JP2010103911A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To read a document high in quality by using a line image sensor (CMOS sensor), by changing an image exposure time and a read speed, and by changing the gain of an amplifier in the CMOS sensor. <P>SOLUTION: In this image reader, the CMOS sensor is provided with column amplifiers for individual elements and an amplifier for the final stage. An exposure time to the CMOS sensor is determined in reading, the gain of each column amplifier is set in accordance with the exposure time in outputting a signal on a pixel basis by a transfer pulse, and a high-precision read mode is achieved by adjusting normal white and black image signal levels to each other by changing and setting the gain of the final-stage amplifier (the S/N ratio of the amplifier is improved by lowering the gain and the dynamic range of the sensor is expanded). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion device, for example, a one-dimensional and two-dimensional photoelectric conversion device that performs image reading such as a facsimile, an image scanner, and a digital copying machine. In particular, a method for reading a document image during document conveyance with a document conveyance means and a fixed document set on a document table glass, moving a mirror table with document illumination means to control the document image. The present invention relates to an image reading apparatus using a photoelectric conversion element that can be mounted on an image formability apparatus that employs both reading methods.

  Conventionally, a reading system using a reduction optical system CCD has been used as an image reading system for facsimiles, image scanners, digital copiers, and the like (for example, see Patent Document 1).

In recent years, the development of a contact image sensor (CIS: Contact Image Sensor) of the same magnification system using a single crystal silicon chip in multiple mountings has been remarkable.
JP 2002-40578 A JP-A-6-139342

  However, in the above-described photoelectric conversion device such as CCD or CIS, due to structural factors, when the image reading time is changed and the image light accumulation time is changed so as to read with high image quality, An amplifier cannot be provided at the output stage of the shift register corresponding to the output of each photoelectric conversion element. Therefore, it is necessary to change the gain to the output value of each photoelectric conversion element by the amplifier at the final output stage.

However, changing the gain of the amplifier at the final output stage including variations in photoelectric conversion elements cannot be configured inside the CCD line sensor.
Although it can be realized by reducing the light amount and slowing the reading speed, it is generally difficult to control dimming with a light source such as a xenon lamp. Further, when the light quantity is changed, the above-mentioned problems occur when the light quantity is changed. In addition, in the document disclosed in Patent Document 2, there is a proposal for performing high-precision reading using a second illumination unit different from the first illumination unit, but this includes two illumination units. The cost is expected to increase accordingly.

  Therefore, as a solution to the conventional problem, a CMOS line sensor (hereinafter referred to as a CMOS sensor) that can configure an amplifier (column amplifier) at the output stage of each photoelectric conversion element is used. Since an amplifier and other circuits can be incorporated in the CMOS, this problem can be solved by incorporating a circuit that performs the following functions.

  First, an amplifier (column amplifier) provided for each output of each photoelectric conversion element and a gain adjusting means 1 for adjusting the gain of the column amplifier group are provided. Next, a final stage amplifier for outputting an output signal from each column amplifier from the line sensor and a gain adjusting means 2 for adjusting the gain of the final amplifier are provided. Each gain adjusting means determines the gain of each amplifier by receiving a signal for adjusting the gain from the outside.

  By providing the gain adjusting means 1 and the gain adjusting means 2 as described above and by reducing the image reading speed, reading can be performed in the high image quality mode.

  The slow reading speed increases the image light accumulation time and widens the dynamic range of the CMOS sensor.

  In order to output the image signal from the CMOS sensor, the image signal level from the CMOS sensor is made equal to that in the normal reading mode by using the gain adjusting unit 1 and the gain adjusting unit 2, so that the image can be obtained even in the high quality mode. A signal can be output.

  By combining the CMOS sensor and the reading mode with the above configuration, it is possible to easily realize reading control between the high-accuracy reading mode and the normal mode without changing the light amount and without performing any adjustment on the optical system.

  According to the present invention, when the reading mode is designated as the high-accuracy mode, the accumulation time to be exposed to the line sensor is changed, and the gain of the column amplifier and the gain of the final stage amplifier are changed according to the time compared with the normal reading time. Can be lowered. By reducing the gain itself, the S / N ratio at the time of conversion from the amplifier to the image data can be reduced.

  Further, since it can be performed from the outside of the line sensor only by inputting a gain adjustment signal of the column amplifier and the final stage amplifier, a large-scale peripheral circuit is not required, and the cost can be reduced.

  Furthermore, since the amount of light is not changed, there is an advantage that there is no need to make adjustments in the optical system.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  FIG. 2 is an explanatory diagram of a photoelectric conversion element in a CMOS sensor, and FIG. 3 is an explanatory diagram of a conventional CCD sensor.

  The configuration of the CMOS sensor will be described below based on the explanatory diagram of FIG. Image light read from the optical reading device and the document by a known optical system is exposed to the CMOS sensor from the reading device via a known reflection mirror, optical lens, or the like. By irradiating the image light to the CMOS sensor for a predetermined time, an image for one line is accumulated in the sensor, and an amplifier (column amplifier) corresponding to each photoelectric conversion pixel according to the image light accumulated at the timing from the external clock To the final output stage amplifiers OS1 and OS2. Output from the CMOS sensor from the final stage amplifiers OS1 and OS2 can be used as an image signal. Next, a reset circuit (not shown) prepares for reading the next one line image. Thus, by sequentially obtaining image data for each line, outputting it to the image forming apparatus, and reading it, the original image can be displayed as an image on a medium such as paper or a display. Alternatively, the read data can be stored or obtained by sequentially transferring to the page memory or the storage medium.

  The structure of the CCD sensor is as illustrated in FIG. Here, a shift gate and an analog shift register are configured for each photoelectric conversion element, and image reading control is performed line by line as in the CMOS sensor. After reading one line of image data, the photoelectric conversion element is reset by the ΦRS signal, and the reading is sequentially performed after preparing for the next reading. By doing so, the original image can be read, and finally the original image can be displayed as an image on a medium such as paper or a display. Alternatively, the read data can be stored or obtained by sequentially transferring to the page memory or the storage medium.

  FIG. 1 shows a block diagram of means necessary for carrying out the present invention. FIG. 1 is different from FIG. 2 in that the odd-numbered and even-numbered photoelectric conversion elements are not divided into column amplifiers and output amplifiers. However, if there are two configurations in FIG. It is clear that the same effect can be obtained by using the same control as the configuration.

  The control unit 1 is a control unit that controls the image reading apparatus and performs control in the high-precision reading mode according to the present invention. In the embodiment, a one-chip type microcomputer (hereinafter referred to as a microcomputer) is used. As is well known, this microcomputer includes a storage means (ROM) for performing control on the chip, a storage means (RAM) for performing arithmetic processing, and an input / output port for performing control. . In addition, the square area indicated by the alternate long and short dash line is configured in the line memory sensor internal area.

  Further, as shown in FIG. 2, if the column amplifier group and the output amplifier 5 are separated by odd and even photoelectric conversion elements, if there are two internal configurations of the CMOS sensor of FIG. It is clear that it is good. In this case, only two gain adjustment means for the column amplifier and two gain adjustment means for the output amplifier are required. Therefore, description will be made in the form of FIG.

  Hereinafter, the present invention will be described with reference to FIG.

  First, a description will be given of reading the internal configuration of the line sensor. Before performing the reading control, the image signal level of the photoelectric conversion element described above is set to the reference dark part level by the reset signal RST. Next, the strip-shaped image light obtained from a known reading optical system is exposed on the photoelectric conversion elements provided in a line along the image light on the line sensor. Next, electric power is transmitted from the column amplifier paired with the photoelectric conversion element to the output amplifier 5, and is output from the image element as an image signal for one line from the output amplifier 5. The photoelectric conversion elements for one line are returned to the reference dark part level from the reset circuit 2 and the RST signal. By sequentially performing these controls for the scanning length of image reading, the document can be read.

  An object of the present invention is to change the exposure time determined according to the reading speed between high-accuracy reading and normal reading, and to increase the exposure time in the high-accuracy mode, thereby increasing the photoelectric conversion with respect to the normal reading mode. Expand the dynamic range of the element. Next, in the next high-accuracy reading mode from the photoelectric conversion element, the gains of the column amplifier and the final stage amplifier are lowered by the amount corresponding to the expansion of the dynamic range of the photoelectric conversion element. By reducing the gain of this amplifier, the S / N ratio generated in the amplifier is raised. A high-accuracy reading mode is realized by performing the above rough control. Hereinafter, the control of the present invention will be described in detail.

  By selecting the high-quality reading mode from the operation unit 6 in FIG. 1, the control unit 1 that controls the image reading apparatus and this embodiment selects and executes the high-quality mode on the display unit of the operation unit 6. Display that it is in the middle. In this embodiment, liquid crystal is displayed on the liquid crystal according to the operation input from the liquid crystal as the display means provided on the operation unit means 6 and the panel switch or the plurality of operation switches provided on the liquid crystal as the operation input means. ing. Next, when the start key on the operation unit 6 is pressed, reading is started in the high image quality mode according to the present invention.

  The control means 1 confirms that the scanner unit to be read is at the home position by a known home position detection means (not shown), and returns to the home position when it is not at the home position. ) Is used to return to the home position and at the same time, the original illumination lamp for reading is turned on to prepare for the reading operation. When it is at the home position and the light quantity of the illumination lamp reaches a predetermined value, the control means 1 moves the scanner unit in the reading direction (to read the entire document surface) by the document length in order to read the document next. Control. Further, when an image sensor (not shown) that detects that the front end of the image has been detected as having come to the image reading start position, image light obtained by an illumination lamp, mirror, optical lens, or the like to read the original image Reading is started by the CMOS sensor that projects

  When the high-precision reading mode is set, there is an advantage that the exposure time can be increased and the dynamic range output of the photoelectric conversion element can be increased. Therefore, the control unit 1 performs control as follows using the gain adjusting unit 3 and the gain adjusting unit 4. Using these means, the control means 1 reads the data value based on the current reading mode from the storage means and determines the gain adjustment value of each amplifier. Here, what is used as an example of the signal from the control means 1 to each adjustment means is a pulse signal, and the gain is adjusted by setting the duty of the pulse according to the reading mode.

  By performing this control, the voltage width of the signal level from the CMOS line sensor corresponding to the CMOS sensors “white” and “black” is made the same as the output voltage width value in the high-precision reading mode and the normal reading mode. be able to.

  By performing the above control, the conditions such as the light quantity of the optical system are the same, and the only difference is the scan speed, but the dynamic range of the photoelectric conversion element is expanded, and the column amplifier and the final stage are By determining the gain value of the amplifier and controlling the gain, the image reading operation can be realized by separating the high-precision reading mode and the normal reading mode.

  The above control is an example of reading control for one line, and reading of all images is possible by sequentially reading line by line over the length of the image length as in a known method. That is, when the image signal S is output from the read operation for one line and the output amplifier, the reset circuit 2 is operated by the RST signal to start the read operation for the next line, and the photoelectric conversion element is initialized to the dark level. Do. Read control starts again after initialization, and then resets. By repeating this control and performing a reading operation for the image length, scanning of one page is performed to realize image reading.

  FIG. 4 shows the flow of the present invention. The default setting of the reading mode of the reading apparatus according to the present embodiment is set to the normal reading mode. When the high image quality mode is selected by input from the operation unit 6, the control is performed as described above, and the reading control is started in the high image quality mode.

  The adjustment unit 1 that adjusts the gain value of the column amplifier and the adjustment unit 2 that adjusts the gain value of the final-stage amplifier according to the image reading mode whose setting has been changed by the user performs control for changing the setting value. 5 is a routine of image reading shown in FIG.

  This routine is a routine for setting gain values of the gain adjusting means 3 and the gain adjusting means 4. According to the set reading mode, the gain value of the column gain is set to A1 (S-2) when the accuracy is high, and A2 (S-4) when the normal reading mode is set, and A1 <A2.

  This is because the dynamic range of the CMOS sensor is increased by extending the exposure time in the high-accuracy reading mode, and thus it is necessary to lower the gain. Another reason is to reduce the gain of the amplifier to suppress noise from the amplifier and improve the S / N ratio.

  Next, the gain of the amplifier at the final stage is set to B1 (S-3) in the high-precision reading mode, and is set to B2 (S-5) in the normal reading mode. This is the same reason as the previous column amplifier, because the dynamic range of the CMOS sensor is widened by increasing the exposure time in the high-precision reading mode, and it is necessary to reduce the gain. This is to suppress the noise from and improve the S / N ratio.

  The present invention is realized by executing S-1 → S-2 → S-3 in FIG. 4 in the high-precision reading mode and executing S-1 → S-4 → S-5 in the normal reading mode.

  As described above, the present invention is realized by changing the gain value of each amplifier between the high-precision reading mode and the normal reading mode.

It is a figure explaining the circuit structure of the photoelectric conversion apparatus of this invention. 1 is a block diagram of an image forming apparatus equipped with a photoelectric conversion device of the present invention. 3 is a timing chart of the photoelectric conversion device of the present invention. It is the general flow which sets the gain of the column amplifier and the output amplifier 5 at the time of reading control of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control means 2 Reset circuit 3 Gain adjustment means 4 Gain adjustment means 5 Output amplifier 6 Operation part means

Claims (2)

A plurality of photoelectric conversion elements;
An optical signal output line for outputting an optical signal via an amplifier circuit (hereinafter referred to as a column amplifier) corresponding to the photoelectric conversion element on a one-to-one basis and transmitting the optical signal to an output amplifier;
A gain adjusting means 1 for changing the gain of each column amplifier in accordance with the exposure time;
Reset means for resetting the photoelectric conversion element to a fixed potential by an external signal;
As a means for outputting an optical signal to the optical signal output line in order from the plurality of column amplifiers, an output amplifier means for outputting, as an image signal, signals sequentially output from the optical signal output line using an external clock;
Gain adjusting means 2 for determining the gain of the output amplifier according to the exposure time and the output of the column amplifier selected by the external pulse;
An optical signal is output to the optical signal output line in order from the photoelectric conversion element, the column amplifier, and the external pulse, and a line sensor that outputs an image signal from the output amplifier is provided.
The exposure time of the image light to the line sensor is changed according to the read mode set as the high image quality mode or the normal image quality for the line sensor, and the gain control means 1 and the gain control means 2 are further changed. An image reading apparatus comprising: control means for reading an image signal from the line sensor by changing gains of the column amplifier and the output amplifier means.   The image reading apparatus according to claim 1, wherein the line sensor is a CMOS sensor.

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