JP2007088621A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device capable of obtaining images of higher image quality and improving the product yield. <P>SOLUTION: A digital camera 20 equipped with a CCD 2 is provided with a notch filter (NF) 52 connected to the output terminal of a blue signal B out of imaging signals. The NF 52 works when the color temperature of a subject is smaller than a predetermined threshold and the amplification values for red and blue signals R, B are larger than a predetermined threshold. The NF 52 applies steep attenuation to a signal of 1/2fs that is the Nyquist frequency of 1/2 of the sampling frequency fs, where the sampling frequency fs is the frequency of a transfer clock of an imaging signal, and outputs a signal B' in which the vertical flaw caused by the transfer failure of a VCCD 11 is suppressed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging device equipped with a solid-state imaging device.

  A CCD image sensor (CCD) is known as a solid-state imaging device mounted on an imaging device such as a digital camera or a camera-equipped mobile phone. The CCD is two-dimensionally arranged in a matrix, and is provided for each of a plurality of photoelectric conversion elements (pixels) that convert incident light into signal charges corresponding to the amount of light and store it, and for each vertical column of photoelectric conversion elements. Image pickup according to a signal charge having a plurality of vertical CCDs that vertically transfer signal charges from photoelectric conversion elements and a horizontal CCD that horizontally transfers signal charges for one line (row) transferred from the vertical CCD Output a signal.

The CCD as described above is known to generate a so-called smear that produces a bright vertical band in an image when a white defect due to a defective pixel or a high-luminance subject is photographed. Various techniques have been proposed (see Patent Documents 1 to 4).
JP 2000-101925 A JP 2002-314055 A JP 2005-39727 A JP 2005-101791 A

  In the CCD, in addition to the above-mentioned white scratches and smears, when the transfer efficiency of the vertical CCD is poor, the crosstalk of the signal charges of adjacent pixels increases, and a streaky step (vertical line) appears in the finally obtained image. There was a problem of scratching. This problem is particularly noticeable when red and blue are transferred by the vertical CCDs in the same column, or when the subject is dark.

  Conventionally, however, there has been no method for effectively suppressing this vertical line flaw, so a CCD with poor transfer efficiency has to be repelled at the inspection stage at the time of product shipment, and the product yield has been significantly reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an imaging apparatus capable of obtaining a higher quality image and improving the product yield.

  In order to achieve the above object, the present invention provides a plurality of photoelectric conversion elements arranged two-dimensionally and a plurality of photoelectric conversion elements that are provided for each vertical column of the photoelectric conversion elements and vertically transfer signal charges from the photoelectric conversion elements. In an imaging apparatus having a vertical CCD and a horizontal CCD that horizontally transfers a signal charge for one line transferred from the vertical CCD and mounted with a solid-state imaging device that outputs an imaging signal corresponding to the signal charge, the vertical CCD The present invention is characterized by comprising vertical line flaw suppressing means for suppressing vertical line flaws caused by transfer defects.

  The vertical line flaw suppression means is preferably operated when red and blue are transferred by a vertical CCD in the same column.

  Further, it is preferable that the vertical line flaw suppression means operates when the color temperature of the subject imaged by the solid-state image sensor is smaller than a preset threshold value.

  It is preferable that the vertical line flaw suppression unit operates when an amplification value for a red signal and a blue signal among the imaging signals is larger than a preset threshold value.

  It is preferable that the vertical line flaw suppression means is a specific band attenuation filter that applies sharp attenuation to a signal having a specific frequency corresponding to the vertical line flaw.

  In this case, it is preferable that the specific band attenuation filter is connected to an output of a blue signal of the imaging signals. Further, the specific frequency is preferably a Nyquist frequency that is ½ of the frequency of the transfer clock of the imaging signal as a sampling frequency.

  It is preferable that the vertical line flaw suppression means is an ISO sensitivity adjustment means that lowers the ISO sensitivity within a preset value range.

  The solid-state imaging device has a line memory that temporarily accumulates signal charges for one line transferred from the vertical CCD and outputs the signal charges to the horizontal CCD, and the vertical line flaw suppression means includes the vertical CCD and the line In the line memory and / or the horizontal CCD, a potential potential when transferring the signal charge between the memory and / or the line memory and the horizontal CCD becomes steep toward the rear stage. It is preferable that the voltage adjusting means increase the applied voltage.

  According to the imaging apparatus of the present invention, since the vertical line flaw suppression means for suppressing the vertical line flaw caused by the transfer defect of the vertical CCD is provided, a higher quality image can be obtained and the product yield can be improved. Can do.

  In FIG. 1, a CCD 2 is provided for each of a plurality of photoelectric conversion elements (PD) 10 for converting incident light into signal charges corresponding to the amount of light and storing the signals, and for each vertical column of PDs 10. A plurality of vertical CCDs (VCCDs) 11 for vertical transfer, a horizontal CCD (HCCD) 12 for horizontally transferring signal charges for one line transferred from the VCCD 11, and a signal voltage (imaging) for the signal charges transferred by the HCCD 12. A floating diffusion amplifier (FDA) 13 that converts the signal into a signal and outputs the signal.

  The PDs 10 are formed so that the outer shape thereof is an octagon, and are arranged in a honeycomb shape at a predetermined pitch. On the PD 10, a color filter and a micro lens (not shown) are stacked. Note that RGB notation in the figure indicates the arrangement of red, green, and blue by color filters, and the CCD 2 transfers red and blue by the VCCD 11 in the same column.

  The VCCD 11 employs a so-called two-phase CCD. As indicated by dotted arrows in the figure, the VCCD 11 receives signal charges from the PDs 10 via transfer gates (not shown), and sequentially transfers the signal charges from the top to the bottom in the figure.

  The HCCD 12 is connected to the last stage of the VCCD 11. The HCCD 12 transfers the signal charges for one line received from the VCCD 11 to the FDA 13 one column at a time from the right to the left in the figure, as indicated by the dotted arrows in the figure.

  In FIG. 2, the digital camera 20 on which the CCD 2 is mounted as a solid-state image sensor is controlled overall by a CPU 22 through a bus 21. The digital camera 20 includes an optical system 23, an analog signal processing circuit 24, an A / D conversion circuit (A / D) 25, a buffer memory 26, a compression / decompression processing circuit 27, a YC processing circuit 28, a photometry / ranging circuit 29, and It consists of a timing generator (TG) 30 and the like.

  The optical system 23 includes an imaging lens 31 including a focus lens and a zoom lens and a diaphragm 32. A lens motor 33 and an iris motor 34 are connected to the imaging lens 31 and the diaphragm 32. These motors 33 and 34 are stepping motors, and their operations are controlled by drive pulses transmitted from a motor driver 35 connected to the photometry / ranging circuit 29.

  The lens motor 33 moves the zoom lens of the imaging lens 31 to the wide side or the tele side. Further, the focus lens of the image pickup lens 31 is moved in accordance with zooming magnification of the zoom lens, etc., and the focus adjustment is performed so that the shooting conditions are optimized. The iris motor 34 operates the aperture 32 to adjust exposure. The focus adjustment and the exposure adjustment by the motors 33 and 34 are performed based on the photometry / distance measurement result of the subject by the photometry / distance measurement circuit 29.

  The analog signal processing circuit 24 performs known analog signal processing such as correlated double sampling, amplification, and white balance adjustment on the imaging signal output from the CCD 2 and outputs the processed signal to the A / D 25. The A / D 25 converts the analog signal input from the analog signal processing circuit 24 into a digital image signal and outputs the digital image signal to the buffer memory 26. The buffer memory 26 temporarily stores the image signal digitized by the A / D 25.

  The compression / decompression processing circuit 27 compresses the image data stored in the buffer memory 26 by a predetermined compression method, for example, the JPEG method, and decompresses the compressed image data to restore the original data. The image data compressed by the compression / decompression processing circuit 27 is stored in the memory card 37 via the card I / F 36.

  The YC processing circuit 28 converts the image data stored in the buffer memory 26 into a luminance signal Y and color difference signals Cr and Cb. The image data YC converted by the YC processing circuit 28 is converted into an analog composite signal by the LCD driver 38 and displayed on the LCD 39 as a through image.

  The photometry / ranging circuit 29 detects the luminance of the subject and the distance to the subject, and drives and controls the motor driver 35 so as to obtain an appropriate focal length and exposure amount based on the detection result. The timing generator (TG) 30 is connected to the CCD driver 40 that controls the driving of the CCD 2 together with the analog signal processing circuit 24, the A / D 25, and the YC processing circuit 28 described above. The TG 30 transmits timing signals (clock pulses) to these units. The CCD driver 40 controls the operation of the CCD 2 based on the timing signal transmitted from the TG 30.

  A release button 41, an operation unit 42, and an EEPROM 43 are connected to the CPU 22. The release button 41 is a two-stage push switch. When the release button 41 is lightly pressed (half-pressed), various photographing preparation processes such as automatic exposure adjustment (AE) and automatic focus adjustment (AF) are performed. In this state, when the release button 41 is pressed once more (fully pressed), the imaging signal for one screen subjected to the imaging preparation processing is converted into image data, and then the above-described YC processing and compression processing are performed. And stored in the memory card 37.

  The operation unit 42 is a zoom operation button for zooming the zoom lens to the wide side or the tele side, a menu button operated when displaying a menu screen on the LCD 39 or determining a selection, and a cursor within the menu screen. It includes a cross key to be moved, a mode dial for switching the operation mode (still image shooting mode, moving image shooting mode, playback mode, setting mode, etc.) of the digital camera 20. The CPU 22 operates each unit of the digital camera 20 based on the release button 41 and the operation input signal from the operation unit 42 described above.

  In the EEPROM 43, various control programs and setting information are recorded. The CPU 22 reads out this information from the EEPROM 43 to the built-in RAM, and executes various processes.

  As shown in FIG. 3, the analog signal processing circuit 24 is provided with a color separation unit 50 and a pixel interpolation unit 51. The color separation unit 50 separates the imaging signal output from the CCD 2 into rgb (red, green, and blue) three-color signals and transmits the signals to the pixel interpolation unit 51. The pixel interpolation unit 51 uses a rgb signal color-separated by the color separation unit 50 to create a signal for all pixels including the RGB signal of the virtual pixel at a position where the PD 10 does not actually exist.

  A notch filter (NF) 52 that is a specific band attenuation filter is connected to the output end of the blue signal B of the pixel interpolation unit 51. In the NF 52, the color temperature of the subject required when white balance adjustment is performed by the analog signal processing circuit 24 is smaller than a preset threshold (for example, 3000K), and the amplification values for the red and blue signals R and B are large. When the threshold value is larger than a preset threshold value, that is, when the subject is dark and the gain of amplification is increased.

  As shown in FIG. The NF 52 performs a filter operation on the blue signal B using predetermined filter coefficients τ1 to τ5 and k1 to k3. That is, as shown in FIG. 5, the NF 52 sets the frequency of the transfer clock of the imaging signal as the sampling frequency fs and applies a steep attenuation to the signal having the Nyquist frequency ½ fs, and the signal B ′ Is output. The blue signal B ′ that has passed through the NF 52 is one in which vertical line flaws caused by defective transfer of the VCCD 11 are suppressed. The analog signal processing circuit 24 performs the following processes on the signal B ′ and the red and green signals R and G output from the pixel interpolation unit 51.

  On the other hand, when the color temperature of the subject is higher than a preset threshold and / or the amplification values for the red and blue signals R and B are smaller than the preset threshold, the NF 52 does not operate. The analog signal processing circuit 24 performs the following processes on the signals R, G, and B output from the pixel interpolation unit 51.

  Next, the operation of the digital camera 20 having the above configuration will be described. First, when shooting a subject with the digital camera 20, the power switch of the operation unit 42 is operated to turn on the digital camera 20, and the mode dial is operated to set the still image shooting mode or the moving image shooting mode. select.

  Under the photographing mode, the subject light incident through the imaging lens 31 and the diaphragm 32 is incident on the PD 10 of the CCD 2. In the CCD 2, incident light is converted into a signal charge by the PD 10, and under the control of the CCD driver 40, the signal charge from each PD 10 is transferred from the HCCD 12 to the FDA 13 through the VCCD 11, and converted to a signal voltage (imaging signal) by the FDA 13. And output to the analog signal processing circuit 24.

  In the analog signal processing circuit 24, the image separation signal output from the CCD 2 by the color separation unit 50 is separated into rgb three-color signals, and the pixel interpolation unit 51 generates signals for all the pixels including the RGB signals of the virtual pixels. . When the color temperature of the subject is lower than a preset threshold value and the amplification values for the red and blue signals R and B are larger than the preset threshold value, the NF 52 is activated.

  When the NF 52 is activated, the blue signal B is sharply attenuated with respect to the signal having the Nyquist frequency 1/2 fs of the frequency fs of the transfer clock of the imaging signal, and the vertical line scratch due to the transfer failure of the VCCD 11 is caused. It is output as a suppressed signal B ′. The subsequent processes in the analog signal processing circuit 24 are performed on the signal B ′ output from the NF 52 and the red and green signals R and G output from the pixel interpolation unit 51.

  On the other hand, when the color temperature of the subject is larger than the preset threshold and / or the amplification value for the red and blue signals R and B is smaller than the preset threshold, the NF 52 is not activated and the original Each processing is performed on the signals R, G, and B as they are.

  In the analog signal processing circuit 24, various analog signal processes are performed on the imaging signal. The image signal processed by the analog signal processing circuit 24 is converted into a digital image signal by the A / D 25 and temporarily stored in the buffer memory 26.

  The image data stored in the buffer memory 26 is read out to the YC processing circuit 28, converted into the luminance signal Y and the color difference signals Cr and Cb, and then displayed as a through image on the LCD 39 via the LCD driver 38. . When the release button 41 is pressed halfway in this state, the operation of each unit is controlled by the CPU 22 based on the detection result of the photometry / ranging circuit 29, and photographing preparation processing is performed.

  When shooting is executed by fully pressing the release button 41 after shooting preparation processing, the image data currently recorded in the buffer memory 26 is compressed by the compression / decompression processing circuit 27 in the still image shooting mode, and the card The data is stored in the memory card 37 via the I / F 36.

  On the other hand, under the moving image shooting mode, the image data is stored at a constant frame rate (for example, 30 frames / second) until the release button 41 is fully pressed again. At the same time, ambient sounds are recorded via a microphone (not shown). The sound recorded by the microphone is stored in the memory card 37 in association with the image data.

  As described above, since the NF 52 is used to suppress the vertical line flaw caused by the transfer failure of the VCCD 11, it is possible to obtain an image with good image quality in which the vertical line flaw is not conspicuous. In addition, the allowable range of the VCCD 11 can be expanded at the product inspection stage.

  In addition to using the NF 52 of the above-mentioned embodiment as a method for suppressing the vertical line scratch caused by the transfer failure of the VCCD 11, as shown in FIG. 6, the ISO sensitivity adjustment unit 60 in the CCD driver 40 uses photometry / The ISO sensitivity set based on the detection result of the distance measuring circuit 29 may be lowered within a preset value range. For example, when the ISO sensitivity is 200 (net ISO sensitivity 180), the ISO sensitivity 160 is lowered to the lower limit. As a result, the amplified value in the analog signal processing circuit 24 is lowered, and vertical line flaws can be suppressed.

  As shown in FIG. 7, when a CCD 70 having a line memory (LM) 71 that temporarily accumulates signal charges for one line transferred from the VCCD 11 and outputs the signal charges to the HCCD 12 is used, the CCD driver shown in FIG. In the voltage adjusting unit 80 in 40, the potential potential when the signal charge is transferred between the VCCD 11 and the line memory 71 and / or the line memory 71 and the HCCD 12 becomes steep toward the subsequent stage, that is, The voltage applied to the line memory 71 and / or the HCCD 12 may be increased so that the signal charge can be easily transferred.

  In this case, for example, as schematically shown in FIG. 9, the voltage applied to the LM 71 is increased from normal 5.0 V to 10.0 V, and the voltage applied to the HCCD 12 is increased from normal 3.3 V to 5.0 V. Raise to. In this way, the transfer efficiency of signal charges from the last stage of the VCCD 11 to the LM 71 and from the LM 71 to the HCCD 12 is improved, and vertical line scratches can be suppressed as in the above-described method. In addition, since the voltage is increased only when the color temperature of the subject is smaller than the preset threshold and the amplification values for the red and blue signals R and B are larger than the preset threshold, the voltage is increased. The increase in power consumption due to this can be suppressed to the extent that it does not become a problem.

  In the above embodiment, the CCDs 2 and 70 in which the PDs 10 are arranged in the honeycomb form have been described as examples. However, a so-called Bayer arrangement may be used, and the arrangement of RGB by the color filters is not particularly limited. Further, when all pixels are read out, red and blue are transferred by the vertical CCD in the same column, and when the present invention is applied to a CCD that does not transfer red and blue at interline reading, vertical line scratches are particularly noticeable in the same column. Vertical line flaws may be suppressed only at the time of all pixel readout in which red and blue are transferred by the vertical CCD.

  In the above embodiment, the digital camera 20 has been described as an example of the imaging device. However, the present invention is not limited to this, and the present invention can also be applied to other imaging devices such as a camera-equipped mobile phone.

It is a figure which shows schematic structure of CCD. It is a block diagram which shows the internal structure of a digital camera. It is a block diagram which shows the internal structure of an analog signal processing circuit. It is a figure which shows the structure of a notch filter. It is a graph which shows the characteristic of a notch filter. It is a block diagram which shows the internal structure of the CCD driver in another embodiment of this invention. It is a figure which shows schematic structure of CCD in another embodiment of this invention. It is a block diagram which shows the internal structure of the CCD driver in another embodiment of this invention. It is explanatory drawing showing the transition of the electric potential between the vertical CCD, line memory, and horizontal CCD in another embodiment of this invention.

Explanation of symbols

2, 70 CCD
10 Photoelectric conversion element (PD)
11 Vertical CCD (VCCD)
12 Horizontal CCD (HCCD)
13 Floating diffusion amplifier (FDA)
20 Digital camera 22 CPU
24 Analog signal processing circuit 29 Photometry / ranging circuit 40 CCD driver 52 Notch filter (NF)
60 ISO sensitivity adjuster 71 Line memory (LM)
80 Voltage regulator

Claims (9)

A plurality of photoelectric conversion elements arranged two-dimensionally, a plurality of vertical CCDs that are provided for each vertical column of photoelectric conversion elements and vertically transfer signal charges from each photoelectric conversion element, and one line transferred from the vertical CCD In an imaging device having a horizontal CCD that horizontally transfers a signal charge of minutes, and equipped with a solid-state imaging device that outputs an imaging signal corresponding to the signal charge,
An image pickup apparatus comprising a vertical line flaw suppression means for suppressing a vertical line flaw caused by a transfer failure of a vertical CCD.   2. The imaging apparatus according to claim 1, wherein the vertical line flaw suppression means operates when red and blue colors are transferred by a vertical CCD in the same column.   The image pickup apparatus according to claim 1, wherein the vertical line flaw suppression unit operates when a color temperature of a subject imaged by the solid-state image sensor is smaller than a preset threshold value.   4. The vertical line flaw suppression means operates when an amplification value for a red signal and a blue signal among the image pickup signals is larger than a preset threshold value. Imaging device.   5. The specific band attenuation filter according to claim 1, wherein the vertical line flaw suppression unit is a specific band attenuation filter that applies sharp attenuation to a signal having a specific frequency corresponding to the vertical line flaw. Imaging device.   The imaging device according to claim 5, wherein the specific band attenuation filter is connected to an output of a blue signal of the imaging signals.   The image pickup apparatus according to claim 5 or 6, wherein the specific frequency is a Nyquist frequency that is a half of the transfer frequency of the image pickup signal as a sampling frequency.   The imaging apparatus according to claim 1, wherein the vertical line flaw suppression unit is an ISO sensitivity adjustment unit that lowers the ISO sensitivity within a preset value range. The solid-state imaging device has a line memory that temporarily accumulates signal charges for one line transferred from the vertical CCD and outputs the signal charges to the horizontal CCD.
In the vertical line flaw suppression means, the potential potential when transferring the signal charge between the vertical CCD and the line memory and / or the line memory and the horizontal CCD becomes steep toward the subsequent stage. 5. The imaging apparatus according to claim 1, wherein the imaging apparatus is a voltage adjusting unit that increases a voltage applied to the line memory and / or the horizontal CCD.

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