JP2006157341A - Smear correcting method and signal processor for solid-state imaging device, and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of miscorrection wherein noise is amplified and regarded as a smear component to be subtracted from a signal in a video period when not a smear, but the noise is superposed on a signal in a vertical blanking period as the gain of AGC is increased in a method of simply subtracting the signal in the vertical blanking period from the signal in the video period. <P>SOLUTION: When the smear is corrected, not a smear detected value detected by a smear detector 211 is subtracted as it is, but a smear correction value obtained by multiplying the smear detected value by a correction coefficient through a multiplier 212 is subtracted by a subtractor 214 from an imaging signal in the video period, and the smear correction value is set according to, for example, the lightness of a subject image. For example, the smear correction value is made smaller and smaller as the subject image is darker and darker, and when the quantity of light of the subject image is less than a threshold, the smear correction value is minimized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a smear correction method for a solid-state imaging device, a signal processing device for the solid-state imaging device, and an imaging device.

  Here, the imaging apparatus is a solid-state imaging device as an imaging device, an optical system that forms an image of a subject on the imaging surface of the solid-state imaging device, and a camera module including a signal processing circuit of the solid-state imaging device, Assume a camera system equipped with the camera module.

  There is a so-called smear as a phenomenon unique to a charge transfer type solid-state image sensor represented by a solid-state image sensor, in particular, a CCD (Charge Coupled Device) image sensor. Here, smear means that when a very bright (bright) subject (for example, the sun, car light, etc.) exists in the captured image, the charges excited by the image light of the subject are transferred to peripheral pixels or vertically. This is a vertical streak-like bright line that can be formed in the vertical direction of the captured image by leaking into the image. This smear contributes to the deterioration of image quality.

  In a CCD image sensor, when charges excited by image light of a very bright subject leak into, for example, a vertical transfer unit, a smear component resulting from the smear component is an effective pixel region in which a pixel signal is actually used as an imaging signal ( (Region corresponding to the video period) as well as a so-called optical black region (region corresponding to the vertical blanking period), which is a pixel region in which the pixels are optically shielded. Here, since there is no input of image light from the subject in the optical black area, in principle, only a smear component exists in the vertical transfer portion of the optical black area.

  In view of this point, in order to improve image quality degradation due to smear, conventionally, a signal obtained in the vertical blanking period from an imaging signal including a smear component obtained in the video period, that is, a signal in the optical black area is regarded as a smear component. Thus, smear correction is performed by taking out only the original imaging signal (see, for example, Patent Document 1).

JP-A-4-334274

  However, in the above-described conventional technique in which the vertical blanking period signal is simply subtracted from the video period signal, for example, when an image is captured in a dark environment, an AGC (Automatic Gain Control) control amount (gain) is set. If the vertical blanking period signal contains noise instead of smear, the noise is also amplified and regarded as a smear component, and error correction is performed to subtract from the video period signal. Therefore, the image quality of the entire screen may be deteriorated, for example, vertical stripes are generated due to the erroneous correction.

  The present invention has been made in view of the above-described problems, and the object of the present invention is to provide a smear correction method for a solid-state image sensor capable of preventing image quality deterioration due to erroneous smear correction, and a signal for the solid-state image sensor. It is to provide a processing device and an imaging device.

  In order to achieve the above object, in the present invention, a smear signal is detected, and a smear correction value based on the smear signal is arbitrarily set, preferably according to the brightness of the subject image, and the set smear correction value is set. Is subtracted from the imaging signal in the video period to perform smear correction.

  In the smear correction, the detected smear signal is not subtracted as it is from the image signal during the video period, but the smear correction value set based on the smear signal is subtracted, while the smear correction value is set to, for example, the brightness of the subject image. For example, when imaging is performed in a dark environment, that is, when the brightness of the subject image is dark, the smear correction value is set lower than in normal imaging. As a result, when noise is added to the signal in the vertical blanking period instead of smear, even if the noise is amplified by AGC, the noise component is subtracted as it is as a smear component from the imaging signal in the video period. Instead, the smear correction value set low is subtracted. As a result, it is possible to avoid erroneous smear correction.

  According to the present invention, it is possible to avoid erroneous correction of smear, particularly during imaging in a dark surrounding environment, thereby preventing image quality deterioration due to the erroneous correction and obtaining a high-quality captured image. it can.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system block diagram illustrating a configuration example of an imaging apparatus according to the present invention. In FIG. 1, image light incident from a subject (not shown) is imaged on an imaging surface (light receiving surface) of a solid-state imaging device, for example, a CCD image sensor 12 by an optical system including a lens 11.

  As is well known, the CCD image sensor 12 includes an effective pixel region (region corresponding to a video period) in which a pixel signal including a photoelectric conversion element is actually used as an imaging signal, and an optical black region in which the pixel is optically shielded. (Region corresponding to the vertical blanking period), and outputs the signal of the optical black region as a black level reference signal, and photoelectrically converts the image light incident on the effective pixel region pixel by pixel Output as.

  This CCD image sensor 12 has a CCD drive circuit 13 that reads signal charges photoelectrically converted in each pixel to a vertical transfer unit, drives transfer of a vertical transfer unit and a horizontal transfer unit, and electrical signals of signal charges. Driving such as conversion to is performed. The imaging signal output from the CCD image sensor 12 is subjected to processing such as CDS (Correlated Double Sampling) and AGC (Automatic Gain Control) in an analog front end (AFE) unit 14. Then, it is supplied to the video signal processing circuit 20.

  The video signal processing circuit 20 includes a smear correction circuit 21, a luminance detection unit 22, a sync generator 23, a timing generator 24, a controller 25, and the like according to the present invention.

  In principle, the smear correction circuit 21 detects smear from a signal in a vertical blanking period (a period corresponding to an optical black area), and detects the smear component from an imaging signal in a video period (a period corresponding to an effective pixel area). The smear correction is performed by subtraction, and details thereof will be described later.

  The luminance detection unit 22 integrates luminance signal components for a certain period, for example, one frame period, and takes a weighted average value for a plurality of frames (for example, about 15 frames) to respond to the luminance (brightness) of the subject image. The obtained luminance information (brightness information) is obtained and given to the controller 25.

  The sync generator 23 generates a vertical synchronization signal VD and a horizontal synchronization signal HD, which are the reference for the operation of the entire system, and supplies them to the smear correction circuit 21, the luminance detection unit 22, the timing generator 24, and the like.

  The timing generator 24 generates various timing signals for driving the CCD image sensor 12 via the CCD drive circuit 13 based on the vertical synchronization signal VD and the horizontal synchronization signal HD, for example, a read pulse, a vertical transfer pulse, and a horizontal transfer pulse. A pulse signal such as a shutter pulse is generated.

  The controller 25 is constituted by, for example, a microcomputer (hereinafter referred to as a microcomputer), and controls the entire system including control for smear correction according to the present invention. Specifically, in accordance with the luminance information given from the luminance detection unit 22, the AGC amount for determining the AGC gain in the analog front end unit 14, the shutter value for determining the shutter speed during the electronic shutter operation, and the like are set. In addition, control for setting a correction coefficient for determining a smear correction value for smear correction described later is performed.

  The nonvolatile memory 15 stores (stores) an adjustment amount of a smear correction value set in accordance with the characteristics of the CCD image sensor 12 and the analog front end unit 14 and the performance of a smear detector 211 described later. Therefore, the controller 25 sets a correction coefficient for determining the smear correction value based on the adjustment amount stored in the nonvolatile memory 15 when performing the smear correction.

  FIG. 2 is a block diagram showing an example of the configuration of the smear correction circuit 21. As apparent from FIG. 2, the smear correction circuit 21 according to this example includes a smear detector 211, a multiplier 212, a correction coefficient register 213, and a subtracter 214.

  Of the image pickup signal output from the CCD image sensor 12, the optical black region signal is used as a black level reference signal in the subsequent signal processing. On the other hand, when there is a very bright (bright) subject, such as the sun or car light, in the captured image, the charge excited by the image light of the subject leaks into the surrounding pixels and vertical transfer unit Since the smear that extends also extends to the optical black region, this smear signal is superimposed on the signal in the optical black region.

  The smear detector 211 detects an optical black region signal among the imaging signals output from the CCD image sensor 12 in synchronization with a vertical blanking signal VBLK indicating a vertical blanking period. Specifically, since the remaining signal obtained by subtracting the black level from the signal in the optical black region becomes a smear signal (smear component), the smear signal is detected and stored in an internal memory (not shown).

  The multiplier 212 supplies a multiplication result obtained by multiplying the smear detection value detected by the smear detector 211 by the correction coefficient supplied from the correction coefficient register 213 to the subtracter 214 as a smear correction value. In the correction coefficient register 213, the controller 25 shown in FIG. 1 corrects the smear correction value set according to the brightness of the subject image based on the adjustment amount of the smear correction value stored in the nonvolatile memory 15. Coefficients are stored.

  That is, the controller 25, the multiplier 212, and the correction coefficient register 213 arbitrarily set a smear correction value based on the smear signal detected by the smear detector 211, specifically, according to the brightness (luminance) of the subject image. It constitutes possible setting means.

  The subtracter 214 is a multiplication result of the multiplier 212 from the imaging signal output from the CCD image sensor 12 (the smear signal is superimposed when smear occurs) in the video period (period corresponding to the effective pixel area). Subtract the smear correction value. Thereby, as a subtraction result of the subtracter 214, a video signal after smear correction for removing the smear signal superimposed on the imaging signal from the imaging signal in the video period is obtained.

  Here, the setting of the smear correction value according to the brightness of the subject image will be described more specifically along the flowchart of FIG. 4 with reference to FIG. 3 showing the relationship between the subject light amount and the correction coefficient. The process for setting the smear correction value is executed by a microcomputer constituting the controller 25.

  When the subroutine for this processing is called, the microcomputer takes in a luminance integrated value (luminance information) indicating the brightness of the subject image from the luminance detecting unit 22 (step S11), and a plurality of frames (for example, 15 for the luminance integrated value). Based on the weighted average value, a shutter value that determines the shutter speed of the electronic shutter and an AGC amount that determines the gain of AGC in the analog front end unit 14 are calculated (step S12).

  The relationship between the luminance integrated value and the AGC amount will be described. As shown in FIG. 3, when the luminance integrated value ≦ Vth1, that is, when the imaging target is a dark subject image, the maximum value is set as the AGC amount, and the luminance integrated value ≧ When Vth2, that is, when the imaging target is a bright subject image, a minimum value is set as the AGC amount. In the range of Vth1 <luminance integral value <Vth2, the luminance of the subject image increases as the luminance integral value increases. Accordingly, the AGC amount gradually decreases from the maximum value to the minimum value, for example, linearly.

  After calculating the shutter value and the AGC amount, the microcomputer determines whether or not the subject light amount (brightness of the subject image) is less than or equal to the first threshold value Vth1 based on the AGC amount (step S13), and subject light amount ≦ Vth1. When the imaging object is a dark subject image, the smear detection value detected by the smear detector 211 has the largest AGC amount, and the influence of noise becomes the largest, and the smear signal value is reliable. Since it is extremely low, a minimum value, for example, 0.20 is set as a correction coefficient to be multiplied by the smear detection value (step S14).

  Next, the microcomputer determines whether or not the subject light amount is greater than or equal to the second threshold value Vth2 based on the AGC amount (step S15). When the subject light amount ≧ Vth2, that is, when the imaging target is a bright subject image, smear detection is performed. Since the smear detection value detected by the detector 211 is extremely reliable as a smear signal value due to the minimum AGC amount, a maximum value, for example, 1.00 is set as a correction coefficient to be multiplied by the smear detection value ( Step S16). Thereby, smear detection value = smear correction value.

  If it is determined that the subject light quantity ≦ Vth1 or the subject light quantity ≧ Vth2, that is, Vth1 <subject light quantity <Vth2, the influence of noise increases due to the increase in the amount of AGC as the dark subject image becomes, and the smear detection value As the smear signal value becomes less reliable, the correction coefficient is gradually reduced, for example, linearly as the subject light quantity decreases, that is, the brightness of the subject image becomes darker (step S17). Negative correction.

  As described above, in the smear correction, the smear detection value detected by the smear detector 211 is not subtracted as it is from the image signal during the video period, but the multiplier 212 multiplies the smear detection value by the correction coefficient. While the obtained smear correction value is subtracted by the subtractor 214, the smear correction value is set according to the brightness of the subject image, for example, the smear correction value is decreased as the subject image becomes darker, and the subject light amount By setting the smear correction value to the minimum when the value is less than or equal to the first threshold value Vth1 and making the smear correction passive, it is possible to avoid erroneous smear correction.

  That is, when noise is added to the signal in the vertical blanking period instead of smear, even if the noise is amplified by AGC, the noise component is detected as a smear component as it is and subtracted from the imaging signal in the video period. Instead, the smear detection value detected by the smear detector 211 is multiplied by a correction coefficient set lower than that in the case of a bright subject image to set the smear correction value low, thereby reducing smear correction. By subtracting the correction value, erroneous correction is not performed in which the noise component is directly subtracted from the imaging signal during the video period as a smear component.

  In this way, erroneous correction of smear can be avoided, so that even in the case of imaging in a dark ambient environment, even if noise is riding on the vertical blanking period signal instead of smear, the vertical Since an unnatural image such as a streak can be prevented from being captured, a high-quality captured image can be obtained.

  As for the correction coefficient to be multiplied by the smear signal value detected by the smear detector 211, the value of the point A corresponding to the first threshold value Vth1 and the value of the point B corresponding to the second threshold value Vth2 in FIG. These are set according to the characteristics of the CCD image sensor 12 and the analog front end unit 14 and the performance of the smear detector 211, and stored in the nonvolatile memory 15 (see FIG. 1) as an adjustment amount of the smear correction value. By setting the correction coefficient based on the adjustment amount, it is possible to absorb the difference in smear detection value due to the characteristics of the CCD image sensor 12 and the analog front end unit 14 and the performance of the smear detector 211.

It is a system block diagram which shows the structural example of the imaging device which concerns on this invention. It is a block diagram which shows an example of a structure of a smear correction circuit. It is a figure which shows the relationship of a subject light quantity-a correction coefficient. It is a flowchart which shows the procedure of the process which sets a smear correction value according to the brightness of a to-be-photographed image.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Lens, 12 ... CCD image sensor, 13 ... CCD drive circuit, 14 ... Analog front end (AFE) part, 15 ... Nonvolatile memory, 20 ... Video signal processing circuit, 21 ... Smear correction circuit, 22 ... Luminance detection part , 23 ... Sync generator, 24 ... Timing generator, 25 ... Controller, 211 ... Smear detector, 212 ... Multiplier, 213 ... Correction coefficient register, 214 ... Subtractor

Claims (8)

A first step capable of detecting a smear signal and arbitrarily setting a smear correction value based on the smear signal;
And a second step of subtracting the smear correction value set in the first step from an imaging signal in a video period. The smear correction method for a solid-state imaging device according to claim 1, wherein in the first step, the smear correction value is set according to the brightness of a subject image. Smear detection means for detecting a smear signal from an imaging signal output from the solid-state imaging device;
Setting means capable of arbitrarily setting a smear correction value based on the smear signal detected by the smear detection means;
A signal processing apparatus for a solid-state imaging device, comprising: a subtracting unit that subtracts the smear correction value set by the setting unit from an imaging signal in a video period. The signal processing apparatus for a solid-state imaging element according to claim 3, wherein the setting means sets the smear correction value according to the brightness of a subject image. The setting means includes
Multiplication means for multiplying the smear signal detected by the smear detection means by a correction coefficient;
5. The signal processing apparatus for a solid-state imaging device according to claim 4, further comprising a control unit that controls the correction coefficient in accordance with brightness of a subject image. Storage means for storing an adjustment amount of the smear correction value;
The signal processing apparatus for a solid-state imaging device according to claim 3, wherein the setting means sets the smear correction value based on the adjustment amount stored in the storage means. A solid-state image sensor;
An optical system that forms image light of a subject on the imaging surface of the solid-state imaging device;
A signal processing circuit that detects a smear signal from an image pickup signal output from a solid-state image pickup device, arbitrarily sets a smear correction value based on the smear signal, and subtracts the image pickup signal of a video period. Imaging device. The imaging apparatus according to claim 7, wherein the signal processing circuit sets the smear correction value according to brightness of a subject image.

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