JP2017046090A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in that if displacement due to, for example, environmental temperature change occurs in a reading part, dust cannot be detected.SOLUTION: As preparation processing, a control section executes first light-grey black difference calculation processing in which first light-grey black difference data is calculated by subtracting first black data from first light-grey data. As reading pre-processing, the control section executes: second light-gray black difference calculation processing in which second light-grey black difference data is calculated by subtracting second black data from second light-grey data; determination data calculation processing in which determination data is calculated by dividing the second light-grey black difference data by the first light-gray difference data; standard deviation calculation processing in which a determination standard deviation is calculated by calculating a standard deviation for the determination data; determination range setting processing in which the larger the determination standard deviation, the wider the determination range is set; and position specifying processing in which the position of a pixel the determination data of which is not within the determination range is specified as the position of an abnormal pixel.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image reading apparatus.

  In general, in an image reading apparatus, a white reference member is used as a light distribution reference member for shading correction, and an image of a document passing through the white reference member is read. However, when a white reference member is used, a show-through phenomenon in which a density change on the back side of the document affects the front surface may occur. In order to reduce the show-through phenomenon, various image reading apparatuses that perform shading correction using a gray reference member having a lower reflectance than the white reference member have been proposed. For example, Patent Document 1 discloses an image reading apparatus in which a non-white reference member is provided on a document guide of a document feeder.

  Patent Document 2 discloses an image reading apparatus that detects that dust such as dust attached to a white reference member affects white reference data. The image reading apparatus described in Patent Document 2 performs dust detection by comparing white reference data obtained by reading a white reference member with a predetermined threshold, and a white reference equal to or less than a predetermined threshold in which dust is detected. Data is linearly interpolated using surrounding white reference data.

JP 2000-125044 A JP 2007-68047 A

  When a CIS (abbreviation of Contact Image sensor) is used as a reading unit of an image reading apparatus, a CIS casing, a substrate on which a light receiving element is arranged, and a rod lens that focuses light on the light receiving element are mutually connected. There may be a positional shift that changes the positional relationship. For example, each member of the CIS housing, substrate, and rod lens expands and contracts depending on the environmental temperature when a material having a high coefficient of thermal expansion such as resin is used. For this reason, a positional shift occurs between the CIS housing, the substrate, and the rod lens due to a change in environmental temperature. Due to the generated positional deviation, a change in the amount of light received by each light receiving element occurs and the output of each light receiving element changes.

  Consider a case where dust detection is performed in an image reading apparatus provided with a non-white reference member described in Patent Document 1 as in the image reading apparatus described in Patent Document 2. When the positional deviation due to the environmental temperature change described above occurs, the reference data obtained by reading the non-white reference member changes due to the change in the output of each light receiving element. As a result, there arises a problem that dust detection is not accurately performed.

  Accordingly, the present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an image reading apparatus capable of accurately detecting dust even when a positional deviation due to a change in environmental temperature or the like occurs in a constituent member of a reading unit. To do.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided a gray reference member that is disposed in a transport path through which a document is transported and has a lower reflectance than white, and the document passes through the gray reference member. A reading unit that sometimes irradiates light on a document to read an image of the document on a pixel-by-line basis, a correction unit that corrects shading of image data read by the reading unit based on correction data, a storage unit, and preprocessing And a control unit that executes a pre-reading process, and the control unit outputs, as the preliminary process, 1 from the reading unit when the reading unit is turned off and a document is read. First black data acquisition processing for acquiring first black data of each pixel in the line, and each pixel in one line output from the reading unit when the reading unit irradiates and reads the gray reference member No. 1 Ash Day First gray data acquisition processing, and subtracting the first black data from the first gray data for each pixel in one line to obtain first gray light difference data for each pixel in one line And a first gray-black difference calculation process stored in the storage unit, and as the pre-reading process, when the reading unit is turned off and the gray reference member is read from the reading unit Second black data acquisition processing for acquiring second black data of each pixel in one output line, and one line output from the reading unit when the reading unit irradiates and reads the gray reference member Second gray data acquisition processing for acquiring second gray data of each pixel in the pixel, and subtracting the second black data from the second gray data in each pixel in one line Second gray light black for calculating second gray light black difference data of each pixel Minute calculation processing and discrimination data calculation processing for calculating discrimination data for each pixel in one line by dividing the second gray / light black difference data by the first gray / light black difference data in each pixel in one line A standard deviation calculation process for calculating a standard deviation of the discrimination data to calculate a discrimination standard deviation; a discrimination range setting process for setting a discrimination range wider as the discrimination standard deviation is larger; and the discrimination data is the discrimination range And a position specifying process for specifying a pixel position of a pixel not inside as an abnormal pixel position.

  According to a specific aspect of the present invention, the determination range setting process includes an average process for calculating an average value of the determination data as a determination average value. The determination range setting process has a first determination standard deviation. When the value is equal to or less than a predetermined value, a range in which the upper limit of the discrimination range is a value obtained by adding 4% to the discrimination average value and a lower limit of the discrimination range is a value obtained by subtracting 4% from the discrimination average value. When the discrimination standard deviation is greater than a first predetermined value and less than or equal to a second predetermined value, the upper limit of the discrimination range is a value obtained by adding 5% to the discrimination average value, and the lower limit of the discrimination range Is set as the discrimination range, and when the discrimination standard deviation is larger than the second predetermined value and not more than the third predetermined value, the upper limit of the discrimination range Is increased by 6.5% to the discrimination average And a range in which the lower limit of the discrimination range is 6.5% less than the discrimination average value is set as the discrimination range, the discrimination standard deviation is greater than a third predetermined value, and a fourth predetermined When the value is less than or equal to the value, a range in which the upper limit of the discrimination range is 8.5% higher than the discrimination average and the lower limit of the discrimination range is 8.5% lower than the discrimination average Set as the discrimination range, and when the discrimination standard deviation is greater than a fourth predetermined value and less than or equal to a fifth predetermined value, the upper limit of the discrimination range is a value obtained by adding 10.5% to the discrimination average value; and A range in which the lower limit of the determination range is 10.5% less than the determination average value is set as the determination range, and when the determination standard deviation is larger than a fifth predetermined value, the upper limit of the determination range is set. A value that is 13% higher than the discriminant average, and The range of a value obtained by 13% split down on the discriminant average the lower limit of the serial determination range is set as the determination range.

  According to a specific aspect of the present invention, the reading unit includes a light source and a large number of photoelectric conversion elements divided into a plurality of blocks, and the standard deviation calculation process is performed on one line of the plurality of blocks. The standard deviation is calculated by using the discrimination data of all the pixels existing in the block that is output first, and the discrimination standard deviation is calculated.

  According to the first aspect of the present invention, as the preliminary processing, the first gray / light black difference calculation processing subtracts the first black data from the first gray / light data at each pixel in one line. First gray light black difference data of each pixel is calculated, stored in the storage unit, and as a pre-reading process, the second gray light black difference calculation process is performed from the second gray light data for each pixel in one line. The black data is subtracted to calculate the second gray light black difference data of each pixel in one line, and the discrimination data calculation process calculates the second gray light black difference data in each pixel in one line. Divide by the black difference data to calculate the discrimination data for each pixel in one line, the standard deviation calculation process calculates the standard deviation of the discrimination data, calculates the discrimination standard deviation, and the discrimination range setting process The larger the standard deviation is, the wider the discrimination range is set. Identifies the pixel position of a pixel that is not within the discrimination range as an abnormal pixel position. Accordingly, the larger the discrimination standard deviation is, the wider the discrimination range is set, so that an abnormal pixel position that is a dust position can be detected with high accuracy.

  According to a specific aspect of the present invention, the determination range setting process sets the upper limit of the determination range to a value obtained by adding 4% to the determination average value when the determination standard deviation is equal to or less than the first predetermined value, The range where the lower limit is 4% discounted to the discriminant average value is set as the discriminant range, and when the discriminant standard deviation is larger than the first predetermined value and less than or equal to the second predetermined value, the upper limit of the discriminant range is discriminated average A range in which the lower limit of the discrimination range is 5% less than the discrimination average value is set as the discrimination range, the discrimination standard deviation is greater than the second predetermined value, and the third predetermined value If the value is less than or equal to the value, the upper limit of the discrimination range is set to a value that is 6.5% higher than the discrimination average value, and the range that is the lower limit of the discrimination range to a value that is 6.5% lower than the discrimination average value is set as the discrimination range And the discriminant standard deviation is larger than the third predetermined value and not larger than the fourth predetermined value. The upper limit of the discrimination range is 8.5% higher than the discrimination average and the lower limit of the discrimination range is 8.5% lower than the discrimination average. When the standard deviation is larger than the fourth predetermined value and equal to or smaller than the fifth predetermined value, the upper limit of the determination range is set to a value obtained by adding 10.5% to the determination average value, and the lower limit of the determination range is set to 10. A range with a value reduced by 5% is set as the discrimination range, and when the discrimination standard deviation is larger than the fifth predetermined value, the upper limit of the discrimination range is set to a value that is 13% extra of the discrimination average value, and the lower limit of the discrimination range Is set as a discrimination range. Therefore, since the determination range is set in consideration of the variation of the determination standard deviation, it is possible to reduce the influence of the variation of the determination standard deviation and detect the abnormal pixel position with high accuracy.

  According to a specific aspect of the present invention, the standard deviation calculation process calculates the standard deviation using the discrimination data of all the pixels present in the block output first in one line among the plurality of blocks. The discrimination standard deviation is calculated. Therefore, the positional deviation due to the environmental temperature tends to be large at the end of the reading unit. A high discrimination standard deviation can be calculated.

1 is a front view showing an internal configuration of an image reading apparatus 1 according to an embodiment of the present invention. 2 is an enlarged view illustrating a configuration of a reading unit 24 of the image reading apparatus 1. 3 is a block diagram illustrating a configuration of a light receiving unit 31 of a reading unit 24. FIG. 2 is a block diagram illustrating an electrical configuration of the image reading apparatus 1. FIG. It is a flowchart which shows a maintenance main process. It is a flowchart which shows gray light black difference data LGBdif1 memory | storage M16. It is a flowchart which shows a reading main process. It is a flowchart which shows reference | standard data CD calculation R7.

[Embodiment]
Hereinafter, an image reading apparatus 1 according to an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the vertical direction and the front-back direction are indicated by arrows.

<Mechanical Configuration of Image Reading Apparatus 1>
In FIG. 1, the image reading apparatus 1 includes a paper feed tray 2, a main body 3, and a paper discharge tray 4. The operation unit 5 and the display unit 6 are disposed on the upper surface of the main body unit 3. The operation unit 5 includes a power switch and various setting buttons, and receives operation commands and the like from the user. For example, the operation unit 5 includes a selection button for selecting one of a three-color mode and a mono mode and an operation button for setting a resolution. The display unit 6 includes an LCD and displays the status of the image reading apparatus 1.

  A conveyance path 20 is formed inside the main body 3. 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. A paper feed roller 21, a separation pad 22, a pair of upstream transport rollers 23, a reading unit 24, a platen glass 25, and a 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 side conveyance roller 23 and the downstream side conveyance roller 26 are driven by a conveyance motor MT (see FIG. 4). The platen glass 25 is light transmissive and is disposed along the transport path 20 below the transport 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.

  In the present embodiment, the document GS is placed on the paper feed tray 2 so that the reading surface of the document GS faces the placement surface of the paper feed tray 2. The reading unit 24 is disposed below the conveyance path 20 and reads an image on the reading surface of the document GS passing through the platen glass 25. The document sensor 27 is disposed in the paper feed tray 2 and 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. Is done.

(Detailed configuration of the reading unit 24)
A detailed configuration of the reading unit 24 will be described with reference to FIGS. 2 and 3. 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 light emitted from the light source 30 is reflected by the reading surface of the document GS or the like, the optical member 32 guides the reflected light to the light receiving unit 31. In the present embodiment, when the color mode is selected, an image of the one-line original GS is read by sequentially turning on the three color light emitting diodes. When the mono mode is selected, one line of the original GS is read by turning on a specific one of the three colors, for example, a green light emitting diode.

  The gray reference plate 34 is disposed at a position facing the reading unit 24 via the conveyance path 20. The gray reference plate 34 has a lower reflectance than white, which is the background color of the document GS. When the document GS is not present on the conveyance path 20, the light emitted from the light source 30 is reflected by the gray reference plate 34, and the reflected light is received by the light receiving unit 31 through the optical member 32. The optical member 32 includes a rod lens extending in the main scanning direction MD. The gray density of the gray reference plate 34 in the present embodiment 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 as will be described later is turned on with the maximum light amount. .

  In FIG. 3, the light receiving unit 31 has six sensor IC chips CH1 to CH6 arranged linearly in the main scanning direction MD, and each sensor IC chip has a number of photoelectric ICs arranged in the main scanning direction MD. The conversion element 33 is included, and a shift register (not shown) and an amplifier are incorporated. The first pixel is a pixel at an end portion on the side not adjacent to the sensor IC chip in the sensor IC chip CH1, and the last pixel is an end portion on the side not adjacent to the sensor IC chip in the sensor IC chip CH6. It is a pixel. The pixel numbers are assigned from the first pixel to the last pixel in order. As for the chip number, the first sensor IC chip CH1 having the first pixel is 1, and the last sensor IC chip CH6 having the last pixel is 6. In the present embodiment, the light receiving unit 31 has six sensor IC chips CH1 to CH6, but may have more than six sensor IC chips. The sensor IC chips CH1 to CH6 have different output characteristics. One line is a pixel group composed of the first pixel to the last pixel.

<Electrical Configuration of Image Reading Apparatus 1>
The electrical configuration of the image reading apparatus 1 will be described with reference to FIG. 4, the image reading apparatus 1 includes a CPU 40, a ROM 41, a RAM 42, a flash PROM 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. Prepare as. 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 programs for executing various operations of the image reading apparatus 1 such as a maintenance main process, a reading main process, and a subroutine process in each main process, which will be described later. The CPU 40 controls each unit according to the program read from the ROM 41. The flash PROM 43 is a readable and writable nonvolatile memory, and stores various data generated by the control process of the CPU 40, for example, various data calculated by the maintenance main process. 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 to the reading unit 24 a signal for controlling turning on / off of the light source 30 and a signal for controlling a current value flowing through the light source 30 based on a command from the CPU 40. To do. Further, the device control unit 44 operates each pixel as shown in FIG. 3 in order to sequentially operate the large number of photoelectric conversion elements 33 of the sensor IC chips CH1 to CH6 of the light receiving unit 31 based on a command from the CPU 40. A clock signal CLK for transfer and a serial-in signal SI for simultaneously transferring electric signals of all the photoelectric conversion elements to the shift register are transmitted to the light receiving unit 31. Upon receiving these control signals from the device control unit 44, the reading unit 24 turns on the light source 30 and transmits an analog signal corresponding to the amount of light received by the light receiving unit 31 to the AFE 45. Here, the maximum light amount irradiated by the light source 30 is a light amount determined from a predetermined maximum current value and a maximum period during which the light source 30 can be turned on at the interval of the serial-in signal SI.

  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. For example, if the resolution is 10 bits, the gradation is from “0” to “1023”. In this case, the AFE 45 converts the analog signal transmitted from the reading unit 24 into 10-bit (0 to 1023) gradation data as digital data. The digital data converted by the AFE 45 is transmitted to the image processing unit 46. The image processing unit 46 is composed of an ASIC that is a dedicated IC for image processing, and performs various types of image processing on the digital data. The image processing includes various correction processes such as shading correction and γ correction. The image processing unit 46 can be set not to perform various types of image processing, or can be set to perform all image processing. The image processing unit 46 performs the set image processing on the digital data to generate digital image data. The digital image data 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.

<Operation of Embodiment>
Next, the operation of the image reading apparatus 1 will be described with reference to the drawings. The image reading apparatus 1 mainly executes a maintenance main process executed before reading the document GS and a read main process for reading the document GS. The processing of steps M1 to M16 during the maintenance main processing, the processing of steps R1 to R8 during the reading main processing, and the processing of the steps of each subroutine are processing executed by the CPU 40. In the present embodiment, the data processing executed by the CPU 40 for each pixel of one line is processing executed for each pixel of three colors in the color mode, and is processing executed for each pixel of a specific color in the mono mode. . In this embodiment, a color mode will be described.

(Maintenance main processing)
The maintenance main process shown in FIG. 5 is performed when an operator such as a service person operates the operation unit 5 of the image reading apparatus 1 before the image reading apparatus 1 is shipped from the factory or when a service person performs maintenance inspection after the shipment. Start by operating according to a special operating method. In this embodiment, a case where 600 DPI is used as the reading resolution and the color mode is used will be described.

  First, when an operator places a special white reference document WGS serving as a white reference on the paper feed tray 2, the document sensor 27 detects the white reference document WGS. It is determined whether there is a white reference document WGS according to the detection signal from the document sensor 27 (M1). When the white reference original WGS is present (M1: Yes), the CPU 40 proceeds to process M2. When there is no white reference original WGS (M1: No), the CPU 40 proceeds to processing M11 and displays an error message notifying that the original placement state is incorrect on the display unit 6 (M11). When the process M11 ends, the maintenance main process ends.

  If it is determined in process M1 that there is a white reference document WGS (M1: Yes), the CPU 40 causes the drive circuit 47 to feed the white reference document WGS to the platen glass 25, and the device control unit 44, AFE 45, and image. The processing unit 46 is initialized (M2). Specifically, the CPU 40 transmits a drive command to the drive circuit 47 to feed the white reference document WGS placed on the paper feed tray 2 to the platen glass 25. Further, the CPU 40 acquires the settings of the clock signal CLK and the serial-in signal SI corresponding to the reading resolution of 600 DPI from the flash PROM 43 and sets them in the device control unit 44. The CPU 40 acquires the signal setting for the light source 30 corresponding to the color mode from the flash PROM 43 and sets it in the device control unit 44. The CPU 40 acquires the offset adjustment value and the gain adjustment value of the AFE 45 from the flash PROM 43 and sets them in the AFE 45. Here, the offset adjustment value is a value for shifting the level of the analog signal input to the AFE 45, and the gain adjustment value is a value for adjusting the gain of the analog signal input to the AFE 45. The CPU 40 sets the image processing unit 46 so as not to perform various image processing.

  The CPU 40 adjusts the light amount of the light source 30 (M3). Specifically, the CPU 40 irradiates light from the light source 30 toward the white reference document WGS, and the light amount ST of each color is set so that the analog signal when the reflected light is read becomes the maximum of the input range of the AFE 45. Adjust. The light quantity ST is determined by the lighting period and current value for each color in one line of the light source 30.

  The CPU 40 acquires white data WH (M4). Specifically, the CPU 40 turns on the light source 30 with the light quantity ST of each color, and reads the white reference document WGS. Then, the CPU 40 acquires the read digital image data of each pixel of each color of one line as white data WH.

  The CPU 40 acquires black data BK1 (M5). Specifically, the CPU 40 turns off the light source 30 and reads the white reference document WGS. The read digital image data of each pixel of one color of one line is acquired as black data BK1.

  The CPU 40 calculates the black and white difference data WBdif (M6). Specifically, the CPU 40 subtracts the black data BK1 from the white data WH of each pixel of each color in one line and stores it in the RAM 42 as black and white difference data WBdif of each pixel of each color in one line.

  The CPU 40 acquires the black and white difference upper value WBhr (M7). Specifically, the CPU 40 acquires the black and white difference data WBdif of 16 pixels in order from the largest value among the red and black difference data WBdif of one line calculated in the process M6 as the black and white difference upper value WBhr corresponding to red. Similarly, the CPU 40 obtains the black / white difference data WBdif of 16 pixels in order from the largest value in the blue / black difference data WBdif as the black / white difference upper value WBhr corresponding to blue, and the black / white difference data WBdif of 16 pixels in the largest order from the black / white difference data WBdif. The difference data WBdif is acquired as a monochrome difference upper value WBhr corresponding to green.

  The CPU 40 stores the pixel position Phr of the monochrome difference upper value WBhr (M8). The CPU 40 stores in the flash PROM 43 the pixel position Phr where the monochrome difference upper value WBhr of 16 pixels of each color obtained in process M7 is present in association with the monochrome difference upper value WBhr.

  The CPU 40 stores the monochrome difference data WBdif (M9). The CPU 40 stores, in the flash PROM 43, the black-and-white differential data WBdif of each pixel of each color calculated in process M6.

  When the process M9 is completed, the CPU 40 puts the image reading apparatus 1 in a standby state until the set key arranged on the operation unit 5 is pressed (M10). When the operator removes the white reference document WGS and the set key is pressed, the CPU 40 determines whether or not the document sensor 27 is off. If the CPU 40 determines that the document sensor 27 is off (M10: Yes), the CPU 40 proceeds to process M12. If the CPU 40 determines that the document sensor 27 is on (M10: No), the CPU 40 proceeds to processing M11. In step M11, the CPU 40 causes the display unit 6 to display an error message notifying that the document placement state is incorrect (M11), and the maintenance main process ends.

  If it is determined in process M10 that there is no document (M10: Yes), the CPU 40 acquires the ash data GR1 (M12). Specifically, the CPU 40 irradiates the gray reference plate 34 with the light amount ST of each color, and acquires the read digital image data of each pixel of each color of one line as the ash data GR1.

  The CPU 40 acquires the ash data maximum value GRmax (M13). The CPU 40 acquires the maximum value of the ash data GR1 in each color as the ash data maximum value GRmax among the ash data GR1 of each pixel of each color acquired in the process M12. The CPU 40 stores the ash data maximum value GRmax of each color in the flash PROM 43 in association with each color.

  The CPU 40 acquires the gray-black difference upper value GBhr1 (M14). Specifically, the CPU 40 subtracts the black data BK1 from the gray data GR1 for each pixel of each color in one line to calculate gray black difference data GBdif1 for each pixel of each color in one line. The CPU 40 acquires the gray-black difference data GBdif1 of 16 pixels existing at the pixel position Phr in the gray-black difference data GBdif1 for each color as the gray-black difference upper value GBhr1.

  The CPU 40 turns on the light source 30 with the maximum light amount of each color (M15). Specifically, the CPU 40 turns on the light source 30 with a maximum current value predetermined for each color and a maximum lighting period at a reading resolution of 600 DPI.

  The CPU 40 stores gray light black difference data LGBdif1 in the flash PROM 43 (M16). Although details will be described later, the CPU 40 acquires gray data LGR1 of each pixel of each color of one line when the gray reference plate 34 is irradiated with the maximum light amount of each color. The CPU 40 calculates gray light black difference data LGBdif1 by subtracting the black data BK1 from the light gray data LGR1 in each pixel of each color of one line. The CPU 40 determines the abnormal pixel position PED as the abnormal pixel position PED from the calculated gray-black difference data LGBdif1 which is an abnormal value greatly different from the normal value when the gray reference plate 34 is read due to dust or the like. Remember as. The CPU 40 calculates the average value of all the pixels of the gray light black difference data LGBdif1 for each color, and stores it in the flash PROM 43 as the gray light black difference average value LGBdifave1. The CPU 40 stores gray-black difference data LGBdif1 of each pixel of each color in one line in the flash PROM 43. When the process M16 ends, the maintenance main process ends.

(Gray light black difference data LGBdif1 storage M16)
When the gray / black difference data LGBdif1 storage (M16) shown in FIG. 6 is started, the CPU 40 acquires gray / light data LGR1 (MA1). Specifically, the CPU 40 irradiates the gray reference plate 34 with the light source 30 turned on with the maximum light amount of each color, and acquires the read digital image data of each pixel of each color of one line as gray data LGR1. To do.

  The CPU 40 calculates gray-black difference data LGBdif1 (MA2). Specifically, the CPU 40 subtracts the black data BK1 from the gray data LGR1 for each color pixel in one line to calculate gray light black difference data LGBdif1 for each color pixel in one line.

  The CPU 40 calculates the discrimination data RT1 (MA3). Specifically, the CPU 40 divides the gray light black difference data LGBdif1 by the black and white difference data WBdif in each line of red pixels to calculate discrimination data RT1 for each line of red pixels.

  The CPU 40 calculates an average value AVE1 that is an average value of the discrimination data RT1 in each of the sensor IC chips CH1 to CH6 (MA4). Specifically, the CPU 40 divides the discrimination data RT1 of each line of red pixels into a data group of each sensor IC chip. The CPU 40 calculates the average value of the discrimination data RT1 in the data group in the data group of each sensor IC chip divided in red as the average value AVE1 of each red chip.

  The CPU 40 calculates a threshold value TH1 (MA5). Specifically, the CPU 40 adds the maintenance addition value to the average value AVE1 of each sensor IC chip calculated in the process MA4, and calculates the white threshold value WTH1. The CPU 40 subtracts the maintenance subtraction value from the average value AVE1 of each sensor IC chip to calculate the black threshold value BTH1. The threshold value TH1 means the white threshold value WTH1 or the black threshold value BTH1. Here, the maintenance addition value and the maintenance subtraction value are values corresponding to 5% of the average value AVE1 of each sensor IC chip in the present embodiment, and are the same value. Since the maintenance addition value and the maintenance subtraction value are the same value, the influence of the black dust that lowers the output and the white dust that increases the output on the gray light black difference data LGBdif1 used in the main reading process is within the same level. be able to.

  The CPU 40 sets the target pixel (MA6). Specifically, if the target pixel is set, the CPU 40 sets the next pixel of the set target pixel as the target pixel, and if the target pixel is not set, sets the first pixel as the target pixel. To do. The CPU 40 obtains the pixel number of the target pixel by counting the set number of times after the first pixel is set as the target pixel, and stores it in the RAM 42. The CPU 40 stores a value obtained by adding 1 to the quotient obtained by dividing the pixel number by the number of pixels of each sensor IC chip in the RAM 42 as the chip number. Hereinafter, the sensor IC chip including the target pixel is referred to as a target sensor IC chip.

  The CPU 40 determines whether or not the target pixel is an abnormal pixel (MA7). Specifically, the CPU 40 determines that the red gray light difference data LGBdif1 of the target pixel is equal to or greater than the black threshold value BTH1 corresponding to the chip number of the target sensor IC chip and the white threshold value corresponding to the chip number of the target sensor IC chip. It is determined whether it is within the range of WTH1 or less. If it is within the range (MA7: No), it is determined that the pixel is not an abnormal pixel, and the process proceeds to process MA11. If it is not within the range (MA7: Yes), it is determined that the pixel is abnormal, and the process proceeds to process MA8.

  The CPU 40 determines whether or not the number of abnormal pixels is within a line upper limit value that is a reference value for the number of abnormal pixels in one line (MA8). Specifically, the CPU 40 adds 1 to the counter CTa that represents the number of abnormal pixels in one line. The CPU 40 determines whether or not the counter CTa exceeds the line upper limit value (for example, 25 pixels). When it exceeds (MA8: No), it is determined that the number of abnormal pixels has exceeded the line upper limit value, and the process proceeds to an error display process (MA9). If not exceeding (MA8: Yes), the CPU 40 determines that the number of abnormal pixels is within the line upper limit value, and proceeds to processing MA10. When it exceeds in process MA8 (MA8: No), CPU40 displays an error on a display part (MA9), and complete | finishes gray light difference data storage process (M16).

  If not exceeded in the process MA8 (MA8: Yes), the CPU 40 stores the pixel position of the target pixel in the flash PROM 43 as the abnormal pixel position PED (MA10). Specifically, the CPU 40 stores the pixel number of the target pixel in the flash PROM 43 as the abnormal pixel position PED.

  The CPU 40 determines whether or not the target pixel is the final pixel (MA11). Specifically, the CPU 40 determines whether or not the pixel number of the target pixel matches the pixel number indicating the final pixel. If they match (MA11: Yes), the CPU 40 deletes the pixel number, chip number, and counter CTa stored in process MA6, and proceeds to process MA12. If not matched (MA11: No), the CPU 40 proceeds to process MA6.

  If the two match in the process MA11 (MA11: Yes), the CPU 40 calculates a gray-light black difference average value LGBdiffave1 (MA12). Specifically, the CPU 40 calculates the average value of gray light black difference data LGBdif1 of all pixels of one line in each color, and stores it in the flash PROM 43 as gray light black difference average value LGBdifave1.

  The CPU 40 stores the gray-black difference data LGBdif1 of each pixel of each color of one line calculated in the process MA2 in the flash PROM 43 (MA13). When the process MA13 ends, the gray-black difference data LGBdif1 storage process (M16) ends.

(Reading main process)
The reading main process shown in FIG. 7 is started when the user places the document GS on the paper feed tray 2 and presses the color reading start button of the operation unit 5. The main reading process of this embodiment will be described when 600 DPI is set as the reading resolution and the color mode is set.

  The CPU 40 initializes the device control unit 44, the AFE 45, and the image processing unit 46 (R1). Specifically, the CPU 40 acquires the settings of the clock signal CLK and the serial-in signal SI corresponding to the reading resolution of 600 DPI from the flash PROM 43 and sets them in the device control unit 44. The CPU 40 acquires the signal setting for the light source 30 in the color mode from the flash PROM 43 and sets it in the device control unit 44. The CPU 40 acquires the offset adjustment value and the gain adjustment value of the AFE 45 from the flash PROM 43 and sets them in the AFE 45. The CPU 40 sets settings for not performing various image processing in the image processing unit 46.

  The CPU 40 adjusts the light amount of the light source 30 (R2). The CPU 40 irradiates light from the light source 30 toward the gray reference plate 34 and adjusts the light amount ST of each color so that the maximum value of the digital image data when the reflected light is read becomes the gray data maximum value GRmax. To do.

  The CPU 40 acquires the ash data GR2 (R3). Specifically, the CPU 40 irradiates the gray reference plate 34 with the light amount ST of each color, and acquires the read digital image data of each pixel of each color of one line as the ash data GR2.

  The CPU 40 acquires black data BK2 (R4). Specifically, the CPU 40 turns off the light source 30 and reads the gray reference plate 34. The read digital image data of each pixel of one color of one line is acquired as black data BK2.

  The CPU 40 acquires the gray-black difference upper value GBhr2 (R5). Specifically, the CPU 40 subtracts the black data BK2 from the gray data GR2 in each pixel of each color of one line, and calculates gray black difference data GBdif2 of each pixel of each color of one line. The CPU 40 acquires the gray-black difference data GBdif2 of 16 pixels existing at the pixel position Phr in the gray-black difference data GBdif2 for each color of one line as the gray-black difference upper value GBhr2.

  The CPU 40 turns on the light source 30 with the maximum light amount of each color (R6). Specifically, the CPU 40 turns on the light source 30 with a maximum current value predetermined for each color and a maximum lighting period at a reading resolution of 600 DPI.

  The CPU 40 calculates the reference data CD (R7). Although details will be described later, the CPU 40 acquires gray data LGR2 of each pixel of each color of one line when the gray reference plate 34 is irradiated with the maximum light amount of each color. The CPU 40 calculates gray light black difference data LGBdif2 by subtracting the black data BK2 from the light gray data LGR2 in each pixel of each color of one line. The CPU 40 determines the values of the abnormal pixels which are abnormal values greatly different from the normal values when the gray reference plate 34 is read due to dust or the like for the gray-black difference data LGBdif1 and LGBdif2 as the values of the peripheral pixels. Replace. The CPU 40 calculates the average value of all the pixels of the gray light black difference data LGBdif2 for each color of one line as the gray light black difference average value LGBdifave2. The CPU 40 multiplies the monochrome difference data WBdif, a variation ratio SCRT, which will be described later, an average value ratio AVRT, which will be described later, and an ash ratio GRRT, which will be described later, to calculate reference data CD for each pixel of each color of one line.

  The CPU 40 executes a reading process (R8). Specifically, the CPU 40 sets setting values for performing various image processing in the image processing unit 46. The CPU 40 outputs a command to the drive circuit 47 and causes the document to be conveyed by the drive circuit. The CPU 40 reads the conveyed document GS, performs shading correction for each color based on the reference data CD calculated in process R7, and executes various correction processes to generate digital image data. When the reading process (R8) ends, the reading main process ends.

(Standard data CD calculation R7)
When the reference data CD calculation (R7) shown in FIG. 8 is started, the CPU 40 acquires gray data LGR2 (RA1). Specifically, the CPU 40 irradiates the gray reference plate 34 with the light source 30 turned on at the maximum light amount of each color, and acquires the read digital image data of each pixel of each color of one line as gray data LGR2. To do.

  The CPU 40 calculates gray light difference data LGBdif2 (RA2). Specifically, the CPU 40 subtracts the black data BK2 from the gray data LGR2 in each pixel of each color in one line to calculate gray light black difference data LGBdif2 of each pixel in each color in one line.

  The CPU 40 calculates the discrimination data RT2 (RA3). Specifically, the CPU 40 divides the gray light black difference data LGBdif2 by the gray light black difference data LGBdif1 in each line of red pixels to calculate discrimination data RT2 for each line of red pixels.

  The CPU 40 calculates an average value AVE2 that is an average value of the red sensor IC chips (RA4). Specifically, the CPU 40 divides the discrimination data RT2 of each line of red pixels into a data group of each sensor IC chip. In the data group of each sensor IC chip divided into red, the CPU 40 calculates the average value of the discrimination data RT2 in the data group as the average value AVE2 of each red chip.

  The CPU 40 calculates the discrimination standard deviation LGSD (RA5). Specifically, the CPU 40 calculates a deviation SD that is a value obtained by subtracting the red discrimination data RT2 by the red average value AVE2 of the sensor IC chip CH1 in each pixel included in the sensor IC chip CH1. The CPU 40 calculates the discrimination standard deviation LGSD by calculating the root mean square of the deviations SD of all the pixels included in the sensor IC chip CH1. That is, the CPU 40 divides a value obtained by adding the deviations SD of all the pixels included in the sensor IC chip CH1 by the number of pixels included in the sensor IC chip CH1. The CPU 40 calculates the discriminant standard deviation LGSD by calculating the square root of the value calculated by the division.

  The CPU 40 calculates the read addition value LGAD1 and the read subtraction value LGAD2 (RA6). Specifically, when the discrimination standard deviation LGSD is 0.01 or less, the CPU 40 multiplies the average value AVE2 by 0.04 which is 4%, and calculates the read addition value LGAD1 of each red sensor IC chip. To do. Similarly, the CPU 40 multiplies the average value AVE2 by 0.04 to calculate a read subtraction value LGAD2 for each red sensor IC chip. When the discrimination standard deviation LGSD is larger than 0.01 and equal to or smaller than 0.02, the CPU 40 multiplies the average value AVE2 by 0.05 which is 5%, and reads the added value LGAD1 of each red sensor IC chip. Is calculated. Similarly, the CPU 40 multiplies the average value AVE2 by 0.05 to calculate a read subtraction value LGAD2 for each red sensor IC chip. When the standard deviation LGSD is greater than 0.02 and less than or equal to 0.03, the CPU 40 multiplies the average value AVE2 by 6.5%, which is 6.5%, and adds the read value of each sensor IC chip in red. LGAD1 is calculated. Similarly, the CPU 40 multiplies the average value AVE2 by 0.065 to calculate the read subtraction value LGAD2 for each red sensor IC chip. When the standard deviation LGSD is greater than 0.03 and less than or equal to 0.04, the CPU 40 multiplies the average value AVE2 by 8.5%, 0.085, and adds the read value of each sensor IC chip in red. LGAD1 is calculated. Similarly, the CPU 40 multiplies the average value AVE2 by 0.085 to calculate the read subtraction value LGAD2 for each red sensor IC chip. When the standard deviation LGSD is greater than 0.04 and less than or equal to 0.05, the CPU 40 multiplies the average value AVE2 by 0.105, which is 10.5%, and adds the read addition value of each sensor IC chip in red LGAD1 is calculated. Similarly, the CPU 40 multiplies the average value AVE2 by 0.105 to calculate the read subtraction value LGAD2 for each red sensor IC chip. When the standard deviation LGSD is larger than 0.05, the CPU 40 multiplies the average value AVE2 by 0.13 which is 13% to calculate the read addition value LGAD1 of each red sensor IC chip. Similarly, the CPU 40 multiplies the average value AVE2 by 0.13 to calculate the read subtraction value LGAD2 for each red sensor IC chip. In the present embodiment, the read addition value LGAD1 and the read subtraction value LGAD2 are the same value. Since the read addition value LGAD1 and the read subtraction value LGAD2 are the same value, the influence on the read image quality caused by the black dust that lowers the output and the white dust that increases the output can be within the same level. In addition, a numerical value for discriminating the standard deviation LGSD (for example, 0.01 if the discriminating standard deviation LGSD is 0.01 or less), a read addition value LGAD1 and a read subtraction value LGAD2 are calculated. A numerical value that is sometimes multiplied by the average value AVE (for example, 0.04 that is 4% is multiplied by the average value AVE2 to calculate the read addition value LGAD1 of each red sensor IC chip, 0.04 The numerical value to be multiplied by the average value AVE when calculating the reading addition value LGAD1 and the reading subtraction value LGAD2 is set slightly larger than the numerical value for determining the standard deviation LGSD. Yes. By setting in this way, it is possible to calculate the threshold value TH2 for detecting only an abnormal value indicating an output larger than the standard deviation LGSD, which is a variation in normal values.

  The CPU 40 calculates a threshold value TH2 (RA7). Specifically, the CPU 40 adds the read addition value LGAD1 of each sensor IC chip having the same red color to the average value AVE2 of each red sensor IC chip calculated in the process RA4, and the white threshold value WTH2 of each red sensor IC chip. Is calculated. The CPU 40 subtracts the read subtraction value LGAD2 of each red sensor IC chip from the average value AVE2 of each red sensor IC chip, and calculates the black threshold value BTH2 of each red sensor IC chip. The threshold value TH2 means the white threshold value WTH2 or the black threshold value BTH2.

  The CPU 40 sets the target pixel (RA8). Similarly to the process MA6, specifically, if the target pixel is set, the CPU 40 sets the next pixel of the set target pixel as the target pixel, and if the target pixel is not set, the CPU 40 A pixel is set as a target pixel. The CPU 40 acquires the pixel number of the target pixel and stores it in the RAM 42 as in the process MA6. The CPU 40 stores the chip number of the target sensor IC chip including the target pixel in the RAM 42 as in the process MA6.

  The CPU 40 determines whether or not the target pixel is an abnormal pixel (RA9). Specifically, the CPU 40 determines that the gray-black difference data LGBdif2 of the target pixel in red is greater than or equal to the black threshold BTH2 corresponding to the chip number of the target sensor IC chip, and the white threshold corresponding to the chip number of the target sensor IC chip. It is determined whether it is within the range of WTH2 or less. If it is not within the range (RA9: Yes), the CPU 40 determines that the target pixel is an abnormal pixel and proceeds to process RA10. If it is within the range, the CPU 40 determines whether or not the pixel position of the target pixel is the abnormal pixel position PED. If it is the abnormal pixel position PED (RA9: Yes), the CPU 40 determines that the target pixel is an abnormal pixel. The process proceeds to process RA10. If it is not the abnormal pixel position PED (RA9: No), it is determined that the target pixel is not an abnormal pixel, and the process proceeds to process RA11.

  The CPU 40 replaces the gray light black difference data LGBdif1 and LGBdif2 of the target pixel with gray light black difference data LGBdif1 and LGBdif2 of the peripheral pixels (RA10). Specifically, the CPU 40 replaces the gray light black difference data LGBdif1 of the target pixel in each color with gray light black difference data LGBdif1 of the pixel included in the target sensor IC chip, and replaces the light gray difference data LGBdif2 of the target pixel with the target sensor. Replaced with gray-black difference data LGBdif2 of pixels included in the IC chip. The pixel position replaced with gray light black difference data LGBdif1 and the pixel position replaced with gray light black difference data LGBdif2 are the same pixel position.

  The CPU 40 determines whether the target pixel is the last pixel (RA11). Specifically, the CPU 40 determines whether or not the pixel number stored in the process RA6 matches the pixel number indicating the final pixel. If they match (RA11: Yes), the CPU 40 stores the pixel number stored in the process RA8. The chip number is erased, and the process proceeds to process RA10. If they do not match (RA11: No), the process proceeds to process RA8.

  The CPU 40 calculates a gray-light black difference average value LGBdiffave2 (RA12). Specifically, the CPU 40 calculates the average value of the gray light black difference data LGBdif2 of all the pixels of one line of each color, and stores it in the flash PROM 43 as the gray light black difference average value LGBdifave2.

  The CPU 40 calculates the fluctuation ratio SCRT (RA13). Specifically, the CPU 40 divides the gray light black difference data LGBdif2 by the gray light black difference data LGBdif1 in each pixel of each color of one line, and calculates a variation ratio SCRT of each pixel of each color of one line.

  The CPU 40 calculates the average value ratio AVRT (RA14). Specifically, the CPU 40 calculates the average value ratio AVRT by dividing the gray-light black difference average value LGBdiffave1 by the gray-light black difference average value LGBdiffave2.

  The CPU 40 calculates the ash ratio GRRT (RA15). Specifically, the CPU 40 divides the gray-black difference upper value GBhr2 by the gray-black difference upper value GBhr1 at each pixel position Phr of each color, and calculates an average value of 16 pixel values obtained by the division for each color. Calculated as the ash ratio GRRT.

  The CPU 40 calculates the reference data CD (RA16). Specifically, the CPU 40 multiplies the black-and-white difference data WBdif by the variation ratio SCRT for each pixel of each line of color stored in the process M9, and multiplies the variation ratio SCRT for each color of one line by the value obtained. Multiply the ash ratio GRRT and multiply the value obtained by multiplying the ash ratio GRRT by the average value ratio AVRT to calculate the reference data CD for each pixel of each color in one line.

<Effect of embodiment>
In the present embodiment, black data BK1 acquisition M5 acquires black data BK1 in the maintenance main process. In the gray light difference data LGBdif1 storage M16, the light gray data LGR1 acquisition MA1 acquires gray light data LGR1. Gray light black difference data LGBdif1 calculation MA2 subtracts black data BK1 from light gray data LGR1 to calculate gray light black difference data LGBdif1. In the main reading process, black data BK2 acquisition R4 acquires black data BK2. In the reference data CD calculation R7, gray data LGR2 acquisition RA1 acquires gray data LGR2. Gray light black difference data LGBdif2 calculation RA2 calculates gray light black difference data LGBdif2 by subtracting black data BK2 from light gray data LGR2. The discrimination data RT2 calculation RA3 calculates the discrimination data RT2 for each red pixel in one line by dividing the gray light black difference data LGBdif2 by the gray light black difference data LGBdif1 in each pixel of each color in one line. The discrimination standard deviation LGSD calculation RA5 calculates a deviation SD that is a value obtained by subtracting the discrimination data RT2 by the average value AVE2 of the sensor IC chip CH1 in each pixel included in the sensor IC chip CH1, and is included in the sensor IC chip CH1. The discriminant standard deviation LGSD is calculated by calculating the root mean square of the deviations SD of all pixels. The read addition value LGAD1 and the read subtraction value LGAD2 calculation RA6 are obtained by multiplying the average value AVE2 by 0.04 which is 4% when the discrimination standard deviation LGSD is 0.01 or less, and reading the red sensor IC chips. The addition value LGAD1 is calculated, the average value AVE2 is multiplied by 0.04, and the read subtraction value LGAD2 of each red sensor IC chip is calculated. The discrimination standard deviation LGSD is greater than 0.01 and less than or equal to 0.02. In this case, the average value AVE2 is multiplied by 0.05 which is 5% to calculate the read addition value LGAD1 of each sensor IC chip of red, and the CPU 40 multiplies the average value AVE2 by 0.05, The read subtraction value LGAD2 of each red sensor IC chip is calculated. When the standard deviation LGSD is larger than 0.02 and equal to or smaller than 0.03, the average value AVE2 is 6%. To calculate the read addition value LGAD1 of each red sensor IC chip, and multiply the average value AVE2 by 0.06 to calculate the read subtraction value LGAD2 of each red sensor IC chip, and the standard deviation LGSD Is greater than 0.03 and less than or equal to 0.04, the average value AVE2 is multiplied by 0.07 which is 7% to calculate the read addition value LGAD1 of each red sensor IC chip, and the average value AVE2 Is multiplied by 0.07 to calculate the read subtraction value LGAD2 of each red sensor IC chip. When the standard deviation LGSD is greater than 0.04 and less than or equal to 0.05, the average value AVE2 is 8% Multiplying by 0.08, the read addition value LGAD1 of each red sensor IC chip is calculated, the average value AVE2 is multiplied by 0.08, and the read subtraction value LGAD of each red sensor IC chip is calculated. When the standard deviation LGSD is larger than 0.05, the average value AVE2 is multiplied by 0.1 which is 10% to calculate the read addition value LGAD1 of each red sensor IC chip, and the average value AVE2 Is multiplied by 0.1 to calculate the read subtraction value LGAD2 of each red sensor IC chip. The threshold value TH2 calculation RA7 adds the read addition value LGAD1 to the average value AVE2 of each sensor IC chip, calculates the white threshold value WTH2, subtracts the read subtraction value LGAD2 from the average value AVE2 of each sensor IC chip, and black threshold value BTH2 Is calculated. In the process RA9 for determining whether the target pixel is an abnormal pixel, the gray-black difference data LGBdif2 of the target pixel in red is not less than the black threshold value BTH2 corresponding to the chip number of the target sensor IC chip, and the target sensor IC chip It is determined whether or not it is within the range equal to or less than the white threshold value WTH2 corresponding to the chip number. If it is not within the range (RA9: Yes), it is determined that the target pixel is an abnormal pixel. It is determined whether or not the pixel position of the target pixel is the abnormal pixel position PED, and if it is the abnormal pixel position PED (RA9: Yes), it is determined that the target pixel is an abnormal pixel and is not the abnormal pixel position PED ( RA9: No) determines that the target pixel is not an abnormal pixel. Therefore, since the determination range is set in consideration of the variation of the determination standard deviation, it is possible to reduce the influence of the variation of the determination standard deviation and detect the abnormal pixel position with high accuracy. Furthermore, since the amount of misalignment due to environmental temperature tends to be large at the end of the reading unit, using only the first block discrimination data that is output first, the detection accuracy of the abnormal pixel position is faster. A high discrimination standard deviation can be calculated.

[Correspondence between embodiment and invention]
The image reading device 1 and the gray reference plate 34 are examples of the image reading device and the gray reference member of the present invention. The reading unit 24 and the AFE 45 are examples of the reading unit of the present invention. The device control unit 44 is an example of a correction unit of the present invention. The flash PROM 43 and the CPU 40 are examples of the storage unit and the control unit of the present invention. The black data BK1 acquisition M5 is an example of a first black data acquisition process of the present invention. The gray data LGR1 acquisition MA1 is an example of the first gray data acquisition process of the present invention. Gray light black difference data LGBdif1 calculation MA2 is an example of first gray light black difference calculation processing of the present invention. The black data BK2 acquisition R4 is an example of a second black data acquisition process of the present invention. The gray data LGR2 acquisition RA1 is an example of the second gray data acquisition process of the present invention. Gray light black difference data LGBdif2 calculation RA2 is an example of the second gray light black difference calculation process of the present invention. The discrimination data RT2 calculation RA3 is an example of the discrimination data calculation process of the present invention. The discrimination standard deviation LGSD calculation RA5 is an example of the standard deviation calculation process of the present invention. The read addition value LGAD1, the read subtraction value LGAD2 calculation RA6, and the threshold TH2 calculation RA7 are an example of the determination range setting process of the present invention. Processes RA8 to RA11 are examples of the position specifying process of the present invention. The process RA4 is an example of the average process of the present invention.

[Modification]
The present invention is not limited to this embodiment, and various modifications can be made without departing from the spirit of the present invention. An example of the modification will be described below.

  (1) The image reading apparatus 1 according to the present embodiment may be applied to a multi-function machine including a printer unit. In this embodiment, one reading unit 24 and one gray reference plate 34 are provided. However, in order to read both sides of the document GS, two reading units, two gray reference plates, May be provided.

  (2) In the present embodiment, the maintenance main process shown in FIG. 5 and the reading main process shown in FIG. 7 are all executed by the CPU 40. However, the present invention is not limited to this configuration. For example, part of the maintenance main processes M3 to M9 and M12 to M16 and part of the reading main processes R2 to R8 may be executed by the image processing unit 46, the device control unit 44, or the AFE 45. Alternatively, the maintenance main process may be executed by an external device independent of the image reading device 1, such as a computer.

  (3) In this embodiment, the color mode has been described in the maintenance main process shown in FIG. 5 and the reading main process shown in FIG. 7, but a mono mode may be used. In the color mode, one color is one line, but in the mono mode, one color is one line. In the case of the color mode, in the process RA6, the average value AVE2 is multiplied by 4%, 5%, 6.5%, 8.5%, 10.5%, and 13% to obtain the read addition value LGAD1, and The reading subtraction value LGAD2 was calculated, but in the case of the mono mode, reading is performed by multiplying the average value AVE2 by 4.5%, 5.5%, 7%, 9%, 11%, and 13.5%. The addition value LGAD1 and the read subtraction value LGAD2 may be calculated.

  (4) In this embodiment, the discrimination standard deviation LGSD is determined using five values of 0.01, 0.02, 0.03, 0.04, and 0.05. Alternatively, the discriminant standard deviation LGSD may be determined by using more than five values or by using less than five values.

DESCRIPTION OF SYMBOLS 1 ... Image reading device, 5 ... Operation part, 24 ... Reading part, 30 ... Light source, 31 ... Light receiving part, 33 ... Photoelectric conversion element, 40 ... CPU, 43 ... Flash PROM, 44 ... Device control part, 45 ... AFE, 46. Image processing unit

Claims (3)

A gray reference member that is arranged in a conveyance path through which the document is conveyed and has a lower reflectance than white,
A reading unit that irradiates the original with light when the original passes through the gray reference member and reads an image of the original for each pixel in units of lines;
A correction unit that corrects shading of image data read by the reading unit based on correction data;
A storage unit;
A controller that executes pre-reading processing after executing pre-processing, and
The controller is
As the pre-processing,
A first black data acquisition process for acquiring first black data of each pixel in one line output from the reading unit when the reading unit is turned off and reads;
First gray data acquisition processing for acquiring first gray data of each pixel in one line output from the reading unit when the reading unit irradiates and reads the gray reference member;
First gray data difference of each pixel in one line is calculated by subtracting the first black data from the first gray data in each pixel in one line, and is stored in the storage unit. Gray light black difference calculation processing, and
As the pre-reading process,
A second black data acquisition process for acquiring second black data of each pixel in one line output from the reading unit when the reading unit is turned off and reads;
A second gray data acquisition process for acquiring second gray data of each pixel in one line output from the reading unit when the reading unit irradiates and reads the gray reference member;
A second gray light black difference calculation process for subtracting the second black data from the second gray data for each pixel in one line to calculate second gray light black difference data for each pixel in one line; ,
A discrimination data calculation process for calculating discrimination data for each pixel in one line by dividing the second gray light black difference data by the first gray light black difference data in each pixel in one line;
A standard deviation calculation process for calculating a standard deviation of the discrimination data and calculating a discrimination standard deviation;
A determination range setting process for setting a wider determination range indicating a normal value range of the determination data as the determination standard deviation is larger;
And a position specifying process for specifying a pixel position of a pixel whose discrimination data is not within the discrimination range as an abnormal pixel position. The determination range setting process includes an average process for calculating an average value of the determination data as a determination average value,
In the determination range setting process, when the determination standard deviation is less than or equal to a first predetermined value, the upper limit of the determination range is a value obtained by adding 4% to the determination average value, and the lower limit of the determination range is the determination average value. Set the range to be a value obtained by discounting 4% to the discrimination range,
When the discriminant standard deviation is larger than the first predetermined value and less than or equal to the second predetermined value, the upper limit of the discriminating range is set to a value obtained by adding 5% to the discriminating average value, and the lower limit of the discriminating range is set to the discriminant average. A range that is 5% discounted on the value is set as the discrimination range,
When the discrimination standard deviation is greater than a second predetermined value and less than or equal to a third predetermined value, the upper limit of the discrimination range is set to a value that is 6.5% higher than the discrimination average value, and the lower limit of the discrimination range is A range that is 6.5% discounted to the discrimination average value is set as the discrimination range,
When the discriminant standard deviation is greater than a third predetermined value and less than or equal to a fourth predetermined value, the upper limit of the discriminating range is 8.5% higher than the discriminating average value, and the lower limit of the discriminating range is A range that is 8.5% less than the discrimination average value is set as the discrimination range,
When the discrimination standard deviation is larger than a fourth predetermined value and not more than a fifth predetermined value, the upper limit of the discrimination range is set to a value obtained by adding 10.5% to the discrimination average value, and the lower limit of the discrimination range is A range that is 10.5% discounted to the discrimination average value is set as the discrimination range,
When the discrimination standard deviation is larger than a fifth predetermined value, the upper limit of the discrimination range is a value obtained by adding 13% to the discrimination average value, and the lower limit of the discrimination range is reduced by 13% to the discrimination average value The image reading apparatus according to claim 1, wherein the range is set as the determination range. The reading unit includes a light source and a large number of photoelectric conversion elements divided into a plurality of blocks,
The standard deviation calculation processing calculates the standard deviation of the discrimination by calculating the standard deviation of the discrimination data of all pixels existing in a block that is output first in one line among the plurality of blocks. The image reading apparatus according to claim 1 or 2.

Images