JP6044126B2 - Image reading apparatus, image forming apparatus, gain adjustment method and program - Google Patents

Description

  The present invention amplifies an analog image signal obtained by optically reading and outputting a document, converts it to digital image data, and adjusts an amplification factor applied when the digital image data is amplified and output. The present invention relates to an apparatus, an image forming apparatus including the image reading apparatus, an amplification factor adjusting method, and a computer-readable program for executing the method.

  The scanner irradiates a document with light, guides reflected light from the document to a line sensor arranged in a sensor substrate (SBU), and performs photoelectric conversion by the line sensor to read the document. Specifically, as shown in FIG. 1, a document 12 is placed on the upper surface of the contact glass 1, and the document 12 is irradiated with light from a light source 2 disposed below the contact glass 1. The first traveling body 6 in which the light source 2 is disposed also includes a first mirror 3 that deflects reflected light from the document 12. The reflected light deflected by the first mirror 3 is reflected in the second traveling body 7. Is incident on. A second mirror 4 and a third mirror 5 are arranged on the second traveling body 7, and the reflected light from the first mirror 3 is sequentially deflected and incident on the imaging lens 8.

  The imaging lens 8 reduces and focuses the incident reflected light on the light receiving surface of the line sensor 9 on the SBU 10. The line sensor 9 performs photoelectric conversion and thereby reads a document. At the time of reading the document, the scanner 11 moves the first traveling body 6 at a constant speed in the sub-scanning direction A, which is the longitudinal direction of the document 12, and interlocks with the first traveling body 6 for the second traveling. The body 7 moves at half the speed of the first traveling body 6. FIG. 1 also shows a reference white plate 13 which is a white member of uniform density extending in the main scanning direction perpendicular to the sub-scanning direction A for obtaining correction data in shading correction or the like. Shading correction is an image correction process for removing density unevenness.

  As shown in FIG. 2, the SBU 10 performs photoelectric conversion by the line sensor 9, converts the obtained analog image signal into digital image data, and outputs the digital image data. Therefore, the SBU 10 includes a clamp circuit 14, a sample and hold (S / H) circuit 15, an analog programmable gain amplifier (APGA) 16, an analog / digital converter (ADC) 17, and a digital programmable gain amplifier. A signal processing IC having (DPGA) 18 is provided, and the analog image signal converted by the line sensor 9 is input into the signal processing IC through a buffer and AC coupling (not shown).

  The analog image signal input into the signal processing IC is corrected to a black level by the clamp circuit 14. The S / H circuit 15 performs sample-and-hold that keeps the level of the analog image signal that is constantly changing at a certain point in time for continuous image data. The APGA 16 amplifies to a voltage suitable for A / D conversion by the ADC 17 based on the set amplification factor (analog gain). After A / D conversion by the ADC 17, the DPGA 18 amplifies the digital image data based on the set amplification factor (digital gain), and outputs it to an image processing unit (not shown) in the subsequent stage. The gain is an amplification factor, for example, 2 times, 4 times, 8 times, or the like.

  When the power is turned on or when returning from the energy saving mode, the reference white plate 13 is read, and each gain is adjusted so that the read level becomes an arbitrary level (white target value) set in advance. A gain after adjustment is set in the APGA 16 and the DPGA 18. The reading level is composed of a plurality of pixel values in one line arranged in the main scanning direction. An example of the reading level of one line is as shown in FIG. In FIG. 3, the left side is the reading level of the reference white plate 13 before gain adjustment, and the right side is the reading level of the reference white plate 13 after gain adjustment. In the above gain adjustment, since the peak value with the highest reading level before gain adjustment is lower than the white target value, the gain is determined so that the peak value becomes the white target value.

  Usually, the gain exceeds a value of 1023 digits if the output digital image data is not saturated, for example, 10-bit data, taking into account the white target value, the variation in the light amount of the light source 2 and the variation in the density of the reference white plate 13. Not set to a value. In one example, it is set to 900 LSB or the like. LSB is a unit used synonymously with digit which is a quantization unit of A / D conversion.

  After the gain adjustment, the reference white plate 13 is read again, and it is confirmed that the read level (white level) is a value near the white target value, and that the gain is an appropriate value. If the value is not appropriate, adjust again. If there is an abnormality in the white level or gain due to the non-lighting of the light source 2 or a decrease in the amount of light, an error state is set.

  Conventionally, the following methods have been proposed as a method for determining the gain (see, for example, Patent Documents 1 and 2). In the method described in Patent Document 1, a reference white plate is read, a white level is detected therefrom, a peak level is detected from the white level detected in each scanning line, and processing such as averaging and multiple addition averaging is performed. The gain value is determined by obtaining a peak value and adjusting the peak value to the target output level. In the method described in Patent Document 2, the peak level in one line is detected, and the gain is determined so that the peak level is within the tolerance range of the white level target value.

  However, in the method described in Patent Document 1, since the peak level of each scanning line of the reference white plate is detected and averaged, the peak level such as white scratches including noise is not detected. In the method described in Patent Document 2, only the peak level in one line is detected, and the peak level such as white scratches including noise is not detected. When dust is attached to the reference white plate or when white scratches are present, a peak level protruding in the line image data when the reference white plate is read by the reflected light from the dust or white scratches is observed. When such dust and white scratches are present, it is difficult to accurately adjust the gain of the APGA 16 and DPGA 18. Further, the circuit for processing the read signal of the image continues to output the maximum value determined by the number of output bits and enters an error state. In this case, there is a possibility that the operation of the entire apparatus including this circuit is stopped.

  In view of this problem, when determining the analog gain in automatic gain adjustment, the peak level in one line is detected, the analog gain is determined so that the peak value becomes the maximum within the target value range, and the analog gain is determined. After setting, the maximum peak level in multiple lines is detected, and it is determined whether or not the maximum peak level has exceeded the target value. If so, the analog gain is lowered by one step, and the peak level in multiple lines is detected again. A technique has been proposed in which the digital gain is determined so that the peak level is closest to the target value, gain adjustment is optimally performed, output saturation is prevented, and an error state is avoided (see Patent Document 3).

  In the technique described in Patent Literature 3, when determining the analog gain, the analog gain is determined by comparing the peak value in one line with the target value. In such a method of determining the analog gain by detecting only the peak value in one line, there is a high possibility that the peak level of white scratches including noise cannot be detected. This is because a white defect is not always present in the one line of the reference white plate read to determine the analog gain. Therefore, when white scratches are read with the adjusted reference white plate, the target value is exceeded, and the analog gain must be lowered by one step with high probability.

  According to Patent Document 3, since this analog gain can only be lowered by one step, when the gain setting step is small, the white scratch reading level may exceed the target value when reading the reference white plate after gain adjustment. There is. In addition, when an analog gain error or the like is taken into consideration, the possibility further increases. For example, the gain error is −10% before the analog gain is lowered by one step, and the gain error is + 10% after being lowered by one step. When the target value is exceeded in this way, error processing is performed, and usually the gain adjustment is performed again, which affects the start-up time.

  Therefore, even if there are white scratches on the reference white plate, it is possible to set the optimum gain in a short time, and minimize the probability that the read level of the reference white plate after gain adjustment exceeds the target value to minimize the error state. It has been desired to provide an apparatus and a method that can avoid this and realize high-speed startup.

In view of the above-described problems, the present invention provides a reading unit that optically reads a document and outputs it as an analog image signal, a first amplification unit that amplifies the analog image signal based on a set first amplification factor, and an amplified signal. An image reading apparatus comprising: conversion means for converting an analog image signal into digital image data; and second amplification means for amplifying the converted digital image data based on a set second amplification factor,
A peak value which is the maximum level is detected from the signal levels of a plurality of lines of digital image data after the reference image is read by the reading unit and amplified by the first amplification unit and the second amplification unit, and the signal level for the plurality of lines Detecting processing means for calculating an average value by averaging
The first amplification factor is calculated and set in the first amplification unit so that the detected peak value becomes a predetermined target value, and the reference image is read by the reading unit after setting the peak value, the average value, and the first amplification factor. The image reading further includes a control unit that reads again and calculates the second amplification factor using the peak value and the calculated average value detected by the detection processing unit and the target value, and sets the second amplification factor in the second amplification unit. An apparatus is provided.

  By providing the image reading apparatus of the present invention, even when dust adheres to the reference white plate and there are white scratches, the optimum gain setting can be performed in a short time, and the white level after gain adjustment is achieved. The probability of exceeding the target value can be minimized, and an error state of the image reading apparatus can be avoided and high-speed startup can be realized.

The figure which illustrated the hardware constitutions of the image reading apparatus. The figure which showed the structural example of the sensor board | substrate with which the image reading apparatus shown in FIG. The figure which illustrated the reading level of the reference white board before and after gain adjustment. 1 is a diagram illustrating a hardware configuration of an image forming apparatus according to an embodiment. FIG. 5 is a diagram illustrating a configuration example of an image reading apparatus included in the image forming apparatus illustrated in FIG. 4. 6 is a flowchart showing the flow of a first embodiment of gain adjustment performed by the image reading apparatus shown in FIG. 5. The figure which illustrated each value which an image reading device holds. The figure which illustrated the reading level of the reference white board before and after gain adjustment when not considering an analog gain error. 6 is a flowchart showing a flow of a second embodiment of gain adjustment performed by the image reading apparatus shown in FIG. 5. 6 is a flowchart showing the flow of a third embodiment of gain adjustment performed by the image reading apparatus shown in FIG. 5.

  FIG. 4 is a diagram illustrating a configuration example of the image forming apparatus according to the present exemplary embodiment. The image forming apparatus includes an image reading apparatus that reads a document. Examples of the image forming apparatus include an MFP (Multi Function Peripheral), but may be a printer, a copying apparatus, a scanner apparatus, a FAX apparatus, or the like. Here, the image forming apparatus will be described as an MFP.

  The image forming apparatus is disposed adjacent to the main body 100, an image reading device 200 installed on the upper portion of the main body 100, an automatic document feeder (ADF) 300 mounted on the image reading device 200, and the main body 100. And a large-capacity paper feeding device 400 that can supply a large amount of paper, and a paper post-processing device 500 that is arranged adjacent to the main body 100 and performs post-processing such as discharging paper. Is done.

  The main body 100 includes an image writing unit 110, an image forming unit 120, a fixing unit 130, a duplex conveying unit 140, a paper feeding unit 150, a vertical conveying unit 160, and a manual feeding unit 170. In addition, it further includes a CPU for controlling the main body 100 (not shown), a memory for storing programs read and executed by the CPU, a storage device such as an HDD, and a network I / F for connecting to a network. Composed.

  The image writing unit 110 is configured by an exposure apparatus including a laser diode (LD) that is a light source. The image writing unit 110 modulates the LD based on the image information of the document read by the image reading device 200, and irradiates the surface of the photosensitive drum 121 with laser light by a scanning optical system such as a polygon mirror and an fθ lens. Laser writing is performed on the photosensitive drum 121.

  The image forming unit 120 includes an electrophotographic drum 121, a developing unit 122 provided along the outer periphery of the photosensitive drum 121, a transfer unit 123, a cleaning unit 124, and an electrophotographic unit such as a charging unit and a discharging unit (not shown). Includes imaging elements of the scheme. The developing unit 122 attaches toner to the photosensitive drum 121 on which laser writing has been performed, and forms a toner image (developed image) on the surface of the photosensitive drum 121. The transfer unit 123 transfers the toner image formed on the surface of the photosensitive drum 121 onto a sheet. The cleaning unit 124 removes the toner remaining on the photosensitive drum 121 after the transfer. The charging unit charges the photosensitive drum 121 to perform laser writing, and the neutralizing unit neutralizes the photosensitive drum 121 after transfer.

  The fixing unit 130 fixes the toner image transferred to the sheet by the transfer unit 123 to the sheet by applying temperature and pressure. The double-sided conveyance unit 140 is provided downstream of the fixing unit 130 in the paper conveyance direction, and includes a first switching claw 141 that switches the paper conveyance direction to the paper post-processing device 500 side or the double-sided conveyance unit 140 side, , The reverse conveyance path 142 guided by the switching claw 141, the image forming side conveyance path 143 that conveys the reversed paper again to the transfer unit 123 side, and the post-processing side conveyance that conveys the reversed paper to the paper post-processing apparatus 500. And a path 144. Further, the double-sided conveyance unit 140 includes a second switching claw 145 at a branch portion between the image forming side conveyance path 143 and the post-processing side conveyance path 144.

  In FIG. 4, the sheet feeding unit 150 includes four sheet feeding stages. The sheet feeding unit 150 pulls out the sheet stored in the sheet feeding stage selected by the pickup roller 401 and the sheet feeding roller and sends the sheet to the vertical conveyance unit 160. The vertical conveyance unit 160 conveys the paper fed from each paper feed stage to the registration roller 161 immediately before the upstream of the transfer unit 123 in the paper conveyance direction. The registration roller 161 feeds the paper to the transfer unit 123 in time with the leading edge of the toner image on the photosensitive drum 121. The manual feed unit 170 includes an openable and closable manual feed tray 171, and opens the manual feed tray 171 as necessary to supply paper from the manual feed tray 171. Even when a sheet is fed from the manual feed tray 171, the sheet is conveyed by the registration roller 161 at the conveyance timing.

  The large-capacity paper feeding device 400 stacks and supplies a large number of sheets of the same size. In the large-capacity paper feeding device 400, the bottom plate 402 rises as the paper is consumed, and the paper can always be picked up from the pickup roller 401. The paper fed from the pickup roller 401 is transported from the vertical transport unit 160 to the nip of the registration roller 161.

  The paper post-processing apparatus 500 performs predetermined processing such as punching, alignment, stapling, and sorting. In the embodiment shown in FIG. 4, a punch 501, a staple tray (alignment) 502, a stapler 503, and a shift tray 504 are provided to realize the above processing. For this reason, when the paper carried into the paper post-processing apparatus 500 from the main body 100 is punched, the punch 501 punches the paper one by one. Thereafter, if there is no particular processing, the paper is discharged to the proof tray 505, and when sorting, stacking, and sorting, the paper is discharged to the shift tray 504. In the embodiment shown in FIG. 4, the sorting is performed by reciprocating the shift tray 504 by a predetermined amount in the direction perpendicular to the sheet conveyance direction. In addition, sorting can be performed by moving the paper in a direction perpendicular to the paper transport direction on the paper transport path.

  When alignment is performed, the paper that has been punched or not punched is sent to the lower transport path 506, and the staple tray 502 is aligned in the direction perpendicular to the paper transport direction by the trailing edge fence, and the jogger The fence is aligned in the direction parallel to the paper transport direction. When binding is performed, a predetermined position of a bundle of aligned sheets, for example, two predetermined positions of a corner portion and a central portion are bound by a stapler 503, and discharged to a shift tray 504 by a discharge belt. In the embodiment shown in FIG. 4, the lower conveyance path 506 includes a pre-stack conveyance path 507, and stacks a plurality of sheets during conveyance to avoid interruption of the image forming operation on the main body 100 side during post-processing. Be able to.

  The image reading apparatus 200 is optically read by the ADF 300 onto the document table 210, and reads the stopped document, and enters the coupling lens through the first mirror, the second mirror, and the third mirror as shown in FIG. Then, the imaged read image is read by a photoelectric conversion element such as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor. The read image data is subjected to predetermined image processing by an image processing unit (not shown) and temporarily stored in a memory (not shown). Thereafter, at the time of image formation, the image writing unit 110 reads out from the memory, modulates according to the read image data, and performs optical writing on the photosensitive drum 121.

  The ADF 300 is a device that automatically feeds a plurality of documents, and is attached to the surface of the document table 210 of the image reading apparatus 200 so that it can be opened and closed. The ADF 300 may be capable of reading only one side of a document or may have a double-sided reading function.

  The hardware configuration of the image reading apparatus 200 is substantially the same as the hardware configuration illustrated in FIG. 1, and includes a contact glass, a light source, a first mirror, a second mirror, a third mirror, a first traveling body, and a second traveling body. A SBU having an imaging lens and a line sensor. Like the conventional SBU 10 shown in FIG. 2, this SBU is a line sensor as a reading means, a clamp circuit, an S / H circuit, an APGA as a first amplifying means, an ADC as a converting means, and a second amplifying means. Although provided with DPGA, this image reading apparatus 200 includes a circuit for performing gain adjustment in addition to them.

  FIG. 5 is a diagram illustrating a configuration example of the image reading apparatus 200. The image reading apparatus 200 shown in FIG. 5 includes an APGA 220, an ADC 221, and a DPGA 222, and a gain control circuit 223 as a control unit and a detection processing circuit 224 as a detection processing unit for performing gain adjustment. Further, the image reading apparatus 200 performs photoelectric conversion, gives a sensor 225 as a line sensor that inputs an analog image signal V_sig to the APGA 220, and gives a sensor clock signal Sensor_clk to the sensor 225, and performs gain control circuit 223 and detection. And a timing generation circuit 226 for supplying a clock signal CLK and a synchronization signal SYNC to the processing circuit 224. Here, for simplification, the clamp circuit and the S / H circuit are omitted.

  The sensor 225 is the above-described CCD image sensor or CMOS image sensor, and is a line sensor that reads a signal level for one line in the main scanning direction. The timing generation circuit 226 gives the clock signal CLK to the sensor 225, the gain control circuit 223, and the detection processing circuit 224, and operates the sensor 225, the gain control circuit 223, and the detection processing circuit 224, and the gain control circuit 223 and the detection processing circuit. The synchronization signal SYNC is supplied to 224, and the gain control circuit 223 and the detection processing circuit 224 are operated in synchronization with the reading operation by the sensor 225.

  The APGA 220, the ADC 221, and the DPGA 222 are the same as the APGA 16, the ADC 17, and the DPGA 18 shown in FIG. The detection processing circuit 224 operates in synchronization with the operation of the sensor 225 by the synchronization signal SYNC from the timing generation circuit 226, and a plurality of lines of digital image data D_sig output from the DPGA 222 of the reference white plate read by the sensor 225. The maximum level is detected as the peak value peak_max from the signal level of minutes, and the average value ave is calculated by averaging those signal levels. The reference white board is a member that is read to obtain a reference image.

  Specifically, since each line has a plurality of pixel values, the maximum pixel value is detected as the peak value peak_max from all the pixel values of the plurality of lines. Then, the average value ave is calculated by adding all these pixel values and dividing by the number of pixels. The detection processing circuit 224 includes a memory, and stores the detected peak value peak_max and the calculated average value ave in the memory. Here, the data is stored in the memory of the detection processing circuit 224, but may be stored in an external storage device.

  The gain control circuit 223 also operates in synchronization with the operation of the sensor 225 by the synchronization signal SYNC from the timing generation circuit 226, acquires the peak value peak_max and the average value ave from the detection processing circuit 224, and from the acquired average value ave An analog gain Again for the analog image signal V_sig and a digital gain Dgain for the digital image data D_sig are calculated and set in the APGA 220 and the DPGA 222, respectively. Thereby, the APGA 220 and the DPGA 222 can amplify and output the input analog image signal V_sig and digital image data D_sig based on the set gain.

  Gain adjustment in the image reading apparatus 200 will be described in detail with reference to FIG. FIG. 6 is a flowchart illustrating a first embodiment of gain adjustment performed by the image reading apparatus 200. This process is started from step 600 when the power of the image reading apparatus 200 is turned on or when the image reading apparatus 200 returns from the energy saving mode. In step 602, the gains set in the APGA 220 and the DPGA 222 are initialized, and the analog gain Again of the APGA 220 and the digital gain Dgain of the DPGA 222 are set to 1 times which is the lowest gain. In step 604, the peak value peak_max and the average value ave held in the memory by the detection processing circuit 224 are reset. These values are reset to default values set in advance, for example.

  In step 606, the sensor 225 reads the reference white plate for a plurality of lines with the minimum gain set, and performs photoelectric conversion to output an analog image signal V_sig. The analog image signal V_sig is amplified by the APGA 220, converted to digital image data D_sig by the ADC 221, and amplified by the DPGA 222. In step 608, the detection processing circuit 224 detects the peak value peak_max from the signal levels for a plurality of lines of the digital image data D_sig output from the DPGA 222, calculates the average value ave by averaging the signal levels, Each value in the memory of the detection processing circuit 224 is updated with these values. If it is reset to the default value in the above, the peak value detected from the default value and the calculated average value are updated.

Thereafter, the detection processing circuit 224 sends the peak value peak_max and the average value ave stored in the memory to the gain control circuit 223. In step 610, the gain control circuit 223 calculates the ratio of the average value ave peak value Peak_max, stored in the memory of the gain control circuit 223 and the ratio as k _1. The ratio k ₁ is calculated by dividing peak value peak_max an average value ave. This ratio is not limited to the memory provided in the gain control circuit 223, but a storage device can be provided outside and stored in the storage device.

  In step 612, the gain control circuit 223 sets the analog value that is set in the APGA 220 so that the peak value peak_max does not exceed the preset white target value agc_trg multiplied by 0.9 and has the maximum gain. Calculate the gain Again. In this embodiment, it is assumed that the analog gain Again can be set to four times of 1, 2, 4 and 8 times, and the error of the analog gain Again is ± 10%. The multiplication by 0.9 takes this error into account.

  In this way, since the peak value is detected from the signal levels for multiple lines, the peak level including noise can be detected more reliably, and even if there is a white scratch on the reference white plate, analog The adjustment accuracy of the gain Again can be improved. Further, since the white target value agc_trg is multiplied by 0.9 in consideration of the error of the analog gain Again, the probability of exceeding the white target value agc_trg can be reduced.

  In Step 612, the gain control circuit 223 calculates a calculated value N (N = agc_trg × 0.9 / peak_max) less than 2 by dividing the white target value agc_trg by 0.9 by the peak value peak_max. It is determined whether or not. If N is less than 2, if the analog gain Again is set to 2 times or more, the white target value agc_trg may be exceeded. Therefore, the process proceeds to step 614, where the gain control circuit 223 determines the analog gain Again to be 1 time, and APGA 220 Set to 1 times. When N is 2 or more, the process proceeds to step 616, and the gain control circuit 223 determines whether N is 2 or more and less than 4. If N is in the range, the process proceeds to step 618, where the gain control circuit 223 determines the analog gain Again to be 2 times, and sets APGA 220 to 2 times. This is because if the analog gain Again is set to 4 times or more, the white target value agc_trg may be exceeded.

  When N is 4 or more, the process proceeds to step 620, and the gain control circuit 223 determines whether N is 4 or more and less than 8. If N is in the range, the process proceeds to step 622, where the gain control circuit 223 determines the analog gain Again to be 4 times and sets the APGA 220 to 4 times. When N is 8 times or more, the process proceeds to step 624, where the gain control circuit 223 determines the analog gain Again to be 8 times and sets 8 times in the APGA 220. After the gain control circuit 223 sets the analog gain Again in the APGA 220 in this way, the process proceeds to step 626, where the sensor 225 reads the reference white plate for a plurality of lines again and outputs the analog image signal V_sig.

The APGA 220 amplifies the analog image signal V_sig based on the set analog gain Again, the ADC 221 performs A / D conversion, and the DPGA 222 performs amplification while maintaining the digital gain Dgain at a state of 1x. Outputs image data D_sig. In step 628, the detection processing circuit 224 receives the digital image data D_sig, detects the peak value peak_max again, and calculates the average value ave. Then, the detection processing circuit 224 updates the values stored in the memory with these values. Thereafter, the detection processing circuit 224 sends these values to the gain control circuit 223. In step 630, the gain control circuit 223 calculates the ratio k ₂ of the average value ave peak value peak_max from these values. The ratio k ₂ is calculated by dividing peak value peak_max an average value ave. In step 632, it compares the _{k 1} and _{k 2} calculated to determine whether _{k 1} is greater than _{k 2.}

Here, the peak value peak_max, the average value ave, the ratios k ₁ and k ₂ , the analog gain Again, and the white target value agc_trg before and after determining the analog gain Again are exemplified as shown in the table of FIG. In this example, since the analog gain Again is determined to be double, APGA 220 is set to double, and as a result, the average value ave obtained by reading the reference white plate again is 600 LSB / 10 bits before the determination of 300 LSB / bit. It is twice 10 bits. However, the peak value peak_max is not double the 400 LSB / 10 bit before the determination, but is 700 LSB / 10 bit which is smaller than the double. For this reason, the ratios k ₁ and k ₂ between the peak value peak_max and the average value ave are different values, and k ₁ before the determination is larger than k ₂ after the determination.

Referring again to FIG. 6, if it is determined that k ₁ is larger in step 632, the process proceeds to step 634, to 1x set as a minimum of the gain, multiplies the white target value Agc_trg, it at step 628 The digital gain Dgain (Dgain = 1 × agc_trg / (ave × k ₁ )) set in the DPGA 222 is calculated by dividing by the calculated average value ave and further by the larger k ₁ . After the calculation, the obtained digital gain Dgain is set in the DPGA 222, and this process is terminated in step 638.

Or Step 632 k ₁ and k ₂ are the same, when it is determined that the of k ₂ is large, the process proceeds to step 636, to 1x set as a minimum of the gain, multiplies the white target value Agc_trg, step it The digital gain Dgain (Dgain = 1 × agc_trg / (ave × k ₂ )) set in the DPGA 222 is calculated by dividing by the average value ave calculated in 628 and further dividing by the larger k ₂ . After the calculation, the obtained digital gain Dgain is set in the DPGA 222, and this process is terminated in step 638.

Incidentally, in the example shown in FIG. 7, since more of _{k 1} is larger, 1-fold, white target value 900LSB / 10bit, average 600LSB / _10bit, with k 1 = 1.33, a digital gain = (1 × 900) /(600×1.33)=1.127 and this can be set in the DPGA 222. Further, as described above, when setting by an integer such as 1 time, 2 times, 4 times, or 8 times, it is necessary to set the value within a range not exceeding the white target value agc_trg. It can be set to 1 which is an integer closest to 127 and smaller than that. The gain to be set is not limited to 1 times, 2 times, 4 times, and 8 times as described above, but may be other integer times, and may be a fractional number as shown in 1.127 above. May be.

  In the gain adjustment in the image reading apparatus 200, the peak value including noise is detected as much as possible, and the analog gain Again and the digital gain Dgain are determined based on the detected peak value. Even if it exists, gain adjustment can be performed accurately. Moreover, the probability that the adjusted white scratch reading level exceeds the white target value agc_trg can be minimized. As a result, an error state of the image reading apparatus 200 can be avoided, and high-speed startup when the power is turned on or when returning from the energy saving mode can be realized.

  In the embodiment shown in FIG. 6, when calculating the analog gain Again, the white target value agc_trg is multiplied by 0.9 to take into account the error of the analog gain Again, but a problem when this is not considered will be briefly described. . For example, as shown in FIG. 8, when the initially set analog gain Again is 1 times which is the lowest gain, the peak value peak_max of the reference white plate reading level before the analog gain adjustment is 440LSB / 10 bits, Assume that the set white target value agc_trg is 900 LSB / 10 bits.

  When the error of the analog gain Again is not taken into account, the white target value agc_trg / peak value peak_max is 2 or more and less than 4, so the analog gain Again is determined to be double. This is because even if it is doubled, 440 × 2 = 880 LSB / 10 bits, which is smaller than 900 LSB / 10 bits of the white target value agc_trg.

  However, when the error of the analog gain Again is ± 10%, the actual analog gain Again is not doubled but 1.9 times to 2.1 times. For example, when the analog gain Again is 1.9 times, 440 × 1.9 = 836LSB / 10 bits, which is smaller than the white target value agg_trg, but when the analog gain Again is 2.1 times, 440 × 2.1 = 924LSB / 10 bits, which exceeds the white target value agc_trg. Then, the image reading apparatus 200 enters an error state.

  In order to cope with such a problem, the reading level of the reference white plate is corrected to a white target value agc_trg × 0.9 instead of the white target value agc_trg itself. The value agc_trg is not exceeded, and the image reading apparatus 200 can be prevented from entering an error state. If the error is ± 20%, the white target value agc_trg can be corrected by multiplying by 0.8, and the gain can be determined using the corrected value.

  In the embodiment shown in FIG. 6, after setting the minimum gain and resetting the peak value and average value stored in the memory of the detection processing circuit 224, the reference white plate is read to determine the analog gain Again, , Read the reference white plate again, determine the digital gain Dgain, set it, and adjusted the gain. In this embodiment, initialization is performed every time the gain adjustment is performed, but in the reading of the reference white board after the digital gain Dgain is set, the white target value agc_trg is not exceeded, and the processing is completed normally without an error. In this case, it is desirable to use the analog gain Again, digital gain Dgain, and peak value set at that time as initial values in the next gain adjustment. This is because when a larger peak value is detected, the peak value is updated, but when the peak value used as the initial value is larger, the value can be held as it is. This improves the accuracy of detecting the peak value each time gain adjustment is performed, enables more optimal gain setting, and further reduces the probability that the reference whiteboard reading level after gain adjustment exceeds the white target value agg_trg. it can.

  FIG. 9 is a flowchart illustrating a second embodiment of gain adjustment performed by the image reading apparatus 200. In the second embodiment, the gain and peak value when the processing ends normally are used as initial values. Similarly to the first embodiment shown in FIG. 6, the second embodiment shown in FIG. 9 also starts processing when the power of the image reading apparatus 200 is turned on or when returning from the energy saving mode (step). 900).

  In step 902, it is first determined whether or not the previous gain adjustment has been completed normally. For example, log information can be acquired in gain adjustment, and the log information can be referenced to determine whether an error has been output. This is because an error is output if the white target value agc_trg is exceeded in the confirmation process. In the confirmation process, the analog gain Again and digital gain Dgain are calculated in the gain adjustment, and after setting them, the reference white plate as the reference image is read again and the amplified value does not exceed the white target value agc_trg. This is a process for confirming this. This is an example, and any method can be adopted as long as it can be determined whether or not the process has been completed normally.

  If it is determined that the process has not been completed normally, the process proceeds to step 904, where the gain control circuit 223 initializes the analog gain Again and the digital gain Dgain set in the APGA 220 and DPGA 222, and makes the minimum gain one time. Set. In step 906, the peak value peak_max and the average value ave stored in the memory of the detection processing circuit 224 are reset. On the other hand, if it is determined that the processing has been completed normally, the gain and each value set last time can be used as the initial value, and the process directly proceeds to step 908.

In step 908, with the image reading apparatus 200 set to the lowest gain or the previous gain, the sensor 225 reads the reference white board for a plurality of lines and outputs an analog image signal V_sig. The subsequent processing of steps 910 to 940 is the same as the processing of steps 608 to 638 shown in FIG. In step 912, step 914, step 918, and step 922, the peak value peak_max used when calculating the ratio k ₁ and the calculated value N is the previous peak when reading is performed with the previous gain set. A value is used.

  In the image reading apparatus 200, the light amount of the light source is reduced due to long-term use or the like. For this reason, appropriate digital image data D_sig can be output by increasing the gain corresponding to the decrease in the amount of light. However, in the second embodiment shown in FIG. 9, when there is no error and the processing ends normally, the gain is determined using the peak value peak_max that is held, and therefore the gain cannot be increased. Therefore, when the previous average value calculated by the detection processing circuit 224 is held as ave_old, and the calculated average value ave is smaller than the value obtained by multiplying the average value ave_old by a certain coefficient, the light source light amount is reduced. The gain is initialized, the peak value and the average value are reset, and the gain can be adjusted again.

  FIG. 10 is a flowchart illustrating a third embodiment of gain adjustment performed by the image reading apparatus 200. The third embodiment shown in FIG. 10 starts processing when the image reading apparatus 200 is turned on or returned from the energy saving mode, similarly to the second embodiment shown in FIG. 1000). In step 1002, it is first determined whether or not the previous gain adjustment has been completed normally. If it is determined that the processing has not been completed normally, the process proceeds to step 1004, where the gain control circuit 223 initializes the analog gain Again and the digital gain Dgain set in the APGA 220 and DPGA 222, and sets the minimum gain to 1 time. Set. In step 1006, the peak value peak_max and the average value ave stored in the memory of the detection processing circuit 224 are reset. On the other hand, if it is determined that the processing has been completed normally, the gain or each value set last time can be used as the initial value, and the process directly proceeds to step 1008.

  In step 1008, with the image reading apparatus 200 set to the lowest gain or set to the previous gain, the sensor 225 reads the reference white plate for a plurality of lines and outputs an analog image signal V_sig. The analog image signal V_sig is amplified and converted by the APGA 220, the ADC 221, and the DPGA 222. In step 1010, the detection processing circuit 224 detects the peak value peak_max from the signal levels for a plurality of lines of the digital image data D_sig output from the DPGA 222, calculates the average value ave by averaging these signal levels, Each value in the memory of the detection processing circuit 224 is updated by the value. This memory also stores the previous average value as ave_old.

  The detection processing circuit 224 sends the peak value peak_max, the average value ave, and the previous average value ave_old to the gain control circuit 223. In step 1012, the gain control circuit 223 determines whether or not the average value ave is larger than a value obtained by multiplying the average value ave_old by t. t is a constant coefficient and is a numerical value greater than 0 and less than or equal to 1. For example, t can be a value such as 0.8 or 0.9.

  If the average value ave is larger in step 1012, the process proceeds to step 1016, and if smaller, the process proceeds to step 1014. In step 1014, the average value ave is set to the average value ave_old, and the average value ave_old stored in the memory is updated. Then, the process returns to step 1004 to initialize the gain and reset the peak value peak_max and the average value ave. Note that the processing in steps 1016 to 1044 is the same as the processing in steps 912 to 940 shown in FIG. In this way, even when the light amount of the light source is reduced, it is possible to adjust to an optimum gain according to the light amount.

  The memory of the detection processing circuit 224 stores the detected peak value peak_max, the calculated average value ave, the previous average value ave_old, the peak value detected so far, and the calculated average value as history information. be able to. The peak value peak_max and the average value ave can be stored in order each time the gain adjustment is completed. For this reason, the gain control circuit 223 determines whether or not a certain number of peak values and average values stored in order are within a certain range, and if within a certain range, there is almost no fluctuation and stable. It can be determined that the peak value sufficiently including noise can be detected, and that the light amount of the light source hardly fluctuates. For this reason, when reading the reference white plate, the sensor 225 can read, for example, what had been 100 lines so far by reducing the number of lines to 50 lines. This is because the gain can be adjusted sufficiently even if the number of lines is reduced. Since the reading time is shortened by reducing the number of lines in this way, the image reading apparatus 200 can be started up more quickly.

  The image processing apparatus of the present invention, the image reading apparatus including the image processing apparatus, the image forming apparatus, and the image processing method have been described in detail with the above-described embodiments. However, the present invention is limited to the above-described embodiments. However, other embodiments, additions, changes, deletions, and the like can be changed within a range that can be conceived by those skilled in the art, and as long as the operations and effects of the present invention are exhibited in any aspect, the present embodiment It is included in the scope of the invention. Therefore, a computer-readable program for executing the image processing method can also be provided. This program can be provided by being stored in a recording medium such as a CD-ROM, DVD, USB memory, SD card, etc., or stored in a server connected to a network and via a network in response to a download request. It is also possible to provide.

DESCRIPTION OF SYMBOLS 1 ... Contact glass, 2 ... Light source, 3 ... 1st mirror, 4 ... 2nd mirror, 5 ... 3rd mirror, 6 ... 1st traveling body, 7 ... 2nd traveling body, 8 ... Imaging lens, 9 ... Line Sensors, 10 ... SBU, 11 ... Scanner, 12 ... Original, 13 ... Reference white plate, 14 ... Clamp circuit, 15 ... S / H circuit, 16 ... APGA, 17 ... ADC, 18 ... DPGA, 100 ... Main body, 110 ... Image Writing unit 120... Image forming unit 121 121 Photoconductor drum 122 122 Developing unit 123 Transfer unit 124 Cleaning unit 130 Fixing unit 140 Double-sided conveying unit 141 First switching claw 142 ... Reverse conveyance path, 143 ... Image forming side conveyance path, 144 ... Post-processing side conveyance path, 145 ... Second switching claw, 150 ... Paper feed section, 160 ... Vertical conveyance section, 161 ... Registration roller, 170 ... Manual feed section , 71: manual feed tray, 200 ... image reading device, 210 ... document table, 220 ... APGA, 221 ... ADC, 222 ... DPGA, 223 ... gain control circuit, 224 ... detection processing circuit, 225 ... sensor, 226 ... timing generation circuit, DESCRIPTION OF SYMBOLS 300 ... ADF, 400 ... Large capacity feeder, 401 ... Pickup roller, 402 ... Bottom plate, 500 ... Paper post-processing device, 501 ... Punch, 502 ... Staple tray, 503 ... Stapler, 504 ... Shift tray, 505 ... Proof tray 506: Lower transport path 507: Pre-stack transport path

Japanese Patent No. 4127603 Japanese Patent No. 4778337 JP 2011-211259 A

Claims (8)

Reading means for optically reading a document and outputting it as an analog image signal, first amplification means for amplifying the analog image signal based on a set first amplification factor, and the amplified analog image signal as digital image data An image reading apparatus comprising: a converting means for converting to digital data; and a second amplifying means for amplifying the converted digital image data based on a set second amplification factor,
A peak value that is the maximum level is detected as a first peak value from the signal levels of a plurality of lines of digital image data after the reference image is read by the reading unit and amplified by the first amplification unit and the second amplification unit. Detection processing means for averaging the signal levels for the plurality of lines and calculating an average value as a first average value ;
The first amplification factor is calculated and set in the first amplifying means within a range where the detected first peak value does not exceed a predetermined target value , and a ratio between the first peak value and the first average value is set. Control means for calculating as the first ratio ,
The detection processing means detects the peak value as a second peak value for the re-reading of the reference image after setting the first amplification factor in the first amplification means, and the average value is set to the first value. 2 Calculated as an average value,
The control means calculates a ratio between the second peak value and the second average value as a second ratio, and a larger ratio between the first ratio and the second ratio and the second average value. An image reading apparatus that calculates the second amplification factor so that a value obtained by multiplying and becomes the target value and sets the second amplification factor in the second amplification unit . The control means corrects the target value in consideration of an error of the first amplification factor, and calculates the first amplification factor within a range in which the first peak value does not exceed the corrected target value. the image reading apparatus according to 1. The reference image is read by the reading unit after setting the second amplification factor, and the first amplification unit and the second amplification unit do not exceed the target value and the first amplification factor adjustment is normally completed. Storage means for storing the amplification factor and the second amplification factor and the peak value used to calculate the second amplification factor, and the second amplification factor stored in the storage means at the next amplification factor adjustment 1 using the amplification factor and the second gain and the said peak value as an initial value, the image reading apparatus according to claim 1 or 2. The storage means also stores the average value used for calculating the second amplification factor, and the control means calculates a new average value calculated by the detection processing means during the next amplification factor adjustment. 4. The image reading apparatus according to claim 3 , wherein the first amplification factor and the second amplification factor are newly calculated when the average value is smaller than a value obtained by multiplying the average value and a constant coefficient stored in the storage unit. It further includes history information storage means for storing the peak value and the average value as history information each time amplification factor adjustment is completed, and the control means stores a fixed number of the peak values sequentially stored in the history information storage means. And the average value is determined to be within a certain range, and when it is determined to be within the certain range, the reading means reduces the number of lines for detecting the peak value and reduces the reference image. reading of the image reading apparatus according to any one of claims 1-4. An image forming apparatus including an image reading apparatus according to any one of claims 1 to 5, and an image forming unit for forming an image of the image read by the image reading apparatus. Reading means for optically reading a document and outputting it as an analog image signal, first amplification means for amplifying the analog image signal based on a set first amplification factor, and the amplified analog image signal as digital image data A gain adjustment method executed by an image reading apparatus including a conversion means for converting to a second amplification means for amplifying the converted digital image data based on a set second gain,
Reading a reference image by the reading unit, amplifying by the first amplifying unit and the second amplifying unit, and outputting digital image data of the reference image;
The peak value which is the maximum level is detected as a first peak value from the signal levels for a plurality of lines of the output digital image data, and the signal levels for the plurality of lines are averaged to obtain an average value as a first average value. A calculating step;
The first amplification factor is calculated and set in the first amplification means within a range in which the first peak value does not exceed a predetermined target value, and a ratio of the first peak value to the first average value is set to a first value. Calculating as a ratio of
Re-reading the reference image by the reading means, amplifying by the first amplifying means and the second amplifying means, and outputting the digital image data of the reference image again;
Detecting a peak value as a second peak value from a plurality of signal levels of the digital image data output again, and averaging the signal levels of the plurality of lines to calculate an average value as a second average value When,
A value obtained by calculating a ratio between the second peak value and the second average value as a second ratio and multiplying the larger one of the first ratio and the second ratio by the second average value. Calculating the second amplification factor so that becomes the target value, and setting the second amplification factor in the second amplification means. The program for making a computer perform each step contained in the adjustment method of the amplification factor of Claim 7 .