JPH06245149A - Picture element defect correction device - Google Patents

Abstract

PURPOSE:To obtain an excellent picture without being restricted by quantity of level and a spread around a projected portion by distinguishing accurately a substantial signal from a signal resulting from a picture element defect, detecting and correcting the defect. CONSTITUTION:Picture element data gn-1, rn-0.5, gn, rn+0.5, gn+1 for 5 picture elements in total being a noted picture element, its preceding and succeeding picture elements and their preceding and succeeding picture elements are extracted by flip-flop circuits 1-4, and adders 11-14 and comparator circuits 21-24 are used to apply arithmetic operation and discrimination to the picture element data. An AND circuit 30 ANDs discrimination outputs from the comparator circuits 21-24, a picture element defect is discriminated when the four following equations are all satisfied, a detection circuit outputs a detection signal to allow a correction circuit 60 to provide a correction signal; gn-gn-1> a1... (1), (gn-gn-1)b1>rn-0.5-gn-1... (3), gn-gn+1>a2 (2), and (gn-gn+1)b2>rn+0.5-gn+1... (4), where a1>a2 and b1>b2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pixel defect correcting apparatus for detecting and correcting a pixel defect existing in a solid-state image sensor in an image sensor using a solid-state image sensor such as CCD.

[0002]

2. Description of the Related Art Generally, it is known that in a solid-state image pickup device formed of a semiconductor such as CCD, image quality is deteriorated due to local crystal defects of the semiconductor. An image defect in which a constant bias voltage is always added to the imaging output according to the amount of incident light appears as a high-intensity white dot on the monitor screen if this image defect signal is processed as it is. There is. In addition, those having low photosensitivity appear as black dots and are called black scratches (hereinafter, pixel defects are called scratches).

Conventionally, the detection of scratches as described above is disclosed in, for example, Japanese Patent Laid-Open No. 61-261974. This method is a method of detecting a pixel in which the pixel of interest has an output larger or smaller than a peripheral pixel by a certain amount or more as a flaw. It detects a pixel having an output.

Hereinafter, the case of detecting a white defect in the horizontal direction of the CCD will be described. First, the conventional pixel defect correction device in this case will be specifically described.

The white flaw normally projects by one pixel with respect to the surrounding pixels. For example, the relationship between the pixel of interest and the pixels before and after it is represented as shown in FIG. Therefore, the pixel of interest is compared with the adjacent pixels before and after the pixel, and if the pixel of interest is larger than the pixels before and after a certain level, it can be regarded as a flaw.

A block diagram for realizing the above contents is shown in FIG. The input signal is a plurality of flip-flops (hereinafter F
The pixel value of interest and the pixel values y _n-1 , y _n , and y _{n + 1} before and after it, which are sequentially sent, are obtained through 1 and 2 (abbreviated as F). For these signals, adders 11 and 12 and comparison circuits 21 and 2
2. The following calculation is performed by the AND circuit 30.

[0007] _{y n-1 -y n> a} 1 (1) y n + 1 -y n> a 2 (2) a 1, a 2 , the protruding against y _n-1, y _{n + 1} of the y _n It is a threshold value of quantity, and is considered here as a ₁ = a ₂ = a (> 0).

As described above, when the value of the pixel of interest is more than a certain level above the values of the surrounding pixels, it is regarded as a flaw and a detection output is output. The correction circuit is controlled by the detection output.

Regarding the correction of pixel defects, Japanese Patent Laid-Open No. 62-
Several methods are shown in the 8666 publication. For example, a method of substituting one pixel or two pixels before, a method of substituting the average of previous and next pixel values, or a method of thinking in the vertical direction and substituting by one pixel above, an average of upper and lower pixel values There is a method of replacing with.

Here, it is assumed that the correction circuit substitutes the average of the pixel values before and after, and the block diagram is as shown in FIG. 3, and the operation is as follows. Input signal is FF
5 and FF6, the value of the pixel of interest in the center and the pixel values before and after it are extracted. An average value of these pixel values before and after the pixel of interest is calculated and used as a correction signal. According to the detection output of the detection circuit, normally, the value of the pixel of interest in the center is output, and when it is determined that there is a flaw, a correction signal is output.

As described above, a pixel protruding from the value of the surrounding pixels by a certain level or more can be detected as a flaw and can be corrected so as not to be noticeable.

[0012]

However, according to the method described above, a signal such as a point light source is erroneously determined as a flaw because it is projected even though it is a signal.

For example, in the case of a CCD output signal as shown in FIG. 5B where only one point is bright in the dark surroundings, the signal at the center is erroneously determined as a flaw and is erroneously corrected. As a result, a signal that should be present, such as the correction circuit output signal in FIG. 5B, is missing.

As described above, when there is a signal from the point light source, the image quality is deteriorated and there is a problem that a good image cannot be obtained.

Further, in an actual system, even if there are white scratches, not only the projection of one pixel due to the filter etc. but also a slight spread as shown in FIG. In the time series, some protrusion is also seen in the rearward adjacent pixels.

In this case, according to the conventional method, the detection of the protrusion amount of the flaw is limited by a in FIG. 6 (b).
There is a problem in that the detection accuracy of the scratch is lowered and the detection cannot be performed if the protrusion amount is not so large.

The present invention solves such a conventional problem, and an image including a signal such as a point light source is obtained by accurately discriminating a signal and a flaw with a simple structure and correcting only the flaw. Also in the above, there is provided a pixel defect correction device capable of obtaining a good image without deteriorating the original image quality.

[0018]

SUMMARY OF THE INVENTION The pixel defect correcting apparatus of the present invention has a flaw by detecting the protruding signal and the adjacent pixels independently when the pixel shift of the CCD is performed. The detection power of is improved.

When the second CCD is displaced from the first CCD by half a pixel, pixel shift is performed,
In an actual system, the white flaw is affected by the LPS of the CDS filter and the pre-filter before A / D conversion, so that a signal with only one pixel protruding as shown in FIG. As in the case of b), the adjacent pixel g _{n + 1 in the} backward direction also protrudes in time series with respect to the target pixel.

In the conventional example, the image of interest for adjacent pixels
Large or small amount of elementary protrusion (g_n-G_{n + 1}, G _n-G_n-1) Left and right pair
Since it is a name, the key that asymmetrically spreads as shown in Fig. 6 (b).
The power to detect_n-G_{n + 1}Will be limited by.

Therefore, by making g _n -g _{n + 1} smaller than g _n -g _n-1 for left-right asymmetric detection,
It is possible to improve the flaw detection power without increasing malfunctions even if the flaws are on the same level of signal.

A signal such as a point light source is used as an optical LPF.
As shown in FIG. 5B, the pixel values adjacent to each other by half a pixel are projected due to the influence of, for example, so that it may be possible to distinguish from a flaw by this. As shown in c), the point light source and the flaw can be more clearly distinguished by asymmetrically determining the protrusion amount of the pixel (r _n-0.5 , r _{n + 0.5} ) that is half pixel adjacent to the pixel of interest. It becomes possible to do.

As described above, by effectively utilizing the pixel shift technique and performing the left and right independent comparison calculation processing, it is possible to discriminate between a flaw and a signal without being limited by the size of the level and the spread around the protrusion. .

[0024]

According to the present invention, as compared with the conventional flaw detection circuit,
Since it is possible to accurately distinguish between a signal and a flaw even if the flaw has a small level, it is possible to correct only the flaw and obtain a good image without degrading the original image quality.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. A block diagram of an embodiment of the present invention is shown in FIG. Incident light passes through a lens and an optical LPF, is separated into R, G, and B color signals by a prism, and reaches CCDs 71 to 73 corresponding to the respective color signals. R and B CCDs 72 and 73 are arranged at positions shifted by half a pixel in the horizontal direction with respect to the G CCD 71. These are photoelectrically converted by the CCDs, and are passed through the CDS circuits 91 to 93, pre-filters 94 to 96 before A / D conversion, and A / D converters 81 to 83.
Converted to digital signal. A detection circuit detects a flaw from this signal and outputs a detection signal. The correction circuit 60 is controlled by this detection signal.

FIG. 1 is a circuit diagram of a detection circuit according to an embodiment of the present invention.
It is shown in the detection part of. Since the R signal and the B signal have the same relationship with the G signal, the case where the G signal and the R signal are input to the detection circuit is shown here. The following operations are performed in this block diagram.

Firstly, G inputted, the signal R passes through the CCD of FF 51, operates in the same f _CK clock FF 52, at 2f _CK rate by a selector 40 which operates at a 2f _CK G, into a serial signal of R signal To be converted. Then F
If, for example, a G signal is used as a pixel of interest by F1 to FF4, a G signal g _n and g _n−1 and g _{n + 1} around one pixel thereof and further r _n-0.5 and r _{n + 0.5} around 0.5 pixel thereof. 5 pixels in total are extracted. Here, the clock of FF1 to FF4 is 2f _CK
Is. For these pixel data, adders 11-1
4. The following calculation is performed using the comparison circuits 21 to 24.

G _n −g _n−1 > a ₁ (3) g _n −g _{n + 1} > a ₂ (4) (g _n −g _n−1 ) b ₁ > r _{n −0.5} −g _{n−1 (5) (g n -g n} + 1) b 2> r n + 0.5 -g n + 1 (6) _{except, a 1> a 2 (>} 0), is b _1> b _2.

In equations (3) and (4), it is determined that the condition that the pixel of interest is projected above the peripheral pixels by a certain value or more is satisfied. As a result, it is determined that the necessary condition for the scratch is satisfied. a ₁ and a ₂ are threshold values for determining that the protrusion amount is a certain value or more,
By setting the values a ₁ > a ₂ (> 0) which are independent on the left and right sides, it becomes possible to detect scratches more accurately. These calculations are performed using the adders 11 and 12 and the comparison circuits 21 and 22.

In equations (5) and (6), the difference between the pixel that is half a pixel away from the target pixel and the pixel that is one pixel away from the target pixel is the protrusion amount obtained by the above equations (3) and (4). It is a conditional expression that it is less than or equal to the coefficient times. Thus, the spread of the signal from the point light source or the like and the spread in the case of a flaw are discriminated to distinguish between the flaw and the signal. b ₁ and b ₂ are coefficients for determining the threshold value representing the protrusion amount of the peripheral pixels with respect to the protrusion amount of the pixel of interest, and by setting the left and right independent values b ₁ > b ₂ , the signal of the point light source or the like can be obtained. It is possible to distinguish more clearly from scratches. These operations are performed by the adders 13, 14,
This is performed using the comparison circuits 23 and 24.

The AND circuit 30 includes four comparison circuits 21-2.
Each 1-bit output of 4 is ANDed and it is determined that all of the above four expressions are satisfied. When all of the four expressions are satisfied, it is determined that there is a flaw, the detection circuit outputs a detection signal, and the correction circuit 40 is controlled to output the correction signal.

FIG. 2 shows a block diagram of the correction circuit according to the embodiment of the present invention. The input signal passes through FF5 to FF8,
The value of the pixel of interest in the center and the pixel values before and after that pixel are extracted. Here, the clock of FF5 to FF8 is 2f _CK . The average value of these values is obtained from the pixel values of one pixel before and after the pixel of interest and used as the correction signal. According to the detection output of the detection circuit, when it is determined that there is no flaw, the value of the pixel of interest in the center is output, and when it is determined that there is a flaw, a correction signal is output. Also,
Time adjustment with the detection circuit shall be performed as necessary.

In the above embodiment, only the horizontal direction has been described, but the same applies to the vertical direction, and processing that combines both the horizontal direction and the vertical direction is also possible.

[0034]

As is apparent from the above description, according to the present invention, even if a flaw exists on a signal having a similar level, erroneous detection and correction are not performed, and the signal level of a point light source or the like is not corrected. The signal and flaw can be clearly distinguished from each other without being limited by the size of the image and the spread around the protrusion, and the flaw can be detected accurately, so only the flaw is corrected and the original image quality is not deteriorated, and a good image is obtained. Can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an overall configuration of a pixel defect correction device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a correction circuit of a pixel defect correction device according to an embodiment of the present invention.

FIG. 3 is a block diagram of a correction circuit of a conventional pixel defect correction device.

FIG. 4 is a block diagram of a detection circuit of a conventional pixel defect correction device.

FIG. 5 is a signal waveform diagram of a conventional pixel defect correction device.

FIG. 6 is a signal waveform diagram to be solved by the present invention.

[Explanation of symbols]

 1-4 flip-flop 60 correction circuit 61 1st arithmetic processing circuit 62 2nd arithmetic processing circuit 63 3rd arithmetic processing circuit 64 4th arithmetic processing circuit 71-73 Solid-state image sensor 81-83 Sampling circuit

Claims (1)

[Claims] 1. A plurality of solid-state image pickup devices in which a second solid-state image pickup device is displaced by half a pixel with respect to the first solid-state image pickup device, and signals read from the plurality of solid-state image pickup devices are sampled. Sampling circuit, the value of the first pixel of the first solid-state imaging device from the output of the sampling circuit, and the second and third values of the second solid-state imaging device that are half pixel adjacent to the first pixel. The pixel value of
An extraction circuit that extracts the values of the fourth and fifth pixels of the first solid-state image sensor that are adjacent to the first pixel by one pixel; the value of the first pixel and the value of the fourth pixel; Of the first pixel and the value of the first pixel and the value of the fifth pixel, and compares it with a second constant value. A second arithmetic processing circuit, obtains a difference between the value of the second pixel and the value of the fourth pixel, and calculates a difference between the value of the first pixel and the value of the fourth pixel as a third value. A third arithmetic processing circuit that compares the value of the third pixel with a value of the fifth pixel, and obtains a difference between the value of the third pixel and the value of the fifth pixel. A fourth arithmetic processing circuit for comparing the difference from the value of 4 with a value obtained by multiplying by a fourth coefficient, and a logical product circuit for taking the logical product of the outputs of the first, second, third and fourth arithmetic processing circuits. When, Serial pixel defect correction apparatus and a correction circuit for correcting the output of the sampling circuit by the output of the AND circuit.