JP2010009283A - Image reading device, image reading method and computer program for image reading - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more certainly read an image formed on a medium that is a reading target. <P>SOLUTION: This image reading device reading the reading target image MK formed in a specific position RF on the medium MS that is the reading target carries the medium MS to a carriage direction and obtains a medium image representing the medium MS. The image reading device includes: an inclination angle calculation part calculating inclination angles θf, θb of the medium MS to the carriage direction about a plurality of parts EF, EB of the medium MS from the obtained medium image; a reading position setting part setting a reading position AR on the medium image corresponding to the specific position RF based on the inclination angles θf, θb and positions of the plurality of parts EF, EB; and an image reading part reading the reading target image MK from the reading position on the medium image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image reading technique for reading an image formed on a medium.

  As an input means to a computer, an optical mark reader (OMR) that optically reads a mark written with a pencil or the like on a form such as paper (also called “medium”) is used. The OMR acquires the image data representing the reflectance distribution of the form by conveying the form and receiving reflected light from the form by the linear image sensor during the conveyance. The OMR reads the marks entered in the form by analyzing the image data thus obtained.

  Thus, when image data is acquired by transporting a form, if the form is inclined with respect to the transport direction (called “skew”), the mark entry position in the image data changes in the transport direction. . Therefore, the inclination of each form is detected, and the mark entry position is specified according to the detected inclination.

JP 2000-67247 A

  However, when the form is meandering or rotating during conveyance, the inclination of the form cannot be specified. Therefore, in the conventional OMR, the mark entry position cannot be accurately specified depending on the conveyance state of the form, and the reading accuracy of the mark entered on the form may be lowered. This problem is not limited to OMR, and is a problem common to various image reading apparatuses for reading an image formed at a specific position on a medium.

  SUMMARY An advantage of some aspects of the invention is that it provides a technique that enables an image formed on a medium to be read more reliably.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
An image reading apparatus that reads a reading target image formed at a specific position on a medium that is a reading target, the medium image acquisition unit configured to acquire the medium image representing the medium by conveying the medium in a conveying direction; An inclination angle calculation unit that calculates an inclination angle of the medium with respect to the transport direction for each of a plurality of positions of the medium from a medium image, a position of the plurality of positions with respect to the medium, and an inclination angle at each of the plurality of positions An image reading apparatus comprising: a reading position setting unit that sets a reading position on the medium image corresponding to the specific position, and an image reading unit that reads the reading target image from the reading position on the medium image .

  According to this application example, reading positions corresponding to specific positions on the medium are set based on the positions of the plurality of positions on the medium and the inclination angles of the plurality of positions calculated from the medium image. For this reason, it is possible to read the image to be read more reliably regardless of the conveyance state of the medium.

[Application Example 2]
The image reading apparatus according to Application Example 1, wherein the plurality of locations are positions on the medium that are set in advance on a front side and a rear side of the medium in the transport direction.

  Normally, the change in the inclination of the medium due to the conveyance state is the largest between the front side and the rear side in the conveyance direction. In this application example, the reading position is set based on a plurality of inclination angles set on the front side and the rear side. For this reason, it is possible to read the reading target image by a simpler method while maintaining the reading accuracy of the reading target image.

[Application Example 3]
The image reading apparatus according to Application Example 2, wherein the plurality of locations are sides of the front side and the rear side of the medium, and the inclination angle calculation unit is configured to calculate the front side and the rear side of the medium. An image reading apparatus in which an angle formed by a side direction and a direction orthogonal to the transport direction is an inclination angle.

  Even when the medium meanders or rotates, generally, the distortion between the front side and the rear side of the medium on the medium image is small. Therefore, a plurality of locations for calculating the tilt angle are defined as the sides of the front side and the back side of the medium, and the angle between the direction of the side at the location and the direction perpendicular to the transport direction is used to more accurately tilt the medium. The corner can be calculated.

[Application Example 4]
4. The image reading apparatus according to Application Example 2 or 3, wherein the reading position setting unit includes positions and inclination angles of the plurality of positions set on the front side and the rear side, and the specific position with respect to the medium. An image reading apparatus that calculates an inclination angle of the medium at the specific position based on the position in the transport direction and sets the reading position based on the inclination angle.

  According to this application example, when the inclination of the medium gradually changes, the inclination angle used for setting the reading position can be made closer to the actual inclination angle of the medium. Therefore, it is possible to more reliably read the image to be read.

[Application Example 5]
The image reading apparatus according to any one of Application Examples 1 to 3, wherein the reading position setting unit divides the medium image into a plurality of divided regions corresponding to the plurality of locations, and the plurality of divided regions An image reading device that sets the reading position based on respective inclination angles of the plurality of corresponding positions.

  According to this application example, even when the medium meanders or rotates during conveyance, the tilt angle used for setting the reading position can be set for each divided region. For this reason, it is possible to read the image to be read more reliably.

  Note that the present invention can be realized in various modes. For example, an image reading device, an image reading method, a computer program for realizing the functions of these devices and methods, a recording medium recording the computer program, a data signal including the computer program and embodied in a carrier wave, etc. It is realizable with the aspect of.

Next, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
B. Second embodiment:
C. Variation:

A. First embodiment:
FIG. 1 is a schematic configuration diagram showing a configuration of a mark reading apparatus as a first embodiment. The mark reading apparatus 100 is an apparatus for reading a mark written on a form (medium) such as paper using a pencil or the like. The mark reading apparatus 100 according to the present embodiment includes a control unit 200 and an image input mechanism 300. The control unit 200 is configured as a computer having a CPU 210, a ROM 220, a RAM 230, an external interface 240, and an input / output port 250.

  The CPU 210 implements functions as the image input unit 212 and the image processing unit 214 by executing a program stored in the ROM 220 or the RAM 230. Specific functions of the image input unit 212 and the image processing unit 214 will be described later. The CPU 210 exchanges data with the image input mechanism 300 via the input / output port 250 and exchanges data with an external device (not shown) via the external interface 240.

  The image input mechanism 300 connected to the input / output port 250 includes an image sensor 310 and a transport mechanism 320. The image sensor 310 receives reflected light from a linear area (detection area) on a form in which a mark is entered, and linear image data (line) representing the distribution of the color density (density) of the detection area. This is a linear image sensor that outputs (image). The transport mechanism 320 is a mechanism for transporting a form.

  The image input unit 212 of the control unit 200 controls the transport mechanism 320 to transport the form, and accumulates line images output from the image sensor 310. Specifically, the image input unit 212 controls the transport mechanism 320 to transport the form. The image input unit 212 accumulates the line image output from the image sensor 310 every time the form is conveyed by a predetermined length. The image input unit 212 acquires image data (surface image) representing a two-dimensional distribution of density by scanning the form in the transport direction in this way.

  The image processing unit 214 cuts out an image of a reading region corresponding to a region (entry field) where a mark is entered from the surface image acquired by the image input unit 212. Next, the image processing unit 214 analyzes the cut-out image and specifies the contents to be entered in the form. The contents entered in the form specified by the image processing unit 214 are supplied to the external device via the external interface 240.

  FIG. 2 is an explanatory diagram showing the configuration of the image input mechanism 300. The image input mechanism 300 includes an image sensor 310, a light source 330, a transport path base 340, and four transport rollers 322a to 322d as the transport mechanism 320 (FIG. 1). The document MS in which the mark is entered is transported in the transport direction along the transport path CTP indicated by the one-dot chain line as the transport rollers 322a to 322d rotate. The image input mechanism 300 includes a feeder for taking a form into the image input mechanism 300, other transport rollers, and the like as the transport mechanism 320, but the illustration thereof is omitted in FIG.

  The light source 330 emits light toward the transport path CTP. The light emitted from the light source 330 is reflected by the form MS or the conveyance path base 340. The image sensor 310 receives reflected light from a linear detection area LDA orthogonal to the conveyance direction. Since the conveyance path base 340 has a lower reflectance than the base (unfilled portion) of the form MS, all pixels of the line image output by the image sensor 310 when the form MS is not applied to the position of the detection area LDA are: A pixel having a density value corresponding to the reflectance of the transport path base 340 is obtained.

  FIG. 3 is an explanatory diagram showing an example of a form MS on which marks are read by the mark reading device 100 (FIG. 1). The form MS is conveyed upward (F direction) in the figure substantially along the vertical direction (column direction) of the form MS as the transport rollers 322a to 322d (FIG. 2) rotate. In the form MS of FIG. 3, ten timing marks TM are arranged in the column direction along the left side (L direction side) of the form MS. The form MS is also provided with six entry fields RF corresponding to the respective timing marks TM. The six entry fields RF are arranged in a row direction orthogonal to the column direction at a predetermined column pitch pc interval. The leftmost entry field RF is located at the center of the left side of the form MS by a left margin ml.

  In these entry fields RF, a mark MK is entered with a pencil or the like. In the present embodiment, the background of the form MS is white. However, the background color does not necessarily have to be white as long as the reflectance is different from any of the timing mark TM, the mark MK, and the conveyance path base 340.

  FIG. 4 is a flowchart showing a flow of mark reading processing by the mark reading apparatus 100 (FIG. 1). The mark reading process is started as the mark reading apparatus 100 is activated.

  In step S110, CPU 210 (FIG. 1) determines whether or not form MS is detected. Specifically, the line image output from the image sensor 310 (FIG. 2) includes pixels (white pixels) corresponding to the reflectance of the background of the form MS, that is, pixels whose density is lower than a predetermined threshold. Determine whether or not. If the line image includes white pixels, it is determined that the form MS has been detected, and the process proceeds to step S120. On the other hand, if the line image does not include white pixels, it is determined that the form MS has not been detected. Then, step S110 is repeatedly executed until white pixels are included in the line image.

  In step S120, the image input unit 212 accumulates the line images output from the image sensor 310, and generates a surface image. Accumulation of line images is continuously performed while a form exists in the detection area LDA, that is, while white pixels are included in the line image.

FIG. 5 is an explanatory diagram illustrating an example of the surface image IS acquired in step S120. In the example of FIG. 5, the form MS is conveyed while maintaining a constant angle θ ₀ . Therefore, in the surface image IS, an image of the area corresponding to the form MS (form image) is called counterclockwise (hereinafter simply referred to as “counterclockwise”) from the transport direction toward the paper surface, and the same applies to the clockwise direction. Called) by an angle θ ₀ . Hereinafter, the form image is also referred to as a form MS. In addition, images corresponding to the timing mark TM, entry field RF, and mark MK formed on the form MS are also referred to as timing mark TM, entry field RF, and mark MK, respectively.

  In step S130 of FIG. 4, the image processing unit 214 sets a reading area AR for reading a mark on the surface image IS. As shown in FIG. 5, the reading area AR is set as a rectangular area that is not inclined with respect to the plane image IS. Therefore, the process of cutting out the reading area AR from the surface image IS can be performed more easily. A specific method for setting the reading area AR will be described later.

In the example of FIG. 5, the form MS is conveyed in a tilted state. Therefore, the direction orthogonal to the transport direction, that is, the horizontal direction of the plane image IS (hereinafter also simply referred to as “horizontal direction”) and the arrangement direction of the entry field RF (that is, the row direction) are shifted by an angle θ ₀ . . Therefore, the reading area AR is set at a position shifted upward (conveyance direction) from the timing mark TM to the right (R direction).

  In step S140 of FIG. 4, the image processing unit 214 analyzes the image of the mark reading area AR set in step S130, and determines whether or not a mark is written in the reading area AR. A determination result as to whether or not a mark is entered is output to an external device via the external interface 240. After determining whether or not there is a mark in step S140, the process returns to step S110, and steps S110 to S140 are repeatedly executed.

  FIG. 6 is an explanatory diagram showing how the image processing unit 214 determines the presence or absence of a mark in the reading area AR. In the example of FIG. 6, the reading area AR is a rectangular area having 12 pixels vertically and 30 pixels horizontally. As shown in FIG. 6, when the mark MK is written, the image in the reading area AR includes black pixels (indicated by hatching) with high density. Therefore, the image processing unit 214 calculates the number of pixels (black pixels) whose density is higher than a predetermined threshold in the image of the reading area AR. When the ratio of the calculated number of black pixels to the number of pixels in the entire reading area AR (number of pixels in the area) is higher than a predetermined reference value, the image processing unit 214 determines that the mark MK has been entered. Note that the image processing unit 214 of this embodiment determines whether or not the mark MK is written based on the ratio of the number of black pixels to the number of pixels in the area, but the mark MK is written by another method. It is also possible to determine whether or not. Whether or not a mark is entered can be determined based on, for example, the integrated value of the densities of all the pixels in the reading area AR.

  As described above, in the mark reading apparatus 100, the image of the reading area AR is cut out from the form image acquired from the image input mechanism 300, and the mark MK written in the form MS is read by analyzing the cut out image. . In this embodiment, the analysis is performed without deforming the image in the reading area AR by making the reading area AR into a rectangle that is not inclined with respect to the transport direction. However, the shape of the reading area AR is appropriately changed. It can also be changed. In this case, the image in the reading area AR is deformed as necessary. However, a rectangular area that is not inclined with respect to the transport direction is preferably used as the reading area AR in that the possibility that the image of the mark MK is blurred by the deformation process can be reduced.

  FIG. 7 is a flowchart showing the flow of the reading area setting process executed in step S130 of FIG. FIG. 8 is an explanatory diagram showing how the reading area AR is set.

  In step S210, the image processing unit 214 calculates the inclination θf at the front end EF of the form MS. The inclination θf (hereinafter also referred to as “front-side inclination angle θf”) at the front end EF is, for example, a horizontal reference shifted laterally by a predetermined distance L1, L2 from the position Xf0 of the white pixel when the form MS is detected. A distance ΔXf (= Xf2−Xf1) between the positions Xf1 and Xf2 and a distance ΔYf (= Y2−Y1) between the foremost positions Yf1 and Yf2 at which white pixels are detected at the horizontal reference positions Xf1 and Xf2, respectively. And can be calculated by the following equation (1).

θf = tan ⁻¹ (ΔYf / ΔXf) (1)

  As is clear from the equation (1), the front side inclination angle θf is a positive value when the inclination of the form MS is clockwise, and is a negative value when the form MS is counterclockwise. The relationship between the direction of inclination of the form MS and the front side inclination angle θf is not necessarily limited to this. That is, the front inclination angle θf may be negative when the inclination is clockwise, and the front inclination angle θf may be positive when the inclination is counterclockwise. However, in this case, the position in the vertical direction in setting the position of the reading area AR, which will be described later, is set in the opposite direction to the present embodiment.

  The horizontal reference positions Xf1 and Xf2 are on the left side (L direction side) of the position Xf0 when the position Xf0 of the white pixel when the form MS is detected is on the right side (R direction side) of the surface image IS. ). On the other hand, when the position Xf0 of the white pixel when the form MS is detected is on the left side of the surface image IS, it is set on the right side of the position Xf0.

  When calculating the front inclination angle θf, if the white image is not detected within a predetermined distance from the upper end of the surface image IS, the lateral reference position Xf1 is set to the inner side by reducing the distance L1. It is preferable to detect the front end EF. Even when the distance L1 is equal to or less than the predetermined lower limit value, it is more preferable to interrupt the process when no white pixel is detected.

  The front side inclination angle θf can be obtained by other methods. For example, the horizontal reference positions Xf1 and Xf2 can be set inward by a predetermined distance from both ends in the horizontal direction of the surface image IS, and the front side inclination angle θf can be obtained as described above. It is also possible to detect the positions of the two vertices of the front end EF of the form MS from the surface image IS and calculate the front side inclination angle θf based on the detected positions of the two vertices. Further, without using the angle formed by the front end EF and the lateral direction, the angle formed by the direction of the right side (R direction side) or the left side (L direction side) of the form MS in the vicinity of the front end and the transport direction is inclined forward. It is also possible to set the angle θf.

  In step S220 of FIG. 7, the image processing unit 214 calculates the inclination θb at the rear end EB of the form MS. The inclination θb at the rear end EB (hereinafter also referred to as “rear inclination angle θb”) is calculated based on the distance between the horizontal reference positions and the detection position of the white image at the horizontal reference position, as with the front inclination angle θf. can do.

As described above, in the example of FIG. 8, the form MS is conveyed in a state of being inclined counterclockwise at a constant angle θ ₀ . Therefore, in steps S210 and S220, both the front side inclination angle θf and the rear side inclination angle θb are calculated as −θ ₀ . In other words, the inclination angles at the two positions of the front end and the rear end of the form MS are each calculated as −θ ₀ .

  In step S230 of FIG. 7, the image processing unit 214 detects the timing mark TM. The timing mark TM can be detected as, for example, a black pixel area adjacent to a gray pixel. Note that the gray pixels, that is, the pixels corresponding to the transport path base 340 exist in an area outside the form MS in the surface image IS.

  When the timing mark TM is detected, the image processing unit 214 calculates a correction angle θ for each detected timing mark TM in step S240. The correction angle θ includes a distance Lt between the vertices of the left end of the form MS in the transport direction (vertical direction), a distance Lu from the upper left end of the form MS to the center of the left end of the timing mark TM (reading reference position), and the front end EF. And using the inclinations θf and θb of the rear end EB, the following equation (3) is used.

θ = θf−Lu / Lt × (θb−θf) (3)

  In step S250, the image processing unit 214 sets a rectangular reading area AR that is not inclined with respect to the plane image IS based on the reading reference position. The reading area AR extends from the reading reference position and is separated from the reading reference position by a distance LXi (i is an integer equal to or greater than 1) on the straight line (reference line) BL inclined clockwise by the correction angle θ. The position (reading position) is arranged at the center.

  The distance LXi is a distance when there is no inclination between the corresponding entry field RF and the left end of the form MS. When the form is inclined, the distance from the left end of the form MS to the entry field RF becomes shorter as the inclination angle θ increases. However, the amount of change in the distance from the left end of the form MS to the entry field RF is sufficiently small when the angle θ is small. For this reason, even if the horizontal position of the reading area AR is set regardless of the inclination angle θ, the deviation between the reading area and the entry field RF can be kept sufficiently small as long as the inclination is normal. However, the distance LXi may be changed according to the correction angle θ.

  In the example of FIG. 8, the reading area AR at the left end (L direction end) is arranged at a position separated from the reading reference position in the right direction (R direction) by the left margin ml. The six reading areas AR are arranged in the horizontal direction at an interval of the column pitch pc. That is, in the example of FIG. 8, the value represented by the following formula (4) is used for the distance LXi.

LXi = ml + (i−1) × pc (4)

  On the other hand, the reading area AR is arranged on the reference line BL. Therefore, as shown in FIG. 8, the position of the reading area AR substantially coincides with the position of the entry field RF that is largely shifted in the transport direction (vertical direction) when the form MS is tilted.

  After the reading area AR is set in step S250 (FIG. 7), the process returns to the mark reading process of FIG. Then, as described above, in step S140, the presence / absence of the mark MK is determined from the image of the reading area AR.

  FIG. 9 is an explanatory diagram illustrating a state in which the reading area AR is set when the inclination of the form MS continuously changes during conveyance. In the surface image ISa shown in FIG. 9, since the inclination of the form MS changes during conveyance, the front side inclination angle θf and the rear side inclination angle θb are different. Therefore, the correction angle θ calculated by the above equation (3) is set to a different value for each timing mark TM, and the inclination of the reference line BLa is different for each timing mark. Thus, the reading area AR determined for each timing mark TM is set to an area that covers the entry field RF regardless of the position of the timing mark TM in the vertical direction.

  FIG. 10 is an explanatory diagram showing how the reading area AR is set in the first comparative example. FIG. 10 shows the arrangement of the reading areas AR set based only on the front side inclination angle θf when the inclination of the form MS changes during conveyance, as in FIG. In the first comparative example, the reading area AR is set on the reference line BLb inclined by the front side inclination angle θf from the timing mark TM. Therefore, for the timing mark TM on the rear end EB side of the form MS, the reading area AR is set at a position outside the corresponding entry field RF. As described above, since the reading area AR deviates from the entry field RF, in the first comparative example, there is a possibility that the mark recorded in the entry field RF may not be detected even if the image cut out from the reading area AR is analyzed.

FIG. 11 is an explanatory diagram showing how the reading area AR is set in the second comparative example.
FIG. 11 shows the arrangement of the reading area AR set based only on the rear side inclination angle θb when the inclination of the form MS changes during conveyance as in FIG. In the second comparative example, the reading area AR is set on the reference line BLc inclined by the rear inclination angle θb from the timing mark TM. Therefore, for the timing mark TM on the front end EF side of the form MS, the reading area AR is set at a position outside the corresponding entry field RF. As described above, also in the second comparative example, the mark recorded in the entry field RF may not be detected as in the first comparative example.

  On the other hand, in the first embodiment, the inclinations θf and θb are calculated for the two sides of the front end EF and the rear end EB of the form MS, and the reading area AR is determined based on the calculated inclinations θf and θb of the two sides. Set. Therefore, as shown in FIG. 9, even when the inclination of the form MS changes during conveyance, it is possible to set a reading area AR that can cover the entry field RF. As described above, in the first embodiment, it is possible to more reliably detect the presence or absence of a mark even when the inclination of the form MS changes during conveyance.

  In the first embodiment, the correction angle θ is calculated separately for each timing mark TM, but the correction angle θ may not be calculated separately for all timing marks TM. For example, the form MS may be divided into a plurality of areas in the transport direction, and the reading area AR may be set using the correction angle θ calculated for each divided area. When the form MS is divided into three or more areas, the correction angle θ corresponding to the intermediate divided area is determined based on, for example, the positional relationship of the timing marks TM and the direction of the sides of the form MS in the horizontal direction. The

  In the first embodiment, the timing mark TM is detected, the correction angle θ corresponding to the detected timing mark TM is calculated and the reading area AR is set, but the reading area AR is not used. It is also possible to set AR. However, it is more preferable to set the reading area AR using the timing mark TM in that the reading area AR can be set even if the mark reading apparatus 100 does not have information regarding the arrangement of the entry field RF in the form MS.

  When the reading area AR is set without using the timing mark TM, the correction angle θ used for setting the reading area AR is the length in the vertical direction (FIG. 3) of the form MS and the front end or rear end of the entry field RF. Based on the distance from. That is, the inclination of the form in the entry field RF for determining the position of the reading area AR is determined based on the positional relationship between the form and the entry field RF in the transport direction (that is, substantially the vertical direction of the form MS).

B. Second embodiment:
FIG. 12 is an explanatory diagram showing how the reading area AR is set when the inclination of the form MS changes discontinuously during conveyance. FIG. 12 shows a surface image ISd in a case where the inclination of the form MS changes greatly only once during conveyance. In the second embodiment, the form MS is divided into two in the transport direction, and a reading area AR is set for each of the divided areas. In the second embodiment, the image processing unit 214 detects a bending point VP where the inclination of the form MS has changed from the surface image ISc. For the timing mark TM in front of the bending point VP (F direction), the correction angle θ is set to the front inclination angle θf, and for the timing mark TM in the rear of the bending point VP (B direction), The correction angle θ is set to the rear inclination angle θb. After setting the correction angle θ in this way, the reading area AR that can cover the entry field RF as shown in FIG. 12 can be set by setting the reading area as in the first embodiment.

  The inflection points VP correspond to the longitudinal direction reference positions Y1 to Y4 set to have a predetermined positional relationship with the longitudinal length of the surface image ISd, and the longitudinal direction reference positions Y1 to Y4. It is determined based on the positions of the left end (L direction end) PE1 to PE4. Specifically, among the left ends PE1 to PE4 of the form MS at the vertical reference positions Y1 to Y4, a straight line ELF passing through the two points PE1 and PE2 on the front side (F direction side) and 2 on the rear side (B direction side). A straight line ELB passing through the points PE3 and PE4 is obtained. A position where these two straight lines intersect is a bending point VP.

  When three of the left ends PE1 to PE4 at the four vertical reference positions Y1 to Y4 are present on a straight line, the bending point VP cannot be obtained accurately. Therefore, the image processing unit 214 brings the vertical reference position closest to the left end off the straight line closer to the left end. After the change of the vertical reference position, the image processing unit 214 further obtains the position of the left end, and changes the vertical reference position until there are no three left ends on the straight line. Thus, the bending point VP can be accurately obtained by repeatedly changing the vertical direction reference positions Y1 to Y4. In addition, it is more preferable that the amount of change of the vertical direction reference position is reduced every time it is repeated.

  The vertical reference position can be set by other methods. For example, two left end positions (for example, the left front end of the form MS and the left rear end of the form MS) of the front side and the rear side are taken, and the vertical position that bisects the straight line connecting the left front end and the left rear end. It is also possible to obtain the vertical reference position based on the positional relationship between the left end, the left front end, and the left rear end.

  It is also possible to determine the bending point VP by dividing the left side of the form MS into a plurality of line segments and combining adjacent line segments whose difference in inclination is a predetermined threshold value or less. In this case, a plurality of bending points can be obtained. When a plurality of bending points are obtained, the correction angle is determined based on the slope of the line segment.

  In the second embodiment, the correction angle θ is set to the front tilt angle θf for the timing mark TM in front of the bending point VP, and the correction angle is set for the timing mark TM behind the bending point VP. Although θ is set to the rear inclination angle θb, the correction angle θ for these timing marks TM can be determined based on the inclinations of the front straight line ELF and the rear straight line ELB. is there.

C. Variation:
In addition, this invention is not restricted to the said Example and embodiment, It can implement in a various aspect in the range which does not deviate from the summary, For example, the following deformation | transformation is also possible.

C1. Modification 1:
In each of the above embodiments, the present invention is applied to the mark reading apparatus 100. However, the present invention is generally applied to various image reading apparatuses that read an image formed at a specific position on a medium such as paper. Can do. The present invention can also be applied to, for example, a barcode or QR code (registered trademark of Denso Wave Co., Ltd.) reader printed on a medium, an optical character recognition device (OCR), or the like.

C2. Modification 2:
In the above embodiment, a part of the configuration realized by hardware may be replaced with software, and conversely, a part of the configuration realized by software may be replaced by hardware.

1 is a schematic configuration diagram showing a configuration of a mark reading apparatus as a first embodiment. 3 is an explanatory diagram showing a configuration of an image input mechanism 300. Explanatory drawing which shows an example of the form MS by which a mark is read by a mark reading apparatus. 6 is a flowchart showing a flow of mark reading processing by the mark reading device. Explanatory drawing which shows an example of the surface image acquired in step S120. Explanatory drawing which shows a mode that the presence or absence of the mark in a reading area is determined. 5 is a flowchart showing the flow of a reading area setting process executed in step S130 of FIG. Explanatory drawing which shows a mode that the setting of a reading area is performed. Explanatory drawing which shows a mode that a reading area | region is set when the inclination of a form is changing continuously during conveyance. Explanatory drawing which shows a mode that the reading area | region is set in the 1st comparative example. Explanatory drawing which shows a mode that the reading area | region is set in the 2nd comparative example. Explanatory drawing which shows a mode that a reading area | region is set when the inclination of a form is changing discontinuously during conveyance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Mark reading apparatus 200 ... Control part 210 ... CPU
212: Image input unit 214: Image processing unit 220: ROM
230 ... RAM
DESCRIPTION OF SYMBOLS 240 ... External interface 250 ... Input / output port 300 ... Image input mechanism 310 ... Image sensor 320 ... Conveyance mechanism 322a-322d ... Conveyance roller 330 ... Light source 340 ... Conveyance path base

Claims (7)

An image reading apparatus that reads a reading target image formed at a specific position on a medium that is a reading target,
A medium image acquisition unit configured to acquire the medium image representing the medium by conveying the medium in a conveyance direction;
An inclination angle calculation unit for calculating an inclination angle of the medium with respect to the transport direction for each of a plurality of locations of the medium from the medium image;
A reading position setting unit that sets a reading position on the medium image corresponding to the specific position based on the positions of the plurality of positions with respect to the medium and the inclination angles at the plurality of positions;
An image reading apparatus comprising: an image reading unit that reads the reading target image from the reading position on the medium image. The image reading apparatus according to claim 1,
The plurality of locations are positions on the medium set in advance on the front side and the rear side of the medium in the transport direction. The image reading apparatus according to claim 2,
The plurality of locations are sides of the front side and the rear side of the medium,
The inclination angle calculation unit is an image reading apparatus in which an angle formed by a direction of a side between the front side and the rear side of the medium and a direction orthogonal to the transport direction is an inclination angle. The image reading apparatus according to claim 2, wherein
The reading position setting unit is configured to set the specific position based on the positions and inclination angles of the plurality of positions set on the front side and the rear side, and the position of the specific position with respect to the medium in the transport direction. An image reading apparatus that calculates an inclination angle of the medium and sets the reading position based on the inclination angle. The image reading apparatus according to any one of claims 1 to 3,
The reading position setting unit divides the medium image into a plurality of divided regions corresponding to the plurality of locations, and the reading positions in the plurality of divided regions are based on respective inclination angles of the plurality of locations. The image reading device to set. An image reading method for reading a read target image formed at a specific position on a medium to be read,
A medium image representing the medium is acquired by conveying the medium in a conveying direction;
From the medium image, for each of a plurality of locations on the medium, calculate an inclination angle of the medium with respect to the transport direction,
Based on the position of the plurality of locations with respect to the medium and the inclination angle at each of the plurality of locations, a reading position on the medium image corresponding to the specific position is set,
An image reading method for reading the reading target image from the reading position on the medium image. A computer program for reading a read target image formed at a specific position on a medium to be read,
A function of acquiring a medium image representing the medium by conveying the medium in a conveying direction;
A function of calculating an inclination angle of the medium with respect to the transport direction for each of a plurality of locations of the medium from the medium image;
A function of setting a reading position on the medium image corresponding to the specific position based on the position of the plurality of positions with respect to the medium and the inclination angle at each of the plurality of positions;
The computer program which makes a computer implement | achieve the function which reads the said reading object image from the said reading position on the said medium image.

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