JP5803387B2 - Image reading apparatus, image forming apparatus, light amount adjusting method, and program - Google Patents

Description

  The present invention relates to an image reading apparatus that performs light amount adjustment of a light source, irradiates the original with light of the adjusted light amount, and reads an image of the original, an image forming apparatus including the image reading apparatus, a light amount adjustment method, and a method thereof The present invention relates to a device-readable program for executing.

  An image reading device such as a scanner device is used as a device for reading a document. This image reading apparatus irradiates a document with light, photoelectrically converts light transmitted through the document or reflected from the document, and analog data obtained as an electric signal is converted into an A / D (analog / digital) conversion circuit. Is converted into digital data, and the digital data is output as image data of a document. In general, this image reading apparatus uses a photoelectric conversion element array in which a plurality of photoelectric conversion elements are arranged in a single row at regular intervals in a main scanning direction called an image sensor, and the image sensor is arranged in the sub-scanning direction of a document. By moving or transporting the document in the sub-scanning direction, the document can be read and image data can be output.

  In such an image sensor in which a plurality of photoelectric conversion elements are arranged in a row, individual sensitivity differences occur between the individual photoelectric conversion elements. Also, the light source has individual differences for each light source, and the temperature dependency and the change with time are different, so that the illuminance varies. With this, it is impossible to read an image with a constant quality.

  Therefore, in order to absorb these variations, sensitivity differences, etc. most efficiently and A / D convert the output of the photoelectric conversion element with a large dynamic range, the output value which is digital data output by reading the reference white plate, A technique has been proposed in which white level adjustment is performed by performing gain adjustment and light amount adjustment inside an AFE (Analog Front End) in order to match a predetermined target value (see, for example, Patent Document 1).

  In this technique, the white level adjustment can increase the resolution by using a dynamic range as much as possible so that the A / D conversion circuit does not overflow, that is, the output of digital data after A / D conversion is not saturated. It is intended. Here, a method for performing white level adjustment in the image reading apparatus will be briefly described.

  The white level adjustment is performed before the original to be read is read. When power is turned on, the image reading device turns on the light source, moves the carriage to the lower part of the reference white plate, reads the reference white plate, and obtains an output value. The output value is a value such as 180 of 0 to 255 in 256 gradations. The output value is obtained for all pixels in the main scanning direction by the image sensor, the peak value which is the largest output value is detected from the obtained output values, and the peak value is used to detect the peak value of the previous stage of the A / D converter circuit. The gain (amplification degree) of the amplifier is adjusted and the light quantity of the light source is adjusted.

  FIG. 1 is a diagram illustrating a relationship between a pixel position in the main scanning direction and an output value. With reference to FIG. 1, white level adjustment by light amount adjustment of a light source performed by the image reading apparatus will be specifically described. First, the light quantity of a light source is set to a predetermined value, light is irradiated, and the reference white plate is read. This reading is performed for all effective pixels in the main scanning direction, and the peak value which is the largest output value is detected from the obtained output values. In FIG. 1, since the output value of the pixel at the center among the pixels arranged in the main scanning direction is the largest, this output value is detected as a peak value.

  Next, a light amount adjustment value for determining the detected peak value to be a predetermined target value is determined. Hereinafter, a specific example will be described. First, the light intensity adjustment value is set to 1, the peak value when the reference white plate is read is 150, the adjustment target value is set to 200, the light source is turned off, and the output value in the dark state where the light is not incident (black level) ) Is 10. In this case, the light intensity gain that indicates how many times the peak adjustment value can be obtained with respect to the light intensity adjustment value that was initially set is the difference between the adjustment target value and the black level, and the peak value. And the difference between the black level and (200-10) / (150-10) = 1.36. From this, it can be seen that in order to obtain the adjustment target value of 200, the light quantity when the light quantity adjustment value is 1 should be increased 1.36 times. For this reason, the light amount adjustment value is reset to 1.36 and the white level adjustment is completed.

  This adjustment target value takes into consideration possible fluctuation factors such as fluctuations in the amount of light from the light source. Under any circumstances, the output value obtained by reading the reference white plate does not exceed the maximum 255 shown in FIG. Generally, the target value is set. This output value includes the black level.

  In the above method, since the black level is assumed to be a constant value and the black level does not change, the peak value in all effective pixels in the main scanning direction when the reference white plate is read is set to a predetermined target value. It is very easy to obtain the light amount amplification factor for achieving this.

  However, in the CIS (Contact Image Sensor) of the equal-magnification optical system, the black level varies depending on the pixel position in the main scanning direction, and therefore, as described above, similar to the CCD (Charge Coupled Device) image sensor of the reduction optical system. The method cannot be used to accurately calculate the light amount gain.

  Here, a conventional method for black level adjustment will be described. In this method, a reduction optical system CCD image sensor is used as the image sensor. Since the CCD image sensor has the number of pixels that can ensure an effective reading width with one sensor chip, the black level output to each pixel in the sensor chip in the state where no light is incident is the same. Value. FIG. 2 is a diagram showing a circuit configuration used for adjusting the black level in the conventional image reading apparatus.

  The CCD image sensor 100 outputs an image signal to the sample hold circuit 101 in synchronization with the drive pulse generated by the drive timing signal generation circuit 105. The sample hold circuit 101 performs sampling using the image signal sample pulse generated by the drive timing signal generation circuit 105, and holds the sampled image signal. Then, the sample hold circuit 101 converts the sampled image signal into continuous analog data and inputs it to the black level correction circuit 102.

  The black level correction circuit 102 corrects the black level variation output from the CCD image sensor 100 and inputs the corrected analog data to the amplification circuit 103. The amplifier circuit 103 amplifies the inputted analog data to a reference voltage level for A / D conversion, and sends the amplified analog data to the A / D conversion circuit 104. The A / D conversion circuit 104 converts it into 8-bit digital data. In addition, the drive timing signal generation circuit 105 generates signals necessary for the black level correction circuit 102 and the A / D conversion circuit 104 and inputs them to these circuits.

  The black offset level detection circuit 106 receives an input of the output value after A / D conversion from the A / D conversion circuit 104, and adjusts the offset level for each column of pixels arranged in the main scanning direction. In other words, the black offset level detection circuit 106 takes the difference between the input output value and the black level target value so that the black level correction circuit 102 has a constant black level, and uses the difference as the black level correction circuit 102. Send to.

  Specifically, the black offset level detection circuit 106 outputs the output value output from the A / D conversion circuit 104 of the light-shielded pixel (OPB pixel) of the CCD image sensor 100 in, for example, 255 gradations (8 bits). The offset level is adjusted for each column of pixels arranged in the main scanning direction so as to be 10. In this adjustment, if the output value from the A / D conversion circuit 104 is 20, the black offset level detection circuit 106 sends a difference 10 from the adjustment target value 10 to the black level correction circuit 102, and the black level correction circuit In 102, correction is performed to reduce the black level by about 10. Since the black level can be adjusted by applying feedback through the black offset level detection circuit 106 in this way, the black level can always be a constant (fixed) value.

  In the above-described black level adjustment, there is no problem when using a reduction optical system image reading apparatus having a number of pixels that can ensure an effective reading width with one sensor chip, such as a CCD image sensor. However, a problem arises when using an image reading apparatus of a 1 × optical system such as CIS. That is, in the CIS, a plurality of sensor chips composed of a plurality of pixels are arranged at the same sub-scanning position, that is, a plurality of sensor chips are arranged in a line at regular intervals in the main scanning direction. This is because the final-stage output buffer in the sensor chip has a slight individual difference, and the black level varies from sensor chip to sensor chip due to a variation factor for each sensor chip.

  FIG. 3 shows the relationship between the black level read by CIS and the pixel position in the main scanning direction. FIG. 3 shows that the black level is different because each sensor chip has an individual difference. Each sensor chip is set to a constant value with the sensor chip width.

  In the case of CIS in which the sensor chip is a CMOS (Complementary Metal Oxide Semiconductor) sensor, as shown in FIG. 4, the CMOS sensor has a buffer 111 for each effective pixel 110, and each buffer 111 is connected to each shift register 112. A final output buffer 113 is connected to one of the shift registers 112. Also in CIS, since there is an individual difference for each sensor chip, the black level is different for each sensor chip as shown in FIG. Further, when looking at each sensor chip, since each effective pixel 110 has a buffer 111, as shown in FIG. 5B, due to individual differences of the buffer 111 for each effective pixel 110, the sensor chip has a buffer 111. However, the black level is different for each effective pixel 110.

  Even in such a case where the black level is different, since the variation range of the black level is determined for each sensor chip, it is possible to assume the maximum black level that can be generated. For this reason, the light amount gain can be obtained by the above-described method applied to the pixel reading apparatus of the reduction optical system, and the light amount adjustment can be performed by setting the light amount adjustment value based on the light amount gain. However, with this method, output saturation can be avoided, but since the proportion of the black level in the output value increases, the dynamic range of the A / D conversion circuit cannot be effectively used in most individuals. As a result, the number of effective gradations is reduced, and the SN (signal / Noize) performance of the image data is deteriorated.

  On the other hand, adopting a method that calculates the light intensity gain considering the black level as a value smaller than the true value, there is a high possibility that output saturation will occur when a highly reflective document is scanned. This causes a problem that image data faithful to the reflectance cannot be acquired.

  Therefore, in an image reading apparatus including an image sensor in which a plurality of photoelectric conversion elements are arranged in a line at regular intervals in the main scanning direction as in CIS, when the light source is turned off and incident light is set to zero. Even if the black level varies from pixel to pixel or from chip to chip, by adjusting the amount of light, it is possible to maximize the dynamic range of the A / D converter circuit without causing output saturation. It has been desired to provide an image reading apparatus that can be used.

  In view of the above problems, the present invention provides a light source that irradiates light on a document, an image reading unit that reads the document by photoelectrically converting light from the document, a reference white plate that is read by the image reading unit, and an image reading unit. There is provided an image reading apparatus including a light amount adjusting means for adjusting a light amount of a light source in order to match an output value obtained by reading and outputting a reference white plate with a target value.

  The light quantity adjusting means provided in the image reading apparatus is the largest output value of all the pixels in the main scanning direction output by turning on the light source and executing the reading of the reference white plate in the main scanning direction. Peak detection means for detecting a peak value and a peak position of a pixel indicating the peak value, and the main scanning direction output by outputting the reference white plate in the main scanning direction with the light source turned off The peak value matches the target value using the black level detection means that detects the output value at the peak position as the black level corresponding value from the output values of all the pixels, and the target value, peak value, and black level corresponding value. A parameter for amplifying the light amount to be calculated, applying the parameter to the first light amount adjustment value used for the light amount adjustment set for the light source, calculating the second light amount adjustment value, and adjusting the second light amount adjustment Change setting to value And a light intensity adjustment value calculating means.

  By adjusting the amount of light in this way, even after irradiating light from the light source after the adjustment and reading the reference white plate, the peak value becomes the target value and does not exceed the target value. In addition, not to assume the maximum black level that can be generated, but to use the black level at the pixel position that shows the actually read peak value, so that the dynamic range of the A / D conversion circuit can be utilized to the maximum extent possible. Can do.

  The image reading unit includes an image sensor including a plurality of photoelectric conversion elements arranged in a line in the main scanning direction. When read by an image reading means including such an image sensor, the black level value varies for each photoelectric conversion element to be read. However, the black level value read by the photoelectric conversion element that reads the pixel position indicating the peak value is changed. By acquiring and adjusting the amount of light using the black level, the dynamic range of the A / D conversion circuit can be effectively utilized to the maximum extent as described above.

  The image sensor can be configured as three color image sensors that output output values of red (R), green (G), and blue (B). In this case, the peak detecting means detects a peak value and a peak position for each color, the black level detecting means detects a black level corresponding value for each color, and the light amount adjustment value calculating means calculates a parameter for each color. Then, the smallest parameter among the parameters calculated for each color is selected and applied to the first light amount adjustment value.

  The RGB output values obtained by reading the reference white plate with each sensor are non-uniform, and the non-uniformity differs for each photoelectric conversion element. For this reason, the output saturation can be avoided by using the amplification factor which is the smallest parameter as described above and adjusting the range in which all the RGB colors do not exceed the target value.

  The image reading apparatus can further include output value determination means for determining whether or not the peak value matches the target value. After adjusting the amount of light, the image reading unit reads the reference white plate again and the peak detecting unit detects the peak value, and then the output value determining unit compares the peak value with the target value to determine whether they match. Can do. In rare cases, the peak value may exceed the target value when the reference white plate is read again. Since this results in output saturation, this output saturation can be avoided by adjusting the light amount again.

  The image reading means reads the reference white plate over a plurality of columns in the sub-scanning direction with the light source turned on, and the peak detection means has a plurality of pixels having the same pixel position in the main scanning direction and different pixel positions in the sub-scanning direction. An average output value is averaged for each pixel position in the main scanning direction, and the largest average output value calculated for each pixel position is detected as the peak value. can do. Thereby, a random noise component can be removed and a peak value can be detected with high accuracy.

  Further, the image reading means reads the reference white plate over a plurality of columns in the sub-scanning direction with the light source turned off, and the black level detection means has the same pixel position in the main scanning direction and the pixel position in the sub-scanning direction. An average output value obtained by averaging a plurality of output values with different values is calculated for each pixel position in the main scanning direction, and the average output value at the peak position is calculated from the average output values calculated corresponding to the positions of each pixel. It can be detected as a black level corresponding value. Also in this case, the random noise component can be removed and the peak value can be detected with high accuracy.

  In response to the power being turned on and before entering the energy saving mode, the image reading device preferably turns on the light source and starts reading the reference white plate by the image reading means. The light source light amount deteriorates with time as the image reading apparatus is used. By adjusting the light amount each time the power is turned on, the light source light amount can always be adjusted to a predetermined light amount regardless of the degree of deterioration of the light source light amount. Therefore, it is possible to maintain provision of high-quality image data.

  Further, it is preferable that the light amount adjustment is performed immediately before shifting to the energy saving mode, and the light amount adjustment is not performed when returning from the energy saving mode. As described above, the light amount adjustment is performed immediately before the transition and is not performed at the time of return, so that the return time from the energy saving mode can be shortened.

  In the present invention, an image forming apparatus including the above-described image reading apparatus can be provided, and a light amount adjusting method executed by the image reading apparatus can also be provided. In addition, a program readable by an image reading apparatus for executing the method can be provided, and the program can be provided in a download format, but can be recorded on a recording medium and the recording medium can be provided. It is.

The figure which showed the relationship between the pixel position of a main scanning direction, and an output value. The figure which showed the structure of the conventional image reading apparatus. The figure which showed the relationship between the pixel position of a main scanning direction, and a black level value. The figure which showed the buffer and register structure of the CMOS sensor with which an image reading apparatus is provided. The figure which showed the relationship between the black level value read by the CMOS sensor, and the pixel position of a main scanning direction. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. 1 is a diagram illustrating a circuit configuration of an image reading apparatus according to an embodiment. The figure which showed the lighting timing of the light source. FIG. 3 is a functional block diagram of an image reading apparatus that performs white level adjustment. The flowchart which showed the flow of the process in the case of employ | adopting the structure shown in FIG. 9 and performing white level adjustment. The figure which showed the relationship between the pixel position of the main scanning direction after white level adjustment, and after adjustment, and an output value. The figure which showed the relationship between the pixel position of the main scanning direction in the case of using a color image sensor, and an output value. The figure which showed the relationship between the pixel position of the main scanning direction after white level adjustment, and after adjustment, and an output value. 14 is a flowchart showing a flow of processing for preventing white level adjustment from failing as shown in FIG.

  FIG. 6 is a diagram showing a schematic configuration of the image forming apparatus of the present embodiment. The image forming apparatus shown in FIG. 6 includes an automatic document feeder (ADF) 200 having a function as an image reading apparatus, a paper feeding unit 210, and an image forming unit 220.

  The ADF 200 will be briefly described. The ADF 200 includes a document table on which documents are stacked, document guides provided on both sides of the document table, a calling roller for conveying documents to a reading position, a sheet feeding belt, and a conveyance roller rotated by the sheet feeding belt. And a separation roller. The ADF also includes a conveyance roller for conveying the document through the reading position, a paper discharge roller for discharging the document, and a registration sensor that detects the conveyance timing of the document to the reading position.

  In addition, the ADF 200 includes an image reading unit in order to provide a function as an image reading apparatus. The image reading unit includes an original table glass on which an original is placed, a light source that irradiates light to the original through the original table glass, a mirror that reflects reflected light from the original in a predetermined direction, a lens that focuses the light from the mirror, and a lens. An image sensor such as a CIS to which the focused light is incident is provided. This image sensor functions as an image reading means, photoelectrically converts incident light into an electric signal (analog data), converts it into a digital signal (digital data) by an A / D conversion circuit, and performs image processing after image processing. The digital data is input to the image forming unit 220.

  The image reading unit includes a reference white plate made of a white plate having a reflectance of 100% facing a light source at a predetermined position on the platen glass. The reference white plate is used for calibration of the reference reflectance, that is, white level adjustment described later.

  The paper feeding unit 210 includes paper feeding cassettes 211 and 212 that store recording papers having different paper sizes, and various rollers that transport the recording papers stored in the paper feeding cassettes 211 and 212 to the image forming position of the image forming unit 220. And a sheet feeding means 213.

  The image forming unit 220 executes an image forming process based on the image data of the document read by the image reading unit in the ADF 200. The image forming unit 220 includes an exposure device 221, a photosensitive drum 222, a developing device 223, a transfer belt 224, and a fixing device 225. The exposure device 221 irradiates a laser or the like based on the image data, and forms an electrostatic latent image on the surface of the photosensitive drum 222. For this reason, a voltage is applied to the photosensitive drum 222 in advance by the electric withstand device. The electrostatic latent image formed on the surface of the photosensitive drum 222 is visualized by the toner attached by the developing device 223.

  A toner image is formed on the surface of the photosensitive drum 222 by the developing device 223, and the toner image is transferred to the transfer belt 224 as the photosensitive drum 222 rotates. The transfer belt 224 is moved by a plurality of rollers, and transfers the toner image onto the recording paper supplied by the paper supply unit 210. The recording paper onto which the toner image has been transferred is conveyed to the fixing device 225. The fixing device 225 melts the toner by heating and fixes the toner to the recording paper by pressurization. Thereafter, the recording paper is conveyed to a paper discharge tray and discharged.

  FIG. 7 is a diagram illustrating a circuit configuration of an image reading unit included in the ADF 200 illustrated in FIG. The image reading unit 300 includes a light source 301 including an LED (Light-Emitting Diode) array, a fluorescent lamp, a cold cathode tube, and the like. The image reading unit 300 includes a plurality of sensor chips 302 arranged in a line at regular intervals in the main scanning direction (direction corresponding to the width direction of the document), and a plurality of amplifiers individually connected to each sensor chip 302. A circuit 303 and a plurality of A / D conversion circuits 304 individually connected to each amplifier circuit 303 are provided.

  The image reading unit 300 turns off the light source 301, reads the reference white plate with the plurality of sensor chips 302, and corrects the black level that is the dark output value that is A / D converted by the A / D conversion circuit 304. The image processing unit 305 includes a correction unit, a shading correction unit that corrects color unevenness, and the like, and includes an image processing unit 305 that performs various types of image processing, a frame memory 306, an output control circuit 307, and an I / F circuit 308.

  The sensor chip 302 includes a photoelectric conversion element called a 1 × contact image sensor and a condenser lens. A lighting signal is sent from the controller 310 to the light source 301 before the document is transported to the reading position of the ADF 200. Accordingly, the light source 301 is turned on and irradiates the light toward a document (not shown). The light reflected from the document is reflected by the above-described mirror, converged by the lens, and incident on the plurality of sensor chips 302. Each sensor chip 302 converts incident light into an electrical signal and reads it as analog image information. At that time, each sensor chip 302 reads image information in synchronization with a timing signal from the controller 310. The analog image information read by each sensor chip 302 is sent as analog data to the amplifier circuit 303 connected thereto, amplified, and then converted into digital data by the A / D conversion circuit 304.

  The digital data is input to the image processing unit 305, and after offset components are removed by black level correction, shading correction and the like are performed and temporarily stored in the frame memory 306. The output control circuit 307 outputs the digital data temporarily stored in the frame memory 306 to the I / F circuit 308 in synchronization with the timing signal from the controller 310. The I / F circuit 308 sends the output digital data to the main body control unit 320.

  The main body control unit 320 is mounted on the image forming unit 220, receives the digital data as digital image information, and instructs the image forming unit 220 to perform image forming processing based on the digital image information. Control the formation process. The main body control unit 320 transmits and receives various information to and from the controller 310 via an interface (not shown). For example, the main body control unit 320 receives an input of an image reading request from an operation panel (not shown) and transmits a reading start signal to the controller 310. In addition, the main body control unit 320 transmits a document feed signal, a registration stop signal, and the like to the controller 310.

  The controller 310 receives a detection signal from each sensor, a reading start signal from the main body control unit 320, and the like. Then, the controller 310 activates each motor, controls the operation of each motor, sends a lighting signal to the light source 301 to the image reading unit 300, and sends a timing signal to the sensor chip 302 and the output control circuit 307. Also supply power.

  The image reading unit 300 receives a lighting signal from the controller 310 and turns on the light source 301 to read the document. For this reading, the light amount of the light source 301 is adjusted and an appropriate amount of light is emitted. It is considered important. This is because the quality of the image obtained by reading is affected.

  The light amount adjustment of the light source in the case where an LED is used as the light source 301 will be described with reference to FIG. FIG. 8 is a diagram showing the lighting timing of the light source. In FIG. 8, XLSYNC is a one-line synchronization signal that is “L” for a period corresponding to several pixels at the head of the line. LED_ON is a signal that is in the lighting period “H” in synchronization with the rise of the XLSYNC period.

  The light amount adjustment can be realized by adjusting the assertion period of the LED_ON signal. The LED_ON signal is a signal generated based on the reference clock inside the controller 310, and the assertion period is adjusted by, for example, providing a register for setting the number of reference clocks in the controller 310 and setting the reference clock set in the register. This can be realized by adopting a configuration that counts the number and outputs a signal, and changes the number of reference clocks to be set.

  This light amount adjustment is performed by setting a light amount adjustment value so that an output value that matches a predetermined target value is obtained when the image forming apparatus is shipped from the factory. In the example of the LED, it is performed by setting a reference clock number as a light amount adjustment value in a register. Actually, the light amount adjustment is called white level adjustment because the light amount adjustment value is set so that the output value obtained by reading the reference white plate matches the target value.

  Therefore, the white level adjustment performed in the image reading unit 300 will be described. When the white level adjustment is performed only at the time of shipment from the factory and the light source light amount is determined, the effective gradation number of the A / D conversion circuit 304 becomes small due to a decrease in the light source light amount over time, and the SN performance of the image data deteriorates. End up. Therefore, by performing the white level adjustment every time the power is turned on, it is possible to prevent deterioration in image quality due to a decrease in light source light amount over time.

  FIG. 9 shows a functional block diagram of the image reading unit 300 for performing the white level adjustment. In FIG. 9, as a configuration for performing white level adjustment, a white level data acquisition unit 330, a peak value detection unit 331, a peak position detection unit 332, a black level data acquisition unit 333, and a black level corresponding value detection unit. 334 and a light amount adjustment value calculation unit 335. Since the image processing unit 305 performs image processing, the image reading unit 300 includes a memory that stores software for executing the image processing, and a processor that reads and executes the software from the memory. For this reason, a program for adjusting the white level is stored in a memory, and the processor can read out and execute the program, thereby causing the processor to function as each unit. The functions of the above-described units can be realized by the controller 310 or the main body control unit 320.

  The controller 310 sends a lighting signal to the light source 301 and turns on the light source 301 based on a light amount setting value set to a constant light amount, for example, a light amount A. The controller 310 also sends timing signals to the plurality of sensor chips 302, the plurality of sensor chips 302 reads the reference white plate, and the A / D conversion circuit 304 outputs digital data. The white level data acquisition unit 330 acquires output values at all pixel positions in the main scanning direction output from the A / D conversion circuit 304. The white level data acquisition unit 330 sends the acquired output values to the peak value detection unit 331 and the peak position detection unit 332. The peak value detection unit 331 detects the peak output value as the peak value and holds the peak value. The peak position detection unit 332 uses the position of the pixel indicating the peak value in the main scanning direction as the peak position. Detect and hold its peak position.

  The controller 310 sends an instruction to stop lighting to the light source 301, turns off the light source 301, and the plurality of sensor chips 302 read the reference white plate with the incident light being zero, and output analog data. The A / D conversion circuit 304 converts the analog data into digital data, and the black level data acquisition unit 333 acquires the converted digital data, that is, output values at all pixel positions in the main scanning direction. The black level data acquisition unit 333 sends the acquired output values to the black level corresponding value detection unit 334. The black level corresponding value detection unit 334 reads with the light source 301 turned off, and detects the output value at the peak position as the black level corresponding value from the obtained output values.

  The light amount adjustment value calculation unit 335 uses the peak value detected by the peak value detection unit 331, the black level correspondence value detected by the black level correspondence value detection unit 334, and a preset target value for light amount adjustment. Then, the light amount amplification factor G is calculated. Here, the light amount amplification factor G is an amplification factor to the light amount B such that the peak value in all pixels in the main scanning direction when the reference white plate is read with the light amount A is set to the target value, and B = G It has the relationship represented by xA.

  Specifically, since the output value (white level, that is, the optical signal component) at the time of reading the reference white plate, excluding the black level from the peak value, is proportional to the light amount, the light amount amplification factor G is equal to the target value described above. Expressed by the difference between the black level and the difference between the peak value and the black level, where T is the target value, b (x) is the black level, and a (x) is the peak value, .

  If the target value T is a value that can read an original with a reflectance of 100% without being saturated, the original read value will not be saturated with any reflectance of the original. Can be output.

  The light amount adjustment value calculation unit 335 sets the light amount adjustment value of the light source so that the light amount A becomes G times in order to obtain the light amount B as the target value T. In the case of an LED light source, the light amount is proportional to the light source lighting period, and the light source lighting period can be set by the reference clock number. Therefore, the light amount B is obtained by multiplying the reference clock number for the light amount A by G. The reference clock number can be obtained. Therefore, the light amount adjustment value calculation unit 335 performs the light amount adjustment for obtaining the light amount B by obtaining the reference clock number by multiplying G in this way and setting the reference clock number in a register included in the controller 310. be able to.

  FIG. 10 is a flowchart showing the flow of white level adjustment performed by the image reading apparatus. This white level adjustment can be performed when the apparatus power supply is turned on. When it is executed when the power is turned on, in response to the power being turned on, the process starts from step 1000. In step 1005, the light source 301 is turned on based on the light amount adjustment value set last time. In the above example, the light amount adjustment value is a value set so as to be the light amount A.

  In response to the apparatus power being turned on, the controller 310 refers to the light amount adjustment value set in the register, generates a lighting signal (LED_ON signal), and sends the lighting signal to the light source 301. The light source 301 receives the lighting signal and starts lighting.

  Next, in step 1010, the reference white plate is read by the plurality of sensor chips 302, and each analog data obtained by photoelectric conversion is sent to each A / D conversion circuit 304, and each A / D conversion circuit 304 receives each digital data. The white level data acquisition unit 330 acquires all digital data as output values.

  In step 1015, the peak value detection unit 331 detects the peak value, which is the largest output value, from the output values of all the pixels in the main scanning direction acquired by the white level data acquisition unit 330, and holds the peak value. The position detection unit 332 detects the position of the pixel indicating the peak value in the main scanning direction as a peak position, and holds it.

  Thereafter, in step 1020, the light source 301 is turned off. In step 1025, the reference white plate is read by the plurality of sensor chips 302, and the analog data obtained by photoelectric conversion is sent to the A / D conversion circuit 304 for A / D conversion. Circuit 304 converts to digital data. In this case, the black level data acquisition unit 333 acquires the digital data as an output value.

  In step 1030, the black level corresponding value detection unit 334 refers to the peak position of the pixel indicating the peak value obtained when the reference white plate is read as the light amount A held by the peak position detection unit 332 in step 1015. The output value at the peak position is detected as a black level corresponding value.

  In step 1035, the light amount adjustment value calculation unit 335 substitutes the peak value detected in step 1015, the black level corresponding value detected in step 1030, and the target value in the above equation 1, and uses the light amount gain as a parameter for adjusting the light amount. G is calculated.

  In step 1040, the light amount adjustment value calculation unit 335 obtains a new light amount adjustment value by multiplying the set light amount adjustment value by G in order to obtain the light amount B as the target value, and the new light amount adjustment. Change the setting to a value. When the light source is an LED, the number of reference clocks can be used as the light amount adjustment value. Therefore, the number of reference clocks set to be the amount of light A is multiplied by G to obtain the number of reference clocks for the amount of light B. By changing the setting in the register of the controller 310, a new light amount adjustment value can be set.

  When this setting change is completed, the process proceeds to step 1045 to end the white level adjustment.

  The configuration for performing white level adjustment and the flow of the processing have been described in detail so far. Next, the effect will be described. FIGS. 11A and 11B are diagrams showing output values obtained by reading the reference white plate before and after white level adjustment. Reading is performed for all pixels in the main scanning direction, and FIG. 11 illustrates four of them.

  FIG. 11A is a diagram showing an output value obtained by reading a reference white plate before white level adjustment, together with its pixel position. FIG. 11A is a bar graph in which the lower filled portion is the black level, the upper white portion is the white level, and the highest output value is the peak value. Further, the position of the pixel indicating the peak value is the peak position, and the output value obtained when the light source is turned off obtained at the peak position is the black level corresponding value.

  For example, it is assumed that 100 is detected as the peak value and 30 is detected as the black level corresponding value at the peak position. It is assumed that the target value is set to 200 indicated by a broken line. In this case, by substituting these into the above equation 1 and calculating the light quantity gain G, a value of about 2.4 is obtained for G. For this reason, by multiplying the set light quantity adjustment value by 2.4, a new light quantity adjustment value is obtained, and by changing the setting to the new light quantity adjustment value, the light quantity B whose peak value becomes the target value is obtained. Can be obtained.

  FIG. 11B shows an output value obtained by reading the reference white plate with the light amount B together with the pixel position. FIG. 11B shows the output value after white level adjustment. Since the white level is adjusted and the light amount is adjusted so that the peak value becomes the target value, the obtained result is 200, as shown in FIG. 11B, where the peak value matches the target value. ing.

  In this white level adjustment, since the peak value is adjusted to the target value, the output value does not exceed the target value after adjustment, and as a result, output saturation can be avoided. Further, since only the white level excluding the black level corresponding value is multiplied by G to match the target value, the black level does not change before and after the adjustment, and only the white level is amplified. As a result, the A / D conversion circuit The dynamic range of 304 can be used effectively.

  The image sensor for reading an image includes a three-line sensor having three colors such as red (R), green (G), and blue (B) used for reading a color image. This three-line sensor performs photoelectric conversion by an image sensor for each color, converts it to digital data by an A / D conversion circuit 304 connected to the image sensor for each color, and acquires digital data for each color.

  When this three-line sensor is used as an image sensor, as shown in FIG. 12, it is known that when white light is irradiated with a constant amount of light and the reference white plate is read, the output value of each color becomes non-uniform. . It is also known that the heterogeneity varies from individual to individual. Therefore, adjustment is necessary in order to make effective use of the dynamic range of the A / D conversion circuit 304 as much as possible without saturating the output of all RGB.

  Therefore, when such a three-line sensor is used, the adjustment described below can be performed. Similar to the white level adjustment described above, the light source is turned on, the reference white plate is read by the image sensor of each color, and the output values of all the pixels in the main scanning direction are obtained for each color. Then, for each color, the peak value and the peak position, which are the largest output values, are detected from the output values. Further, the light source 301 is turned off and the output values of all the pixels in the main scanning direction are acquired for each color, and the output value at the peak position is detected as the black level corresponding value from among the output values for each color. Thereafter, the peak value, the target value, and the black level corresponding value are substituted into the above formula 1, and the light amount amplification factor G is obtained for each color.

  From here on, the portion different from the white level adjustment described above is selected, and the smallest one of the light intensity gains G obtained for each color is selected. This selection can be executed by the light amount adjustment value calculation unit 335. The reason for selecting the smallest value in this way is to set the new light intensity adjustment value obtained by multiplying the set light intensity adjustment value by G and multiplying it by G in order to set the peak value to the target value. This is because, if an amplification factor other than the smallest one is employed, some colors exceed the target value and output saturation occurs.

  Specifically, when a document with a high reflectance is read, if the target value is exceeded, the analog data is saturated at the time of input of analog data to the A / D conversion circuit 304, and an output faithful to the reflectance is obtained. This is because it has the harmful effect of being unable to do so.

  The processing after selecting the smallest light quantity amplification factor G is the same as the white level adjustment described above, and the light quantity adjustment value is multiplied by G, the new light quantity adjustment value obtained by the G multiplication is changed, and white End level adjustment.

  Usually, if the peak value is detected and the amount of light is adjusted so that the peak value becomes the target value, it is considered that output saturation does not occur. However, because there are individual sensitivity differences of the sensor chip, individual differences of the output buffer, etc., the output value is not uniform for all pixels in the main scanning direction, and the white level and the black level differ depending on the pixel position. Even when the light amount is adjusted so that the peak value becomes the target value, output saturation may occur.

  For example, in FIG. 13A, the reference white plate is read before white level adjustment, and 100 and 110 are obtained as the output values of the pixel positions m and n in the main scanning direction, and the output value 110 of the pixel position n is the peak value. Has been detected. Further, the light source 301 is turned off and the reference white plate is read, and an output value of 20 at the pixel position m and 50 as an output value of the pixel position n are obtained. As a result, the white level at the pixel position m is 100-20 = 80, and the white level at the pixel position n is 110-50 = 60.

  In this example, in order to set the peak value 110 to the target value 200, the light amount amplification factor G is calculated as 2.5 using the above Equation 1. For this reason, the light amount adjustment value is changed to a value multiplied by 2.5. The result is shown in FIG. In FIG. 13B, the output value at the pixel position n of the pixel indicating the peak value becomes 200, which is the same as the target value by this white level adjustment, but the output value at the pixel position m is 220, which greatly exceeds the target value. ing. This can cause output saturation.

  In order to prevent this, an output value determination unit that detects a peak value from output values obtained by further reading a reference white plate after white level adjustment and determines whether or not the peak value matches a target value. Can be provided. Since the white level adjustment is performed once, the peak value detected after the adjustment is either the target value or exceeds the target value as described above.

  The white level adjustment performed by the image reading apparatus including the output value determination unit will be described in detail with reference to the flowchart shown in FIG. This white level adjustment is performed when the power is turned on. The processing is started from step 1400, and in step 1405, the light source 301 is turned on based on the set light amount adjustment value. For example, the light amount adjustment value is a value set so that the light amount becomes the light amount A.

  Next, in step 1410, the reference white plate is read by the plurality of sensor chips 302, the analog data obtained by photoelectric conversion is sent to the A / D conversion circuit 304, and the A / D conversion circuit 304 converts it into digital data. The white level data acquisition unit 330 acquires the digital data as an output value (white level).

  In step 1415, the peak value detection unit 331 detects the peak value, which is the largest output value, from the output values of all the pixels in the main scanning direction acquired by the white level data acquisition unit 330, and holds the peak value. The position detection unit 332 detects the position of the pixel indicating the peak value in the main scanning direction as a peak position, and holds it.

  When the detection of the peak value and the peak position is completed, in step 1420, the output value determination unit determines whether or not the detected peak value matches the target value. If it is determined that the peak value matches the target value, the process proceeds to step 1450 to end the white level adjustment. On the other hand, if it is determined that they do not match, the process proceeds to step 1425 and adjustment is performed.

  In step 1425, the light source 301 is turned off, and in step 1430, the reference white plate is read by the plurality of chip sensors 302, and analog data obtained by photoelectric conversion is sent to the A / D conversion circuit 304. Converts to digital data. In this case, the black level data acquisition unit 333 acquires the digital data as an output value.

  In step 1435, the peak position of the pixel indicating the peak value obtained when the reference white plate is read as the light amount A held by the peak position detection unit 332 in step 1415 is referred to, and the output value of the peak position is set to the black level. Detect as a corresponding value.

  In step 1440, the light amount adjustment value calculation unit 335 calculates the light amount amplification factor G by substituting the peak value detected in step 1415, the black level corresponding value detected in step 1435, and the target value into the above equation 1.

  In step 1445, the light amount adjustment value calculation unit 335 obtains a new light amount adjustment value by multiplying the set light amount adjustment value by G in order to obtain the light amount B as the target value. Change the setting to. When the light source is an LED, the number of clocks can be used as the light amount adjustment value. Therefore, the number of clocks set to be the amount of light A is multiplied by G to obtain the number of clocks of the amount of light B, A new light amount adjustment value can be set by changing the setting in the register of the controller 310.

  When this setting is completed, the process returns to step 1405, the light source 301 is turned on again, and the reference white plate is read. As a result, in step 1420, if the peak value matches the target value, the white level adjustment ends, and if not, the adjustment is performed again. By repeating the adjustment in this way, the peak value can be adjusted to be equal to or less than the target value, and as a result, output saturation can be avoided.

  The white level data acquisition unit 330 shown in FIG. 9 can include an averaging circuit inside, and averages the data of a plurality of lines for each pixel or each sensor chip, and uses the average value to calculate the peak value. Detection or the like can be performed. After reading all pixels in the main scanning direction, that is, for one line with the image sensor, the image sensor is moved in the sub-scanning direction by one pixel, the next line is read, and further moved in the sub-scanning direction by one pixel. Further, it is possible to read a plurality of lines by repeatedly reading the next line. After reading a plurality of lines in this way, an average value is calculated by averaging the output values read for a plurality of pixels in the sub-scanning direction with the same pixel position in the main scanning direction, and calculated for each pixel position. The largest average value among the average values can be detected as the peak value.

  In this way, by reading a plurality of lines and using the average value, it is possible to remove the random noise component of each pixel and detect the peak value with higher accuracy. As a result, more accurate light amount adjustment can be realized.

  In the above description, the white level data acquisition unit 330 includes the averaging circuit. However, the black level data acquisition unit 333 may include the averaging circuit. As a result, even when reading with the light source turned off, it is possible to read a plurality of lines, adopt an averaged value, obtain a black level from which random noise components have been removed, and achieve higher accuracy. Black level data can be acquired. As a result, more accurate light amount adjustment can be realized.

  It is known that generally used light sources such as white LEDs and xenon lamps deteriorate with time. The white level adjustment is performed once at the time of product shipment. However, if the white level adjustment is not performed thereafter, the dynamic range of the A / D conversion circuit 304 is narrowed as time passes, and gradually. The image quality deteriorates. Therefore, white level adjustment can be performed as appropriate to prevent deterioration of image quality, but the timing for the adjustment can be made when the system power is turned on. By appropriately adjusting the white level in this way, the dynamic range of the A / D conversion circuit 304 can be maintained effectively in any light source amount state, and as a result, high The provision of quality image data can be maintained.

  In recent years, due to the trend of environmental protection and energy saving, efforts have also been made to meet standards proposed for energy saving, such as Energy Star and Zero Energy Stand by Mode (ZESM), in the design of scanners and digital multifunction devices. Has been continued. These standards are intended to save energy and limit energy consumption when in a standby state. The standby state is a state in which, after the main power source is turned on, when there is a state in which the main power source is not used for a certain period, a part of the power supply is stopped and a return command is waited after the period.

  Currently, in the energy saving mode during standby of the digital multi-function peripheral, the fixing heater, operation panel, and the like that consume large power are turned off or switched to low voltage operation. The same applies to the image reading apparatus, and the operation panel or the like is turned off or switched to low power operation.

  On the other hand, when using a digital MFP that is in a standby state, turn the power back on, or return from a low power operation to a normal operation state, and wait for the user to enter a usable state (standby state). It was. This waiting time is perceived as longer than the actual time for the user, resulting in a stressing result.

  In order to solve this problem, the white level adjustment can be performed immediately before shifting to the energy saving mode. Thereby, since the white level adjustment can be omitted when returning from the energy saving mode, the waiting time of the user can be shortened, and the stress applied to the user can be reduced. The timing for performing the white level adjustment is obtained, for example, by obtaining a period obtained by subtracting the time for performing the white level adjustment from the set time for shifting to the energy saving mode before shifting to the energy saving mode. Can be the time when the state in which the is not used has reached the required period. Since this is an example, the present invention is not limited to this, and it is also possible to execute the state when the state not used is arbitrarily set after the transition to the energy saving mode.

  So far, the present invention has been described with respect to the image reading apparatus and the white level adjustment performed by the image reading apparatus with the above-described embodiments. However, the present invention is not limited to the above-described embodiments, and other embodiments are described. It is possible to make changes within the range that can be conceived by those skilled in the art, such as forms, additions, changes, deletions, and the like, as long as the effects and effects of the present invention are exhibited in any aspect It is.

  Therefore, in the present invention, it is possible to provide an image forming apparatus provided with the image reading apparatus and a computer readable program for realizing processing for performing white level adjustment. The program includes a flexible disk, a CD-ROM. It is also possible to provide a recording medium stored in a recording medium such as a DVD or an SD card. In addition, this program can be stored in a server device connected to a network and downloaded to make a general-purpose scanner device, digital multifunction peripheral, etc. function as an image reading device that performs white level adjustment. It is.

DESCRIPTION OF SYMBOLS 100 ... CCD image sensor 101 ... Sample hold circuit 102 ... Black level correction circuit 103 ... Amplification circuit 104 ... A / D conversion circuit 105 ... Drive timing signal generation circuit 106 ... Black offset level detection circuit 110 ... Valid pixels, 111... Buffer, 112... Shift register, 113... Final output buffer, 200... ADF, 210 ... paper feed unit, 211, 212 ... paper feed cassette, 213 ... paper feed means, 220 ... image forming unit, 221. Exposure device 222... Photosensitive drum 223. Developing device 224 Transfer belt 225 Fixing device 300 Image reading unit 301 Light source 302 Sensor chip 303 Amplifier circuit 304 A / D conversion Circuit 305 ... Image processing unit 306 ... Frame memory 307 ... Output control circuit 308 ... I / F circuit 310 ... Controller, 320 ... Main body control unit, 330 ... White level data acquisition unit, 331 ... Peak value detection unit, 332 ... Peak position detection unit, 333 ... Black level data acquisition unit, 334 ... Black level corresponding value detection unit, 335 ... Light intensity adjustment value calculation unit

Japanese Patent Laid-Open No. 2007-081696

Claims (10)

A light source for irradiating light on the original, an image reading unit for reading the original by photoelectrically converting light from the original, a reference white plate read by the image reading unit, and the image reading unit for reading the reference white plate An image reading apparatus including a light amount adjusting unit configured to adjust a light amount of the light source in order to match an output value output to a target value, wherein the light amount adjusting unit includes:
The light source is turned on, and the image reading means executes the reading of the reference white plate in the main scanning direction and outputs the largest peak value among the output values of all the pixels in the main scanning direction, and the peak value Peak detecting means for detecting the peak position of the pixel shown;
The light source is turned off, and the output value at the peak position among the output values of all the pixels in the main scanning direction output by the image reading means executing the reading of the reference white plate in the main scanning direction corresponds to the black level. Black level detection means for detecting as a value;
Using the target value, the peak value, and the black level corresponding value, a parameter for amplifying the peak value to a light amount that matches the target value is calculated, and the light amount set for the light source An image reading apparatus comprising: a light amount adjustment value calculating unit that calculates a second light amount adjustment value by applying the parameter to a first light amount adjustment value used for adjustment, and changes the setting to the second light amount adjustment value.   The image reading apparatus according to claim 1, wherein the image reading unit includes an image sensor including a plurality of photoelectric conversion elements arranged in a line in the main scanning direction.   The image sensor is configured as three color image sensors that output the output values of each color of red (R), green (G), and blue (B), and the peak detection unit includes the peak value for each color. Detecting the peak position, the black level detecting means detects the black level corresponding value for each color, and the light amount adjustment value calculating means calculates the parameter for each color, and calculates the calculated for each color. The image reading apparatus according to claim 2, wherein the smallest parameter among the parameters is selected and applied to the first light amount adjustment value.   The image reading apparatus according to claim 1, further comprising an output value determination unit that determines whether or not the peak value matches the target value.   The image reading unit reads the reference white plate over a plurality of columns in the sub-scanning direction in a state where the light source is turned on, and the peak detection unit has the same pixel position in the main scanning direction and the pixel in the sub-scanning direction. An average output value obtained by averaging a plurality of output values at different positions is calculated for each pixel position in the main scanning direction, and the largest average output value is calculated from the average output values calculated corresponding to the positions of the pixels. The image reading apparatus according to claim 1, wherein the image reading device is detected as the peak value.   The image reading unit reads the reference white plate across a plurality of columns in the sub-scanning direction in a state where the light source is turned off, and the black level detection unit has the same pixel position in the main scanning direction and the pixel in the sub-scanning direction An average output value obtained by averaging a plurality of output values having different positions is calculated for each pixel position in the main scanning direction, and the peak position is calculated from the average output values calculated corresponding to the positions of the pixels. The image reading apparatus according to claim 1, wherein an average output value is detected as the black level corresponding value.   The image reading apparatus turns on the light source in response to the power being turned on and before entering the energy saving mode, and starts reading the reference white plate by the image reading unit. The image reading device according to any one of?   An image forming apparatus comprising the image reading apparatus according to claim 1. A light source for irradiating light on the original, an image reading unit for reading the original by photoelectrically converting light from the original, a reference white plate read by the image reading unit, and the image reading unit for reading the reference white plate A method executed by an image reading apparatus including a light amount adjusting unit configured to adjust a light amount of the light source in order to match an output value output to a target value, wherein the light amount adjusting unit includes:
The light source is turned on, and the image reading means executes the reading of the reference white plate in the main scanning direction and outputs the largest peak value among the output values of all the pixels in the main scanning direction, and the peak value Detecting a peak position of the indicated pixel;
The light source is turned off, and the output value at the peak position among the output values of all the pixels in the main scanning direction output by the image reading means executing the reading of the reference white plate in the main scanning direction corresponds to the black level. Detecting as a value;
Using the target value, the peak value, and the black level corresponding value, a parameter for amplifying the peak value to a light amount that matches the target value is calculated, and the light amount set for the light source Applying the parameter to the first light amount adjustment value used for adjustment to calculate a second light amount adjustment value and changing the setting to the second light amount adjustment value. An image reading apparatus comprising: a light source that irradiates light on a document; an image reading unit that reads the document by photoelectrically converting light from the document; and a reference white plate that is read by the image reading unit. A program readable by the image reading device for executing a process of adjusting the light amount of the light source in order to match an output value obtained by reading and outputting the reference white plate with a target value,
The light source is turned on, and the image reading means executes the reading of the reference white plate in the main scanning direction and outputs the largest peak value among the output values of all the pixels in the main scanning direction, and the peak value Detecting a peak position of the indicated pixel;
The light source is turned off, and the output value at the peak position among the output values of all the pixels in the main scanning direction output by the image reading means executing the reading of the reference white plate in the main scanning direction corresponds to the black level. Detecting as a value;
Using the target value, the peak value, and the black level corresponding value, a parameter for amplifying the peak value to a light amount that matches the target value is calculated, and the light amount set for the light source A program for causing the image reading apparatus to execute a step of calculating a second light amount adjustment value by applying the parameter to a first light amount adjustment value used for adjustment and changing the setting to the second light amount adjustment value.