JP2016036076A - Shading correction device and image processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shading correction device and an image processing device that can perform accurate shading correction.SOLUTION: When shading data under stained manuscript reading which are achieved before the manuscript is read are replaced by initial shading data of an unstained initial manuscript, the initial shading data are corrected so that the ripple unevenness and amplitude of the shading data under manuscript reading are matched. The shading correction is performed by the corrected initial shading data, whereby occurrence of a periodical streak caused by the difference in amplitude of AC components of the shading data can be prevented, and accurate shading correction can be performed.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a shading correction apparatus and an image processing apparatus.

  In the image reading apparatus, shading correction is performed in order to correct the variation in the light amount distribution for each main scanning position of the reading optical system and the variation in the sensitivity for each sensor chip pixel. Specifically, shading correction of input data is performed using, for example, a reading result (shading data) of a white density reference member.

  Japanese Patent Application Laid-Open No. 2010-011297 discloses an image in which the initial shading data and the shading data acquired immediately before reading a document are different in light quantity, thereby reducing the change in the amplitude of rod lens cycle unevenness. A processing device is disclosed. This image processing apparatus corrects the light amount ratio (the ratio of the initial shading data to the entire main scanning area of the shading data acquired immediately before reading the document or the average value of the specific area of the main scanning) to the initial shading data without any dirt. To replace and interpolate. Thereby, the change of the amplitude of the rod lens period nonuniformity resulting from the above-mentioned difference in the amount of light can be reduced.

  However, in the conventional technique including the image processing apparatus disclosed in Patent Document 1, there is a problem in that vertical stripes are generated at a place where dirt is detected and replaced with initial shading data. That is, an amplitude difference due to ripple unevenness occurs between the rod lenses between the shading data acquired immediately before reading the original and the initial shading data. As a result, vertical stripes are generated. For this reason, there has conventionally been a problem that it cannot be said that accurate shading correction is performed.

  SUMMARY An advantage of some aspects of the invention is that it provides a shading correction apparatus and an image processing apparatus capable of performing accurate shading correction.

  In order to solve the above-described problems and achieve the object, the present invention provides a first DC component extraction unit that extracts first DC component data from initial data that is shading data serving as a reference read from a density reference member. A first AC component extraction unit that extracts first AC component data that is a difference between the extracted first DC component data and initial data; and a concentration reference member that is later in time than the initial data. A second DC component extraction unit that extracts second DC component data from the current data that is the read shading data, and second AC component data that is the difference between the extracted second DC component data and the initial data A second AC component extraction unit for extracting the first AC component data, a first peak detection unit for detecting a first maximum value that is the maximum absolute value of the first AC component data, and an absolute value of the second AC component data A second peak detection unit that detects a second maximum value that is a maximum value of the correction value, and a correction magnification that calculates an AC correction magnification of the shading data by dividing the second maximum value by the first maximum value A calculation unit, a correction data generation unit that generates corrected shading data by adding the first DC component data to the first AC component data multiplied by the AC correction magnification, and the corrected shading data are used. A shading correction unit that performs a shading correction process on the input data and outputs the result.

  According to the present invention, there is an effect that accurate shading correction can be performed.

FIG. 1 is a schematic diagram of a reading module (CIS). FIG. 2 is a diagram for explaining the reason why the amplitude of the ripple in the main scanning light quantity distribution varies. FIG. 3 is a diagram for explaining vertical stripes generated in an output document or output data due to a ripple amplitude difference. FIG. 4 is a sectional view of a multifunction peripheral (MFP) according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view of an automatic document conveyance mechanism provided in the MFP according to the first embodiment. FIG. 6 is a block diagram of a controller that controls the automatic document conveyance mechanism provided in the MFP according to the first embodiment and peripheral circuits of the controller. FIG. 7 is a block diagram of a second reading unit provided in the MFP according to the first embodiment. FIG. 8 is a block diagram of the white correction unit of the MFP according to the first embodiment. FIG. 9 is a diagram for explaining an operation for extracting an AC component of shading data at the time of document reading in the white correction unit of the MFP according to the first embodiment. FIG. 10 is a diagram for explaining the operation of generating corrected shading data in the white correction unit of the MFP according to the first embodiment. FIG. 11 is a diagram for explaining the generation operation of shading data for correcting the amplitude difference between the initial shading data and the original reading shading data in the white correction unit of the MFP according to the first embodiment. FIG. 12 is a diagram illustrating a state in which specific level fluctuations occur in the shading data during document reading due to the influence of dirt adhering to the density reference member. FIG. 13 is a block diagram of the white correction unit of the MFP according to the second embodiment. FIG. 14 is a diagram for explaining the operation of generating corrected shading data in the white correction unit of the MFP according to the second embodiment. FIG. 15 is a block diagram of the white correction unit of the MFP according to the third embodiment. FIG. 16 is a diagram for explaining the operation of generating corrected shading data in the white correction unit of the MFP according to the third embodiment. FIG. 17 is a diagram for explaining an inconvenience when a specific level fluctuation occurs in data by shading correction. FIG. 18 is a block diagram of the white correction unit of the MFP according to the fourth embodiment. FIG. 19 is a diagram for explaining the operation of generating corrected shading data in the white correction unit of the MFP according to the fourth embodiment. FIG. 20 is a block diagram of the white correction unit of the MFP according to the fifth embodiment. FIG. 21 is a diagram for explaining the operation of generating corrected shading data in the white correction unit of the MFP according to the fifth embodiment.

  Hereinafter, as an example, an MFP (Multifunction Peripheral) according to an embodiment to which the present invention is applied will be described in detail with reference to the drawings. Note that the MFP is an electronic device having one or more of a printing function, a copying function, a scanner function, and a facsimile function, for example.

(Overview)
In an electronic apparatus such as an MFP that reads an image, shading correction is performed to correct variation in light amount distribution for each main scanning position of the reading optical system and variation in sensitivity for each sensor chip pixel. Specifically, the reading result (shading data) of the density reference member having a predetermined white color is set to “SD”, the input data is set to “Din”, and the calculation of the following equation (1) is performed on the input data. “Dout”, which is the result of the shading correction, is obtained.

  Dout = Din / SD (Expression 1)

  Here, when the shading data used for the shading correction is generated, if dirt is attached to the density reference member, the value of the shading data at the place where the dirt is attached becomes a value for which accurate shading correction is difficult. This is because, for example, pixels corresponding to locations where dirt attached to the density reference member is attached along the main scanning direction (direction in which the pixels are arranged) of a reading optical system such as a line-shaped image sensor. This means that the pixel data is not accurately subjected to shading correction. For this reason, it corresponds to a location where the density reference member is contaminated on one image generated by scanning the reading optical system in the sub-scanning direction orthogonal to the two-dimensional direction with respect to the main scanning direction. This causes inconvenience in which streaky noise appears.

  Specifically, when black stains are attached to the density reference member, the reading light is absorbed by the black stains, and the reflected light is diffusely reflected, so that incident light to the pixel corresponding to the black stain attachment portion is not detected. This causes a drop in the value of the generated shading data. When shading data having such a drop is used for shading correction, the value of the denominator of the above equation 1 becomes small, resulting in a large shading correction result and white streaks (insufficient shading correction). Similarly, when white dirt adheres to the density reference member, the amount of reflection of the reading light increases due to the white dirt. For this reason, the incident light with respect to the pixel corresponding to the spot where the white dirt is attached becomes larger than the other spots, and the value of the generated shading data becomes a large value. When this large value of shading data is used for shading correction, the value of the denominator of the above equation 1 becomes large, resulting in a small shading correction result and black streaks (excessive shading correction).

  In order to prevent the generation of such streaky noise, the density reference member is changed by changing the relative position of the image sensor of the image reading unit and the density reference member with a movable mechanism when generating shading data. It is conceivable to reduce the influence of dirt, scratches, and the like. That is, reading of a plurality of locations on the density reference member is performed while moving the image sensor in the sub-scanning direction. Then, each shading data corresponding to a plurality of locations where the reading has been performed is averaged. As a result, it is possible to generate shading data in which the influence of dirt and scratches is reduced. Alternatively, a plurality of locations are read while rotating the density reference member formed by the rotating roller. As a result, it is possible to generate shading data in which the influence of dirt and scratches is reduced.

  However, in many cases, a reading module such as a contact image sensor (CIS: Compact Image Sensor) for reading the back side of a document is fixed in a small space in an ADF (Auto Document Feeder) apparatus. For this reason, when the concentration reference member and the movable mechanism are provided in the ADF apparatus, the ADF apparatus becomes complicated, large, and expensive.

  Here, the following method can reduce the influence of dirt and scratches on the density reference member without providing a movable mechanism. That is, the initial shading data acquired in advance with a clean concentration reference member is stored in a nonvolatile memory. The initial shading data is compared with the shading data acquired immediately before reading the document. Data at pixel positions whose comparison results are greater than or equal to a predetermined value is determined as data affected by dirt or scratches. Then, the data affected by the contamination is interpolated by replacing the initial shading data without the contamination with the light amount ratio corrected. The light amount ratio is the ratio of the entire area of the main scan or the average value of the specific area of the main scan between the initial shading data and the shading data acquired immediately before reading the document. Thereby, it is possible to reduce the influence of dirt and scratches on the density reference member without providing a movable mechanism.

  However, even in such a method, at the place where the dirt is detected and replaced with the initial shading data, the amplitude difference of the ripple unevenness that occurs at the rod lens interval between the shading data acquired immediately before reading the original and the initial shading data is detected. The resulting vertical streak occurs.

  This will be specifically described below. FIG. 1 shows a schematic diagram of a reading module (CIS). The figure which attached | subjected the code | symbol of (a) of FIG. 1 is an exploded perspective view of the principal part of a reading module. The figure which attached | subjected the code | symbol of (b) of FIG. 1 is an enlarged view of the principal part of a reading module. The figure which attached | subjected the code | symbol of (c) of FIG. 1 is a figure which shows the output waveform corresponding to each rod lens of a reading module.

  As shown in FIG. 1A, the reading module has a rod-shaped light guide 1 and light sources 2 such as LEDs provided at both ends of the light guide 1, respectively. doing. LED is an abbreviation for “Light Emitting Diode”. The light guide 1 irradiates light from the light source unit 2 to the density reference member and the original. Further, the reading module has a line sensor 3 that converts reflected light of light irradiated on the density reference member and the document into a reading signal. The line sensor 3 is formed by arranging a plurality of reading sensors (hereinafter referred to as pixels) 3a in a line along the main scanning direction, as can be seen from the enlarged view with the reference numeral (b) in FIG. ing. Further, the reading module has a rod lens array 4 that condenses the reflected light of the light applied to the density reference member and the original on the line sensor 3. The rod lens array 4 is formed by arranging a plurality of rod lenses 4a in a line along the main scanning direction, as can be seen from the enlarged view with the reference numeral (b) in FIG.

  Such a reading module condenses the reflected light on the line sensor 3 using the rod lens 4. For this reason, as can be seen from the figure labeled (c) in FIG. 1, the output of the line sensor 3 (the level of the read signal) increases near the center of the rod lens 4a where the reflected light is collected, The output of the line sensor 3 is low at the end of the rod lens 4a. For this reason, a position where the output is high and a position where the output is low occur periodically in the period of the rod lens 4a.

  Here, due to heat generation due to continuous lighting of the light source unit 2 at the time of document reading, environmental light temperature, and the like, the light amount is reduced and the ripple amplitude of the main scanning light amount distribution varies. FIG. 2 is a diagram for explaining the reason why the amplitude of the ripple in the main scanning light quantity distribution varies. 2 is a diagram showing the output of the pixel 3a when the rod lens 4a is not thermally expanded. 2B is a diagram showing the output of the pixel 3a after the rod lens 4a has been thermally expanded.

  As can be seen by comparing the figures labeled (a) and (b) in FIG. 2, when the diameter of the rod lens 4a changes due to thermal expansion, the relative relationship between the rod lens 4a and the pixel 3a. The positional relationship shifts with time in the sub-scanning direction. The sub-scanning direction is a direction that is two-dimensionally orthogonal to the main scanning direction. The substrate of the line sensor 3 also extends in the sub-scanning direction due to thermal expansion. When the substrate of the line sensor 3 extends in the sub-scanning direction, the relative positional relationship between the rod lens 4a and the pixel 3a shifts with time in the sub-scanning direction. If the thermal expansion coefficients of the rod lens 4a and the substrate of the line sensor 3 are equal, the sub-scanning light quantity distribution does not shift. However, the thermal expansion coefficients of the rod lens 4a and the substrate of the line sensor 3 are different from each other. For this reason, the amount of reflected light received by the line sensor 3 is reduced.

  FIG. 3 is a diagram for explaining vertical stripes generated in an output document or output data due to a ripple amplitude difference. In FIG. 3A, the dotted waveform is initial shading data generated at an initial stage such as at the time of factory shipment. In the figure attached with the reference numeral (a) in FIG. 3, the solid line waveform is the original reading shading data generated when the original is read. In FIG. 3B, the dotted waveform is initial shading data generated at an initial stage such as at the time of factory shipment. In FIG. 3B, the thin line waveform is shading data at the time of document reading generated at the time of document reading. In the drawing with the symbol (b) in FIG. 3, the thick line waveform is the original reading shading data (corrected shading data) corrected by the initial shading data.

  When performing the shading correction, the original reading shading data affected by the contamination is replaced with the initial shading data without the contamination by correcting the light amount ratio. The light quantity ratio is the ratio of the average value of the initial shading data and the original scanning whole shading data or the specific area of the main scanning. When replacing with the initial shading data, even in the corrected shading data in which the light quantity ratio is corrected, it is difficult to accurately reproduce the ripple of the shading data at the time of document reading, and there may be a difference between the two. In this case, corrected shading data that is brighter than the original or darker than the original is generated. For this reason, a bright streak or a dark streak is generated as shown in a diagram in which the reference numeral (c) in FIG.

(First embodiment)
As will be described below, the MFP according to the embodiment replaces the original shading data at the time of reading, which is acquired immediately before reading the original, with the original shading data without the original, and replaces the initial shading data with the original reading. Correction is made so that the ripple unevenness and amplitude of the shading data match. As a result, it is possible to prevent inconvenience that a bright streak or a dark streak occurs in the output document or output data, and to enable accurate shading correction.

  FIG. 4 is a sectional view of the MFP according to the embodiment. As shown in FIG. 4, the MFP according to the embodiment includes an automatic document feeder (ADF) 10, a paper feeding unit 20, and an image forming unit 30. The paper feed unit 20 includes paper feed cassettes 21 and 22 that store recording papers having different paper sizes. In addition, the paper feed unit 20 includes a paper feed mechanism 23 including various rollers that transport the recording paper stored in the paper feed cassettes 21 and 22 to the image forming position of the image forming unit 30.

  The image forming unit 30 includes an exposure device 31, a photosensitive drum 32, a developing device 33, a transfer belt 34, and a fixing device 35. The image forming unit 30 exposes the photosensitive drum 32 by the exposure device 31 based on the image data of the original read by the image reading unit in the ADF 10, and forms a latent image on the photosensitive drum 32. Further, the image forming unit 30 develops the developing device 33 by supplying toner of different colors to the photosensitive drum 32. Then, the image forming unit 30 transfers the image developed on the photosensitive drum 32 to the recording paper supplied from the paper feeding unit 20 by the transfer belt 34 and then the toner image transferred to the recording paper by the fixing device 35. The toner is melted to fix the color image on the recording paper.

  FIG. 5 is an enlarged view of a cross section of the ADF 10. FIG. 6 is a block diagram of the controller 11 that controls the ADF 10 and peripheral circuits of the controller 11. The ADF 10 conveys the read original to a fixed reading unit, and reads an image while conveying the original at a predetermined speed. The ADF 10 includes a document setting unit A, a separation feeding unit B, a registration unit C, a turn unit D, a first reading conveyance unit E, a second reading conveyance unit F, a paper discharge unit G, and a stack unit H. The document setting unit A sets a read document bundle. The separation feeding unit B separates and feeds the originals one by one from the set original bundle. The registration unit C has a function of primarily abutting and aligning the fed document and a function of pulling out and transporting the aligned document. The turn part D turns the document to be conveyed and conveys the document surface toward the reading side (downward). The first reading conveyance unit E reads the surface image of the document from below the contact glass. The second reading conveyance unit F reads the back image of the original after reading. The paper discharge unit G discharges the original whose front and back have been read out of the apparatus. The stack unit H stacks and holds documents after reading.

  The original bundle 130 to be read is set on the original table 132 including the movable original table 131 with the original surface facing upward. Further, the width direction of the document bundle 130 is positioned in a direction perpendicular to the conveyance direction by a side guide (not shown). The document set is detected by the set filler 133 and the document set sensor 100 and transmitted to the main body control unit 122 by the I / F 114.

  Further, the document length detection sensor 134 or 135 provided on the document table surface (a reflective sensor or an actuator type sensor capable of detecting even one document) is used to approximate the length of the document in the conveyance direction. Determined.

  The movable document table 131 is configured to be movable (movable up and down) in the directions a and b indicated by arrows in FIG. When the set of documents is detected by the set filler 133 and the document set sensor 100, the movable document table 131 moves the bottom plate raising motor 112 in the normal direction so that the uppermost surface of the document bundle 130 contacts the pickup roller 148. 131 is raised. The pickup roller 148 operates in the c direction and the d direction indicated by arrows in FIG. 5 by a cam mechanism using the pickup motor 108 as a drive source. The pick-up roller 148 is raised by the movable original table 131 and is pushed by the upper surface of the original on the movable original table 131 to rise in the c direction.

  When the print key is pressed from the operation unit 121 and a document feed signal is transmitted from the main body control unit 122 to the controller 11 via the I / F 114, the pickup roller 148 is driven to rotate by the normal rotation of the feed motor 109. Then, several (ideally one) documents on the document table 132 are picked up. The rotation direction is a direction in which the uppermost document is conveyed to the sheet feeding port.

  The paper feed belt 136 is driven in the paper feed direction by the normal rotation of the paper feed motor 109. The reverse roller 137 is rotationally driven in the direction opposite to the paper feeding direction by the forward rotation of the paper feeding motor 109, separates the uppermost document and the original document thereunder, and feeds only the uppermost document. It has become. More specifically, the reverse roller 137 contacts the paper feeding belt 136 with a predetermined pressure. The reverse roller 137 rotates counterclockwise in response to the rotation of the paper feed belt 136 when it is in direct contact with the paper feed belt 136 or in a state of being in contact with one original. The reverse roller 137 is set so that the follower force is lower than the torque of the torque limiter when two or more originals enter between the paper feed belt 136 and the reverse roller 137. In this case, the reverse roller 137 rotates in the clockwise direction, which is the original driving direction, and functions to push back the excess original. Thereby, it is possible to prevent double feeding of documents.

  The document separated into one sheet by the action of the paper feed belt 136 and the reverse roller 137 is further fed by the paper feed belt 136, the leading edge is detected by the abutting sensor 105, and the pull-out roller 138 is further advanced and stopped. I hit it. Thereafter, the original is conveyed by a predetermined distance from the detection of the abutting sensor 105 and pressed against the pull-out roller 138 with a predetermined amount of deflection. In this state, the paper feed motor 109 is stopped and the drive of the paper feed belt 136 is stopped. At this time, the pickup motor 108 is rotated, the pickup roller 148 is retracted from the upper surface of the document, and the document is fed only by the conveying force of the paper feed belt 136. As a result, the leading edge of the document enters the nip between the pair of upper and lower rollers of the pull-out roller 138, and alignment (skew correction) of the leading edge is performed.

  The pull-out roller 138 has a skew correction function. The pull-out roller 138 is a roller for conveying the skew-corrected document after separation to the intermediate roller 139 and is driven by the reverse rotation of the paper feed motor 109. At this time (when the paper feed motor 109 rotates in reverse), the pull-out roller 138 and the intermediate roller 139 are driven, but the pickup roller 148 and the paper feed belt 136 are not driven.

  A plurality of document width sensors 104 are arranged in the depth direction and detect the size in the width direction perpendicular to the transport direction of the document transported by the pull-out roller 138. Further, the length of the document in the conveyance direction is detected by using a motor pulse generated by reading the leading edge and the trailing edge of the document with the butting sensor 105.

  When the document is conveyed from the registration unit C to the turn unit D by driving the pull-out roller 138 and the intermediate roller 139, the conveyance speed at the registration unit C is higher than the conveyance speed at the first reading conveyance unit E. Set to As a result, the processing time for sending the document to the reading unit is shortened. When the leading edge of the document is detected by the reading entrance sensor 103, before the leading edge of the document enters the nip between the upper and lower rollers of the reading entrance roller 140, the document feeding speed is reduced to be the same as the reading feeding speed. Start. At the same time, the reading motor 110 is driven to rotate forward, and the reading inlet roller 140, the reading outlet roller 141, and the CIS outlet roller 142 are driven. When the registration sensor 107 detects the leading edge of the document, the document is decelerated over a predetermined conveyance distance, temporarily stops before the reading position 143, and transmits a registration stop signal to the main body control unit 122 via the I / F 114. To do.

  Subsequently, when a reading start signal is received from the main body control unit 122, the document whose registration has been stopped is transported at an increased speed so as to rise to a predetermined transport speed before the leading end of the document reaches the reading position. When the leading edge of the document detected by the pulse count of the reading motor 110 reaches the reading unit, a gate signal indicating an effective image area in the sub-scanning direction of the first surface is sent to the main body control unit 122 from the first reading unit. Sent until the trailing edge of the document is removed.

  In the case of single-sided document reading, the document that has passed through the first reading conveyance unit E is conveyed to the paper discharge unit G through the second reading unit. At this time, when the leading edge of the document is detected by the paper discharge sensor 106, the paper discharge motor 111 is driven to rotate forward, and the paper discharge roller 144 rotates counterclockwise. Further, the discharge motor drive speed is reduced immediately before the trailing edge of the document comes out of the nip between the upper and lower roller pairs of the discharge roller 144 by the discharge motor pulse count from the detection of the leading edge of the document by the discharge sensor 106. As a result, it is possible to prevent inconvenience that the document discharged onto the discharge tray 145 jumps out of the discharge tray 145.

  In the case of double-sided document reading, the controller for the second reading unit 113 is detected at the timing when the document leading edge reaches the second reading unit 113 by the pulse count of the reading motor after the discharge sensor 106 detects the document leading end. A gate signal indicating an effective image area in the sub-scanning direction is transmitted from 11 until the trailing edge of the original passes through the reading unit. The second reading roller 146 suppresses the floating of the document in the second reading unit. The second reading roller 146 also serves as a reference white portion (density reference member) for acquiring shading data by the second reading unit 113.

  FIG. 7 is a block diagram of the main part of the electric circuit of the second reading unit 113. As shown in FIG. 7, the second reading unit 113 includes the light source unit 2 including an LED, a fluorescent lamp, a cold cathode tube, or the like. The light source unit 2 constitutes an irradiation unit that irradiates light in the main scanning direction together with a light guide (not shown).

  The second reading unit 113 includes a plurality of pixels (photoelectric conversion elements) 3a arranged in the main scanning direction (a direction corresponding to the document width direction), a plurality of amplifier circuits 202 connected to each pixel 3a, and each amplifier circuit. A plurality of A / D converters 203 connected to 202 are also provided. The output signal of the A / D conversion unit 203 includes a black level offset component in addition to the signal component. The second reading unit 113 includes a black correction unit 204 that removes a black level offset component.

  The white correction unit 205 performs white correction processing on the output signal of the black correction unit 204, thereby removing adverse effects on the image data due to unevenness of the light source unit 2 and uneven sensitivity of each pixel 3a. As will be described in detail later, the white correction unit 205 replaces the dirty original reading shading data acquired by reading the density reference member immediately before reading the original with the original initial shading data without dirt. The initial shading data is corrected so that the ripple unevenness and the amplitude of the shading data at the time of document reading match. This prevents the inconvenience that bright or dark streaks occur in the output document or output data.

  The second reading unit 113 also includes an image processing unit 206, a frame memory 207, an output control circuit 208, an I / F circuit 209, and the like.

  Prior to the conveyance of the document to the reading position where reading is performed by the second reading unit 113, a lighting signal for ON control of lighting is supplied from the controller 11 to the light source unit 2. As a result, the light source unit 2 is turned on, light is irradiated onto a document (not shown), and reflected light is generated. The reflected light from the original is condensed and received by each pixel 3a by the rod lens 4a. Each pixel 3a generates a read signal that is an electrical signal corresponding to the received reflected light. The read signal is amplified by the amplifier circuit 202 and then digitized into read data by the A / D converter 203. For example, when the read data is 8 bits, the black level is “0” and the white level is “255”.

  The read data is subjected to offset component removal processing by the black correction unit 204, and shading correction described later is performed by the white correction unit 205. Further, the read data is temporarily stored in the frame memory 207 after being subjected to an inter-line correction process or the like by the image processing unit 206. Thereafter, the read data is converted into a data format that can be processed by the main body control unit 122 by the output control circuit 208 and then supplied to the main body control unit 122 via the I / F circuit 209. In addition to the lighting signal of the light source unit 2 described above, the controller 11 sends the second reading unit 113 a timing at which the leading edge of the document reaches the reading position by the second reading unit 113 (image data after that timing is stored). A timing signal for notifying that the data is treated as valid data, a power source, and the like are supplied.

  Next, the shading correction operation in the white correction unit 205 will be described. FIG. 8 is a functional block diagram of the white correction unit 205. As shown in FIG. 8, the white correction unit 205 includes a first storage unit 301, a second storage unit 302, a smoothing unit 303, an AC component extraction unit 304, a peak detection unit 305, and a smoothing unit 306. ing. The white correction unit 205 includes an AC component extraction unit 307, a peak detection unit 308, an AC correction magnification calculation unit 309, a correction data generation unit 310, and a shading correction unit 311.

  The smoothing unit 303 is an example of a first DC component extraction unit. The AC component extraction unit 304 is an example of a first AC component extraction unit. The smoothing unit 306 is an example of a second DC component extraction unit. The AC component extraction unit 307 is an example of a second AC component extraction unit. The peak detection unit 305 is an example of a first peak detection unit. The peak detection unit 308 is an example of a second peak detection unit. The AC correction magnification calculator 309 is an example of a correction magnification calculator.

  As shown in FIG. 6, the smoothing unit 303 to the shading correction unit 311 are configured such that the controller 11 executes a shading correction program stored in the storage unit 101 such as a hard disk drive device, a ROM, or a RAM. It is a function that can be realized. ROM is an abbreviation for “Read Only Memory”. RAM is an abbreviation for “Random Access Memory”. In this example, the smoothing unit 303 to the shading correction unit 311 of the white correction unit 205 will be described as being realized by software, but a part or all of the smoothing unit 303 to the shading correction unit 311 is performed. May be realized by hardware.

  Further, the shading correction program may be provided as a file in an installable format or an executable format recorded on a recording medium readable by a computer device such as a CD-ROM or a flexible disk (FD). Further, the program may be provided by being recorded on a computer-readable recording medium such as a CD-R, a DVD, a Blu-ray disc (registered trademark), or a semiconductor memory. DVD is an abbreviation for “Digital Versatile Disk”. Further, the shading correction program may be provided by being installed via a network such as the Internet. The shading correction program may be provided by being incorporated in advance in a ROM or the like in the device.

  In such a white correction unit 205, input data obtained by reading a non-dirty density reference member (in this example, the above-described second reading roller 146) at the initial stage such as when the MPF according to the embodiment is shipped from the factory, The initial shading data is stored in the first storage unit 301. Then, the initial shading data stored in the first storage unit 301 is transferred to and stored in the second storage unit 302 composed of a nonvolatile memory or the like.

  Next, at the time of document reading, the density reference member is read just before reading the document, and this is stored in the first storage unit 301 as shading data at the time of document reading. FIG. 9A is a diagram showing an example of shading data at the time of document reading. As can be seen from FIG. 9A, the original reading shading data has a waveform in which a periodic fluctuation component corresponding to the lens pitch of the rod lens 4a is superimposed.

  The smoothing unit 306 removes the periodic fluctuation component corresponding to the lens pitch of the rod lens 4a from the original reading shading data read from the first storage unit 301, thereby obtaining the original reading shading data. A direct current component is generated. FIG. 9B is a waveform diagram of a DC component generated from shading data at the time of document reading.

  The AC component extraction unit 307 extracts an AC component that is a difference between the DC component of the original reading shading data generated by the smoothing unit 306 and the original reading shading data read from the first storage unit 301. . The figure which attached | subjected the code | symbol of (c) of FIG. 9 has shown the waveform of the alternating current component extracted by the alternating current component extraction part 307. FIG.

  On the other hand, the smoothing unit 303 and the AC component extraction unit 304 also extract the DC component from the initial shading data stored in the second storage unit 302 in the same manner as described above, and the difference between the DC component and the initial shading data from the initial shading data. To extract the AC component.

  Next, the value of the AC component of the initial shading data of the x-th pixel on the main scanning axis is “Ainit (x)”, and the value of the DC component is “Dinit (x)”. Similarly for the original reading shading data, the AC component value of the x pixel original reading shading data on the main scanning axis is “Apre (x)” and the direct current component value is “Dpre (x)”. " A plurality of blocks each having a certain number of pixels are set in the main scanning direction, and the processing described below is performed in units of blocks.

  The peak detector 308 detects “Apre_amp []”, which is the maximum absolute value of the AC component Pre (x) of the shading data at the time of document reading in the block. A variable with parentheses ([]), such as Apre_amp [], is an array, and a block number is placed in the parentheses. The same applies to the following description. Further, the peak detection unit 305 detects “Ainit_amp []”, which is the maximum absolute value of the AC component Ainit (x) of the initial shading data in the above-described block.

  Specifically, in the figure attached with the reference numeral (a) in FIG. 10, an example of each waveform of the alternating current component Ainit (x) of the initial shading data and the alternating current component Apre (x) of the shading data at the time of document reading. Show. In the diagram with the reference numeral (a) in FIG. 10, the dotted waveform is the AC component Ainit (x) of the initial shading data. In FIG. 10A, the solid line waveform is the waveform of the AC component Apre (x) of the shading data at the time of document reading. As shown in FIG. 10A, the peak detection unit 308 includes a maximum value Apre_amp [] of the absolute value of the AC component Apre (x) of the original reading shading data and the initial shading. The absolute maximum value Ainit_amp [] of the AC component Ainit (x) of the data is detected for each block.

  Next, the AC correction magnification calculator 309 calculates the AC correction magnification α [] for each block using the following equation 2 as shown in the figure with the symbol (b) in FIG. To do.

  α [] = (Apre_amp []) / (Ainit_amp []) (Expression 2)

  In Equation 2, when Ainit_amp [] = 0, α [] = 0.

  Next, the correction data generation unit 310 performs the following equation 3 as a first procedure. Thereby, the correction data generation unit 310 calculates the corrected AC component Acor (x) obtained by multiplying the AC component Ainit (x) of the initial shading data of each block by the corresponding AC correction magnification α []. .

  Acor (x) = Ainit (x) × α [] (Expression 3)

  In FIG. 10C, the dotted waveform is the waveform of the AC component Ainit (x) of the initial shading data of each block before multiplication processing (before correction) with the correction magnification α []. . On the other hand, in the diagram with the reference numeral (c) in FIG. 10, the solid line waveform indicates the AC component Ainit (x) of the initial shading data of each block after the multiplication processing (after correction) with the correction magnification α []. ). As can be seen from FIG. 10C, the value of the AC component Ainit (x) of the initial shading data is the difference in amplitude from the AC component Apre (x) of the shading data during document reading. It is corrected accordingly.

  Next, the correction data generation unit 310 performs the following equation 4 as a second procedure. As a result, the correction data generation unit 310 adds the corrected AC component Acor (x) and the DC component Dinit (x) of the initial shading data and performs shading data SD (x) for the x pixel on the main scanning axis. Is calculated.

  SD (x) = Acor (x) + Dinit (x) (Expression 4)

  The correction data generation unit 310 generates the shading data SD (x) for all the pixels by performing the operations of Equation 3 and Equation 4 for all the pixels, and supplies the shading correction unit 311 with the shading data SD (x). Supply.

  FIG. 11 is a diagram schematically illustrating a generation process of the shading data SD (x). 11A is a waveform diagram of the corrected AC component Acor (x) corrected by the correction magnification α [] from the AC correction magnification calculator 309. FIG. 11B is a waveform of the direct current component Dinit (x) of the initial shading data generated by the smoothing unit 303. 11 is a waveform diagram of shading data generated by the correction data generation unit 310. That is, the corrected AC component Acor (x) shown in the diagram with the symbol (a) in FIG. 11 and the DC component Dinit (x) of the initial shading data shown in the diagram with the symbol (b) in FIG. Are added (formula 4 described above). As a result, as shown in FIG. 11C, the amplitude difference between the AC component Ainit (x) of the initial shading data and the AC component Apre (x) of the shading data at the time of document reading. It is possible to generate shading data SD (x) for correcting the above.

  Next, the shading correction unit 311 performs a shading correction process on the read data (input data) from the black correction unit 204 using the shading data SD (x) corrected by the correction data generation unit 310. The waveform of the solid line in FIG. 12 shows the waveform of the shading data at the time of document reading in which specific fluctuations occur at the timing corresponding to the location where dirt or the like is attached by reading the density reference member to which dirt or the like is attached. Yes. Further, the dotted waveform in FIG. 12 indicates the shading data SD (x) for correcting the amplitude difference between the alternating current component Ainit (x) of the initial shading data and the alternating current component Apre (x) of the original shading data. The waveform is shown.

  Even if there is a specific fluctuation in the shading data during document reading due to dirt attached to the density reference member, it is replaced with the initial shading data acquired when the density reference member is not dirty. Since shading correction is performed, it is possible to prevent inconvenience that vertical stripes occur in an image due to contamination of the density reference member.

  Further, when the original reading shading data is replaced with the initial shading data, the amplitude between the AC component Ainit (x) of the initial shading data and the AC component Apre (x) of the original reading shading data is matched. The initial shading data is corrected. For this reason, it is possible to perform accurate shading correction, and it is possible to provide a print image or image data in which the occurrence of periodic streaks caused by the difference in the amplitude of the AC component of the shading data is prevented.

  As can be seen from the above description, the MFP according to the first embodiment reads the original reading shading data, which is obtained immediately before the original is read, when the original reading shading data with the dirt is replaced with the initial shading data without the dirt. The initial shading data is corrected so that the ripple unevenness and the amplitude of the hourly shading data match. Then, shading correction is performed using the corrected initial shading data. Accordingly, it is possible to perform accurate shading correction that prevents the occurrence of periodic streaks caused by the difference in the amplitude of the AC component of the shading data.

(Second Embodiment)
Next, an MFP according to the second embodiment of the present invention will be described. In the MFP of the first embodiment described above, the maximum absolute value of each amplitude of the AC component Ainit (x) of the initial shading data and the AC component Apre (x) of the shading data during document reading is used. The correction magnification of the initial shading data was determined. In contrast, in the MFP according to the second embodiment, the correction factors on the positive side and the negative side of the AC component Ainit (x) of the initial shading data and the AC component Apre (x) of the shading data at the time of document reading are set. It is determined separately. Hereinafter, only the difference between the first embodiment and the second embodiment will be described, and a duplicate description will be omitted.

  FIG. 13 is a functional block diagram of the white correction unit 205 provided in the MFP according to the second embodiment. Of the functional blocks shown in FIG. 13, the functional blocks of the peak detector 321, peak detector 322, AC correction magnification calculator 323, and correction data generator 324 are the same as those in the first embodiment. It is a difference.

  As shown in the diagram with the symbol (a) in FIG. 14, the peak detection unit 321 includes the maximum value Ainit_max [] of the AC component Ainit (x) of the initial shading data and the minimum for each block described above. The value Ainit_min [] is detected. Further, as shown in the diagram with the symbol (a) in FIG. 14, the peak detection unit 322 has a maximum value Apre_max [] of the AC component Apre (x) of the document reading shading data for each of the blocks described above. , And the minimum value Apre_min [] is detected. In FIG. 14A, for example, Ainit_max [N] indicates the maximum value of the AC component Ainit (x) of the initial shading data of the Nth block.

  The AC correction magnification calculator 323 calculates the correction magnification α_p [] on the positive side for each block as shown in the drawing with the symbol (b) in FIG. To do. Further, the AC correction magnification calculator 323 calculates the negative correction magnification α_n [] for each block as shown in the diagram with the symbol (b) in FIG. To calculate.

  Positive side correction magnification α_p [] = (Apre_max []) / (Ainit_max []) (Expression 5)

  In Equation 5, when Ainit_max [] = 0, α_p [] = 0.

  Negative correction magnification α_n [] = (Apre_min []) / (Ainit_min []) (Expression 6)

  In Equation 6, when Ainit_min [] = 0, α_n [] = 0.

  Next, when Ainit (x) ≧ 0, the correction data generation unit 324 performs an arithmetic operation according to the following equation (7), whereby the AC component Ainit (x) of the initial shading data corresponding to the positive waveform for each block is calculated. ) Is multiplied by the correction magnification α_p []. Note that “when Ainit (x) ≧ 0” indicates a case where the value of the AC component Ainit (x) of the initial shading data is a positive value. As a result, the correction data generation unit 324 generates the AC component Acor (x) of the initial shading data with the positive side corrected, as shown in the drawing with the reference numeral (c) in FIG.

  Acor (x) = Ainit (x) × α_p [] (Expression 7)

  Similarly, when Ainit (x) <0, the correction data generation unit 324 performs an arithmetic operation according to the following equation (8), so that the AC component Ainit (x) of the initial shading data corresponding to the negative waveform for each block is calculated. ) Is multiplied by the correction magnification α_n []. Note that “when Ainit (x) <0” indicates that the value of the AC component Ainit (x) of the initial shading data is a negative value. As a result, the correction data generation unit 324 generates the AC component Acor (x) of the initial shading data with the negative side corrected, as shown in the diagram with the sign (c) in FIG.

  Acor (x) = Ainit (x) × α_n [] (Expression 8)

  Next, the correction data generation unit 324 performs the calculation of Equation 9 below, and corrects both the positive and negative sides of the initial shading data AC component Acor (x) and the initial shading data DC component Dinit ( x) is added. By this calculation, the correction data generation unit 324 generates shading data SD (x) corresponding to both the positive side correction and the negative side correction described above.

  SD (x) = Acor (x) + Dinit (x) (Expression 9)

  The shading correction unit 311 uses the shading data SD (x) generated by the correction data generation unit 324 and corresponding to the above-described correction on both the positive side and the negative side, and reads data (input) from the black correction unit 204. Data) is subjected to shading correction processing.

  As is apparent from the above description, the MFP according to the second embodiment individually sets the positive and negative correction magnifications. As a result, even if the waveform of the AC component Ainit (x) of the initial shading data is an asymmetric waveform on the positive side and the negative side, the value of the AC component Ainit (x) of the initial shading data is changed to the shading data at the time of document reading. Can be adjusted to the value of the AC component Apre (x). For this reason, the occurrence of periodic streaks caused by the difference in the amplitude of the AC component of the shading data can be prevented more strongly, and the same effect as that of the MFP of the first embodiment can be obtained.

(Third embodiment)
Next, an MFP according to the third embodiment of the present invention will be described. In the MFP of each of the embodiments described above, the maximum value or the minimum value of each amplitude of the AC component Ainit (x) of the initial shading data and the AC component Apre (x) of the shading data at the time of document reading is used. The correction factor of the initial shading data for each block was determined. On the other hand, in the MFP according to the third embodiment, the average value of the AC component Ainit (x) of the initial shading data and the average value of the AC component Apre (x) of the shading data at the time of document reading. Thus, the correction magnification of the AC component Ainit (x) of the initial shading data for each block is determined. Hereinafter, only the difference between each of the above-described embodiments and the third embodiment will be described, and redundant description will be omitted.

  FIG. 15 is a functional block diagram of the white correction unit 205 provided in the MFP according to the third embodiment. In the functional block of FIG. 15, the peak detection units 305, 308, 321, and 322 are not necessary, and the AC correction magnification calculation unit 331 uses the above average value to determine the AC component Ainit of the initial shading data for each block. The point of determining the correction magnification of (x) is a difference from the above-described embodiments.

  That is, in the case of the MFP according to the third embodiment, the AC correction magnification calculator 331 shown in FIG. 15 has the AC component Ainit () of the initial shading data as shown in FIG. Depending on the value of x), the following calculation is performed for each block described above. That is, when Ainit (x)> 0, the AC correction magnification calculation unit 331 performs the calculation of the following equation (10), so that the AC component Ainit (x) of the initial shading data and the AC component of the shading data during document reading “R_p (x)”, which is a ratio to Apre (x), is calculated.

  R_p (x) = (Apre (x)) / (Ainit (x)) (Expression 10)

  Note that the AC correction magnification calculation unit 331 increments the value of the variable Num_p [] indicating the number of pixels satisfying Ainit (x)> 0 in the block when the calculation of Equation 10 is performed. In other words, the AC correction magnification calculator 331 performs an operation for calculating “R_p (x)”, which is the above-mentioned ratio, in each block, as shown in the diagram with the symbol (a) in FIG. Perform every hour.

  When Ainit (x) <0, the AC correction magnification calculation unit 331 performs the calculation of Equation 11 below, so that the AC component Ainit (x) of the initial shading data and the AC component of the shading data at the time of document reading are calculated. “R_n (x)”, which is a ratio to Apre (x), is calculated.

  R_n (x) = (Apre (x)) / (Ainit (x)) (Expression 11)

  Note that the AC correction magnification calculator 331 increments the value of the variable Num_n [] indicating the number of pixels that satisfy Ainit (x) <0 in the block when the calculation of Equation 11 is performed. In other words, the AC correction magnification calculator 331 performs an operation for calculating “R_n (x)”, which is the above-mentioned ratio, in each block, as shown in the diagram with the symbol (a) in FIG. Perform every hour. In addition, the AC correction magnification calculator 331 does not perform calculation when Ainit (x) = 0.

  Next, the AC correction magnification calculator 331 calculates the correction magnification α_p [] on the positive side by performing the following equation 12 for each block. Further, the AC correction magnification calculator 331 calculates the negative correction magnification α_n [] by performing the following equation 13 for each block. The positive correction magnification α_p [] is an average value of a plurality of R_p (x) in each block. Similarly, the negative correction magnification α_n [] is also an average value of a plurality of R_n (x) in each block. In the following equations (12) and (13), “ΣR_p (x)” and “ΣR_n (x)” indicate the sum of R_p (x) and the sum of R_n (x) in each block, respectively. Yes.

  α_p [] = (ΣR_p (x)) / (Num_p []) (Expression 12)

  α_n [] = (ΣR_n (x)) / (Num_n []) (Expression 13)

  The correction data generation unit 324 uses the correction magnification α_p [], which is an average value on the positive side, as shown in the diagram with the symbol (b) in FIG. 16, and the AC component Ainit (x) of the initial shading data. Is corrected for each block. Further, as shown in the drawing with the sign (b) in FIG. 16, the correction data generation unit 324 uses the correction magnification α_n [] that is the negative average value to use the alternating current component Ainit ( The value of x) is corrected for each block.

  Here, FIG. 17 shows initial shading used for correction when the maximum value or minimum value of the AC component Apre (x) of the shading data at the time of document reading changes due to dirt or the like adhering to the density reference member. It shows how the value of the AC component Ainit (x) of the data becomes an inappropriate value. That is, the diagram with the symbol (a) in FIG. 17 shows a state in which a so-called spike noise-like abnormal value appears in the AC component Apre (x) of the shading data during document reading.

  In FIG. 17A, the two abnormal values appearing in the AC component Apre (x) of the N-block original reading shading data are equal to or less than the maximum value or less than the minimum value. . For this reason, as shown in the figure with the symbol (b) in FIG. 17, by calculating the positive and negative correction magnifications described above (see the above formulas 5 and 6), As shown in FIG. 17C, the AC component Ainit (x) of the initial shading data of the Nth block is corrected to a value suitable for shading correction with an accurate correction magnification.

  On the other hand, in the figure attached with the reference numeral (a) in FIG. 17, the two abnormal values appearing in the AC component Apre (x) of the shading data at the time of reading of the (N + 1) th document are the maximum or minimum values. The value is over. In this case, when the above-described correction magnifications on the positive side and the negative side (see the above formulas 5 and 6) shown in FIG. As shown in the figure with the reference numeral (c), the AC component Ainit (x) of the initial shading data of the (N + 1) th block is corrected with an inaccurate correction magnification due to the abnormal value described above, and is not suitable for shading correction. There is a risk of value.

  However, in the case of the MFP according to the third embodiment, as described with reference to FIG. 16, the AC component Ainit (x) of the initial shading data on the positive side and the AC component Apre (x) of the shading data at the time of document reading The AC component Ainit (x) of the initial shading data is corrected for each block using an average value of a plurality of R_p (x) as a correction magnification α_p []. In the case of the MFP of the third embodiment, a plurality of R_n (x), which is the ratio of the AC component Ainit (x) of the initial shading data on the negative side to the AC component Apre (x) of the shading data at the time of document reading. Is used as the correction magnification α_n [] to correct the AC component Ainit (x) of the initial shading data for each block.

  Thus, as shown in the diagram with the symbol (a) in FIG. 17, even when a singular maximum or minimum value appears in the block, the above-mentioned averaging results in a value close to normal. A correction magnification can be generated to enable accurate shading correction. For this reason, it is possible to increase the resistance of the density reference member to dirt, such as when dirt having a large density change adheres to the density reference member. Therefore, the occurrence of periodic streaks caused by the difference in the amplitude of the AC component of the shading data can be prevented more strongly, and the same effects as those of the MFPs of the above-described embodiments can be obtained.

(Fourth embodiment)
Next, an MFP according to the fourth embodiment of the present invention will be described. The MFP according to the fourth embodiment estimates the correction magnification of an abnormal block having a large number of pixels whose values vary specifically from the correction magnification of normal blocks before and after the abnormal block. Then, the AC component Ainit (x) of the initial shading data is corrected with the estimated correction magnification and used for shading correction, thereby enabling accurate shading correction. Hereinafter, only the difference between each of the above-described embodiments and the fourth embodiment will be described, and redundant description will be omitted.

  FIG. 18 is a functional block diagram of the white correction unit 205 provided in the MFP according to the fourth embodiment. In the functional block of FIG. 18, the abnormality detection unit 341, the AC correction magnification calculation unit 342, and the output selection unit 343 are different from the above-described embodiments.

  That is, in the case of the MFP according to the fourth embodiment, the abnormality detection unit 341 shown in FIG. 18 includes the original reading shading data stored in the first storage unit 301 and the initial storage stored in the second storage unit 302. Shading data is supplied. The anomaly detection unit 341 compares the shading data to detect a pixel in which a specific variation occurs in the shading data at the time of document reading due to contamination of the density reference member. As such an abnormality detection unit 341, for example, a technique disclosed in JP 2010-011297 A or the like can be used.

  A pixel in which a specific variation occurs is referred to as “abnormal pixel”. A block including abnormal pixels is referred to as an “abnormal block”. In contrast, a pixel that is not an abnormal pixel is referred to as a “normal pixel”. A block composed of only normal pixels is referred to as a “normal block”.

  In the example shown in FIG. 19A, the N block is an abnormal block, the N−1 block corresponding to the block before the N block, and the N + 1 block corresponding to the block after the N block. Are examples of normal blocks. In FIG. 19A, the dotted waveform is an example of the waveform of the AC component Ainit (x) of the initial shading data. In FIG. 19A, the solid line waveform is an example of the waveform of the AC component Apre (x) of the original reading shading data. First, the AC correction magnification calculator 342 will be described in the second or third embodiment with respect to all normal blocks and abnormal blocks as illustrated in the diagram with the symbol (a) in FIG. The positive correction magnification α_p [] and the negative correction magnification α_n [] are calculated by any of the methods described above.

  Next, the AC correction magnification calculator 342 performs linear interpolation using the correction magnifications of a pair of normal blocks sandwiching an abnormal block (or a block group composed of a plurality of abnormal blocks), thereby performing an abnormal block. Recalculate the correction magnification. That is, in the case of the example shown in FIG. 19B, the AC correction magnification calculator 342 performs linear interpolation using the correction magnification of the normal block close to the N block that is an abnormal block. Thus, an approximate value is calculated, and this approximate value is used as the correction magnification of the N block that is an abnormal block. In the example shown in FIG. 19B, the AC correction magnification calculator 342 corrects the N-1 and N + 1 blocks, which are normal blocks before and after the N block that is an abnormal block. An approximate value is calculated by performing linear interpolation using, and this approximate value is used as the correction magnification of the N block that is an abnormal block.

  Specifically, the AC correction magnification calculator 342 recalculates the correction magnification α_p [N] on the positive side of the N block, which is an abnormal block in this example, by using the linear interpolation equation shown below. The negative correction magnification α_n [N] is calculated and recalculated using the linear interpolation formula shown in the following equation (15).

  α_p [N] = α_p [N−1] + ((α_p [N + 1] −α_p [N−1]) × {N− (N−1)}) / {(N + 1) − (N−1)}.・ ・ (Formula 14)

  α_n [N] = α_n [N−1] + ((α_n [N + 1] −α_n [N−1]) × {N− (N−1)}) / {(N + 1) − (N−1)}. .. (Formula 15)

  In this example, the abnormal block correction magnification is estimated (recalculated) by linear interpolation using normal blocks before and after the abnormal block. However, for example, the above estimation may be performed using any one of the plurality of normal blocks before or after the abnormal block. Further, for example, the above estimation is performed using a normal block two blocks before the abnormal block, a normal block one block before the abnormal block, a normal block one block after the abnormal block, and a normal block two blocks after the abnormal block. As described above, the above estimation may be performed using two or more normal blocks.

  Next, the correction data generation unit 324 adds the correction factor α_p [N] on the positive side calculated by the AC correction magnification calculation unit 342 and the negative side to the AC component Ainit (x) of the initial shading data from the AC component extraction 304. Is multiplied by the correction magnification α_n [N]. As a result, as shown in the diagram with the reference numeral (c) in FIG. 19, the AC component Ainit (x) of the initial shading data of the N−1 block and the N + 1 block, which are normal blocks, is further optimized in shading. Corrected to data. Further, the AC component Ainit (x) of the initial shading data of the N block that is an abnormal block is also corrected to the optimum value of the shading data estimated from the preceding and succeeding normal blocks.

  Next, the correction data generation unit 324 multiplies the correction magnification by the AC component Ainit (x) of the initial shading data corrected and the DC component Dinit (x) of the initial shading data supplied from the smoothing unit 303. Are added to generate shading data for shading correction.

  Next, the output selection unit 343 is supplied with the original reading shading data read from the first storage unit 301 and the initial shading data corrected by the correction data generation unit 324. Further, the block selection signal from the abnormality detection unit 341 is supplied to the output selection unit 343. This block discrimination signal is a signal indicating that the block for which shading correction is to be performed by the shading correction unit 311 is a normal block or an abnormal block.

  When the block determination signal supplied from the abnormality detection unit 341 indicates a normal block, the output selection unit 343 selects the original reading shading data read from the first storage unit 301 and performs shading correction. To the unit 311. That is, when the block on which shading correction is to be performed by the shading correction unit 311 is a normal block, the original reading shading data read from the first storage unit 301 is supplied to the shading correction unit 311.

  In contrast, when the block determination signal supplied from the abnormality detection unit 341 indicates that the block is an abnormal block, the output selection unit 343 selects the initial shading data corrected by the correction data generation unit 324, and This is supplied to the shading correction unit 311. That is, when the block on which shading correction is to be performed by the shading correction unit 311 is an abnormal block, the approximate value (corrected initial shading data) estimated by the above-described linear interpolation is supplied to the shading correction unit 311. The

  The shading correction unit 311 performs shading correction of normal blocks using the original reading shading data. In addition, the shading correction unit 311 performs shading correction of the abnormal block using the approximate value (corrected initial shading data) estimated by the above-described linear interpolation.

  When dirt adheres to a wide range of the density reference member, the value of the abnormal pixel group having a specific value is dominant, and the correction magnification is calculated, which makes it difficult to calculate an accurate correction magnification. . However, in the case of the MFP according to the fourth embodiment, the shading correction data having an appropriate value is used by estimating the correction magnification of the abnormal block including the abnormal pixel using the values of the normal blocks around the abnormal block. In addition to performing more accurate shading correction, the same effects as those of the above-described embodiments can be obtained.

(Fifth embodiment)
Next, an MFP according to a fifth embodiment of the invention will be described. The MFP of each of the embodiments described above corrects the AC component Ainit (x) of the initial shading data. On the other hand, the MFP of the fifth embodiment corrects the DC component Dinit (x) as well as the AC component Ainit (x) of the initial shading data. Hereinafter, only the differences between the above-described embodiments and the fifth embodiment will be described, and redundant description will be omitted.

  FIG. 20 is a functional block diagram of the white correction unit 205 provided in the MFP according to the fifth embodiment. In the functional block of FIG. 20, the abnormality detection unit 341, the DC correction magnification calculation unit 351, the DC component correction unit 352, the AC component correction unit 353, and the output selection unit 354 are different from the above-described embodiments. It has become. The abnormality detection unit 341 also serves as an abnormal pixel detection unit.

  That is, in each figure attached with the reference numerals (a), (b), and (c) in FIG. 21, the waveform of the quadratic curve indicates the waveform of the DC component Dpre (x) of the shading data at the time of document reading. A gentle curved waveform (substantially linear waveform) indicates the waveform of the direct current component Dinit (x) of the initial shading data. In the case of the MFP of the fifth embodiment, the direct current component Dinit (x) of the initial shading data, as shown in the respective drawings with reference numerals (a), (b), and (c) in FIG. The DC component Dpre (x) of the original reading shading data is supplied from the smoothing unit 303 and the smoothing unit 306 to the DC correction magnification calculation unit 351, respectively.

  In the case of the MFP according to the fifth embodiment, the abnormality detection unit 341 compares the DC component of the original reading shading data with the DC component of the initial shading data, so that it is unique due to contamination of the density reference member. A pixel in which a general fluctuation occurs is detected. Specifically, the abnormality detection unit 341 includes the direct current component Dpre (x) of the original reading shading data and the direct current component Dinit (x) of the initial shading data illustrated in FIG. ). Thereby, the abnormality detection unit 341 detects the Tth pixel Dpre (T) and the Uth pixel Dpre (U) as abnormal pixels. This abnormal pixel detection output (abnormal pixel detection signal) is supplied to the DC correction magnification calculator 351 and the output selector 354.

  The DC correction magnification calculator 351 calculates the DC component correction magnification β (x) at the position x on the main scanning axis by performing the following equation (16). The DC correction magnification calculator 351 calculates a DC component correction magnification β (x) for all pixels on the main scanning axis.

  β (x) = Dpre (x) / Dinit (x) (Expression 16)

  Next, the DC correction magnification calculation unit 351 calculates an approximate value by linear interpolation using the correction magnification β (x) of two normal pixels sandwiching the abnormal pixel detected by the abnormality detection unit 341, and calculates this approximate value. It is assumed that the abnormal pixel correction magnification β (x). That is, the DC correction magnification calculator 351 recalculates using the normal pixels before and after the abnormal pixel correction magnification β (x).

  Specifically, in the figure attached with the reference numeral (a) in FIG. 21, there is a portion where a large drop has occurred in the output level of the DC component Dpre (x) of the shading data at the time of document reading. The S-th pixel Dpre (S) that is the starting point of the drop in the output level is a normal pixel. Further, the Vth pixel Dpre (V) serving as the end point of the drop in the output level is a normal pixel. In contrast, T-th pixel Dpre (T) and U-th pixel Dpre (S) and V-th pixel Dpre (V) of DC component Dpre (x) of the shading data at the time of document reading are present. The second pixel Dpre (U) is an abnormal pixel. That is, the Tth pixel Dpre (T) and the Uth pixel Dpre (U) are abnormal pixels that cause a drop in the output level of the DC component Dpre (x) of the shading data at the time of document reading.

  The DC correction magnification calculator 351 uses the DC component correction magnifications β (S) and β (V) of the S-th and V-th normal pixels, and approximates by linear interpolation shown in the following equations 17 and 18. Calculate the value. By this calculation, the DC correction magnification calculator 351 recalculates the DC component correction magnifications β (T) and β (U) corresponding to the T-th and U-th abnormal pixels which are abnormal pixels in this example. (presume.

  β (T) = β (S) + ({β (V) −β (S)} × (TS)) / (V−S) (Expression 17)

  β (U) = β (S) + ({β (V) −β (S)} × (U−S)) / (V−S) (Expression 18)

  Next, the DC component correction unit 352 multiplies the correction magnification β (x) calculated by the DC correction magnification calculation unit 351 and the DC component Dinit (x) of the initial shading data supplied from the smoothing unit 303. The multiplication processing result is taken as the corrected DC component. That is, the DC component correction unit 352 calculates the corrected DC component Dcor (x) by performing the calculation of the following equation (19).

  Dcor (x) = β (x) × Dinit (x) (Equation 19)

  As a result, as shown in the diagram with the reference numeral (b) in FIG. 21, even when the output level drops in the direct current component Dinit (x) of the initial shading data, the reference numeral (c) in FIG. As shown in the figure attached, the DC component Dinit (x) in which the drop in the output level is corrected can be generated. That is, as shown in FIG. 21B, the correction magnification β (T) for the Tth abnormal pixel recalculated (estimated) from the correction magnification of the normal pixel and the Uth abnormal pixel. The DC component Dpre (T) and the DC component Dpre (U) corresponding to the Tth and Uth abnormal pixels are corrected with the correction magnification β (U). As a result, as shown in FIG. 21C, a drop in the output level of the DC component Dpre (T) and the DC component Dpre (U) corresponding to the Tth and Uth abnormal pixels. Can be corrected.

  On the other hand, the AC component correction unit 353 generates the AC component Acor (x) obtained by correcting the initial shading data in the same manner as the correction data generation unit 324 described above. That is, the AC component correction unit 353 performs the calculation shown in the following equation 20 when Ainit (x) ≧ 0. As a result, the AC component Acor (x) corrected by multiplying the AC component Ainit (x) of the initial shading data by the AC positive correction factor α_p [] calculated by the AC correction factor calculation 342 is obtained. Generate.

  Acor (x) = Ainit (x) × α_p [] (Expression 20)

  The AC component correction unit 353 performs the calculation shown in the following Equation 21 when Ainit (x) <0. As a result, the AC component Acor (x) corrected by multiplying the AC negative component correction factor α_n [] calculated by the AC correction magnification calculation 342 with the AC component Ainit (x) of the initial shading data is corrected. Generate.

  Acor (x) = Ainit (x) × α_n [] (Expression 21)

  Next, an abnormal pixel detection signal is supplied to the output selection unit 354 while an abnormal pixel whose DC component has an abnormal value is detected by the abnormality detection unit 341. When the abnormal pixel detection signal is not supplied, the output selection unit 354, as shown in the following formula 22, the direct current component Dpre (x) of the original reading shading data and the direct current component Pre ( Shading data SD (x) is generated by adding x). That is, in this case, the shading data SD (x) means that the original reading shading data is used as it is. When the abnormal pixel detection signal is not supplied, the output selection unit 354 supplies the original reading shading data to the shading correction unit 311 as shading data SD (x).

  SD (x) = Apre (x) + Dpre (x) (Expression 22)

  On the other hand, when an abnormal pixel detection signal is supplied from the abnormality detection unit 341, the output selection unit 354 is corrected with the corrected AC component Acor (x) as shown in Equation 23 below. The DC component Dcor (x) is added, and the added output is selected as shading data SD (x) for abnormal pixels and supplied to the shading correction unit 311.

  SD (x) = Acor (x) + Dcor (x) (Expression 23)

  The shading correction unit 311 performs shading correction of normal pixels using the document reading shading data. In addition, the shading correction unit 311 performs shading correction of abnormal pixels using the shading data in which the DC component corrected to the approximate value by the linear interpolation described above is corrected.

  As is clear from the above description, the MFP of the fifth embodiment approximates the correction magnification of the DC component of the abnormal pixel by linear interpolation from the correction magnification of the DC component of the surrounding normal pixels. Then, the DC component of the abnormal pixel is overwritten (recalculated) by the product of the DC component correction magnification and the DC component of the initial shading data. Thereby, even when the DC component changes between the original reading shading data and the initial shading data, the DC component value of the abnormal pixel can be corrected to a value suitable for shading correction. For this reason, more accurate shading correction can be performed, and the same effects as those of the above-described embodiments can be obtained.

  Each of the above-described embodiments has been described by way of example, and is not intended to limit the scope of the present invention. Each of these novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. Each embodiment and modifications of each embodiment are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Light guide 2 Light source part 3 Line sensor 3a Pixel 4 Rod lens array 4a Rod lens 11 Controller 146 2nd reading roller (density reference member)
205 white correction unit 301 first storage unit 302 second storage unit 303 smoothing unit 304 AC component extraction unit 305 peak detection unit 306 smoothing unit 307 AC component extraction unit 308 peak detection unit 309 AC correction magnification calculation unit 310 correction data generation 311 Shading correction unit 321 Peak detection unit 322 Peak detection unit 323 AC correction magnification calculation unit 324 Correction data generation unit 331 AC correction magnification calculation unit 341 Abnormality detection unit 342 AC correction magnification calculation unit 343 Output selection unit 351 DC correction magnification calculation unit 352 DC component correction unit 353 AC component correction unit 354 Output selection unit

JP 2010-011297 A

Claims (10)

A first DC component extraction unit that extracts first DC component data from initial data that is shading data serving as a reference read from the density reference member;
A first AC component extraction unit that extracts first AC component data that is a difference between the extracted first DC component data and the initial data;
A second DC component extraction unit that extracts second DC component data from current data that is shading data read from the density reference member later in time than the initial data;
A second AC component extraction unit that extracts second AC component data that is a difference between the extracted second DC component data and the initial data;
A first peak detector that detects a first maximum value that is a maximum absolute value of the first AC component data;
A second peak detector that detects a second maximum value that is a maximum absolute value of the second AC component data;
A correction magnification calculator that calculates an AC correction magnification of shading data by dividing the second maximum value by the first maximum value;
A correction data generation unit that generates corrected shading data by adding the first DC component data to the first AC component data multiplied by the AC correction magnification;
A shading correction device, comprising: a shading correction unit that performs a shading correction process on input data using the corrected shading data. The first peak detection unit detects the maximum value on the positive side of the first AC component data as the first maximum value,
The shading correction apparatus according to claim 1, wherein the second peak detection unit detects a maximum value on the positive side of the second AC component data as the second maximum value. The first peak detector detects a positive maximum value and a negative minimum value of the first AC component data;
The second peak detector detects a maximum value on the positive side and a minimum value on the negative side of the second AC component data;
The correction magnification calculation unit divides the maximum value on the positive side detected by the second peak detection unit by the maximum value on the positive side detected by the first peak detection unit, While calculating the AC correction magnification of the positive-side shading data, the negative-side minimum value detected by the second peak detection unit is used as the negative-side minimum value detected by the first peak detection unit. To calculate the AC correction magnification of the negative-side shading data.
The correction data generation unit performs correction by adding the first DC component data to the first AC component data obtained by multiplying the positive AC correction magnification and the negative AC correction magnification, respectively. The shading correction apparatus according to claim 1, wherein the shading data is generated. The first peak detection unit, the second peak detection unit, the correction magnification calculation unit, and the correction data generation unit are block units corresponding to a predetermined number of pixels of a reading module that reads the density reference member The detection of the maximum value, the detection of the minimum value, the calculation of the AC correction magnification, or the generation of the corrected shading data is performed in any one of claims 1 to 3. The shading correction device according to item. A first DC component extraction unit that extracts first DC component data from initial data that is shading data serving as a reference read from the density reference member;
A first AC component extraction unit that extracts first AC component data that is a difference between the extracted first DC component data and the initial data;
A second DC component extraction unit that extracts second DC component data from current data that is shading data read from the density reference member later in time than the initial data;
A second AC component extraction unit that extracts second AC component data that is a difference between the extracted second DC component data and the initial data;
A correction magnification calculation unit that calculates a ratio between the first AC component data and the second AC component data every predetermined time and calculates an average value of the plurality of ratios as an AC correction magnification of shading data; ,
A correction data generation unit that generates corrected shading data by adding the first DC component data to the first AC component data multiplied by the AC correction magnification;
A shading correction device, comprising: a shading correction unit that performs a shading correction process on input data using the corrected shading data. The correction magnification calculation unit divides the first AC component data and the second AC component data into a positive side and a negative side, and the ratio and an AC correction magnification that is an average value of the ratio, respectively. Perform the calculation
The correction data generation unit multiplies the positive first AC component data by the positive AC correction magnification, and multiplies the negative first AC component data by the negative AC correction magnification. The shading correction apparatus according to claim 5, wherein the shading correction apparatus performs processing. The correction magnification calculator and the correction data generator are
The ratio is calculated, the AC correction magnification is calculated, and the corrected shading data is generated in units of blocks corresponding to a predetermined number of pixels of a reading module that reads the density reference member. The shading correction apparatus according to claim 5 or 6. By comparing the initial data and the current data, an abnormality detection unit that detects the current data indicating an abnormal value;
An output selection unit that selects one of the current data and the corrected shading data from the correction data generation unit and supplies the selected shading data to the shading correction unit;
The correction magnification calculator, when the current data indicating an abnormal value is detected, AC correction of the first AC component data corresponding to the current data of a normal value close to the current data indicating an abnormal value Using the magnification, an AC correction magnification that is an approximate value is calculated, and the AC correction magnification of the calculated approximate value is output as an AC correction magnification of the first AC component data corresponding to the current data indicating the abnormal value. And
The correction data generation unit corrects the first AC component data corresponding to the current data indicating an abnormal value with the AC correction magnification calculated as the approximate value,
The output selection unit selects the corrected shading data from the correction data generation unit while the current data indicating an abnormal value is detected by the abnormality detection unit, and the abnormality detection unit selects an abnormal value. The shading correction apparatus according to any one of claims 1 to 7, wherein the current data is selected when the current data indicating is not detected. An abnormal pixel detection unit that detects an abnormal pixel indicating an abnormal value of the DC component among the pixels of the reading module that reads the density reference member by comparing the DC component of the initial data and the DC component of the current data. When,
By dividing the second DC component data by the first DC component data, the DC correction magnification of the DC component data is calculated, and the normal pixel of the normal value DC component close to the abnormal pixel is supported. A DC correction magnification calculator that calculates a DC correction magnification that is an approximate value using the DC correction magnification that is output, and outputs the calculated DC correction magnification of the approximate value as a DC correction magnification corresponding to the abnormal pixel;
A DC component correction unit that multiplies the DC correction magnification and performs level correction of the first DC component data,
The output selecting unit generates the corrected shading data by adding the level-corrected first DC component data to the first AC component data, and the abnormal pixel detecting unit generates the abnormal The corrected shading data is supplied to the shading correction unit while a pixel is detected, and the current data is supplied to the shading correction unit while the abnormal pixel is not detected by the abnormal pixel detection unit. 9. The shading correction apparatus according to claim 8, wherein An image processing apparatus comprising the shading correction apparatus according to any one of claims 1 to 9.

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