KR102198748B1 - Method for detecting soft defective pixels in infrared camera for detection of acquired bad pixels - Google Patents

Abstract

A method of detecting soft defective pixels in a thermal camera is disclosed. Outputting a representative pixel by performing, by the median filter module, performing median filtering on a pixel of a predetermined area of an image of the thermal camera; A step of detecting, by a bad pixel detection module, a bad pixel of the image using a representative pixel output from the intermediate value filter module. According to the above-described method of detecting soft defective pixels of a thermal camera, the contrast of the pixels is improved to the level of visual identification, the intermediate value filter module and the intermediate value are calculated, and the defective pixels are detected by comparing each pixel through a comparator module. As a result, it is possible to detect acquired defective pixels due to aging of the thermal imager, and it is possible to cope with statistical judgment errors of determining the original defective pixels as normal pixels. As in the conventional method, it is not necessary to input a separate reference image for each thermal camera, and by detecting and compensating for defective pixels by itself, it is convenient and the accuracy of detecting defective pixels of an aging thermal camera is very high compared to the existing one.

Description

Detecting soft defective pixels of thermal imaging camera for detection of acquired defective pixels{METHOD FOR DETECTING SOFT DEFECTIVE PIXELS IN INFRARED CAMERA FOR DETECTION OF ACQUIRED BAD PIXELS}

The present invention relates to a thermal camera, and more particularly, to a method for detecting soft defective pixels of a thermal camera, and more specifically to a method for detecting and compensating for a soft defective pixel of a thermal camera.

In the thermal camera, each pixel basically has a characteristic difference during the factory shipment process.

Thermal imaging cameras include defective pixels from the factory shipment, and pixel compensation is performed for such defective pixels through non-formality correction in a later use process.

On the other hand, when the thermal camera is shipped from the factory, normal pixels may be changed to defective pixels due to long-term use. Although the original defective pixels can be easily compensated for and used in the conventional manner, there is no appropriate means for error compensation for acquired defective pixels due to long-term use.

In addition, when the factory shipment is determined to be good or bad, if it is statistically determined to be more normal, it is specified as normal pixels and shipped. In this case, a statistical judgment error in which the defective pixel is determined to be a normal pixel may occur.

As such, there is a need for a method of detecting and compensating for a statistical determination error of the original defective pixel and the acquired defective pixel.

10-0415051 10-1656173

An object of the present invention is to provide a method for detecting soft defective pixels in a thermal camera.

The method for detecting a soft defective pixel of a thermal camera according to an object of the present invention includes the steps of: a median filter module performing median filtering on a pixel of a predetermined area of an image of the thermal camera and outputting a representative pixel; The defective pixel detection module may be configured to include the step of detecting a defective pixel of the image using the representative pixel output from the intermediate value filter module.

Here, the bad pixel interpolation module may be configured to further include performing interpolation on the bad pixels detected by the bad pixel detection module.

In addition, the step of outputting a representative pixel by performing, by the median filter module, performing median filtering on pixels of a predetermined area of the image of the thermal camera, may include performing median filtering on pixels of the 3X3 area of the image. Can be configured.

In the method for detecting soft defective pixels of a thermal camera according to the object of the present invention, the median filter module sequentially performs median filtering on pixels of a 3X3 area of an image of the thermal camera to output a representative pixel. step; The defective pixel detection module may be configured to include the step of detecting a defective pixel of the image using the representative pixel output from the intermediate value filter module.

Here, the bad pixel interpolation module may be configured to further include performing linear interpolation on the bad pixels detected by the bad pixel detection module.

In addition, the intermediate value filter module may be configured as a low-pass filter.

In the above-described method for detecting soft defective pixels of a thermal camera according to the object of the present invention, the median filter module sequentially performs median filtering on pixels in an nXn region of an image of the thermal camera to output representative pixels. Step to do; Detecting, by a bad pixel detection module, a bad pixel of the image using the representative pixel output from the intermediate value filter module; The bad pixel interpolation module may be configured to include performing linear interpolation on the bad pixels detected by the bad pixel detection module.

Here, the step of performing linear interpolation on the bad pixels detected by the bad pixel detection module by the bad pixel interpolation module may be configured to perform bidirectional linear interpolation on the bad pixels detected by the bad pixel detection module. .

In addition, the intermediate value filter module may be configured as a low-pass filter.

In the above-described method for detecting soft defective pixels of a thermal camera according to the object of the present invention, the median filter module performs median filtering on 8 surrounding pixels excluding a center pixel of a 3X3 area for an image of the thermal camera. Outputting a representative pixel; Detecting, by a bad pixel detection module, whether the center pixel is defective using the representative pixel output from the intermediate value filter module; Bypassing the detected normal pixel when the defective pixel interpolation module is detected as a normal pixel by the defective pixel detection module, and interpolating the detected defective pixel when the defective pixel detection module is detected as a defective pixel Can be configured to

Here, the step of detecting, by the defective pixel detection module, whether the center pixel is defective using the representative pixel output from the intermediate value filter module, performs bidirectional linear interpolation on the defective pixel detected by the defective pixel detection module. Can be configured to

In addition, the intermediate value filter module may be configured as a low-pass filter to have a characteristic robust against impuse noise.

In the above-described method for detecting soft defective pixels of a thermal camera according to the object of the present invention, the median filter module applies to the image immediately after the aging of the thermal camera, except for the center pixel of the nXn region. Outputting a representative pixel by performing an intermediate value filtering for; Detecting, by a bad pixel detection module, whether the center pixel is defective using the representative pixel output from the intermediate value filter module; The bad pixel interpolation module may be configured to include linear interpolation of the bad pixels detected by the bad pixel detection module.

Here, the step of linearly interpolating the defective pixel detected by the defective pixel detection module by the defective pixel interpolation module includes bypassing the detected normal pixel when the defective pixel detection module detects the defective pixel. When a pixel detection module detects a defective pixel, it may be configured to bidirectionally linearly interpolate the detected defective pixel.

And in nXn, n is an odd number.

According to the above-described method for detecting soft defective pixels of the thermal camera, the intermediate value of the intermediate filter module and the surrounding pixels is calculated, and the defective pixels are detected by comparing each pixel through the comparator module. It is possible to detect a pixel and to respond to a statistical judgment error of determining a source defective pixel as a normal pixel. That is, there is an effect of finding defective pixels that are not detected even after aging of the thermal camera.

As in the conventional method, it is not necessary to input a separate reference image for each thermal camera, and by detecting and compensating for defective pixels by itself, it is convenient and the accuracy of detecting defective pixels of an aging thermal camera is very high compared to the existing one.

In addition, by improving the contrast of the pixels to the level of visual identification and detecting defective pixels, there is an effect of making it possible to easily distinguish the difference in contrast for each area, and there is an effect of finding defective pixels at the level of visual identification.

1 is a block diagram of an apparatus for detecting soft defective pixels of a thermal camera according to an exemplary embodiment of the present invention.
2 is a schematic diagram of a configuration for detecting a soft defective pixel of a thermal camera according to an embodiment of the present invention.
3 to 7 are flowcharts illustrating a method of detecting a soft defective pixel of a thermal camera according to an exemplary embodiment of the present invention.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and will be described in detail in specific details for carrying out the invention. However, this is not intended to limit the present invention to a specific embodiment, it is to be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention. In describing each drawing, similar reference numerals have been used for similar elements.

Terms such as first, second, A, and B may be used to describe various elements, but the elements should not be limited by the terms. These terms are used only for the purpose of distinguishing one component from another component. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. The term and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being "connected" or "connected" to another component, it is understood that it may be directly connected or connected to the other component, but other components may exist in the middle. Should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in this application. Does not.

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

1 is a block diagram of an apparatus for detecting soft defective pixels of a thermal camera according to an exemplary embodiment of the present invention, and FIG. 2 is a schematic diagram of a configuration of detecting a soft defective pixel of a thermal camera according to an exemplary embodiment of the present invention.

Referring first to FIG. 1, the apparatus 100 for detecting soft defective pixels of a thermal camera according to an embodiment of the present invention includes a contrast improvement module 110, a median filter module 120, a comparator module 130, and a bidirectional linear. It may be configured to include an interpolation module 140.

The apparatus 100 for detecting soft defective pixels of a thermal imager is configured to detect defective pixels through median filtering and comparison between the center pixel and neighboring pixels by itself, unlike the detection and compensation of the existing original defective pixel by comparing the reference image. do.

The apparatus 100 for detecting soft defective pixels of the thermal imaging camera can detect acquired defective pixels due to the aging of the thermal imaging camera, and can respond to a statistical judgment error of determining a source defective pixel as a normal pixel during a factory shipment process. That is, defective pixels remaining after aging of the thermal camera can be found.

Since the reference image generated at the time of shipment from the factory is not used, the detection accuracy of the defective pixels of the aging thermal imaging camera is improved.

On the other hand, it is configured to detect defective pixels by improving the contrast of the pixels to the level of visual identification, thereby finding the defective pixels at the level of visual identification.

Hereinafter, a detailed configuration will be described.

The contrast improvement module 110 may be configured to improve contrast by receiving a pixel stream of a thermal camera.

The contrast improvement module 110 may be configured to smooth the pixel stream by moving it to a contrast of a band that can be recognized by the human eye.

The contrast improvement module 110 has an advantage of enabling easy identification of contrast differences for each area of an image.

The median filter module 120 may be configured to perform median filtering on surrounding pixels excluding the center pixel of the nXn region on the image of the thermal camera. A representative pixel value of a neighboring pixel can be found through median filtering.

Here, n is an odd number, and nXn may be 3X3, 5X5, 7X7, or the like.

In the example of FIG. 2, the value of the center pixel is 12, and the median value of 8 surrounding pixels, that is, the representative pixel value, is 11.

The median filter module 120 may sequentially perform median filtering by using each pixel of the pixel stream as a center pixel.

The intermediate value filter module 120 is a low-pass filter and may be configured to have characteristics that are robust to impulse noise.

The defective pixel detection module 130 may be configured to detect whether the center pixel is defective using the representative pixel output from the intermediate value filter module 120.

The bad pixel detection module 130 may be configured with a comparator module 130. The bad pixel detection module 130 may be input by adding or subtracting a predetermined constant value, as necessary, to a median value for which median value filtering is performed by the median filter module 120, that is, representative pixels of surrounding pixels.

In addition, a value of a center pixel whose contrast is improved by the contrast improvement module 110 may be input to the comparator module 130.

Meanwhile, as shown in FIG. 2, the comparator module 130 may be configured to calculate a difference between a representative pixel and a center pixel, and to determine the size by comparing the calculated difference with a predetermined threshold value.

The comparator module 130 is configured to determine that the center pixel is a normal pixel when the difference between the representative pixel and the center pixel is less than the threshold value, and determine the center pixel as a defective pixel when the difference between the representative pixel and the center pixel is greater than the threshold value. Can be. If the center pixel has a level difference greater than or equal to a predetermined threshold with respect to the representative value of the surrounding pixels, it is determined as a defective pixel.

The comparator module 130 may be configured to sequentially determine whether or not each pixel of the pixel stream is positive or negative.

Here, the threshold value may be variably set.

The threshold may be set as in Equations 1, 2, and 3 below.

가 산정되기 위한 시간은 열상 카메라 운용 초기화 이후 1분 이상 이어야 한다. 여기서,

는 충분히 작은 값을 취하기 위한 조건으로서, 최대 픽셀값의 10 %로 설정될 수 있다.Threshold

The time to be calculated should be at least 1 minute after the thermal camera operation is initialized. here,

Is a condition for taking a sufficiently small value, and may be set to 10% of the maximum pixel value.

의 최소값 및 최대값 제한을 걸어줄 수 있다.And as shown in Equation 2, the threshold value

Limits on the minimum and maximum values of can be set.

When the defective pixel interpolation module 140 is detected as a normal pixel by the defective pixel detection module 130, the detected normal pixel is bypassed, and when the defective pixel detection module 130 is detected as a defective pixel, the detected It can be configured to interpolate bad pixels.

The bad pixel interpolation module 140 may be a bidirectional linear interpolation module 140.

The bidirectional linear interpolation module 140 may change a bad pixel into a normal pixel through bidirectional linear interpolation.

3 to 7 are flowcharts illustrating a method of detecting a soft defective pixel of a thermal camera according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the median filter module 130 outputs a representative pixel by performing median filtering on a pixel of a predetermined area of an image of the thermal camera (S101).

In this case, it may be configured to perform median filtering for pixels in the 3X3 area of the image.

Next, the defective pixel detection module 130 detects a defective pixel of the image using the representative pixel output from the intermediate value filter module 120 (S102).

Next, the bad pixel interpolation module 140 performs interpolation on the bad pixels detected by the bad pixel detection module 130 (S103).

Referring to FIG. 4, the median filter module 120 sequentially performs median filtering on pixels in a 3X3 area of the image of the thermal camera and outputs a representative pixel (S201).

Here, the median filter module 120 may be configured as a low-pass filter.

Next, the defective pixel detection module 130 detects a defective pixel of the image using the representative pixel output from the intermediate value filter module 120 (S202).

Next, the bad pixel interpolation module 140 performs linear interpolation on the bad pixels detected by the bad pixel detection module 130 (S203).

Referring to FIG. 5, the median filter module 120 outputs a representative pixel by sequentially performing median filtering on pixels in an nXn region of an image of a thermal camera (S301).

Next, the defective pixel detection module 130 detects a defective pixel of the image using the representative pixel output from the intermediate value filter module 120 (S302).

Next, the bad pixel interpolation module 140 performs linear interpolation on the bad pixels detected by the bad pixel detection module 130 (S303).

Here, it may be configured to perform bidirectional linear interpolation on the defective pixel detected by the defective pixel detection module 130.

Referring to FIG. 6, the median filter module 120 outputs a representative pixel by performing median filtering on 8 surrounding pixels excluding a center pixel of a 3X3 area on an image of a thermal camera (S401). .

Next, the defective pixel detection module 130 detects whether the center pixel is defective using the representative pixel output from the intermediate value filter module 120 (S402).

Here, it may be configured to perform bidirectional linear interpolation on the defective pixel detected by the defective pixel detection module 130.

Next, when the defective pixel interpolation module 140 is detected as a normal pixel by the defective pixel detection module 130, the detected normal pixel is bypassed, and when the defective pixel detection module is detected as a defective pixel, the detected defect Pixels are interpolated (S403).

Here, the intermediate value filter module 120 may be configured as a low-pass filter to have characteristics robust to impulse noise.

Referring to FIG. 7, the median filter module 120 performs median filtering on 8 surrounding pixels excluding the center pixel of the nXn area on the image immediately after aging of the thermal camera, Is output (S501).

At this time, n is an odd number in nXn.

Next, the defective pixel detection module 130 detects whether the center pixel is defective using the representative pixel output from the intermediate value filter module 120 (S502).

Next, the bad pixel interpolation module 140 linearly interpolates the bad pixels detected by the bad pixel detection module 130 (S503).

Here, when the defective pixel detection module 130 is detected as a normal pixel, the detected normal pixel is bypassed, and when the defective pixel detection module 130 is detected as a defective pixel, the detected defective pixel is bidirectionally linearly interpolated. Can be configured.

Although described with reference to the above embodiments, those skilled in the art can understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention described in the following claims. There will be.

110: contrast improvement module
120: median filter module
130: bad pixel detection module (comparator module)
140: bad pixel interpolation module (bidirectional linear interpolation module)

Claims (1)

Improving the contrast by receiving, by the contrast improvement module, a pixel stream of the thermal camera;
Outputting a representative pixel by performing, by a median filter module, filtering a pixel in a predetermined area of the image of the thermal camera;
Detecting, by a bad pixel detection module, a bad pixel of the image using the representative pixel output from the intermediate value filter module;
A bad pixel interpolation module comprising the step of performing linear interpolation on the bad pixels detected by the bad pixel detection module,
The intermediate value filter module outputting a representative pixel by performing intermediate value filtering on a pixel of a predetermined area of an image of the thermal imaging camera,
It is configured to output a representative pixel having an intermediate pixel value of the remaining pixels by performing intermediate value filtering on pixels other than the center pixel among all pixels included in the 3X3 area of the image,
The step of improving the contrast by receiving, by the contrast improvement module, a pixel stream of a thermal camera,
It is configured to smooth the pixel stream by moving to a contrast of a band that can be identified by the naked eye,
The step of detecting, by the bad pixel detection module, a bad pixel of the image using the representative pixel output from the intermediate value filter module,
In the intermediate value filter module, a predetermined constant value is added to or subtracted from a representative pixel, which is a median value output through median filtering, and inputted to a comparator,
The step of detecting, by the bad pixel detection module, a bad pixel of the image using the representative pixel output from the intermediate value filter module,
The difference between the representative pixel and the center pixel is calculated using the comparator, the calculated difference is compared with a predetermined threshold value, and as a result of the comparison, if the calculated difference is less than the threshold value, the center pixel is normalized. It is determined as a pixel, and when the calculated difference is greater than the threshold value, the center pixel is determined as a bad pixel,
The step of performing, by the bad pixel interpolation module, linear interpolation on the bad pixels detected by the bad pixel detection module,
When the defective pixel detection module is detected as a normal pixel, the detected normal pixel is bypassed, and when the defective pixel detection module is detected as a defective pixel, the detected defective pixel is bidirectionally linearly interpolated,
The time at which the threshold value is determined is one minute or more elapsed after the operation of the thermal camera is initialized. A method of detecting soft defective pixels of a thermal camera for detecting acquired defective pixels.

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