Image reading device

Abstract

To provide an image reading device that can accurately read an image.SOLUTION: An image reading device comprises: a conveying roller; a plurality of line image sensors; first acquisition means that acquires the coordinates of a plurality of dot patterns on the basis of read data acquired by reading a chart on which a first dot column and a second dot column are printed, which are formed by arranging the plurality of dot patterns in a conveyance direction; second acquisition means that acquires the distance between the coordinates of the dot patterns adjacent to each other; and third acquisition means that acquires a correction value for the line image sensors to read an image. On a chart 400, a dot pattern 401 of the first dot column and a dot pattern of the second dot column are arranged shifted from each other in the conveyance direction by a distance D / M. The third acquisition means acquires the correction value on the basis of the distance in the conveyance direction between the coordinates of the dot patterns 401 of the first dot column and the distance in the conveyance direction between the coordinates of the dot patterns of the second dot column.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an image reading device. [Background technology]

[0002] Image reading devices for large-format documents generally use multiple small-sized line image sensors, which are cost-effective. Because multiple line image sensors are used, it is necessary to stitch together the data read by each line image sensor. In this case, if the document transport roller is misaligned, an error will occur in the process of stitching together the data.

[0003] 14(a) and (b) are explanatory diagrams of an example of an image reading device using multiple line image sensors. FIG. 14(a) shows the configuration of a reading unit of the image reading device, and FIG. 14(b) shows the misalignment that occurs during reading. The image reading device shown as an example is configured to transport an original 110 by upstream original transport rollers 107 and downstream original transport rollers 108 (hereinafter, when both are referred to simultaneously, they will be written as original transport rollers 107 and 108), and to read the original by multiple line image sensors (hereinafter, CIS) 106. The multiple CISs 106 are arranged in a staggered pattern in the width direction that intersects with the transport direction of the original.

[0004] When the multiple line image sensors 106 obtain results, the respective results are joined together at a joining position 113. At this time, if either or both of the document transport rollers 107 and 108 are misaligned, an error occurs in the joining position due to the misalignment in the transport direction between the line image sensors. For example, when a straight line pattern 1403 is read as shown in FIG. 14B, due to the misalignment of the document transport rollers 107 and 108, the result may be read as a wobbly line 1404, which causes a misalignment in the joining position when the patterns are joined together.

[0005] In response to the above problems, a configuration is known in which calibration processing is performed to obtain and correct in advance an error component during reading due to eccentricity deviation of a document conveyance roller. In Patent Document 1, in the calibration processing, a document printed with a plurality of dot patterns is read, and based on the position data of the read dot patterns, a configuration is disclosed in which the eccentricity deviation of document conveyance rollers 107 and 108 is obtained using curve approximation processing.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the above configuration, the influence of eccentricity of the conveyance mechanism was obtained by performing curve approximation based on the coordinate interval ratio of the acquired dot patterns. In order to accurately obtain the eccentricity deviation of document conveyance rollers 107 and 108 and perform high-precision image reading, it is preferable to perform curve approximation processing based on more data using a document printed with more dot patterns. However, in order to distinguish between reading a dot pattern and dust, a dot pattern of a certain size is required, and the number of patterns printed on the document, that is, the number of data used for curve approximation, may be limited.

[0008] In view of the above problems, an object of the present invention is to provide an image reading apparatus that can read an image with high precision. To provide.

Means for Solving the Problems

[0009] To achieve the above object, the image reading apparatus of the present invention includes: A conveyance roller that conveys a document in a conveyance direction; A plurality of line image sensors that read an image of a document conveyed by the conveyance roller First acquisition means for acquiring coordinates of a plurality of the dot patterns based on read data obtained by reading a chart in which a first dot column and a second dot column, each configured by arranging a plurality of dot patterns in the conveyance direction, are printed at different positions in the width direction intersecting the conveyance direction Second acquisition means for acquiring a distance between coordinates of adjacent dot patterns based on the coordinates acquired by the first acquisition means Third acquisition means for acquiring a correction value for reading an image by the line image sensor based on the distance acquired by the second acquisition means Comprising In the chart, the dot patterns of the first dot column and the dot patterns of the second dot column are arranged shifted from each other in the conveyance direction The third acquisition means acquires the correction value based on a conveyance direction distance between coordinates of dot patterns adjacent to each other in the conveyance direction of the first dot column and a conveyance direction distance between coordinates of dot patterns adjacent to each other in the conveyance direction of the second dot column, acquired by the second acquisition means.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an image reading apparatus capable of reading an image with high accuracy.

Brief Description of the Drawings

[0011]

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Figure 14

Modes for Carrying Out the Invention

[0012] Hereinafter, with reference to the drawings, modes for carrying out the present invention will be exemplarily and specifically described based on examples. Note that the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, the scope of the present invention is not intended to be limited to the following embodiments.

[0013] [First Embodiment] First, the first embodiment according to the present invention will be described. Although details will be described later, the image reading apparatus according to the first embodiment includes the document conveyance rollers 107 and 108 and a plurality of CISs (line image sensors) 106, similar to the image reading apparatus described with reference to FIGS. 14(a) and (b). In the first embodiment, a correction value for correcting a reading error due to the eccentricity of the document conveyance rollers 107 and 108 is obtained by reading a specific pattern in advance. The influence due to the eccentricity of the document conveyance rollers 107 and 108 specifically refers to the variation in the amount of document conveyance per unit rotation angle that occurs when the axes of the document conveyance rollers 107 and 108 are displaced from the center due to manufacturing tolerances or the like. The conveyance amount in a unit interval may be more or less depending on the phase of the roller, and the error amount due to the eccentricity of the document conveyance rollers 107 and 108 becomes zero when added for one rotation of the rollers. Here, the unit interval is an interval determined by the rotation angle of the document conveyance rollers 107 and 108.

[0014] <Configuration of Image Reading Apparatus> First, the basic configuration of the image reading apparatus according to the first embodiment will be described. FIGS. 1(a) to 1(c) are explanatory views of the image reading apparatus according to the first embodiment. FIG. 1(a) is a perspective view showing the appearance of a sheet feed type scanner 100 which is an image reading apparatus according to the first embodiment. The scanner 100 has a document feed slot 101 and a document feed tray 102 on the front side of the apparatus main body. The user places the leading edge of the document on the document feed tray 102 so that the central part of the document is positioned at the center of the feed slot, and slides it on the tray to insert it into the document feed slot 101. The document feed slot 101 is designed to allow a certain degree of positional deviation and inclination during insertion with respect to the width in the main scanning direction p of the document that the scanner 100 can read. Regarding the configuration of the document feed path, it will be described later with reference to FIG. 1(b). For the sake of explanation, a coordinate axis is set as shown in FIG. 1(a), and this coordinate axis is similarly applied to other drawings. Specifically, the direction from one end side to the other end side in the width direction of the scanner 100 is the x direction, the depth direction from the front side to the back side of the scanner 100 is the y direction, and the vertical direction from the lower side to the upper side of the scanner 100 is the z direction. The x direction is substantially parallel to the width direction of the document inserted into the scanner 100, and the document conveyance direction is substantially parallel to the y direction which intersects the x direction. In the first embodiment, the x direction, the y direction, and the z direction are orthogonal to each other.

[0015] The scanner 100 is provided with an operation unit 103 constituted by physical keys, a touch panel, an LCD panel, etc. on the upper surface of the apparatus main body, and is configured to be able to set reading conditions and input document sizes. Also, an upper cover 104 is attached to the upper surface of the scanner 100, and by opening the upper cover 104 upward, access to the reading unit etc. becomes possible, and the scanner 100 is configured so that the maintenance of the apparatus main body can be performed.

[0016] Figures 1(b) and 1(c) are schematic diagrams showing the internal configuration of the scanner 100. Figure 1(b) is a cross-sectional view, and Figure 1(c) is a top view. In the cross-sectional view of Figure 1(b), the left side is the upstream side and the right side is the downstream side with respect to the paper feeding direction of the document 110, and the document 110 is conveyed from the left side to the right side (y direction). The document 110 fed by the user via the document feeder 102 is discharged from the back of the main body through a flat conveyance path.

[0017] The document detection sensor 105 is a sensor that detects the insertion of the document 110. When the document detection sensor 105 detects the insertion of the document 110, the control unit 202 (see Figure 2) of the scanner 100 rotates the upstream document conveyance roller 107 to draw the document 110 into the main body. The end detection sensor 112 is a sensor used to detect the leading end of the document 110 drawn into the main body by the rotation of the upstream document conveyance roller 107. The detection result of the end detection sensor 112 is also used to determine the reading start position of the document 110 and to detect the position of the trailing end of the document 110.

[0018] Inside the main body, the document 110 passes between the glass plate 109 and the document pressing plate 111. The document pressing plate 111 functions to press the document 110 against the glass plate 109 with a predetermined pressure. The CIS 106 is a line image sensor in which light receiving elements are arranged in the main scanning direction p (X direction in the figure), and is composed of a plurality of chips each composed of a plurality of light receiving elements. The reading surface of the CIS 106 faces the glass plate 109 and is designed such that the reading focus position is located at the contact surface between the document 110 and the glass plate 109.

[0019] The downstream document conveyance roller 108 is configured to be driven by a belt (not shown) following the upstream document conveyance roller 107, and has the role of discharging the document that has passed through the area where the document pressing plate 111 presses against the glass plate 109 to the downstream side. The control unit 202 described later is composed of each detection sensor, a motor (not shown) for rotating the upstream document conveyance roller 107, a circuit board for controlling the CIS 106 and the operation unit 103, and the like.

[0020] As shown in the top view of FIG. 1(c), in the scanner 100, a plurality of (five in the first embodiment) CISs 106 are arranged in a staggered manner in the main scanning direction p. The scanner 100 reads with each CIS 106, and the control unit 202 performs a process of connecting the data read by each CIS 106 at the connection position 113.

[0021] FIG. 2 is a block diagram showing the hardware configuration of the scanner 100 in the present embodiment. In the scanner 100, the control unit 202 that controls image reading and the like includes a CPU 204, a memory 208, a motor driver 207, an interface (hereinafter referred to as IF) unit 203, an A / D conversion unit 206, and a power supply unit 205. The operation unit 103 is configured by a touch panel with a Liquid Crystal Display (LCD). On the LCD of the operation unit 103, information regarding the document to be read and the settings of the reading device is displayed according to an instruction from the CPU 204. Also, the user can change inputs to the scanner 100, such as various settings, by performing touch panel operations on the operation unit 103 while checking the information displayed on the LCD of the operation unit 103.

[0022] The conveyance motor 201 is controlled by the CPU 204 via the motor driver 207 to rotate the upstream document conveyance roller 107 and the downstream document conveyance roller 108. The outputs of the document detection sensor 105 and the end detection sensor 112 are input to the CPU 204. The CPU 204 performs control such as determining the driving timing of the plurality of CISs 106 based on changes in the output signals of these sensors and the state of the conveyance motor 201.

[0023] ​A plurality of CISs 106 output the read images as analog signals to the control unit 202. The analog signals output from the plurality of CISs 106 are converted into digital signals by respective A / D conversion units 206 and input to the CPU 204. The CPU 204 processes the data converted into digital signals by respective A / D conversion units 206 and can transmit the data as image data to an external device connected via USB or LAN or the like through the IF unit 203. The power supply unit 205 generates voltages required for respective units and supplies power. The memory 208 can store image data for a plurality of lines.

[0024] <Calibration Process> Hereinafter, the flow of the calibration process of reading the original document 110 using the CIS 106 and obtaining correction values will be described with reference to FIG. 3. FIG. 3 is a flowchart of the calibration process by the scanner 100. Note that the correction value acquisition timing may be to acquire correction values in advance, or to acquire correction values each time of reading. Alternatively, the scanner 100 may be configured to prompt the user to acquire correction values periodically, such as once for a plurality of readings or once within a predetermined period.

[0025] When acquiring correction values in advance, read a predetermined original document prepared in advance at the time of factory shipment or at the user's site to obtain correction values, and thereafter apply the same correction values for each reading. In this case, since it is not necessary to acquire correction values for each reading, the reading time can be shortened and productivity can be improved.

[0026] On the other hand, when acquiring correction values for each reading, acquire correction values by reading a predetermined original document before reading or by reading an original document with a correction value acquisition pattern printed on the header part of the original document. In this case, since the current error components can be corrected at any time, highly accurate reading can be realized.

[0027] In the calibration process, first in step S301, the CPU 204 accepts the input of pressing the calibration start button on the operation unit 103 by the user. By this step, the scanner 100 enters a state of waiting for the insertion of a dedicated document for calibration. Hereinafter, for simplicity, "step S~" is abbreviated as "S~".

[0028] In S302, the CPU 204 determines whether it has detected the insertion of the calibration document 110 set by the user. If the determination result of this step is true and the insertion of the document 110 is detected, the process proceeds to S303. On the other hand, if the determination result of this step is false and the insertion of the document 110 is not detected, the detection determination of the insertion of the document 110 is performed again in S302.

[0029] In S303, the CPU 204 controls the conveyance motor 201 to convey the document 110 to the reading start position. When the document 110 is conveyed to the reading start position, the process proceeds to S304.

[0030] In S304, the CPU 204 starts the image reading operation and saves the data obtained by reading (referred to as reading data) in the memory 208.

[0031] In S305, the CPU 204 determines whether the reading of a predetermined length has been completed in S304. If the determination result of this step is true and the reading of the predetermined length has been completed, the process proceeds to S306. On the other hand, if the determination result of this step is false and the reading of the predetermined length has not been completed, the reading operation is continued until the reading of the predetermined length is completed, and the determination is performed again in S305.

[0032] In S306, the CPU 204 ends the image reading operation and conveys the document 110 to the paper discharge position. Then, when the image reading operation ends, the process proceeds to S307.

[0033] In S307, the CPU 204 performs correction value acquisition processing. The correction value obtained in this step is stored in the memory 208 and read out and applied during normal reading operations. Note that S307 may be started before the conveyance of the original 110 to the paper discharge position is completed.

[0034] <Correction value acquisition processing> Next, the process of acquiring correction values based on the read pattern, that is, the details of the correction value acquisition processing in S307 of FIG. 3, will be described with reference to FIGS. 4(a), (b) and 5. FIG. 4 is a diagram showing a calibration chart 400 which is a pattern for correction value acquisition processing in the first embodiment. The calibration chart 400 is an example of the original 110 for calibration. FIG. 4(a) shows approximately the whole of the calibration chart 400, and FIG. 4(b) is an enlarged view of the left end region and the right end region of the region A surrounded by the dotted line in FIG. 4(a), showing the details of the calibration chart 400.

[0035] As shown in FIG. 4(a), on the calibration chart 400, a plurality of circular dot patterns 401 each consisting of a plurality of ON dots with a pixel value of 1 are printed in isolation from each other. While the scanner 100 conveys the original 110 with the original conveyance rollers 107, 108, the CIU 106 reads the dot pattern 401. As the pattern arrangement on the original, a plurality of circular dot patterns 401 are printed over the width Xr of the readable area of the scanner 100 and the circumferential length Yr which is the circumferences of the original conveyance rollers 107, 108. Note that a plurality of dot patterns 401 more than the circumferences of the original conveyance rollers 107, 108 may be printed. Also, in this specification, the dot pattern 401 is also referred to as a grid point.

[0036] A more detailed arrangement of the dot pattern 401 will be described with reference to FIG. 4(b). Hereinafter, the main scanning direction p in the calibration chart 400 is described as a direction parallel to the x direction, which is the width direction of the calibration chart 400, and the sub-scanning direction q is described as a direction parallel to the y direction, which is the conveyance direction of the calibration chart 400. In the calibration chart 400, a plurality of columns are formed in which a plurality of dot patterns 401 are arranged at equal intervals in the sub-scanning direction q, and these columns are formed side by side in the main scanning direction p.

[0037] The dot pattern 401 at one end of the main scanning direction p and one end of the sub-scanning direction q of the calibration chart 400, that is, the dot pattern 401 at the upper left corner of FIG. 4(b), is defined as the dot pattern 401a. At this time, dot patterns 401 are arranged at equal intervals at a distance D from the dot pattern 401a in the sub-scanning direction q, forming a first dot column, which is a column of dot patterns 401. Also, with respect to the dot patterns 401 in the first dot column, dot patterns 401 for two dots are arranged at equal intervals at a distance D in the main scanning direction p (x direction). That is, three first dot columns composed of dot patterns 401 having the same coordinates in the sub-scanning direction q are formed. The collection of dot patterns 401 formed by these three first dot columns extending in the sub-scanning direction q is defined as the dot pattern group Gr1. Similarly, the calibration chart 400 has a total of M dot pattern groups (dot pattern groups) each composed of three dot columns of dot patterns 401 arranged at equal intervals in the sub-scanning direction q.

[0038] Dot pattern group Gr2 is adjacent to dot pattern group Gr1 in the main scanning direction p and is composed of three columns of second dot columns. In the first embodiment, the distance between dot patterns 401 of dot pattern group Gr1 and dot pattern group Gr2 that are adjacent to each other in the main scanning direction p is distance D. The dot patterns 401 of dot pattern group Gr2 are the dot patterns 401 from the third dot to the fifth dot in the main scanning direction p from dot pattern 401a of dot pattern group Gr1. The sub-scanning direction position of the dot patterns 401 of dot pattern group Gr2 is shifted by a distance D / M with respect to the dot patterns 401 of dot pattern group Gr1. That is, the amount of shift in the sub-scanning direction q of dot pattern 401 is the distance obtained by equally dividing distance D into M parts.

[0039] Similarly, the sub-scanning direction position of the dot patterns 401 of dot pattern group Gr3 adjacent to dot pattern group Gr2 is shifted by a distance D / M with respect to the dot patterns 401 of dot pattern group Gr2. In this way, with respect to the dot patterns 401 of adjacent dot pattern groups, dot patterns 401 are arranged with a shift of distance D / M in the sub-scanning direction q to form dot pattern groups, and a total of M dot pattern groups are formed. That is, the sub-scanning direction position of the dot patterns 401 of dot pattern group GrM is shifted by a distance (D×(M - 1)) / M with respect to the dot patterns 401 of dot pattern group Gr1. Note that dot pattern group GrM is the dot pattern group located at the end on the opposite side of dot pattern group Gr1 in the width direction of calibration chart 400. Dot pattern group GrM is composed of three columns of Mth dot columns. By such an arrangement method of dot patterns 401, dot pattern groups from dot pattern group Gr1 to dot pattern group GrM are formed. With such an arrangement, when looking at the entire dot pattern area it can be seen that dots of other dot pattern groups are interpolated at equal intervals between dots in the sub-scanning direction q of the reference dot pattern group Gr1.

[0040] Here, the number of divisions M, which is also the total number of dot pattern groups, is preferably defined as a number such that M ≧ D / (2×R) when the radius of the dot pattern 401 is R. This is because when the number of divisions M satisfies the above formula and the deviation amount in the sub-scanning direction q between dot pattern groups is set to D / M, all the dot patterns 401 are arranged without gaps in the sub-scanning direction q. In other words, by satisfying the above conditions, when all the dot patterns 401 are arranged at the same position in the main scanning direction p, the dot patterns 401 adjacent to each other in the sub-scanning direction q overlap. In the first embodiment, the dot chart is arranged such that the deviation between the sub-scanning coordinates between adjacent dot pattern groups is D / M, but this is not limited to this, and it is also suitable to set the deviation between sub-scanning coordinates as a multiple of D / M.

[0041] FIG. 5 is a flowchart of the correction value acquisition process according to the first embodiment. In the correction value acquisition process, the processes of S501 to S506 are performed in order. In the correction value acquisition process, first, in S501, the CPU 204 functions as an acquisition means for acquiring the center coordinates of the circular dot pattern 401, and acquires the center coordinates of each circular dot pattern 401 from the read data acquired by the image reading operation. In the acquisition process of each correction value described later, the center coordinates acquired in this step are used.

[0042] In S502, the CPU 204 performs a process for acquiring the inclination angle of the CIS 106. The plurality of circular dot patterns 401 are arranged concentrically such that the sum of the coordinates from the reference coordinates is 0. In the first embodiment, the inclination angle is acquired using this arrangement relationship. The process for acquiring the inclination angle in this step is a process for suppressing the deviation of the connection position 113 when the read data is joined together. With the information on the inclination angle of the CIS 106 obtained in this step, it becomes possible to perform the joining of the read image with high precision later. In the acquisition process of each correction value described later, the correction value corresponding to the inclination angle of the CIS 106 acquired in S502 is applied in advance and then the process is performed.

[0043] In S503, the CPU 204 performs a process of obtaining the magnification in the sub-scanning direction by the document conveyance rollers 107 and 108. The process of obtaining the magnification in the sub-scanning direction by the document conveyance rollers 107 and 108 is a process of obtaining the magnification in the sub-scanning direction due to the diameter error of the document conveyance rollers 107 and 108 that affects the entire reading result of the scanner 100.

[0044] In S504, the CPU 204 performs a process of suppressing the influence due to the eccentricity of the document conveyance rollers 107 and 108. This step is a process for correcting the reading error in the sub-scanning direction q due to the eccentricity of the document conveyance rollers 107 and 108 that affects the entire reading result of the scanner 100, for example, by obtaining the eccentricity rate of the document conveyance rollers 107 and 108.

[0045] In S505, the CPU 204 performs a process of obtaining the magnification in the main-scanning direction due to the step difference between chips. The process of obtaining the magnification in the main-scanning direction due to the step difference between chips is a process for correcting the reading error in the main-scanning direction p due to the gap between each chip inside the CIS 106.

[0046] In S506, the CPU 204 performs a process of obtaining the splicing position. The process of obtaining the splicing position is a process for accurately splicing the reading results of each CIS 106, and is a process of obtaining the splicing position 113 by applying in advance the correction values corresponding to each step obtained from the results of S502 to S505. Thus, the calibration involving the acquisition of each correction value is completed.

[0047] <Center coordinate acquisition process> Next, the process of obtaining the center coordinate 601 of the circular dot pattern 401 based on the read data, that is, the details of the center coordinate derivation process of S501 in FIG. 5, will be described with reference to FIGS. 6 and 7.

[0048] FIG. 6 is an explanatory diagram of a circular dot pattern 401 of a calibration chart 400 that is a target for calibration reading. FIG. 6 shows an enlarged view of the circular dot pattern 401 and an enlarged view of the binarized dot pattern 401. In the enlarged view, the dot pattern 401 is shown in gray in order to clearly show the center coordinates 601 of the dot pattern 401. The circular dot pattern 401 is configured to be a pattern that is relatively large with respect to the pixels to be read by the scanner 100.

[0049] FIG. 7 is a flowchart of the center coordinate acquisition process according to the first embodiment. In the center coordinate acquisition process, first, in S701, the CPU 204 extracts all the pixel data in the main scanning direction p of the CIS 106 at the target position in the sub-scanning direction q of the CIS 106 from all the read data. Here, the target position in the sub-scanning direction q is the position in the sub-scanning direction q when extracting data by regarding one pixel in the sub-scanning direction q as one line, and in the center coordinate acquisition process, pixel data is extracted one pixel at a time in the sub-scanning direction q.

[0050] In S702, the CPU 204 determines whether there are pixels in which the gradation value continuously exceeds the threshold Xt in the main scanning direction p based on the pixel data extracted in S701. In the determination, binarization is performed for each pixel as shown on the right side of FIG. 6 for the image data. If the determination result of this step is true, that is, if there are pixels in which the gradation value continuously exceeds the threshold Xt in the main scanning direction p, the process proceeds to S703. On the other hand, if the determination result of this step is false, that is, if there are no pixels in which the gradation value continuously exceeds the threshold Xt in the main scanning direction p, the process proceeds to S705. Note that the threshold Xt used in this step is set in advance, and the data is stored in the memory 208.

[0051] In S703, the CPU 204 acquires the center coordinates in the main scanning direction p of the dot pattern 401. Specifically, the position of the central pixel of the continuous pixels whose gradation value exceeds the threshold Xt is acquired as the center coordinates in the main scanning direction p.

[0052] In S704, the CPU 204 determines whether the acquisition of the central coordinates in all main scanning directions p, that is, the central coordinates in the main scanning direction p for all lines in the sub-scanning direction q, has been completed. If the determination result in this step is true, that is, if the acquisition of the central coordinates in all main scanning directions p has been completed, the process proceeds to S706. On the other hand, if the determination result in this step is false, that is, if there are central coordinates that have not been acquired among the central coordinates in all main scanning directions p, the process proceeds to S705.

[0053] In S705, the CPU 204 advances the target position in the sub-scanning direction q by one pixel in the sub-scanning direction q. Then, the process proceeds to S701, and pixel data extraction is performed at the new target position. In this way, the steps of S701 to S705 are repeated until the acquisition of the central coordinates in all main scanning directions p is completed.

[0054] In S706, the CPU 204 takes the average of the acquired central coordinates in the main scanning direction p, and sets the obtained average value as the center coordinates 601 of the circular dot pattern 401 that is a grid point. The position of the center coordinates 601 in the sub-scanning direction q can be, for example, the position of the line at the center in the sub-scanning direction q among the lines where pixels with a gradation value exceeding the threshold Xt are continuous in the main scanning direction p. In this way, in the scanner 100, the CPU 204 functions as a first acquisition means for acquiring the coordinates of each of the plurality of dot patterns 401 printed on the calibration chart 400.

[0055] In addition, when considering the reading error due to dust when obtaining the central coordinates in the main scanning direction p, it is preferable to increase the dot pattern 401. Also, when considering the reading error due to the gap between the chips of the CIS 106, when obtaining the coordinates in the main scanning direction p, it is necessary to select a portion that does not span between the chips to obtain the center coordinates.

[0056] The shape of the dot pattern does not necessarily have to be circular, but a substantially circular shape as shown in FIG. 6 is desirable. This is because the substantially circular shape is less affected by the error components during reading when obtaining the center coordinates 601. For example, when there is an inclination of the original at the time of original setting, if the shape of the dot pattern is square, it is difficult to determine whether, among the pixel data in the main scanning direction p of the read image data of the CIS 106, the pixel whose gradation value continuously exceeds the threshold Xt in the main scanning direction p. The substantially circular shape is easier to distinguish continuous pixel data whose gradation value continuously exceeds the threshold Xt in the main scanning direction p than a square. Further, when the dot pattern is substantially circular, it is not necessary to perform the process of obtaining the center coordinates for all lines in the sub-scanning direction q as in S704 to S706 of FIG. 7. That is, on the premise that the dot pattern is substantially circular, it is possible to obtain the center coordinates 601 of the dot pattern by estimating pixel data whose gradation value continuously exceeds the threshold Xt in the main scanning direction p, so that the time required for obtaining the center coordinates can be shortened.

[0057] <Sub-scanning direction magnification acquisition process> Next, the sub-scanning direction magnification acquisition process in the first embodiment, that is, the details of the sub-scanning direction magnification acquisition process of S503 in FIG. 5, will be described with reference to FIGS. 8, 9(a), (b), and 10.

[0058] FIG. 8 is a flowchart of the sub-scanning direction magnification acquisition process according to the first embodiment. In S801, the CPU 204 determines the main scanning section that is the acquisition target of the sub-scanning direction magnification. The main scanning section determined in this step is the main scanning area read by one of the plurality of CIS internal chips constituting one CIS 106.

[0059] In S802, the CPU 204 selects the coordinates to be processed based on the center coordinate data of the circular dot pattern 401. Specifically, the CPU 204 searches for the center coordinates 601 of the circular dot pattern 401 included in the main scanning section determined in S801 in the sub-scanning direction q. Then, from the center coordinates 601 detected by the search, first, a reference point and a main scanning distance measurement point are selected. The reference point and the main scanning distance measurement point are the center coordinates 601 of the dot pattern 401 having the same coordinates in the sub-scanning direction q on the chart. As the reference point and the main scanning distance measurement point, points in a positional relationship sandwiching the pixel located at the center in the main scanning section of the sensor chip that reads a predetermined main scanning section are selected. Here, among the two selected center coordinates 601, the center coordinate 601 on the main scanning direction reference side (head pixel side) is selected as the reference point, and the other center coordinate 601 is selected as the main scanning distance measurement point.

[0060] After selecting the reference point and the main scanning distance measurement point, the CPU 204 selects a sub-scanning distance measurement point. The sub-scanning distance measurement point is the center coordinate of the circular dot pattern 401 having the same coordinates in the main scanning direction p on the chart, and the coordinate point at a position where the distance between the reference point and the main scanning distance measurement point and the distance between the reference point and the sub-scanning distance measurement point are the same on the chart is selected. In this way, the CPU 204 obtains the main scanning direction distance (conveying direction) between the reference dot pattern serving as a reference and the dot pattern adjacent to the reference dot pattern in the main scanning direction p. Similarly, the CPU 204 obtains the sub-scanning direction distance (width direction distance) between the reference dot pattern and the dot pattern adjacent to the reference dot pattern in the sub-scanning direction q.

[0061] FIGS. 9(a) and (b) are explanatory diagrams of the method for reading the dot pattern 401 according to the first embodiment. FIG. 9(a) shows the positional relationship between the chart on which the circular dot pattern 401 is printed and the chip 901 in the CIS 106 that performs the reading. FIG. 9(b) is FIG. 9(a ) It represents the positional relationship of the center coordinates 601 of a plurality of dot patterns 401 obtained based on the data obtained by reading the pattern shown. In FIGS. 9(a) and (b), among the plurality of center coordinates 601, a total of 18 coordinates, namely coordinates A11, A21, ···, A91, A12, A21, ···, A92, are shown as the coordinates read by one chip 901. A11 and A12 are arranged adjacent to each other in the main scanning direction p, and A11 and A21 are arranged adjacent to each other in the sub-scanning direction q. Here, as an example, it represents a state where the center coordinates 601 of the dot pattern 401 are read with a shift in the main scanning direction p and the sub-scanning direction q respectively due to the inclination of the CIS106 and the inclination of the chart in the set original document. For such data, when A11(x11, y11) is selected as the reference coordinate (reference point), A12(x12, y12) is selected as the main scanning distance measurement point, and A21(x21, y21) is selected as the sub-scanning distance measurement point.

[0062] In S803, the CPU 204 performs conversion of each distance measurement point to the relative coordinates centered on the coordinate A11 which is the reference coordinate. When the coordinate of A11 after conversion is A11a(0, 0), A12 is converted to A12a(x12a, y12a), and A21 is converted to A21a(x21a, y21a). At this time, x12a = x12 - x11, y12a = y12 - y11, x21a = x21 - x11, y21a = y21 - y11. At this time, y21a is synonymous with the sub-scanning direction distance (conveying direction distance) between A11a and A21a, and y12a is synonymous with the main scanning direction distance (width direction distance) between A11a and A12a. Hereinafter, specific explanations will be made using these coordinates. FIG. 10 shows an image of the coordinate data after conversion.

[0063] In S804, the CPU 204 corrects the coordinates (in this example, the coordinates A12a and A21a after transformation) transformed in S803 based on the correction value for the tilt information of the CIS 106 obtained in the tilt angle acquisition process of S502. When the tilt angle of the corresponding chip is determined to be φ by the immediately preceding tilt detection of the CIS 106, A12a and A21a are transformed into A12b (x12b, y12b) and A21b (x21b, y21b) respectively with the coordinate A11a as the reference point. Here, if the tilt of the CIS 106 or the chip 901 is mechanically limited and the tolerance does not affect the reading result, it is also possible to omit the correction process. By S804, the main scanning direction distance x21b, which is the distance between the reference point and the transformed main scanning ranging point A12b, and the sub-scanning direction distance y12b, which is the distance between the reference point and the transformed sub-scanning ranging point A21b, can be obtained.

[0064] In S805, the CPU 204 stores the main scanning direction distance x21b and the sub-scanning direction distance y12b obtained in S804 in the memory 208 as distance data at the coordinate A11 which is the reference coordinate. This is the flow of the process for acquiring the conveyance data information at one reference point, and the same process is also performed for other arranged center coordinates 601. In the scanner 100, the CPU 204 functions as a second acquisition means for acquiring the distance in the main scanning direction p and the distance in the sub-scanning direction q between the coordinates of the dot pattern 401 based on the coordinates of the dot pattern 401. Further, the second acquisition means also acquires correction data by correcting these distances based on the correction value for the tilt information of the CIS 106.

[0065] In S806, the CPU 204 determines whether there remains a center coordinate 601 that can be selected as a reference point based on the stored center coordinate data. If the determination result of this step is true, that is, if there remains no center coordinate 601 that can be selected as a reference point, the process proceeds to S807. On the other hand, if the determination result of this step is false, that is, if there remains a selectable center coordinate 601, the center coordinate 601 of the circular dot pattern 401 shifted by one in the sub-scanning direction q from the center coordinate 601 selected as the reference point immediately before is selected. In this way, while shifting the reference point in the sub-scanning direction q, the CPU 204 acquires a plurality of distances in the main scanning direction p and the sub-scanning direction q between the coordinates of the dot pattern 401.

[0066] In this way, the center coordinates from A11 to A(N - 1)1 are selected as reference points. The distances to each ranging point are acquired with the selected reference point as the center and recorded in the memory 208. When A(N - 1)1 is selected as the reference point, AN1 becomes the sub-scanning ranging point with respect to A(N - 1)1, and since there is no subsequent data, the process ends. When the distance data in all intervals is complete, in S807, the CPU 204 reads out that data from the memory 208 and obtains the sub-scanning direction magnification Ms. The sub-scanning direction magnification Ms is a value obtained by dividing the sum of the main scanning direction distances by the sum of the sub-scanning direction distances and can be obtained by the following formula (1).

[0067] (Equation 1) Ms = (y21b + y31b + ··· + yN1b) / (x12b + x22b + ··· + x(N - 1)2b) Equation (1)

[0068] The sub-scanning direction magnification Ms obtained by the above calculation can be reflected in the line reading start trigger generation timing, magnification correction in image processing, etc.

[0069] <Suppression of the influence due to the eccentricity of the original conveying roller> Next, the suppression process for the influence of eccentricity of the document conveyance rollers 107 and 108 in the first embodiment, that is, the details of the suppression process in S504 of FIG. 5, will be described with reference to FIGS. 11, 12, and 13(a) to (c). FIG. 11 is a flowchart of the suppression process for the influence of eccentricity of the document conveyance rollers 107 and 108 according to the first embodiment.

[0070] For obtaining the error due to eccentricity, the sub-scanning direction distances (y21b, y31b, ···, yN1b) in the converted coordinate data used when obtaining the sub-scanning direction magnification Ms described above can be used. In the suppression process for the influence of eccentricity, first, in S1101, for obtaining the error due to high-precision eccentricity, the sub-scanning direction magnification acquisition flow shown in FIG. 8 is executed with the region expanded to a plurality of main scanning intervals. Here, in the process of S801, not one sensor chip but the sensor chips necessary for reading all the dot pattern groups (Gr1 to GrM) with different sub-scanning coordinates are targeted. Also, in the process of S802, a pair of two columns of dot patterns 401 having the same sub-scanning coordinates (dot patterns within the same dot pattern group) is selected from the coordinate data of the dot pattern 401 obtained by the analysis by the CPU 204 as the processing target coordinates. Thereafter, the processes from S803 to S806 are performed to obtain the converted coordinate data of the data of all the target sensor chips. By the process of S1101, the converted coordinate data of the dot pattern 401 in the region to be acquired and the sub-scanning direction magnification Ms are obtained.

[0071] In S1102, the sub-scanning direction distance is obtained from the converted coordinate data obtained in S1101, and the value is divided by the sub-scanning direction magnification Ms. The sub-scanning direction distance means the distance (yN1b) between the converted coordinate data adjacent to the sub-scanning direction q indicated by y21a in FIG. 10. The CPU 204 obtains the distance between each of the converted coordinate data, and divides the value by the sub-scanning direction magnification Ms. When the sub-scanning direction distances divided by the sub-scanning direction magnification Ms are Δy2, Δy3, ···, ΔyN, ΔyN = yN1b / Ms. FIG. 12 shows the sub-scanning direction distance Δy (Δy2 It is an explanatory diagram of ~ΔyN). FIG. 12 shows the relationship between the pattern arrangement of the dot pattern 401 of the calibration chart 400 and the distance in the sub-scanning direction after division obtained by reading and performing arithmetic processing on it. Here, the distances in the sub-scanning direction after division in the dot pattern group GrX are represented by ΔyX2 to ΔyXN. Also, the relative distance in the sub-scanning direction with respect to the coordinates of the dot pattern group Gr1 is represented by Δya.

[0072] The divided distance Δy in the sub-scanning direction is recorded in the memory 208 in pairs with the relative coordinates when the reference coordinate is 0. The same process is performed on all coordinate data.

[0073] The distance Δy in the sub-scanning direction acquired in S1102 can be regarded as the conveyance amount per short-term interval of the document conveyance rollers 107 and 108. Therefore, in S1103, the CPU 204 acquires an approximate curve with the vertical axis being the distance Δy in the sub-scanning direction (conveyance amount per unit interval) and the horizontal axis being the cumulative added value y of the distance Δy in the sub-scanning direction (conveyance amount added value). FIGS. 13(a) to (c) are explanatory diagrams of a method for generating an approximate curve according to the first embodiment. First, the CPU 204 creates a sequence of numbers such that the horizontal axis is the cumulative added value y and the vertical axis is Δy using the distance Δy in the sub-scanning direction acquired from the coordinate data corresponding to the dot pattern group Gr1. An example of plotting the created sequence of numbers on a graph is shown in FIG. 13(a). Subsequently, as shown in FIG. 13(b), the value of Δy is plotted at a position where the y coordinate is shifted by Δya with respect to the plot of the dot pattern group Gr1 by inserting the numerical value of the distance Δy in the sub-scanning direction acquired from the coordinate data corresponding to the dot pattern group Gr2 into this sequence of numbers. Similarly, by inserting the numerical values of the distances Δy in the sub-scanning direction for the other dot pattern groups Gr3 to GrM, a sequence of numbers represented by a graph plotted at short intervals as shown in FIG. 13(c) is created. Based on this sequence of numbers, an equation for the approximate curve is obtained by the least squares method.

[0074] For example, in the case of a configuration where the dot pattern 401 of the calibration chart 400 is arranged side by side in the sub-scanning direction q without shifting in the main scanning direction p, the data obtained for creating the approximation curve is limited to that shown in Fig. 13(a). However, in the first embodiment, since the dot pattern 401 of the calibration chart 400 is arranged with a shift in the sub-scanning direction q, as shown in Fig. 13(c), an approximation curve can be created with high precision based on more data.

[0075] In S1104, the CPU 204 stores the timing correction value. By using the equation of the approximation curve obtained in S1103, it becomes possible to obtain a correction value for reading an image by the CIS 106 at an arbitrary rotation angle of the document conveyance rollers 107 and 108. In this example, the correction value for reading an image by the CIS 106 is a value for correcting the generation timing of the read start trigger. In the memory 208 of the scanner 100, a table for holding the timing correction value for the conveyance amount per unit interval is stored, and the timing correction value acquired in S1104 is held in this table. In the scanner 100, the CPU 204 functions as a third acquisition means for acquiring a correction value for correcting the generation timing of the read start trigger of the CIS 106 based on the distance between dot patterns and the conveyance amount per unit interval of the document conveyance rollers 107 and 108.

[0076] The timing correction data held in the timing correction table is read out during a normal reading operation and used to finely adjust the generation timing of the line read start trigger. As a result of this fine adjustment, for a section where the conveyance amount in a unit interval is larger than the theoretical value, the generation timing of the line read start trigger becomes earlier than the initial value, and for a section where the conveyance amount in a unit interval is smaller than the theoretical value, the generation timing becomes later than the initial value. Thereby, even when there is a variation in the conveyance amount due to the eccentricity of the document conveyance rollers 107 and 108, the line read cycle becomes constant and the reading quality can be improved.

[0077] <Effect of the Configuration of the First Embodiment> According to the configuration of the first embodiment, by using the read data of the dot patterns 401 arranged at different main scanning coordinates so as to interpolate between the dot patterns in the sub-scanning direction q, even when the distance between the dot patterns cannot be made short, the eccentricity effect can be obtained with high resolution. As a result, it becomes possible to obtain an approximate curve formula with high accuracy, and it becomes possible to determine the generation timing of the read start trigger with high accuracy, and the scanner 100 can read an image with high accuracy.

[0078] When performing calibration reading, if dust or dirt adheres to the calibration chart, it becomes easier to erroneously detect the center coordinates of the pattern when the size of the dot pattern is small. By using this technology, it is possible to make the size of the dot pattern large enough not to be affected by dust or dirt. If only the coordinates of the dot patterns arranged on the same main scanning coordinate are used, the interval of the plots becomes wide, and there is a possibility that the accuracy near the maximum amplitude value of the curve cannot be obtained sufficiently. However, according to the scanner 100 described above, it is possible to obtain an approximate curve formula with higher accuracy using a large amount of coordinate data. At the same time, since it is possible to obtain an approximate curve formula from a large amount of coordinate data, according to the scanner 100 described above, it is also possible to reduce the influence of minute coordinate fluctuations caused by reading errors.

[0079] In the application of the present invention, the processing described as being performed by one device in each of the above-described embodiments may be shared and executed by a plurality of devices. Alternatively, the processing described as being performed by different devices may be executed by one device. For example, a plurality of CPUs may be provided in the scanner 100, and each CPU may function as a first acquisition unit that acquires the coordinates of the dot pattern 401, a second acquisition unit that acquires the distance between the coordinates of the dot pattern 401, and a third acquisition unit that acquires a correction value. Thus, in a computer system, how each function is realized by a hardware configuration can be flexibly changed.

[0080] The disclosure of this embodiment includes the following configurations. (Configuration 1) A conveyance roller that conveys a document in the conveyance direction, A plurality of line image sensors that read an image of the document conveyed by the conveyance roller, Based on the reading data obtained by reading a chart in which a first dot column and a second dot column, each configured by arranging a plurality of dot patterns in the conveyance direction, are printed at different positions in the width direction intersecting the conveyance direction, a first acquisition means for acquiring the coordinates of the plurality of dot patterns, A second acquisition means for acquiring the distance between the coordinates of adjacent dot patterns based on the coordinates acquired by the first acquisition means, A third acquisition means for acquiring a correction value for correcting the generation timing of the reading start trigger of the line image sensor based on the distance acquired by the second acquisition means, and In the chart, the dot patterns of the first dot column and the dot patterns of the second dot column are arranged shifted from each other in the conveyance direction, The third acquisition means acquires the correction value based on the conveyance direction distance between the coordinates of adjacent dot patterns in the conveyance direction of the first dot column and the conveyance direction distance between the coordinates of adjacent dot patterns in the conveyance direction of the second dot column, both acquired by the second acquisition means. An image reading apparatus characterized by this. (Configuration 2) The image reading apparatus according to Configuration 1, wherein the correction value is a value for correcting the generation timing of the reading start trigger. (Configuration 3) The chart includes a plurality of the first dot columns in which the positions of the dot patterns in the conveyance direction are the same as each other, the plurality of the first dot columns arranged side by side in the width direction, and a plurality of the second dot columns in which the positions of the dot patterns in the conveyance direction are the same as each other, the plurality of the second dot columns arranged side by side in the width direction. The image reading apparatus according to Configuration 1, characterized by this. (Configuration 4) The second acquisition means obtains the width direction distance between the coordinates of dot patterns adjacent to each other in the width direction in the plurality of first dot columns, and in the width direction in the plurality of second dot columns the width direction distance between the coordinates of dot patterns adjacent to each other, and obtains The third acquisition means acquires the correction value based on the plurality of conveyance direction distances and the plurality of width direction distances acquired by the second acquisition means. The image reading apparatus according to Configuration 3. (Configuration 5) The third acquisition means divides the width direction distance by the magnification in the sub-scanning direction, which is a value obtained by dividing the sum of the plurality of conveyance direction distances by the sum of the plurality of width direction distances, and plots the result according to the equation of the approximate curve obtained thereby, and acquires the correction value. The image reading apparatus according to Configuration 4. (Configuration 6) In the chart, the distance between dot patterns adjacent to each other in the width direction is uniform at distance D, The chart has M dot pattern groups each composed of a plurality of dot columns in which the positions of the dot patterns in the conveyance direction are the same as each other, The deviation amount in the conveyance direction between the dot pattern of the first dot column and the dot patterns of the dot columns other than the first dot column is a multiple of D / M. The image reading apparatus according to any one of Configurations 3 to 5. (Configuration 7) When the radius of the dot pattern is R, M satisfies M≧D / (2*R). The image reading apparatus according to Configuration 6. (Configuration 8) The line image sensor has a plurality of chips each composed of light receiving elements, In the chart, at least one or more dot pattern groups are arranged corresponding to the positions in the width direction of the plurality of chips. The image reading apparatus according to Configuration 6. (Configuration 9) The image reading apparatus according to Configuration 1, wherein the dot pattern is arranged over the circumferential length of the transport roller in the transport direction of the chart. (Configuration 10) The dot pattern is circular, The image reading apparatus according to Configuration 1, wherein the first acquisition means acquires the circular center coordinates of the dot pattern as the coordinates of the dot pattern. (Configuration 11) The image reading apparatus according to Configuration 1, wherein the second acquisition means acquires a plurality of transport direction distances between the coordinates of dot patterns adjacent in the transport direction while shifting a reference coordinate in the transport direction based on the coordinates acquired by the first acquisition means. (Configuration 12) The image reading apparatus according to Configuration 1, wherein the plurality of line image sensors are arranged in a staggered pattern in the width direction.

Explanation of Reference Numerals

[0081] 100... Scanner (image reading apparatus), 106... Line image sensor (CIS), 110... Document, 204... CPU (first acquisition means, second acquisition means, third acquisition means), 400... Calibration chart (chart), 401... Dot pattern

Claims

1. A conveyance roller that conveys the original in the conveyance direction, A plurality of line image sensors that read an image of the original conveyed by the conveyance roller, Based on the read data obtained by reading a chart in which a first dot column and a second dot column, each composed of a plurality of dot patterns arranged in the conveyance direction, are printed at different positions in the width direction intersecting the conveyance direction, a first acquisition means for acquiring the coordinates of the plurality of dot patterns, A second acquisition means for acquiring the distance between the coordinates of adjacent dot patterns based on the coordinates acquired by the first acquisition means, A third acquisition means for acquiring a correction value for reading an image by the line image sensor based on the distance acquired by the second acquisition means, Comprising, In the chart, the dot patterns of the first dot column and the dot patterns of the second dot column are arranged shifted from each other in the conveyance direction, The third acquisition means acquires the correction value based on the conveyance direction distance between the coordinates of dot patterns adjacent to each other in the conveyance direction of the first dot column acquired by the second acquisition means and the conveyance direction distance between the coordinates of dot patterns adjacent to each other in the conveyance direction of the second dot column. An image reading apparatus characterized by this.

2. The image reading apparatus according to claim 1, wherein the correction value is a value for correcting the generation timing of a reading start trigger.

3. The chart includes a plurality of the first dot columns in which the positions of the dot patterns in the conveyance direction are the same as each other, and the plurality of the first dot columns arranged side by side in the width direction, and a plurality of the second dot columns in which the positions of the dot patterns in the conveyance direction are the same as each other, and the plurality of the second dot columns arranged side by side in the width direction. The image reading apparatus according to claim 1, characterized by having this.

4. The second acquisition means acquires the width direction distance between the coordinates of dot patterns adjacent to each other in the width direction in the plurality of the first dot columns and the width direction distance between the coordinates of dot patterns adjacent to each other in the width direction in the plurality of the second dot columns, The third acquisition means acquires the correction value based on the plurality of conveyance direction distances and the plurality of width direction distances acquired by the second acquisition means. The image reading apparatus according to claim 3, characterized by this.

5. The image reading apparatus according to claim 4, wherein the third acquisition means acquires the correction value according to an approximate curve equation obtained by plotting the width direction distance divided by a magnification in the sub-scanning direction, which is a value obtained by dividing the sum of the plurality of conveyance direction distances by the sum of the plurality of width direction distances.

6. In the chart, a plurality of the dot patterns are arranged at equal intervals with a distance D in the width direction, The chart has M dot pattern groups each composed of a plurality of dot columns in which the positions of the dot patterns in the conveyance direction are the same as each other, The image reading apparatus according to claim 3, wherein a deviation amount in the conveyance direction between the dot pattern of the first dot column and the dot pattern of the second dot column is a multiple of D / M.

7. When the radius of the dot pattern is R, The image reading apparatus according to claim 6, wherein M satisfies M≧D / (2×R).

8. The line image sensor has a plurality of chips each composed of light receiving elements, The image reading apparatus according to claim 6, wherein in the chart, at least one or more dot pattern groups are arranged corresponding to the positions of the plurality of chips in the width direction.

9. The image reading apparatus according to claim 1, wherein in the conveyance direction of the chart, the dot pattern is arranged over the circumferential length of the conveyance roller.

10. The dot pattern is circular, The image reading apparatus according to claim 1, wherein the first acquisition means acquires the circular center coordinates of the dot pattern as the coordinates of the dot pattern.

11. The image reading apparatus according to claim 1, wherein the second acquisition means acquires a plurality of conveyance direction distances between the coordinates of adjacent dot patterns in the conveyance direction while shifting a reference coordinate in the conveyance direction based on the coordinates acquired by the first acquisition means.

12. The image reading apparatus according to claim 1, wherein a plurality of the line image sensors are arranged in a staggered pattern in the width direction.

Images