JP4110956B2 - Solid-state imaging device having pixel defect correction function and pixel defect correction method for solid-state imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state imaging device having a pixel defect correction function and a pixel defect correction method for the solid-state imaging device, and more particularly to a solid-state imaging having a pixel defect correction function having a function of correcting pixel defects of a solid-state imaging device by signal processing. The present invention relates to a device and a pixel defect correction method for a solid-state imaging device .
[0002]
[Prior art]
In recent years, video cameras (solid-state imaging devices) using a solid-state imaging element such as a CCD (charge transfer element) have been commercialized as devices for imaging an image. In a solid-state imaging device used for this video camera, in order to obtain a video signal with good image quality, it is important that all pixels on the solid-state imaging device have no defects or defects.
[0003]
This is because when a pixel on a solid-state image sensor has a defect or a defect, a so-called white defect occurs, that is, the pixel always becomes a white spot regardless of the type and brightness of the subject. This is because it may cause a significant decrease in.
[0004]
Thus, various solid-state imaging devices having a pixel defect correction function have been proposed (see, for example, Patent Document 1 and Patent Document 2). In the conventional solid-state imaging device described in Patent Document 1, an image signal obtained by a solid-state imaging device is digitized, and then an abnormal image signal (white defect) due to a pixel defect is corrected, and an outline correction circuit is used. Thus, it is automatically determined whether the pixel is a defective pixel by determining whether the level of the absolute value of the contour correction signal is equal to or higher than a predetermined value.
[0005]
Further, in the conventional solid-state imaging device described in Patent Document 2, the iris is closed when white scratches are detected, and the gain of the automatic gain control circuit (AGC circuit) of the analog signal processing unit that processes the imaging signal is increased to increase the threshold level. A pixel having the above signal is determined as a defect, and a temperature detection unit for detecting the temperature of the solid-state imaging device or its surroundings is provided, and a defective pixel of the solid-state imaging device is detected according to the detected temperature. A configuration for changing the threshold level is disclosed.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 3-236689 (page 2-3)
[Patent Document 2]
JP-A-6-350926 (Page 3, FIG. 2, FIG. 15)
[0007]
[Problems to be solved by the invention]
However, in the conventional solid-state imaging device described in Patent Document 1, processing corresponding to variations between the solid-state imaging device and the AGC circuit is not performed at the time of detecting a white flaw, and therefore there is a possibility of detection omission due to variations in temperature and circuit constants. There is a problem in pixel defect correction performance.
[0008]
Further, in the conventional solid-state imaging device described in Patent Document 2, the iris is closed when white scratches are detected, the gain of the AGC circuit is increased, and a pixel having a signal of a detection level or higher is determined as a defect. The level (threshold level) is variable according to the internal temperature of the imaging apparatus and the gain of the circuit system. However, since the table used to make the detection level variable according to the internal temperature of the solid-state imaging device and the gain of the circuit system is fixed, the detection accuracy of white flaws decreases depending on the table accuracy. There is also a problem that a temperature detection circuit is required.
[0009]
The present invention has been made in view of the above points, and a solid- state imaging device and a solid- state imaging device having a pixel defect correction function capable of reducing detection omission due to variations in characteristics, temperature, and circuit constants of a solid-state imaging device when white scratches are detected An object of the present invention is to provide a pixel defect correction method for an apparatus .
[0010]
Another object of the present invention is to provide a solid-state imaging device having a pixel defect correction function capable of shortening the detection time of pixel defects and a pixel defect correction method for the solid-state imaging device .
[0011]
Furthermore, another object of the present invention is to provide a solid-state imaging device having a pixel defect correction function having an inexpensive configuration that does not require a temperature detection circuit and can reduce the capacity of a memory for writing detected pixel defect position coordinates. Another object of the present invention is to provide a pixel defect correction method for a solid-state imaging device .
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the first invention is an analog having at least a solid-state imaging device that outputs an imaging signal at a level corresponding to the amount of incident light, and a function that varies a master black level of the imaging signal based on an external control signal. Processing means, interpolation processing means for interpolating the output image signal of the analog processing means, detection means for detecting white flaws from the output signal of the interpolation processing means, and when white flaws are detected, the interpolation processing means is turned off. In addition, the number of detections including the noise level detected by the detecting means is changed by supplying an external control signal to the analog processing means in a state where the light incident on the solid-state imaging device is blocked, and changing the master black level stepwise. Computing means for calculating the coordinates of the white scratch when the set value is not more than the set value; storage means for storing the coordinates of the white scratch calculated by the computing means in the memory; Reads the coordinates of the white defects stored in Li, have a control means for interpolation by the interpolation processing means using the surrounding pixels to the pixels of the coordinates as a defective pixel, the arithmetic means, solid as a set value Set the maximum number of white defects that can be accepted as the number of white defects in the image sensor, and change the master black level step by step when the number of detections including the noise level detected by the detection means falls below the set value. The detection operation is terminated .
[0013]
According to the present invention, in an image pickup apparatus that corrects defective pixels having white flaws by interpolation processing, the master black level is set in a state where the interpolation processing means is turned off at the time of white flaw detection and light incident on the solid-state image pickup device is blocked. And the coordinates of the white scratch when the number of detected white scratches including the noise level detected by the detection means is equal to or less than the set value are calculated. The influence of variations in circuit constants can be minimized.
[0015]
In the present invention, when the number of detections including the detected noise level is equal to or less than the upper limit of the allowable number of white flaws, the white flaw detection operation for changing the master black level stepwise can be completed. .
[0016]
In order to achieve the above object, the second invention stores the memory means of the first invention in the memory with white scratch coordinates within a predetermined upper limit and in a predetermined priority order. It is characterized by doing. In the present invention, the number of coordinates of white scratches stored in the memory can be limited.
Furthermore, in order to achieve the above object, the third invention, a solid-state imaging device which outputs the level imaging signal according to the amount of incident light, the function of varying based master black level of the image signal to an external control signal Pixel defect correction in a solid-state imaging device comprising at least analog processing means, interpolation processing means for performing interpolation processing on the output image pickup signal of the analog processing means, and detection means for detecting white flaws from the output signal of the interpolation processing means A method,
When detecting white flaws, with the interpolation processing means turned off and the light incident on the solid-state image sensor blocked, the external control signal is detected by the detection means by changing the master black level stepwise by the analog processing means. A calculation step of calculating the coordinates of white scratches when the number of detected white scratches including a noise level is equal to or less than a set value, a step of storing in the memory the coordinates of white scratches calculated by the calculation step, and a memory And a control step of interpolating the surrounding pixel with the pixel at the coordinate position as a defective pixel by interpolation processing means using the pixel at the coordinate position as a defective pixel. set the number of upper limit acceptable as white flaws number of defective, detecting the number of white spots, including the noise level detected by the detecting means becomes equal to or smaller than the set value In point, characterized by terminating the white defect detecting operation is changed stepwise the master black level.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a block diagram of an embodiment of a solid-state imaging device having a pixel defect correction function according to the present invention. In this embodiment, an example of an imaging device (video camera) of a three-plate solid-state imaging device of G (green), B (blue), and R (red) is shown. The present invention can also be applied to a three-plate type imaging apparatus using G.
[0018]
In FIG. 1, a green solid-state image pickup device 1G, a blue solid-state image pickup device 1B, and a red solid-state image pickup device 1R each using a CCD (charge transfer device) are irradiated with incident light from a subject, and the incident light corresponds to the corresponding light. An analog processing unit 2G including AGC (automatic gain control) and the like as a green signal (G signal), a blue signal (B signal), and a red signal (R signal) by converting into an electrical signal corresponding to the light amount of the wavelength component, 2B and 2R are supplied to perform predetermined analog signal processing.
[0019]
The G, B, and R signals extracted from the analog processing units 2G, 2B, and 2R are separately supplied to ADCs (A / D converters) 3G, 3B, and 3R, converted into digital signals, and then interpolated. Predetermined interpolation processing is performed by the processing units 4G, 4B, and 4R, and further, digital signal processing is performed by DSPs (digital signal processing units) 7G, 7B, and 7R, and white defect detection processing units 8G, 8B, and 8R perform white signal processing. Scratches are detected. Digital signals output from the DSPs 7G, 7B, and 7R are converted into analog signals by DACs (D / A converters) 9G, 9B, and 9R, respectively, and output as G signals, B signals, and R signals.
[0020]
The central processing unit (CPU) 5 receives white defect detection signals from the white defect detection units 8G, 8B, and 8R, generates a control signal according to a predetermined correction algorithm based on the white defect detection signals, and generates analog processing units 2G, 2B, and 2R, interpolation processing units 4G, 4B, and 4R are supplied, and white scratch coordinate values are transmitted to and received from the memory 6.
[0021]
Next, the white scratch detection processing and its correction processing algorithm are shown in the flowchart of FIG. 2, the diagram of the defective pixel coordinates of FIG. 3, and the white scratch detection explanatory diagram when the master black level of FIG. The description will be made with reference to them.
[0022]
First, it is selected whether or not to enter the detection mode after power-on (step S1 in FIG. 2). In the detection mode, the CPU 5 performs iris close and AGC gain increase (steps S2 and S3 in FIG. 2) and interpolation. The operations of the processing units 4G, 4B, and 4R are turned off (step S4 in FIG. 2). Therefore, when white flaws are detected, incident light is blocked and does not enter the solid-state image sensor 1G for green, the solid-state image sensor 1B for blue, and the solid-state image sensor 1R for red.
[0023]
Subsequently, the CPU 5 initializes the number n of times of changing the master black level step by step and the maximum value m of the detected number and increases the master black level to a predetermined value (steps S5, S6 , S7 in FIG. 2). ). Here, the master black level is a reference of the black level. For example, when the DC setup value of the DC setup unit in the analog signal processing units 2G, 2B, 2R is changed according to the control signal from the CPU 5. Variable.
[0024]
Subsequently, the CPU 5 receives white scratch detection signals of the detection level or higher from the white scratch detection units 8G, 8B and 8R as inputs, and the number of white scratches of the detection level or higher per frame is less than m, or the value of n is The operation of decreasing the master black level in steps until it becomes 0 is repeated (steps S8 to S11 in FIG. 2).
[0025]
FIG. 4 shows a state during operation in which the master black level is gradually reduced. The detection after the master black level reduction operation is configured by a digital circuit, but in order to facilitate understanding of the configuration and operation, the waveform diagram based on the analog signal as shown in FIG. 4 will be described. use.
[0026]
FIG. 4 shows signals at each stage when the number n of times of changing the master black level is initially set to “5”, in the order of (a) to (e) (n = 5 to n = 1). Performs the master black level reduction operation. When n ≧ 3 in FIGS. 4A to 4C, noise levels other than white scratches are detected. However, when n <3 in FIGS. 4D and 4E, only white scratches are detected. Yes. The maximum value m of the number of detections at this time is set to an upper limit number that can be accepted as the number of white flaws of the solid-state imaging device. Thereby, even when the initial value n = 5, the detection time can be shortened without performing the above operation n times.
[0027]
That is, in the example of FIG. 4, when n = 2 shown in FIG. 4D, the number of white scratches detected is less than the upper limit number m, so the white scratch detection operation is terminated at this stage (FIG. 2). In step S10), since the white scratch detection operation at the stage of n = 1 is not performed, the detection time is shortened. When the above detection operation conditions are satisfied, the detection operation is terminated, and the CPU 5 writes the detected coordinates in the memory 6 (step S12 in FIG. 2).
[0028]
In the example of FIG. 4, the detected coordinates when n = 2 in (d) are written in the memory 6, but the upper limit is set for the number of coordinates written in the memory 6 to reduce the memory capacity. Within this upper limit, the coordinate data is written in the memory 6 with priority under the following conditions.
[0029]
(A) G, R, B order. And (B) in descending order of detection level.
The combination and order of (A) and (B) are arbitrary, but this priority condition is set from the viewpoint of giving priority to the order in which white scratches are conspicuous on the screen. For example, the reason why priority is given to the order of the G signal, the R signal, and the B signal in (A) is that if the output level is the same, the sensitivity is higher in the order of the color signals in terms of human visual characteristics.
[0030]
Thus, the operation in the detection mode is completed, and the operation common to that in the detection mode off state is entered. That is, the CPU 5 reads the detected coordinate value of the memory 6 and transmits a flag for interpolation at timing synchronized with the input signal to the interpolation processing units 4G, 4B, and 4R (step S13 in FIG. 2). Based on this, for example, when the defective pixel coordinates to be interpolated are (x, y) as shown in FIG. 3, the interpolation processing unit 4G has two adjacent pixels G (x, y) adjacent to the upper and lower sides of the defective pixel coordinates. Interpolation is performed with an average value of a total of four pixels, that is, the pixels G (x, y−1) and G (x, y + 1) and the two pixels G (x−1, y) and G (x + 1, y) adjacent to the left and right. . That is, the interpolation processing unit 4G has the following defective pixel interpolation formula G (x, y) = {G (x-1, y) + G (x + 1, y) + G (x, y-1) + G (x, y + 1)}. / 4
The value obtained by performing the above calculation is the value of the pixel G (x, y) in the defective pixel coordinates. The other interpolation processing units 4B and 4R also perform interpolation processing based on the same defective pixel interpolation formula (step S14 in FIG. 2). Finally, normal signal processing is performed by the DSPs 7G, 7B, and 7R (step S15 in FIG. 2).
[0031]
As described above, according to the present embodiment, there is a possibility of detecting white flaws within the value of the maximum value m allowable as the number of white flaw defects, but it is unlikely that real white flaws will be detected. Therefore, detection omission due to variations in the characteristics, temperature, and circuit constants of the solid-state imaging devices 1G, 1B, and 1R can be reduced.
[0032]
It should be noted that due to variations in image pickup devices, variations in circuit constants, changes in usage environment temperature, etc., there is a situation where the master black level is considerably low (a level that is lower than the horizontal axis in FIG. 4). Conceivable. In such a situation, white scratches that cannot be detected are generated by the method of changing the detection level in stages. However, in the configuration in which the master black level is changed as in the present invention, the target detection can be performed even under such a situation.
[0033]
The present invention is not limited to the above-described embodiment. For example, defective pixels may be average-interpolated from eight pixels around the defective pixels, and defective pixels may be based on more pixels. It is also possible to perform interpolation by weighting according to the distance from the. The master black level, the detection level value, and the m value may be different independent controls and different values for the R signal, the G signal, and the B signal, respectively.
[0034]
【The invention's effect】
As described above, according to the present invention, in an imaging device that corrects defective pixels having white flaws by interpolation processing, the noise detected by changing the master black level step by step when white flaws are detected. By calculating the coordinates of white scratches when the number of detected white scratches including the level is less than or equal to the set value, the effect of variations in the characteristics, temperature, and circuit constants of the solid-state image sensor has been minimized. It is possible to greatly reduce the possibility of detecting and detecting genuine white flaws, and to detect white flaws with high accuracy without depending on the table accuracy as compared with the prior art.
[0035]
Further, according to the present invention, when the number of detections including the detected noise level is equal to or less than the upper limit of the allowable number of white scratches, the white scratch detection operation for gradually changing the master black level is terminated. Thus, the pixel defect detection time can be shortened.
[0036]
Furthermore, according to the present invention, since the number of white scratch coordinates stored in the memory is limited, the capacity of the memory for writing the detected pixel defect position coordinates can be reduced, and a temperature detection circuit is not required. Therefore, the imaging apparatus can be configured at a low cost.
[0037]
Furthermore, according to the present invention, the master black level is changed even in a usage situation in which the master black level is considerably low due to variations in imaging elements, variations in circuit constants, changes in usage environment temperature, and the like. The target white scratch can be detected.
[Brief description of the drawings]
FIG. 1 is a block diagram of an embodiment of the present invention.
FIG. 2 is a flowchart showing an algorithm for white defect detection processing and correction processing in FIG. 1;
FIG. 3 is an explanatory diagram of defective pixel coordinates and a defective pixel interpolation formula.
FIG. 4 is an explanatory diagram of white flaw detection when the master black level is changed stepwise according to the present invention.
[Explanation of symbols]
1G Green solid-state image sensor 1B Blue solid-state image sensor 1R Red solid-state image sensor 2G, 2B, 2R Analog processing units 3G, 3B, 3R ADC (A / D converter)
4G, 4B, 4R Interpolation processing unit 5 Central processing unit (CPU)
6 Memory 7G, 7B, 7R Digital processing processor (DSP)
8G, 8B, 8R White scratch detection processing unit 9G, 9B, 9R DAC (D / A converter)

Claims (3)

A solid-state imaging device that outputs an imaging signal at a level corresponding to the amount of incident light;
Analog processing means having at least a function of varying a master black level of the imaging signal based on an external control signal;
Interpolation processing means for performing interpolation processing on the output imaging signal of the analog processing means;
Detecting means for detecting white scratches from the output signal of the interpolation processing means;
When detecting a white flaw, the external processing signal is supplied to the analog processing means in a stepwise manner while the interpolation processing means is turned off and light incident on the solid-state image sensor is blocked. Calculating means for calculating the coordinates of white scratches when the number of detections including the noise level detected by the detection means is equal to or less than a set value;
Storage means for storing the coordinates of the white scratch calculated by the calculation means in a memory;
Reads the coordinates of the white defects stored in the memory, have a control means for interpolation by said interpolating means with a surrounding pixels pixel of the coordinate position as a defective pixel,
The arithmetic means sets an upper limit number allowable as the number of defective white defects of the solid-state imaging device as the set value, and when the detection number including the noise level detected by the detection means becomes equal to or less than the set value A solid-state imaging device having a pixel defect correction function , wherein the white defect detection operation for changing the master black level stepwise is terminated . Said storage means, the coordinates of the white defects, within the number of upper limit set in advance, and, with the pixel defect compensation function according to claim 1, characterized in that stored in the memory in a predetermined priority Solid-state imaging device. A solid-state imaging device that outputs an imaging signal at a level corresponding to the amount of incident light ;
Analog processing means having at least a variable functions based master black level before Symbol image signal to an external control signal,
Interpolation processing means for performing interpolation processing on the output imaging signal of the analog processing means ;
Detecting means for detecting white scratches from the output signal of the interpolation processing means ;
A pixel defect correction method in a solid-state imaging device comprising:
When white scratches are detected, the external processing signal is changed stepwise by the analog processing means while the interpolation processing means is turned off and the light incident on the solid-state image sensor is blocked. Calculating the coordinates of the white scratch when the number of detected white scratches including the noise level detected by the detection means is equal to or less than a set value;
Storing the coordinates of the white scratch calculated in the calculation step in a memory;
A control step of reading the coordinates of white scratches stored in the memory, and interpolating by the interpolation processing means using peripheral pixels with the pixel at the coordinate position as a defective pixel, and
The calculation step sets an upper limit number allowable as the number of white scratch defects of the solid-state imaging device as the set value, and the detected number of white scratches including a noise level detected by the detection unit is equal to or less than the set value. At this point, the white defect detection operation for changing the master black level stepwise is terminated.

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