JP2011109381A - Image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image that reduces an influence of a foreign substance on image quality and an influence of light distribution characteristics of an image reading part and sensitivity difference for each reading sensor pixel, for preventing or reducing an increase in time required for a series of shading correction. <P>SOLUTION: Image data of a document to be generated by abnormal pixels is estimated using image data generated by normal pixels adjacent to the abnormal pixels and having been subjected to shading correction, to generate shading-corrected image data (the image data obtained by reducing a bad influence on the image quality by the foreign substance) which is estimated to be generated by the abnormal pixels by a reading operation for acquiring an document image if there is no foreign substance, and to determine white reference data for the abnormal pixels by inversely calculating image data to which the shading correction has not been applied, using an operational expression to be used for the shading correction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention belongs to the technical field of image processing apparatuses such as copiers and multi-function machines, and in particular, when foreign matter adheres to a white reference member used for obtaining a white reference value or the like necessary for performing shading correction processing. The present invention relates to a technique for preventing or reducing deterioration in image quality due to the foreign matter.

  In general, in an image reading apparatus provided in a copying machine or the like, shading correction is performed to correct an error in image data caused by a light distribution characteristic of a scanner (image reading unit) and a sensitivity difference for each pixel of a reading sensor. . In this shading correction, a white reference member (white reference plate or white reference roller) provided in the image reading device is read by a scanner, and an actual original is read based on reading data (white reference value) of the white reference member. Document reading data obtained when scanned by the scanner is corrected.

  In this type of image reading apparatus, if a foreign matter such as dirt or dust is present on the scanner reading target surface of the white reference member or the optical path between the white reference member and the sensor, the pixel ( An error occurs in the pixel value of the abnormal portion) due to the influence of the foreign matter, and the white reference value is not uniform.

  In such an image subjected to the shading correction using the white reference value, vertical stripes are generated in the image of the abnormal part or the image quality is deteriorated, so that it is not possible to obtain accurate original read image data. . As a measure for avoiding such a situation, it is conceivable to perform cleaning or automatic cleaning by the user for the abnormal part, but it takes time and effort for the user.

  In recent years, there has been proposed a technique for preventing or reducing deterioration in image quality due to the foreign matter by image processing without performing such cleaning by the user or automatic cleaning (for example, Patent Documents 1 and 2 below).

  In Patent Document 1 below, while the original does not reach the reading position, the target area corresponding to a predetermined width (for L lines) is read on the peripheral surface of the reading roller to calculate the L line average value, The entire circumference of the reading roller is read to calculate the entire circumference average value, and the L line average value is compared with the entire circumference average value to determine whether the L line average value can be adopted as shading data. In the case where it cannot be adopted, it has been proposed that the average value of the entire circumference is adopted as the shading data and the reading target area for acquiring the next L line average value is moved.

  Further, in Patent Document 2 below, when there are a plurality of abnormal pixels continuously affected by the foreign matter in the image data obtained by the reading operation on the white reference plate, the abnormal pixel array A technique of searching for two normal pixels outside the range, dividing the abnormal pixel column into two equal parts, replacing one half with one normal pixel, and replacing the other half with the other normal pixel. Proposed.

JP 2002-290671 A JP 2002-359742 A

  However, when the L-line average value cannot be used as shading data as in the technique described in Patent Document 1, if the entire circumference average value is used as shading data, an image of foreign matters such as dust and dirt is included. Data will be used as shading data, and appropriate shading correction will not be possible, and since shading correction will be performed after obtaining the average value for the entire circumference, it will take a long time to obtain image data after shading correction processing. .

  Further, when the L line average value cannot be used as the shading data, the reading target area for acquiring the next L line average value is moved, so that the time required for the reading operation of the image reading apparatus is increased. There is a fear.

  In the technique described in Patent Document 2, shading correction is performed on a pixel-by-pixel basis to correct light distribution unevenness of the illumination means for illuminating the white reference plate and the original and to correct the sensitivity of the sensor that performs the reading operation. Considering that it is preferable to be a thing, the method of simply replacing with normal pixels as described above is when the unevenness of light distribution changes irregularly or there is a sensitivity difference in each pixel of the sensor. It is hard to say that appropriate shading correction is performed.

  The present invention has been made to solve the above-described problems. The effect of foreign matter on image quality and the arrangement of a scanner (image reading unit) are prevented while preventing or reducing an increase in the time required for a series of shading correction processes. It is an object of the present invention to propose a technique capable of obtaining an image in which the optical characteristics and the influence due to the sensitivity difference for each reading sensor pixel are reduced.

  According to the first aspect of the present invention, an image reading unit that performs an image reading operation, a white reference member that serves as a white reference, and a first reading that causes the image reading unit to perform an image reading operation on the white reference member. A control unit, a first white reference data storage unit that stores image data obtained by a reading operation based on an instruction from the first reading control unit as first white reference data indicating a white reference value, and the first Abnormal image data caused by a foreign matter on the optical path including the white reference member is detected from image data of each pixel obtained by a reading operation based on an instruction from the reading control unit, and the abnormality among the pixels of the image reading unit is detected. An abnormal pixel detection unit that detects a pixel that has generated image data as an abnormal pixel, a second reading control unit that causes the image reading unit to read an image on a document, and a reading operation based on an instruction from the second reading control unit Gain in A first shading correction processing unit that performs shading correction processing on image data of a predetermined area of the original document using the first white reference data stored in the first white reference data storage unit; The foreign object exists temporarily using image data generated by predetermined pixels excluding the abnormal pixels detected by the abnormal pixel detection unit in the image data after the shading correction processing by the first shading correction processing unit. If not, the image data presumed to be generated by the abnormal pixel by the reading operation based on the instruction of the second reading control unit, and the image data after the first shading correction processing is converted into the abnormal data. An estimation data generation unit that generates the estimation data for the pixel and the estimation data generated by the estimation data generation unit are used. Then, if the foreign matter does not exist, the image data estimated to be generated by the abnormal pixel by the reading operation based on the instruction of the first reading control unit is used as the second white color for the abnormal pixel. A second white reference data generation unit that generates second white reference data as reference data and image data generated by the abnormal pixel by a reading operation based on an instruction from the second reading control unit. The shading correction processing is performed using the second white reference data for the abnormal pixel, and the image data generated by the pixels other than the abnormal pixel by the reading operation based on the instruction of the second reading control unit, A second shady for performing shading correction processing using the first white reference data for the pixel generated by the first white reference data generation unit And an image processing apparatus.

  According to the present invention, for the white reference data in the abnormal pixel, the shading correction processing by the first shading correction processing unit is performed on the image data of the document generated by the pixel other than the abnormal pixel (normal pixel). Since image data with reduced adverse effects on image quality due to the foreign matter is generated by estimation using subsequent image data, and the image data is obtained by back calculation of shading correction processing, the influence of the foreign matter on the image quality Thus, it is possible to obtain an image in which the light distribution unevenness of the image reading unit and the influence of the sensitivity difference for each pixel are reduced.

  In the image processing apparatus according to claim 1, as in the invention according to claim 2, the image reading unit includes n (n> 1) pixels arranged in a row. The first reading control unit further performs an image reading operation with respect to the white reference member in a state where an illumination operation with respect to the white reference member of an illumination unit provided in the image reading unit is turned off. And a black reference data storage unit for generating image data obtained by a reading operation based on an instruction from the first reading control unit as black reference data indicating a black reference value. When numbers in the pixel column direction are assigned to the pixels belonging to the predetermined area of the document in the image data obtained by the instruction of the control unit, the pixel k (= 1, 2,..., N−1, For n), the black reference data generation The black reference data generated in step B is B (k), the first white reference data stored in the first white reference data storage unit is W (k), and is generated in the pixel according to an instruction from the second reading control unit. When the image data is I (k) and the number of gradations of the image data is L, the first shading correction processing unit {(I (k) −B (k)) / (W (k) − B (k))} × L is the image data Ish (k) after the shading correction processing for the pixel k, and the estimated data generation unit performs the shading correction processing by the first shading correction processing unit. Of the subsequent image data Ish (k), the image data Ish (j) generated by the pixel j in the pixel region including the pixel adjacent to the abnormal pixel i or the abnormal pixel group including the abnormal pixels i is used. Temporary When the foreign matter is not present in the image, the image is estimated to be generated at the abnormal pixel i by the reading operation based on the instruction of the second reading control unit, and the shading correction processing by the first shading correction processing unit The subsequent image data Ish ′ (i) is generated as estimated data, and the second white reference data generation unit {L (I (i) −B (i)) / Ish ′ (i)} + B (I) may be generated as the second white reference data for the abnormal pixel i.

  According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, the predetermined area of the original is a leading area of the original having a predetermined width.

  According to the present invention, the leading area of the document is often a plain area where no image is formed, and thus is suitable as an area for acquiring the first white reference data and the second white reference data. It is. Since the first white reference data and the second white reference data are obtained from the image data of the head region of the document, the first white reference necessary for performing shading correction processing on the image data of the document. Compared with the case where the data and the second white reference data are calculated using the image data of the entire document, the time required for the calculation can be shortened, and an increase in the time required for a series of shading correction processes can be prevented. Can be reduced.

  According to a fourth aspect of the present invention, in the image processing apparatus according to any one of the first to third aspects, the image reading unit is at least one of a CCD and a CIS.

  According to the present invention, for an image obtained by at least one of CCD and CIS, the influence of foreign matter on the image quality and the influence of the light distribution characteristics of the scanner (image reading unit) and the sensitivity difference for each reading sensor pixel are reduced. Images can be obtained. In particular, CIS is particularly effective because of uneven light distribution and large sensitivity differences among pixels.

  According to the present invention, an increase in time required for a series of shading correction processes is prevented or reduced, and the influence of foreign matter on image quality, light distribution characteristics of a scanner (image reading unit), and sensitivity difference for each reading sensor pixel. An image with reduced influence can be obtained.

1 is a longitudinal sectional view schematically showing an internal configuration of a multifunction machine 1 which is an embodiment of an image processing apparatus according to the present invention. FIG. 3 is an enlarged view of the inside of a document feeding unit and a scanner unit. FIG. 3 is a block diagram illustrating an electrical configuration of the multifunction machine. It is a figure which shows the streak-like image resulting from a foreign material. It is a block diagram which shows the detailed structure of a shading correction | amendment part. It is a figure which shows the table stored in a white reference memory and a black reference memory. FIG. 6 is an explanatory diagram of a predetermined leading area of a document that is a detection target of abnormal pixel candidates by an abnormal pixel candidate detection unit. It is explanatory drawing of the normal pixel which produces | generates the image data used by the calculation of an estimated value calculating part. It is explanatory drawing of the calculation method of the estimated data by an estimated value calculating part. It is a flowchart which shows a series of shading correction processes by the 1st and 2nd reading control part and a shading correction part. FIG. 6 is a graph showing black reference data B (k), white reference data W (k), document image data I (k), and document image data Ish (k) after the first shading correction.

  Embodiments of an image processing apparatus according to the present invention will be described below with reference to the drawings. In the following embodiments, as an embodiment of an image processing apparatus according to the present invention, an embodiment in which functions are integrated in a multifunction machine having functions such as a color copy, a scanner, a facsimile, and a printer will be described as an example.

  FIG. 1 is a vertical cross-sectional view schematically showing the internal configuration of the multifunction machine 1 according to the present embodiment. 1 is roughly composed of an image reading unit 2 and an apparatus body 3. The image reading unit 2 includes a document feeding unit 21 and a scanner unit 22. The document feeder 21 realizes ADF, and includes a document tray 241, a paper feed roller 232, a transport drum 233, a paper discharge roller pair 234, and a paper discharge tray 235.

  The document tray 241 is a place where the document is placed. The documents placed on the document tray 241 are taken one by one by the paper feed roller 232 and conveyed to the conveyance drum 233. The document that has passed through the transport drum 233 is discharged to a discharge tray 235 by a discharge roller 234.

  The scanner unit 22 optically reads an image of a document and generates image data, and is provided in the apparatus main body 3. The scanner unit 22 includes a contact glass 221, a light source 222, a first mirror 223, a second mirror 224, a third mirror 225, a first carriage 226, a second carriage 227, an imaging lens 228, and a CCD (Charge Coupled). Device) 229.

  In the scanner unit 22, a white fluorescent lamp such as a cold cathode fluorescent tube is used as the light source 222, and the first mirror 223, the second mirror 224, the third mirror 225, the first carriage 226, the second carriage 227, and the imaging lens. 228 guides light from the document to the CCD 229. Since the scanner unit 22 uses a white fluorescent lamp such as a cold cathode fluorescent tube as the light source 222, it is superior in color reproducibility to the CIS 231 described later in which a three-color LED or the like is used as the light source.

  The CIS 231 is a line sensor and is provided on the downstream side of the document conveyance direction with respect to the reading position of the scanner unit 22 in the document conveyance path. The CIS 231 is provided at a position for reading a surface opposite to the document surface read by the scanner unit 22 in the document conveyance path.

  The contact glass 221 constitutes a surface on which an original is placed, the light source 222 and the first mirror 223 are supported by the first carriage 226, and the second mirror 224 and the third mirror 225 are the second It is supported by a carriage 227.

  As a document reading method of the image reading unit 2, there are a flatbed reading mode in which the scanner unit 22 reads a document placed on the contact glass 221 and an ADF reading mode in which the document is read by the ADF and the document is read during the conveyance. is there.

  In the flat bed reading mode, the light source 222 irradiates the document placed on the contact glass 221, and the reflected light for one line in the main scanning direction in which the pixels of the CCD 229 that is a one-dimensional image sensor are arranged is the first mirror 223. The second mirror 224 and the third mirror 225 are reflected in this order and enter the imaging lens 228. The light incident on the imaging lens 228 is imaged on the light receiving surface of the CCD 229. Such an operation is performed line by line in parallel with the movement of the first carriage 226 and the second carriage 227 in the direction orthogonal to the main scanning direction (sub-scanning direction, arrow Y direction). The CCD 229 simultaneously processes the image data of the original for one line, and outputs the image data to the A / D converter 216 (see FIG. 3) in units of one line.

  In the ADF reading mode, the originals placed on the original tray 241 are taken into the original conveying path one by one by the paper feed roller 232, and the image reading position 230 provided in the conveying path from the conveying drum 233 to the discharge tray 235. When the document passes above, the light source 222 irradiates the document, and the reflected light for one main scanning line is reflected in the order of the first mirror 223, the second mirror 224, and the third mirror 225 to the imaging lens 228. Incident. The light incident on the imaging lens 228 is imaged on the light receiving surface of the CCD 229. Such an operation is performed line by line in parallel with the conveyance of the document by the conveyance drum 233. The CCD 229 simultaneously processes the image data of the original for one line, and outputs the image data to the A / D converter 216 (see FIG. 3) in units of one line. In the following description, those not specifically described will be described on the assumption that an original is automatically fed in the ADF reading mode and an image is read.

  Further, the document feeder 21 has a document reversing mechanism including a switching guide 236, a reversing roller pair 237, and a reversing conveyance path 238. The original whose surface (one side of the original) is read by the first ADF reading is reversed using the original reversing mechanism and re-conveyed, so that the CCD 229 can read the back side (the other side of the original) again. Can be done. This document reversing mechanism operates only when reading both sides, and does not operate when reading one side. After reading the back side during single-sided reading and double-sided reading, the switching guide 236 is switched to the upper side, and the document that has passed through the transport drum 233 is discharged to the discharge tray 235 by the discharge roller pair 234. After the front side reading at the time of double-sided reading, the switching guide 236 is switched to the lower side, and the document that has passed through the conveying drum 233 is conveyed to the nip portion of the reverse roller pair 237. Thereafter, the switching guide 236 is switched to the upper side and the reverse roller pair 237 rotates in the reverse direction, whereby the original is re-conveyed to the conveyance drum 233 via the reverse conveyance path 238. Hereinafter, a mode in which both sides of a document are read using the document reversing mechanism is referred to as a double-sided reversal reading mode or a high image quality mode.

  Further, in the ADF reading mode, the image reading unit 2 according to the present embodiment causes the CCD 229 to read the front surface of the document while the document is being conveyed as described above, and at the same time reads the back side of the document by the CIS 231. Can be performed. That is, the front side of the original fed from the original tray 241 is read by the CCD 229 when passing over the image reading position 230, and the back side is read when passing through the CIS 231. By using the CCD 229 and the CIS 231 in this way, it is possible to read both sides of a document with one pass.

  The multifunction device 1 includes an apparatus main body 3 and a stack tray 6 disposed on the left side of the apparatus main body 3. The apparatus main body 3 includes a plurality of paper feed cassettes 461, a paper feed roller 462 that feeds sheets (recording media) one by one from the paper feed cassette 461 and conveys them to the recording unit (image forming unit) 40, and a paper feed cassette 461. And a recording unit 40 that forms an image on the sheet conveyed from the printer. Further, a manual feed tray 471 is provided. The manual feed tray 471 has a size that is not stored in any paper feed cassette, a paper on which an image is already formed on one side (back paper), or an OHP sheet. An arbitrary recording medium can be placed, and is fed into the apparatus main body 3 one by one by a paper feed roller 472.

  The recording unit 40 is based on a charge eliminating device 421 that removes residual charges from the surface of the photosensitive drum 43, a charging device 422 that charges the surface of the photosensitive drum 43 after charge removal, and image data acquired by the scanner unit 22. The laser beam is output to expose the surface of the photosensitive drum 43, and an exposure device 423 that forms an electrostatic latent image on the surface of the photosensitive drum 43, and on the photosensitive drum 43 based on the electrostatic latent image, Developing devices 44C, 44M, 44Y, and 44K that form toner images of each color of cyan (C), magenta (M), yellow (Y), and black (K), and toner images of each color that are formed on the photosensitive drum 43 A transfer drum 49 on which toner images are transferred, a transfer device 41 that transfers the toner image on the transfer drum 49 to a sheet, and a sheet on which the toner image has been transferred is heated to set the toner image on the sheet. And a fixing device 45 for. Note that toner is supplied to each color of cyan, magenta, yellow, and black from a toner supply container (toner cartridge) (not shown). Further, conveyance roller pairs 463 and 464 that convey the sheet that has passed through the recording unit 40 to the stack tray 6 or the discharge tray 48 are provided.

  When forming images on both sides of the paper, after the image is formed on one side of the paper by the recording unit 40, the paper is nipped between the pair of transport rollers 463 on the discharge tray 48 side. In this state, the transport roller pair 463 is rotated in the reverse direction to switch back the paper, and the paper is sent to the paper transport path L to be transported again to the upstream area of the recording unit 40. The recording unit 40 forms an image on the other surface. After being applied, the paper is discharged to the stack tray 6 or the discharge tray 48.

  Further, in front of the apparatus main body 3, an operation screen and a display screen such as various messages are displayed. For example, a display unit 51 having a touch panel and operation buttons for inputting various operation commands (numeral key group 53, And an operation unit 5 having a start button 55 and the like. The display unit 51 is configured by an LCD (Liquid Crystal Display), an ELD (Electronic Luminescent Display), or the like, and displays selection screens such as paper size selection, magnification selection, and density selection.

  FIG. 2 is an enlarged view of the inside of the document feeder 21 and the scanner unit 22.

  As shown in FIG. 2, the white reference plate 10, which is an example of a white reference member, is provided at a position deviated from the image reading position 230 and capable of image reading by the scanner unit 22. The white reference plate 10 is a white belt-like member attached to the contact glass 221 so as to extend in the main scanning direction (direction orthogonal to the paper surface in FIG. 2).

  Further, a shading roller 11 as another example of the white reference member is provided at a position facing the CIS 231 and capable of reading an image by the CIS 231. The shading roller 11 is a roller member whose rotating shaft extends in the main scanning direction and whose peripheral surface is white. The shading roller 11 is rotated by power supplied from a driving source (not shown), thereby conveying the sheet conveyed to the image reading position of the CIS 231 toward the paper discharge roller pair 234.

  Next, the electrical configuration of the multifunction machine 1 will be described. FIG. 3 is a block diagram illustrating an electrical configuration of the multifunction machine 1.

  As shown in FIG. 3, the multifunction device 1 includes a CPU 211, a RAM 212, a ROM 213, a first reading control unit 214, a second reading control unit 215, an A / D conversion unit 216, and a shading correction unit 217. The image processing unit 218 is connected to each other so as to be communicable with each other via a data bus BUS.

  The CPU 211 controls the overall operation of the multifunction device 1 and controls the operation of each unit in the multifunction device 1 according to a program stored in the ROM 212 or an unillustrated HDD. The RAM 212 is used as a work area when the CPU 211 controls each part of the multifunction machine 1 according to the program. The ROM 213 stores the program.

  By the way, normally, there is uneven light distribution of illumination by the light source 222 of the scanner unit 22 and the light source 231a of the CIS 231 and there is a sensitivity difference between the pixels of the CCD 229 and the CIS 231. If there is such light distribution unevenness or pixel sensitivity difference, an error occurs in the pixel value of each pixel for the same color.

  On the other hand, in the multifunction machine 1 according to the present embodiment, the surface of the white reference plate 10, the peripheral surface of the shading roller 11, or the optical path between the white reference plate 10 and the scanner unit 22, the shading roller 11 and the CIS 231 Foreign matter such as dirt and dust may enter the optical path between the two. When such foreign matter is present, among the pixels of the scanner unit 22 and the CIS 231, the image data generated by the pixel capturing the foreign matter is different from the image data obtained when the foreign matter is not present An error occurs.

  When such an error occurs, the obtained image data is different from the image data after the shading correction process when the foreign matter is not present. As a result, a streak-like image (see FIG. 4) extending in the sub-scanning direction is formed at a position in the main scanning direction of the paper corresponding to the pixel position of the pixel capturing the foreign matter, or the image quality of the entire image is degraded. To do.

  In the present embodiment, the influence on the image quality due to the uneven light distribution of the illumination by the light sources 222 and 231a and the sensitivity difference between the pixels of the CCD 229 and the CIS 231 and the influence on the image quality due to the foreign matter are eliminated. Process. As a process for eliminating the influence of the former, a shading correction process described later is performed.

  Here, regarding the pixels that are affected by both the influence of the former and the influence of the latter, an error caused by each influence is included, but the error caused by one influence and the influence caused by the other influence are included. The ratio with the error cannot be known from the image data of the pixel.

  Therefore, in the multifunction machine 1 according to the present embodiment, the following processing is performed in order to eliminate such a problem. In the following description, the scanner unit 22 and the CIS 231 are collectively referred to as an image reading unit, and the white reference plate 10 and the shading roller 11 are collectively referred to as a white reference member.

  The first reading control unit 214 controls the reading operation of the image reading unit (the scanner unit 22 and the CIS 231). Specifically, the reading operation of the image reading unit includes an illumination operation by the light source 222 of the scanner unit 22 and the light source 231a of the CIS 231, an operation of moving the first and second carriages 226 and 227 of the scanner unit 22, and the operation of the scanner unit 22. This is a light receiving operation by the CCD 229 or the CIS 231.

  When an image reading instruction (including an image forming instruction) is input from the start button 55, the first reading control unit 214 should perform an image reading operation based on the image reading instruction of the scanner unit 22 and the CIS 231. Before the image reading unit is recognized and the image reading unit performs an image reading operation on the document, the image reading unit is caused to perform an image reading operation on the white reference member corresponding to the image reading unit.

  That is, when the image reading unit to perform the image reading operation is the scanner unit 22, the first reading control unit 214 moves the first carriage 226 and the second carriage 227 to the position of the white reference plate 10 in the sub-scanning direction. Let In this state, the first reading control unit 214 scans the white surface of the white reference plate 10 by irradiating the white surface of the white reference plate 10 with the light source 222 of the scanner unit 22 for a plurality of lines in the sub-scanning direction. Let the unit 22 perform it. As a result, image data indicating a white reference value for shading correction for the white reference plate 10 is generated by the scanner unit 22, and the image data is output from the scanner unit 22 as white reference data.

  Further, the first reading control unit 214 turns off the light source 222 and does not irradiate the white surface of the white reference plate 10 with light, and scans the white surface for a plurality of lines in the sub-scanning direction. Let the unit 22 perform it. As a result, image data indicating the black reference value for shading correction for the white reference plate 10 is generated by the scanner unit 22, and the image data is output from the scanner unit 22 as black reference data.

  On the other hand, when the image reading unit to be subjected to the image reading operation is the CIS 231, the first reading control unit 214 performs the image reading operation on the peripheral surface while irradiating the peripheral surface of the shading roller 11 with the light source 231a of the CIS 231. The CIS 231 is caused to perform a plurality of lines in the scanning direction. As a result, image data indicating a white reference value for shading correction for the shading roller 11 is generated by the CIS 231, and the image data is output from the CIS 231 as white reference data.

  Further, the first reading control unit 214 turns off the light source 231a and does not irradiate the circumferential surface of the shading roller 11 with light, and performs the image reading operation on the circumferential surface to the CIS 231 for a plurality of lines in the sub-scanning direction. Let it be done. As a result, image data indicating the black reference value for shading correction for the shading roller 11 is generated by the CIS 231, and the image data is output from the CIS 231 as black reference data.

  In the present embodiment, the reading operation is performed for a plurality of lines, and for each pixel position aligned in the main scanning direction, white reference data for the white reference plate 10 and black reference data for the white reference plate 10. The white reference data for the shading roller 11 and the black reference data for the shading roller 11 are output from the scanner unit 22 and the CIS 231 for each of the plurality of lines.

  These data are averaged for each pixel arranged in the main scanning direction by an unillustrated averaging processing unit, and the averaged white reference data and black reference data are stored in a white reference memory 250 and It is output to the black reference memory 251.

  Accordingly, white reference data and black reference data for the white reference plate 10 are calculated for each pixel of the CCD 229, and white reference data and black reference data for the shading roller 11 are calculated for each pixel of the CIS 231. One at a time.

  For example, the number of pixels arranged in the main scanning direction of the scanner unit 22 (the number of pixels in one line) is n (number), and numbers 1, 2,..., N−1, n are sequentially arranged from one end. , White reference data W (1) and black reference data B (1) are provided for pixel 1 of the scanner unit 22, and white reference data W (2) and black reference data B (2) are provided for pixel 2. For the pixel n, white reference data W (n) and black reference data B (n) are calculated.

  The reading operation may be performed for one line, and the white reference data and the black reference data obtained by the reading operation may be output to the white reference memory 250 and the black reference memory 251 as they are.

  The second reading control unit 215 causes the scanner unit 22 and the CIS 231 to perform an image reading operation on an original after the reading operation based on an instruction from the first reading control unit 214 is completed.

  In the following description, the reading operation of the image reading unit based on the instruction of the first reading control unit 214 for obtaining the white reference data and the black reference data as described above is referred to as a reference value acquisition reading operation. The reading operation of the image reading unit based on the instruction of the second reading control unit 214 for obtaining the document image is referred to as a document image acquisition reading operation.

  The A / D conversion unit 216 reads the read image data (the white reference data, the black reference data, and the original image data) including analog electrical signals sent from the CCD 229 and the CIS 231 of the scanner unit 22 from a predetermined number of bits. A / D conversion processing for converting into digital read image data is performed. The A / D conversion unit 216 outputs the read image data after A / D conversion to the shading correction unit 217, the first and second reading control units 214 and 215, and the like.

  The shading correction unit 217 performs shading correction on the document image data obtained by the document image acquisition reading operation using the white reference data and black reference data obtained by the reference value acquisition reading operation. It is. FIG. 5 is a block diagram showing a detailed configuration of the shading correction unit 217.

  As shown in FIG. 5, the shading correction unit 217 includes a white reference memory 250, a black reference memory 251, an abnormal pixel candidate detection unit 252, an abnormal pixel candidate storage unit 253, a shading correction processing unit 254, and a white background determination. Unit 255, abnormal pixel counting unit 256, estimated value calculation unit 257, white reference correction value calculation unit 258, white reference correction value memory 259, and switching unit 260.

  In the following description, it is assumed that the number of pixels of the scanner unit 22 and the number of pixels of the CIS 231 are the same number n. For convenience of description, the pixel k of the scanner unit 22 (k = 1, 2,..., N−1). , N) and white reference data for CIS 231 pixels k (k = 1, 2,..., N−1, n) are both “W (k) (k = 1, 2, .., N−1, n) ”and the black reference data for the pixel k (k = 1, 2,..., N−1, n) of the scanner unit 22. Also, the black reference data for the pixel k (k = 1, 2,..., N−1, n) of the CIS 231 is also “B (k) (k = 1, 2,..., N−1, n) "in the same expression form.

  As shown in FIG. 6, the white reference memory 250 is provided for each pixel k (k = 1, 2,..., N−1, n) of the image reading unit obtained by the reference value acquisition reading operation. White reference data W (k) (k = 1, 2,..., N−1, n) are stored in a table format, and the black reference memory 251 is obtained by the reference value acquisition reading operation. Black reference data B (k) (k = 1, 2,..., N−1) for each pixel k (k = 1, 2,..., N−1, n) of the obtained image reading unit. , N).

  Although not shown in FIG. 6, the white reference memory 250 and the black reference memory 251 include a table of white reference data W (k) corresponding to the scanner unit 22 and the CIS 231, and black reference data B (k). Are stored in the table.

  The abnormal pixel candidate detection unit 252 includes the white reference data for each pixel k (k = 1, 2,..., N−1, n) of the image reading unit obtained by the reference value acquisition reading operation. W (k) (k = 1, 2,..., N−1, n) and a predetermined head region corresponding to a blank portion of the document, which is assumed to be a solid color where no document image exists (see FIG. 7). ) On the original image data I (k) (k = 1, 2,...) Obtained from each pixel k (k = 1, 2,..., N−1, n) in the original image acquisition reading operation. .., N-1, n) are compared with respect to the same pixel, and the brightness of the white reference data is reduced due to foreign matter adhering to the white reference member. Pixels whose image data shows a relatively higher luminance than the white reference data are marked as abnormal pixels. It is detected as.

  The predetermined head area is an area having a plurality of predetermined lines arranged in the sub-scanning direction (an area indicated by a width A in FIG. 7). Therefore, the image data of the original is generated by the number of lines in the predetermined head area by each pixel k (k = 1, 2,..., N−1, n), but the average of the illustration is omitted. The processing unit averages the pixels arranged in the main scanning direction, and the averaged image data is obtained from each pixel k (k = 1, 2,..., N−1, n). Original image data I (k) (k = 1, 2,..., N−1, n) is set, and each image data I (k) is compared with the white reference data W (k). .

  The abnormal pixel candidate storage unit 253 stores abnormal pixel candidates detected by the abnormal pixel candidate detection unit 252.

  The shading correction processing unit 254 converts the image data obtained from each pixel k (k = 1, 2,..., N−1, n) by the reading operation for document image acquisition with respect to the head region of the document into an image. Averaging is performed for each pixel of the reading unit, and the averaged image data Iave (k) (k = 1, 2,..., N−1, n) is stored in the white reference memory 250. White reference data W (k) (k = 1, 2,..., N−1, n) for the same pixel k and black reference data B for the same pixel k stored in the black reference memory 251. (K) (k = 1, 2,..., N−1, n) is used to perform a shading correction process (hereinafter referred to as a first shading correction process) based on the following formula (1). .

Ish (k) = {(Iave (k) −B (k)) / (W (k) −B (k))}
× L (1)
The Ish (k) is image data for the head region obtained from each pixel k (k = 1, 2,..., N−1, n), and after the first shading correction processing. The image data of each pixel k, and “L” is the number of gradations of the image data. FIG. 11 shows an example of a graph of black reference data B (k), white reference data W (k), original image data Iave (k), and original image data Ish (k) after the first shading correction.

The white background determination unit 255 determines whether or not the leading area of the document is white. The following process can be adopted as the white background determination process by the white background determination unit 255. That is, the white background determination unit 255 performs the first processing by the shading correction processing unit 254 of the image data regarding the head region of the document obtained from each pixel k (1, 2,..., N−1, n). An average value AVE (Ish) of the image data Ish (1), Ish (2),..., Ish (n−1), Ish (n) after one shading correction processing is calculated. That is, the white background determination unit 255
AVE (Ish) = {Ish (1) + Ish (2) +...
+ Ish (n-1) + Ish (n)} / n
Is calculated.

  Further, the white background determination unit 255 determines the smallest image data among the image data Ish (1), Ish (2),..., Ish (n−1), Ish (n) as image data MIN (Ish). Extract as

  When the average value AVE (Ish) is smaller than the predetermined white average reference value L and the minimum value MIN (Ish) is larger than the predetermined minimum white background reference value M, the white background determination unit 255 That is, when the following expressions (2) and (3) are satisfied at the same time, it is determined that the leading area is white, and otherwise, it is determined that the leading area is not white.

Average value AVE (Ish) <white average reference value L (2)
Minimum value MIN (Ish)> White background minimum reference value M (3)
The case where the expression (2) is not satisfied is a case where the head area which is the reading target of the reference value acquisition reading operation is whiter than expected, and the expression (3) is not satisfied. Is a case where an image exists in the head area. Accordingly, the white background determination unit 255 determines that the head area is white when the head area is not white as expected and no image exists in the head area.

  The white average reference value L is a white reference value indicating a predetermined white average luminance, and is 220, for example, when the image data is represented by 256 gradations. The white background minimum reference value M is a white background minimum reference value indicating a predetermined minimum white brightness, and is 128 when the image data is expressed in, for example, 256 gradations. The white average reference value L and the white background minimum reference value M are stored in the ROM 213 in advance. The white background determination unit 255 outputs this determination result to the white reference correction value calculation unit 258.

  Here, it is assumed that the larger the value of the image data (pixel value), the whiter (the luminance is higher). When the image data is set so as to be black (the luminance is low) as the value of the image data is large, the magnitude relations of the expressions (2) and (3) are reversed.

  The abnormal pixel counting unit 256 counts the number of abnormal pixel candidates stored in the abnormal pixel candidate storage unit 253 when the white background determination unit 255 determines that the head region is white.

  The estimated value calculation unit 257 outputs image data Iave (k) (k = 1, 2, n) about the head region obtained from each pixel k (k = 1, 2,..., N−1, n). .., N−1, n), the abnormal pixel candidate storage among the image data Ish (k) (k = 1, 2,..., N−1, n) after the first shading correction processing. If the foreign object does not exist using image data of predetermined normal pixels that are pixels other than the abnormal pixels (hereinafter referred to as normal pixels) stored in the unit 253, the original image Image data after the first shading correction process estimated to have been generated at the abnormal pixel by the reading operation for acquisition, that is, an estimated value of original correct image data after the shading correction process of the abnormal pixel is generated as estimated data. Is.

  For example, as shown in FIG. 8, the estimated value calculation unit 257 assumes that the abnormal pixels are pixels i to (i + m) (1 <i <n, 1 ≦ i + m <n). A normal pixel (i-1) and a normal pixel (i + m + 1) adjacent to the abnormal pixel group are selected as pixels, and the image data Iave (i-1) and normal pixel (i + m + 1) of the normal pixel (i-1) are selected. Image data presumed to have been generated at the abnormal pixels i to (i + m) by the reading operation for document image acquisition by the linear interpolation using the image data Iave (i + m + 1) if the foreign matter is not attached. The image data after the first shading correction processing is generated as estimated data Ish ′ (i) to Ish ′ (i + m).

  That is, when m = 10, as shown in FIG. 9, the image data of the document generated by each pixel in a two-dimensional coordinate system in which the pixel arrangement in the main scanning direction is the horizontal axis and the image data is the vertical axis. , The estimated value calculation unit 257 causes the straight line X passing through the point P (i−1) corresponding to the normal pixel (i−1) and the point P (i + 11) corresponding to the normal pixel (i + 11). And the image data Iave (i) to Iave (i + 10) corresponding to the points P (i) to P (i + 10) corresponding to the abnormal pixels i to (i + 10) on the straight line X are temporarily Image data that is estimated to have been generated by the abnormal pixels i to (i + 10) by the document image acquisition reading operation and the image data after the first shading correction processing is the estimated data. Generate as

  Here, since the image data Ish after the first shading correction processing is free from the influence of uneven light distribution and sensitivity difference between the pixels, the correct estimation data Ish ′ for the abnormal pixel i is obtained by simple linear interpolation or the like. (I) can be estimated.

  Note that the image data Iave (i) before the first shading correction processing includes the influence due to uneven light distribution and sensitivity differences between the pixels, so that the image data Iave ( When the estimation data Ish ′ (i) for the abnormal pixel i is to be estimated by simple linear interpolation using i), the influence due to uneven light distribution and sensitivity difference between the pixels is calculated for the abnormal pixel i. When the correction white reference data W ′ (i), which will be described later, is not correctly reflected, and shading correction processing is performed on the image data of the document output from the abnormal pixel i with the correction white reference data W ′, the image data It is not possible to eliminate the effects of uneven light distribution and sensitivity differences between pixels.

  The white reference correction value calculation unit 258 uses the estimated data Ish ′ (i) to Ish ′ (i + m) generated by the estimated value calculation unit 257, and if the foreign matter is not attached, Image data that is estimated to be generated by each of the abnormal pixels i to (i + m) by the reading operation for acquisition, and is the image data before the first shading correction processing by the shading correction processing unit 254, is used as each abnormal pixel. New white reference data (hereinafter referred to as corrected white reference data) W ′ (i) to W ′ (i + m) for i to (i + m) are generated.

That is, the white reference correction value calculation unit 258 generates corrected white reference data W ′ (i) for a certain abnormal pixel i, for example, W ′ (i) = {L (Iave (i) −B (i)) / Ish ′ (i)} + B (i) (4)
Calculated by

  Here, the estimated data Ish ′ (i) for the abnormal pixel i is estimated in a state in which unevenness of light distribution of the image reading unit and sensitivity difference for each pixel are eliminated, and the calculation used for the shading correction process According to the equation (4), which is a reverse calculation equation of the equation (1), Ish ′ (i) for the abnormal pixel i and Iave (i), W () including information on the light distribution unevenness and the sensitivity difference for each pixel. The corrected white reference data W ′ (i) for the abnormal pixel i can be appropriately corrected by calculating the corrected white reference data W ′ (i) for the abnormal pixel i from i). (I) can be calculated.

  Therefore, the shading correction is performed on the image data obtained from the abnormal pixel i when the image reading unit performs the reading operation on the image area of the document using the corrected white reference data W ′ (i). Therefore, it is possible to eliminate or reduce the influence due to the light distribution unevenness and the sensitivity difference for each pixel.

  When the white reference correction calculation unit 258 receives a notification from the white background determination unit 255 that the leading area of the document is white, the corrected white reference data W ′ (i) for the calculated abnormal pixels i to (i + m). ) To W ′ (i + m) are stored in the white reference correction value memory 259, and white reference data W (1) to W (1) of normal pixels 1 to (i−1) and (i + m + 1) to n other than the abnormal pixels are stored. i−1), W (i + m + 1) to W (n) are transferred from the white reference memory 250 to the white reference correction value memory 259.

  On the other hand, when the white reference correction calculation unit 258 receives a notification from the white background determination unit 255 that the leading area of the document is not white, the calculated white reference data W ′ (i) to W ′ (i + m) are calculated. Discard without storing in the white reference correction value memory 259.

  The shading correction processing unit 254 stores corrected white reference data W ′ (i) to W ′ (i + m) for the abnormal pixels i to (i + m) in the white reference correction value memory 259 and normal pixels 1 to 1 other than the abnormal pixels. When white reference data W (1) to W (i-1) and W (i + m + 1) to W (n) of (i-1), (i + m + 1) to n are stored, these white reference data are stored. Is used to perform shading correction processing (second shading correction processing) on image data in a region (image region) other than the top region of the document obtained by the document image acquisition reading operation.

  On the other hand, when the white reference data is not stored in the white reference correction value memory 259, the shading correction processing unit 254 determines the white reference data W (k) (k = 1, 2,..., N−1, n) is used to perform shading correction processing on the image data in the region (image region) other than the top region of the document obtained by the document image acquisition reading operation (second). Shading correction processing).

  The switching unit 260 switches an object to be communicably connected to the shading correction processing unit 254 between the white reference memory 250 and the white reference correction value memory 259. That is, when performing the first shading correction process, the switching unit 260 connects the white reference memory 250 and the shading correction processing unit 254 so that they can communicate with each other, and the white reference data W ( k) (k = 1, 2,..., n−1, n) is taken into the shading correction processing unit 254.

  If the white reference data is not stored in the white reference correction value memory 259 before the second shading correction process, the switching unit 260 switches between the white reference memory 250 and the shading correction processing unit 254. The white reference data W (k) (k = 1, 2,..., N−1, n) stored in the white reference memory 250 is connected to be communicable so that the shading correction processing unit 254 takes in the white reference data. If the white reference data is stored in the white reference correction value memory 259 before performing the second shading correction process, the white reference correction value memory 259 and the shading correction processing unit 254 are connected to be communicable. The corrected white reference data W ′ (i) to W ′ (i + m) and the white reference data W (1) to W (i−1), W ( + M + 1) ~W (n) is to be incorporated into the shading correction processing unit 254.

  The image processing unit 218 performs various image processing related to the image data after the second shading correction processing sent from the second shading correction processing unit 254. For example, the image processing unit 218 performs correction processing such as level correction and gamma correction, image processing processing such as image data compression or expansion processing, enlargement or reduction processing on the image data.

  FIG. 10 is a flowchart showing a series of shading correction processes by the first and second reading control units 214 and 215 and the shading correction unit 217. Here, it is assumed that there is a foreign object on the white reference plate 10 or on the optical path between the white reference plate 10 and the scanner unit 22, and the scanner unit 22 needs to read the image of the document. However, the same processing is performed when a foreign object exists on the peripheral surface of the shading roller 11 or on the optical path between the shading roller 11 and the CIS 231 and it is necessary to read the image of the document with the CIS 231.

  As shown in FIG. 10, when the start button 55 of the operation unit 5 is pressed by the operator and an image reading instruction is accepted by the operation unit 5 (YES in step # 1), the first reading control unit 214 turns on the light source 222. In a state where the light is extinguished, the image reading unit is operated to read the white reference plate 10 (step # 2). As a result, black reference data B (k) (k = 1, 2,..., N−1, n) is output from the image reading unit, and this black reference data B (k) (k = 1, 2). ,..., N−1, n) are stored in the black reference memory 251 (step # 3).

  At this time, the first reading control unit 214 may cause the scanner unit 22 to read an image of only one line, and the pixel value of one line of pixels may be used as the black reference data B (k). The first reading control unit 214 may cause the scanner unit 22 to read an image for a plurality of lines, and an average value of pixel values of the pixels for the plurality of lines may be used as the black reference data B (k).

  Subsequently, the first reading control unit 214 operates the scanner unit 22 with the light source 222 turned on to read the white reference plate 10 (step # 4). As a result, white reference data W (k) (k = 1, 2,..., N−1, n) is output from the image reading unit, and the white reference data W (k) (k = 1, 2). ,..., N−1, n) are stored in the white reference memory 250 (step # 5).

  At this time, the first reading control unit 214 causes the scanner unit 22 to read an image of only one line, and the pixel values of pixels for one line are set to the white reference data W (k) (k = 1, 2, .., N−1, n), or the first reading control unit 214 causes the scanner unit 22 to perform image reading for a plurality of lines, and the average value of the pixel values of the pixels for the plurality of lines. May be the white reference data W (k) (k = 1, 2,..., N−1, n).

  Then, the first reading control unit 214 conveys the document on the document tray 241 to the document feeding unit 21 to the image reading position 230 by the scanner unit 22, and reads the document image by the scanner unit 22 at the image reading position 230. (Step # 6).

  When the abnormal pixel candidate detection unit 252 acquires the image data Iave (k) (k = 1, 2,..., N−1, n) of the leading edge region of the document (step # 7), the white reference The data W (n) and the image data Iave (k) (k = 1, 2,..., N−1, n) of the original read by the image reading unit are compared, and each original image is formed. Among the pixels, a pixel having a luminance higher than the pixel value of the white reference data W (k) at the corresponding pixel position (the same pixel position as each pixel forming the original image) is detected as an abnormal pixel candidate (step # 8).

  For example, the abnormal pixel candidate detection unit 252 includes, in the document image obtained by the reading operation in step # 6, a blank area within a certain range from the document front end in the document transport direction (for example, a region from the document front end to 150 mm). ) As a document image used for the comparison, it is determined whether white reference data W (k) <image data Iave (k) is satisfied, and pixels satisfying white reference data W (k) <image data Iave (k) are determined. If present, the abnormal pixel candidate detection unit 252 causes the abnormal pixel candidate storage unit 253 to store the pixel position in the main scanning direction for the pixel corresponding to the condition. For example, referring to FIG. 11, the pixel position in the main scanning direction where white reference data W (k) <image data Iave (k) is stored.

  Next, the shading correction processing unit 254 of the shading correction unit 217 uses the white reference data W (k) stored in the white reference memory 250 and the black reference data B (k) stored in the black reference memory 251. Thus, the first shading correction is performed on the leading area of the document image read in step # 6 (step # 9).

  Subsequently, the white background determination unit 255 stores the average value AVE (Ish) and the minimum value MIN (Ish) of the pixel values of each pixel constituting the head region of the original image after the first shading correction, and is stored in the ROM 213. Using the average white reference value L and the minimum white background reference value M, a white background determination process is performed to determine whether the conditions expressed by the equations (2) and (3) are satisfied (step # 10), and the abnormal pixel count The unit 256 counts the number of abnormal pixel candidates stored in the abnormal pixel candidate storage unit 253 (step # 11).

  Next, the estimated value calculation unit 257 performs the first shading correction processing on the image data for the head region obtained from each pixel k (k = 1, 2,..., N−1, n). Normal image data other than the abnormal pixels i to (i + m) stored in the abnormal pixel candidate storage unit 253 among the image data Ish (k) (k = 1, 2,..., N−1, n). The original image when the foreign object is not attached by an interpolation operation using image data of normal pixels (i−1) and normal pixels (i + m + 1) adjacent to the abnormal pixel group, for example. Image data after the first shading correction process estimated to have been generated at the abnormal pixels i to (i + m) by the reading operation for acquisition is generated as estimated data Ish ′ (i) to Ish ′ (i + m) (step #) 12).

  Further, the white reference correction value calculation unit 258 uses the estimation data Ish ′ (i) to Ish ′ (i + m) generated by the estimated value calculation unit 257, and if the foreign matter is not attached, Image data before the first shading correction processing by the shading correction processing unit 254, which is estimated to have been generated by the respective abnormal pixels i to (i + m) by the reference value acquisition reading operation, is used as the abnormal pixels i to The corrected white reference data W ′ (i) to W ′ (i + m) for (i + m) is generated (step # 13).

  The shading correction processing unit 254 then corrects white reference data W ′ (i) to W ′ (i + m) for the abnormal pixels i to (i + m) and normal pixels 1 to (i−1) other than the abnormal pixels. , (I + m + 1) to n white reference data W (1) to W (i-1) and W (i + m + 1) to W (n), the original of the original obtained by the original image acquisition reading operation is used. Shading correction processing (second shading correction processing) is performed on the image data in the region (image region) other than the head region (step # 14), and the image data after the second shading correction processing is output to the image processing unit 218. (Step # 15).

  As described above, in the present embodiment, the white reference data for abnormal pixels is image data generated by pixels other than abnormal pixels (normal pixels), and shading correction processing by the shading correction processing unit 254 is performed. Using the image data after performing (first shading correction processing), if there is no adhesion of the foreign matter, the image data estimated to have been generated by the abnormal pixels by the document image acquisition reading operation ( Image data with reduced adverse effects on image quality due to the foreign matter) and image data after the first shading correction processing is generated, and if the foreign matter is not attached from the image data, the reference Image data presumed to have been generated at the abnormal pixel by the value acquisition reading operation, that is, the correct white reference for the abnormal pixel Data is obtained by calculating inversely using an arithmetic expression used for shading correction processing, so that the influence of foreign matter on image quality, light distribution unevenness of the image reading unit, and sensitivity difference for each pixel An image with reduced influence can be obtained.

  In addition, since the first white reference data Ish (k) and the second white reference data Ish ′ (k) are obtained from the image data of the leading area of the document, shading correction processing is performed on the image data of the document. Compared to the case where the first white reference data Ish (k) and the second white reference data Ish ′ (k) necessary for the calculation are calculated using the image data of the entire document, the time required for the calculation is shortened. It is possible to prevent or reduce an increase in the time required for a series of shading correction processes.

  In this case, the following modifications may be employed instead of or in addition to the embodiment.

  (1) In the first embodiment, the abnormal pixel candidate detection unit 252 includes each pixel k (k = 1, 2,...) Of the image reading unit obtained by the reference value acquisition reading operation. The white reference data W (k) (k = 1, 2,..., n−1, n) for n−1, n) and the margin of the document that is assumed to be a solid color where no document image exists. Document image data Iave (k) (obtained from each pixel k (k = 1, 2,..., N−1, n) in the document image acquisition reading operation for a predetermined head region corresponding to the region. k = 1, 2,..., n−1, n), but the present invention is not limited thereto, and the image data Iave (k) plus a predetermined value Q and the white reference data You may make it compare the magnitude with W (k).

  Accordingly, as shown in FIG. 11, in the first embodiment, the existence range of pixels in which the document image data is larger than the white reference data is Z1, but as described above, the document image data The existence range of pixels in which Iave (k) plus a predetermined value Q is larger than the white reference data W (k) is Z2, which is wider than the range Z1, and the presence or absence of abnormal pixels can be reliably detected. It becomes.

  (2) In the first embodiment, the estimated value calculation unit 257 includes the image data Iave (i−1) and the pixel of the pixel (i−1) adjacent to the pixel group of the abnormal pixels i to (i + m). By linear interpolation using the image data Iave (i + m + 1) of (i + m + 1), it is estimated that the abnormal pixels i to (i + m) are generated by the original image acquisition reading operation if the foreign matter is not attached. The generated image data is generated as estimated data Ish ′ (i) to Ish ′ (i + m). However, the present invention is not limited to this. For example, the estimated data Ish ′ (i) to Ish ′ (i + m) In addition, the image data Iave (i-1) of the pixel (i-1) adjacent to the pixel group of the abnormal pixels i to (i + m), or the image data Iave (i + m + 1) of the pixel (i + m + 1) is uniform. It may be or with.

  Alternatively, an average value of each image data of a pixel group including a plurality of pixels including the pixel (i−1) adjacent to the pixel group of the abnormal pixels i to (i + m) is calculated as the estimated data Ish ′ (i) to Ish. It is good also as' (i + m). For example, the estimated data Ish ′ (i) to Ish ′ (i + m) are all converted into the image data Iave (i−1) of the pixel (i−1) and the image data Iave (i−2) of the pixel (i-2). ), Image data Iave (i-3) of the pixel (i-3), and image data Iave (i-4) of the pixel (i-4).

  Alternatively, each image data of a pixel group including a plurality of pixels including the pixel (i−1) and a pixel including a plurality of pixels including the pixel (i + m + 1) adjacent to the pixel group of the abnormal pixels i to (i + m). The average value of each group of image data may be the estimated data Ish ′ (i) to Ish ′ (i + m).

  For example, the estimated data Ish ′ (i) to Ish ′ (i + m) are all converted into the image data Iave (i−1) of the pixel (i−1) and the image data Iave (i−2) of the pixel (i-2). ), Image data Iave (i-3) of the pixel (i-3), image data Iave (i + m + 1) of the pixel (i + m + 1), image data Iave (i + m + 2) of the pixel (i + m + 2), and image data Iave of the pixel (i + m + 3) It is good also as an average value with (i + m + 3).

  (3) The MFP 1 according to the first embodiment includes both the scanner unit 22 and the CIS 231 as the image reading unit, but includes only one of the scanner unit 22 and the CIS 231. The series of shading correction processes according to the first embodiment may be performed on the image reading unit.

  (4) The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the first to third embodiments, the MFP 1 is shown as an example of the image forming apparatus according to the present invention. However, the image forming apparatus according to the present invention is not limited to the MFP 1, It may be a copier, a facsimile machine or the like.

DESCRIPTION OF SYMBOLS 1 Multifunction machine 2 Image reading part 22 Scanner part 222 Light source 229 CCD
231 CIS
231a Light source 10 White reference plate 11 Shading roller 214 First reading control unit 215 Second reading control unit 217 Shading correction unit 218 Image processing unit 250 White reference memory 251 Black reference memory 252 Abnormal pixel candidate detection unit 253 Abnormal pixel candidate storage unit 254 Shading correction processing unit 255 White background determination unit 256 Abnormal pixel count unit 257 Estimated value calculation unit 258 White reference correction value calculation unit 259 White reference correction value memory 260 switching unit

Claims (4)

An image reading unit for performing an image reading operation;
A white reference member which is a white reference;
A first reading control unit that causes the image reading unit to perform an image reading operation on the white reference member;
A first white reference data storage unit that stores image data obtained by a reading operation based on an instruction from the first reading control unit as first white reference data indicating a white reference value;
Abnormal image data caused by foreign matter on the optical path including the white reference member is detected from the image data of each pixel obtained by the reading operation based on the instruction of the first reading control unit, and each pixel of the image reading unit is detected. Among them, an abnormal pixel detector that detects the pixel that generated the abnormal image data as an abnormal pixel,
A second reading control unit for causing the image reading unit to perform an image reading operation on a document;
The first white reference data stored in the first white reference data storage unit is used for image data of a predetermined area of the document among image data obtained by a reading operation based on an instruction from the second reading control unit. A first shading correction processing unit that uses the shading correction process,
Using the image data generated by predetermined pixels excluding the abnormal pixels detected by the abnormal pixel detection unit among the image data after the shading correction processing by the first shading correction processing unit, the foreign matter is temporarily present. If there is no image data that is estimated to have been generated by the abnormal pixel by a reading operation based on an instruction from the second reading control unit, the image data after the first shading correction processing is converted into the abnormal pixel. An estimated data generation unit that generates as estimated data for
Using the estimated data generated by the estimated data generating unit, if the foreign matter does not exist, it is estimated that the abnormal pixel is generated by the reading operation based on the instruction of the first reading control unit. Second white reference data generating unit for generating image data as second white reference data for the abnormal pixel;
The second white reference data for the abnormal pixel generated by the second white reference data generation unit is used for the image data generated by the abnormal pixel by the reading operation based on the instruction of the second reading control unit. For the pixel generated by the first white reference data generation unit with respect to image data generated by a pixel other than the abnormal pixel by a reading operation based on an instruction of the second reading control unit while performing a shading correction process And a second shading correction processing unit that performs a shading correction process using the first white reference data. The image reading unit includes n (n> 1) pixels arranged in a row,
The first reading control unit further causes the image reading unit to perform an image reading operation with respect to the white reference member in a state where an illumination operation with respect to the white reference member of an illumination unit provided in the image reading unit is turned off. ,
A black reference data storage unit that generates image data obtained by a reading operation based on an instruction from the first reading control unit as black reference data indicating a black reference value;
Of the image data obtained by the instruction of the second reading control unit, when the pixels belonging to the predetermined area of the document are numbered in the pixel column direction, the pixel k (= 1, 2,... n-1, n), the black reference data generated by the black reference data generation unit is B (k), the first white reference data stored by the first white reference data storage unit is W (k), When the image data generated by the pixel according to the instruction of the second reading control unit is I (k) and the number of gradations of the image data is L, the first shading correction processing unit is
{(I (k) −B (k)) / (W (k) −B (k))} × L
Is the image data Ish (k) after the shading correction processing for the pixel k,
The estimated data generation unit includes pixels adjacent to the abnormal pixel group including the abnormal pixel i or the plurality of abnormal pixels i in the image data Ish (k) after the shading correction processing by the first shading correction processing unit. Using the image data Ish (j) generated by the pixel j in the pixel area, if the foreign matter does not exist, the image data Ish (j) is generated at the abnormal pixel i by a reading operation based on an instruction from the second reading control unit. An image presumed to be generated and image data Ish ′ (i) after the shading correction processing by the first shading correction processing unit is generated as estimation data,
The second white reference data generation unit
{L (I (i) −B (i)) / Ish ′ (i)} + B (i)
The image processing apparatus according to claim 1, wherein the second white reference data for the abnormal pixel i is generated.   The image processing apparatus according to claim 1, wherein the predetermined area of the document is a leading area of the document having a predetermined width.   The image processing apparatus according to claim 1, wherein the image reading unit is at least one of a CCD and a CIS.

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