WO2022104816A1 - Temperature compensation method and system for thermal camera - Google Patents

Abstract

Disclosed in the present invention are a temperature compensation method and system for a thermal camera, belonging to the technical field of thermal cameras. Aiming at the problems of low precision and low measurement accuracy of thermal cameras in the prior art, the present invention provides a temperature compensation method and system for a thermal camera. A temperature sensor is connected in front of the thermal camera and combined with a black body. The effects caused by factors such as drift of the camera itself, non-uniformity of the thermal camera, refractive index of the temperature sensor, ambient temperature and measurement distance are calibrated by calculating a function of the temperature measured by the thermal camera, the actual temperature of the temperature sensor, the temperature of the block body, the ambient temperature and the distance of a measured entity. The present invention realizes temperature compensation for a thermal camera with low cost and high precision, and the corresponding calibration is real-time. After the thermal camera leaves the factory, the thermal camera only needs to be calibrated once and can be used all the time. The black body does not need to be equipped during measurement, so high measurement precision and good reliability can be obtained with low cost.

Description

A kind of thermal camera temperature compensation method and system technical field

The present invention relates to the technical field of thermal cameras, and more particularly, to a temperature compensation method and system for thermal cameras.

Background technique

Thermal cameras are also known as infrared cameras. Any object can radiate infrared rays as long as the temperature is higher than thermodynamic zero, and the infrared rays radiated by different temperatures are also different. Thermal cameras detect the health of the body through temperature based on this principle. Thermal cameras have relatively high requirements for operating temperature. Since thermal cameras can only achieve an accuracy of about ±2 degrees Celsius or even ±5 degrees Celsius, and the ambient temperature and the distance between the face and the camera will affect the final reading, so The error is extremely large.

Conventional thermal cameras all provide an automatic calibration mechanism (shutter), which can be set at intervals, such as automatic calibration once after 1 to 5 minutes. However, the measurement error generated within the interval set by the automatic calibration mechanism cannot be calibrated in real time in time, and the measurement accuracy requirements cannot be met during measurement.

In the prior art, a black body with a known temperature is placed in the measurement area, the temperature of the black body is read by a thermal camera, and the temperature of the entire measurement screen is calibrated by comparing it with the actual temperature of the black body. This method requires the use of black body coordination during measurement. Since the unit price of the black body is between several hundred and several thousand dollars, the price is relatively high, and the relative position of the camera and the black body must be fixed using the traditional measurement method. If there is a position offset, it cannot be calibrated. . Moreover, the working environment of the black body has certain requirements, and the traditional measurement method also has high requirements on the ambient temperature.

SUMMARY OF THE INVENTION

1. Technical problems to be solved

Aiming at the problems of low precision and low measurement accuracy of thermal cameras in the prior art, the present invention provides a temperature compensation method and system for thermal cameras. Calibration to improve measurement accuracy.

2. Technical solutions

The object of the present invention is achieved through the following technical solutions.

A temperature compensation method for a thermal camera, the thermal camera is connected with a temperature sensor coated with black body paint, the temperature sensor is arranged in front of the thermal camera, and a function is fitted according to the temperature of the temperature sensor measured by the thermal camera and the actual temperature of the temperature sensor The offset of the thermal camera is calibrated; the black body is set in front of the thermal camera, and the fitting function is based on the temperature measured by the thermal camera and the black body temperature. The resulting thermal camera measurement errors are calibrated. By setting the temperature sensor and the black body in front of the thermal camera, the invention calibrates the influence of multiple factors on the measurement data of the thermal camera, so as to obtain high-precision measurement results and improve the measurement accuracy.

Further, include the following steps:

Step 1: The thermal camera is connected with the temperature sensor coated with black body paint. The temperature sensor is set in front of the thermal camera. According to the thermal camera's multiple measured temperatures Tx _1i of the temperature sensor at different temperatures, and the thermal camera measures the temperature corresponds to the actual temperature of the temperature sensor Ty _1i , the function f1 between the temperature measured by the thermal camera and the actual temperature of the temperature sensor is obtained by linear fitting, i is a natural number greater than 1, and the expression of the function f1 is Ty _1i =n ₁ *Tx _1i , n ₁ is the thermal camera drift compensation coefficient, the drift of the thermal camera itself is calibrated by the function f1, resulting in errors;

Step 2: Set a black body with uniform heat in front of the thermal camera, the black body covers the entire screen, set different black body temperatures, save the data image corresponding to the thermal camera, and obtain the measured temperature and The function f2 between the black body temperatures, through which the camera inhomogeneity is calibrated by the function f2 causes errors;

Step 3: Set different temperatures Ty _3i on the black body reflective surface, and read the temperature Tx _3i0 of the black body reflective surface measured by the thermal camera. The measured temperature Tx _{3i0 is} first calibrated by the function f1 and the function f2 to obtain the calibrated temperature Tx _3i , and the thermosensitive temperature is obtained. The function f3 between the camera temperature Tx _3i and the black body reflective surface temperature Ty _3i , the formula of the function f3 is Ty _3i =n ₃ *Tx _3i , n ₃ is the compensation coefficient of the temperature sensor reflectivity, and the function f3 is used to calibrate the reflectivity of the temperature sensor cause errors;

Step 4: Set different ambient temperatures Ty _4i , read the temperature measured by the thermal camera Tx _4i calibrated by the function f3 in the different ambient temperatures Ty _4i , and obtain the measurement of the thermal camera through the difference between the ambient temperature and the temperature measured by the thermal camera The ambient temperature calibration coefficient n ₄ between the temperature Tx _4i and the ambient temperature Ty _4i obtains the function f4, that is, Ty _4i =Tx _4i *n ₄ , and the error caused by the ambient temperature is calibrated by the function f4;

Step 5: Read the temperature Ty _5i of the black body at different distances from the thermal camera, and obtain the function f5 between the measured temperature Tx _5i of the thermal camera and the measured distance after calibration by the function f4. The function f5 is a polynomial formula, and the specific calculation formula is Ty _5i =n ₅₁ *Tx _5i ^m-1 +n ₅₂ *Tx _5i ^m-2 +...+n _5(m-1) *Tx _5i ¹ +n _5m , distance coefficient n ₅ =[n ₅₁ ,n ₅₂ ,... , n _5(m-1) , n _5m ], where m is an integer greater than 1, and the error caused by the measurement distance is calibrated by the function f5.

Further, the thermal camera in step 1 is connected with the temperature sensor through a bus, and the thermal camera obtains the actual temperature of the temperature sensor through the bus. The temperature sensor and the thermal camera of the present invention are connected by a bus, and the thermal camera can directly read the temperature of the temperature sensor through the I2C bus.

Further, in step 2, first set the black body temperature T, collect several pictures, take the average temperature of each pixel in the picture, set the black body temperature repeatedly, save the image data of the black body reflection surface at different temperatures, and go through the function f2. Linear correction is used to obtain the temperature after calibration of each coordinate point of the thermal camera. When performing temperature non-uniformity calibration, first obtain multiple pictures at the same set temperature, average the temperatures of the multiple pictures, and save them as thermal data images for the calculation of camera non-uniformity compensation.

Further, set the black body temperature as T ₁ to save the thermal data image Img T ₁ , set the black body temperature T ₂ , save the thermal data image Img T ₂ , and calculate the position of each pixel in the image as (x, y), Slope gain and offset offset, the formula is as follows:

offset[x,y]＝T ₁ -gain[x,y]*ImgT ₁ [x,y] (2)

In the above formula, Img T1[x, y] represents the temperature of the pixel of the data image Img T1 at the (x, y) coordinate point, and Img T2[x, y] represents the temperature of the pixel of the data image Img T2 at the (x, y) coordinate point. Temperature, build function f2 by slope gain and offset offset, ie T[x,y]=gain[x,y]*Img[x,y]+offset[x,y], where Img[x,y] is The temperature of the (x,y) pixel point measured by the thermal camera, T[x,y] is the temperature after the unevenness calibration, and the unevenness of the camera is calibrated by the function f2, resulting in errors. The thermal camera simultaneously obtains the temperature of all areas of the captured image during measurement, that is, the temperature of each pixel in the image whose position coordinates are (x, y). The non-uniformity generated by the sensitive camera at different positions of the picture is linearly corrected. During linear correction, the slope gain and offset offset are calculated for the position coordinates (x, y) of each pixel in the image, and the temperature after calibration of each coordinate point is obtained.

Further, in step 3, first set the temperature of the black body reflective surface, after the temperature is stable, measure the temperature of the black body reflective surface several times and then take the average value, the average value is the temperature measured by the thermal camera; Compute module read. The computing module of the present invention uses the embedded minicomputer TX2 box of NVIDIA, and its serial port is an ordinary USB interface. After connecting with the black body, click the center of the black body, select the black body temperature scanning range, and scan from the low temperature range to the high temperature range.

Further, the temperatures are respectively set in a low temperature range and a high temperature range, the low temperature range is 26 to 30°C, and the high temperature range is 40 to 42°C. In order to ensure the accuracy of the measurement, different temperature ranges need to be set when setting the black body temperature, which is divided into a high temperature range and a low temperature range in the present invention.

Furthermore, the distance between the black body and the thermal camera is smaller than a fixed value. In order to ensure the accuracy of the measurement, during the temperature compensation of the present invention, the distance between the black body and the thermal camera is set to be less than 10cm, and if the distance is too large, the accuracy of the thermal camera calibration is easily reduced.

The present invention performs temperature compensation through a high-precision temperature sensor. Since the temperature sensor can read the temperature of the environment in real time, the thermal camera can be calibrated in real time. According to the statistical comparison of the limited number of experimental data, the absolute value of the actual temperature difference between the thermal camera and the black body after the temperature compensation of the present invention is 0.133°C, the average value of the error is 0.0026, the standard deviation (std) of the error is 0.1718, and the error The proportion of pixels whose absolute value is less than 0.3 degrees Celsius is about 92%, and the proportion of pixels whose absolute value is less than 0.5 degrees Celsius can reach 99.44%, and the accuracy and precision are greatly improved.

A thermal camera temperature compensation system, using the thermal camera temperature compensation method to calibrate the thermal camera, the system includes a temperature sensor connected with the thermal camera, and also includes a black body. Through the temperature sensor and the black body, the thermal camera is calibrated using the thermal camera calibration method. After the thermal camera leaves the factory, this system is used for calibration. After the calibration is completed, the high-precision temperature sensor connected to the thermal camera can be used. The measurement value of the thermal camera is calibrated in real time to improve the measurement accuracy.

Further, the temperature sensor is coated with black body paint. Taking into account the cost issue, a temperature sensor coated with black body paint is used to replace the black body, and it is connected with a thermal camera to achieve real-time temperature calibration. The temperature sensor has an accuracy of ±0.1°C in the range of -20°C to 50°C. In order to improve the accuracy and precision of temperature measurement by thermal cameras, a high-precision temperature sensor is used for temperature compensation, which can provide 16-bit temperature results with a resolution of 0.0078°C, at -20°C to 50°C The accuracy within the range is ±0.1°C.

The invention realizes the temperature compensation of the thermal camera with low cost and high precision, and the corresponding calibration is real-time. After the thermal camera leaves the factory, since the camera itself is connected to the temperature sensor, real-time calibration can be realized through the temperature sensor, and only one calibration is required. It can be used all the time with higher accuracy (±0.3 degrees Celsius). The temperature compensation method of the invention has higher accuracy and precision for the calibration of the thermal camera than the prior art, has high reliability, and is suitable for wide application.

3. Beneficial effects

Compared with the prior art, the advantages of the present invention are:

The temperature compensation method of the present invention achieves higher precision. The temperature read by a thermal camera in the prior art fluctuates around 2-5 degrees Celsius. According to the limited number of experimental data, on the data set collected by the calibrated thermal camera of the present invention from 0.5 meters to 5 meters, the absolute value of the difference between the temperature of a single point read and the actual temperature of the black body is 0.133 degrees Celsius, and the error is 0.133 degrees Celsius. The average value is 0.0026, the standard deviation (std) of the error is 0.1718, the proportion of pixels with an absolute value of error less than 0.3 degrees Celsius is about 92%, and the proportion of pixels with an absolute value of error less than 0.5 degrees Celsius can reach 99.44%. Its measurement accuracy and accuracy degree increased significantly.

The temperature compensation method of the invention realizes real-time calibration. In order to improve the accuracy, a high-precision temperature sensor is used in front of the thermal camera. The high-precision temperature sensor reads the temperature of the environment in real time, and the thermal camera reads the temperature of the high-precision temperature sensor in real time. Through the comparison of the corresponding values of the high-precision temperature sensor and the thermal camera, the measured temperature is calibrated in real time, combined with the calibration of the inhomogeneity of the thermal camera through the black body, and the fitting between the ambient temperature and the distance of the measured entity obtained through the black body. The curve has lower requirements on the ambient temperature and humidity during measurement, and is suitable for various measurement environments.

The implementation of the present invention requires lower cost, and does not need to be equipped with high-cost equipment such as a black body during measurement, and the black body only needs to be used during calibration after leaving the factory. The thermal camera also only needs to be calibrated once after leaving the factory, and then it can be used all the time, and the cost of after-sales maintenance is lower. It can be solved by setting parameters.

Description of drawings

1 is a comparison diagram of a temperature curve after calibration of the thermal camera of the present invention and an actual temperature value;

Fig. 2 is the connection schematic diagram of the temperature sensor and the thermal camera of the present invention;

3 is a schematic diagram of the connection position of the black body and the thermal camera during the non-uniformity calibration of the present invention;

The drawings are marked as follows: 1. High-precision temperature sensor; 2. Thermal camera; 3. Black body reflective surface.

Detailed ways

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

Example

When the traditional thermal camera 2 measures the temperature of a face, due to the influence of temperature or different measurement environments, errors are prone to occur, which affects the temperature measurement accuracy. Improve the accuracy of temperature measurement.

The accuracy of the thermal camera is determined by factors such as temperature drift, temperature non-uniformity (Non Uniformity), temperature sensor offset, ambient temperature and test distance of the thermal camera 2 itself. The thermal camera calibration system of this embodiment includes a thermal camera 2 and a black body. The thermal camera 2 is connected to a high-precision temperature sensor 1, and the temperature sensor is a temperature sensing chip. The high-precision temperature sensing chip used in this embodiment provides 16-bit temperature results and can reach a resolution of 0.0078°C. The high-precision temperature sensor 1 can achieve up to ±0.1°C in the range of -20°C to 50°C without calibration. accuracy.

The temperature compensation method of the thermal camera 2 in this embodiment will be described below through specific calibration steps.

Step 1. Calibrate the drift of the thermal camera 2 itself:

The thermal camera 2 is connected with a temperature sensor, the temperature sensor is arranged in front of the thermal camera 2, the temperature sensor is coated with black body paint, and the thermal camera 2 uses the temperature sensor to calibrate the drift of the camera itself.

The drift of the thermal camera 2 itself is between ±2 degrees Celsius to ±5 degrees Celsius. Since the drift of the camera itself is the drift of the entire image, there will be no error in the measurement temperature of a certain part or point in the image, but the measurement in other places is normal. Therefore, if the exact temperature of a part of the image is known, the temperature of the entire screen can be compensated.

Using the thermal cameras 2 to perform multiple measurements on a certain part or a point of the temperature sensor at different times and at different temperatures, the i thermal cameras 2 measure temperatures Tx _1i , where i is a natural number greater than 1. The actual temperature Ty _1i corresponding to the temperature sensor when the temperature measured by the thermal camera 2 is obtained through the bus. For discrete data Tx _1i and Ty _1i , use linear fitting to obtain the function f1 between the temperature measured by the thermal camera and the actual temperature of the temperature sensor. The expression of f1 is Ty _1i =n ₁ *Tx _1i , where n ₁ is the thermal The camera drift compensation coefficient, using the function f1 to calibrate the camera itself drifts to cause errors.

In the prior art, the thermal camera 2 is calibrated by additionally setting a black body, which is expensive and requires high ambient temperature. In this embodiment, the issue of economy is considered comprehensively. As shown in FIG. 2, the thermal camera 2 is connected to the high-precision temperature sensor 1, and the temperature sensor is coated with high-reflection black body paint. Through various calibration algorithm experiments, the black body is coated. The temperature sensor of lacquer is equivalent to a black body, which can achieve a similar effect to the black body, and greatly reduce the cost while ensuring the accuracy.

The high reflectivity black body paint is oily 95 black body paint with a reflectivity of 0.95±0.02. The thermal camera 2 reads the temperature of the high-precision temperature sensor 1 through the I2C bus, and the thermal camera 2 also measures the temperature sensor. According to the actual temperature of the temperature sensor and the temperature measured by the thermal camera, the parameter n ₁ of the function f1 after linear fitting is updated in real time, and the measured temperature of the thermal camera 2 is calibrated in real time through this parameter n ₁ , as shown in Figure 2, the high The precision temperature sensor 1 is located at the upper left of the thermal camera 2, about 20cm away from the thermal camera 2. The temperature sensor does not need to maintain a fixed position with the thermal camera 2 during use, even if the temperature sensor position shifts during use, as long as Correcting the reference area of the temperature sensor for the thermal camera 2 will not affect the temperature measurement and data acquisition.

Step 2. Calibrate the thermal camera inhomogeneity:

The thermal camera 2 is composed of a thermal imaging dot matrix, and the values obtained by objects of the same temperature at different screen positions will be inconsistent. The non-uniformity of the thermal camera 2 refers to the inconsistency of values obtained by objects of the same temperature at different screen positions. In step 2, a thermally uniform black body is set at a fixed position in front of the thermal camera 2, as shown in FIG. Set different black body temperatures, save the data image corresponding to the thermal camera 2, and obtain the function f2 between the temperature measured by the thermal camera 2 and the black body temperature for the coordinates (x, y) of each pixel at the position of the data image, through the function The f2 calibration camera non-uniformity causes errors.

As shown in Figure 3, the distance D between the black body reflective surface 3 and the thermal camera 2 is about 10cm during calibration, and the temperature fluctuation of the entire black body image is within 0.3°C. The data image Img T1; when the black body temperature is set to T2, a data image Img T2 of the thermal camera 2 is saved.

First set the temperature T1 in the low temperature interval, the temperature range of the low temperature interval is 26 to 30 °C, wait for the temperature to stabilize, that is, when the temperature fluctuation of the reflective surface of the black body is less than 0.3 °C, collect several pictures, and take the temperature average for all pixels in the image. Value obtained data image Img T1. Then set the black body temperature to the high temperature interval temperature T2, the high temperature interval temperature range is 40 to 42 ℃, wait for the temperature to stabilize, that is, when the temperature fluctuation of the black body's reflective surface is less than 0.3 ℃, collect several pictures, for all pixels in the image The temperature average was obtained for the data image Img T2. By measuring the average value of the image data twice, the slope gain and offset offset of the temperature non-uniformity compensation function of the thermal camera are calculated to obtain the compensated temperature. The calculation formulas of gain and offset are as follows:

offset[x,y]＝T ₁ -gain[x,y]*ImgT ₁ [x,y] (2)

In the above formula, Img T ₁ [x, y] represents the temperature of the data image Img T1 at the (x, y) coordinate point, and Img T ₂ [x, y] represents the data image Img T2 at the (x, y) coordinate point The temperature of the pixel, gain[x, y] represents the slope gain of the (x, y) coordinate point pixel, and offset[x, y] represents the offset offset of the (x, y) coordinate point pixel. The function f2 is constructed by gain and offset, that is, T[x,y]=gain[x,y]*Img[x,y]+offset[x,y], where Img[x,y] is measured by thermal camera 2 The temperature of the (x,y) pixel point, T[x,y] is the temperature after non-uniformity calibration. Use the function f2 to linearly correct the original measured temperature, so as to obtain the temperature after calibration of each coordinate point, that is, to obtain the measured value of the thermal camera after the inhomogeneity calibration.

Step 3. Calibration for the reflectivity of the temperature sensor:

Steps 1 and 2 calibrate the temperature of the thermal camera itself. Step 1 calibrates by reading the temperature at the position of the high-precision temperature sensor 1 in the image and calculating the difference with the actual temperature of the high-precision temperature sensor 1 . In step 2, the non-uniformity calibration has not taken into account the different reflectivity of the temperature sensor and the reflectivity of the black body, and the temperature sensor is very important in the thermal imaging system of the thermal camera 2. Since the high-precision temperature sensor 1 still has certain errors, After the camera drift calibration in step 1 and the non-uniformity calibration in step 2, the blackbody temperature sweep calibration is used in step 3 to further calibrate the reflectivity of the temperature sensor.

The black body temperature scanning calibration process is simply to fit the relationship between the temperature of a certain point read by the thermal camera 2 after the first two steps of calibration and the actual temperature of the point. The actual temperature of the point is obtained by reading the black body temperature. get. Since the temperature has fluctuation and is an interval, the relationship between the temperature of a certain point read by the thermal camera 2 after calibration and the actual temperature of the black body is calculated by dynamically setting the temperature of the black body.

When calibrating, put the black body in front of the thermal camera 2, and connect the black body to the serial port of the TX2 box. The TX2 box is an embedded small computer of NVIDIA, and its serial port is an ordinary USB interface. After the two are connected, the TX2 box can read the black body. temperature. The temperature of the black body reflective surface 3 is set, and the black body reflective surface 3 is the plane of the temperature read by the thermal camera 2 . After connecting directly to the TX2 box, click the center of the black body with the mouse, and select the black body temperature scanning range. The scanning range starts from the temperature in the low temperature range to the temperature in the high temperature range. The interval temperature is generally 40 to 42°C.

After each temperature measurement point is stable, the thermal camera 2 reads the temperature of the selected area, selects the temperature read from multiple pictures, and takes the average temperature, which is the final reading of the thermal camera 2 . At this time, the independent variable of the function f3 is the reading of the thermal camera 2 after uniformity calibration and high-precision sensor calibration; the strain variable of the function f3 is the temperature of the black body, which is our target temperature. Fit the temperature measured by the independent variable thermal camera and the actual temperature of the strain variable black body to obtain the function f3.

Specifically, set a black body in front of the thermal camera 2, set different temperatures Ty _3i on the black body reflective surface 3, and read the temperature Tx _3i0 of the black body reflective surface 3 measured by the thermal camera 2. The measured temperature Tx _3i0 first passes through the function f1 and the function The calibrated temperature Tx _3i is obtained by f2 calibration, and the function f3 between the temperature Tx _3i measured by the thermal camera 2 and the temperature Ty _3i of the black body reflective surface 3 is obtained. The formula of the function f3 is Ty _3i =n ₃ *Tx _3i , where n ₃ is Temperature sensor reflectivity compensation coefficient. Tx _3i is the temperature measured by the thermal camera 2 Tx _3i0 is calibrated according to the function f2 and then according to the measured temperature of the function f1, the expression formula is Tx _3i = (gain×Tx _3i0 +offset)*n ₁ , the function f3 is used to calibrate Camera 2 causes errors due to the reflectivity of the temperature sensor.

The thermal camera 2 is not connected to the black body in actual use, and the use of the black body here is only for calculating the fitting function f3. The user reads the temperature after calibrating the drift and non-uniformity of the camera itself, and further corrects it through the linear transformation function f3 calibrated by the temperature sensor, so that the temperature read by the thermal camera 2 is more accurate.

Step 4. Calibration for ambient temperature:

Different ambient temperatures will affect the measurement of the thermal camera 2. Since thermal radiation will reach the lens to heat the lens, and the camera itself will also heat up, it is easy to cause the lens to radiate heat to the thermal imaging chip, thereby affecting the temperature in degrees. Although the thermal camera 2 itself also has an ambient temperature calibration, after actual measurement, the ambient temperature calibration standard of the thermal camera 2 itself is relatively low. Moreover, the thermal imaging system in this embodiment needs to read a high-precision temperature sensor to calibrate the camera drift, so that the system needs to perform more accurate ambient temperature calibration.

For ambient temperature calibration, set different ambient temperatures, such as ambient temperature T3 and T4, read the readings V1 and V2 after calibration in step 3, draw the correlation curve between the readings V1 and V2 and the ambient temperatures T3 and T4, and calculate Linear ambient temperature calibration coefficient n ₄ , n ₄ =(V2-V1)/(T3-T4).

The ambient temperature calibration process requires a temperature-controlled, or slowly rising or falling temperature test environment. When calibrating, first place the black body in front of the thermal camera 2 and set the temperature of the black body. Then run the software, set the relevant parameters, click the center of the black body with the mouse and collect data. At this time, the independent variable in the function f4 is the ambient temperature, and the dependent variable is the temperature of the black body read. Observe the influence of the ambient temperature on the final reading, fit and calculate the functional relationship between the two, and obtain the function f4 between the temperature measured by the thermal camera 2 and the ambient temperature, that is, Ty _4i =Tx _4i *n ₄ , Tx _4i is the current difference In the ambient temperature, the thermal camera 2 measures the temperature after calibration in step 3, and Ty _4i represents the temperature compensation number after the ambient temperature calibration, and the ambient temperature of the thermal camera 2 is compensated by the function f4.

Step 5. Calibration for test distance:

The thermal camera 2 measures temperature by reading energy at far infrared wavelengths. In the process of transmission, the energy of infrared light will be absorbed by the air and attenuated, so the farther the distance is, the lower the measured temperature. The temperature of the same black body is measured at different distances, the distance coefficient is calculated according to the temperature range of the object, the compensation _formula function f5 is determined by the distance coefficient n5, and the test distance of the thermal camera 2 is calibrated.

The calibration process for the test distance is as follows, first place the black body in front of the thermal camera 2, and set the temperature of the black body. Then by moving the distance of the black body, read the temperature of the black body at the corresponding distance. At this time, the independent variable in the function f5 is the distance between the black body and the camera, and the dependent variable is the temperature of the black body read by the camera. By fitting the data, the relationship between the independent variable and the dependent variable, that is, the function f5, is obtained. The function f5 is a polynomial formula, and the specific calculation formula is Ty _5i =n ₅₁ *Tx _5i ^m-1 +n ₅₂ *Tx _5i ^m-2 +...+n _5(m-1) *Tx _5i ¹ +n _5m , the distance coefficient n ₅ =[n ₅₁ ,n ₅₂ ,...,n _5(m-1) ,n _5m ], where m is an integer greater than 1, Tx _5i is the measured temperature calibrated by the thermal camera 2 in step 4, and Ty _5i Indicates the temperature compensation value after distance calibration. When the distance between the object and the camera is known, the temperature after calibration can be obtained through the distance compensation coefficient n ₅ and the polynomial order m. In this embodiment, the polynomial order m=7.

The temperature fluctuation read by the thermal camera 2 in the prior art is about 2-5 degrees Celsius. According to the limited number of experimental data, the absolute value of the difference between the temperature of a single point read and the actual temperature of the black body is 0.133 degrees Celsius on the data set collected by the thermal camera 2 calibrated in the present invention from 0.5 meters to 5 meters. , the average value of the error is 0.0026, the standard deviation (std) of the error is 0.1718, the proportion of pixels with an absolute value of error less than 0.3 degrees Celsius is about 92%, and the proportion of pixels with an absolute value of error less than 0.5 degrees Celsius can reach 99.44%. Accuracy is greatly improved.

Figure 1 shows a comparison between the temperature curve of the thermal camera 2 after calibration and the actual temperature of the black body in this embodiment. The test data of the thermal camera 2 on the black body after calibration is represented by a dotted line, and the actual temperature of the black body is represented by a solid line. It can be seen from Figure 1 that the dotted line and the solid line almost overlap, that is, the temperature curve tested by the thermal camera after calibration and the actual temperature curve of the black body almost overlap, indicating that the calibrated thermal camera 2 has high measurement accuracy and high precision. In practical applications, the thermal camera 2 does not need to be equipped with a black body, and can achieve high-precision temperature measurement only through the temperature sensor connected to itself, and the cost is reduced under the condition of ensuring the accuracy.

The invention and its embodiments have been described above schematically, and the description is not restrictive. The invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. What is shown in the accompanying drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto, and any reference signs in the claims shall not limit the related claims. Therefore, if those of ordinary skill in the art are inspired by it, and without departing from the purpose of the present invention, any structure and embodiment similar to this technical solution are designed without creativity, which shall belong to the protection scope of this patent. Furthermore, the word "comprising" does not exclude other elements or steps, and the word "a" preceding an element does not exclude the inclusion of "a plurality" of that element. Several elements recited in a product claim can also be implemented by one element by means of software or hardware. The terms first, second, etc. are used to denote names and do not denote any particular order.

Claims (10)

1. A temperature compensation method for a thermal camera, characterized in that the thermal camera is connected with a temperature sensor coated with black body paint, the temperature sensor is arranged in front of the thermal camera, and the temperature of the thermal camera is measured according to the temperature of the thermal sensor and the actual The temperature fitting function calibrates the offset of the thermal camera; the black body is set in front of the thermal camera, and the fitting function is based on the temperature measured by the thermal camera and the black body temperature. Thermal camera measurement errors due to temperature and measurement distance are calibrated.
2. A thermal camera temperature compensation method according to claim 1, characterized in that, comprising the following steps:

   Step 1: The thermal camera is connected with the temperature sensor coated with black body paint. The temperature sensor is set in front of the thermal camera. According to the thermal camera's multiple measured temperatures Tx _1i of the temperature sensor at different temperatures, and the thermal camera measures the temperature corresponds to the actual temperature of the temperature sensor Ty _1i , the function f1 between the temperature measured by the thermal camera and the actual temperature of the temperature sensor is obtained by linear fitting, i is a natural number greater than 1, and the expression of the function f1 is Ty _1i =n ₁ *Tx _1i , n ₁ is the drift compensation coefficient of the thermal camera, and the drift of the thermal camera itself is calibrated by the function f1 to cause errors;

   Step 2: Set a black body with uniform heat in front of the thermal camera, the black body covers the entire screen, set different black body temperatures, save the data image corresponding to the thermal camera, and obtain the measured temperature and The function f2 between the black body temperatures, through which the camera inhomogeneity is calibrated by the function f2 causes errors;

   Step 3: Set different temperatures Ty _3i on the black body reflective surface, and read the temperature Tx _3i0 of the black body reflective surface measured by the thermal camera. The measured temperature Tx _{3i0 is} first calibrated by the function f1 and the function f2 to obtain the calibrated temperature Tx _3i , and the thermosensitive temperature is obtained. The function f3 between the camera temperature Tx _3i and the black body reflective surface temperature Ty _3i , the formula of the function f3 is Ty _3i =n ₃ *Tx _3i , n ₃ is the compensation coefficient of the temperature sensor reflectivity, and the function f3 is used to calibrate the reflectivity of the temperature sensor cause errors;

   Step 4: Set different ambient temperatures Ty _4i , read the temperature measured by the thermal camera Tx _4i calibrated by the function f3 in the different ambient temperatures Ty _4i , and obtain the measurement of the thermal camera through the difference between the ambient temperature and the temperature measured by the thermal camera The ambient temperature calibration coefficient n ₄ between the temperature Tx _4i and the ambient temperature Ty _4i obtains the function f4, that is, Ty _4i =Tx _4i *n ₄ , and the error caused by the ambient temperature is calibrated by the function f4;

   Step 5: Read the temperature Ty _5i of the black body at different distances from the thermal camera, and obtain the function f5 between the measured temperature Tx _5i of the thermal camera and the measured distance after calibration by the function f4. The function f5 is a polynomial formula, and the specific calculation formula is Ty _5i =n ₅₁ *Tx _5i ^m-1 +n ₅₂ *Tx _5i ^m-2 +...+n _5(m-1) *Tx _5i ¹ +n _5m , distance coefficient n ₅ =[n ₅₁ ,n ₅₂ ,... , n _5(m-1) , n _5m ], where m is an integer greater than 1, and the error caused by the measurement distance is calibrated by the function f5.
3. A temperature compensation method for a thermal camera according to claim 2, wherein the thermal camera and the temperature sensor in step 1 are connected through a bus, and the thermal camera obtains the actual temperature of the temperature sensor through the bus.
4. A temperature compensation method for a thermal camera according to claim 2, characterized in that, in step 2, the black body temperature T is set first, a number of pictures are collected, the temperature average value is obtained for each pixel in the picture, and the setting is repeated for many times. Black body temperature, save the image data of the black body reflection surface at different temperatures, and obtain the temperature after calibration of each coordinate point of the thermal camera through the linear correction of the function f2.
5. The temperature compensation method for a thermal camera according to claim 4, wherein the black body temperature is set to T ₁ to save the thermal data image Img T ₁ , the black body temperature T ₂ is set to save the thermal data image Img T ₂ , For each pixel at the position of (x, y) in the image, calculate the slope gain and offset offset, the formula is as follows:

   

   offset[x,y]＝T ₁ -gain[x,y]*ImgT ₁ [x,y] (2)

   In the above formula, Img T ₁ [x, y] represents the temperature of the data image Img T1 at the (x, y) coordinate point, and Img T ₂ [x, y] represents the data image Img T2 at the (x, y) coordinate point The temperature of the pixel, the function f2 is constructed by the slope gain and the offset offset, that is, T[x,y]=gain[x,y]*Img[x,y]+offset[x,y], where Img[x,y ] is the temperature of the (x, y) pixel measured by the thermal camera, T[x, y] is the temperature after non-uniformity calibration, and the non-uniformity of the camera is calibrated by the function f2, resulting in errors.
6. The temperature compensation method for a thermal camera according to claim 2, wherein in step 3, the temperature of the black body reflective surface is set first, and after the temperature is stable, the temperature of the black body reflective surface is measured for several times and an average value is obtained, and the average value is The thermal camera measures the temperature; the actual temperature of the black body reflective surface is read by the calculation module connected with the black body.
7. A temperature compensation method for a thermal camera according to claim 3, 4 or 6, wherein the temperature is set in a low temperature interval and a high temperature interval, wherein the low temperature interval is 26 to 30°C, and the high temperature interval is 26°C to 30°C. The temperature range is 40 to 42°C.
8. A temperature compensation method for a thermal camera according to claim 1, wherein the distance between the black body and the thermal camera is less than a fixed value.
9. A thermal camera temperature compensation system, characterized in that a thermal camera temperature compensation method according to any one of claims 1-8 is used to calibrate the thermal camera, and the system includes connecting with the thermal camera The temperature sensor also includes the black body.
10. A temperature compensation system for a thermal camera according to claim 9, wherein the temperature sensor is coated with black body paint.

Images