JP6106566B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus and an image forming apparatus including the image reading apparatus, and more particularly to a technique for limiting the level of an analog pixel signal output from an image sensor.

  In an image reading apparatus using a CCD sensor, light from a light source is irradiated on a document on a platen glass, and a part of reflected light on the document surface is imaged on a light receiving surface of the CCD sensor. The CCD sensor reads the image by converting the image formed on the light receiving surface into an electric signal for each pixel. Such an image reading apparatus is usually an apparatus for reading a flat document image, and is configured to form an image on a CCD sensor light receiving surface with a part of diffusely reflected light diffused on the document surface.

  However, for example, when scanning a three-dimensional glossy object such as a precious metal or a wristwatch as a manuscript or a glossy object such as a glossy credit card, the irradiation light depends on the reflectance and the way of placing (reflection angle) of the glossy object. Is reflected regularly by the curved surface of the glossy object, the output of the CCD sensor may exceed the input range of the subsequent AFE (analog processing unit) and become an abnormal image.

  As a method for solving the above problem, Patent Document 1 describes a technique in which a limiter circuit is provided between a CCD sensor and an AFE so as not to exceed the input range of the AFE.

Japanese Patent No. 4389828

  However, the limiter circuit shown in Patent Document 1 includes a reference voltage source, two diodes connected in series, a transistor, a resistor, and a capacitor, and has a problem that the circuit configuration is complicated. In order to solve this problem, for example, it is assumed that a voltage dividing resistor is provided between the CCD sensor and the AFE to limit the pixel signal output from the CCD sensor within the input range of the AFE.

  However, in this configuration, since the level of all pixel signals output from the CCD sensor is attenuated by the voltage dividing resistor, the level of the pixel signal is uniformly lowered even when an abnormal image does not appear, and the dynamic range is lowered. There is a problem.

  An object of the present invention is to provide an image reading apparatus and an image forming apparatus that suppress a decrease in dynamic range while having a simple circuit configuration.

(1) An image reading apparatus according to an aspect of the present invention includes: a light source that irradiates a document; an image sensor that receives reflected light from the document and outputs an analog pixel signal; A processing unit that processes the pixel signal output from the image sensor; and a first path that connects the image sensor and the processing unit, wherein the first path is the pixel output from the image sensor. A voltage dividing unit for attenuating a signal at a predetermined voltage dividing ratio for attenuating the signal to a level within the input range of the processing unit; a voltage dividing path for outputting the pixel signal to the processing unit via the voltage dividing unit; and unbranched pressure path for outputting the pixel signal to the processing unit without passing through the dividing unit, a switch for selecting the partial pressure path or the unbranched pressure path, a pixel signal outputted from the partial pressure path Predetermined A amplifier unit for amplifying an amplification factor, the first path, and outputs a pixel signal of one row among the odd and even columns of the image sensor to the processing unit, different from the one of the column When the second path for outputting the pixel signal of the other column of the image sensor to the processing unit without being attenuated and the switch selects the voltage dividing path, the pixel signal output from the second path is abnormal. A determination unit that determines whether or not an image is included; and when the determination unit determines that an abnormal image is included, the pixel signal of the one column that has been attenuated is amplified by the amplification unit The interpolated pixel signal of the other column is interpolated using the pixel signal thus obtained, and the interpolated pixel signal of the other column and the pixel signal of the one column adjacent to the pixel signal are combined. Generate line image signal, When the determination unit determines that the abnormal image is not included, the attenuated pixel signal of the one column and the pixel signal of the other column adjacent to the pixel signal are combined to generate one line A synthesizing unit that generates an image signal, and the synthesizing unit outputs a pixel signal for one line in the other column and a pixel signal for one line in the one column output from the determination unit. Processing for combining each of the pixel signals for one line of the one column stored in the buffer and the pixel signals for one line of the other column in order from the top pixel Do.

  According to this configuration, when the voltage dividing path is selected by the switch, the pixel signal output from the image sensor is attenuated to a level within the input range of the processing unit by the voltage dividing unit, and is input to the processing unit. After the processing is performed, the amount of attenuation is compensated by amplification with a predetermined amplification factor. On the other hand, when the non-voltage dividing path is selected by the switch, the pixel signal output from the image sensor is output without being attenuated.

As described above, in this configuration, when a glossy object is read, the switch can select a voltage dividing path to prevent a pixel signal exceeding the input range from being input to the processing unit. On the other hand, when reading a normal document, the switch can select a non-voltage-dividing path, and image quality deterioration due to reduction of the dynamic range can be suppressed. Furthermore, since the pixel signal is attenuated using the voltage dividing unit, it is possible to prevent the pixel signal exceeding the input range from being input to the processing unit with a simple circuit configuration.
Further, according to this configuration, when it is determined that the pixel signal of one of the odd or even columns includes an abnormal image, the pixel signal is attenuated and then amplified by the amplifying unit and input to the synthesizing unit. Then, the pixel signals in the other column different from the one column are input to the synthesis unit without being attenuated. Then, after the pixel signal of the other column is interpolated by the pixel signal of one adjacent column by the combining unit, the adjacent pixel signals are combined. Therefore, it is possible to prevent an abnormal image in which the pixel signal has an abnormal value from being output as an output image.
Further, according to this configuration, when an abnormal image is not included, the attenuated pixel signal of one column and the adjacent non-attenuated pixel signal of the other column are combined to form a one-line image. A signal is generated. Therefore, it is possible to suppress the reduction of the dynamic range as compared with the configuration in which all pixel signals are attenuated.

Further comprising an operation unit for accepting a selection instruction of glossy object reading mode from User chromatography The said switch, when the glossy object reading mode is selected, may select the content pressure path.

  According to this configuration, the user can set the image reading apparatus to a mode suitable for reading a glossy object simply by inputting a selection instruction for selecting the glossy object reading mode.

  According to this configuration, when it is determined that the pixel signal of one column that is an odd column or an even column includes an abnormal image, the pixel signal is attenuated and then amplified by the amplifying unit and input to the combining unit. Pixel signals in the other column different from the one column are input to the synthesis unit without being attenuated. Then, after the pixel signal of the other column is interpolated by the pixel signal of one adjacent column by the combining unit, the adjacent pixel signals are combined. Therefore, it is possible to prevent an abnormal image in which the pixel signal has an abnormal value from being output as an output image.

  According to this configuration, when an abnormal image is not included, the attenuated pixel signal of one column and the adjacent non-attenuated pixel signal of the other column are combined to form an image signal of one line. Generated. Therefore, it is possible to suppress the reduction of the dynamic range as compared with the configuration in which all pixel signals are attenuated.

Before Symbol combining unit, when the switch selects the unbranched pressure path, and the pixel signals of the one row that is not attenuated, and a pixel signal of the other row adjacent to the pixel signal by combining, One line of image signal may be generated.

  According to this configuration, when a normal document is read, the pixel signal of one non-attenuated column and the pixel signal of the other non-attenuated column adjacent thereto are combined, so that the dynamic range is reduced. Can be maintained.

An image forming apparatus according to another aspect of the present invention includes the above-described image reading device and an image forming unit that forms an image using an image signal output from the image reading device.

  According to this configuration, it is possible to provide an image forming apparatus that can obtain the above effects.

  According to the present invention, when a glossy object is read, the switch can select a voltage dividing path, and a pixel signal exceeding the input range can be prevented from being input to the processing unit. On the other hand, when reading a normal document, the switch can select a non-voltage-dividing path, and image quality deterioration due to reduction of the dynamic range can be suppressed. Furthermore, since the pixel signal is attenuated using the voltage dividing unit, it is possible to prevent the pixel signal exceeding the input range from being input to the processing unit with a simple circuit configuration.

1 is a configuration diagram illustrating an example of a configuration of a multifunction peripheral that is an example of an image forming apparatus including an image reading apparatus according to a first embodiment of the present invention. 2 is a configuration diagram illustrating an example of a configuration of a document feeder and an image reading apparatus. FIG. (A) is a diagram showing how the image reading device reads a planar document, and (B) is a diagram showing how the image reading device reads a three-dimensional glossy object. 1 is a block diagram illustrating an example of a configuration of a multifunction machine according to Embodiment 1 of the present invention. 4 is a flowchart illustrating an example of the operation of the image reading apparatus according to the first embodiment of the present invention. It is a block diagram which shows an example of a structure of the multifunctional device which concerns on Embodiment 2 of this invention. 10 is a flowchart illustrating an example of processing of the image reading apparatus according to Embodiment 2 of the present invention.

(Embodiment 1)
Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram illustrating an example of a configuration of a multifunction machine 1 that is an example of an image forming apparatus including an image reading device 4 according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the multi-function device 1 has a plurality of functions such as a copy function, a printer function, a scanner function, and a facsimile function. The multi-function device 1 is disposed at the top of the main body 2, the stack tray 3 provided on the left side of the main body 2, the operation unit 36 for the user to input various operation commands and the like. The image reading device 4 and a document feeder 5 disposed above the image reading device 4 are provided.

  The main body 2 is transported from a plurality of paper feed cassettes 23, a paper feed roller 24 that feeds out originals (recording paper) from the paper feed cassette 23 one by one to the image forming unit 25, and the paper feed cassette 23. And an image forming unit 25 for forming an image on the original.

  The image forming unit 25 outputs a laser beam or the like based on image data acquired by the image reading device 4 to be described later, an optical unit 27 that exposes the photosensitive drum 26, and a toner image on the photosensitive drum 26. And a developing unit 28 to be formed. The image forming unit 25 further includes a transfer unit 29 that transfers the toner image on the photosensitive drum 26 to the original, and a pair of rollers 30 and 31 that heat the original to which the toner image has been transferred and fix the toner image on the original. And a fixing device 32. The image forming unit 25 further includes transport roller pairs 34 and 35 that are provided in a paper transport path in the image forming unit 25 and transport documents to the stack tray 3 or the discharge tray 33.

  The operation unit 36 includes a start key 361 for a user to input execution instructions for various functions provided in the multifunction device 1, a numeric keypad 362 for inputting the number of copies, and a liquid crystal display having a touch panel function. And a display unit 363 for displaying information. In addition, the operation unit 36 includes a reset key 364 for resetting the setting contents set on the display unit 363, a stop key 365 for stopping a printing (image forming) operation being performed, a copy function, a printer function, A function switching key 366 for switching between a scanner function and a facsimile function is provided.

  FIG. 2 is a configuration diagram illustrating an example of the configuration of the document feeder 5 and the image reading device 4. As shown in FIG. 2, the document feeder 5 includes a document tray 51, a sheet feed roller 52, a transport drum 53, a sheet discharge roller 54, and a sheet discharge tray 55, and includes an ADF (Auto Document Feeder). Is configured. The originals placed on the original tray 51 are taken one by one by the paper feed roller 52 and conveyed to the conveyance drum 53. The document that has passed through the transport drum 53 is discharged to a discharge tray 55 by a discharge roller 54.

  The image reading device 4 optically acquires an image of a document and outputs an image signal. For example, as shown in FIG. 2, the image reading device 4 includes a contact glass 411, a light source (light source unit) 42, a first mirror 431, a second mirror 432, a third mirror 433, a first carriage 46, a second carriage 47, A condenser lens 48 and a CCD (Charge Coupled Device) (image sensor) 49 are provided.

  The contact glass 411 is a place where a document to be read is placed. The light source 42 and the first mirror 431 are supported by the first carriage 46, and the second mirror 432 and the third mirror 433 are supported by the second carriage 47.

  In the image reading device 4, there are two types of modes: a flat bed reading mode for reading a document placed on the contact glass 411, and an ADF reading mode for conveying the document by the document feeding unit 5 and reading the document in the middle of conveyance. It is possible to read the original by (method).

  In the flat bed reading mode, the light source 42 irradiates light toward one line (reading target line) extending in the main scanning direction of the reading target in the document placed on the contact glass 411. Then, the reflected light from the reading target line is reflected in the order of the first mirror 431, the second mirror 432, and the third mirror 433, and enters the condenser lens 48. The light incident on the condenser lens 48 is condensed and emitted to the CCD 49. The CCD 49 photoelectrically converts the received light.

  The CCD 49 is a one-dimensional image sensor, which simultaneously processes an image of a document for one line and outputs an analog signal representing the intensity of received light as a voltage. When the reading for one line is completed, the first carriage 46 and the second carriage 47 are moved in a direction (sub-scanning direction, arrow Y direction) perpendicular to the main scanning direction (direction perpendicular to the paper surface) of the document. The line is read.

  On the other hand, in the ADF reading mode, the originals placed on the original tray 51 are taken in one by one by the paper feed roller 52, and the originals are provided with a reading window 410 provided in the conveyance path from the conveyance drum 53 to the paper discharge tray 55. When passing through the gap portion of the guide plate 59, the light source 42 irradiates the reading target line with light through the reading window 410. The reflected light from the reading target line is reflected in the order of the first mirror 431, the second mirror 432, and the third mirror 433, and enters the condenser lens 48. The light incident on the condenser lens 48 is condensed and emitted to the CCD 49. The CCD 49 photoelectrically converts the received light. When the reading for one line is completed, the document is conveyed in the sub-scanning direction by the document feeder 5, and the next line is read.

  FIG. 3A is a diagram illustrating a state in which the image reading device 4 reads a planar document 301, and FIG. 3B is a diagram illustrating a state in which the image reading device 4 reads a three-dimensional glossy object 302. It is. As shown in FIG. 3A, when the original 301 is read, the reflected light from the original of the light emitted from the light source 42 becomes irregularly reflected light, and a part thereof enters the CCD 49. On the other hand, as shown in FIG. 3B, when the glossy object 302 is read, the reflected light of the light emitted from the light source 42 from the glossy object 302 enters the CCD 49 as regular reflection light.

  Therefore, the amount of reflected light incident on the CCD 49 is significantly larger when reading the glossy object 302 than when reading the original 301. The input range of the analog front end (AFE) provided at the rear stage of the CCD 49 is set to the range of the pixel signal output from the CCD 49 when the original 301 is read. Therefore, when the glossy object 302 is read, a problem that the pixel signal input to the AFE exceeds the input range of the AFE occurs.

  In order to solve this problem, a voltage dividing resistor having a voltage dividing ratio of (maximum output of the CCD sensor) × (voltage dividing ratio) ≦ (AFE input range) is provided between the CCD 49 and the AFE, and the level of the pixel signal Can be attenuated and amplified to a necessary range by an amplifier provided in the subsequent stage.

  However, in this case, since the pixel signal is attenuated even when the original 301 is read, the dynamic range may be lowered and the image quality may be deteriorated.

  Therefore, in the present embodiment, image deterioration is prevented by not attenuating when reading the original 301, and an abnormal image is not generated when the glossy object 302 is read. This will be specifically described below.

  FIG. 4 is a block diagram showing an example of the configuration of the multifunction machine 1 according to the first embodiment of the present invention. The multifunction device 1 includes an image sensor 400, a first path 401, an AFE 402, an amplification unit 403, an image forming unit 404, a control unit 405, and an operation unit 406.

  The image sensor 400 is constituted by the CCD image sensor 49 shown in FIG. 1, receives light reflected from the original of the light emitted from the light source 42 (see FIG. 2), and outputs an analog pixel signal corresponding to the received light quantity. Output. Here, the image sensor 400 employs, for example, a one-line line sensor in which a plurality of pixels are arranged in the main scanning direction. The main scanning direction is a direction orthogonal to the document transport direction. The image sensor 400 sequentially outputs pixel signals generated at each pixel to the first path 401. Specifically, the image sensor 400 sequentially outputs the pixel signal of each pixel to the first path 401 in order from the one end pixel in the main scanning direction to the other end pixel.

  In the case where the image sensor 400 is configured by a line sensor of a plurality of lines, the image sensor 400 is, for example, at one end in the main scanning direction of the line sensor in the first row in the sub-scanning direction (document transport direction). The pixel signal of each pixel is sequentially output to the first path 401 in the order from the pixel toward the other end pixel, and when this is completed, the pixel signal of the line sensor in the second row is output to the first line sensor in the same manner as the line sensor in the first row. The pixel signal is output in such a manner as to be output to the path 401. The image sensor 400 is not limited to a CCD image sensor, and a CMOS image sensor may be employed.

  In this embodiment, an analog voltage signal whose value increases as the amount of light increases is used as the pixel signal. However, this is an example, and an analog voltage signal whose value decreases as the amount of light increases may be employed as the pixel signal.

  The first path 401 outputs pixel signals sequentially output from the image sensor 400 to the AFE 402. The first path 401 includes a non-voltage dividing path 4011, a voltage dividing path 4012, a switch 4013, a voltage dividing unit 4014, and a capacitor C1.

  The voltage dividing unit 4014 is provided on the voltage dividing path 4012, attenuates the pixel signal output from the image sensor 400 at a predetermined voltage dividing ratio, and outputs it to the AFE 402 via the capacitor C1. Here, when the maximum value of the pixel signal is Amax and the maximum value Bmax of the input range of the AFE 402, the voltage divider 4014 attenuates the pixel signal at a predetermined voltage division ratio R that satisfies the conditional expression of Amax × R ≦ Bmax. For example, as the voltage dividing ratio R, a value lower than Bmax / Amax by a predetermined margin is employed.

  Here, the voltage dividing unit 4014 includes resistors R1 and R2. One end of the resistor R1 is connected to the image sensor 400 via the switch 4013, the other end is connected to the AFE 402 via the capacitor C1, and is grounded via the resistor R2. Assuming that the resistance values of the resistors R1 and R2 are R1 and R2, R1 and R2 adopt values at which R1 / (R1 + R2) is a voltage dividing ratio R.

  One end of the voltage dividing path 4012 is connected to the image sensor 400 via the branch point P1, and the other end is connected to the connection point P2. The pixel signal output from the image sensor 400 is passed through the voltage dividing unit 4014 and the capacitor C1. And output to the AFE 402.

  One end of the non-voltage dividing path 4011 is connected to the image sensor 400 via the branch point P1, and the other end is connected to the connection point P2. The pixel signal output from the image sensor 400 is not passed through the voltage dividing unit 4014. Output to AFE 402.

  The switch 4013 selects the non-voltage dividing path 4011 or the voltage dividing path 4012 as a connection destination of the output terminal O1 of the image sensor 400. Specifically, the switch 4013 is configured by an analog switch including buffers A1 and A2. The buffer A1 has an input terminal and an output terminal connected to the non-voltage dividing path 4011 and includes a control terminal CT1. The buffer A2 has an input terminal and an output terminal connected to the voltage dividing path 4012, and includes a control terminal CT2. When a high level signal is output from the control unit 405, a high level signal is input to the control terminal CT1, a low level signal is input to the control terminal CT2, and the switch 4013 connects the output terminal O1 to the non-voltage dividing path 4011. Let On the other hand, when a low level signal is output from the control unit 405, a low level signal is input to the control terminal CT1 and a high level signal is input to the control terminal CT2, and the switch 4013 connects the output terminal O1 to the voltage dividing path 4012. Connect. As described above, the switch 4013 selects the non-voltage dividing path 4011 or the voltage dividing path 4012 as a connection destination of the image sensor 400 according to the signal output from the control unit 405. The capacitor C1 is provided between the connection point P2 and the AFE 402, and cuts the DC component of the pixel signal.

  The AFE 402 includes a processing unit 4021. The processing unit 4021 removes noise components from the input analog pixel signal by clamping processing for determining a black level, CDS (correlated double sampling) processing for removing noise components from the clamped pixel signals, and the like. A / D conversion processing is performed to convert the obtained pixel signal into a digital pixel signal, which is output to the amplifying unit 403.

  The amplifying unit 403 amplifies the digital pixel signal output from the processing unit 4021, which is a pixel signal output via the voltage dividing path 4012, and outputs the amplified signal to the image forming unit 404. Here, the amplifying unit 403 amplifies the pixel signal with a predetermined amplification factor for returning the pixel signal attenuated by the voltage dividing unit 4014 to the original level. For example, if the voltage dividing ratio R of the voltage dividing unit 4014 is 50%, the amplifying unit 403 may amplify the pixel signal with a double amplification factor. In addition, when the switch 4013 selects the voltage dividing path 4012, the amplifying unit 403 performs processing for amplifying the pixel signal in accordance with an instruction from the control unit 405. On the other hand, when the switch 4013 selects the non-voltage dividing path 4011, the amplifying unit 403 does not perform the process of amplifying the pixel signal in accordance with an instruction from the control unit 405.

  The image forming unit 404 is configured by the image forming unit 25 shown in FIG. 1, and forms an image using an image signal composed of pixel signals output from the amplifying unit 403.

  The control unit 405 is composed of, for example, a microcontroller, and governs overall control of the multifunction machine 1. In the present embodiment, the control unit 405 outputs a low level signal to the switch 4013 particularly when the operation unit 406 receives an instruction to select a glossy object reading mode that causes the image reading apparatus 4 to read a glossy object. Then, the output terminal O1 is connected to the voltage dividing path 4012.

  On the other hand, the control unit 405 outputs a high-level signal to the switch 4013 when the operation unit 406 receives an instruction to select a normal reading mode that causes the image reading device 4 to read a flat document, and sets the output terminal O1 to the non-output terminal O1. It is connected to the partial pressure path 4011. Thus, when the glossy object reading mode is selected by the user, the pixel signal is output to the AFE 402 via the voltage dividing path 4012, and when the user selects the normal reading mode, the pixel signal passes through the non-voltage dividing path 4011. To the AFE 402.

  Note that when the normal reading mode is selected by the user, the control unit 405 outputs an instruction not to execute the amplification process to the amplification unit 403, and stops the amplification process by the amplification unit 403. In this case, the amplification unit 403 passes through the pixel signal and outputs it to the image forming unit 404. Thereby, it is possible to prevent the non-attenuated pixel signal output from the non-voltage dividing path 4011 from being amplified.

  The operation unit 406 includes the operation unit 36 illustrated in FIG. 1, receives a selection instruction from the user for setting the image reading apparatus 4 to the glossy object reading mode or the normal reading mode, and notifies the control unit 405 of the selection instruction.

  FIG. 5 is a flowchart showing an example of the operation of the image reading apparatus 4 according to the first embodiment of the present invention. First, when the operation unit 406 receives a selection instruction for selecting the glossy object reading mode from the user (YES in S501), the control unit 405 causes the switch 4013 to select the voltage dividing path 4012 (S502).

  Next, the CCD image sensor 400 reads an image of a glossy object (S503), and sequentially outputs pixel signals to the AFE 402 via the voltage dividing path 4012. As a result, the pixel signal is attenuated by the voltage dividing ratio R by the voltage dividing unit 4014, clamp processing, CDS processing, and A / D conversion processing are performed by the AFE 402 and then input to the amplifying unit 403.

  Next, the amplifying unit 403 amplifies the input pixel signal with a predetermined amplification factor (S504), and outputs it to the image forming unit 404.

  On the other hand, when the operation unit 406 receives an instruction to select the normal reading mode from the user in S501 (NO in S501), the control unit 405 causes the switch 4013 to select the non-voltage dividing path 4011 (S505).

  Next, the image sensor 400 reads an image of the document (S506). As a result, the pixel signal is input to the AFE 402 without being attenuated, and after the clamp processing, CDS processing, and A / D conversion processing are performed by the AFE 402, the image forming unit 404 is not attenuated by the amplification unit 403. Is input.

  As described above, according to the first embodiment, the pixel signal is attenuated and input to the AFE 402 only when the glossy object reading mode is selected, so that it is possible to prevent the occurrence of an abnormal image when the glossy object is read. In addition, it is possible to prevent image quality deterioration when a normal document is read.

(Embodiment 2)
In the image forming apparatus according to the second embodiment, for example, the same first path 401 as that of the first embodiment is connected to the output terminals O1 of the even columns of the image sensor 400, and the output terminals O2 of the pixels of the odd columns. Is characterized in that the second path 501 having no voltage dividing function is connected. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  FIG. 6 is a block diagram illustrating an example of the configuration of the multifunction machine 1 according to the second embodiment of the present invention. The second path 501 has one end connected to the odd-numbered output terminal O <b> 2 of the image sensor 400 and the other end connected to the AFE 402. The capacitor C2 is provided on the second path 501 and cuts the DC component of the pixel signal.

  The AFE 402 includes processing units 4021 and 4022. The processing unit 4021 performs clamp processing, CDS processing, and A / D conversion on the pixel signals in the odd columns, and outputs the result to the determination unit 502. The processing unit 4022 performs clamp processing, CDS processing, and A / D conversion on the pixel signals in the even columns, and outputs the result to the amplification unit 403.

  When the switch 4013 selects the voltage dividing path 4012, the determination unit 502 determines whether or not an abnormal image is included in the odd-numbered pixel signals output from the second path 501. Here, the determination unit 502 monitors, for example, the peak value of the pixel signal for one line in the odd-numbered column, and if it is equal to or greater than a predetermined peak threshold, the image for the one line includes an abnormal image. judge. On the other hand, if the peak value of the pixel signal for one line in the odd-numbered column is less than the peak threshold value, the determination unit 502 determines that the abnormal image is not included in the image for the one line. As the peak threshold value, a predetermined value indicating an abnormal image is employed.

  Note that when the switch 4013 selects the non-voltage dividing path 4011, the determination unit 502 does not perform the above-described determination process, and passes through the odd-numbered pixel signals and outputs them to the combining unit 503. Here, the determination unit 502 is notified from the control unit 405 of information indicating whether the switch 4013 has selected the voltage dividing path 4012 or the non-voltage dividing path 4011, and the switch 4013 determines whether the switch 4013 selects the non-voltage dividing path 4011 or What is necessary is just to judge whether the partial pressure path | route 4012 was selected.

  When the determining unit 502 determines that the abnormal image is included, the combining unit 503 outputs the pixel signal of the odd column to the pixel signal of the adjacent even column that is output via the voltage dividing path 4012. The signal is interpolated, and the odd-numbered pixel signals and the adjacent even-numbered pixel signals are combined to generate a one-line image signal. Here, the synthesis unit 503 assumes that the index that defines the arrangement order of the pixels in the odd and even columns is i, the pixel signal in the odd column is ODD (i), and the pixel signal in the even column is EVEN (i). , ODD (i) = EVEN (i) to interpolate the odd-numbered pixel signals. Then, if the combined pixel signal is G (i), the combining unit 503 has G (i) = (ODD (i) + EVEN (i)) / 2, that is, ODD (i) and EVEN (i). May be generated as a combined pixel signal.

  Here, when the voltage division ratio R is 50% and both the odd and even columns are attenuated, the dynamic range of the pixel signal G (i) is reduced to 50% compared to the case where both the odd and even columns are not attenuated. Is done. In this case, the dynamic range of the pixel signal is reduced to 50% even in a place where no glossy object exists, and image quality deterioration occurs.

  On the other hand, when the determining unit 502 does not determine that an abnormal image has occurred, the combining unit 503 uses the odd-numbered pixel signal ODD (i) output from the second path 501 and the adjacent even-numbered pixel signal. Thus, the pixel signal EVEN (i) output via the voltage dividing path 4012 is combined to generate a one-line image signal. Here, the combining unit 503 may generate, for example, G (i) = (ODD (i) + EVEN (i)) / 2 as a combined pixel signal.

  When the switch 4013 selects the non-voltage dividing path 4011, the synthesizing unit 503 is an even-numbered pixel signal adjacent to the odd-numbered pixel signal output from the second path 501, and the non-voltage-divided signal The pixel signal output via the path 4011 is combined to generate a one-line image signal.

  In the example of FIG. 6, when only the even-numbered columns are attenuated, the dynamic range of the odd-numbered columns is 100%, but the dynamic range of the even-numbered columns is reduced to 50%. , (100 + 50) / 2 = 75% reduction, and reduction of the dynamic range can be suppressed as compared with the case where both the odd and even columns are attenuated.

  FIG. 7 is a flowchart showing an example of processing of the image reading apparatus 4 according to Embodiment 2 of the present invention. S701 is the same as S501 in FIG. In step S <b> 702, the control unit 405 causes the switch 4013 to select the voltage dividing path 4012. Next, the image sensor 400 reads an image of a glossy object (S703). Here, the odd-numbered pixel signals output from the second path 501 are subjected to clamp processing, CDS processing, and A / D conversion processing by the processing unit 4021, input to the determination unit 502, and output from the first path 501. The even-numbered pixel signals are attenuated by the voltage divider 4014, clamped, CDS processed, and A / D converted by the processor 4022 and input to the amplifier 403.

  Next, the amplifying unit 403 amplifies the input pixel signals of even columns (S704). Next, the determination unit 502 compares the pixel signals in the odd columns with the peak threshold value and determines whether or not an abnormal image has occurred (S705). If it is determined that an abnormal image has occurred (YES in step S705), the combining unit 503 interpolates the odd-numbered pixel signals with the adjacent even-numbered pixel signals, and then combines the adjacent pixel signals to generate one line. The pixel signal is generated (S706). In this case, since the odd-numbered columns and the even-numbered columns are both attenuated, the dynamic range is reduced to 50% compared to the case where the odd-numbered columns and the even-numbered columns are not attenuated.

  On the other hand, if it is determined that no abnormal image has occurred (NO in S705), the combining unit 503 combines the odd-numbered pixel signals and the attenuated adjacent even-numbered pixel signals (S707). One line of image signal is generated. In this case, only the even-numbered columns are attenuated and the odd-numbered columns are not attenuated. Therefore, compared with the case where both the even-numbered columns and the odd-numbered columns are attenuated, the reduction of the dynamic range is suppressed to 75%.

  Here, the combining unit 503 is provided with, for example, a buffer that holds pixel signals for odd lines and lines and a buffer that holds pixel signals for even lines and lines. Then, the synthesis unit 503 sequentially stores the pixel signals output from the determination unit 502 and the amplification unit 403 in both buffers, and when the pixel signal for one line is stored, the determination result of the determination unit 502 is displayed. Based on this, the processing of S706 or S707 may be started in order from the first pixel of one line stored in the buffer. By doing so, the processing of S706 or S707 can be performed on the pixel signal input to the combining unit 503 before the occurrence of the abnormal pixel is detected.

  If NO in S701, that is, if the normal reading mode is set, the switch 4013 selects the non-voltage dividing path 4011 (S708). Next, the image sensor 400 reads an image of the document (S709). Next, the synthesizing unit 503 synthesizes the pixel signals of the odd-numbered columns and the pixel signals of the adjacent even-numbered columns that are not attenuated (S710), and generates a one-line image signal. In this case, both the odd and even columns are not attenuated, and the dynamic range is maintained at 100%.

  As described above, in the second embodiment, when the glossy object reading mode is set, if an abnormal image does not occur, only the even-numbered columns are attenuated, so that the reduction of the dynamic range can be suppressed.

  In FIG. 6, the first path 401 is an even-numbered column and the second path 501 is an odd-numbered column, but this embodiment is not limited to this, and the first path 401 is an odd-numbered column and the second path 501 is an even-numbered column. It may be a row.

400 Image sensor 401 First path 402 AFE
403 Amplifying unit 404 Image forming unit 405 Control unit 406 Operation unit 501 Second path 502 Discriminating unit 503 Combining unit 4011 Non-voltage dividing path 4012 Voltage dividing path 4013 Switch 4014 Voltage dividing unit 4021 Processing unit 4022 Processing unit 4104 Voltage dividing unit

Claims (4)

A light source for illuminating the document;
An image sensor that receives reflected light from the original of the light emitted from the light source and outputs an analog pixel signal;
A processing unit for processing the pixel signal output from the image sensor;
A first path connecting the image sensor and the processing unit,
The first route is
A voltage dividing unit that attenuates the pixel signal output from the image sensor at a predetermined voltage dividing ratio that attenuates the pixel signal to a level within an input range of the processing unit;
A voltage dividing path for outputting the pixel signal to the processing unit via the voltage dividing unit;
A non-voltage dividing path for outputting the pixel signal to the processing unit without going through the voltage dividing unit;
A switch for selecting the voltage dividing path or the non-voltage dividing path ;
An amplification unit that amplifies the pixel signal output from the voltage dividing path at a predetermined amplification rate ,
The first path outputs pixel signals of one of the odd and even columns of the image sensor to the processing unit,
A second path for outputting the pixel signal of the other column of the image sensor different from the one column to the processing unit without attenuating;
A determination unit that determines whether an abnormal image is included in the pixel signal output from the second path when the switch selects the voltage dividing path;
When it is determined by the determination unit that an abnormal image is included, the pixel signal of the one column that has been attenuated and amplified by the amplification unit is used for the other column adjacent to the other column. The pixel signal is interpolated, and the interpolated pixel signal of the other column and the pixel signal of the one column adjacent to the pixel signal are combined to generate a one-line image signal. A combining unit that combines the attenuated pixel signal of the one column and the pixel signal of the other column adjacent to the pixel signal to generate a one-line image signal when it is determined that the pixel signal is not included And further comprising
The synthesizing unit includes buffers that store pixel signals for one line of the other column output from the determination unit and pixel signals for one line of the one column output from the amplification unit, respectively. An image reading apparatus that performs the process of combining the pixel signals for one line of the one column stored in the buffer and the pixel signals for one line of the other column in order from the top pixel . An operation unit for receiving a glossy object reading mode selection instruction from a user;
The image reading apparatus according to claim 1, wherein the switch selects the voltage dividing path when the glossy object reading mode is selected. When the switch selects the non-voltage dividing path, the combining unit combines the pixel signal of the one column that is not attenuated and the pixel signal of the other column adjacent to the pixel signal, the image reading apparatus according to claim 1 or 2 wherein generating an image signal of the line. An image reading apparatus according to any one of claims 1 to 3 ,
An image forming apparatus comprising: an image forming unit that forms an image using an image signal output from the image reading apparatus.

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