KR100822849B1 - Black level compensating apparatus for a camera and method thereof - Google Patents

Abstract

An apparatus and a method for compensating a camera black level are provided to compensate black level variation, caused by radiation applied when acquiring a subject image through an image sensor by using a signal acquired by a reference image sensor for blocking light under the same condition, thereby effectively compensating nonlinear black level distortion of the image and accordingly improving reliability and images of a radiation tolerant camera. An image sensor unit(110) acquires an image of a subject in a state of being exposed to radiation, and outputs the image as an analog image signal. A reference image sensor unit(120) outputs only effects by radiation as an analog image signal in a state when light is blocked. A low path filter(130) removes high frequency components from the analog image signal of the reference image sensor unit. A compensating unit(140) compensates the analog image signal of the image sensor unit based on the output of the filtering unit, and outputs an analog image signal where image distortion is compensated.

Description

Camera black level compensation device and its method {BLACK LEVEL COMPENSATING APPARATUS FOR A CAMERA AND METHOD THEREOF}

1 is a structure of a radiation-resistant camera using a scratch tube element.

2 is a structure of a radiation-resistant camera using a solid-state imaging device.

3 is a block diagram illustrating the configuration of a camera using a solid-state imaging device.

4 is an exemplary view showing an image change of the camera exposed to the radiation environment.

5 is a graph showing the state of black level change of a camera exposed to radiation;

Figure 6 is a block diagram showing the configuration of an embodiment of the present invention.

7 is a graph illustrating an image signal according to an embodiment of the present invention.

8 is a graph illustrating an image signal of an output terminal obtained through an embodiment of the present invention.

Figure 9 is a block diagram showing the configuration of another embodiment of the present invention.

10 is a system configuration diagram showing a system configuration to which the embodiments of the present invention are applied.

** Description of symbols for the main parts of the drawing **

10: scratch tube sensor 11: photoelectric part

12: Electron gun 13: deflection coil

20: radiation-resistant camera 21: radiation shielding housing

22: mirror 23: solid-state image sensor

24: image sensor signal processing unit 30: image sensor unit

31: timing generator 32: sink insertion unit

110: first image sensor 120: second image sensor

130: low pass filter 140: calculator

150: low pass filter 160: integrator

200: camera unit 300: camera management unit

310: display unit

The present invention relates to a camera black level compensation device and a method thereof, and more particularly, to a camera black level compensation device capable of compensating a black level of an image sensor image nonlinearly changed by radiation by using an image of a reference image sensor. It is about a method.

Although the development of energy to replace the depletion of fossil energy is actively being carried out around the world, the development of the next generation energy has not gained any visible effect, and in reality, the dependency on energy through nuclear power generation is increasing.

At present, in many countries including Korea, nuclear power generation accounts for a low percentage of total production energy, but it is common to see that the generation of nuclear power generation will gradually increase until a breakthrough energy source is developed.

As the necessity of nuclear power generation is urgently needed, new establishment of nuclear power plants and expansion of existing nuclear power plants occur frequently all over the world.However, the nuclear industry is still very low in the whole industry. This limited technological progress is also very late.

For example, in the case of a camera for monitoring a radioactive area in a nuclear power plant, a normal camera cannot obtain a normal image and is easily burned down even at a low level of radiation exposure, and thus cannot be used continuously. Although a dedicated camera is used, the technical improvement is progressing slowly compared to the required degree.

1 illustrates a structure of a conventional image sensor, and as illustrated, an image sensor may generate an electric image when an image obtained from a subject is formed on a thin film of the photoelectric unit 11, and the electron gun 12 may emit an electron beam. It operates by scanning and converting into an electronic signal to obtain a video signal. A deflection coil 13 is used to control the direction of the electron beam. Since the image sensor has a high radiation resistance (2 × 10 ⁸ rad), although it is the oldest commercial image sensor, it is still used in some areas where radiation resistance is required. However, due to their large size and complex operation, only a few are used for monitoring in the radiation area including nuclear power plants.

2 shows a schematic structure of a radiation-resistant camera 20 using a solid-state image sensor 23 such as a CCD or a CMOS. The CCD or CMOS image sensor 23 does not operate normally when directly exposed to gamma rays. Since it is impossible to protect the image sensor 23 and the image sensor signal processing unit 24 with a radiation shielding housing 20 made of a material capable of shielding radiation as shown, and indirectly by using a mirror 22 A method of providing a subject image to the image sensor 23. In some cases, a plurality of mirrors may be used to prevent vertical inversion of an image by using a mirror structure such as a periscope.

3 is a block diagram showing the basic configuration of a camera using a solid-state image sensor image sensor, as shown in the image sensor unit 30 and the image signal provided by the image sensor unit 30 as an image image A timing for providing a timing for acquiring an image to the image sensor part 30 and a timing for acquiring an image to the image sensor part 30 and a timing for providing the timing to the sink insertion part 32 according to a standard; Generation section 31; The video signal provided through the sink inserter 32 is an analog TV video signal (NTSC, PAL, etc.).

However, as shown, the gamma ray may be introduced into the image sensor unit 30, which causes a non-linear rise of the black level.

FIG. 4 illustrates a phenomenon in which a black level rise occurs when gamma rays are introduced into the image sensor unit. As shown in FIG. 4, the screen becomes darker nonlinearly toward the lower left portion.

FIG. 5 is a graph illustrating a non-linear rise of the black level caused by the gamma rays shown in FIG. 4. As shown in FIG. 4, the reference black level without gamma rays maintains a constant voltage regardless of the position of the line. It can be seen that the actual black level measured when exposed to gamma rays increases nonlinearly toward the subsequent line.

When the maximum black level of the video signal is changed, the image becomes dark or gray, so that a good quality image cannot be obtained. This phenomenon significantly deteriorates the reliability of the radiation-resistant camera. In radiation-resistant cameras that are difficult to process, it is difficult to resolve these distortions directly at the camera stage in real time.

In order to prevent distortion of an image caused by the inflow of radiation as described above, an object of the present invention is to block light in the same condition by changing the black level due to the incoming radiation when the subject image is acquired through the image sensor. The present invention provides a camera black level compensation device and a method for compensating using a signal acquired by a reference image sensor to prevent distortion of an image to improve image quality and reliability of a radiation resistant camera.

Another object of the embodiments of the present invention is to remove the high-frequency components from the output after obtaining the output by the radiation flowing into the image sensor of the same standard that cut the light to the image distortion caused by the radiation inflow of the image sensor outputting an analog signal The present invention provides a camera black level compensation device and a method for compensating only distortion of an image without increasing local noise due to radiation inflow.

Another object of the embodiments of the present invention is to automatically compensate for the output of an image sensor that outputs an analog image signal in a radiation environment based on the output of an image sensor in the same environment that blocks light, thereby automatically adjusting the aperture according to the radiation environment. The present invention provides a camera black level compensation device and a method for implementing an auto iris function and compensation for nonlinear brightness distortion.

Still another object of the embodiments of the present invention is to compensate for a black level change caused by radiation flowing in when obtaining an image of a subject through an image sensor using a signal acquired by a reference image sensor that blocks light under the same conditions. By low-pass filtering the output of the reference image sensor and integrating it to determine the radiation dose by its value, it provides simultaneous information of the radiation dose and image by improving the image quality in the radioactive environment and simultaneously identifying the radiation dose in the area. Of course, it is possible to selectively check the radiation amount where the camera is directed, to replace the dedicated radiation level meter, or to assist in reconfirming whether the measured amount of the dedicated radiation level meter is normal. Camera black level compensation device that can be used for post-processing of video To provide the method.

In order to achieve the above object, the camera black level compensation apparatus according to an embodiment of the present invention includes an image sensor unit for obtaining an image of the subject in the state exposed to radiation and outputting it as an analog image signal; A reference image sensor unit outputting only an effect of radiation as an analog image signal in a state where light is blocked; A filtering unit to remove high frequency components from the analog image signal of the reference image sensor unit; And a compensator configured to compensate the analog video signal of the image sensor unit based on the output of the filtering unit and output an analog video signal compensated for image distortion.

Here, it is preferable that the image sensor unit and the reference image sensor unit have the same specification and an external exposure environment, and the filtering unit passes only below the line frequency in order to block the effect of the brightness change of the pixel randomly generated by the radiation. It is preferred to include a lowpass filter.

The control unit may further include an integrating unit integrating the output of the filtering unit for a predetermined time to quantify the analog image signal output by the reference image sensor unit during the corresponding time, and then output the voltage corresponding to the radiation dose.

In addition, the camera black level compensation apparatus according to another embodiment of the present invention includes an image sensor unit for obtaining an image of the subject in the state exposed to radiation and outputting it as an analog image signal; A reference image sensor unit outputting only an effect of radiation as an analog image signal in a state where light is blocked; A first filtering unit which removes high frequency components from the analog image signal of the reference image sensor unit; A compensator configured to reduce the output of the first filtering unit by differential amplification from the analog image signal of the image sensor unit, and output the compensated analog image signal by raising the differential amplified signal by a reference black level voltage; A second filtering unit which receives an output of the first filtering unit and passes only a frequency lower than a filtering frequency of the first filtering unit; And an integrating unit for integrating the output of the second filtering unit according to the frame of the image and outputting it as a voltage according to the radiation dose.

In addition, the camera black level compensation method according to an embodiment of the present invention includes a first step of obtaining a subject image signal distorted by the inflow of radiation from the first image sensor having radiation resistance; A second step of acquiring an image signal affected by radiation from a second image sensor unit disposed in the same environment as the first image sensor unit while shielding light with a material transmitting radiation; And a third step of correcting and outputting the analog image signal obtained from the first image sensor unit based on the analog image signal obtained through the second image sensor unit.

Here, in the third step, an image signal from which a high frequency component is removed from the image signal obtained from the second image sensor is used for correction.

In addition, the camera black level compensation method according to an embodiment of the present invention is a fourth step of outputting the voltage information for measuring the radiation dose by removing the high-frequency components from the image signal obtained through the second image sensor and integrated It may be made to include more.

In addition, the camera black level compensation method according to another embodiment of the present invention includes a first step of obtaining a subject image signal distorted due to radiation inflow from one or more image sensor unit having a radiation resistance characteristic; A second step of shielding light but shielding it with a material that transmits radiation and obtaining an image signal affected by radiation from a reference image sensor unit disposed in the same environment as the one or more image sensor units; And a third step of compensating and outputting each analog video signal obtained from the at least one image sensor unit based on the analog video signal obtained through the reference image sensor unit.

The present invention as described above will be described in detail with reference to the accompanying drawings and embodiments.

6 is a block diagram showing the configuration of an embodiment of the present invention, as shown in the first image sensor 110 for obtaining an image of the subject and outputting it as an analog signal, and the first image sensor 110 In addition, a second image sensor unit 120 having the same standard as the first image sensor unit 110 is prepared, and the entire sensing area of the second image sensor unit 120 blocks light but does not transmit radiation. After shielding with a material (for example, aluminum foil, etc.) 121, it is disposed so as to be exposed to the same environment as the first image sensor 110. The output of the first image sensor unit 110 and the output of the second image sensor unit 120 filtered by the low pass filter 130 are calculated using the operation unit 140 to compensate for image distortion. .

The first image sensor 110 refers to a module configured to provide an image sensor for converting an optical signal into an electrical signal and a driving timing of the image sensor, and to insert an sink to output an analog image signal. Various types of solid state image sensors (CCD or CMOS type sensors) may be used. As the image sensor, it is preferable to use a sensor having resistance to a radioactive environment, and more preferably, a CMOS Active Pixel Sensor (APS).

When the first image sensor unit 110 is exposed to a radiation environment, the black level is nonlinearly distorted as shown in FIGS. 4 and 5 under the influence of gamma rays having the shortest wavelength among the radiations.

Therefore, in order to compensate for the distortion, the second image sensor 120 having the same standard as the first image sensor 110 is further configured in the present embodiment. In this case, the second image sensor unit 120 shields light by applying a material 121 such as a metal thin film that blocks light but transmits gamma rays to the sensing area. As a result, the second image sensor unit 120 operates as a reference sensor, which is a means for measuring the degree of black level distortion caused by pure gamma rays.

Therefore, when the analog image output of the second image sensor unit 120 is subtracted from the distorted analog image output of the first image sensor unit 110 using the calculator 140, nonlinear black level distortion may be compensated. Will be.

However, it should be noted that the image distortion caused by gamma rays does not merely cause the nonlinear distortion of the black level. That is, gamma rays affect any of the cells of the image sensor, which change every image field and frame. In other words, the effects of the gamma rays are mixed with the image signal in the form of high frequency noise, and one of the effects of these effects is that the black level is changed nonlinearly. Therefore, when the output of the second image sensor unit 120 is simply subtracted from the outputs of the different first image sensor unit 110, the high frequency noise is duplicated so that the nonlinear distortion of the black level may be compensated. The noise incorporated into the image is almost doubled, which can further intensify image distortion.

Therefore, as shown in the figure, a low pass filter 130 is further configured at the output of the second image sensor unit 120 to block the high frequency noise component. Since the measurement target of the second image sensor unit 120 is a non-linear distortion of the black level generated by the influence of the gamma rays, it is considered that this is a low frequency component as shown in FIG. 5, so that the actual gamma rays are randomly generated in the cells. This is because even if the effects are eliminated, there is no problem in obtaining a nonlinear change in the black level to compensate for the distortion of the black level. In order to select only the low frequency component and remove the high frequency component, it is preferable to cut off a signal having a frequency higher than the line frequency at which each image line of each frame is obtained, which is automatically or manually depending on the image to be obtained and the degree of compensation. Can be determined. Such filtering and compensation of the reference signal can be easily performed because the signals are all analog video signals having the same sync signal.

As shown in the drawing, an analog image signal including gamma ray noise obtained through the first image sensor unit 110 is applied to a non-inverting terminal of the operation unit 140 that is illustrated in the form of an operational amplifier, and the reference sensor The first image sensor unit 110 is applied by applying an analog signal from which the high frequency signal is removed from the analog image signal obtained through the second image sensor unit 120 used as an inverting terminal of the operation unit 140 and performing calculation. The compensating analog image signal can be output by compensating only the nonlinear distortion signal of the black level at the output of. However, one more thing to be considered here is that in order for the output analog video signal to become a practically usable video signal, it is necessary to shift the voltage by the reference black level or add the voltage further.

FIG. 7 illustrates an image of a black level distortion obtained by the first image sensor and a signal obtained by the second image sensor. As shown in FIG. The signal is obtained. Thus, adding them together yields a signal close to zero. That is, even when the actual video information is included, a signal having a black level of 0 is obtained, and thus cannot be a normal video signal by itself.

In order to obtain the preferred video signal shape as shown in FIG. 8, the reference black level voltage must be further added to the result of calculating the signals of FIG. 7 or the signal must be shifted by the corresponding voltage.

Therefore, the operation unit 140 may be configured as an operational amplifier for subtracting and adding, or may be configured as a differential amplifier for performing a corresponding function. The calculation unit 140 may be exposed to a radiation environment together with the image sensor units 110 and 120, and may be disposed at a position outside the radiation environment through wiring, but for easy modularization and handling, the image sensor units It is preferable to be disposed in a radiation environment together with (110, 120), for this purpose, the calculation unit 140 should be made of devices with good radiation resistance characteristics. In other words, it is difficult to obtain high radiation resistance when using a general-purpose dedicated chip, and newly constructing a circuit capable of the same function with discrete devices having radiation characteristics such as passive elements and bipolar transistors. desirable.

Such a function can be adaptively performed according to the influence of radiation, in particular gamma rays, to compensate for the distortion of the black level, and this function corresponds to the auto iris function (Auto Iris). In other words, it compensates for brightness and black level by the environment without additional control or adjustment, which can achieve very good image quality improvement in the field of radiation camera which has no choice but to use analog signal to improve radiation characteristics. It is a means.

FIG. 9 is a block diagram illustrating another embodiment of the present invention. As shown in FIG. 9, an output of the second image sensor unit 120 compensates for an image distorted by radiation of the first image sensor unit 110. In addition to the intended use is shown to be configured for additional use.

The analog image output of the second image sensor 120 is filtered through the low pass filter 130 to remove high frequency components that may distort the image itself, and then output the value as a value for compensation. In this configuration, the low frequency filter partially removes a signal (black level distorted analog signal) through the integrator 160 through the low pass filter 130. To output the radiation dose for a certain time as a standardized voltage value.

The voltage value is different according to the integral amount, and the DC voltage value (the radiation amount obtained by DC) output corresponding to the radiation dose may have nonlinearity, but the second image sensor unit 120 outputs the integral period. Quantify by setting according to the period of the analog video signal (e.g., one field (odd field, even field), one frame (sum of odd field and even field), or a combination thereof) It is possible to measure the radiation dose where the second image sensor unit 120 is located at a predetermined accuracy by matching the integral value with a corresponding table according to the actually measured radiation dose or by using a specific equation or algorithm. It becomes possible. At this time, as shown, instead of integrating the output of the low pass filter 130 from which the high frequency component is removed from the analog image signal provided by the second image sensor unit 120 to the integrator 160 as it is, the second low range is interposed therebetween. The pass filter 150 may be further added to further filter high frequency components that may cause sudden fluctuations in the measured value (configured to pass only a lower frequency than the low pass filter 130 in front) to stabilize the measured value. Can be.

In other words, through the configuration as shown in the image through the automatic iris adjustment function of the radiation camera to compensate for the non-linear black level distortion, it is possible to check the radiation dose only with the camera at a remote location.

In particular, since the illustrated second image sensor unit 120 provides a compensation value for black level distortion of the unit image sensor unit with respect to the current radiation environment, the second image sensor unit 120 is intended to construct a camera using one or more image acquisition image sensors. Even if it is, even if the number can be configured singly without increasing the number, only the configuration of the calculation unit 140 shown in the image acquisition image sensor unit need only be configured.

FIG. 10 illustrates the overall structure of the radiation-resistant camera system described above. As shown in FIG. 10, the radioactive region is composed of elements or structures having radiation-resistant characteristics and an image signal of which black level distortion due to radiation is compensated for by a reference sensor. A camera unit 200 for outputting a voltage representing a radiation dose is disposed, and receives a voltage corresponding to the image signal and the radiation dose provided by the camera unit 200, the control unit and power to the camera unit 200 The management unit 300 to provide a non-radiation area other than the radiation area is disposed. The display unit 310 is connected to the management unit 300 to display the image signal to the user.

The management unit 300 may have a relay function to internally provide the video signal to the display unit 310, and convert the analog video signal into a digital video signal and provide it to a display unit of a digital display method if necessary. It may have a function of storing / image filtering the digital video signal. In addition, a function of converting the voltage provided as the radiation measurement voltage into a radiation dose using a radiation dose matching table and the like may be added to the display unit 310.

In addition, if necessary, the radiation dose may be added to an analog video signal or a digital video signal by an on-screen display (OSD) method, and the post-processing of an image signal obtained through the camera unit 200 may be performed. The radiation dose obtained can be used for image processing such as varying the degree of noise removal.

In particular, the radiation dose corresponding to the voltage can be individually calibrated using the calibration process through the actual measurement after generating the reference table. And performance can be improved.

As described above, the camera black level compensation apparatus and the method according to an embodiment of the present invention is a reference image sensor that blocks the light in the same condition to change the black level due to the incoming radiation when the subject image obtained through the image sensor By compensating using the obtained signal, the nonlinear black level distortion of the image can be effectively compensated, thereby improving the image and reliability of the radiation camera.

In addition, the camera black level compensation apparatus and method according to an embodiment of the present invention obtained the output by the radiation flowing into the image sensor of the same standard that cuts off the image distortion caused by the radiation inflow of the image sensor outputting the analog signal Then, by compensating with the value obtained by removing the high frequency component from the output, only the distortion of the image is selected and compensated without increasing local noise due to the inflow of radiation, thereby greatly improving the quality of the image under a radiation environment.

In addition, the camera black level compensation apparatus and method according to an embodiment of the present invention to compensate for the output of the image sensor for outputting the analog image signal in the radiation environment based on the output of the image sensor in the same environment that cut off the radiation By implementing an auto iris function that is actively adjusted according to the environment, and effectively compensating for the nonlinear black level, the image quality of the camera, which requires the use of an analog signal in order to increase radiation resistance, is especially improved for dark subjects. It has the effect of providing a clear discernment of the information.

In addition, the camera black level compensation apparatus and the method according to an embodiment of the present invention is a signal obtained by the reference image sensor that blocks the light in the same conditions of the black level change due to the incoming radiation when obtaining the subject image through the image sensor In addition, the output of the reference image sensor may be low-pass filtered and then integrated to determine the radiation dose by the value, thereby improving image quality in the radioactive environment and simultaneously detecting the radiation dose in the region. In addition to providing simultaneous information on the amount of radiation and images, it is possible to selectively check the amount of radiation where the camera is directed, replace the dedicated radiation level meter, or assist in the normal measurement of the measured amount of the radiation level meter. It can be reconfirmed and can be used for post-processing of the image. Has an excellent effect.

Claims (16)

An image sensor unit which acquires an image of a subject in a state of being exposed to radiation and outputs it as an analog image signal; A reference image sensor unit outputting only an effect of radiation as an analog image signal in a state where light is blocked; A filtering unit to remove high frequency components from the analog image signal of the reference image sensor unit; And a compensator for compensating the analog image signal of the image sensor unit based on the output of the filtering unit to output an analog image signal compensated for image distortion. The method of claim 1, wherein the compensator receives an analog image signal of the image sensor unit as a non-inverting terminal, and receives a signal of the filtering unit as an inverting terminal to subtract the signal of the filtering unit from an analog image signal of the image sensor unit. Camera black level compensation device comprising an amplifier. The camera black level compensation apparatus of claim 1, wherein the compensation unit is formed of a discrete element including a passive element and a transistor instead of an operational amplifier element. The apparatus of claim 1, wherein the compensation unit subtracts an output of the filtering unit from an analog image signal of the image sensor unit, and generates a compensated image signal by adding a reference black level voltage. The camera black level compensation apparatus of claim 1, wherein the image sensor unit and the reference image sensor unit have the same standard and an external exposure environment. The apparatus of claim 1, wherein the image sensor unit and the compensator may be plural, and in this case, the reference image sensor unit is one. The camera black level compensation device of claim 1, wherein the filtering unit includes a low pass filter that passes only the line frequency of the analog video signal. The method of claim 1, further comprising: an integrating unit integrating the output of the filtering unit for a predetermined time to quantify the analog image signal output by the reference image sensor unit during the corresponding time, and then output the voltage corresponding to the radiation dose. Camera black level compensation device. The camera black level compensation apparatus of claim 8, wherein the integration time is based on a frame period of an image output by the reference image sensor. An image sensor unit which acquires an image of a subject in a state of being exposed to radiation and outputs it as an analog image signal; A reference image sensor unit outputting only an effect of radiation as an analog image signal in a state where light is blocked; A first filtering unit which removes high frequency components from the analog image signal of the reference image sensor unit; A compensator configured to reduce the output of the first filtering unit by differential amplification from the analog image signal of the image sensor unit, and output the compensated analog image signal by raising the differential amplified signal by a reference black level voltage; A second filtering unit which receives an output of the first filtering unit and passes only a frequency lower than a filtering frequency of the first filtering unit; And an integrating unit for integrating the output of the second filtering unit according to the frame of the image and outputting it as a voltage according to the radiation dose. 11. The camera black level compensation apparatus of claim 10, wherein the compensation unit and the integration unit are configured in an area free of radiation. A first step of obtaining a subject image signal distorted by radiation inflow from a first image sensor unit having radiation resistance characteristics; A second step of acquiring an image signal affected by radiation from a second image sensor unit disposed in the same environment as the first image sensor unit while shielding light with a material transmitting radiation; And correcting and outputting the analog image signal obtained from the first image sensor based on the analog image signal obtained through the second image sensor. 13. The camera black level compensation method of claim 12, wherein the third step uses an image signal from which a high frequency component is removed from the image signal obtained from the second image sensor. 13. The camera black level of claim 12, further comprising a fourth step of outputting voltage information for measuring radiation dose by removing high frequency components from the image signal obtained through the second image sensor and integrating them. Compensation method. The method of claim 12, wherein the third step is corrected by adding an inverse phase of the analog image signal obtained through the second image sensor unit to the analog image signal obtained from the first image sensor unit and adding a black level voltage as a reference. And outputting an analog video signal. A first step of respectively acquiring a subject image signal distorted by radiation inflow from one or more image sensor units having radiation resistance characteristics; A second step of shielding light but shielding it with a material that transmits radiation and obtaining an image signal affected by radiation from a reference image sensor unit disposed in the same environment as the one or more image sensor units; And compensating for each of the analog image signals obtained from the at least one image sensor unit based on the analog image signal obtained through the reference image sensor unit.

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