Image reading device, image forming apparatus, and sampling timing setting method

Abstract

To provide an image reading device, an image forming apparatus, and a sampling timing setting method that can prevent a reduction in the quality of read image data.SOLUTION: An image forming apparatus 100 comprises: an image reading unit 2 that has a CCD, and outputs digital signals corresponding to an object to be read; a temporary setting processing unit 74 that temporarily sets a plurality of timings to sampling timings of analog signals that are sequentially output from the CCD; a first acquisition processing unit 75 that acquires, by using the image reading unit 2, the plurality of digital signals corresponding to a plurality of reference images different from each other in density, every time the sampling timing is temporarily set; and a setting processing unit 77 that sets the sampling timings on the basis of the plurality of digital signals acquired by the first acquisition processing unit 75 corresponding respectively to the temporary sampling timings.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image reading apparatus, an image forming apparatus, and a sampling timing setting method. [Background technology]

[0002] In an image reading device such as a scanner, an analog signal corresponding to light emitted from a light source and reflected by a reading target such as a document is converted into a digital signal (read image data) output from a photoelectric conversion unit such as a CCD (Charge Coupled Device). Also, an image reading device that adjusts the sampling timing of the analog signal based on the read image data read from a white reference board is known as a related technique (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-9018 Summary of the Invention [Problem to be solved by the invention]

[0004] In the image reading device, depending on the sampling timing, moire may occur in the read image data. Also, depending on the sampling timing, the color of the read image data may differ from the color of the object to be read. However, the image reading device according to the above-mentioned related art cannot suppress deterioration of the quality of the read image data, such as the occurrence of moire or changes in color.

[0005] An object of the present invention is to provide an image reading apparatus, an image forming apparatus, and a sampling timing setting method that are capable of suppressing deterioration in the quality of read image data. [Means for solving the problem]

[0006] An image reading device according to one aspect of the present invention includes an image reading unit, a provisional setting processing unit, a first acquisition processing unit, a second acquisition processing unit, and a setting processing unit. The image reading unit has a photoelectric conversion unit that outputs an analog signal corresponding to light emitted from a light source and reflected by a reading target, and outputs a digital signal corresponding to the reading target. The provisional setting processing unit provisionally sets a plurality of predetermined timings in sequence as sampling timings of the analog signals. The first acquisition processing unit acquires a plurality of the digital signals corresponding to a plurality of reference images having different densities using the image reading unit each time the sampling timing is provisionally set by the provisional setting processing unit. The second acquisition processing unit acquires specific data including either or both of a correlation coefficient between the density of the reference image and the signal value of the digital signal and a specific value related to a fluctuation range of the digital signal along a main scanning direction, based on the plurality of the digital signals acquired by the first acquisition processing unit. The setting processing unit sets the sampling timing based on the specific data for each provisional sampling timing acquired by the second acquisition processing unit.

[0007] An image forming apparatus according to another aspect of the present invention includes the image reading device described above, and forms an image based on the digital signal output by the image reading device.

[0008] A sampling timing setting method according to another aspect of the present invention is executed by an image reading device having a photoelectric conversion unit that outputs an analog signal corresponding to light emitted from a light source and reflected by a reading target, and an image reading unit that outputs a digital signal corresponding to the reading target, and includes a provisional setting step, a first acquisition step, a second acquisition step, and a setting step. In the provisional setting step, a plurality of predetermined timings are provisionally set as the sampling timings of the analog signals in sequence. In the first acquisition step, the image reading unit is used to acquire a plurality of the digital signals corresponding to a plurality of reference images having different densities each time the sampling timing is provisionally set by the provisional setting step. In the second acquisition step, specific data including either or both of a correlation coefficient between the density of the reference image and the signal value of the digital signal and a specific value related to the fluctuation range of the digital signal along the main scanning direction is acquired based on the plurality of the digital signals acquired by the first acquisition step. In the setting step, the sampling timing is set based on the specific data for each of the provisional sampling timings acquired by the second acquisition step. Effect of the Invention

[0009] According to the present invention, it is possible to suppress deterioration in the quality of read image data. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing a system configuration of the image forming apparatus according to the embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram showing the configuration of the ADF and image reading unit of the image forming apparatus according to the embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the configuration of a color reference plate of the image forming apparatus according to the embodiment of the present invention. [Diagram 5]FIG. 5 is a diagram showing the configuration of a reading control unit of the image forming apparatus according to the embodiment of the present invention. [Figure 6] FIG. 6 is a flowchart showing an example of a sampling timing setting process executed in the image forming apparatus according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the following embodiment is an example of the present invention, and is not intended to limit the technical scope of the present invention.

[0012] [Configuration of image forming apparatus 100] First, the configuration of an image forming apparatus 100 according to an embodiment of the present invention will be described with reference to Fig. 1 to Fig. 3. Fig. 1 is a cross-sectional view showing the configuration of the image forming apparatus 100. Fig. 3 is a cross-sectional view showing the configurations of the ADF 1 and the image reading unit 2.

[0013] The image forming apparatus 100 is a multifunction machine having multiple functions such as a scanning function for reading an image of an original document, a printing function for forming an image on a sheet based on image data, a fax function, a copy function, etc. The image forming apparatus 100 may be a fax machine, a copy machine, etc.

[0014] 1 and 2, an image forming apparatus 100 includes an ADF (Auto Document Feeder) 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, an operation display unit 5, a storage unit 6, and a control unit 7. An apparatus including the image reading unit 2 and the control unit 7 is an example of the image reading apparatus of the present invention.

[0015] The ADF 1 transports an original document whose image is to be read by the image reading unit 2. Specifically, as shown in Fig. 1 and Fig. 3, the ADF 1 includes an original document placement unit 11, an original document transport path 12, a plurality of transport rollers 13, an original document guide 14, and a paper discharge unit 15. The ADF 1 is also provided so as to be able to change its position between a closed position in which it covers an original document table 21 (described later) and an open position in which it exposes the original document table 21, and also serves as an original document cover for an original document placed on a first contact glass 211 of the original document table 21.

[0016] In the ADF 1, each transport roller 13 rotates by receiving a rotational driving force supplied from a drive motor (not shown). As a result, the document placed on the document placement unit 11 is transported along a document transport path 12 formed inside the ADF 1. The document transported along the document transport path 12 is guided by a document guide 14 to a reading position P1 (see FIG. 3) on the second contact glass 212 of the document table 21, and then discharged to the paper discharge unit 15.

[0017] The image reading unit 2 realizes the scanning function.

[0018] The image forming unit 3 realizes the printing function. For example, the image forming unit 3 forms an image on a sheet by an electrophotographic method. For example, the image forming unit 3 includes a photosensitive drum, a charging roller, an optical scanning device, a developing device, a transfer roller, a cleaning device, a fixing device, and a paper discharge tray. The image forming unit 3 forms an image based on the read image data output by the image reading unit 2.

[0019] The paper feed unit 4 supplies sheets to the image forming unit 3. For example, the paper feed unit 4 includes a paper feed cassette, a sheet transport path, and a plurality of transport rollers.

[0020] The operation display unit 5 is a user interface of the image forming apparatus 100. The operation display unit 5 includes a display unit and an operation unit. The display unit displays various information in response to control instructions from the control unit 7. For example, the display unit is a liquid crystal display. The operation unit inputs various information to the control unit 7 in response to user operations. For example, the operation unit is a touch panel.

[0021] The storage unit 6 is a non-volatile storage device. For example, the storage unit 6 is a flash memory. The storage unit 6 may be a solid state drive (SSD) or a hard disk drive (HDD).

[0022] The control unit 7 performs overall control of the image forming apparatus 100. As shown in FIG. 2, the control unit 7 includes a CPU 71, a ROM 72, and a RAM 73. The CPU 71 is a processor that executes various arithmetic processing. The ROM 72 is a non-volatile storage device in which information such as a control program for causing the CPU 71 to execute various processing is stored in advance. The RAM 73 is a volatile or non-volatile storage device used as a temporary storage memory (work area) for various processing executed by the CPU 71. The CPU 71 executes the various control programs stored in the ROM 72. In this way, the control unit 7 performs overall control of the image forming apparatus 100.

[0023] The control unit 7 may be configured with an electronic circuit such as an application specific integrated circuit (ASIC). The control unit 7 may be a control unit provided separately from a main control unit that performs overall control of the image forming apparatus 100.

[0024] [Configuration of image reading unit 2] Next, the configuration of the image reading unit 2 will be described with reference to Figs. 1 to 5. Here, Fig. 4 is a view of the color reference plate 213 as viewed from below. Also, Fig. 5 is a block diagram showing the configuration of the reading control unit 27. Note that in Fig. 4, the first reference image 214 and the second reference image 215 are each hatched. Also, in Fig. 5, the reading control unit 27 and the AFE circuit 32 are shown by dashed lines. Also, in Fig. 5, the modulated clock signal output from the SSCG 31 is shown by a dashed line with an arrow. Also, in Fig. 5, the transmission path of the image signal output from the CCD 26 is shown by a solid line with an arrow.

[0025] As shown in FIG. 1, the image reading section 2 includes a document table 21, a reading unit 22, a mirror 23, a mirror 24, an optical lens 25, a CCD (Charge Coupled Device) 26, and a reading control section 27.

[0026] The document table 21 is provided on the upper part of the housing of the image forming apparatus 100. As shown in Fig. 1 and Fig. 3, the document table 21 includes a first contact glass 211, a second contact glass 212, and a color reference plate 213. An original is placed on the first contact glass 211. The second contact glass 212 is provided at a position relative to the document table 21 facing the document guide 14 of the ADF 1 in the closed position.

[0027] As shown in Fig. 3, the color reference plate 213 is provided on the upper surface of the end of the first contact glass 211 facing the second contact glass 212. As shown in Fig. 4, the color reference plate 213 is a flat member that is elongated in the main scanning direction D2 (see Fig. 4). The color reference plate 213 has a plurality of reference images on the surface facing the first contact glass 211. Specifically, the color reference plate 213 has a first reference image 214 and a plurality of second reference images 215 (215A to 215H).

[0028] 4, the first reference image 214 is a strip-shaped image that is long in the main scanning direction D2. For example, the first reference image 214 is an image having a color represented by "N9.0" in the Munsell color system.

[0029] As shown in FIG. 4, each of the second reference images 215 is a strip-shaped image elongated in the main scanning direction D2. Each of the second reference images 215 has a density different from that of the first reference image 214. The second reference images 215 have different densities from each other. Specifically, the second reference image 215A is an image having a color represented by "N1.0" in the Munsell color system. The second reference image 215B is an image having a color represented by "N2.0" in the Munsell color system. The second reference image 215C is an image having a color represented by "N3.0" in the Munsell color system. The second reference image 215D is an image having a color represented by "N4.0" in the Munsell color system. The second reference image 215E is an image having a color represented by "N5.0" in the Munsell color system. The second reference image 215F is an image having a color represented by "N6.0" in the Munsell color system. The second reference image 215G is an image having a color represented by "N7.0" in the Munsell color system. The second reference image 215H is an image having a color represented by "N8.0" in the Munsell color system.

[0030] The first reference image 214 is the image with the lowest density among the multiple reference images included in the color reference plate 213. The formation area of ​​the first reference image 214 on the color reference plate 213 functions as a white reference plate. The second reference image 215A is the image with the highest density among the multiple reference images included in the color reference plate 213. The first reference image 214 and the multiple second reference images 215 are examples of the multiple reference images of the present invention. Moreover, the color reference plate 213 is an example of the reference image portion of the present invention. The number of the reference images included in the color reference plate 213 does not have to be limited to nine. Moreover, the color of each of the reference images included in the color reference plate 213 does not have to be limited to an achromatic color.

[0031] The image reading unit 2 can read an image from a document by one of two reading methods. Specifically, the image reading unit 2 can read an image from a document placed on the first contact glass 211. The image reading unit 2 can also read an image from a document transported by the ADF 1.

[0032] The reading unit 22 is provided below the first contact glass 211. The reading unit 22 is configured to be movable in the sub-scanning direction D1 shown in FIG. 1 by a moving mechanism (not shown). As shown in FIG. 1, the reading unit 22 includes a light source 221 and a mirror 222. The light source 221 includes a plurality of white LEDs arranged along a main scanning direction D2 (see FIG. 4) perpendicular to the sub-scanning direction D1. The light source 221 emits one line of white light in the main scanning direction D2 toward the document table 21. The light emitted from the light source 221 passes through the first contact glass 211 or the second contact glass 212 and is reflected by the reading object. The reading object includes the document placed on the first contact glass 211, the document transported by the ADF 1, and the color reference plate 213. The mirror 222 reflects the light emitted from the light source 221 and reflected by the reading object to the mirror 23.

[0033] In the image reading section 2, when an image is read from a document placed on the first contact glass 211, the reading unit 22 is moved to a position below the first contact glass 211. As a result, light emitted from the light source 221 passes through the first contact glass 211 and is reflected by the document placed on the first contact glass 211. In addition, the reading unit 22 is moved in the sub-scanning direction D1. As a result, the light irradiated onto the document by the light source 221 is scanned in the sub-scanning direction D1.

[0034] Furthermore, in the image reading section 2, when an image is read from a document transported by the ADF 1, the reading unit 22 is moved to a position below the second contact glass 212. Specifically, the reading unit 22 is moved to a position where the light emitted from the light source 221 passes through the reading position P1 (see FIG. 2). As a result, the light emitted from the light source 221 passes through the second contact glass 212 and is reflected by the document transported by the ADF 1 passing through the reading position P1.

[0035] Furthermore, in the image reading section 2, when an image is read from the color reference plate 213, the reading unit 22 is moved to a position below the color reference plate 213. As a result, light emitted from the light source 221 passes through the first contact glass 211 and is reflected by the color reference plate 213 provided on the first contact glass 211.

[0036] The mirror 23 reflects the light reflected by the mirror 222 of the reading unit 22 to the mirror 24. The mirror 24 reflects the light reflected by the mirror 23 to the optical lens 25. The optical lens 25 collects the light reflected by the mirror 24 and makes it incident on the CCD 26.

[0037] The CCD 26 is an image sensor having a plurality of photoelectric conversion elements arranged along the main scanning direction D2 (see FIG. 4). The CCD 26 outputs an analog signal corresponding to light emitted from a light source 221 and reflected by the object to be read. The analog signal output from the CCD 26 is input to a reading control unit 27. The CCD 26 is an example of a photoelectric conversion unit of the present invention. The photoelectric conversion unit of the present invention may be a CIS (Contact Image Sensor).

[0038] As shown in FIG. 5, the read control unit 27 includes an SSCG (Spread Spectrum Clock Generator) 31, an AFE (Analog Front End) circuit 32, and a DSP (Digital Signal Processor) 33.

[0039] The SSCG 31 modulates a predetermined clock signal output from an oscillator (not shown) by spectrum spreading. The SSCG 31 outputs a modulated clock signal obtained by modulating the clock signal by spectrum spreading. The modulated clock signal output from the SSCG 31 is input to the CCD 26, the AFE circuit 32, and the DSP 33. By providing the SSCG 31, the peak level of electromagnetic radiation (EMI) generated in the image reading unit 2 is reduced.

[0040] The CCD 26 is driven based on the modulated clock signal output from the SSCG 31. Specifically, the CCD 26 outputs the analog signal corresponding to one line of the read image at a cycle based on the modulated clock signal output from the SSCG 31.

[0041] The AFE circuit 32 is a circuit that processes the analog signal output from the CCD 26. The AFE circuit 32 processes the analog signal output from the CCD 26 at a cycle based on the modulated clock signal output from the SSCG 31.

[0042] As shown in FIG. 5, the AFE circuit 32 includes an S / H (sample / hold) circuit 41, an amplifier circuit 42, and an ADC (analog-to-digital converter) 43.

[0043] The S / H circuit 41 samples the signal level of the analog signal at a sampling period based on the modulated clock signal, and outputs a sampling signal of the sampled signal level.

[0044] The amplifier circuit 42 amplifies the sampling signal output from the S / H circuit 41 .

[0045] The ADC 43 converts the amplified sampling signal (analog signal) output from the amplifier circuit 42 into a digital signal.

[0046] The AFE circuit 32 outputs the sampling signal converted into a digital signal by the ADC 43 as the read image data.

[0047] The DSP 33 executes various image processing operations on the read image data output from the AFE circuit 32. The DSP 33 outputs the read image data after image processing at a cycle based on the modulated clock signal output from the SSCG 31. As a result, the read image data (the digital signal) corresponding to the reading target is output from the image reading unit 2. The read image data output from the DSP 33 is stored in the storage unit 6.

[0048] Incidentally, an image reading device that adjusts the sampling timing of the analog signal by the S / H circuit 41 based on the read image data read from a white reference plate is known as a related art.

[0049] Here, in the conventional image reading device, depending on the sampling timing, moire may occur in the read image data. Also, in the conventional image reading device, depending on the sampling timing, the color of the read image data may differ from the color of the read target. However, the image reading device according to the related art cannot suppress deterioration of the quality of the read image data, such as the occurrence of moire or change in color.

[0050] In contrast, in the image forming apparatus 100 according to the embodiment of the present invention, it is possible to suppress the deterioration of the quality of the read image data, as will be described below.

[0051] [Configuration of control unit 7] Next, the configuration of the control unit 7 will be described with reference to FIG.

[0052] As shown in FIG. 2, the control unit 7 includes a provisional setting processing unit 74, a first acquisition processing unit 75, a second acquisition processing unit 76, and a setting processing unit 77.

[0053] Specifically, a sampling timing setting program for making the CPU 71 function as each of the above-mentioned processing units is stored in advance in the ROM 72 of the control unit 7. The CPU 71 functions as each of the above-mentioned processing units by executing the sampling timing setting program stored in the ROM 72. Note that some or all of the processing units included in the control unit 7 may be configured with electronic circuits. The sampling timing setting program may also be a program for making a plurality of processors function as each of the processing units included in the control unit 7.

[0054] The provisional setting processing unit 74 provisionally sets a plurality of predetermined candidate timings (one example of a plurality of timings of the present invention) in sequence as the sampling timing of the analog signal.

[0055] The first acquisition processing unit 75 acquires a plurality of the digital signals corresponding to the plurality of reference images (a first reference image 214 and a plurality of second reference images 215) using the image reading unit 2 each time the sampling timing is provisionally set by the provisional setting processing unit 74.

[0056] Specifically, the first acquisition processing unit 75 acquires the plurality of digital signals from the color reference plate 213 .

[0057] For example, the first acquisition processing unit 75 acquires the digital signals corresponding to the reference images (the first reference image 214 and the second reference images 215) in the following procedure.

[0058] First, the first acquisition processing unit 75 acquires the digital signal corresponding to the first reference image 214. That is, the first acquisition processing unit 75 reads the image of the first reference image 214 using the image reading unit 2.

[0059] Next, the first acquisition processing unit 75 executes AGC (Auto Gain Control) to adjust the amplification factor of the amplifier circuit 42 based on the digital signal corresponding to the acquired first reference image 214. This adjusts the amplification factor so that the signal value of the digital signal indicating the image read from the first reference image 214 becomes a predetermined reference value.

[0060] After performing the AGC, the first acquisition processing unit 75 acquires a plurality of the digital signals corresponding to the plurality of second reference images 215. That is, the first acquisition processing unit 75 reads the image of each of the second reference images 215 using the image reading unit 2.

[0061] The first acquisition processing unit 75 may acquire the digital signals corresponding to the second reference images 215 without executing the AGC.

[0062] Further, the first acquisition processing unit 75 may acquire the plurality of digital signals from a reference original including a first reference image 214 and a plurality of second reference images 215, instead of the color reference plate 213. In this case, the image forming apparatus 100 does not need to include the color reference plate 213.

[0063] The second acquisition processing unit 76 acquires predetermined specific data based on the plurality of digital signals acquired by the first acquisition processing unit 75 .

[0064] Here, the specific data includes a correlation coefficient between the density of the reference image and the signal value of the digital signal.

[0065] For example, the second acquisition processing unit 76 acquires the correlation coefficient based on three or more of the digital signals acquired by the first acquisition processing unit 75.

[0066] For example, the second acquisition processing unit 76 acquires the correlation coefficient based on a combination of the density of the second reference image 215 corresponding to each second reference image 215 and the signal value of the digital signal acquired by the first acquisition processing unit 75.

[0067] The specific data also includes a first specific value related to the fluctuation range of the digital signal along the main scanning direction D2 (see FIG. 4).

[0068] For example, the second acquisition processing unit 76 acquires the first specific value based on the digital signal corresponding to the reference image (second reference image 215A) having the highest density among the plurality of digital signals acquired by the first acquisition processing unit 75. The reason why the reference image having the highest density is used to acquire the first specific value is that the higher the density of the reference image, the more likely moire is to appear.

[0069] For example, the second acquisition processing unit 76 performs FFT (Fast Fourier Transform) analysis on the digital signal for one line in the main scanning direction D2 corresponding to the second reference image 215A. Then, the second acquisition processing unit 76 acquires, as the first specific value, the maximum value of the peak value of the amplitude in a region where the frequency is greater than zero in a graph acquired by the FFT analysis, in which the horizontal axis indicates frequency and the vertical axis indicates amplitude. Note that the second acquisition processing unit 76 may acquire, as the first specific value, the difference between the maximum value and the minimum value in the digital signal for one line in the main scanning direction D2 corresponding to the second reference image 215A.

[0070] The specific data also includes a second specific value related to the signal value of the digital signal corresponding to the reference image (first reference image 214) having the lowest density among the plurality of digital signals acquired by the first acquisition processing unit 75. For example, the second specific value is the amplification factor after the execution of the AGC. The second specific value may be the signal value of the digital signal corresponding to the first reference image 214. The specific data may also include two types of the second specific values ​​(the amplification factor after the execution of the AGC, and the signal value of the digital signal corresponding to the first reference image 214).

[0071] The specific data may include only one of the correlation coefficient and the first specific value, and may not include the second specific value.

[0072] The setting processing unit 77 sets the sampling timing based on the specific data for each of the tentative sampling timings acquired by the second acquisition processing unit 76.

[0073] For example, the setting processing unit 77 calculates the spatial distance between the specific data and the predetermined target data for each tentative sampling timing according to the following formula (1). In formula (1), "X" indicates the spatial distance. In formula (1), "A1" indicates the target value of the correlation coefficient included in the target data. In formula (1), "A2" indicates the target value of the first specific value included in the target data. In formula (1), "A3" indicates the target value of the second specific value included in the target data. In formula (1), "B1" indicates the correlation coefficient included in the specific data. In formula (1), "B2" indicates the first specific value included in the specific data. In formula (1), "B3" indicates the second specific value included in the specific data.

[0074] X=((A1-B1) 2 +(A2-B2) 2 +(A3-B3) 2 ) 1 / 2 (1)

[0075] Then, the setting processing unit 77 finally sets the provisional sampling timing corresponding to the smallest spatial distance among the spatial distances corresponding to the provisional sampling timings as the sampling timing.

[0076] The setting processing unit 77 may set the sampling timing based on one or more of the specific data that satisfy a predetermined specific condition among the specific data for each tentative sampling timing acquired by the second acquisition processing unit 76. In other words, the setting processing unit 77 may set the sampling timing by excluding the specific data that does not satisfy the specific condition. For example, the specific condition includes that the correlation coefficient exceeds a predetermined first allowable value. Also, the specific condition may include that the first specific value is equal to or less than a predetermined second allowable value.

[0077] The setting processing unit 77 may calculate the spatial distance between the specific data and the target data for each of the tentative sampling timings according to the following formula (2) instead of the above formula (1). In formula (2), "A3" indicates the target value of the amplification factor after the execution of the AGC included in the target data. In formula (2), "A4" indicates the target value of the signal value of the digital signal corresponding to the first reference image 214 included in the target data. In formula (2), "B3" indicates the amplification factor after the execution of the AGC included in the specific data. In formula (2), "B4" indicates the signal value of the digital signal corresponding to the first reference image 214 included in the specific data. This makes it possible to set the sampling timing that can further improve the quality of the read image data even if the signal value of the digital signal corresponding to the first reference image 214 does not become the reference value even if the AGC is executed.

[0078] X=((A1-B1) 2 +(A2-B2) 2 +(A3-B3) 2 +(A4-B4) 2 ) 1 / 2 (2)

[0079] [Sampling timing setting process] 6, the sampling timing setting method of the present invention will be described together with an example of the procedure of the sampling timing setting process executed by the control unit 7 in the image forming apparatus 100. Here, steps S11, S12, etc. indicate the numbers of the processing procedures (steps) executed by the control unit 7. For example, the sampling timing setting process is executed when a user operation to instruct execution of the sampling timing setting process is accepted on the operation display unit 5.

[0080] <Step S11> First, in step S11, the control unit 7 provisionally sets, as the sampling timing, any one of the plurality of candidate timings that has not been provisionally set as the sampling timing after the start of the sampling timing setting process.

[0081] <Step S12> In step S12, the control unit 7 uses the image reading unit 2 to read the image of the first reference image 214 included in the color reference plate 213. That is, the control unit 7 obtains the digital signal corresponding to the first reference image 214.

[0082] <Step S13> In step S13, the control unit 7 executes the AGC based on the digital signal corresponding to the first reference image 214 acquired by the process of step S12.

[0083] <Step S14> In step S14, the control unit 7 uses the image reading unit 2 to read the images of the second reference images 215 included in the color reference board 213. That is, the control unit 7 obtains the eight digital signals corresponding to the eight second reference images 215. Here, the processes from step S12 to step S14 are an example of a first obtaining step of the present invention, and are executed by the first obtaining processing unit 75 of the control unit 7.

[0084] <Step S15> In step S15, the control unit 7 acquires the specific data including the correlation coefficient, the first specific value, and the second specific value. Here, the process of step S15 is an example of a second acquisition step of the present invention, and is executed by the second acquisition processing unit 76 of the control unit 7.

[0085] Specifically, the control unit 7 obtains the correlation coefficient based on a combination of the density of the second reference image 215 corresponding to each second reference image 215 and the signal value of the digital signal obtained by the process of step S14.

[0086] The control unit 7 also performs the FFT analysis on the digital signal for one line in the main scanning direction D2 corresponding to the second reference image 215A acquired by the process of step S14. Then, the control unit 7 acquires, as the first specific value, the maximum value of the peak value of the amplitude in a region where the frequency is greater than zero in a graph acquired by the FFT analysis, in which the horizontal axis indicates frequency and the vertical axis indicates amplitude.

[0087] Moreover, the control unit 7 acquires the amplification factor after the process of step S13 is executed as the second specific value.

[0088] <Step S16> In step S16, the control unit 7 calculates the spatial distance between the specific data acquired by the process in step S15 and the target data.

[0089] Specifically, the control unit 7 calculates the spatial distance according to the above-mentioned formula (1).

[0090] <Step S17> In step S17, the control unit 7 determines whether or not all the candidate timings have been provisionally set as the sampling timings.

[0091] Here, when the control unit 7 determines that all the candidate timings have been provisionally set as the sampling timings (Yes side of S17), it shifts the process to step S18. On the other hand, when all the candidate timings have not been provisionally set as the sampling timings (No side of S17), the control unit 7 shifts the process to step S11. Here, the processes of step S11 and step S17 are an example of a provisional setting step of the present invention, and are executed by the provisional setting processing unit 74 of the control unit 7.

[0092] <Step S18> In step S18, the control unit 7 finally sets the provisional sampling timing corresponding to the smallest spatial distance among the spatial distances calculated by the process of step S16 as the sampling timing. Here, the processes of steps S16 and S18 are an example of a setting step of the present invention, and are executed by the setting processing unit 77 of the control unit 7.

[0093] Thus, in the image forming apparatus 100, the specific data includes the correlation coefficient and the first specific value. Also, in the image forming apparatus 100, the sampling timing is set based on the specific data for each of the tentative sampling timings. This makes it possible to set the sampling timing taking into consideration the occurrence of moire and changes in color tone. Therefore, it is possible to suppress deterioration in the quality of the read image data, compared to a configuration in which the sampling timing is adjusted based only on the read image data read from the first reference image 214.

[0094] [Notes on the invention] The following will provide an overview of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0095] <Appendix 1> an image reading device comprising: an image reading unit having a photoelectric conversion unit that outputs an analog signal corresponding to light emitted from a light source and reflected by an object to be read, and that outputs a digital signal corresponding to the object to be read; a provisional setting processing unit that provisionally sets a plurality of predetermined timings as sampling timings of the analog signal in sequence; a first acquisition processing unit that acquires a plurality of the digital signals corresponding to a plurality of reference images having different densities using the image reading unit each time the sampling timing is provisionally set by the provisional setting processing unit; a second acquisition processing unit that acquires specific data including either or both of a correlation coefficient between the density of the reference image and the signal value of the digital signal and a specific value related to the fluctuation range of the digital signal along the main scanning direction, based on the plurality of the digital signals acquired by the first acquisition processing unit; and a setting processing unit that sets the sampling timing based on the specific data for each provisional sampling timing acquired by the second acquisition processing unit.

[0096] <Appendix 2> The image reading device described in Appendix 1, wherein the specific data includes the correlation coefficient, the first acquisition processing unit acquires three or more of the digital signals corresponding to three or more of the reference images, and the second acquisition processing unit acquires the correlation coefficient based on the three or more of the digital signals acquired by the first acquisition processing unit.

[0097] <Appendix 3> The specific data includes the specific value, and the second acquisition processing unit acquires the specific value based on the digital signal corresponding to the reference image having the highest density among the multiple digital signals acquired by the first acquisition processing unit.

[0098] <Appendix 4> An image reading device as described in any of Appendices 1 to 3, wherein the specific value is a first specific value, and the specific data includes a second specific value relating to the signal value of the digital signal corresponding to the reference image having the lightest density among the multiple digital signals acquired by the first acquisition processing unit.

[0099] <Appendix 5> 5. The image reading device according to any one of claims 1 to 4, further comprising a reference image section including a plurality of the reference images, wherein the first acquisition processing section acquires a plurality of the digital signals from the reference image section.

[0100] <Appendix 6> 6. An image forming apparatus comprising the image reading apparatus according to any one of claims 1 to 5, and forming an image based on the digital signal output by the image reading apparatus.

[0101] <Appendix 7> a first acquisition step of acquiring a plurality of the digital signals corresponding to a plurality of reference images having different densities using the image reading unit each time the sampling timing is provisionally set by the provisional setting step; a second acquisition step of acquiring specific data including either or both of a correlation coefficient between the density of the reference image and the signal value of the digital signal and a specific value relating to the fluctuation range of the digital signal along the main scanning direction based on the plurality of the digital signals acquired by the first acquisition step; and a setting step of setting the sampling timing based on the specific data for each provisional sampling timing acquired by the second acquisition step. [Explanation of symbols]

[0102] 1 ADF 2 Image reading section 3. Image forming section 4 Paper feed section 5 Operation display section 6 Memory section 7 Control section 22 Reading unit 26 CCD 27 Reading control section 32 AFE circuit 33 DSP 41 S / H circuit 42 Amplification circuit 43 ADC 74 Provisional setting processing section 75 First acquisition processing unit 76 Second acquisition processing unit 77 Setting processing section 100 Image forming device 213 Color reference board 214 First Reference Image 215 Second Reference Image

Claims

1. an image reading unit that has a photoelectric conversion unit that outputs an analog signal corresponding to light emitted from a light source and reflected by an object to be read, and outputs a digital signal corresponding to the object to be read; a provisional setting processing unit that provisionally sets a plurality of predetermined timings as sampling timings of the analog signal in sequence; a first acquisition processing unit that acquires a plurality of the digital signals corresponding to a plurality of reference images having different densities using the image reading unit each time the sampling timing is provisionally set by the provisional setting processing unit; a second acquisition processing unit that acquires specific data including either or both of a correlation coefficient between a density of the reference image and a signal value of the digital signal and a specific value related to a fluctuation range of the digital signal along a main scanning direction, based on the plurality of digital signals acquired by the first acquisition processing unit; a setting processing unit that sets the sampling timing based on the specific data for each of the tentative sampling timings acquired by the second acquisition processing unit; An image reading device comprising:

2. The specific data includes the correlation coefficient, the first acquisition processing unit acquires three or more of the digital signals corresponding to three or more of the reference images; The second acquisition processing unit acquires the correlation coefficient based on three or more of the digital signals acquired by the first acquisition processing unit.

2. The image reading device according to claim 1.

3. The specific data includes the specific value, the second acquisition processing unit acquires the specific value based on the digital signal corresponding to the reference image having the highest density among the plurality of digital signals acquired by the first acquisition processing unit.

2. The image reading device according to claim 1.

4. The specific value is defined as a first specific value, the identification data includes a second identification value related to a signal value of the digital signal corresponding to the reference image having the lowest density among the plurality of digital signals acquired by the first acquisition processing unit; 2. The image reading device according to claim 1.

5. a reference image section including a plurality of the reference images; The first acquisition processing unit acquires a plurality of the digital signals from the reference image portion.

2. The image reading device according to claim 1.

6. The image reading device according to any one of claims 1 to 5 is provided, forming an image based on the digital signal output by the image reading device; Image forming device.

7. 1. A sampling timing setting method executed in an image reading device having an image reading unit that has a photoelectric conversion unit that outputs an analog signal corresponding to light emitted from a light source and reflected by an object to be read, and outputs a digital signal corresponding to the object to be read, comprising: a provisional setting step of provisionally setting a plurality of predetermined timings as sampling timings of the analog signal in sequence; a first acquisition step of acquiring a plurality of the digital signals corresponding to a plurality of reference images having different densities using the image reading unit each time the sampling timing is provisionally set by the provisional setting step; a second acquisition step of acquiring specific data including either or both of a correlation coefficient between a density of the reference image and a signal value of the digital signal and a specific value related to a fluctuation range of the digital signal along a main scanning direction based on the plurality of digital signals acquired by the first acquisition step; a setting step of setting the sampling timing based on the specific data for each of the tentative sampling timings acquired by the second acquisition step; A sampling timing setting method including:

Images