JP2009182582A - Image reader, and device for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of reducing noise contained in output image data when an image is read by an optoelectric transducer and the image data are output. <P>SOLUTION: Analog signals are acquired by reading the image with a CCD (S11), and samplings for detecting DC offset voltage values at a timing a<SB>1</SB>and the timing a<SB>2</SB>are conducted twice and the samplings for detecting voltage values displaying the image signals obtained from the image at the timing b<SB>1</SB>and the timing b<SB>2</SB>are conducted twice (S12 to S15). The analog signals of each voltage value obtained by the samplings at every two times are converted into digital signals by AD conversion sections 36a and 36b (S16). Each converted voltage value is operated and processed by an operation processing section 37 and the image data are output (S17). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image reading apparatus and an image forming apparatus, and more particularly to an image reading apparatus that reads an image by a photoelectric conversion element and outputs image data, and an image forming apparatus including such an image reading apparatus. .

  In general, a digital multi-function peripheral includes an image reading device including a photoelectric conversion element such as a charge coupled device (CCD). Then, an image is formed based on the image data output from the image reading device. Specifically, an analog signal including an image signal obtained by reading an image with a CCD is sampled, a voltage value of the sampled analog signal is converted into a digital signal, and image data is output. Here, the image data is noise due to noise superimposed on the CCD, noise due to a sampling timing shift during AD (analog / digital) conversion, AD conversion error, and rounding error of numerical values when image processing is performed on the image data. There are various noise sources such as noise caused by image compression. It is preferable to remove and adjust such noise as much as possible by correction or the like.

Note that, among a plurality of image reading devices, an image reading device in which variation in adjustment among the devices is improved is disclosed in JP-A-6-105135 (Patent Document 1). According to Patent Literature 1, the image reading apparatus automates the adjustment of the amplitude of the analog image signal, thereby minimizing the variation in the adjustment between the apparatuses.
JP-A-6-105135

  A general waveform of an analog signal obtained from the CCD is shown in FIG. Referring to FIG. 6, an analog signal 101 is a signal obtained by superimposing an image signal on a DC offset voltage of several V (volts) that serves as a reference for obtaining image data. Note that a range indicated by an arrow in FIG. 6 is a range indicating an image of one pixel.

  In order to extract only the image signal component from the analog signal 101, double correlation sampling is generally performed. In the double correlation sampling, sampling is performed at a predetermined timing x for detecting the DC offset voltage value in FIG. 6 and a timing y for detecting a voltage value representing an image signal obtained from the image. The difference between the voltage value at the time y and the voltage value at the timing y is extracted as an image signal component. Note that the number of times of sampling is one each.

  Here, when such double correlation sampling is performed, there are the following problems. First, in the sampling of the voltage value representing the image signal obtained from the image, a theoretically constant value is shown, but when it is affected by noise at the timing of sampling y, it represents the image signal obtained from the image. The voltage value is also affected by noise. Next, in general, the timing of sampling is determined by a clock. However, if the accuracy of the clock is low, the sampling timing may be shifted and noise may be generated.

  An object of the present invention is to provide an image reading apparatus capable of reducing noise included in image data to be output when an image is read by a photoelectric conversion element and image data is output.

  Another object of the present invention is to provide an image forming apparatus capable of forming a high-quality image.

  The image reading apparatus according to the present invention reads an image with a photoelectric conversion element and outputs image data. Here, the image reading apparatus performs sampling for detecting, for each pixel, a DC offset voltage value that is superimposed on an analog signal among analog signals obtained by the photoelectric conversion element and serves as a reference for obtaining image data. One sampling means, a second sampling means for performing sampling for detecting, for each pixel, a voltage value representing an image signal obtained from an image among analog signals obtained by the photoelectric conversion element, and at least a first or Control means for controlling one of the second sampling means to perform a plurality of times, a DC offset voltage value sampled by the first and second sampling means, and a voltage value representing an image signal obtained from the image AD conversion means for converting an analog signal into a digital signal, and AD conversion means And a processing means for outputting the image data by processing the voltage value representing an image signal obtained from the conversion has been DC offset voltage value and image.

  Preferably, the arithmetic processing means performs the arithmetic processing based on a plurality of DC offset voltage values obtained by sampling a plurality of times by the control means or a voltage value obtained by averaging voltage values representing image signals obtained from the images. .

  The arithmetic processing means performs arithmetic processing based on a central voltage value among a plurality of DC offset voltage values obtained by sampling a plurality of times by the control means or a voltage value representing an image signal obtained from an image. You may do it.

  More preferably, the control means performs each sampling in the first and second sampling means a plurality of times.

  More preferably, the photoelectric conversion element is a CCD.

  In another aspect of the present invention, an image forming apparatus includes any of the image reading devices described above.

  According to the present invention, when an image is read by a photoelectric conversion element and image data is output, a DC offset voltage value serving as a reference for obtaining image data or a voltage value representing an image signal obtained from the image is set for each pixel. Since at least one of the samplings for detection is performed a plurality of times, the influence of noise during sampling can be reduced. Therefore, noise included in the output image data can be reduced.

  In addition, since such an image forming apparatus includes an image reading apparatus that can reduce noise included in output image data, a high-quality image can be formed.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a digital multifunction peripheral 10 when an image forming apparatus including an image reading apparatus according to an embodiment of the present invention is applied to the digital multifunction peripheral 10. Referring to FIG. 1, a digital multifunction peripheral 10 displays a control unit 11 that controls the entire digital multifunction peripheral 10, a DRAM 12 for writing and reading image data and the like, and information that the digital multifunction peripheral 10 has. An operation unit 13 that includes a display screen and serves as an interface with the user in the digital multi-function peripheral 10, a document feeder 14 that automatically transports a document to a predetermined document reading position, and a document that has been transported by the document feeder 14 An image reading device 15 that reads the image at a predetermined reading position, an image forming unit 16 that forms the image from a document read by the image reading device 15 and outputs the image to a sheet, and a hard disk 17 that stores image data and the like. A FAX communication unit 18 connected to the public line 20 and a network IF (interface) for connecting to the network 21. And an over scan) section 19.

  The control unit 11 compresses and writes the original data output from the image reading device 15 to the DRAM 12, reads the data written in the DRAM 12, decompresses and encodes it, and outputs it by the image forming unit 16.

  The digital multi-function peripheral 10 operates as a copier by forming an image in the image forming unit 16 via the DRAM 12 using a document read by the image reading device 15. Further, the digital multifunction peripheral 10 forms an image in the image forming unit 16 via the DRAM 12 using the image data transmitted from the personal computer 22 connected to the network 21 through the network IF unit 19, thereby serving as a printer. Operate. Furthermore, the digital multifunction peripheral 10 forms an image in the image forming unit 16 via the DRAM 12 using the image data transmitted from the public line 20 through the FAX communication unit 18, and also by the image reading device 15. The image data of the read original is transmitted to the public line 20 through the FAX communication unit 18 to operate as a facsimile machine.

  In FIG. 1, thick arrows indicate the flow of image data, and thin arrows indicate the flow of control signals or control data.

  Next, the configuration of the image reading device 15 will be described. FIG. 2 is a schematic diagram showing the document feeder 14 and the image reading device 15. FIG. 3 is a block diagram showing the configuration of the image reading device 15. 1 to 3, image reading device 15 includes a reading sensor 30 that reads an image of a document.

  The reading sensor 30 includes a CCD 31 that reads an image on one side (front side) of a document, and a CIS (Contact Image Sensor) 32 that reads an image on the other side (back side) of the document. The CCD 31 reads an image on the surface of the document by irradiating the surface of the document with the light source 33 through the reading glass 34 and receiving the reflected light. The CIS 32 is provided with a reading glass (not shown). The CIS 32 has a built-in light source (not shown). The CIS 32 irradiates the reading surface of the reading glass with light from a light source and receives reflected light from the back side of the document, thereby reading the image on the back side of the document. A document read by the image reading device 15 is conveyed to the position of the reading sensor 30 by the document feeding device 14.

  The image reading device 15 also includes a clock 35, two AD conversion units 36a and 36b that convert the analog signal voltage value obtained by the CCD 31 into a digital signal, and voltage values converted by the AD conversion units 36a and 36b. And an image processing unit 38 for performing image processing on the image data output by the calculation processing unit 37. As the AD conversion units 36a and 36b, analog front-end ICs having three-channel input terminals are used. Having three channels can support three outputs of R, G, and B. The analog front end IC can handle two outputs, and by providing a plurality of analog front end ICs, it can also handle six outputs.

  Next, the case where the CCD 31 included in the image reading device 15 reads an image and outputs image data will be described. FIG. 4 is a flowchart showing the operation of the control unit 11 in this case. 1 to 4, first, when the control unit 11 of the digital multi-function peripheral 10 receives an image reading request, the image is read by the CCD 31 to acquire an analog signal (in FIG. 4, step S <b> 11 and the following steps). , Omit the steps). Thereafter, sampling is performed to detect, for each pixel, the DC offset voltage value and the voltage value representing the image signal obtained from the image among the analog signals obtained by the CCD 31. Sampling is performed according to the clock 35 generated for detecting each voltage value.

  Here, sampling timing will be described with reference to FIG. FIG. 5 is a diagram illustrating the sampling timing described above, and corresponds to FIG. From the viewpoint of easy understanding, the waveform of the analog signal 39 shown in FIG. 5 is a shape obtained by extending the waveform of the analog signal 101 shown in FIG. Both are ranges indicated by arrows.

Referring to FIGS. 1 to 5, according to the clock 35, performs first sampling for detecting the DC offset voltage value at the timing _{a 1} (S12). Next, the second sampling for detecting the DC offset voltage value at timing a ₂ is performed at a timing different from timing a ₁ , that is, the sampling timing with timing a ₁ is shifted (S 13). Here, the control part 11 etc. operate | move as a 1st sampling means. Thereafter, the first sampling is performed to detect a voltage value representing an image signal obtained from the image at timing b ₁ (S14). Next, the second sampling for detecting the voltage value representing the image signal obtained from the image at the timing b ₂ is performed by shifting the timing different from the timing b ₁ , that is, the sampling timing with the timing b _1. (S15). Here, the control unit 11 and the like operate as second sampling means.

The analog signals of the respective voltage values obtained by sampling twice in this way are converted into digital signals by the AD conversion units 36a and 36b (S16). In this case, the voltage value sampled at the _first sampling, that is, the timing a ₁ and the timing b ₁ is converted by the AD conversion unit 36a and sampled at the second sampling, that is, the timing a ₂ and the timing b _2. The converted voltage value is converted by the AD conversion unit 36b. Here, the AD conversion units 36a and 36b operate as AD conversion means.

  Next, each voltage value converted by AD conversion is subjected to arithmetic processing by the arithmetic processing unit 37 to output image data (S17). Here, the arithmetic processing unit 37 and the like operate as arithmetic processing means. Image data D obtained by the arithmetic processing is derived by the following mathematical formula.

D = ((b ₂ + b ₁ ) / 2) − ((a ₂ −a ₁ ) / 2)
That is, here, the calculation process is performed based on two DC offset voltage values obtained by sampling twice and a voltage value obtained by averaging voltage values representing image signals obtained from two images.

When an analog front end IC is used, the output value obtained from the analog front end IC is D ₁ calculated by (b ₁ -a ₁ ) and (b ₂ -a ₂ ) for one pixel image. since a D ₂ calculated, averaged for one pixel of the image is carried out by the following equation.

D = (D ₁ + D ₂ ) / 2
Thereafter, the image processing unit 38 performs image processing from the image data output by the arithmetic processing unit 37 (S18), compresses the image data (S19), and ends the reading of the image data.

  With this configuration, when an image is read by the CCD 31 and image data is output, sampling for detecting a DC offset voltage value or a voltage value representing an image signal obtained from the image for each pixel is performed. Since it is performed once, the influence of noise at the time of sampling can be reduced. That is, even if there is an influence of noise at the time of one sampling, the influence can be reduced. Therefore, noise included in the output image data can be reduced.

  In this case, since the sampling for detecting the DC offset voltage value or the voltage value representing the image signal obtained from the image for each pixel is performed twice, the DC offset voltage value and the image signal obtained from the image are The influence of noise at the time of sampling for detecting the voltage value to be expressed for each pixel can be reduced more reliably.

  In addition, since the digital multifunction peripheral 10 includes the image reading device 15 that can reduce noise included in the output image data, a high-quality image can be formed.

  Note that such a configuration can be configured at low cost because it only increases the number of analog front-end ICs that are general-purpose products as AD conversion units and changes the control of the control unit 11. That is, noise can be effectively reduced by a small-scale configuration change as compared with the conventional configuration.

  In the above embodiment, the arithmetic processing is performed by the above-described mathematical formula. However, the present invention is not limited to this, and it is obtained from a plurality of DC offset voltage values or a plurality of images obtained by sampling a plurality of times. The arithmetic processing may be performed based on the central voltage value among the voltage values representing the received image signal.

  In the above embodiment, sampling for detecting the DC offset voltage value for each pixel and sampling for detecting the voltage value representing the image signal obtained from the image for each pixel are performed twice. However, the present invention is not limited to this, and only one of them may be performed a plurality of times, or three or more samplings may be performed. When only one of them is performed a plurality of times, it is preferable to perform the sampling a plurality of times with priority given to sampling for detecting a voltage value representing an image signal obtained from the image.

  In the above embodiment, the CCD is used as the photoelectric conversion element. However, the present invention is not limited to this, and the CIS may be used as the photoelectric conversion element or used for other photoelectric conversion elements. May be.

  In the above embodiment, the image reading apparatus is controlled by the control unit of the digital multifunction peripheral. However, the present invention is not limited to this, and the image reading apparatus has a control unit that controls the image reading apparatus itself. It is good.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

1 is a block diagram illustrating an overall configuration of a digital multi-function peripheral including an image reading apparatus according to an embodiment of the present invention. It is the schematic which shows an image reading apparatus. It is a block diagram which shows the structure of an image reading apparatus. It is a flowchart which shows operation | movement of the control part at the time of reading an image with an image reader and outputting image data. It is a figure which shows the timing of sampling of an analog signal. It is a figure which shows the general waveform of the analog signal obtained from CCD.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Digital multifunction device, 11 Control part, 12 DRAM, 13 Operation part, 14 Document feeder, 15 Image reader, 16 Image formation part, 17 Hard disk, 18 FAX communication part, 19 Network IF part, 20 Public line, 21 Network , 22 PC, 30 reading sensor, 31 CCD, 32 CIS, 33 light source, 34 reading glass, 35 clock, 36a, 36b AD conversion unit, 37 arithmetic processing unit, 38 image processing unit, 39 analog signal.

Claims (6)

An image reading device that reads an image by a photoelectric conversion element and outputs image data,
A first sampling means for performing sampling for detecting, for each pixel, a DC offset voltage value which is superimposed on the analog signal among the analog signals obtained by the photoelectric conversion element and serves as a reference for obtaining the image data; ,
A second sampling means for performing sampling for detecting, for each pixel, a voltage value representing an image signal obtained from the image among analog signals obtained by the photoelectric conversion element;
Control means for controlling to perform at least one of the first or second sampling means a plurality of times;
AD conversion means for converting an analog signal of the DC offset voltage value sampled by the first and second sampling means and a voltage value representing an image signal obtained from the image into a digital signal;
An image reading apparatus comprising: an arithmetic processing unit that performs arithmetic processing on the DC offset voltage value converted by the AD converting unit and a voltage value representing an image signal obtained from the image and outputs image data. The arithmetic processing means performs arithmetic processing based on a plurality of the DC offset voltage values obtained by sampling a plurality of times by the control means or voltage values obtained by averaging voltage values representing image signals obtained from the images. The image reading apparatus according to claim 1, which is performed. The arithmetic processing means performs arithmetic processing based on a central voltage value among a plurality of the DC offset voltage values obtained by sampling a plurality of times by the control means or a voltage value representing an image signal obtained from the image. The image reading apparatus according to claim 1, wherein: The image reading apparatus according to claim 1, wherein the control unit performs each sampling in the first and second sampling units a plurality of times. The image reading device according to claim 1, wherein the photoelectric conversion element is a CCD. An image forming apparatus comprising the image reading apparatus according to claim 1.

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