown in FIG. 4B, an input image G10 having a document portion 80, a background portion 140, and a shadow portion 90 is obtained as a read image. The document portion 80 corresponds to the document 8, the background portion 140 corresponds to the background plate 14, and the shadow portion 90 corresponds to the shadow 9. The input image G10 is an image obtained by reading a rectangular area including the front, rear, left and right edges of the document 8, and is usually an image including the entire document portion 80 or a part of the image.

  The image processing apparatus 1 detects the amount of inclination of the document 8 by image processing based on the input image G10 having the background portion 140 and the shadow portion 90.

  In FIG. 5, an example of a change in the gradation value MD in the sub-scanning direction of the input image G10 is shown by each curve KS. Each curve KS shown in FIG. 5 corresponds to the position of each pixel different in the main scanning direction. The gradation value MD is lightness or luminance, and is large for bright pixels and small for dark pixels.

  Looking at the change in the gradation value MD in the sub-scanning direction M2 in the input image G10, in the general case where the background color of the document 8 is a light color, the background portion 140 is larger (lighter) and moves to the shadow portion 90. As it moves from the shadow portion 90 to the document portion 80, it gradually becomes smaller (becomes darker).

  Since the surface of the background plate 14 is white or glossy as described above, the gradation value MD0 of the background portion 140 is normally maximized and surely larger than the other portions. The gradation value MD0 of the background portion 140 can be set to the upper limit value of the gradation range or in the vicinity thereof by adjusting the output of the light source 24 or adjusting the sensitivity of the image sensor 27.

  In addition, since the shadow portion 90 is an image of a light-shielded portion of the background plate 14, the gradation value MD of the shadow portion 90 is surely smaller than the gradation value MD0 of the background portion 140. However, the shadow 9 tends to lighten as the distance from the front edge 8a of the document 8 increases due to the influence of the irradiation light. For this reason, the gradation value MD of the shadow portion 90 is large near the background portion 140 and decreases as the distance from the background portion 140 increases.

  On the other hand, the gradation value MD of the original 80 depends on optical characteristics such as the background color of the original 8 and the light reflectance of the surface. Further, when an image exists up to the edge of the document 8, it also depends on the density of the image. Therefore, the gradation value of the document portion 80 is not necessarily larger than the gradation value of the shadow portion 90, and may be almost the same as that of the shadow portion 90.

  Therefore, the image processing apparatus 1 detects the tilt amount SV of the document 8 regardless of the optical characteristics of the document 8 or the like, so that the boundary point between the shadow portion 90 and the document portion 80 (the boundary closer to the document portion 80). Instead, a boundary point KT between the background portion 140 and the shadow portion 90 (a boundary point KT closer to the background portion 140) is detected as a boundary point between the document 8 and the background plate 14. That is, when a plurality of boundary points are detected, the boundary point KT present at the position closest to the background plate 14 in the sub-scanning direction is selected.

  Specifically, the gradation value MD of each pixel is examined in order from the top side in the sub-scanning direction M2, and the position Y in the sub-scanning direction M2 of the first appearing pixel whose gradation value MD is equal to or less than the threshold th3 is determined. This is the boundary point KT. In the same procedure, the boundary point KT is detected for the position X of each pixel in the main scanning direction M1. The threshold value th3 may be referred to as “boundary point threshold value th3”.

  The threshold value th3 satisfies both the condition JK1 that is equal to or smaller than the first threshold value th1 and the condition JK2 that the difference of the background plate 14 from the gradation value MD0 is equal to or larger than the second threshold value th2. The value to be Condition JK1 is a fixed condition. The condition JK2 is a variable condition that changes according to the optical characteristics of the background plate 14 and the output of the light source 24.

  In each curve KS shown in FIG. 5, the gradation value MD decreases from the gradation value MD0 of the background portion 140 as the position in the sub-scanning direction progresses, and the gradation values MD for a plurality of pixels are sampled on the way. Is done. Then, the pixel when the gradation value MD first becomes equal to or less than the threshold value th3 is detected as the boundary point KT. Even when a plurality of pixels having the gradation value MD of the threshold value th3 are detected, the pixel having the threshold value th3 or less first is selected as the boundary point KT.

  When the minimum gradation value MD that satisfies the condition JK2 is larger than the first threshold value th1, the threshold value th3 of the boundary point may be made to coincide with the first threshold value th1. If the minimum gradation value MD that satisfies the condition JK2 is smaller than the first threshold value th1, the minimum gradation value MD that satisfies the condition JK2 may be set as the threshold value th3 of the boundary point.

  The image processing apparatus 1 detects the tilt amount of the shadow 9 corresponding to the front end 8a of the document 8 as the tilt amount SV of the document 8 based on the detected boundary point KT.

  By the way, the width of the shadow 9 becomes non-uniform due to the influence of bending (curving) and lifting of the document 8. In other words, the boundary points KT of the respective positions X in the main scanning direction M1 may not be aligned in a straight line in the main scanning direction M1, but may be arranged so as to draw an irregularly curved curve. According to the image processing apparatus 1, the inclination amount SV of the document 8 can be detected even in such a case.

  FIG. 6 shows an example of the functional configuration of the image processing apparatus 1, and FIG. 7 shows an example of a two-point shift for obtaining the tilt amount group GSVp. FIGS. 8 and 9 show examples of determining the inclination amount SV of the document 8. Further, FIG. 10 shows an example of setting the distance Dx between two points and the shift amount Ds between the two points.

  6, the image processing apparatus 1 includes a boundary point detection unit 301, a boundary point memory 302, an inclination amount detection unit 303, an inclination amount group acquisition unit 304, a document inclination amount determination unit 305, an inclination correction unit 306, and two points. An inter-distance setting unit 307 and the like are provided. These functions are realized by the hardware configuration of the control unit 100 described above and the CPU 101 executing the tilt correction program described above.

  The boundary point detection unit 301 acquires the input image G10 from the scanner 20 serving as an image reading unit, and the document 8 and the background plate 14 (or the background plate 15) from the change in the gradation value MD in the sub-scanning direction M2 in the input image G10. Boundary point KT is detected. As described above, the gradation value MD is gradation information (brightness information) that is larger as it is brighter. However, the gradation information may be larger as the density is darker.

  The boundary point detection unit 301 exists in the vicinity of the background plates 14 and 15 in the sub-scanning direction M2 among the pixels of the input image G10, and the gradation value MD of the brightness information is the first as described above. A position Y of a pixel that is equal to or smaller than the threshold th1 and has a difference between the brightness information of the background plates 14 and 15 and the gradation value MD0 is equal to or larger than the second threshold th2 is detected as a boundary point KT. The procedure for detecting the boundary point KT for each pixel position X in the main scanning direction M1 is as described above.

  The boundary point detection unit 301 stores the boundary point KT detected for each position X in the main scanning direction M1 in the boundary point memory 302. When the maximum value of the size (number of pixels) in the main scanning direction M1 of the input image G10 is, for example, 8192, there is a possibility that a maximum of 8192 boundary points KT may be stored in the boundary point memory 302. Actually, the number of boundary points KT is a number corresponding to the size of the document 8. The boundary point memory 302 is provided in the RAM 102, for example.

  The data stored as the boundary point KT represents the position Y in the sub-scanning direction M2, and may be the pixel number (main scanning line number) in the sub-scanning direction M2 of the input image G10. Alternatively, addresses may be assigned in the order of arrangement of pixels in the main scanning direction M1, and the position X of each boundary point KT in the main scanning direction M1 may be specified by the address in the boundary point memory 302. A set of the position X and the position Y may be stored as data of the boundary point KT.

  Note that the gradation value MD tends to be abnormal at both ends of the input image G10 in the main scanning direction M1. In addition, the gradation value MD may become abnormal (irregular) due to the influence of noise even at portions other than both ends. Therefore, when an irregular boundary point KT is detected, it may be invalidated and excluded from the target of subsequent processing. For example, if the position Y detected as the boundary point KT has a difference equal to or larger than a set threshold value with respect to the position Y of the normal boundary point KT adjacent to the position Y, it is determined as an irregular boundary point KT. For example, it is not stored in the boundary point memory 302.

  As shown in FIG. 7, the inclination amount detection unit 303 is 2 apart from the plurality of boundary points KT detected along the main scanning direction M1 by a distance Dx between the two points set on the boundary point KT. The inclination amount SVp of the points KT1 and KT2 is detected.

  That is, the inclination amount detection unit 303 reads one boundary point KT on the tip side in the main scanning direction M1 as one point KT1 from the boundary point memory 302, and is a position separated from the position X1 of the point KT1 by a distance Dx between the two points. The boundary point KT of X2 is read as the other point KT2. Then, for example, a difference between the point KT2 and the point KT1 (difference in position Y) is calculated as the inclination amount SVp. Since the inclination angle of the line connecting the two points KT1 and KT2 can be calculated based on the inclination amount SVp and the distance Dx between the two points, the inclination amount SVp substantially corresponds to the inclination angle.

  The distance Dx between the two points is shorter than the total length of the input image G10 in the main scanning direction M1, for example, about one quarter. The distance Dx between two points when the number of pixels in the main scanning direction M1 is 8192 is, for example, a distance of 2048 pixels. If the document 8 is A4 size and the number of pixels is 5000, the distance Dx between the two points is, for example, a distance corresponding to 1250 pixels. However, the present invention is not limited to this, and may be about 1/10, 1/5, 1/2, 1/2, or the like of the total length in the main scanning direction M1, or 256 pixels, 512 pixels, or 1024. An appropriate number of pixels such as a pixel may be used.

  The tilt amount group acquisition unit 304 notifies the tilt amount detection unit 303 of the distance that is the shift amount Ds, thereby setting the two points KT1 and KT2 along the main scanning direction M1 (shift amount Ds). Shift them one at a time. Then, by acquiring the inclination amount SVp detected each time the shift is performed from the inclination amount detection unit 303, the inclination amount composed of a plurality of inclination amounts SVp corresponding to one end side of the document 8 (for example, the side of the front end 8a). Group GSVp is obtained.

  For example, when the total number of detected boundary points KT is 7000, the distance Dx between two points is 2048 (pixels), and the shift amount Ds is 1 (pixels), the inclination is composed of about 5000 inclination amounts SVp. The quantity group GSVp is acquired.

  The document inclination amount determination unit 305 determines the inclination amount of one edge as the inclination amount SV of the document 8 based on the inclination amount group GSVp.

  For example, as shown in FIG. 8, the slope amount SVp included in the slope amount group GSVp is counted for each value to obtain the frequency for each value, and the slope amount having the largest frequency among the slope amounts SVp contained in the slope amount group GSVp. SVp (that is, the peak value in the histogram of the inclination amount SVp) is determined as the inclination amount SV of the document 8.

  Alternatively, the inclination amount SVp that is the median value in the distribution of the inclination amounts SVp included in the inclination amount group GSVp is determined as the inclination amount SV of the document 8. In this case, the median value is calculated by applying a known arithmetic expression based on the values of all the inclination amounts SVp.

  As another method, as shown in FIG. 9, assuming that the distribution in the range where the inclination amount SVp is close to 0 is a broad distribution having symmetry, the median value of the symmetric range can be set as the inclination amount SV. In this case, the slope amount SVp, for which the slope amount SVp is a negative predetermined amount, for example, is set as the first slope amount SVp1, and the slope amount SVp having the same frequency as the first slope amount SVp1 is set as the second slope amount SVp2. To do. Then, half of the sum of the first inclination amount SVp1 and the second inclination amount SVp2 may be set as the inclination amount SV of the document 8.

  The point-to-point distance setting unit 307 sets the point-to-point distance Dx according to the size of the document 8 in the main scanning direction M1, and notifies the inclination amount detection unit 303 of the distance.

  As shown in FIG. 10A, when the size of the document 8 is small, the distance Dx (Dx ′) between the two points is made longer than when the size of the document 8 is large. For example, when the document 8 is A3 size, the distance between two points Dx ′ is 2896, and when the document 8 is A4 size, the distance between two points Dx is 2048. In this way, by reducing the distance Dx between the two points as the size of the document 8 in the main scanning direction M1 is shortened, the tilt amount SVp constituting the tilt amount group GSVp is increased, and the tilt amount SV of the document 8 is increased. Ensure the accuracy of detection.

  Further, the tilt amount group acquisition unit 304 sets the shift amount Ds of the two points KT1 and KT2 according to the size of the document 8 in the main scanning direction M1.

  As shown in FIG. 10B, when the size of the document 8 is small, the shift amount Ds (Ds ′) is made shorter than when the size of the document 8 is large. For example, if the document 8 is A3 size, the shift amount Ds' is set to 2, and if the document 8 is A4 size, the shift amount Ds is set to 1. As described above, the shift amount Ds is shortened as the size of the document 8 in the main scanning direction M1 is shortened, so that the tilt amount SVp constituting the tilt amount group GSVp is increased, and the tilt amount SV of the document 8 is detected. To ensure accuracy.

  FIG. 10C shows an example in which both the distance Dx between two points and the shift amount Ds are set according to the size of the document 8 in the main scanning direction M1.

  Returning to FIG. 6, the tilt correction unit 306 performs tilt correction processing on the input image G <b> 10 according to the tilt amount SV of the document 8 determined by the tilt amount determination unit 305. The tilt correction process is a process for generating a corrected image G12 having no tilt by rotating the input image G10 by an angle corresponding to the tilt amount SV. The corrected image G12 is delivered to a means for processing this according to the job.

  An example of the overall processing flow in the image processing apparatus 1 is shown in the flowchart of FIG.

  In FIG. 11, the input image G10 is obtained by reading the image of the document 8 set on the paper feed tray 11 of the automatic document feeder 10 or the platen glass 21 of the scanner 20 (# 101). Based on the gradation value of the pixel of the input image G10, the boundary point KT between the background plates 14 and 15 and the document 8 is detected and held (# 102).

  A distance Dx between two points in the main scanning direction M1 is set (# 103), and an inclination amount SVp between the two points is calculated and held while shifting the two points KT1 and KT2 in the main scanning direction M1 (# 104). . Then, the inclination amount SV of the document 8 is determined based on the inclination amount group GSVp composed of a plurality of inclination amounts SVp (# 105). Thereafter, an inclination correction process according to the inclination amount SV is performed on the input image G10 (# 106).

  According to the above-described embodiment, it is possible to detect the inclination amount SV of the document 8 without using complicated calculation processing such as calculation of an approximate line by the Hough transform or the least square method. Detection of the boundary point KT by comparing the gradation value of the pixel with the threshold th3, detection of the inclination amount SVp for obtaining the difference between the two boundary points KT, and extraction of the predetermined inclination amount SVp from the inclination amount group GSVp The determination of the amount of inclination SV is a process that can be easily realized by hardware. That is, by implementing these processes as hardware, it is possible to detect the tilt amount SV at a higher speed than in the case where only the software is used. Increasing the speed of detection, that is, improving the response to the trigger of detection, is particularly important when images of a plurality of documents 8 are read one after another using the automatic document feeder 10. By quickly detecting the inclination amount SV, the inclination correction for the input image G10 read from each document 8 can be performed earlier.

  In the embodiment described above, since the tilt amount SV is detected using an image including the shadow 9 corresponding to the front edge 8a of the document 8, the tilt amount SV can be detected in the initial stage of reading the document 8, and the tilt Various processes using the quantity SV can be performed at an early timing.

  When detecting the tilt amount SV of the stationary document 8 set on the platen glass 21 regardless of the automatic document feeder 10, the light source unit 22 moves and approaches the rear end of the document 8. A shadow 9 generated on the rear end side of the document 8 may be used.

  In this case, for example, the boundary point detection unit 301 examines each gradation value MD of the pixel from the rear end side in the input image G10, and the first appearing pixel whose gradation value MD is equal to or less than the threshold th3. The position Y in the sub-scanning direction M2 may be set as the boundary point KT.

  Note that the position where the shadow 9 is formed changes depending on the arrangement position of the light source 24, and accordingly, the boundary point KT may be detected in accordance with the position to detect the tilt amount SV. For example, when the document 8 is illuminated from the front side in the moving direction of the light source unit 22, the shadow 9 generated on the front end side of the document 8 is detected in the same manner as the detection of the tilt amount SV when the document 8 is conveyed. The amount of inclination SV may be detected using.

  The image processing apparatus 1 is not limited to the MFP, and may be any device that reads an image of the document 8, and may be a copier, a facsimile machine, an image reader, or the like. An image sensor that reads an image from the document 8 may be disposed in the automatic document feeder 10.

  In addition, the configuration of the whole or each part of the image processing apparatus 1, the processing contents, order or timing, the method of detecting the boundary point KT, the method of determining the inclination amount SV of the document 8, etc., are in accordance with the spirit of the present invention. It can be changed as appropriate.

1 Image processing device (document tilt detection device)
8 Document 8a Front edge (edge)
14, 15 Background plate 20 Scanner (image reading means)
24 light source 200 area (rectangular area)
M1 Main scanning direction M2 Sub scanning direction G10 Input image SV Inclination amount (original document inclination amount)
KT boundary point 301 boundary point detection unit (boundary point detection means)
303 Inclination amount detection unit (inclination amount detection means)
304 Inclination amount group acquisition unit (inclination amount group acquisition means)
305 Document inclination amount determination unit (document inclination amount determination means)
306 Inclination correction unit (inclination correction means)
307 Two-point distance setting unit (two-point distance setting means)
Dx Distance between two points KT1, KT2 Point SVP Amount of inclination Ds of two points Ds Shift amount (distance)
GSVp inclination amount group th1 first threshold th2 second threshold

Claims (7)

An apparatus for detecting the amount of inclination of a sheet-like document placed on or passing through a background plate,
A light source for illuminating the document;
Image reading means for acquiring an input image by reading a rectangular region including at least one edge of the original by a reflected light from the original by the light source in a main scanning direction and a sub-scanning direction perpendicular thereto;
Boundary point detection means for detecting a boundary point between the original and the background plate from a change in gradation value in the sub-scanning direction in the input image;
An inclination amount detecting means for detecting an inclination amount of two points which are on the boundary point and are separated by a set distance between the plurality of boundary points detected along the main scanning direction;
An inclination amount group acquisition means for acquiring an inclination amount group composed of a plurality of inclination amounts corresponding to the one edge by shifting the two points for each set distance along the main scanning direction;
Document inclination amount determining means for determining the inclination amount of the one edge as the inclination amount of the document based on the inclination amount group ;
The background plate is white or shiny;
The boundary point detection means includes
Among the pixels of the input image, the gradation that exists near the background plate in the sub-scanning direction, the tone value of the brightness information is equal to or less than a first threshold value, and the tone information of the brightness information of the background plate Detecting a pixel having a difference to a value equal to or larger than a second threshold as the boundary point;
An apparatus for detecting an amount of inclination of a document. The boundary point detection means includes
When a plurality of the boundary points are detected, a boundary point existing at a position closest to the background plate in the sub-scanning direction is selected.
The document inclination amount detection apparatus according to claim 1 . The inclination amount determining means includes
An inclination amount having the largest frequency among the inclination amounts included in the inclination amount group is determined as an inclination amount of the document;
3. A document inclination amount detection apparatus according to claim 1 or 2 . The inclination amount determining means includes
In the distribution of the inclination amount included in the inclination amount group, an inclination amount that is a median value thereof is calculated as an inclination amount of the document.
3. A document inclination amount detection apparatus according to claim 1 or 2 . A point-to-point distance setting means for setting the distance between the two points;
The point-to-point distance setting means is
Setting the distance between the two points according to the size of the document in the main scanning direction;
Tilt amount detection device of the document according to any one of claims 1 to 4. The inclination amount group acquisition means includes:
The shift amount of the two points is set according to the size of the original in the main scanning direction.
Tilt amount detection device of the document according to any one of claims 1 to 5. A light source that illuminates a sheet-like document disposed on or passing through the surface of the background plate;
Image reading means for acquiring an input image by reading the original in a main scanning direction and a sub-scanning direction perpendicular to the original by reflected light from the original by the light source;
Boundary point detection means for detecting a boundary point between the document and the background plate for one edge of the document from a change in gradation value in the sub-scanning direction in the input image;
An inclination amount detecting means for detecting an inclination amount of two points which are on the boundary point and are separated by a distance between the two points, with respect to the plurality of boundary points detected along the main scanning direction;
An inclination amount group acquisition means for acquiring an inclination amount group composed of a plurality of inclination amounts corresponding to one edge of the document by shifting the two points for each distance set along the main scanning direction;
An inclination amount determining means for determining an inclination amount of the one edge as an inclination amount of the document based on the inclination amount group;
Inclination correction means for performing correction processing on the input image according to the inclination amount of the document determined by the inclination amount determination means ,
The background plate is white or shiny;
The boundary point detection means includes
Among the pixels of the input image, the gradation that exists in the vicinity of the background plate in the sub-scanning direction, the gradation value of the lightness information is equal to or less than a first threshold value, and the lightness information gradation of the background plate Detecting a pixel having a difference to a value equal to or larger than a second threshold as the boundary point;
An image processing apparatus.

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