JP2012253545A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus which performs a correction with high precision by changing a threshold value for pixel defect determination depending on a type of color signal of a correction object pixel.SOLUTION: The imaging apparatus includes: a pixel defect detection correction circuit which detects a pixel defect from an image signal from an imaging device and corrects the detected pixel defect; and a signal processing circuit which processes the corrected image signal by the pixel defect detection correction circuit to transmit a video signal. The pixel defect detection correction circuit 104 includes: a pixel value holding part 202 which holds a pixel signal of a pixel near a correction object pixel; a comparison part 201 which compares a difference between the pixel value of the correction object pixel and the pixel value held in the pixel value holding part with a preset threshold value, and detects the pixel defect of the correction object pixel; and a correction part which interpolates and corrects a defective pixel when a pixel defect is detected. The threshold value is set, for each color, to correspond to a weight factor representing a contribution degree to a luminance signal of a color signal of the correction object pixel, and is changed according to the color signal of the correction object pixel.

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus capable of detecting and correcting pixel defects with high accuracy.

  Patent Document 1 utilizes that the output level of a defective pixel does not change while the output level of a normal pixel is reduced when the lens is brought out of focus when detecting a defect in a solid-state imaging device. It has been shown that pixel defects are reliably detected by comparing the output level of the solid-state imaging device when the lens is out of focus with a predetermined threshold.

JP-A-2005-328134

  Pixel defects that occur in the image sensor include pixel defects that occur in the manufacturing process and pixel defects that accompany temporal changes such as temperature changes or radiation exposure such as cosmic rays. These pixel defects include a so-called “white defect” in which the luminance of the defective portion is increased and a so-called “black defect” in which the luminance of the defective portion is decreased.

  Since the pixel defect that occurs in the manufacturing process is at a fixed position, defect correction is performed at the time of factory shipment to correct the output of the defective pixel with a value interpolated with the output of the neighboring pixel. However, with respect to pixel defects caused by a change in diameter after shipment such as a temperature change, the image quality is deteriorated because the interpolation cannot be performed.

  As a method for solving this problem, there is Patent Document 1 mentioned above. In Patent Document 1, pixel defects are detected based on the output signal of the solid-state imaging device when the lens is in an out-of-focus state, so that it is possible to deal with defective pixels that appear over time.

  By the way, a white spot defect is determined as a white spot defect when a difference between signals of a correction target pixel and a pixel adjacent to the pixel is larger than a preset difference and the difference is positive. When the difference between the signals of the matching pixels is larger than the difference set in advance and the difference is negative, it can be determined that there is a black spot defect.

  For this reason, a monochrome imaging device can correctly determine, but in a color imaging device in which a plurality of color filters are arranged, the pixels of the same color are separated from each other, or a weighting factor for luminance between adjacent pixels Therefore, the defect may not be corrected with a fixed threshold value. Moreover, although it is not a defective pixel, it may correct as a defective pixel.

  The present invention has been made in view of these problems. When correcting the correction target pixel (defective pixel) by comparing the pixel signals of the correction target pixel and the neighboring pixels, the threshold for pixel defect determination is set as the correction target pixel. By switching according to the color signal type, it is possible to perform highly accurate correction.

  In order to solve the above problems, the present invention employs the following means.

  A pixel defect detection and correction circuit for detecting a pixel defect from an image signal from an image sensor, correcting the detected pixel defect, and a signal processing for processing the image signal corrected by the pixel defect detection and correction circuit and transmitting a video signal In an imaging apparatus including a circuit, a pixel defect detection correction circuit is held in a pixel value holding unit that holds a pixel signal of a pixel near the correction target pixel, a pixel value of the correction target pixel, and the pixel value holding unit. A comparison unit that detects a pixel defect of a correction target pixel by comparing a difference between the pixel value and a preset threshold value, and a correction unit that interpolates and corrects the defective pixel when a pixel defect is detected, The color coefficient is set for each color corresponding to the weighting factor indicating the degree of contribution to the luminance signal of the color signal of the correction target pixel, and is switched according to the color signal of the correction target pixel.

  Since the present invention has the above-described configuration, it is possible to perform highly accurate defect correction.

It is a figure explaining the imaging device concerning a 1st embodiment. It is a figure explaining the detail of a defect detection correction circuit. It is a figure explaining operation | movement of a comparator. It is a figure explaining a primary color filter. It is a figure explaining a complementary color filter. It is a figure explaining 2nd Embodiment.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram for explaining an imaging apparatus according to the first embodiment. In this embodiment, a video camera is used as the imaging apparatus.

  In FIG. 1, light incident from a subject via the imaging lens 101 is irradiated to the image sensor 102 to form a subject image. The image sensor 102 is scanned in the horizontal and vertical directions by the drive pulse from the timing generator 106, captures a subject image, and generates an electrical signal. This electric signal is converted into a digital signal by the A / D conversion circuit 103 and input to the defect detection correction circuit 104.

  In the defect detection / correction circuit 104, the threshold value for defect detection (for white defect / for black defect) is appropriately switched according to the color information from the timing generator 106, and an input signal input to the defect detection / correction circuit 104 and a neighboring pixel signal are switched. When it is determined that the input signal is a “normal” signal or a “defective” signal based on the difference and the relationship between the difference and the threshold (for white defect / black defect), and “normal” In this case, an input signal is output to the signal processing circuit 105, and when it is determined as “defect”, an interpolated signal based on the neighboring pixel signal is output to the signal processing circuit 105.

  The signal processing circuit 105 performs various camera signal processing such as noise removal and gamma correction, converts the signal into a TV signal such as an NTSC signal, and outputs it.

  FIG. 2 is a diagram for explaining the details of the defect detection correction circuit 104. An input pixel signal from the image sensor is supplied to the comparator 201 and the data latch 202 of the defect detection correction circuit 104. The data latch 202 is a pixel value holding unit that holds an input pixel signal of the same color before n pixels, for example, and outputs a signal n pixels before to the comparator 201 with respect to the input pixels from the image sensor.

  Color information corresponding to the input pixel is input to the threshold selection circuit 203. In the threshold value selection circuit 203, threshold values (for white defects / for black defects) for each color are set in advance, and a threshold value (for white defects / for black defects) corresponding to the type of input color information is selected. Output to the comparator 201.

  FIG. 3 is a diagram for explaining the operation of the comparator 201. In FIG. 3, the comparator 201 determines whether or not the signal amount of the input pixel signal is larger than the sum of the signal amounts of the white defect threshold value and the signal stored in the data latch 202 (STEP 1). When the signal amount of the signal is larger than the sum of the signal amount of the threshold value for white defect and the signal stored in the data latch 202, it is determined as “white defect”, and the signal interpolated by neighboring pixels (or the signal of the data latch 202) ) Is generated by the correction unit, and the generated signal is output to the signal processing circuit 105 (STEP 2).

  Next, it is determined whether or not the signal amount of the input pixel is smaller than the signal amount obtained by subtracting the black defect threshold from the signal amount of the data latch 202 (STEP 3), and the signal amount of the input pixel is the signal amount of the data latch 202. If it is smaller than the signal amount obtained by subtracting the black defect threshold value from the signal, it is determined as “black defect”, and the signal amount of the data latch 202 corresponding to the signal interpolated from the neighboring pixels is output to the signal processing circuit 105 (STEP 2 Same as). If the “white defect” and the “black defect” are not determined, it is determined as “normal” and an input signal is output to the signal processing circuit 105 (STEP 4). Next, returning to step 1, the next pixel signal is captured.

  Next, the operation of the threshold selection circuit 203 will be described.

FIG. 4 is a diagram illustrating an example of a primary color filter. For example, in an NTSC imaging device, the luminance signal (Y) is based on the input signals of red (R), green (G), and blue (B).
Y = 0.29 * R + 0.60 * G + 0.11 * B
It is generated with the following formula.

When attention is paid to the horizontal 2 * vertical 2 pixels surrounded by a thick frame in FIG. 4, there are two green (G), so the ratio of the weighting factor to the luminance signal (Y) is
R: G: B = 0.29: 0.30: 0.11 (1)
It has become.

  Here, considering the case where each of the red (R), green (G), and blue (B) pixels has a defect, the luminance signal (Y) is affected by the defect at the ratio of the above equation (1). Will appear. For this reason, it is possible to detect pixel defects with high accuracy by adjusting the ratio of the thresholds to the ratio of the above formula (1).

  That is, in the threshold selection circuit 203, a threshold value (for white defect / for black defect) is set in advance for each color at a ratio of approximately the above formula (1), and a pixel for determining the presence or absence of a defect (input to the comparator). The threshold value may be switched and used in accordance with the color information of the pixel).

FIG. 5 is a diagram illustrating an example of a complementary color filter. In the image pickup apparatus using the complementary color filter as shown in FIG. 5, a plurality of ways of assembling the signal processing matrix can be considered. For example, Y = K1 * Ye + K2 * Cy + K3 * Mg + K4 * G
If it is generated by the formula of
Ye: Cy: Mg: G = K1: K2: K3: K4 (2)
Therefore, it is preferable to set a threshold value (for white defect / for black defect) for each color in advance in the ratio of the above expression (2) as in the above expression (1). It should be noted that the same setting may be used for other color arrangements than the above.

  As described above, according to the present embodiment, the threshold for determining whether or not a pixel for defect detection is defective according to the color information in consideration of the degree of influence of the color information of the pixel for defect detection on the luminance signal. (For example, a threshold THr for determining a defect of a red (R) pixel, a threshold THg for determining a defect of a green (G) pixel, and a defect of a blue (B) pixel) The threshold value THb is set so that THr / THg / THb = 0.29 / 0.30 / 0.11, and is input when a pixel for which the presence or absence of a defect is to be determined is input to the comparator. The threshold value is switched according to the color signal of the selected pixel).

  For this reason, even in a color imaging apparatus, pixel defects can be detected and corrected with high accuracy.

  In the present embodiment, the data latch 202 is used to acquire information on the immediately preceding pixel of the same color as a neighboring pixel, and defect detection and defect correction are performed using this information. However, for example, it is also possible to acquire information on the pixel one line before using a line memory, and perform defect detection and defect correction using this information. Also, using a feed (frame) memory or the like, using information such as left and right, one line up and down, diagonal upper right, diagonal lower right, diagonal upper left, diagonal lower left, etc., that is, using information on a wider range of peripheral pixels Defect detection and defect correction can also be performed.

Note that the present invention is particularly effective in an imaging apparatus such as a surveillance camera system that continuously energizes for a long period of time and defective pixels appear over time, like the imaging apparatus described in Patent Document 1. FIG. 6 is a diagram for explaining a second embodiment of the present invention. The configuration of the defect detection and correction circuit is different from that of the first embodiment. 6, the same parts as those shown in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.

  In the imaging apparatus, since the color temperature of the light source to be photographed varies, so-called auto white balance control that automatically controls the color gain so that white can be photographed as white is widely adopted. For example, as the color temperature increases, the red (R) gain is increased and the blue (B) gain is decreased. Conversely, the lower the color temperature, the smaller the red (R) gain and the greater the blue (B) gain. Further, under a light source such as a fluorescent lamp, the green (G) gain may be controlled. In the present embodiment, it is assumed that the auto white balance control is arranged in the signal processing circuit 15.

  When the defect detection correction circuit 104 is arranged in front of the auto white balance control circuit, the auto white balance control circuit changes the gain of each color as described above. For white defect / black defect), it is necessary to consider the gain of each color.

  The threshold selection circuit 303 inputs a gain (representing color temperature information of the light source) for each color (R, G, B) from an auto white balance control unit (not shown), and sets a threshold for each color (for white defect). / For black defect) is changed to a value obtained by multiplying the input gain for each color. The changed threshold value is selected according to the color information of the pixel signal input to the comparator 201 and is output to the comparator 201.

  In this embodiment, when the color temperature of the light source to be photographed is changed, the threshold value is changed according to the color temperature of the light source, so that more accurate pixel defect detection and pixel defect correction can be performed. .

  In addition, this invention is not limited to above-described embodiment, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  In addition, each of the above-described configurations may be configured such that some or all of them are configured by hardware, or are implemented by executing a program by a processor. Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

  As described above, according to the embodiment of the present invention, the comparison unit that compares the difference between the pixel value of the detection correction target pixel and the pixel value held in the pixel value holding unit with a preset threshold value is provided. The threshold value is set in consideration of a weighting factor for the luminance of the pixel determined to be defective, and is switched according to the type of color information of the detection correction target pixel. Also, since the threshold setting is changed according to the white balance state (color temperature of the light source), it becomes possible to detect pixel defects with higher accuracy.

DESCRIPTION OF SYMBOLS 101 Image pick-up lens 102 Image pick-up element 103 A / D conversion circuit 104 Defect detection correction circuit 105 Signal processing circuit 106 Timing generator 201 Comparator 202 Data latch 203 Threshold selection circuit 303 Threshold selection circuit

Claims (4)

A pixel defect detection and correction circuit for detecting a pixel defect from an image signal from an image sensor, correcting the detected pixel defect, and a signal processing for processing the image signal corrected by the pixel defect detection and correction circuit and transmitting a video signal In an imaging apparatus provided with a circuit,
Pixel defect detection and correction circuit
A pixel value holding unit that holds a pixel signal of a pixel in the vicinity of the correction target pixel;
A comparison unit that detects a pixel defect of the correction target pixel by comparing a difference between the pixel value of the correction target pixel and the pixel value held in the pixel value holding unit with a preset threshold;
A correction unit that interpolates and corrects defective pixels when a pixel defect is detected,
The imaging apparatus according to claim 1, wherein the threshold value is set for each color corresponding to a weighting factor indicating a degree of contribution to the luminance signal of the color signal of the correction target pixel, and is switched according to the color signal of the correction target pixel. The imaging device according to claim 1,
An image pickup apparatus, wherein a color represented by a pixel held by the pixel value holding unit and a color represented by a correction target pixel are the same. The imaging device according to claim 1,
The threshold value set for each color is changed according to the gain set for each color signal by the auto white balance control unit. The imaging device according to claim 1,
An imaging apparatus characterized in that a threshold value set for each color is changed according to a color temperature of a light source that illuminates a subject.

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