JP6579017B2 - Image reading device - Google Patents

Description

  The present invention relates to an image reading apparatus.

  An image reading apparatus (such as an image scanner) that reads an image of a document by a reading unit including a light receiving element and a lens is known. In such an image reading apparatus, the image quality may deteriorate due to the positional relationship between the light receiving element and the lens being shifted due to thermal expansion or the like. Various techniques for suppressing the deterioration of the image quality have been proposed (see, for example, Patent Document 1).

  In addition, various methods are known in image reading apparatuses that correct luminance unevenness due to lens characteristics so that an image with uniform brightness is obtained. One such method is shading correction. In the shading correction, the luminance of the image read from the document is corrected based on the conversion characteristics for all the pixels derived in advance when the image reading apparatus is shipped.

JP 2011-188270 A

  An example will be described in which an image read in a state where the positional relationship between the light receiving element and the lens is shifted is corrected by shading correction. In this case, there is a possibility that the image quality of the corrected image is deteriorated due to an imbalance of the conversion characteristics. In addition, since the shift in the positional relationship between the light receiving element and the lens does not always occur uniformly, a measure for uniformly correcting the conversion characteristics for all the pixels has a limited effect.

  An object of the present invention is to provide an image reading apparatus capable of suppressing a deterioration in image quality in accordance with a positional relationship between a light receiving element and a lens.

An image reading apparatus according to the present invention includes a plurality of blocks arranged in a crossing direction that intersects a document conveyance direction, and a plurality of boundaries that are arranged between adjacent blocks and have a reflectance that is discontinuous in the crossing direction. A reading unit including a plurality of light receiving elements arranged in the intersecting direction and capable of receiving light transmitted through the lens and outputting a signal corresponding to the light intensity, and toward the chart member First acquisition means for acquiring a chart image indicating the chart member based on a signal output when reflected light of the light irradiated in this manner is received by the plurality of light receiving elements, and a reference of the chart image Based on the reference information stored in the storage unit that stores the reference information based on the reference image, the chart image acquired by the first acquisition unit, and the storage unit, A calculating means for calculating a deviation amount between the chart image and the reference image at a position corresponding to at least one of the plurality of boundary portions, and a first of the deviation amounts calculated by the calculating means. Based on a specifying means for specifying an amount larger than a threshold value and a signal output when light intensity of reflected light of the light irradiated toward the original is received by the plurality of light receiving elements, the original A second acquisition unit that acquires a document image indicating the first image, and, of the document image acquired by the second acquisition unit, only the corresponding portion corresponding to the shift amount specified by the specifying unit is acquired by the first acquisition unit. Correction means for correcting based on the corresponding portion of the chart image acquired by the means.

  The image reading device corrects the corresponding portion corresponding to any amount larger than the first threshold in the document image based on the corresponding portion of the chart image. For this reason, the image reading apparatus can correct limitedly a portion of the document image having a relatively large deviation amount. The image reading apparatus corrects the corresponding portion of the original image based on the corresponding portion of the chart image. For this reason, the image reading apparatus can perform appropriate correction for a portion having a relatively large deviation amount. Therefore, the image reading apparatus has a higher image quality of the original image when the positional relationship between the light guiding element and the lens that guides light to the light receiving element is deviated than when all pixels of the original image are corrected uniformly. Can be maintained well.

  In the present invention, when the amount of deviation calculated by the calculation means includes any amount that is larger than a second threshold smaller than the first threshold and smaller than the first threshold, the reading unit Changing means for changing the reading speed of the document may be provided. In this case, the image reading apparatus can suppress a deviation in the positional relationship between the lens and the light receiving element by lowering the reading speed to reduce the heat generation amount.

  In the present invention, the changing unit may lower a frequency when signals are periodically detected from the plurality of light receiving elements in order to acquire the original image by the second acquiring unit. In this case, since the image reading apparatus can reduce the amount of heat generated by lowering the frequency, the positional relationship between the lens and the light receiving element can be suppressed. In addition, the changing unit may reduce the conveyance speed of the document. In this case, since the image reading apparatus can reduce the amount of heat generated by lowering the conveyance speed, it is possible to suppress the positional relationship between the lens and the light receiving element. The changing unit may reduce the amount of light emitted toward the chart member and the document. In this case, the image reading apparatus can reduce the amount of heat generated by reducing the amount of light to be irradiated, so that the positional relationship between the lens and the light receiving element can be suppressed.

  In the present invention, the calculation means calculates a deviation amount between the chart image and the reference image at a part of the boundary portions adjacent to each of both end portions in the intersecting direction among the plurality of boundary portions. May be. In this case, the image reading apparatus can detect and correct the overall shift in the positional relationship between the lens and the light receiving element.

  In the present invention, the correction means may determine the original image based on the ratio between the density of the corresponding portion of the chart image acquired by the first acquisition means and the density of the corresponding portion of the reference image. Of these, the corresponding portion may be corrected. In this case, the image reading apparatus can perform correction according to the shift amount when the positional relationship between the lens and the light receiving element shifts with respect to the state where the reference image is acquired based on the ratio.

  In the present invention, when the deviation amount calculated by the calculation means includes any amount that is larger than a second threshold smaller than the first threshold and smaller than the first threshold, the user is notified. You may provide an alerting | reporting means. In this case, the image reading apparatus can notify the user that the positional relationship between the lens and the light receiving element may be shifted.

2 is a diagram illustrating an internal configuration of the image reading apparatus 1. FIG. FIG. 3 is an enlarged view of a configuration of a reading unit 24 of the image reading device 1. It is a figure which shows the chart member. FIG. 3 is an enlarged view of a reading unit 24. 2 is a block diagram illustrating an electrical configuration of the image reading apparatus 1. FIG. It is a flowchart of a main process. It is a flowchart of the main process, and is a continuation of FIG. It is a flowchart of a deviation calculation process. It is a figure for demonstrating the calculation method of deviation | shift amount. It is a figure which shows the range of the pixel number g.

<Mechanical Configuration of Image Reading Apparatus 1>
As shown in FIG. 1, the image reading apparatus 1 includes a paper feed tray 2, a main body 3, and a paper discharge tray 4. An operation unit 5 and a display unit 6 are disposed on the upper surface of the main body unit 3. The operation unit 5 receives an operation command or the like from the user. The operation unit 5 includes a power switch, various setting buttons (a selection button for selecting one of three color modes and a single color mono mode, an operation button for setting resolution), and the like. The display unit 6 is an LCD that can display the state of the image reading apparatus 1.

  The main body 3 has a conveyance path 20 inside. The document GS placed on the paper feed tray 2 is transported in the transport direction FD along the transport path 20 and is discharged to the paper discharge tray 4. The paper feed roller 21, the separation pad 22, the document sensor 27, the pair of upstream transport rollers 23, the reading unit 24, the platen glass 25, and the pair of downstream transport rollers 26 are arranged along the transport path 20.

  The paper feed roller 21 cooperates with the separation pad 22 to feed a plurality of originals GS placed on the paper feed tray 2 one by one. The upstream transport roller 23 and the downstream transport roller 26 are each driven by a transport motor MT (see FIG. 5). The platen glass 25 is light transmissive. The platen glass 25 is disposed along the conveyance path 20 below the conveyance path 20. The transport rollers 23 and 26 transport the document GS so that the document GS fed from the paper feed roller 21 passes over the platen glass 25.

  The document GS is placed on the paper feed tray 2 with the reading surface facing the placement surface of the paper feed tray 2. The reading unit 24 is disposed below the conveyance path 20. The reading unit 24 reads an image on the reading surface of the document GS that passes through the platen glass 25. The document sensor 27 is disposed on the paper feed tray 2. The document sensor 27 is turned on when the document GS is placed on the paper feed tray 2 and turned off when the document GS is not placed on the paper feed tray 2.

<Detailed Configuration of Reading Unit 24 and Chart Member 34>
As shown in FIG. 2, the reading unit 24 includes a light source 30, a light receiving unit 31, and an optical member 32. The light source 30 includes light emitting diodes of three colors of red, green, and blue. When the emitted light from the light source 30 is reflected by the document GS or the like, the optical member 32 guides the reflected light to the light receiving unit 31. When the color mode is selected, the three-color light emitting diodes are sequentially turned on to read an image of the original GS for one line. On the other hand, when the mono mode is selected, an image of the document GS for one line is read by turning on a specific one of the three colors, for example, a green light emitting diode.

  The chart member 34 is disposed at a position facing the reading unit 24 via the conveyance path 20. Of the chart member 34, the color of at least the portion exposed to the transport path 20 is gray. Note that gray has a lower reflectance than white, which is the background color of the document GS. Further, the gray density is close to the black density, and is a density at which the reflection density is lower than the reflection density of white even when the light source 30 is turned on with the maximum light amount. The reason why the chart member 34 is gray is to suppress the occurrence of show-through when the white document GS is read. When the document GS is not present on the transport path 20, the light emitted from the light source 30 is reflected by the chart member 34, and the reflected light is received by the light receiving unit 31 via the optical member 32.

  As shown in FIG. 3, the chart 34 </ b> A is drawn on a portion of the chart member 34 exposed to the conveyance path 20, that is, a portion where the emitted light from the light source 30 is reflected. The chart 34A has a shape in which a plurality of blocks 341 surrounded by a square frame line are arranged in the main scanning direction MD orthogonal to the transport direction FD. The plurality of blocks 341 are adjacent to each other. In the case of FIG. 3, ten blocks 341 are arranged. The length of each block 341 in the main scanning direction MD is denoted as “K”. The frame lines on both sides in the main scanning direction MD of each block 341 overlap with the frame lines of other adjacent blocks 341. A frame line that overlaps between the blocks 341 adjacent to each other in the main scanning direction MD is arranged between the blocks 341 and forms a boundary. Hereinafter, the frame lines on both sides of each block 341 in the main scanning direction MD are referred to as “boundary portions 342”. Note that the color of the frame lines forming the plurality of blocks 341 is black, and has a lower reflectance than the gray color of the chart member 34. For this reason, the reflectance in the main scanning direction MD in the portion of the chart member 34 where the chart 34A is drawn becomes discontinuous at the boundary portion 342.

  As shown in FIG. 4, the optical member 32 includes a plurality of rod lenses 32 </ b> A arranged in the main scanning direction MD orthogonal to the transport direction FD. The light receiving unit 31 includes a plurality of light receiving elements 31A arranged in the main scanning direction MD. Hereinafter, the number indicating the arrangement order of the plurality of light receiving elements 31A is referred to as “pixel number”. Each light receiving element 31A can receive light transmitted through the rod lens 32A and output a signal corresponding to the light intensity. In the present embodiment, the light receiving unit 31 is, for example, a contact image sensor (CIS).

  The diameter of each rod lens 32A, in other words, the length of each rod lens 32A in the main scanning direction MD is expressed as “z”. The length of each light receiving element 31A in the main scanning direction MD is denoted as “r”. In this case, a relationship of “K> z> r” is established between the length “K” of the main scanning direction MD of each block 341 of the chart 34A (see FIG. 3).

<Electrical Configuration of Image Reading Apparatus 1>
As shown in FIG. 5, the image reading apparatus 1 includes a CPU 40, a ROM 41, a RAM 42, a flash memory 43, a device control unit 44, an analog front end (hereinafter referred to as AFE) 45, an image processing unit 46, and a drive circuit 47. As a main component. These components are connected to the operation unit 5, the display unit 6, and the document sensor 27 via the bus 48.

  The ROM 41 stores a program for executing various operations of the image reading apparatus 1 such as main processing (see FIGS. 6 to 8) described later. The CPU 40 controls each unit according to the program read from the ROM 41. The flash memory 43 is a readable / writable non-volatile memory, and stores various data generated by the control processing of the CPU 40. The RAM 42 temporarily stores the calculation result generated by the control process of the CPU 40.

  The device control unit 44 is connected to the reading unit 24, and transmits a signal for controlling turning on and off of the light source 30 and a signal for controlling a current value flowing through the light source 30 to the reading unit 24 based on a command from the CPU 40. To do. Further, the device control unit 44 transmits the output of each light receiving element 31A to the AFE 45 as an analog signal indicating each pixel in synchronization with the clock signal CLK based on a command from the CPU 40.

  The AFE 45 is connected to the reading unit 24 and converts an analog signal transmitted from the reading unit 24 into digital data based on a command from the CPU 40. The AFE 45 has a predetermined input range and resolution, and converts it into, for example, 10-bit (0 to 1023) gradation data. The digital data converted by the AFE 45 is output to the image processing unit 46.

  Hereinafter, a series of operations until digital data is generated in response to the reading unit 24 being controlled by the device control unit 44 is referred to as a “reading operation”. Digital data generated by the reading operation is referred to as “image data”. Each pixel of the image based on the image data corresponds to each light receiving element 31A. For this reason, the pixel number corresponding to each light receiving element 31A is assigned as the pixel number of each pixel of the image.

  The image data is output from the AFE 45 to the image processing unit 46. The image processing unit 46 includes an ASIC that is a dedicated IC for image processing, and performs shading correction on image data generated by the reading operation. The CPU 40 can set parameters necessary for shading correction (hereinafter referred to as “shading parameters”) for the image processing unit 46. The image processing unit 46 performs shading correction on the image data based on the shading parameters set by the CPU 40. The image data subjected to the shading correction is stored in the RAM 42 via the bus 48.

  The drive circuit 47 is connected to the transport motor MT and drives the transport motor MT based on a drive command transmitted from the CPU 40. The drive circuit 47 rotates the transport motor MT according to the rotation amount and the rotation direction commanded by the drive command. When the transport motor MT rotates by a predetermined amount, the transport rollers 23 and 26 rotate by a predetermined angle, and the document GS is transported by a predetermined distance on the transport path 20.

<Correction of document image (first method)>
In the image reading apparatus 1, the mismatch (shading) due to the peripheral light reduction of the rod lens 32 </ b> A is corrected by shading correction by the image processing unit 46. By shading correction, the brightness of the pixels corresponding to the periphery of each rod lens 32A can be suppressed from unevenness in brightness compared to the brightness of the pixels corresponding to the center, and the entire image can be made uniform. .

  An example of a general shading correction (first method) performed in the image reading apparatus 1 will be described as an example, and an outline method will be described. The CPU 40 executes the reading operation with the white reference original in the conveyance path 20 when the image reading apparatus 1 is shipped. Light is emitted from the light source 30 toward the white reference document. Light is reflected on the reference document, and the reflected light is received by the light receiving element 31A. As a result, the reading unit 24 reads the reference document for one line. As described above, the image data of the white reference image for one line generated at the time of shipment is referred to as “reference image (white) data”. The generated reference image (white) data is stored in the flash memory 43. An image based on the generated reference image (white) data is referred to as “reference image (white)”.

  When the shipped image reading apparatus 1 is used by the user, the CPU 40 sets the reference image (white) data stored in the flash memory 43 in the image processing unit 46 as a shading parameter. The CPU 40 starts the reading operation of the document GS placed on the paper feed tray 2. The CPU 40 performs a reading operation in a state where the document GS is on the conveyance path 20. Light is emitted from the light source 30 toward the document GS. The reflected light reflected from the document GS is received by the light receiving element 31A. As a result, the reading unit 24 reads an image of the document GS for one line. Image data of an image on the reading surface of the document GS (hereinafter referred to as “document image data”) is generated for one line. Hereinafter, an image based on the generated document image data is referred to as a “document image”. The generated document image data is output to the image processing unit 46.

  The image processing unit 46 uses reference image (white) data in which the density (hereinafter simply referred to as “density”) of each color (R, G, B) of each pixel of one line of a document image is set as a shading parameter. Divide by the density of each pixel of the reference image (white) based on. As a result, the image processing unit 46 performs shading correction of the document image data.

  The above processing is executed every time the image on the reading surface of the document GS is repeatedly read line by line. As a result, document image data in which the brightness of the entire document image is corrected is generated. The corrected document image data is stored in the RAM 42.

<Correction of document image (second method)>
The rod lens 32 </ b> A may expand due to heat generated during the operation of the image reading apparatus 1. When the rod lens 32A is expanded, the position of the peripheral dimming also changes. For this reason, as in the first method, when shading correction is performed using the reference image (white) data as it is as a shading parameter, the conversion characteristics are unbalanced, thereby making the brightness of the entire original image uniform. There is a possibility that it cannot be corrected.

  The outline method will be described by taking as an example a case where shading correction (second method) for suppressing the influence of the thermal expansion of the rod lens 32A is executed in the image reading apparatus 1. The CPU 40 executes the reading operation in a state where the document is not on the conveyance path 20 when the image reading apparatus 1 is shipped. Light is emitted from the light source 30 toward the portion of the chart member 34 where the chart 34A is drawn. Light is reflected by the chart member 34, and the reflected light is received by the light receiving element 31A. As a result, the reading unit 24 reads the portion of the chart member 34 where the chart 34A is drawn for one line. As described above, the image data of the chart 34A for one line generated at the time of shipment is referred to as “reference image (gray) data”. The generated reference image (gray) data is stored in the flash memory 43 together with the reference image (white) data described in the (first method). Hereinafter, an image based on the reference image (gray) data is referred to as “reference image (gray)”.

  When the shipped image reading apparatus 1 is used by the user, the CPU 40 starts the reading operation of the document GS placed on the paper feed tray 2, that is, in a state where there is no document GS in the transport path 20. The reading operation is executed. Light is emitted from the light source 30 toward the portion of the chart member 34 where the chart 34A is drawn. Light is reflected by the chart member 34, and the reflected light is received by the light receiving element 31A. As a result, the reading unit 24 reads the portion of the chart member 34 where the chart 34A is drawn for one line. As described above, the image data of the chart 34A for one line generated immediately before reading the document GS is referred to as “chart image data”. Hereinafter, an image based on the chart image data is referred to as a “chart image”.

  The CPU 40 calculates the ratio between the density of each pixel of the reference image (gray) and the density of each pixel of the chart image for each common pixel number based on the reference image (gray) data and the chart image data. The CPU 40 corrects the reference image (white) data by multiplying the calculated ratio for each pixel by the density of each pixel of the reference image (white). The CPU 40 sets the corrected reference image (white) data in the image processing unit 46 as a shading parameter.

  The CPU 40 starts the reading operation of the document GS placed on the paper feed tray 2. The CPU 40 performs a reading operation with a document on the conveyance path 20. Light is emitted from the light source 30 toward the document GS. The reflected light reflected from the document GS is received by the light receiving element 31A. As a result, the reading unit 24 reads the image of the original for one line. One line of original image data is generated. The generated document image data is output to the image processing unit 46.

  The image processing unit 46 divides the density of each pixel of the original image for one line by the density of each pixel of the reference image (white) based on the corrected reference image (white) data set as the shading parameter. As a result, the image processing unit 46 performs shading correction of the document image data.

  The above processing is executed every time the image on the reading surface of the document GS is repeatedly read line by line. Thus, the brightness of the entire original image is corrected while suppressing the influence of the thermal expansion of the rod lens 32A.

<Correction of Document Image (Correction Method in the Present Embodiment)>
After the image reading apparatus 1 is shipped, paper dust may adhere to the chart member 34 in accordance with the use of the image reading apparatus 1 by the user. Since the chart member 34 is gray, the attached paper dust is easily noticeable. For this reason, when chart image data is generated in a state where paper dust adheres to the chart member 34, and the density of each pixel of the reference image (white) data is corrected based on the chart image data, the shading correction (second) is performed. There is a possibility that uneven brightness and noise may occur in the original image obtained as a result of the method (ii). On the other hand, the image reading apparatus 1 appropriately implements the shading correction even when paper dust adheres while suppressing the influence of the thermal expansion of the rod lens 32A by executing the following main processing.

  A main process executed by the CPU 40 of the image reading apparatus 1 will be described with reference to FIGS. The main process is started when the CPU 40 executes a program stored in the ROM 41 when the original sensor 27 detects that an original is placed on the paper feed tray 2.

  The CPU 40 executes an initial process (not shown) when the image reading apparatus 1 is shipped. In the initial processing, a reading operation is performed in a state where the white reference document is in the conveyance path 20, and the reference document is read by one line by the reading unit 24. As a result, reference image (white) data is generated. Further, the reading operation is performed in a state where the document is not on the conveyance path 20, and the chart member 34 is read by one line by the reading unit 24. Thereby, reference image (gray) data is generated. The CPU 40 stores the generated reference image (white) data and reference image (gray) data in the flash memory 43. The image reading apparatus 1 is shipped with the reference image (white) data and the reference image (gray) data stored in the flash memory 43, and is used by the user. Therefore, the main process is started in a state where the reference image (white) data and the reference image (gray) data are stored in the flash memory 43.

  Hereinafter, the density of each of the plurality of pixels of the reference image (white) is expressed as W (1), W (2)... W (N) (N is the number of pixels). These are collectively referred to as “W”. The respective densities of the plurality of pixels of the reference image (gray) are denoted as G0 (1), G0 (2)... G0 (N). These are collectively referred to as “G0”.

  As shown in FIG. 6, the CPU 40 adjusts the light amount of the light source 30 to the default light amount L0 and starts light irradiation (S11). The CPU 40 adjusts the frequency of the clock signal CLK output to the reading unit 24 to the default frequency F0 and starts outputting the clock signal CLK (S11).

  The CPU 40 executes a reading operation before the conveyance of the document GS placed on the paper feed tray 2 is started, that is, without the document GS on the conveyance path 20. Light is emitted from the light source 30 toward the portion of the chart member 34 where the chart 34A is drawn. Light is reflected by the chart member 34, and the reflected light is received by the light receiving element 31A. As a result, the reading unit 24 reads the portion of the chart member 34 where the chart 34A is drawn for one line. Chart image data immediately before reading the document is generated (S13). The CPU 40 stores the generated chart image data in the RAM 42 (S13). Hereinafter, the respective densities of the plurality of pixels of the chart image are denoted as G1 (1), G1 (2)... G1 (N). These are collectively referred to as “G1”.

  The CPU 40 reads the reference image (white) data and the reference image (gray) data stored in the flash memory 43 by the initial processing (S15). The CPU 40 executes a deviation calculation process (see FIG. 8) (S17).

  The deviation calculation process will be described with reference to FIG. The CPU 40 reads the chart image data generated by the process of S13 from the RAM 42. Based on the chart image data, the CPU 40 identifies the position (pixel number) of the pixel corresponding to the boundary portion 342 (see FIG. 9) of the chart 34A as follows (S71).

  The chart image data is generated by receiving, by the plurality of light receiving elements 31A, the light reflected at the portion 311 crossing the plurality of boundary portions 342 in the main scanning direction MD in the chart 34A shown in FIG. The density of each pixel in the chart image is based on the light intensity of the light received by the light receiving element 31A corresponding to the position of each pixel. The light intensity of the light reflected by the plurality of boundary portions 342 in the chart 34A is smaller than the light intensity of the light reflected by the portion excluding the plurality of boundary portions 342 in the chart 34A. For this reason, as shown by a graph 34B, the relationship between the pixel number of the light receiving element 31A (horizontal axis of the graph) and the light intensity of the reflected light received by each light receiving element 31A (vertical axis of the graph) is shown. In such a case, the light intensity decreases at a position corresponding to the boundary portion 342. In the chart image, a pixel corresponding to the light receiving element 31A having a smaller light intensity of the received light is expressed with a higher (darker) density. For this reason, the density of the pixel corresponding to the boundary portion 342 in the chart image is higher than the density of the other pixels.

  Based on the chart image data generated by the process of S13 (see FIG. 6), the CPU 40 charts the pixel number of the light receiving element 31A in which the light intensity of the received light is smaller than a predetermined threshold B (see FIG. 9). It is specified as a position corresponding to the boundary portion 342 in 34A (hereinafter referred to as “boundary position”). This means that the pixel number of the pixel having a density larger than the predetermined value in the chart image is specified as the boundary position.

  For example, in FIG. 9, since eleven boundary portions 342 are included in the portion 311, eleven boundary positions are specified by the processing of S71. There may be a case where a plurality of light receiving elements 31A having a light intensity smaller than the threshold value B are continuous and a plurality of pixel numbers are continuous. In this case, the pixel number having the smallest light intensity of the light received by the corresponding light receiving element 31A among the plurality of continuous pixel numbers is specified as the boundary position. Hereinafter, the boundary positions specified based on the chart image data are Pc (1), Pc (2)... Pc (n) (n is the number of boundary portions 342. In FIG. 9, n is “11”. ”.) These are collectively referred to as “Pc”.

  As shown in FIG. 8, the CPU 40 uses the same method as the process of S71 based on the reference image (gray) data read from the flash memory 43 by the process of S15 (see FIG. 6), and the boundary portion 342 of the chart 34A. A boundary position corresponding to is specified (S73). Hereinafter, the boundary positions specified based on the reference image (gray) data are denoted as Pb (1), Pb (2)... Pb (n)). These are collectively referred to as “Pb”.

  The CPU 40 determines each of the boundary positions Pb (1), Pb (2)... Specified by the process of S73 and the boundary positions Pc (1), Pc (2). The difference is calculated for each boundary portion 342 as a deviation amount (S75). Hereinafter, the calculated shift amounts are expressed as ΔP (1), ΔP (2)... ΔP (n).

  Here, when the image reading apparatus 1 is used by a user, a case where the rod lens 32A of the optical member 32 expands due to heat and the position of the peripheral dimming changes will be described as an example. In this case, the boundary position Pc (see S71) specified based on the chart image data is shifted in the main scanning direction MD with respect to the boundary position Pb (see S73) specified based on the basic image (gray) data. . The larger the deviation, the larger the deviation amount ΔP calculated in S75. For example, as shown in FIG. 9, when the relationship between the pixel number based on the basic image (gray) data and the light intensity is indicated by a graph 34C, the rod lens 32A disposed in the region 343 is expanded by heat. Take an example. In this case, the deviation amounts ΔP (2), ΔP (3), ΔP (4), and ΔP (5) included in this range are increased.

  As shown in FIG. 8, the CPU 40 selects one of the calculated deviation amounts ΔP. The CPU 40 determines whether or not the selected deviation amount ΔP is larger than a predetermined threshold Th2 (S77). When it is determined that the deviation amount ΔP is equal to or less than the threshold Th2 (S77: NO), the CPU 40 advances the process to S79. The CPU 40 sets the level of the deviation amount ΔP to “0” (S79). The CPU 40 advances the process to S87.

  If it is determined that the deviation amount ΔP is larger than the threshold Th2 (S77: YES), the CPU 40 advances the process to S81. The CPU 40 determines whether the shift amount ΔP is larger than the threshold value Th1 (S81). The threshold value Th1 is a predetermined value larger than the threshold value Th2 (Th1> Th2). When it is determined that the deviation amount ΔP is equal to or less than the threshold Th1 (S81: NO), the CPU 40 advances the process to S85. The CPU 40 sets the level of the deviation amount ΔP to “1” (S85). The CPU 40 advances the process to S87. On the other hand, when it is determined that the deviation amount ΔP is larger than the threshold Th1 (S81: YES), the CPU 40 sets the level of the deviation amount ΔP to “2” (S83). The CPU 40 advances the process to S87.

  The CPU 40 determines whether or not the above level has been set for all the deviation amounts ΔP calculated in S75 (S87). If it is determined that any amount for which no level has been set remains (S87: NO), the CPU 40 returns the process to S77. The CPU 40 selects any amount ΔP for which no level is set, and repeats the processing of S77 to S85. When it is determined that the level has been set for all of the calculated deviation amounts ΔP (S87: YES), the CPU 40 ends the deviation calculation process and returns the process to the main process (see FIG. 6).

  As shown in FIG. 6, after the deviation calculation process (S17) is completed, the CPU 40 determines whether there is one or more deviation amounts ΔP having a level set to “1” (S19). If the CPU 40 determines that there is no deviation amount ΔP for which the level is set to “1” (S19: NO), the process proceeds to S29.

  When the CPU 40 determines that there is one or more deviation amount ΔP with the level set to “1” (S19: YES), the reading is performed at the time of reading a document GS described later (S51, S53, see FIG. 7). In order to change the reading speed of the document GS by the unit 24, the reading conditions are changed as follows (S21, S23).

  The CPU 40 changes the setting for reducing the reading speed (S21). Specifically, it is as follows. The CPU 40 changes the frequency of the clock signal CLK to a frequency F1 (F0> F1) lower than the default frequency F0. Each light receiving element 31A sequentially outputs an analog signal corresponding to the light intensity of the received reflected light in the cycle of the clock signal CLK. That is, the clock signal CLK corresponds to the reading speed by the plurality of light receiving elements 31A. For this reason, the reading speed is reduced by changing the frequency of the clock signal CLK from F0 to F1. Further, the CPU 40 sets the rotation speed of the transport rollers 23 and 26 to a rotation speed V1 (V0> V1) smaller than the default rotation speed V0. As a result, the transport speed when the document GS is transported by the transport rollers 23 and 26 is decreased, so that the reading speed is decreased. In this state, the transport rollers 23 and 26 have not yet rotated.

  Next, the CPU 40 changes the light amount of the light source 30 to a light amount L1 (L0> L1) smaller than the default light amount L0 (S23). Note that in order to receive the reflected light by the light receiving element 31A, a light amount of a predetermined level or more is required. Here, according to the process of S21 described above, the conveyance speed of the document GS is reduced. The light receiving time during which the light receiving element 31A receives the reflected light becomes longer as the conveyance speed of the document GS is reduced. For this reason, even when the light quantity of the light source 30 is changed to the light quantity L1, the light receiving element 31A can receive the reflected light. That is, the reading speed is substantially reduced by changing the light amount from L0 to L1.

  The CPU 40 starts the reading operation in a state where the light amount of the light source 30 is changed to L1 and the frequency of the clock signal CLK is changed to F1. Light is emitted from the light source 30 toward the portion of the chart member 34 where the chart 34A is drawn. Light is reflected by the chart member 34, and the reflected light is received by the light receiving element 31A. As a result, the reading unit 24 reads the portion of the chart member 34 on which the chart 34A is drawn for one line. Chart image data is generated under the conditions after the light amount and the clock signal CLK are changed (S27). CPU40 memorize | stores the produced | generated chart image data in RAM42 instead of the chart image data memorize | stored in RAM42 by the process of S13 (S27). That is, the CPU 40 is in a state (default state) of the light amount L0 and the frequency F0 of the clock signal CLK by the chart image data generated in the state of the light amount L1 of the light source 30 after the change and the frequency F1 of the clock signal CLK. Update the generated chart image data. The CPU 40 advances the process to S29.

  The CPU 40 selects the boundary positions Pb specified by the process of S73 (see FIG. 8) one by one in ascending order (S29). The CPU 40 determines whether “2” is set as the level of the deviation amount ΔP calculated by the process of S75 (see FIG. 7) based on the selected boundary position Pb (S31). When “0” or “1” is set as the level of the deviation amount ΔP (S31: NO), the CPU 40 advances the process to S37. If it is determined that “2” is set as the level of the deviation amount ΔP calculated based on the selected boundary position Pb (S31: YES), the CPU 40 advances the process to S33.

The CPU 40 extracts the density G1 (g) of the pixel having the pixel number g from the chart image based on the chart image data stored in the RAM 42 by the process of S13 or S27. The CPU 40 extracts the pixel G0 (g) having the pixel number g from the reference image (gray) based on the reference image (gray) data read from the flash memory 43 by the process of S15. The pixel number g is a pixel number that satisfies the following conditional expression (1).
(Pb−X) <g ≦ (Pb + X) (1)

  Here, X is the length K in the main scanning direction MD (see FIG. 3) between the adjacent boundary portions 342 of the chart 34A, and the length r in the main scanning direction MD of one light receiving element 31A (see FIG. 4). ) Is equal to “(K / r) / 2” obtained by dividing the value “K / r” divided by 2. That is, X indicates a value that is half of the number of light receiving elements 31 </ b> A disposed between adjacent boundary portions 342. The pixel number g satisfying the conditional expression (1) has moved to one side in the main scanning direction MD with respect to the boundary position Pb by a pixel (X pixel) corresponding to a half length in the main scanning direction MD of the block 341. Pixels included between the position and the position moved by the other side in the main scanning direction MD with respect to the boundary position Pb, the pixel (X pixel) corresponding to the half length of the block 341 in the main scanning direction MD Indicates the number.

  For example, in FIG. 9, a case where “2” is set as the level of each of the deviation amounts ΔP (3) and ΔP (4) is taken as an example. In this case, as shown in FIG. 10, the pixel number g corresponding to Pb (3) is the boundary position Pb (3) from the position moved by X pixels to one side in the main scanning direction MD with respect to Pb (3). ) Indicates the pixel numbers of the pixels included in the region 344 up to the position moved by X pixels to the other side in the main scanning direction MD. Further, the pixel number g corresponding to Pb (4) is the main scanning direction MD with respect to the boundary position Pb (4) from the position moved by X pixels to one side of the main scanning direction MD with respect to Pb (4). The pixel number of the pixel contained in the area | region 345 between the position which moved to the other side of X by X pixel is shown.

  As shown in FIG. 6, the CPU 40 divides the extracted G1 (g) by G0 (g) to obtain the ratio R (g) (= G1 (g) / G0 (g)) for each pixel number g. (S33). The CPU 40 selects the density W (g) of the pixel having the pixel number g from the reference image (white) data read from the flash memory 43 by the process of S15. The CPU 40 corrects W (g) for each pixel by multiplying the selected W (g) by R (g) (= G1 (g) / G0 (g)) (S35). The reference image (white) data including the corrected W (g) data is used when shading correction (S55, see FIG. 7) is executed later. The CPU 40 advances the process to S37.

  The CPU 40 determines whether all the boundary positions Pb have been selected by the process of S29 (S37). If the unselected boundary position Pb remains (S37: NO), the CPU 40 returns the process to S29. The CPU 40 selects one by one from the unselected boundary position Pb in ascending order (S29), and repeats the processes of S31 to S35. CPU40 advances a process to S51 (refer FIG. 7), when it determines with all the boundary positions Pb having been selected by the process of S29 (S37: YES).

  As shown in FIG. 7, the CPU 40 starts rotation of the paper feed roller 21 and the transport rollers 23 and 26 (see FIG. 1). When the rotation speed of the transport rollers 23 and 26 is set to V1 by the process of S21 (see FIG. 6), the CPU 40 rotates the transport rollers 23 and 26 at the rotation speed V1. On the other hand, when the rotation speed of the transport rollers 23 and 26 is not set to V1 by the process of S21, the CPU 40 rotates the transport rollers 23 and 26 at the default rotation speed V0. As a result, the originals GS placed on the paper feed tray 2 are fed one by one into the transport path 20, and transport of the originals GS is started in the transport path 20 (S51).

  The CPU 40 starts a reading operation. Light is emitted from the light source 30 toward the document GS. The reflected light reflected from the document is received by the light receiving element 31A. As a result, the reading unit 24 reads the image of the original for one line. Document image data is repeatedly generated for each line (S53). The generated document image data is sequentially output from the reading unit 24 to the image processing unit 46 via the AFE 45.

  The CPU 40 sets the reference image (white) data stored in the flash memory 43 in the image processing unit 46 as a shading correction parameter. Here, when the processes of S33 and S35 are executed, the pixel of the reference image (white) with the pixel number g corresponding to the shift amount ΔP for which the level is set to “2” is set to the ratio R (g) = ( = G1 (g) / G0 (g) is corrected by multiplication.

  In response to the setting of the shading parameters by the CPU 40, the shading correction is started by the image processing unit 46 (S55). Specifically, it is as follows. Based on the document image data output from the reading unit 24 via the AFE 45, the image processing unit 46 uses the density of the pixel with the pixel number i in the document image as a reference image (white) set as a shading parameter. Divide by the density of the pixel with pixel number i. The image processing unit 46 executes the above processing for all pixels (pixel number range: 1 ≦ i ≦ N) included in the document image. Accordingly, the image processing unit 46 performs shading correction on the document image data based on the set shading parameter. The document image data subjected to the shading correction is stored in the RAM 42.

  The CPU 40 determines whether all images of the document have been read by repeatedly reading the image of the document line by line (S57). If it is determined that the entire image of the document has not been read (S57: NO), the CPU 40 returns the process to S57. If it is determined that all images of the document have been read (S57: YES), the CPU 40 ends the main process. Thereby, reading of one original is completed.

  When a plurality of documents are placed on the paper feed tray 2, the main process is repeatedly executed for the number of documents.

<Main functions and effects of this embodiment>
As described above, the CPU 40 of the image reading apparatus 1 sets the level of the deviation amount ΔP to “2” when the deviation amount ΔP of the document image is larger than the threshold value Th1 (S83). The CPU 40 calculates the ratio R (g) (= G1 (g) / G0 (g)) for each pixel number g based on the pixel number g corresponding to the shift amount ΔP for which the level “2” is set (S33). ). The CPU 40 corrects W (g) for each pixel by multiplying W (g) by R (g) (S35). The corrected W (g) is set as a shading meter and used during shading correction (S55). In this case, as shown in FIGS. 9 and 10, only the pixels near the boundary positions Pc (3) and Pc (4) where the shift amount ΔP is relatively large are corrected shading parameters (W (g) × R The shading correction is performed by (g)), and the other pixels are subjected to the shading correction by the shading parameter (W (g)) before correction. For this reason, the CPU 40 can correct only a pixel having a relatively large deviation amount ΔP in the original image by the corrected shading parameter. For this reason, by generating the chart image data in a state where the paper dust adheres to the chart member 34, it is possible to limit an area where luminance unevenness or noise occurs in the corrected document image. In addition, since the shading correction using the corrected shading parameter is performed on the portion where the deviation amount ΔP is relatively large, the conversion characteristic is changed according to the change in the position of the peripheral light reduction due to the expansion of the rod lens 32A. It is possible to suppress the occurrence of unbalance. Accordingly, in the portion where the shift amount ΔP is relatively large, the brightness of the entire original image can be corrected uniformly while suppressing the influence of the thermal expansion of the rod lens 32A. Therefore, when the positional relationship between the rod lens 32A and the light receiving element 31A is shifted due to the thermal expansion of the rod lens 32A, the CPU 40 compares the shading correction uniformly for all the pixels of the document image. Good image quality of the original image can be maintained.

  If the CPU 40 determines that there is one or more deviation amount ΔP with the level set to “1” (S19: YES), the image reading device is used when reading the document GS (S51, S53, see FIG. 7). The reading speed of the document GS by the reading unit 24 is changed so that the heat generation of 1 can be suppressed. Specifically, the CPU 40 changes the frequency of the clock signal CLK to a frequency F1 (F0> F1) lower than the default frequency F0 (S21). Further, the CPU 40 sets the rotation speed of the transport rollers 23 and 26 to a rotation speed V1 (V0> V1) smaller than the default rotation speed V0 (S21). Further, the CPU 40 changes the light amount of the light source 30 to a light amount L1 (L0> L1) smaller than the default light amount L0 (S23). That is, when the amount of deviation ΔP is relatively small, the CPU 40 does not correct the shading parameter, but lowers the reading speed to reduce the amount of heat generation, so that the deviation of the positional relationship between the rod lens 32A and the light receiving element 31A itself. Suppress. Thus, the CPU 40 can limit the correction of the shading parameter to a portion where the deviation amount ΔP is relatively large. For this reason, the CPU 40 can suppress the occurrence of uneven brightness and noise in the corrected document image by generating the chart image data in a state where the paper dust adheres to the chart member 34.

<Modification>
The present invention is not limited to the above embodiment, and various modifications can be made. The chart 34A drawn on the chart member 34 has a shape in which a plurality of blocks 341 surrounded by a square frame line are arranged in the main scanning direction MD. The aspect of the chart 34A is not limited to this. For example, each block 341 included in the chart 34A may have a square that does not have a frame line. In this case, the color densities of the blocks 341 adjacent to each other in the main scanning direction MD may be different. Also in this case, the reflectance at the boundary between the blocks 341 is discontinuous in the main scanning direction MD. For this reason, the CPU 40 of the image reading apparatus 1 can detect the difference in light intensity according to the discontinuity of the reflectance by the same method as in the above-described embodiment, so that the boundary position can be specified and the shift amount ΔP can be calculated.

  The CPU 40 compares the ratio R (g) for the pixel of the pixel number g satisfying the conditional expression (1) (for example, the pixels included in the regions 344 and 345) among the densities W of the plurality of pixels in the reference image (white). W (g) was corrected by (= G1 (g) / G0 (g)) and used as a shading parameter. Of W used as a shading parameter, a portion corrected by the ratio R is not limited to the above-described region. For example, when “2” is set as the level of the shift amount ΔP, that is, when it is determined that the shift amount ΔP is larger than the threshold value Th1, the CPU 40 scans the corresponding Pb in W in the main scanning direction. The portions corresponding to the two blocks 341 adjacent to both sides of the MD may be corrected by the ratio R.

  Further, for example, as shown in FIG. 9, when “2” is set as the level of each of the deviation amounts ΔP (3) and ΔP (4) (S31: YES), it corresponds to the deviation amount ΔPb (3). As the pixel number g, a corresponding pixel number between ΔP (2) to ΔP (3) may be extracted. Similarly, a pixel number corresponding to between ΔP (3) to ΔP (4) may be extracted as the pixel number g corresponding to the shift amount ΔPb (4). The CPU 40 may calculate the ratio R for the portion corresponding to the extracted pixel number g (S33) and correct W (S35).

  The CPU 40 generates reference image (white) data and reference image (gray) data by executing initial processing (not shown) at the time of shipment of the image reading apparatus 1, and stores it in the flash memory 43. The initial process may be executed at a timing other than the time when the image reading apparatus 1 is shipped. For example, the initial process may be executed in response to an input of a dedicated command via the operation unit 5 during maintenance of the image reading apparatus 1 by a maintenance worker. Further, the reference image (white) data and the reference image (gray) data are not stored in the flash memory 43 by executing the initial process, but for example, reference image (white) data prepared in advance at the time of shipment. In addition, the reference image (gray) data may be directly stored in the flash memory 43. The boundary positions Pb (1), Pb (2),... May be stored in the flash memory 43 instead of the reference image (gray) data.

  The CPU 40 may change at least one of the clock signal CLK, the rotation speed, and the light amount by the processing of S21 and S23, and does not need to change all of them. The CPU 40 may change the clock signal CLK, the rotation speed, and the amount of light stepwise in accordance with the number of deviation amounts ΔP for which “1” is set as the level. The CPU 40 may change the clock signal CLK, the rotation speed, and the amount of light when the amount of deviation ΔP with “1” set as the level is equal to or greater than a predetermined number of 2 or more. The CPU 40 may adjust the amount of change in the clock signal CLK, the rotation speed, and the amount of light according to the magnitude of the deviation amount ΔP. Note that when the reading speed is reduced to suppress heat generation, the amount of light per each light receiving element 31A may increase. In such a case, it is preferable to adjust the light amount of the light source 30 to be low and the light amount per light receiving element 31A to be the same.

  The CPU 40 may cool the reading unit 24 by a cooling mechanism (not shown) such as a cooling fan (not shown) when the deviation amount ΔP in which “1” is set as the level is included.

  Even when the deviation amount ΔP with “1” set as the level is not included, the CPU 40 does not include the deviation amount ΔP with “2” set as the level. , And / or at least one of the light amounts may be changed.

  For example, as shown in FIG. 9, when there are 11 boundary positions, the CPU 40 has boundary positions Pb (1) and Pb (11) arranged at both ends in the main scanning direction MD, respectively. Deviation amounts ΔP (1) and ΔP (11) between the positions Pc (1) and Pc (11) may be calculated. That is, the CPU 40 may specify the shift amount ΔP only for the boundaries arranged in the vicinity of both ends in the main scanning direction MD among the plurality of boundary positions, and execute the subsequent processing. In this case, the pixel numbers g for calculating the ratio R (g) (= G1 (g) / G0 (g)) by the process of S33 may be all pixel numbers. In this case, a small shift amount that cannot be detected by the determination based on the shift amount ΔP for each fine region can also be detected. For this reason, it is possible to suppress color unevenness or the like before the image starts appearing according to a small shift amount. Note that the boundary position where the deviation amount ΔP is calculated is not limited to the position in the above specific example.

  When the deviation amount ΔP with “1” set as the level is included (S19: YES), the CPU 40 notifies the user in place of the processing of S21 and S23 or simultaneously with any of the processing of S21 and S23. An image for notification may be displayed on the display unit 6. In this case, the user can be informed that the rod lens 32A of the optical member 32 may have been expanded by heat and the position of the peripheral dimming may have changed. Note that the method of notifying the user is not limited to displaying an image on the display unit 6. For example, the CPU 40 may notify the user by outputting a warning sound from a speaker (not shown) included in the image reading apparatus 1.

<Others>
The CPU 40 that performs the process of S13 is an example of the “first acquisition unit” in the present invention. The flash memory 43 that stores the reference image (white) data and the reference image (gray) data is an example of the “storage unit” in the present invention. The CPU 40 that performs the process of S17 is an example of the “calculation unit” in the present invention. The CPU 40 that performs the process of S53 is an example of the “second acquisition unit” in the present invention. The image processing unit 46 that performs the process of S55 is an example of the “correction unit” in the present invention. In the case where an image for notifying the user is displayed on the display unit 6 instead of the processing of S21 and S23 or simultaneously with any of the processing of S21 and S23, the CPU 40 that performs the processing of S21 and S23 It is an example of “notification means”. Each of the regions 344 and 345 is an example of a corresponding portion corresponding to the boundary positions Pb (3) and Pb (4).

1: Image reading device 24: Reading unit 30: Light source 31: Light receiving unit 31A: Light receiving element 32: Optical member 32A: Rod lens 34: Chart member 34A: Chart 40: CPU
43: flash memory 46: image processing unit 341: block 342: boundary

Claims (8)

A plurality of blocks arranged in a crossing direction intersecting the document conveyance direction, and a chart member having a plurality of boundary portions arranged between adjacent blocks and having a reflectance discontinuous in the crossing direction;
A reading unit including a plurality of light receiving elements arranged in the intersecting direction and capable of receiving light transmitted through the lens and outputting a signal corresponding to the light intensity;
First acquisition means for acquiring a chart image indicating the chart member based on a signal output when reflected light of the light irradiated toward the chart member is received by the plurality of light receiving elements;
A storage unit that stores reference information based on a reference image serving as a reference of the chart image;
The chart image and the reference at a position corresponding to at least one of the plurality of boundary portions based on the chart image acquired by the first acquisition means and the reference information stored in the storage unit A calculating means for calculating a deviation amount from the image;
A specifying means for specifying an amount that is greater than a first threshold among the deviation amounts calculated by the calculating means;
Second acquisition means for acquiring a document image indicating the document based on a signal output when the light intensity of reflected light of the light emitted toward the document is received by the plurality of light receiving elements;
Of the original image acquired by the second acquisition unit, only a corresponding part corresponding to the shift amount specified by the specifying unit is used as the corresponding part of the chart image acquired by the first acquisition unit. An image reading apparatus comprising correction means for correcting based on the correction means.   When the deviation amount calculated by the calculating means includes any amount that is larger than the second threshold smaller than the first threshold and smaller than the first threshold, the reading unit reads the original. The image reading apparatus according to claim 1, further comprising changing means for changing a speed.   3. The image according to claim 2, wherein the changing unit lowers a frequency when signals are periodically detected from the plurality of light receiving elements in order to acquire the document image by the second acquiring unit. Reader.   The image reading apparatus according to claim 2, wherein the changing unit reduces a conveyance speed of the document.   5. The image reading apparatus according to claim 2, wherein the changing unit reduces the amount of light emitted toward the chart member and the document. 6.   The calculating means calculates a deviation amount between the chart image and the reference image at a part of the boundary portions adjacent to both ends in the intersecting direction among the plurality of boundary portions. An image reading apparatus according to any one of claims 1 to 5. The correction unit is configured to determine the corresponding part of the document image based on a ratio between the density of the corresponding part of the chart image acquired by the first acquiring unit and the density of the corresponding part of the reference image. The image reading apparatus according to claim 1, wherein:   Informing means for informing the user when the deviation amount calculated by the calculating means includes any amount that is larger than the second threshold value smaller than the first threshold value and smaller than the first threshold value. The image reading apparatus according to claim 1.

Images