KR20160037479A - Method for adjusting contrast of thermal image and apparatus for using the same - Google Patents

Abstract

The present invention relates to a method for adjusting the contrast ratio of a thermal image and a thermal image processing apparatus using the same. Updating to an average minimum value and an average maximum value for an entire image frame is performed using an average minimum value and an average maximum value of an image frame, which is continuously input for a predetermined period, and then a contrast ratio of an image frame input for the next predetermined period is adjusted. Therefore, a user cannot feel a remarkable change in brightness of an image even when an object that is hotter or colder than an average value exists. In addition, the procedure to update an average minimum value and an average maximum value of a histogram of an image is performed while a non-uniform correction process is achieved such that the user cannot recognize any difference, thereby easily achieving the procedure when detecting and tracking an object.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for adjusting a contrast of a thermal image, and a thermal image processing apparatus using the same.

The present invention relates to a method of adjusting a contrast ratio of a thermal image and a thermal image processing apparatus using the same, and more particularly, to a method of adjusting a contrast ratio of a thermal image by using a mean minimum value and an average maximum value of input image frames continuously for a predetermined interval, And adjusting the contrast ratio of the input image frame during the next predetermined period using the updated image contrast ratio and the thermal image processing apparatus using the method.

The contents described in this section merely provide background information on the present embodiment and do not constitute the prior art.

A camera using a sensor such as a general CCD (Charge Coupled Device) / CMOS (Complementary Metal-Oxide Semiconductor) displays an image based on the reflectance of a subject according to a wavelength when a light source is emitted to a subject. On the other hand, a thermal camera has a structure for displaying thermal energy emitted by the subject itself as an image. Therefore, there is an advantage that image acquisition is possible even at nighttime without light because there is no need for a light source.

Such a thermal imaging camera is used in various fields. As a typical example, there are medical / quarantine fields such as a remote thermometer of an entry / exit person at an airport to detect a high-temperature patient, a temperature of a transformer mounted on a pole, Industrial fields such as long distance measurement to judge whether or not there is overheating, and military / security fields such as detection and detection of enemy or abnormal objects in darkness without light.

However, the conventional method using the thermal image sensor has a lower resolution than the CCD / CMOS sensor, and there are many non-uniformity among the pixels. Also, since the temperature range between the background and the target is large, the dynamic range of the image is widened, resulting in artifacts or unnaturalness in image display. Therefore, the technique of adjusting the contrast ratio for enhancing the visibility of the original image in the system using the thermal image sensor is a very important technology that determines the performance of the entire system. In order to adjust the contrast ratio of such a thermal image, conventionally, there are histogram equalization, contrast stretching, and plateau equalization. However, in the conventional method, only the global information of the current frame is considered , And the contrast ratio is improved for each frame. This is problematic in that it is difficult to apply a real-time system, and an artifact is increased and noise amplification is increased due to an excessive contrast ratio improvement.

Korean Patent No. 10-1041136, June 14, 2011 Announcement (Name: Thermal Image Processing Method)

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a method and apparatus for updating an average minimum value and an average maximum value of all image frames using an average minimum value and an average maximum value of image frames continuously input for a predetermined interval And adjusting the contrast ratio of the input image frame during the next predetermined interval using the corrected contrast ratio and the thermal image processing apparatus using the same.

However, the object of the present invention is not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood from the following description.

According to another aspect of the present invention, there is provided a thermal image processing apparatus for processing a plurality of image frames, the method comprising the steps of: A histogram processing unit for calculating an average minimum value and an average maximum value and then updating an average minimum value and an average maximum value of the calculated image frames to an average minimum value and an average maximum value of the histogram of the image; And a contrast ratio processor for adjusting the contrast ratio of the image frame input during the next predetermined interval using the histogram average minimum value and the average maximum value of the image updated through the histogram processing unit.

In this case, the non-uniformity correction unit may perform non-uniformity correction on image frames continuously input for a predetermined period.

Also, the histogram processing unit may update the histogram average minimum value and the average maximum value of the image during the non-uniformity correction of the input image frame during the next predetermined period through the non-uniformity correction unit.

In addition, the histogram processing unit may calculate the minimum and maximum values of the histograms of the image frames for the predetermined period, the non-uniformity of which has been corrected through the non-uniformity correction unit, and calculate an average minimum value And the average maximum value.

According to an aspect of the present invention, there is provided a method for adjusting a contrast ratio of a thermal image, the method comprising: calculating a histogram minimum value and a maximum value of each of image frames input continuously for a predetermined period; Calculating an average minimum value and an average maximum value of the input image frames during the predetermined period based on the histogram minimum value and the maximum value of each of the image frames; Updating an average minimum value and an average maximum value of the calculated image frames to a histogram average minimum value and an average maximum value of the image; And adjusting a contrast ratio of the input image frame for a next predetermined period using the histogram average minimum value and the average maximum value of the updated image.

At this time, updating the histogram average minimum value and the average maximum value of the image may be performed while non-uniformity correction processing is performed on the image frame.

If the histogram mean minimum value and the mean maximum value of the image exist before the step of calculating the histogram minimum value and the maximum value, the histogram average minimum value and the average maximum value of the image are continuously input for the predetermined period And adjusting the contrast ratio of the image frame.

In addition, the present invention can provide a computer readable recording medium on which a program for executing a method of adjusting a contrast of a thermal image according to an embodiment of the present invention as described above is recorded.

According to the thermal image contrast ratio adjusting method and the thermal image processing apparatus using the method of the present invention, the contrast ratio is adjusted using the histogram average minimum value and the average maximum value of the updated image before the non- Thus, the user can not feel the change in brightness of the image to a large extent even if there is a hot or cold object than the average value. Further, by performing the updating process of the histogram average minimum value and the average maximum value of the image during the non-uniformity correction process, the user can not recognize the difference, and thus it becomes easier to detect and track the object.

In addition, various effects other than the above-described effects can be directly or implicitly disclosed in the detailed description according to the embodiment of the present invention to be described later.

FIG. 1 is a schematic view for explaining an operation of a thermal image processor according to an embodiment of the present invention. Referring to FIG.
2 is a block diagram illustrating a main configuration of a thermal image processing apparatus according to an embodiment of the present invention.
3 is a flowchart illustrating a method of adjusting a contrast of a thermal image according to an exemplary embodiment of the present invention.
4 to 5 are diagrams for explaining a method of adjusting a contrast ratio of a video image according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the detailed description of known functions and configurations incorporated herein will be omitted when it may unnecessarily obscure the subject matter of the present invention. This is to omit the unnecessary description so as to convey the key of the present invention more clearly without fading. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. However, it should be understood that the invention is not limited to the specific embodiments thereof, It is to be understood that the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Also, terms including ordinal numbers such as first, second, etc. are used to describe various elements, and are used only for the purpose of distinguishing one element from another, Not used. For example, without departing from the scope of the present invention, the second component may be referred to as a first component, and similarly, the first component may also be referred to as a second component.

In addition, when referring to an element as being "connected" or "connected" to another element, it means that it can be connected or connected logically or physically. In other words, it is to be understood that although an element may be directly connected or connected to another element, there may be other elements in between, or indirectly connected or connected.

Also, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. It is also to be understood that the terms such as " comprising "or" having ", as used herein, are intended to specify the presence of stated features, integers, It should be understood that the foregoing does not preclude the presence or addition of other features, numbers, steps, operations, elements, parts, or combinations thereof.

Now, a method of adjusting a contrast ratio of a thermal image according to an embodiment of the present invention and a thermal image processing apparatus using the same will be described in detail with reference to the drawings. Here, the same reference numerals are used for similar functions and functions throughout the drawings, and a duplicate description thereof will be omitted.

FIG. 1 is a schematic view for explaining an operation of a thermal image processor according to an embodiment of the present invention. Referring to FIG.

Referring to FIG. 1, the image processor 100 of the present invention adjusts the contrast ratio of the image frame and outputs the adjusted contrast image when the image frame is continuously input.

At this time, the thermal image processing apparatus 100 exists in a separate form and can receive a thermal image photographed through an external thermal imaging camera. The thermal image processing apparatus 100 exists as a component in the thermal imaging camera apparatus, You can receive and receive the thermal image. The infrared camera at this time is, for example, an infrared camera that detects infrared rays to form an image.

In addition, the thermal image processing apparatus 100 may receive and receive image frames transmitted from an external device via a communication network (not shown) in real time. The thermal image processing apparatus 100 may be a wireless communication system such as a WLAN (Wireless LAN), a Wi-Fi, a Wibro, a Wimax, a High Speed Downlink Packet Access (HSDPA) (Not shown) such as Ethernet, xDSL (ADSL, VDSL), Hybrid Fiber Coaxial Cable (HFC), Fiber to the Curb (FTTC), and Fiber To The Home . In addition, image frames may be received through a communication network (not shown) according to a communication method of all other widely known or later developed communication methods.

When the image frame is received, the thermal image processing apparatus 100 calculates a minimum value and a maximum value of the histogram of each of the image frames for a predetermined period, calculates an average minimum value and an average maximum value of the input image frames during a predetermined period, The calculated average minimum value and average maximum value of the histogram are updated to the histogram average minimum value and the average maximum value of the image. By using the histogram average minimum value and the average maximum value, the contrast ratio of the input image frame is adjusted for the next predetermined period, and the image frame with the adjusted contrast ratio is output, thereby providing a more visually improved image.

A processor mounted on the thermal image processing apparatus 100 can process a program command for executing the method according to the present invention. In one implementation, the processor may be a single-threaded processor, and in other embodiments, the processor may be a multithreaded processor. Further, the processor is capable of processing instructions stored on the storage device 400.

 The main configuration and operation method of the thermal image processing apparatus 100 will be described in detail with reference to FIG.

2 is a block diagram illustrating a main configuration of a thermal image processing apparatus according to an embodiment of the present invention.

2, the thermal image processing apparatus 100 of the present invention is an apparatus that is embedded in a thermal image camera system in a module form. However, the present invention is not limited thereto.

2, a thermal image processing apparatus 100 according to an exemplary embodiment of the present invention includes an ADC processing unit 10, a pixel correction processing unit 20, a non-uniformity correction unit 30, a histogram processing unit 40, 50).

More specifically, the ADC processor 10 converts an analog image signal output from the thermal image sensor into a digital image signal. At this time, the ADC processing unit 10 can convert a video signal inputted in analog form into a digital video signal of 14 bits or 16 bits and output it.

The pixel correction processing unit 20 performs a preprocessing process before processing the contrast ratio correction, and in particular, can perform a role of correcting defective pixels existing in a frame.

The non-uniformity correction unit 30 performs a role of correcting a fixed noise pattern (non-uniformity of image) generated due to inherent characteristics of the detection sensor. More specifically, a detection sensor capable of detecting a thermal image, such as an infrared ray detection sensor, can not properly detect an image when a predetermined time passes. In other words, the detection sensor is provided for each pixel, Each of the detection sensors has a different offset or a non-uniformity correction due to the temperature of the sensor itself or the change of the surrounding environment. Such a non-uniformity correction state becomes a noise form of the final output image. The non-uniformity correction unit 30 serves to correct such image unevenness, and the nonuniformity correction is generally performed periodically.

Here, the nonuniformity correction unit 30 may perform nonuniformity correction through various known methods. For example, the non-uniformity correction unit 30 can perform non-uniformity correction using a macroblock-based repetitive padding method, that is, a method of defining values of luminance information and chrominance information belonging to an object area outside the object information have. In addition, the non-uniformity correction unit 30 can process the non-uniformity correction based on the image processing. That is, non-uniformity correction can be processed according to an algorithm using image registration between adjacent frames. Also, the image can be output in the freezing state in which the image stops for several seconds while the non-uniformity correction is being performed through the non-uniformity correction unit 30. [

The histogram processing unit 40 generates a histogram in each of the image frames subjected to the non-uniformity correction processing through the non-uniformity correction unit 30, and calculates the minimum and maximum histogram histograms for each image frame using the generated histogram. After calculating the average minimum value and the average maximum value of the input image frames during a predetermined period, the average minimum value and the average maximum value of the calculated image frames are updated to the histogram average minimum value and the average maximum value of the image, And transmits the histogram average minimum value and the average maximum value of the image to the contrast ratio processing unit 50.

At this time, the histogram processing unit 40 according to the embodiment of the present invention updates the average minimum value and the average maximum value of the input image frames for the predetermined period to the average minimum value and average maximum value of the image histogram, The update is performed while the non-uniformity correction processing for the frame is performed.

For example, when the thermal image processing apparatus 100 of the present invention is embedded in an infrared camera that generates 100 frames per second, 100 frames can be received for a predetermined period (1 second). The histogram processing unit 40 calculates the minimum and maximum values of the histogram in each image frame of the 100 frames. The histogram processing unit 40 calculates an average minimum value and an average maximum value of the input image frames based on the histogram minimum value and the maximum value of each of the image frames. That is, the histogram minimum and maximum values of the frames 1 to 100 are calculated, and the average minimum value and average maximum value of the image frames for one second can be calculated.

Thereafter, the histogram processing unit 40 adjusts the average minimum value and the average maximum value of the image frames of the predetermined period to the histogram average minimum value of the image during the non-uniformity correction for the input image frame continuously for a next predetermined period (for example, 1 second) And the average maximum value.

The contrast ratio processor 50 may adjust the contrast ratio of the input image frame during the next predetermined period using the histogram average minimum value and the average maximum value of the updated image through the histogram processing unit 40. [ In addition, the contrast ratio processor 50 of the present invention can adjust the contrast ratio of the input image frame continuously for the predetermined period, if the histogram average minimum value and the average maximum value of the image before update are present.

The main configuration and operation method of the thermal image processing apparatus 100 according to the embodiment of the present invention have been described above. However, not all of the components shown in FIG. 2 are essential components, and the thermal image processing apparatus 100 can be implemented by more components than the components shown in the drawing, The processing apparatus 100 may be implemented. For example, the histogram processing unit 40 may further include a storage unit for storing various types of information calculated by the histogram processing unit 40, and may further include various components for processing a thermal image.

In addition, the elements constituting the thermal image processing apparatus 100 according to the embodiment of the present invention are arranged according to the flow of the sequence of performing the thermal image processing, but it should be noted that it is not limited thereto.

Although the present specification and drawings describe exemplary device configurations, the functional operations and subject matter implementations described herein may be embodied in other types of digital electronic circuitry, or alternatively, of the structures disclosed herein and their structural equivalents May be embodied in computer software, firmware, or hardware, including, or in combination with, one or more of the foregoing. Implementations of the subject matter described herein may be embodied in one or more computer program products, i. E. One for computer program instructions encoded on a program storage medium of the type for < RTI ID = 0.0 & And can be implemented as a module as described above. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter that affects the machine readable propagation type signal, or a combination of one or more of the foregoing.

Hereinafter, a method of adjusting the contrast of a thermal image according to an embodiment of the present invention will be described.

FIG. 3 is a flowchart illustrating a method for adjusting a contrast of a thermal image according to an exemplary embodiment of the present invention. FIGS. 4 and 5 illustrate a method of adjusting a contrast ratio of an image according to an exemplary embodiment of the present invention.

Referring to FIG. 3, a method of adjusting a contrast of a thermal image according to an exemplary embodiment of the present invention is a method in which a thermal image processor 100 sequentially receives input image frames for a predetermined interval, The minimum and maximum histogram histograms of the inputted image frames are calculated (S101). For example, when the thermal imaging apparatus 100 of the present invention is equipped with a thermal imaging camera that generates 100 frames per second, it can receive 100 frames for a predetermined period (1 second). Then, the histogram minimum value and the maximum value are calculated in each image frame of 100 frames.

The thermal image processing apparatus 100 calculates an average minimum value and an average maximum value of the input image frames during the predetermined period based on the minimum and maximum histogram histograms of the image frames. That is, the histogram minimum and maximum values of the frames 1 to 100 are calculated, and the average minimum value and average maximum value of the image frames for one second can be calculated.

Then, while the non-uniformity correction of the input image frame is performed continuously for the next predetermined period (for example, 1 second), the thermal image processing apparatus 100 calculates the average minimum value and the average maximum value of the image frames of the predetermined period as a histogram The average minimum value and the average maximum value are updated (S105).

In operation S107, the contrast ratio of the image frame input in the next interval is adjusted using the histogram average minimum value and the average maximum value of the updated image.

4, an average minimum value and an average maximum value of image frames for the first section 500 are calculated using the image frame of the first section 500 after the non-uniformity correction (NUC) process. The thermal image processing apparatus 100 updates the average minimum value and the average maximum value of the image frames for the first section 500 to the histogram average minimum value and the average maximum value of the image. At this time, The update process is performed while the non-uniformity correction processing of the image frame for the second section 520 is performed. Then, the thermal image processing apparatus 100 adjusts the contrast ratio of the second section 520 after the non-uniformity correction processing, using the histogram average minimum value and the average maximum value of the updated image. At the same time, the thermal image processing apparatus 100 calculates an average minimum value and an average maximum value of image frames for the second section 520, and calculates an average minimum value and an average maximum value of the calculated image frames, The histogram average minimum value and the average maximum value of the image are updated to be used for adjusting the contrast ratio of the image frame. At this time as well, the processing is performed while the non-uniformity correction is performed on the input image frame of the next section.

That is, as shown in FIG. 5A, even if a dynamic region, which is a sudden brightness change region, occurs during image capture using the thermal imaging camera, before the nonuniformity correction processing is performed, the contrast ratio is adjusted And by outputting it, the user can confirm a clearer thermal image.

In other words, according to the present invention, by adjusting the contrast ratio using the histogram average minimum value and the average maximum value of the updated image, before the non-uniformity correction is performed on the image frame inputted in the next period, The brightness of the image is not greatly changed. Further, by performing the updating process of the histogram average minimum value and the average maximum value of the image during the non-uniformity correction process, the user can not recognize the difference, and thus it becomes easier to detect and track the object.

The method of adjusting the contrast ratio of the thermal image according to the embodiment of the present invention has been described above.

The method for adjusting the contrast of a thermal image for image recognition of the present invention as described above may be provided in the form of a computer readable medium suitable for storing computer program instructions and data. A program recorded on a recording medium for implementing a shadow removal method for image recognition according to an embodiment of the present invention includes a step of calculating a histogram minimum value and a maximum value of each of image frames continuously input for a predetermined period, Calculating an average minimum value and an average maximum value of the input image frames during the predetermined period based on the minimum and maximum values of the respective histograms, calculating an average minimum value and an average maximum value of the calculated image frames, Adjusting the contrast ratio of the image frame input during the next predetermined period using the histogram average minimum value and the average maximum value of the updated image, and the like.

At this time, the program recorded on the recording medium can be read and installed in the computer and executed, thereby executing the above-described functions.

In order to allow a computer to read a program recorded on a recording medium and to execute functions implemented by the program, the above-mentioned program may be stored in a computer-readable medium such as C, C ++, JAVA, machine language, and the like.

The code may include a function code related to a function or the like that defines the functions described above and may include an execution procedure related control code necessary for the processor of the computer to execute the functions described above according to a predetermined procedure. In addition, such code may further include memory reference related code as to what additional information or media needed to cause the processor of the computer to execute the aforementioned functions should be referenced at any location (address) of the internal or external memory of the computer . In addition, when a processor of a computer needs to communicate with any other computer or server that is remote to execute the above-described functions, the code may be stored in a memory of the computer using a communication module of the computer, It may further include a communication-related code such as how to communicate with another computer or a server, and what information or media should be transmitted or received during communication.

Such computer-readable media suitable for storing computer program instructions and data include, for example, magnetic media such as hard disks, floppy disks and magnetic tape, compact disk read only memory (CD-ROM) Optical media such as a DVD (Digital Video Disk), a magneto-optical medium such as a floppy disk, and a ROM (Read Only Memory), a RAM , Random Access Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (Electrically Erasable Programmable ROM). The processor and memory may be supplemented by, or incorporated in, special purpose logic circuits.

The computer readable recording medium may also be distributed over a networked computer system so that computer readable code can be stored and executed in a distributed manner. The functional program for implementing the present invention and the related code and code segment may be implemented by programmers in the technical field of the present invention in consideration of the system environment of the computer that reads the recording medium and executes the program, Or may be easily modified or modified by the user.

While the specification contains a number of specific implementation details, it should be understood that they are not to be construed as limitations on the scope of any invention or claim, but rather on the description of features that may be specific to a particular embodiment of a particular invention Should be understood. Certain features described herein in the context of separate embodiments may be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments, either individually or in any suitable subcombination. Further, although the features may operate in a particular combination and may be initially described as so claimed, one or more features from the claimed combination may in some cases be excluded from the combination, Or a variant of a subcombination.

Likewise, although the operations are depicted in the drawings in a particular order, it should be understood that such operations must be performed in that particular order or sequential order shown to achieve the desired result, or that all illustrated operations should be performed. In certain cases, multitasking and parallel processing may be advantageous. Also, the separation of the various system components of the above-described embodiments should not be understood as requiring such separation in all embodiments, and the described program components and systems will generally be integrated together into a single software product or packaged into multiple software products It should be understood.

The present invention relates to a method of adjusting a contrast ratio of a thermal image and a thermal image processing apparatus using the same, and more particularly, to a method of adjusting a contrast ratio of a thermal image by using a mean minimum value and an average maximum value of input image frames continuously for a predetermined interval, And adjusting the contrast ratio of the input image frame during the next predetermined period using the updated image contrast ratio and the thermal image processing apparatus using the method.

According to the present invention, by adjusting the contrast ratio using the histogram average minimum value and the average maximum value of the updated image, before the non-uniformity correction is performed on the image frame to be input in the next predetermined section, even if the user has a hot or cold object It is possible to output a better thermal image because the change in brightness of the image is not greatly felt. The method of adjusting the contrast ratio of the thermal image according to the present invention and the thermal image processing apparatus using the same can be applied to various fields such as industrial, military / security, and the like. In addition, It can be used industrially.

10: ADC processing unit 20: pixel correction processing unit
30: non-uniformity correction unit 40: histogram processing unit
50; Contrast ratio processor

Claims (8)

An average minimum value and an average maximum value of the input image frames are calculated based on the histogram minimum value and the maximum value of each of the image frames continuously input for a predetermined period, A histogram processing unit for updating the maximum value to a histogram average minimum value and an average maximum value of the image; And
A contrast ratio processor for adjusting a contrast ratio of an image frame input during a next predetermined period using the histogram average minimum value and the average maximum value of the image updated through the histogram processing unit;
And an image processing unit for processing the image data. The method according to claim 1,
A non-uniform correction unit that performs non uniformity correction on image frames continuously input for a predetermined period;
Further comprising a processor for processing the thermal image. 3. The method of claim 2,
The histogram processing unit
And updates the histogram average minimum value and the average maximum value of the image during the non-uniformity correction of the input image frame during the next predetermined period through the non-uniformity correction unit. 3. The method of claim 2,
The histogram processing unit
Calculates a minimum value and a maximum value of each histogram of the image frame for the predetermined period in which the non-uniformity is corrected through the non-uniformity correction unit, and calculates an average minimum value and an average maximum value of the input image frames during the predetermined period on the basis thereof And the thermal image processing apparatus. Calculating a histogram minimum value and a maximum value of each of the image frames input continuously for a predetermined period;
Calculating an average minimum value and an average maximum value of the input image frames during the predetermined period based on the histogram minimum value and the maximum value of each of the image frames;
Updating an average minimum value and an average maximum value of the calculated image frames to a histogram average minimum value and an average maximum value of the image; And
Adjusting a contrast ratio of the input image frame for a next predetermined period using the histogram average minimum value and the average maximum value of the updated image;
And adjusting the contrast ratio of the thermal image. 6. The method of claim 5,
Updating the histogram average minimum value and the average maximum value of the image
Wherein the non-uniformity correction process is performed while the non-uniformity correction process is performed on the image frame. 6. The method of claim 5,
Before the step of calculating the histogram minimum value and the maximum value,
When the histogram average minimum value and the average maximum value of the image exist,
Adjusting a contrast ratio of an image frame continuously input for the predetermined period using an average minimum value and an average maximum value of the histogram of the image;
And adjusting the contrast ratio of the thermal image. A computer readable recording medium recording a program for executing the method of adjusting the contrast of a thermal image according to any one of claims 5 to 7.

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