JP6439395B2 - Image reading apparatus, image forming apparatus, and image reading method - Google Patents

Description

  The present invention relates to an image reading apparatus, an image forming apparatus, and an image reading method.

  In an image reading apparatus using a CCD, a CMOS image sensor, or the like, a phenomenon called distortion occurs in which an image is distorted due to the aberration characteristics of a lens used. Distortion is conspicuous in a distortion that spreads or narrows with respect to an ideal imaging position in an imaging apparatus such as a digital camera that mainly uses an area sensor. Further, distortion is caused by a manufacturing error of the lens, individual differences, and the like, and the amount of distortion differs for each lens. In order to correct these distortions, a method is known in which the amount of distortion is measured for each individual lens and correction is performed by referring to the amount of distortion stored in a memory.

  Patent Document 1 discloses an image reading apparatus that corrects the density value and magnification of a floating portion of a document when reading a flat bed. The image reading apparatus described in Patent Document 1 performs edge detection in the main scanning direction for each line to detect a floating portion of a document, and performs density correction and magnification correction according to the document floating information. .

  However, the image reading apparatus described in Patent Document 1 has a problem in that the optical distortion amount of image data due to lens distortion cannot be corrected (distortion correction) when the reading distance of the document changes. .

  The present invention has been made in view of the above, and provides an image reading apparatus, an image forming apparatus, and an image reading method capable of appropriately correcting image data even if a subject reading distance changes. With the goal.

In order to solve the above-described problems and achieve the object, an image reading apparatus according to the present invention includes an image sensor that photoelectrically converts reflected light from a subject via a lens and reads image data of the subject, and the subject A memory that stores in advance optical path length information from the image sensor to the image sensor, and incident / exit angle information in which incident angle data of the reflected light incident on the lens and emission angle data emitted from the lens correspond to each other A pixel position detection unit that detects a pixel position in the main scanning direction of each pixel of the image data of the subject of one line read by the image sensor, the image data, and pixel position data of the detected pixel An edge detection unit for detecting pixel positions at both ends in the main scanning direction of the pixels at both ends of the image data, and the pixel positions at both ends and the pixels at both ends A correction unit that corrects an optical distortion amount of the image data due to distortion of the lens, using the pixel position of each pixel between the positions, the optical path length information, and the incident / exit angle information; The optical path length information is a first optical path length between the lens and the image sensor, and the correction unit is configured to detect each pixel between the both end pixel positions and the both end pixel positions. Using the emission angle data calculated from the pixel position in the main scanning direction and the first optical path length, the first incident angle data is identified by referring to the incident / exit angle information, and the identified first incident angle The optical distortion amount of the image data due to the distortion aberration of the lens is corrected based on the ideal pixel position calculated from the data and the first optical path length, and the pixel shift amount between the pixel positions on both ends and the pixel position. to, be characterized in that .

  According to the present invention, there is an effect that image data can be corrected appropriately even if the reading distance of the subject changes.

FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to the present embodiment. FIG. 2 is a diagram illustrating an example of the configuration of the image reading apparatus and the ADF according to the present embodiment. FIG. 3 is a functional block diagram showing the main part of the functions of the image reading apparatus according to this embodiment. FIG. 4 is a diagram for explaining distortion correction of a conventional image reading apparatus. FIG. 5 is a diagram for explaining a case where a document is lifted when a document is read. FIG. 6 is a diagram for explaining a case where there is a document floating when the document is read. FIG. 7 is a diagram for explaining a case where the document is lifted when the document is read. FIG. 8 is a diagram for explaining a case where the document is lifted when the document is read. FIG. 9 is a diagram illustrating distortion aberration in the line sensor. FIG. 10 is a diagram for explaining the incident / exit angle characteristics indicating the exit angle with respect to the incident angle in the ideal lens. FIG. 11 is a diagram showing the imaging position on the image sensor in the input / output characteristics of the ideal lens. FIG. 12 is a diagram for explaining an incident / exit angle characteristic indicating an exit angle with respect to an incident angle in an actual lens. FIG. 13 is a diagram illustrating the imaging position on the image sensor in the actual input / output characteristics of the lens. FIG. 14 is a diagram for explaining an incident / exit angle characteristic indicating an exit angle with respect to a predetermined incident angle in an actual lens. FIG. 15 is a diagram for explaining an interpolation method of the incident / exit angle characteristics. FIG. 16 is a diagram illustrating the incident / exit angle and the incident / exit angle characteristic of the lens. FIG. 17 is a block diagram illustrating an example of a functional configuration of the image correction unit. FIG. 18 is a diagram illustrating document edge detection. FIG. 19 is a diagram for explaining edge detection of a document. FIG. 20 is a diagram for explaining edge detection of a document. FIG. 21 is a diagram illustrating pixel movement for correcting pixel shift. FIG. 22 is a diagram for explaining the magnification correction. FIG. 23 is a flowchart for explaining an example of the processing operation of the image reading apparatus according to the present embodiment.

  Hereinafter, an embodiment of an image reading apparatus, an image forming apparatus, and an image reading method according to the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by the following embodiment. Moreover, each embodiment can be combined suitably as long as the content is not contradicted. In the following description, an example in which the image forming apparatus according to the present invention is applied to a multifunction peripheral (MFP) will be described. However, the present invention is not limited to this. Note that a multifunction peripheral is a device having at least two functions of a print function (printer function), a copy function (copy function), a scanner function, and a fax function.

  First, a configuration example of the image forming apparatus 300 will be described with reference to FIG. FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus 300 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 300 includes a paper feeding unit 303 and an image forming apparatus main body (image forming unit) 304, and an image reading apparatus 100 and an automatic document feeder (ADF) 200 are mounted on the upper part. Is a digital multi-function machine. Note that the image reading apparatus 100 may be configured such that the ADF 200 is integrated into a single image reading apparatus.

  In the image forming apparatus main body 304, a tandem image forming unit 305, a registration roller 308 that conveys recording paper (recording medium) supplied from the paper supply unit 303 via the conveyance path 307 to the image forming unit 305, and An optical writing device 309, a fixing conveyance unit 310, and a double-sided tray 311 are provided.

  In the image forming unit 305, four photosensitive drums 312 are arranged side by side corresponding to toners of four colors Y, M, C, and K. Around each photosensitive drum 312, image forming elements including a charger, a developing unit 306, a transfer unit, a cleaner, and a static eliminator are arranged.

  In addition, an intermediate transfer belt 313 stretched between the driving roller and the driven roller is disposed between the transfer unit and the photosensitive drum 312 while being sandwiched between the two nips.

  The tandem image forming apparatus 300 configured as described above performs optical writing on the photosensitive drum 312 corresponding to each color for each of Y, M, C, and K colors, and develops each toner of each color by the developing unit 306. Then, primary transfer is performed on the intermediate transfer belt 313 in the order of, for example, Y, M, C, and K.

  Then, the image forming apparatus 300 forms a full-color image on the recording paper by secondarily transferring the full-color image superimposed on the four colors by the primary transfer onto the recording paper, and then fixing and discharging. The image forming apparatus 300 forms an image read by the image reading apparatus 100 on a recording sheet.

  FIG. 2 is a diagram illustrating an example of the configuration of the image reading apparatus 100 and the ADF 200. As shown in FIG. 2, the image reading apparatus 100 is a scanner device mounted on an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine. The image reading apparatus 100 illuminates a document that is a subject (reading object) with irradiation light from the light source 102 and processes a signal received by a CMOS image sensor 109 that photoelectrically converts reflected light from the document. Read the image data of the document. Hereinafter, “subject” is also referred to as “original”.

  Specifically, as shown in FIG. 2, the image reading apparatus 100 includes a contact glass 101 on which a document (subject) is placed, a light source 102 for document exposure, and a first carriage 106 including a first reflection mirror 103. And a second carriage 107 having a second reflecting mirror 104 and a third reflecting mirror 105. The image reading apparatus 100 also corrects various distortions caused by an image sensor 109, which is an RGB color sensor, a lens unit (lens) 108 for forming an image on the image sensor 109, a reading optical system, and the like. A reference white plate (white reference plate) 110 to be used and a slit 111 for reading through a sheet are also provided. The image sensor 109 photoelectrically converts reflected light from the subject via the lens unit 108 and reads image data of the subject. Hereinafter, “lens unit” is also referred to as “lens”.

  The image reading apparatus 100 has an ADF 200 mounted thereon, and is connected via a hinge (not shown) or the like so that the ADF 200 can be opened and closed with respect to the contact glass 101.

  The ADF 200 includes a document tray 201 as a document placing table on which a document bundle composed of a plurality of documents can be placed. The ADF 200 also includes separation / feeding means including a feeding roller 202 that separates documents one by one from a bundle of documents placed on the document tray 201 and automatically feeds them toward the slit 111.

  Further, a guide member 112 is provided on the upstream side of the slit 111 in the document conveying direction. The guide member 112 prevents the document from coming into contact with the slit 111 during document conveyance reading in order to prevent dirt and dust from adhering to the slit 111.

  The image reading apparatus 100 scans the image surface of a fixed document and scans the image of the document in a flat bed reading mode (hereinafter referred to as “pressure plate reading”). Thus, the document is scanned in the direction of arrow A (sub-scanning direction) by a stepping motor (not shown). At this time, the second carriage 107 moves at a speed half that of the first carriage 106 in order to keep the optical path length from the contact glass 101 to the image sensor 109 constant.

  At the same time, the image surface which is the lower surface of the document set on the contact glass 101 is illuminated (exposed) by the light source 102 of the first carriage 106. Then, the reflected light image from the image plane is sequentially sent to the image sensor 109 via the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 and the third reflecting mirror 105 of the second carriage 107, and the lens unit 108. Sent and imaged.

  Then, a signal is output by photoelectric conversion of the image sensor 109, and the output signal is converted into a digital signal. In this way, the image of the document is read, and digital image data is obtained.

  On the other hand, in a sheet-through reading mode (hereinafter referred to as “document feed reading”) in which an original is automatically fed and an image of the original is read, the first carriage 106 and the second carriage 107 move below the slit 111. Thereafter, the document placed on the document tray 201 is automatically fed in the arrow B direction (sub-scanning direction) by the feeding roller 202, and the document is scanned at the position of the slit 111.

  At this time, the lower surface (image surface) of the conveyed document is illuminated by the light source 102 of the first carriage 106. Therefore, the reflected light image from the image plane is sequentially sent to the image sensor 109 via the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 and the third reflecting mirror 105 of the second carriage 107, and the lens unit 108. Sent and imaged. Then, a signal is output by photoelectric conversion of the image sensor 109, and the output signal is converted into a digital signal. In this way, the image of the document is read, and digital image data is obtained. The document whose image has been read is discharged to a discharge port (not shown).

  FIG. 3 is a functional block diagram illustrating a main part of the functions of the image reading apparatus 100. The light source 102 irradiates the original with irradiation light. The image sensor 109 photoelectrically converts reflected light from the document and outputs it as a digital image signal. The image sensor 109 is a line sensor in which a plurality of light receiving elements (not shown) are arranged in the main scanning direction. In the image sensor 109, each light receiving element corresponding to each pixel converts reflected light from the light source 102 into an electric signal, and obtains digital pixel data by an amplifier or an A / D converter (not shown). Further, the image sensor 109 converts digital pixel data, which is parallel data from each light receiving element, into serial data, and synchronizes with the pixel synchronization signal and line synchronization signal from the synchronization signal generation unit 500 to perform digital pixel for each line. Data is transmitted to the image correction unit 502.

  The memory (storage unit) 501 indicates the emission angle with respect to the incident angle of the reflected light from the subject incident on the lens unit 108 in the discrete main scanning direction of the lens unit 108 measured in advance in the manufacturing process of the image reading apparatus 100 or the like. The shown incident / exit angle characteristic (incident / exit angle information) data is stored. Hereinafter, “memory” is also referred to as “storage unit”, and “input / output angle characteristics” are also referred to as “input / output angle information”. The incident / exit angle characteristics (incident / exit angle information) stored in the memory 501 have different characteristics for each individual lens unit 108. For example, the manufactured lens unit 108 can be measured by optical simulation, It can be obtained by providing the output angle value with respect to the discrete incident angle from the manufacturer. The memory 501 stores input / output angle characteristic (input / output angle information) data associated with each lens unit 108. Furthermore, the memory 501 stores in advance a first optical path length (lens-sensor length data) between the lens unit 108 and the image sensor 109, which is optical path length information at the design stage of the image reading apparatus 100, and a subject (original). Information on the second optical path length (document-lens length data) between the lens unit 108 is stored. The memory 501 synchronizes the incident / exit angle information (lens incident / exit angle characteristic data) and optical path length information (optical path length data) of the lens unit 108 in synchronization with the pixel synchronization signal and the line synchronization signal from the synchronization signal generation unit 500. The data is transmitted to the image correction unit 502 for each line. The storage unit 501 includes optical path length information from the subject to the image sensor 109, incident angle data on which incident angle data of reflected light incident on the lens 108 and emission angle data emitted from the lens 108 are associated, and Is stored in advance. The storage unit 501 stores in advance a plurality of pieces of incident / exit angle information (incident / exit angle characteristic data) in which incident angle data and emission angle data set in advance are associated with the lens 108. Details of the incident / exit angle information and the optical path length information will be described later.

  The image correction unit 502 accepts the incident / exit angle information and optical path length information of the lens unit 108 stored in the memory 501, and uses the incident / exit angle information and optical path length information of the lens unit 108 to lift the original when reading the original. Even if it occurs, optimal distortion correction is performed. Note that the image correction unit 502 calculates an incident angle value with respect to an exit angle not stored in the memory 501 by interpolation using two or more exit angle data in the vicinity of the exit angle data stored in the memory 501. The image correction unit 502 corrects the pixel shift in the main scanning direction of all pixels (digital image data) in the main scanning direction received from the image sensor 109, and transfers the corrected pixel to the subsequent stage. Details of the image correction unit 502 will be described later.

  A document size detection unit (subject size detection unit) 503 detects the length of the subject (original) to be read in the main scanning direction. For example, when reading the subject, the document size detection unit 503 detects both ends of the subject in the main scanning direction with a sensor or the like, and acquires the size information of the subject. The document size detection unit 503 transmits the acquired size information of the subject (document) to the image correction unit 502. The “document size detection unit” corresponds to the “subject size detection unit” in the claims.

  Here, an image correction unit of a conventional image reading apparatus will be described with reference to FIG. First, a functional block diagram showing a main part of functions of a conventional image reading apparatus (not shown) is a configuration that does not include the document size detection unit 503 of the image reading apparatus 100 of the present embodiment shown in FIG. FIG. 4 is a diagram for explaining distortion correction of a conventional image reading apparatus. In FIG. 4, the vertical axis represents the amount of pixel shift, and the horizontal axis represents the pixel in the main scanning direction. In addition, R (Red) / G (Green) / B (Blue), which are the three primary colors, are shown.

  In the conventional image reading apparatus, a dedicated original (for example, one having a plurality of vertical lines in the main scan and the interval between the vertical lines being measured) is read by the pressure plate reading described with reference to FIG. By reading, the amount of deviation from the ideal image formation position in all pixels in the main scanning direction is obtained for each color of R (Red) / G (Green) / B (Blue).

  Among the shift amounts, a plurality of pixel positions in the main scanning direction and distortion data of the pixel shift amounts corresponding to the pixel positions are stored in advance in a memory in the image reading apparatus. In the example of FIG. 4, pixel deviation amount data of predetermined “□” is stored in the memory as 17 pixels × 3 (each R / G / B color). This is because when the distortion data for all the pixels in the main scanning direction is stored, the memory capacity becomes enormous.

  The conventional image correction unit obtains distortion data of pixel positions in the main scanning direction that are not stored by interpolation using the stored distortion data under the control of the system side of the image reading apparatus.

  As described above, the distortion data of all the pixels in the main scanning direction can be obtained. Therefore, the conventional image correction unit outputs each main scanning input pixel by shifting the pixel position by the shift amount corresponding to the pixel position. Images can be reproduced at ideal positions. In the example of FIG. 4, each R / G / B color is corrected by moving it to an ideal position for each pixel of the main scanning, that is, the deviation amount becomes 0, so that the spread and narrowing of the distortion aberration image is corrected. At the same time, it is possible to correct a color shift caused by lateral chromatic aberration.

  However, the distortion shift amount data shown in the example of FIG. 4 used by the conventional image correction unit is a shift amount from the ideal image formation position (ideal pixel position) obtained by reading a dedicated document in advance by pressure plate reading. The premise is that the entire surface of the document is in contact with the contact glass when the pressure plate is read.

  FIG. 5 to FIG. 8 are diagrams for explaining a case where the document is lifted when the document is read. As shown in FIG. 5, in the case of reading a document pressure plate, for example, when reading a book or a creased document, there is a place where the document floats from the contact glass 101 near the sub-scanning center. Further, in the case of document transport reading, even when the guide member 112 is installed and the document is lifted and read, strictly speaking, the height of the document reading is not constant within one scan, and the document scanning direction is the same. The document reading distance fluctuates due to various factors such as the presence of a portion where the document once contacts the slit 111 at the front and rear ends, the mechanical configuration, the document conveyance speed, and the paper type.

  As described above, when the document is lifted when the document is read, the distance from the lens to the document becomes long as shown in FIG. 6, and as a result, the image formation position on the image sensor surface has a magnification error in the shrinking direction. Will occur. In FIG. 6, the original reading position and the image formation position on the image sensor surface when there is no original lifting are indicated by solid lines, and the original reading position and the image formation position on the image sensor surface when there is original floating are indicated by dotted lines. Yes. FIG. 7 is a schematic diagram illustrating an example of a read image at the time of reading a pressure plate, and FIG. 8 is a diagram illustrating an example of a read image at the time of document conveyance reading. The example of FIG. 7 is a case where the book shown in FIG. 5 is read, and shows that the magnification is small at a position where the document is lifted from the contact glass 101 in the middle of the sub-scanning direction. Further, the example of FIG. 8 is a case where the guide member 112 shown in FIG. 5 is installed and the original is floated and read. Both ends in the sub-scanning direction are in contact with the contact glass 101, but both ends are in contact with each other. On the other hand, it is shown that the magnification is small at a position where the document floats from the contact glass 101 in the middle portion. As described above, in the read image in which the document is lifted at the time of reading the document, a magnification error occurs, and a distortion shift amount also changes due to the aberration characteristics of the lens.

  FIG. 9 is a diagram illustrating distortion aberration in the line sensor. FIG. 9A shows an input image to the image reading apparatus, and FIGS. 9B and 9C show output images (first example and second example) obtained by reading by the image reading apparatus.

  First, as described with reference to FIG. 2, in the image reading apparatus 100, the original image surface is illuminated (exposed) with the light source 102, and the reflected light passes through the lens unit 108 to the photoelectric conversion element of the image sensor 109. Entered.

  In the image reading apparatus 100 using the line sensor, the lens unit 108 has a spherical surface due to the characteristics of the lens unit 108. Therefore, the ideal imaging position shown in FIG. There may be a distortion in which the interval (position) in the main scanning direction shown in FIG. 9 is narrowed or a distortion in which the interval (position) in the main scanning direction shown in FIG. This is distortion. In addition, when a color sensor is used as the image sensor 109, since the refractive index varies depending on the wavelength of light, color misregistration occurs between R / G / B colors, and chromatic aberration of magnification that causes image blurring occurs. End up. In addition, the aberration depends on the focal length, and the influence of the aberration is reduced as the lens unit 108 has a longer focal distance, and the influence of the aberration increases as the lens unit 108 has a shorter focal distance. In addition, the amount of distortion varies from lens to lens due to the effects of lens manufacturing variation.

  Next, distortion correction will be described with reference to FIGS. FIG. 10 is a diagram for explaining the incident / exit angle characteristics indicating the exit angle with respect to the incident angle in the ideal lens. FIG. 11 is a diagram showing the imaging position on the image sensor in the input / output characteristics of the ideal lens. FIG. 12 is a diagram for explaining an incident / exit angle characteristic indicating an exit angle with respect to an incident angle in an actual lens. FIG. 13 is a diagram illustrating the imaging position on the image sensor in the actual input / output characteristics of the lens.

  As described with reference to FIG. 5 to FIG. 8, when there is a document floating at the time of document reading, the distortion shift amount cannot be corrected only by correcting the magnification error. For example, in the case of a lens having the ideal lens entrance / exit angle characteristics as shown in FIG. 10 for each color of R / G / B, the incident angle when there is no document lift at the end position in the main scanning direction of the document. Is denoted by ωi, the exit angle is denoted by ωo, the incident angle when the document is lifted is denoted by θi, the exit angle is denoted by θo, and the incident angle when the document is not lifted at an arbitrary position in the main scanning direction of the document is denoted by ωi ′, The outgoing angle is indicated by ωo ′, the incident angle when the document is lifted is indicated by θi ′, and the outgoing angle is indicated by θo ′. In all cases, the ideal lens has an incident / exit angle characteristic of incident angle = exit angle, so that distortion does not occur. In the case of an ideal lens, as shown in FIG. 11, when there is no document lift at the end position in the main scanning direction of the document (end image formation position), and when there is document lift (image formation position (image formation) Position) is indicated by B and b, respectively, and the image formation position (image formation position) when there is no document lift at the arbitrary position in the main scanning direction of the document (edge image formation position) and when there is document lift , C and c respectively, the relationship of the following formula (1) is established.

  (B−b) / B = (C−c) / C (1)

  The above equation (1) indicates that the magnification error due to the document floating at the end position in the main scanning direction of the document is the same as the magnification error due to the document floating at an arbitrary position in the main scanning direction of the document. As a result, an ideal lens with an incident angle = an outgoing angle has the same magnification error at any position in the main scanning direction even when the document is lifted. Distortion correction and magnification correction can be performed. In FIG. 11, the original reading position when the original is not lifted and the imaging position on the image sensor surface are indicated by solid lines, and the original reading position when the original is lifted and the imaging position on the image sensor surface are indicated by dotted lines. Show.

  However, in an actual lens to be used, there is no ideal lens in which the incident angle = the outgoing angle because of individual variations among the lenses. For example, in the case of a lens having a lens entrance / exit angle characteristic as shown in FIG. 12, there is an exit angle ωo with respect to the incident angle ωi and document lift when there is no document lift at the end position in the main scanning direction of the document. The exit angle θo with respect to the incident angle θi in this case, the exit angle ωo ′ with respect to the incident angle ωi ′ when the document is not lifted at an arbitrary position in the main scanning direction of the document, and the exit angle θo with respect to the incident angle θi ′ with the document lifted When the document floats when reading the document because 'changes respectively, the ideal imaging position b shown in FIG. 11 at the end position in the main scanning direction of the document and the arbitrary position in the main scanning direction of the document. Since the magnification error in which the pixel is shifted from c to the edge imaging position b ′ and the imaging position c ′ shown in FIG. 13 locally changes, the relationship of Expression (1) does not hold. This is the cause of distortion due to distortion as shown in FIG. In FIG. 12, only one incident / exit angle characteristic data is shown. However, color deviation due to lateral chromatic aberration also occurs due to the deviation of the incident / exit angle characteristic for each color of R / G / B. Therefore, the distortion correction method described with reference to FIG. 4 cannot cope with a case where the document is lifted when the document is read. In FIG. 13, the edge image forming position B ′ and the image forming position C ′ on the image sensor surface when there is no document floating shown in FIG. 11 and the edge on the image sensor surface when there is document floating are shown. A partial imaging position b ′ and an imaging position c ′ are also shown. In FIG. 13, the original reading position and the image formation position on the image sensor surface when there is no original lifting are indicated by solid lines, and the original reading position and the image formation position on the image sensor surface when there is original lifting are indicated by dotted lines. Show.

  Therefore, in the distortion correction according to the present embodiment, the optimum distortion correction is performed even when the document is lifted at the time of reading the document, using the incident / exit angle characteristic data of the lens unit 108 obtained in advance in the manufacturing process of the image reading apparatus 100 or the like. Is.

  First, an outline of image correction in the present embodiment will be described with reference to FIGS. FIG. 14 is a diagram for explaining an incident / exit angle characteristic indicating an exit angle with respect to a predetermined incident angle in an actual lens. FIG. 15 is a diagram for explaining an interpolation method of the incident / exit angle characteristics. FIG. 16 is a diagram illustrating the incident / exit angle and the incident / exit angle characteristic of the lens. In FIG. 14 and FIG. 15, the input / output characteristics indicating the output angle (vertical axis) with respect to the input / output angle (horizontal axis) of the actual lens (lens with distortion) are indicated by “black squares”. In FIG. 16, only the half surface of the document described with reference to FIG. 6 and its imaging position are shown. In addition, the incident / exit angle characteristics also show only 0 ° to 90 °. In the following description, it is assumed that distortion correction is performed on the other half side of the document (not shown) in the same manner.

  As described with reference to FIGS. 10 to 13, in the lens actually used, when the magnification changes, the distortion shift amount also changes nonlinearly in the main scanning direction. The actual lens as shown in FIG. 16 has different entrance / exit characteristics for each individual. For example, the manufactured lens unit 108 is measured by optical simulation, or, for example, the exit from a manufacturer for a discrete incident angle is obtained. It can be obtained, for example, by providing a value of the angle.

  The storage unit 501 stores the incident / exit angle characteristic (incident / exit angle information) data of the lens unit 108 thus obtained in advance. In the example of FIG. 14, 10 points of incident / exit angle characteristic (incident / exit angle information) data of the exit angle data with respect to the predetermined incident angle data indicated by “black square” are stored in advance. Since the incident / exit angle characteristics (incident / exit angle information) of the lens unit 108 are different for each lens, the incident / exit angle characteristic value associated with the lens is stored.

  Also, as shown in FIG. 16, the first optical path length (lens-sensor length data) between the lens unit 108 and the image sensor 109, which is optical path length information in the design stage of the image reading apparatus 100, and the subject ( Information on the second optical path length (document-lens length data) between the document and the lens unit 108 is stored in the storage unit 501 in advance.

  Further, as shown in FIG. 15, arbitrary incident / exit angle characteristic data other than ten incident / exit angle characteristic data of the output angle data with respect to the predetermined incident angle data indicated by “black square” is stored in the storage unit 501. It is calculated by interpolation using two or more incident / exit angle characteristic (input / exit angle information) data in the vicinity of the incident / exit angle characteristic data. For the interpolation, for example, linear interpolation that is easy to calculate is used. The interpolation method is not limited to linear interpolation and is arbitrary. In the example shown in FIG. 14 and FIG. 15, there is one incident / exit angle characteristic data, and it is described assuming a single color (either RGB). The image reading apparatus 100 stores input / output angle characteristic data of each color of R / G / B for the image sensor 109 which is an RGB color sensor, and is input / output angles interpolated by an input / output angle characteristic interpolation unit 409 described later. Characteristic data is calculated.

  Next, when the original is read, edge detection is first performed. Details of edge detection will be described later. If the document does not float when the document is read, the position B ′, which is the image formation position of the image sensor (no document lift) shown in FIG. When B ′ is obtained, the lens-sensor length (first optical path length) = Z stored in the memory (storage unit) 501 is used to calculate the exit angle ωo (document floating) using the following formula (2). None).

Further, even when the original is lifted at the time of reading the original, it can be obtained by using the following formula (2). For example, when the imaging position is b ′ (with document lift) by edge detection, the emission angle θo is calculated by θo = tan ⁻¹ (b ′ / Z).

  Therefore, the exit angle can be obtained using the following equation (2) regardless of whether or not the document is lifted during document reading.

  In the following description, the description will be made using B ′, which is the image forming position (no document lift), and the emission angle ωo. When the emission angle ωo is obtained from the following equation (2), the incident angle ωi of the document end D is obtained from the interpolated incident / exit angle characteristic data in FIG. Since lens-sensor length (first optical path length) = Z is stored in advance in the memory (storage unit) 501, the ideal image formation position B (incidence angle = image formation position in the case of the incident / exit angle characteristics of the output angle) Can be determined using the following equation (3).

  As a result, an image formation position (no document lift) B ′ and an ideal image formation position B obtained by actually reading the original and forming an image on the image sensor are obtained. Since B-B ', which is the difference between B' and B obtained, appears in the image as a distortion pixel shift, the shift in the difference between B-B 'is corrected. That is, the actual image forming position (no document lift) B ′ is replaced with the ideal image forming position B. Note that the ideal imaging position Be of the read image end D is used in magnification correction described later.

  Further, at other image forming positions in the main scanning direction, the image forming position (no document lift) B ′ is shifted (pixels moved) by shifting the difference amount from the ideal image forming position B. The distortion at an arbitrary position in the main scanning direction can be corrected.

  Since the above-described image formation position (no document lift) B ′ changes by a distance corresponding to the number of pixels in the main scanning direction, the value of the ideal image formation position B calculated using the following equations (2) and (3) Also changes according to the value of B ′. Therefore, by using the following formulas (2) and (3), it is possible to correct the shift amount due to distortion at all points in the main scanning direction regardless of whether or not the document is lifted when reading the document. Note that the correction of the shift amount due to distortion is performed for each color of R / G / B at all points in the main scanning direction.

  However, when the document is lifted when the document is read, the above-described distortion correction is performed, but as described with reference to FIGS. 12 and 13, the image is shrunk in the entire main scanning direction. Therefore, in this embodiment, the magnification correction is performed after the distortion correction so as to cope with the case where the document is lifted when the document is read.

  When performing magnification correction, for example, it is necessary to grasp the ideal image formation position when there is no document floating when reading a document. Therefore, the distance A from the document center C is obtained from the document size information (length in the main scanning direction of the document) obtained by the document size detection unit 503 described with reference to FIG. Since the document-lens length (second optical path length) = Y is stored in advance in the memory (storage unit) 501, the document floats when the document is read using the following formulas (4) and (5). When there is no image, Be, which is the ideal image forming position of the document edge D, can be obtained.

  From the ratio between Be calculated from the following formulas (4) and (5) and edge ideal detection position B calculated using the following formula (3) after performing edge detection described later, Since the magnification error is calculated in the same manner as in FIG. 22 and the pixel shift amount at an arbitrary position in the main scanning direction can be obtained using the calculated magnification error data, magnification correction can be performed. In the example of FIG. 16, Be = B and magnification error = 0 when the document does not float when the document is read. However, if there is document floating, Be ≠ B, and it is necessary to correct the magnification. .

  In FIG. 16, the original reading position and the image formation position on the image sensor surface when the original is not lifted are indicated by solid lines, and the original reading position and the image formation position on the image sensor surface when the original is lifted are indicated by dotted lines. Show. Further, the incident angle at the document reading position when there is no document floating is indicated by ωi, the emission angle is indicated by ωo, the incident angle at the document reading position when there is document floating is indicated by θi, and the emission angle is indicated by θo. Further, the image forming position on the image sensor surface of the document edge D when there is no document lift is indicated by Be. The above description is the outline of the image correction in the present embodiment.

  FIG. 17 is a block diagram illustrating an example of a functional configuration of the image correction unit 502. First, as described with reference to FIG. 3, digital image data input from the image sensor 109 and input / output angle characteristic data of the lens unit 108 input from the memory 501 as data input to the image correction unit 502. And optical path length data (document-lens length data, lens-sensor length data), document size data input from the document size detection unit 503, and pixel synchronization signal and line synchronization signal input from the synchronization signal generation unit 500. is there. As output data, output image data corrected by the correction unit 405 (distortion correction and magnification error correction) is output.

  The image correction unit 502 includes a pixel position detection unit 400, an edge detection unit 401, an emission angle calculation unit 402, an incident angle output unit 403, an ideal pixel position calculation unit 404, a correction unit 405, and an incident angle calculation unit. 406, a document edge pixel position calculation unit 407, a magnification error calculation unit 408, and an incident / exit angle characteristic interpolation unit 409. About each said part, all or some of these may be software (program), and may be a hardware circuit. Moreover, a form in which some of the above-described units are mounted on the image reading apparatus 100 may be employed.

  First, digital image data input to the image correction unit 502 is input to the pixel position detection unit 400, the edge detection unit 401, and the correction unit 405.

  The pixel position detection unit 400 detects the pixel position in the main scanning direction of each pixel of one line of subject image data read by the image sensor 109. The pixel position detection unit 400 uses an internal counter to count each pixel data in the main scanning direction of the input digital pixel data based on the pixel synchronization signal, and to detect the pixel position of each pixel (image formation on the image sensor). Position) Output data. When the reading of each pixel position on one line in the main scanning direction is completed, the pixel position data on one line in the main scanning direction can be obtained by resetting the count value in synchronization with the line synchronization signal. . All pixel position data in the main scanning direction is output to the edge detection unit 401 and the correction unit 405. Further, all pixel position data in the main scanning direction is output to the emission angle calculation unit 402 via the edge detection unit 401.

  The edge detection unit 401 uses the image data and pixel position data in the main scanning direction of each detected pixel to detect both end pixel positions (end pixel positions) in the main scanning direction of both end pixels of the image data. To do. The edge detection unit 401 detects both end pixel positions (end pixel positions) during a subject reading operation. In addition, the edge detection unit 401 determines the pixel position between the upper limit threshold and the lower limit threshold in which the read density level of the read image data in the main scanning direction is set in advance as the both end pixel positions (end pixel positions). ) To detect. The edge detection unit 401 detects both end pixel positions (end pixel positions) using a value obtained by averaging the read density levels of the image data in the main scanning direction for each of a plurality of preset lines in the sub-scanning direction. . The edge detection unit 401 detects both end pixel positions (end pixel positions) of the read image data from the pixel position data and the image data input from the pixel position detection unit 400 by an edge detection method described later. To do. The detected both-end pixel position data is used as information on both-end ideal pixel position data to be output to the magnification error calculation unit 408 in the subsequent stage. Further, pixel position data of each pixel between both end pixel positions is output to the emission angle calculation unit 402.

  Here, the edge detection method of this embodiment is demonstrated using FIGS. 18-20. 18 to 20 are diagrams for explaining edge detection of a document.

  In order to perform the image correction (distortion correction) described with reference to FIGS. 14 to 16, edge detection is used to obtain the document width in the main scanning direction for each sub-scanning line. In edge detection, as shown in FIG. 18, the reading level of the image in the main scanning direction is monitored to detect the edge portion of the document. Since a shadow is generated between the document and the background member at the edge portion of the document, a reading level threshold is provided in advance so that the variation level of the shadow can be detected. In the example of FIG. 18, the document width in the main scanning direction of the read document can be obtained from the pixel position in the main scanning direction of the leftmost end x1 of the document whose reading level is equal to or less than the threshold and the rightmost end x2 of the document. Note that the value of the reading level threshold can be set arbitrarily.

  Here, for example, a case where dust is attached to the background member or the contact glass will be described. For example, as shown in FIG. 19, there is a case where dust is present at the right end outside the document area. The reading level at this time is equal to or less than the threshold set in advance above. In this case, the rightmost end x2 of the document is detected on the right side of the original edge, resulting in an incorrect document width. Accordingly, in consideration of erroneous detection, by setting the upper and lower reading level threshold values in advance, the edge detection accuracy can be improved by not detecting an edge when the threshold value is lower than the lower limit threshold value. . At this time, it is necessary to provide a threshold for the number of pixels in the main scanning direction so as not to erroneously detect pixels between the upper limit and the lower limit of the reading level threshold. For example, if there are continuous pixels between the upper limit and the lower limit of the reading level threshold value, it can be regarded as an edge of the document. For example, by setting the threshold number of pixels in the main scanning direction to 2 pixels or more, Document edge detection can be performed without erroneously detecting a dust portion.

  However, as shown in FIG. 20, for example, in the case of a document with a low document reading level, even after straddling the edge portion of the document, it falls below the lower limit of the reading level threshold, and the above-described edge detection method cannot cope. . Accordingly, by setting an upper limit on the threshold value of the number of pixels in the main scanning direction when the above-described dust is not erroneously detected, it is possible to cope with a document with a low reading level. In the examples of FIGS. 18 to 20, when the reading level threshold is lower than the lower limit and the pixel count threshold in the main scanning direction is 2 pixels or more and less than 4 pixels, it is determined as dust within the threshold and erroneously detected. do not do. Further, if it is outside the threshold range of the number of pixels in the main scanning direction, it is possible to deal with a document such as the example of FIG. In addition, each threshold value mentioned above can be set arbitrarily.

  In the above description, the edge detection is performed for each line in the main scanning direction. However, the present invention is not limited to this. For example, the edge detection is performed by dividing the block into blocks of several lines in the sub scanning direction. You may go. Note that edge detection is performed by dividing into blocks for each of a plurality of lines in the sub-scanning direction, thereby improving the reading speed of one scan of the entire document and improving the dust detection accuracy described with reference to FIGS. be able to. That is, for example, in the dust detection described in the example of FIG. 19, if the dust reading level is between the upper and lower limits of the threshold, it cannot be detected, but the block for each of the plurality of lines in the sub-scanning direction Thus, the influence of dust can be smoothed by averaging the reading level.

  Returning to FIG. 17, the description will be continued. The emission angle calculation unit 402 uses the pixel position data input from the pixel position detection unit 400 and the first optical path length data between the lens unit 108 and the image sensor, which is optical path length data, in the main scanning direction. The emission angle data for the pixel position data of each pixel is calculated by the following equation (2).

ωo = tan ⁻¹ (B ′ / Z) (2)

  The emission angle data for the pixel position data of each pixel in the main scanning direction calculated by the above equation (2) is output to the incident angle output unit 403 at the subsequent stage.

  The incident angle output unit 403 refers to the incident / exit angle characteristic data stored in the storage unit (memory) 501 using the output angle data input from the output angle calculation unit 402, and corresponds to the incident angle data. Angle data (first incident angle data) is specified. As described with reference to FIG. 15, when there is no incident / exit angle characteristic data (incident angle data) corresponding to the emission angle data in the storage unit 501, the input / output angle characteristic interpolation unit 409, which will be described later, stores the storage unit 501. The incident angle data corresponding to the emission angle data (first incident angle data) with reference to the incident / exit angle characteristic data calculated by linear interpolation using two or more emission angle data in the vicinity of the emission angle data stored in Is identified. The incident angle output unit 403 outputs the specified incident angle data (first incident angle data) to the ideal pixel position calculation unit 404 at the subsequent stage.

  The ideal pixel position calculation unit 404 uses the incident angle data (first incident angle data) input from the incident angle output unit 403 and the first optical path length between the lens unit 108 and the image sensor, which is optical path length data. Thus, ideal pixel position data corresponding to the pixel position data of each pixel in the main scanning direction is calculated by the following equation (3).

  B = Z × tan ωi (3)

  The ideal pixel position data corresponding to the pixel position data of each pixel in the main scanning direction calculated by the above equation (3) is output to the correction unit 405 at the subsequent stage. However, both-end ideal pixel position data in the main scanning direction corresponding to both-end pixels of the image data is also output to the correction unit 405 and the magnification error calculation unit 408.

  The correction unit 405 uses the pixel position in the main scanning direction of each pixel between the both end pixel positions and the both end pixel positions, the optical path length information, and the incident / exit angle information to generate an image due to distortion aberration of the lens 108. Correct the amount of optical distortion in the data. Specifically, the correcting unit 405 determines from the pixel position in the main scanning direction of each pixel between the both end pixel positions and the both end pixel positions and the first optical path length (between the lens 108 and the image sensor). Using the calculated emission angle data, the first incident angle data is identified by referring to the incident / exit angle information, the ideal pixel position calculated from the identified first incident angle data and the first optical path length, and both ends Based on the partial pixel position and the pixel shift amount from the pixel position, the optical distortion amount of the image data due to the distortion aberration of the lens 108 is corrected. The correction unit 405 replaces the pixel position data input from the pixel position detection unit 400 and the corresponding pixel data with the ideal pixel position data calculated by the ideal pixel position calculation unit 404. Thereby, pixel shift due to distortion (distortion aberration) is corrected.

  The correction unit 405 uses the length of the subject in the main scanning direction, the second optical path length (between the subject (original) and the lens unit 108), and the first optical path length (between the lens 108 and the image sensor). Thus, the magnification error due to the variation in the second optical path length (document floating at the time of document reading) is corrected. Specifically, the correction unit 405 calculates the second incident angle data from the length of the subject in the main scanning direction and the second optical path length (between the subject (document) and the lens unit 108), and calculates the calculated first incident angle data. Based on the pixel shift amount between the subject end pixel position calculated from the two incident angle data and the first optical path length (between the lens 108 and the image sensor) and the ideal pixel position of the both end pixels, (2) A magnification error due to a change in optical path length (original floating at the time of original reading) is corrected. In addition, the correction unit 405 performs magnification correction on the pixel position where the pixel shift is corrected, using magnification error data calculated by a magnification error calculation unit 408 described later. As described above, the correction unit 405 outputs the output pixel data after correcting the pixel shift due to distortion (distortion aberration) and correcting the magnification error due to the document floating. The details of the magnification correction by document floating will be described later.

  Here, correction of pixel shift in the correction unit 405 will be described with reference to FIG. FIG. 21 is a diagram illustrating pixel movement for correcting pixel shift. The main scanning direction of the image sensor in FIG. 21 is such that the image sensor described with reference to FIG. 16 is shown horizontally and the main scanning direction is the horizontal axis. In the example of FIG. 16, the image formation position of each pixel is indicated by the distance from the document center C. However, in FIG. Note that the pixel position at the optical center is indicated by C on the right side of FIG.

  Hereinafter, the flow of pixel movement in the correction unit 405 will be described. First, (a) the edge detection described above is performed, and it is assumed that the read pixel position of the document edge is the b'th pixel. Next, (b) using the above equations (2) and (3), the ideal pixel position corresponding to the read pixel position b 'at the document edge in (a) is calculated as the b-th pixel. Next, (c) the pixel position b ′ at the document edge is moved to the ideal pixel position b pixel. Thereby, the shift amount due to the distortion of the pixel position is corrected. Next, (d) the edge ideal pixel position B is calculated from the document size information obtained by the document size detection unit 503 using the above equations (4) and (5). Next, (e) the magnification error is calculated using the above formulas (6), (7), and (8), and the pixel shift is performed again from the ideal pixel position b pixel to the end ideal pixel position B pixel. Let Thereby, it can respond also to magnification correction.

  In order to perform distortion correction also at the pixel positions of other pixels, the process returns to (a) again, and the same processing as (a) to (e) is performed for the b ′ + 1 pixel. However, since the magnification error is calculated only at the document edge using the above formulas (6), (7), and (8), the processing of (d) is not necessary for distortion correction in other pixels. is there. In the flow described above, distortion correction and magnification correction are performed. However, as described with reference to FIGS. 7 and 8, since the document floating at the time of document reading occurs locally in the sub-scanning direction, edge detection is performed for each line in the sub-scanning direction.

  Returning to FIG. 17, the description will be continued. The document size data (the length of the subject in the main scanning direction) obtained by the document size detection unit 503 described with reference to FIG. 3 is input to the incident angle calculation unit 406.

  The incident angle calculation unit 406 includes document size data (the length of the subject in the main scanning direction) input from the document size detection unit 503, and the second between the subject (document) that is optical path length data and the lens unit 108. Using the optical path length data, incident angle data (second incident angle data) corresponding to the document size data (the length of the subject in the main scanning direction) is calculated by the following equation (4).

ωi = tan ⁻¹ (A / Y) (4)

  Incident angle data (second incident angle data) corresponding to the document size data (the length of the subject in the main scanning direction) calculated by the above equation (4) is output to the document edge pixel position calculation unit 407 in the subsequent stage. The

  The document (subject) end pixel position calculation unit 407 includes incident angle data (second incident angle data) input from the incident angle calculation unit 406, and first optical path length data between the lens unit 108 and the image sensor. Is used to calculate the document (subject) edge pixel position data in the main scanning direction of the subject by the following equation (5).

  Be = Z × tan ωi (5)

  The document (subject) end pixel position data in the main scanning direction of the subject calculated by the above equation (5) is output to the subsequent magnification error calculation unit 408.

  The magnification error calculation unit 408 includes document (subject) end pixel position data input from the document (subject) end pixel position calculation unit 407, and both end ideal pixel position data input from the ideal pixel position calculation unit 404. , Magnification error data (pixel shift amount) is calculated by the following formulas (6), (7), and (8).

X ′ = (C · X) × (magnification error [%] / 100) (6)
Magnification error (left half) [%] = {(C−x1) − (C−x1 ′)} / (C−x1) × 100 [%] (7)
Magnification error (right half surface) [%] = {(C−x2) − (C−x2 ′)} / (C−x2) × 100 [%] (8)

  The magnification error data calculated by the above formulas (6) to (8) is output to the correction unit 405.

  Here, the magnification correction in the correction unit 405 will be described with reference to FIG. FIG. 22 is a diagram for explaining the magnification correction.

  As described with reference to FIGS. 10 to 13, a magnification error occurs when there is local document floating within one scan for reading the entire document. In the example of FIG. 22, there is shown a case where there is a document floating around the middle in the sub-scanning direction. In the magnification correction according to this embodiment, first, as described with reference to FIGS. In edge detection, the average of the distribution of the reading level (density level) in the main scanning direction is obtained in the sub-scanning direction. For example, the reading level (density level) is a predetermined threshold at the leftmost and rightmost in the main scanning direction The point beyond (2) is the edge (both ends). In the example of FIG. 22, x1 and x2 indicate left and right edge portions, respectively. As described above, the edge detection is performed for each line in the main scanning direction and the magnification is changed due to the floating of the original, in the example of FIG. 22, the left half from the original center C has the end x1 ′ as x1. The magnification is corrected by enlarging the right half from the document center C so that the end x2 ′ is x2.

  When the pixel shift amount due to the document floating is X ′, the pixel position in the main scanning direction is X, and the pixel position of the optical center is C, the pixel shift amount X ′ is expressed by the above equation (6). Therefore, magnification correction is performed by moving the pixel at the X + X ′ pixel position to the X pixel position.

  Further, the magnification error of the above equation (6) can be obtained by the above-described edge detection. For example, in FIG. 22, the edge positions (both ends) when there is no document lift are x1, x2, and document lift occurs. When the edge positions (both ends) are x1 ′ and x2 ′, the magnification error between the left half surface and the right half surface from the document center C is expressed by the above equations (7) and (8). In the example of FIG. 22, the magnification error of the left half of the image is calculated by the above equation (7), the magnification error of the right half of the image is calculated by the above equation (8), and the magnification correction is performed using the obtained magnification error data. I do. Furthermore, by performing edge detection at both ends for each line in the main scanning direction, magnification correction is performed in the entire sub-scanning direction even when the original is lifted locally within one scan for reading the entire original. Is possible.

  Returning to FIG. 17, the description will be continued. The incident / exit angle characteristic interpolating unit 409 is an arbitrary incident / exit angle characteristic (input / exit angle) other than 10 points of incident / exit angle characteristic (incident / exit angle information) data of the emission angle data with respect to predetermined incident angle data stored in the storage unit 501 in advance. (Angle information) data is calculated by interpolation using two or more incident / exit angle information (input / exit angle information) data in the vicinity of the incident / exit angle characteristic (incident / exit angle information) data stored in the storage unit 501. . When the storage unit 501 does not have the incident / exit angle information (incident / exit angle characteristic data) corresponding to the emission angle data, the incident / exit angle characteristic interpolation unit 409 stores two or more near the emission angle data stored in the storage unit 501. The incident / exit angle information (incident / exit angle characteristic data) is calculated by interpolation using the output angle data. For the interpolation, for example, linear interpolation that is easy to calculate is used. Further, the incident / exit angle characteristic interpolation unit 409 receives the incident / exit angle information (incident / exit angle characteristic data) not stored in the storage unit 501 and stores the incident / exit angle information (input / output angle characteristic) stored in the storage unit 501. It is calculated by linear interpolation using two or more incident / exit angle information (incident / exit angle characteristic data) in the vicinity of (data). The interpolation method is not limited to linear interpolation and is arbitrary. The “incident / exit angle characteristic interpolation unit” corresponds to the “interpolation unit” in the claims.

  Next, an example of the processing operation of the image reading apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 23 is a flowchart for explaining an example of the processing operation of the image reading apparatus according to the present embodiment.

  First, the image reading apparatus 100 preliminarily includes optical path length information from the subject (document) to the image sensor 109 (first optical path length data between the lens unit 108 and the image sensor, subject (document) and the lens unit 108. Second incident optical path length data), incident angle data of reflected light incident on the lens 108, and incident angle data (entrance / exit angle characteristic data) associated with the emission angle data emitted from the lens 108; Is stored (step S1). Next, the image reading apparatus 100 illuminates a document that is a subject (reading target) with irradiation light from the light source 102, and processes a signal received by a CMOS image sensor 109 that photoelectrically converts reflected light from the document. The document image data is read (step S2).

  Next, the image reading apparatus 100 detects the pixel position in the main scanning direction of each pixel of the image data of one line of the subject (original) read by the image sensor 109 (step S3). Next, the image reading apparatus 100 uses the image data and pixel position data in the main scanning direction of each pixel of the image data to determine both end pixel positions (edges) in the main scanning direction of both end pixels of the image data. It detects (step S4). Next, the image reading apparatus 100 uses the pixel position in the main scanning direction of each pixel between the both end pixel positions and the both end pixel positions, the optical path length information, and the incident / exit angle information. The amount of optical distortion of the image data due to distortion is corrected (distortion correction) (step S5).

  Next, the image reading apparatus 100 includes the length of the subject (original) in the main scanning direction, the second optical path length between the subject (original) and the lens 108, and the first between the lens 108 and the image sensor 109. Using the optical path length, the magnification error due to the fluctuation of the second optical path length (original floating at the time of original reading) is corrected (step S6). Next, the image reading apparatus 100 outputs the output pixel data after correcting the pixel shift due to distortion (distortion aberration) and correcting the magnification error due to the document floating (step S7), and ends the process.

  As described above, according to the image reading apparatus 100 of the present embodiment, it is possible to achieve the advantageous effect that the image data can be appropriately corrected even if the reading distance of the subject changes.

  Although the embodiments according to the present invention have been described above, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  The program executed by the image reading apparatus 100 of the above-described embodiment is a file in an installable format or an executable format, and is a floppy (registered trademark) disk, a CD (Compact Disk), a CD-R (Compact Disk- (Recordable), CD-ROM (Compact Disc Read Only Memory), DVD (Digital Versatile Disk), SD memory card (SD memory card), USB memory (Universal Serial Bus memory), etc. It may be configured to be provided, or may be configured to be provided or distributed via a network such as the Internet. Various programs may be provided by being incorporated in advance in a ROM or the like.

DESCRIPTION OF SYMBOLS 100 Image reader 101 Contact glass 102 Light source 103 1st reflective mirror 104 2nd reflective mirror 105 3rd reflective mirror 106 1st carriage 107 2nd carriage 108 Lens unit (lens)
109 Image sensor 110 Reference white plate (white reference plate)
111 Slit 112 Guide member 200 ADF
201 Document tray 202 Feed roller 300 Image forming apparatus 303 Paper feed unit 304 Image forming apparatus main body (image forming unit)
305 Image forming unit 306 Developing unit 307 Conveying path 308 Registration roller 309 Optical writing device 310 Fixing and conveying unit 311 Duplex tray 312 Photosensitive drum 313 Intermediate transfer belt 400 Pixel position detecting unit 401 Edge detecting unit 402 Emission angle calculating unit 403 Incident angle output Unit 404 ideal pixel position calculation unit 405 correction unit 406 incident angle calculation unit 407 document edge pixel position calculation unit 408 magnification error calculation unit 409 input / output angle characteristic interpolation unit 500 synchronization signal generation unit 501 memory (storage unit)
502 Image correction unit 503 Document size detection unit

JP-A-10-289302

Claims (13)

An image sensor that photoelectrically converts reflected light from a subject through a lens and reads image data of the subject;
Optical path length information from the subject to the image sensor, and incident / emission angle information in which incident angle data of the reflected light incident on the lens and emission angle data emitted from the lens correspond to each other are stored in advance. A storage unit to
A pixel position detection unit that detects a pixel position in the main scanning direction of each pixel of the image data of the subject of one line read by the image sensor;
Using the image data and the detected pixel position data of each pixel, an edge detection unit that detects pixel positions in both ends of the image data in the main scanning direction;
Using the pixel position of each pixel between the both-end pixel positions and the both-end pixel positions, the optical path length information, and the incident / exit angle information, the image data of the lens due to distortion aberration of the lens is used. A correction unit for correcting the amount of optical distortion;
Equipped with a,
The optical path length information is a first optical path length between the lens and the image sensor,
The correction unit uses the emission angle data calculated from the pixel position in the main scanning direction of each pixel between the both-end pixel positions and the both-end pixel positions and the first optical path length. The first incident angle data is identified with reference to the written exit angle information, the ideal pixel position calculated from the identified first incident angle data and the first optical path length, the both end pixel positions, and the pixel positions Correcting the amount of optical distortion of the image data due to the distortion of the lens based on the amount of pixel deviation with
An image reading apparatus. An image sensor that photoelectrically converts reflected light from a subject through a lens and reads image data of the subject;
Optical path length information from the subject to the image sensor, and incident / emission angle information in which incident angle data of the reflected light incident on the lens and emission angle data emitted from the lens correspond to each other are stored in advance. A storage unit to
A pixel position detection unit that detects a pixel position in the main scanning direction of each pixel of the image data of the subject of one line read by the image sensor;
Using the image data and the detected pixel position data of each pixel, an edge detection unit that detects pixel positions in both ends of the image data in the main scanning direction;
Using the pixel position of each pixel between the both end pixel positions and the both end pixel positions, the optical path length information, and the incident / exit angle information, the image data of the image data due to distortion aberration of the lens A correction unit for correcting the amount of optical distortion;
A subject size detector for detecting the length of the subject to be read in the main scanning direction;
With
The optical path length information is a first optical path length between the lens and the image sensor, and a second optical path length between the subject and the lens,
The correction unit corrects a magnification error due to a variation in the second optical path length using the length of the subject in the main scanning direction, the second optical path length, and the first optical path length;
An image reading apparatus. If there is no previous entry exit angle information corresponding to the emission angle data in the storage unit, enter exit angle before that corresponds to the emission angle data by linear interpolation using two or more emission angle data stored in the storage unit further comprising an interpolation unit for calculating the information,
The image reading apparatus according to claim 1. A subject size detector that detects the length of the subject to be read in the main scanning direction;
The optical path length information is a second optical path length between the subject and the lens,
The correction unit corrects a magnification error due to a variation in the second optical path length using the length of the subject in the main scanning direction, the second optical path length, and the first optical path length;
The image reading apparatus according to claim 1 . The correction unit calculates second incident angle data from the length of the subject in the main scanning direction and the second optical path length, and calculates from the calculated second incident angle data and the first optical path length. The both ends calculated from the first incident angle data and the first optical path length specified using the emission angle data calculated from the subject end pixel position, the pixel position of each pixel and the first optical path length parts based on the pixel shift amount of the ideal pixel position of the pixel to correct the magnification error due to variations in the second optical path length,
The image reading apparatus according to claim 2 , wherein the image reading apparatus is an image reading apparatus. The interpolation unit calculates incident / exit angle information not stored in the storage unit by linear interpolation using two or more input / output angle information stored in the storage unit,
The image reading apparatus according to claim 3. The storage unit stores in advance a plurality of pieces of incident / exit angle information in which incident angle data and exit angle data set in advance are associated with the lens.
The image reading apparatus according to claim 1 or 2, characterized in that. The edge detection unit detects the pixel positions on both ends during the reading operation of the subject;
The image reading apparatus according to claim 1 or 2, characterized in that. The edge detection unit detects a pixel position between a predetermined upper limit threshold and a lower limit threshold as a reading pixel level in the main scanning direction of the read image data as the both end pixel positions;
The image reading apparatus according to claim 1 or 2, characterized in that. The edge detection unit detects the pixel positions at both ends using a value obtained by averaging the read density levels in the main scanning direction of the image data for each of a plurality of preset lines in the sub-scanning direction.
The image reading apparatus according to claim 9.   An image forming apparatus comprising the image reading apparatus according to claim 1. An image sensor that photoelectrically converts reflected light from a subject through a lens, optical path length information from the subject to the image sensor, incident angle data of the reflected light that is incident on the lens, and emitted from the lens An image reading method of an image reading apparatus comprising: a storage unit that stores incident / exit angle information associated with emission angle data,
A pixel position detecting step of detecting a pixel position in the main scanning direction of each pixel of the image data of the subject of one line read by the image sensor;
An edge detection step of detecting both end pixel positions in the main scanning direction of both end pixels of the image data using the image data and pixel position data of the detected pixels.
Using the pixel position of each pixel between the both-end pixel positions and the both-end pixel positions, the optical path length information, and the incident / exit angle information, the image data of the lens due to distortion aberration of the lens is used. and a correction step of correcting the optical distortion amount, only including,
The optical path length information is a first optical path length between the lens and the image sensor,
The correction step uses the emission angle data calculated from the pixel position in the main scanning direction of each pixel between the both end pixel positions and the both end pixel positions, and the first optical path length. The first incident angle data is identified with reference to the written exit angle information, the ideal pixel position calculated from the identified first incident angle data and the first optical path length, the both end pixel positions, and the pixel positions Correcting the amount of optical distortion of the image data due to the distortion of the lens based on the amount of pixel deviation with
An image reading method. An image sensor that photoelectrically converts reflected light from a subject through a lens, optical path length information from the subject to the image sensor, incident angle data of the reflected light that is incident on the lens, and emitted from the lens An image reading method of an image reading apparatus comprising: a storage unit that stores incident / exit angle information associated with emission angle data,
A pixel position detecting step of detecting a pixel position in the main scanning direction of each pixel of the image data of the subject of one line read by the image sensor;
An edge detection step of detecting both end pixel positions in the main scanning direction of both end pixels of the image data using the image data and pixel position data of the detected pixels.
Using the pixel position of each pixel between the both end pixel positions and the both end pixel positions, the optical path length information, and the incident / exit angle information, the image data of the image data due to distortion aberration of the lens A correction step for correcting the amount of optical distortion;
A subject size detection step of detecting a length of the subject to be read in the main scanning direction,
The optical path length information is a first optical path length between the lens and the image sensor, and a second optical path length between the subject and the lens,
The correction unit corrects a magnification error due to a variation in the second optical path length using the length of the subject in the main scanning direction, the second optical path length, and the first optical path length;
An image reading method.

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