JP2015039146A - Image reading device, image forming apparatus, and image reading method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce deterioration of a read image even if a temperature change occurs.SOLUTION: An image reading device comprises: a first generation part for generating reference shading data indicating a reference read level for each pixel on the basis of a plurality of pixel data items on which photoelectric transduction is performed by a photoelectric transducer when reflection light of light with which an irradiation part irradiates a white reference member is image-formed on the photoelectric transducer by each lens; a second generation part for generating correction shading data by correcting the reference read level for each pixel of interest of the reference shading data to a read level at a position shifted in an array direction of pixels on the basis of reference read levels of the pixel of interest and of peripheral pixels around the pixel of interest; and a calculation part which performs calculation for correcting, on the basis of the correction shading data, the plurality of pixel data items on which the photoelectric transduction is performed by the photoelectric transducer when reflection light or transmission light of light with which the irradiation part irradiates a read object is image-formed on the photoelectric transducer by each of a plurality of lenses.

Description

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

  Conventionally, in an image reading apparatus using a contact image sensor (CIS), LEDs are arranged on both ends of a light guide extending in the main scanning direction, and uniform light is transmitted to the original via the light guide. A configuration for irradiating is known. In addition, when the reflected light from the original is imaged on the photoelectric conversion element using an equal-magnification imaging lens (rod lens array), the vertical stripes appear on the read image due to the lens pitch changing due to the influence of heat. There was a problem that would occur.

  Therefore, it is necessary to correct shading data. For example, Patent Literature 1 and Patent Literature 2 disclose techniques for correcting shading data.

  However, the techniques described in Patent Document 1 and Patent Document 2 have a problem in that vertical stripes or unevenness of a read image that occurs with a temperature change cannot be reduced.

  The present invention has been made in view of the above, and an object thereof is to provide an image reading apparatus, an image forming apparatus, and an image reading method capable of reducing deterioration of a read image even when a temperature change occurs. .

  In order to solve the above-described problems and achieve the object, the present invention is arranged by photoelectrically converting, for each pixel, an irradiation unit that irradiates light and reflected light or transmitted light of the light irradiated by the irradiation unit. A photoelectric conversion element for converting into a plurality of pixel data indicating a plurality of pixels, a plurality of arranged lenses for imaging reflected light or transmitted light of light irradiated by the irradiation unit on the photoelectric conversion element, and the irradiation unit When each of the lenses forms an image of reflected light irradiating the white reference member on the photoelectric conversion element, a reference reading level for each pixel is obtained based on a plurality of pixel data photoelectrically converted by the photoelectric conversion element. A reference generation level for each target pixel of the reference shading data, based on a first generation unit that generates reference shading data to be displayed, and a reference read level of the target pixel and peripheral pixels of the target pixel; A second generation unit that generates correction shading data by correcting each of the reading levels at positions shifted in the arrangement direction, and reflected light or transmitted light of light that the irradiation unit irradiates the reading target with, the plurality of lenses An arithmetic unit that performs an operation of correcting a plurality of pixel data photoelectrically converted by the photoelectric conversion element based on the correction shading data when each image is formed on the photoelectric conversion element.

  According to the present invention, it is possible to reduce the deterioration of a read image even if a temperature change occurs.

FIG. 1 is a diagram illustrating a configuration of an image reading apparatus according to an embodiment. FIG. 2 is an enlarged view showing a configuration around the reading unit of the image reading apparatus. FIG. 3 is a diagram showing an outline of the CIS module and its surroundings. FIG. 4 is an enlarged view showing a part of the rod lens array and the photoelectric conversion element in an enlarged manner. FIG. 5 is a diagram illustrating a reading level when the CIS module reads a reference white plate. FIG. 6 is a block diagram illustrating a configuration of the photoelectric conversion element and its periphery in the image reading apparatus. FIG. 7 is a diagram illustrating shading correction performed by the correction unit. FIG. 8 is a diagram illustrating a state where the distribution of the reading level is shifted in the main scanning direction. FIG. 9 is a block diagram illustrating a detailed configuration of the correction unit. FIG. 10 is a diagram illustrating the relationship between the pixel of interest and its surrounding pixels in the cubic function convolution method performed by the second generation unit. FIG. 11 is a chart illustrating calculation parameters. FIG. 12 is a diagram illustrating a state in which the second generation unit divides a pixel column into a plurality of areas. FIG. 13 is a chart illustrating the correction amount switched by the second generation unit. FIG. 14 is a diagram illustrating an outline of an image forming apparatus including the image reading apparatus.

  Exemplary embodiments of an image reading apparatus will be described below in detail with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a configuration of an image reading apparatus 1 according to the embodiment. As shown in FIG. 1, the image reading apparatus 1 includes a reading unit main body (flat bed scanner) 10 and an automatic document feeder (ADF) 12. The image reading apparatus 1 includes a reading unit of an equal magnification optical system in each of the flat bed scanner 10 and the ADF 12, and can read both sides of a document by a single document conveyance in a small space. FIG. 2 is an enlarged view showing a configuration around the reading unit of the image reading apparatus 1.

  The reading unit main body 10 includes a contact glass 100, a reference white plate (white reference member) 102, a reading window 104, and a CIS module 2a. The reading unit main body 10 reads the surface (front) of the document conveyed by the ADF 12 through the reading window 104 by the CIS module 2a. The reference white plate 102 is used to generate reference shading data indicating a reference reading level for each pixel.

  The ADF 12 is arranged on the upper part of the reading unit main body 10 and automatically feeds and conveys a document. A document bundle to be read is set on the top of the ADF 12 with the front surface facing upward. The reverse roller 120 is driven to rotate in the reverse direction to the paper feed by the forward rotation of the paper feed motor, separates the top document and the document under it, and feeds only the top document.

  The original separated into one sheet by the action of the paper feed belt and the reverse roller 120 is further fed by the paper feed belt and abuts against the pull-out roller 122 that is stopped. The pull-out roller 122 has a skew correction function, and conveys the original whose skew has been corrected after separation to the intermediate roller 124.

  When the leading edge of the document is detected by a reading entrance sensor (not shown), the document transportation speed and the scanning transportation speed are set to the same speed before the leading edge of the document enters the nip between the pair of upper and lower rollers of the scanning entrance roller 126. 126, the reading exit roller 128 and the CIS exit roller 132 are driven.

  In response to the reading start signal, the image reading apparatus 1 conveys the original document whose registration has been stopped to the reading position. In the case of single-sided original reading, the original is discharged onto a paper discharge tray 145. In the case of double-sided original reading, the back side of the original is read by the CIS module 2b. Here, the reading roller 130 also serves as a reference white portion (white reference member) for acquiring shading data while suppressing the floating of the document in the reading portion on the back side. The ADF 12 may be provided with a fixed plate-like white reference member instead of the reading roller 130.

  Next, the CIS module 2a will be described in detail. The CIS module 2b is configured similarly to the CIS module 2a. FIG. 3 is a diagram showing an outline of the CIS module 2a and its surroundings. The CIS module 2 a includes, for example, an irradiation unit 20 that extends in one direction and emits light, a rod lens array 22, a photoelectric conversion element 24, and a sensor substrate 26.

  The irradiation unit 20 is provided at each end of a light guide 202 in which a light source unit 200 such as an LED extends in the main scanning direction. The light guide 202, the rod lens array 22, the photoelectric conversion element 24, and the sensor substrate 26 are arranged substantially in parallel.

  As shown in FIG. 4, the rod lens array 22 includes a plurality of rod lenses (equal magnification imaging lenses) 220 having substantially the same diameter arranged in the main scanning direction. Note that “substantially the same” means that the difference is equal to or less than a predetermined threshold. On the sensor substrate 26, for example, photoelectric conversion elements 24 for about 7200 pixels are arranged in the main scanning direction. The rod lens array 22 forms an image on the photoelectric conversion element 24 of the light irradiated by the irradiation unit 20 and the reflected light (or transmitted light) from the white reference member. The photoelectric conversion element 24 converts the amount of light imaged by the rod lens array 22 into a plurality of pixel data (electrical signals) indicating the values of the plurality of pixels 240 arranged in the main scanning direction.

  The rod lens 220 easily collects light near the center and has a high output, but the output decreases at the end. Therefore, the rod lens array 22 periodically generates a high output position and a low output position in the period in which the rod lenses 220 are arranged.

  FIG. 5 is a diagram showing a reading level when the CIS module 2a reads the reference white plate 102. As shown in FIG. As shown in FIG. 4, the rod lens array 22 forms an image at the same magnification on a plurality of pixels 240 of the photoelectric conversion element 24 by one rod lens 220. Therefore, as shown in FIG. 5, when the CIS module 2a reads a reading target (reference white plate 102 or document) having a uniform density in the main scanning direction by irradiating light with a uniform distribution, the rod The amount of light transmitted to the pixel 240 located near the center of the lens 220 is large, and the amount of light transmitted to the pixel 240 located near the end of the rod lens 220 is small. That is, the distribution in the main scanning direction of the pixel value due to the light applied to the photoelectric conversion element 24 is a distribution that matches the arrangement interval of the rod lenses 220.

  FIG. 6 is a block diagram illustrating the configuration of the photoelectric conversion element 24 and its periphery in the image reading apparatus 1. In the image reading apparatus 1, the irradiating unit 20 emits light to the original, and the reflected light from the original is imaged on the photoelectric conversion element 24 via the rod lens array 22, and the photoelectric conversion element 24 performs photoelectric conversion. Convert to analog electrical signal (image data).

  The photoelectric conversion element 24 outputs the photoelectrically converted image data to an AFE (AFE: Analog Front End) 33. The AFE 33 includes an amplification unit 330 and an A / D conversion unit 332. The gain of the amplifying unit 330 can be set in a programmable manner to absorb variations in sensitivity of the photoelectric conversion element 24 and the like. The amplifying unit 330 adjusts the gain when the power is turned on or each time image data is read so that a constant digital output is obtained when the reference white plate 102 is read, and the set value is determined. The AFE 33 amplifies the input analog electric signal with a predetermined gain, and then converts it into digital data.

  Note that the photoelectric conversion element 24 and the AFE 33 operate under the control of the timing control unit 32. The timing control unit 32 operates in synchronization with the reference clock output from the oscillator 30 under the control of the CPU 31. In addition, the photoelectric conversion element 24, the AFE 33, the timing control unit 32, and the like may be configured on the same chip or may be configured individually.

  The image data converted into digital data by the AFE 33 is input to the processing unit 4 at the subsequent stage. The processing unit 4 includes a correction unit 40 and an image processing unit 42. The correction unit 40 performs shading correction using the shading data (detailed with reference to FIGS. 7 and 9). The image processing unit 42 performs predetermined image processing.

  FIG. 7 is a diagram illustrating the shading correction performed by the correction unit 40. As shown in FIG. 7, before the shading correction, there is a reading level distribution described with reference to FIG. The correction unit 40 generates image data having a uniform reading level with respect to uniform reflected light by performing shading correction using shading data generated by reading the reference white plate 102.

  However, in the reference shading data generated by reading the reference white plate 102, when a temperature change occurs in the CIS module 2a, the distribution of the reading level is shifted in the main scanning direction as shown in FIG.

  The fluctuation amount of the distribution of the reading level due to the temperature change is slight, and if shading data is generated every time one original is read, the distribution in the main scanning direction is corrected by shading correction. The image reading apparatus 1 performs an intermittent shading operation for regenerating shading data every time a plurality of originals are read in order to increase reading productivity.

  FIG. 9 is a block diagram illustrating a detailed configuration of the correction unit 40. The correction unit 40 includes a first generation unit 400, a first storage unit 402, a second generation unit 404, a second storage unit 406, and a calculation unit 408.

  When the rod lens array 22 forms an image on the photoelectric conversion element 24 of the reflected light of the light emitted from the irradiation unit 20 to the reference white plate 102, the first generation unit 400 performs a plurality of pixel data photoelectrically converted by the photoelectric conversion element 24. By calculating the average value, reference shading data indicating the reference reading level for each pixel is generated and stored in the first storage unit 402.

  The second generation unit 404 reads the reference shading data stored in the first storage unit 402, generates corrected shading data described later using, for example, a cubic function convolution method, and stores the corrected shading data in the second storage unit 406. . Here, the 2nd production | generation part 404 produces | generates correction | amendment shading data by correct | amending reference | standard shading data according to the temperature change of the CIS module 2a.

  The calculation unit 408 includes a plurality of pieces of pixel data photoelectrically converted by the photoelectric conversion element 24 when the rod lens array 22 forms an image on the photoelectric conversion element 24 of reflected light or transmitted light of the light irradiated to the reading target by the irradiation unit 20. Is corrected using correction shading data.

  Next, the operation of the second generation unit 404 will be described in detail. A streak in the read image is generated by a slight change in the light amount distribution in the main scanning direction due to temperature characteristics of the rod lens array 22 (expansion due to temperature rise, etc.). This change in the light amount distribution is such that the distribution is shifted in the main scanning direction as shown in FIG.

  The second generation unit 404 performs a process of correcting the reference shading data stored in the first storage unit 402 according to the shift amount shown in FIG. Here, the second generation unit 404 performs an interpolation operation using a cubic function convolution method.

  FIG. 10 is a diagram illustrating a relationship between a target pixel (target pixel) and its peripheral pixels in the cubic function convolution method performed by the second generation unit 404. The cubic function convolution method performed by the second generation unit 404 uses the n-th pixel in the main scanning direction as the pixel of interest, and the value of the position where the pixel of interest is shifted by the shift amount d using the data of the four pixels before and after the pixel ( Pixel data).

  The second generation unit 404 selects and calculates one of two types of calculations: a calculation for delaying the pixel of interest in the main scanning direction and a calculation for advancing. In the present embodiment, the shift amount d is a value obtained by dividing one pixel interval into 32 parts.

  As shown in FIG. 10A, when the target pixel is delayed in the main scanning direction, the value of the position where the value of the nth pixel is delayed as the shift amount d is calculated by the following equation 1.

X ′ (n) = W1 × X (n−1) + W2 × X (n)
+ W3 × X (n + 1) + W4 × X (n + 2) (1)

  Here, X ′ (n) is a value at a position where the nth pixel of interest is moved by the shift amount d. X (n) is the value of the nth pixel of interest. W1, W2, W3, and W4 are calculation parameters predetermined according to the shift amount d. FIG. 11 is a chart illustrating calculation parameters (correction parameters). Note that the same values are used for the calculation parameters shown in FIG. 11 regardless of whether the calculation parameters are advanced or delayed.

  As shown in FIG. 10B, when the target pixel is advanced in the main scanning direction, the value of the position where the value of the nth pixel is advanced as the shift amount (1-d) is calculated by the following equation 2. .

X ′ (n) = W1 × X (n−2) + W2 × X (n−1)
+ W3 × X (n) + W4 × X (n + 1) (2)

  Here, X ′ (n) is a value at a position where the n-th pixel of interest is moved by the shift amount (1-d). X (n) is the value of the nth pixel of interest. W1, W2, W3, and W4 are calculation parameters predetermined according to the shift amount d. As described above, the same values are used for the calculation parameters shown in FIG. 11 regardless of whether the calculation parameters are advanced or delayed.

  Further, since the CIS module 2a has a large temperature change in a region close to a portion where the light source unit 200 such as an LED is disposed, the shift amount of pixel data due to the temperature change of the rod lens array 22 is the pixel amount in the main scanning direction. It changes according to the position.

  Therefore, the second generation unit 404 divides the column of pixels 240 indicated by the plurality of pixel data into a plurality of areas arranged in the arrangement direction of the pixels 240, and corrects them using calculation parameters predetermined for each divided area. Generate shading data. Specifically, the second generation unit 404 sets the shift amount d to be corrected according to the shift amount of the pixel data depending on the temperature change of the rod lens array 22.

  FIG. 12 is a diagram illustrating a state in which the second generation unit 404 divides the column of pixels 240 into a plurality of areas (area_1 to area_L).

  Moreover, the 2nd production | generation part 404 switches each correction amount d set for every divided area according to a temperature change for every predetermined time. FIG. 13 is a chart illustrating the correction amount d that the second generation unit 404 switches.

  The shift amount d for each area and the change over time are determined by the configuration of the CIS module 2a and the characteristics of the rod lens array 22 used. Therefore, each correction amount d (d1_t1 to dL_tK) shown in FIG. 13 is determined in advance by measurement.

  For example, in the CIS module 2a in which the light source unit 200 such as an LED is disposed at both ends of the light guide 202, the temperature change at both sides is large and the temperature change at the central part is small.

  In addition, for example, the temperature change is targeted on both sides of the center of the light guide 202, the shift amount on the leading side in the main scanning direction is shifted to the leading side, and the shift amount on the trailing end is shifted to the trailing end. In the case of the characteristics of the CIS module, the shading data is corrected by an operation that advances toward the head side, and the shading data is corrected by an operation that delays the rear end side. In contrast to this characteristic, when the characteristic of the light guide 202 is opposite, the shading data is corrected by a calculation that delays the leading side, and the shading data is corrected by a calculation that advances the trailing end.

  Further, in the CIS module in which the light source unit 200 is arranged on one side, the temperature change on the side on which the light source unit 200 is arranged is large, so that the shading data is corrected by an advance calculation according to the characteristics of the rod lens array 22. The shading data is corrected using any one of the operation to be performed or the operation to correct the shading data by a delay operation.

  Next, the image forming apparatus 5 including the image reading apparatus 1 will be described. FIG. 14 is a diagram illustrating an outline of the image forming apparatus 5 including the image reading apparatus 1. The image forming apparatus 5 is, for example, a copying machine or an MFP (Multifunction Peripheral) having the image reading apparatus 1 and the image forming unit 6.

  The image reading apparatus 1 includes, for example, a photoelectric conversion element including a timing control unit 32, an irradiation unit 20, and the like. The irradiation unit 20 irradiates the original with light. The photoelectric conversion element outputs image data to the image forming unit 6 after performing photoelectric conversion and AD conversion.

  The image forming unit 6 includes a processing unit 60 and a printer engine 62, and the processing unit 60 and the printer engine 62 are connected via an interface (I / F) 64.

  The processing unit 60 includes an image processing unit 602 and a CPU 604. The CPU 604 controls each part of the image forming apparatus 5 such as a photoelectric conversion element.

  The image processing unit 602 performs image processing using the image data output from the image reading apparatus 1 and outputs the image data and the like to the printer engine 62. The printer engine 62 performs printing using the received image data.

  As described above, the image reading apparatus 1 and the image forming apparatus 5 correct the reference reading level for each target pixel of the reference shading data to the reading level at the position shifted in the pixel arrangement direction, thereby correcting the shading data. Therefore, it is possible to reduce deterioration of a read image even if a temperature change occurs.

  In the above embodiment, the image forming apparatus 5 of the present invention has been described as an example in which the image forming apparatus 5 is applied to a multi-function machine having at least two functions among a copy function, a printer function, a scanner function, and a facsimile function. Any image forming apparatus including an image reading apparatus such as a scanner apparatus or a facsimile apparatus can be applied.

DESCRIPTION OF SYMBOLS 1 Image reading apparatus 2a, 2b CIS module 5 Image forming apparatus 6 Image forming part 10 Reading part main body 12 ADF
20 Irradiation unit 22 Rod lens array 24 Photoelectric conversion element 26 Sensor substrate 32 Timing control unit 33 AFE
40 correction unit 200 light source unit 202 light guide 220 rod lens 240 pixel 400 first generation unit 402 first storage unit 404 second generation unit 406 second storage unit 408 calculation unit

JP 2008-125006 A JP 2006-13852 A

Claims (6)

An irradiating unit for irradiating light;
A photoelectric conversion element that photoelectrically converts reflected light or transmitted light of the light emitted by the irradiation unit for each pixel and converts the data into a plurality of pixel data indicating a plurality of arranged pixels;
A plurality of arranged lenses that image reflected light or transmitted light of the light irradiated by the irradiation unit on the photoelectric conversion element;
A reference for each pixel based on a plurality of pixel data photoelectrically converted by the photoelectric conversion element when each of the lenses forms an image of reflected light of the light irradiated to the white reference member by the irradiation unit. A first generator that generates reference shading data indicating a reading level;
By correcting the reference reading level for each target pixel of the reference shading data based on the reference reading level of the target pixel and the surrounding pixels of the target pixel to the reading level at the position shifted in the pixel arrangement direction, respectively. A second generator for generating corrected shading data;
When each of the plurality of lenses forms an image of reflected light or transmitted light of the light irradiated on the reading target by the irradiation unit on the photoelectric conversion element, the correction is performed on the plurality of pixel data photoelectrically converted by the photoelectric conversion element. An image reading apparatus, comprising: an arithmetic unit that performs an arithmetic operation based on shading data. The second generator is
A column of pixels indicated by the plurality of pixel data is divided into a plurality of areas arranged in a pixel arrangement direction, and the correction shading data is generated based on a calculation parameter predetermined for each area. The image reading apparatus according to claim 1. The second generator is
The image reading apparatus according to claim 1, wherein the correction shading data is generated based on a calculation parameter set for each predetermined time. The second generator is
The image reading apparatus according to claim 1, wherein the correction shading data is generated using a cubic function convolution method. An image reading apparatus according to any one of claims 1 to 4,
An image forming apparatus comprising: an image forming unit that forms an image read by the image reading apparatus. Photoelectrically converting the reflected light or transmitted light of the light emitted by the irradiation unit for each pixel, and converting the converted light into a plurality of pixel data indicating a plurality of arranged pixels;
When a plurality of lenses in which reflected light of the light irradiated to the white reference member is imaged on a photoelectric conversion element by the irradiation unit, each pixel is based on a plurality of pixel data photoelectrically converted by the photoelectric conversion element Generating reference shading data indicating a reference reading level of;
By correcting the reference reading level for each target pixel of the reference shading data based on the reference reading level of the target pixel and the surrounding pixels of the target pixel to the reading level at the position shifted in the pixel arrangement direction, respectively. Generating corrected shading data;
When each of the plurality of lenses forms an image of reflected light or transmitted light of the light irradiated on the reading target by the irradiation unit on the photoelectric conversion element, the correction is performed on the plurality of pixel data photoelectrically converted by the photoelectric conversion element. A step of performing a correction based on the shading data;
An image reading method comprising:

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