A non-uniformity correction method for a refrigeration infrared thermal imager in a wide temperature range

Abstract

The application discloses a non-uniformity correction method for a refrigeration infrared thermal imager in a wide temperature range. The wide temperature range is divided into different temperature subranges, and then imaging at different temperatures is carried out in the temperature subranges with the same integration time, so that the linearity of the images in the temperature subranges is ensured, and the images are made uniform in the temperature subranges through correction parameter modification. The application solves the problems of poor non-uniformity and poor image output quality of the refrigeration infrared thermal imager with temperature change, and has a simple correction mathematical model, less parameters and easy engineering implementation, thereby providing better support for improving the temperature resolution and image quality of the infrared thermal imager.

Description

Technical Field

[0001] This invention relates to the field of cooled infrared thermal imager technology, and more specifically to a method for non-uniformity correction in cooled infrared thermal imagers over a wide temperature range. Background Technology

[0002] Because the individual pixels in a cooled infrared thermal imager respond inconsistently, a fixed image noise, also known as non-uniformity, is generated. This non-uniformity can change over extended periods or with variations in ambient temperature. To improve the temperature resolution and image quality of a cooled infrared thermal imager, non-uniformity correction is necessary.

[0003] Commonly used non-uniformity correction methods are mainly temperature calibration correction and adaptive correction. Temperature calibration correction is relatively mature, easy to implement, and widely used. It involves acquiring image data from cooled infrared thermal imagers at high and low temperatures, calculating and saving correction parameters, but its adaptability to changes in ambient temperature is poor. Because the output characteristics of infrared thermal imagers are not perfectly linear, the linearity varies across different temperature ranges, resulting in poor output linearity and difficulty in adapting to wide temperature ranges, leading to poor non-uniformity and unsatisfactory output quality. Adaptive correction, on the other hand, does not require temperature calibration or periodic updates of correction coefficients, overcoming the shortcomings of temperature calibration. However, it is difficult to implement in engineering and is currently still in the laboratory research stage. Summary of the Invention

[0004] In view of this, the present invention provides a method for non-uniformity correction of cooled infrared thermal imagers over a wide temperature range, which can improve the engineering feasibility and environmental adaptability of non-uniformity correction.

[0005] The present invention provides a method for non-uniformity correction of a cooled infrared thermal imager over a wide temperature range. The method divides the operating temperature range of the cooled infrared thermal imager into multiple sub-ranges; places the cooled infrared thermal imager in a temperature chamber and performs imaging at different temperatures within each sub-range; wherein the cooled infrared thermal imager uses the same integration time to perform imaging within the same sub-range; wherein the integration time is the integration time corresponding to the lower limit of the low temperature of the sub-range; and obtains the correction parameters for the sub-range based on the imaging data within the sub-range.

[0006] The cooled infrared thermal imager selects the integration time of the corresponding sub-interval during calibration based on its operating environment temperature, and uses the calibration parameters of that sub-interval to calibrate the imaging results.

[0007] Ideally, imaging should be performed at the lower limit of low temperature and the upper limit of high temperature in the sub-intervals, respectively.

[0008] Preferably, the integration time is the integration time of the cooled infrared thermal imager when the average pixel value of the output image is half of the maximum value at the lower limit temperature point of the sub-interval low temperature.

[0009] Ideally, the operating temperature range of the cooled infrared thermal imager is divided into multiple sub-ranges.

[0010] Preferably, the temperature difference between the sub-intervals is 20°C.

[0011] A preferred method for parameter calibration is as follows:

[0012] Correction gain parameters:

[0013] Correction bias parameters:

[0014] The corrected image is: Y(i,j)=G(i,j)·X(i,j)+O(i,j)

[0015] Where (i, j) ∈ (T, W), T and W are the image height and width, respectively; X(i, j) is the pixel value of the i-th row and j-th column pixel of the image; the subscripts L and H represent the image data at temperatures L and H, respectively; G(i,j) represents the pixel mean of the image, G(i,j) is the gain parameter, O(i,j) is the bias parameter, and Y(i,j) is the corrected image.

[0016] Beneficial effects:

[0017] This invention first divides a wide temperature range into different temperature sub-ranges. Then, within each temperature sub-range, imaging is performed at different temperatures using the same integration time. Although imaging quality is lost when imaging at other temperatures within the same sub-range, the linearity of the image within that range is ensured. The image is made uniform within that temperature range by correcting the parameters.

[0018] This invention solves the problem of poor image output quality and non-uniformity of cooled infrared thermal imagers as temperature changes. It switches the integration time and correction parameters of the infrared thermal imager to the corresponding temperature range based on the temperature detected by the temperature sensor, so that the thermal imager can output uniform images under different temperature ranges. Moreover, the correction mathematical model is simple, has few parameters, and is easy to implement in engineering, providing better support for improving the temperature resolution and image quality of infrared thermal imagers. Attached Figure Description

[0019] Figure 1 This is a block diagram of a non-uniformity correction method for cooled infrared thermal imagers over a wide temperature range. Among them,

[0020] G1, O1, G2, O2, G3, O3, G4, O4, G5, O5 represent the gain and bias of the correction calculation results.

[0021] INT1, INT2, INT3, INT4, and INT5 represent the integration time.

[0022] X L1 ,X L2 ,X L3 ,X L4 ,X L5 This indicates the parameters of the acquired low-temperature image.

[0023] X H1 ,X H2 ,X H3 ,X H4 ,X H5 This indicates the parameters of the acquired high-temperature image.

[0024] Figure 2 This is a flowchart of the non-uniformity correction method for a cooled infrared thermal imager with a wide temperature range according to the present invention. Detailed Implementation

[0025] The following is in conjunction with the appendix Figure 1-2 The present invention will be described in detail with examples.

[0026] In this example, the calibration of a cooled infrared camera covering a wide temperature range of (-40℃, 60℃) is performed as follows:

[0027] Step 1: Fix the cooled infrared thermal imager with temperature sensor onto the structural fixture and place it in the high and low temperature chamber.

[0028] Step 2: Adjust the position of the cooled infrared thermal imager so that its image window is aligned with the wall of the high and low temperature chamber, and then power on the cooled infrared thermal imager. Divide the wide temperature range into sub-ranges with a temperature difference of 20°C.

[0029] Step 3: For the sub-range [-40, -20], set the temperature of the high and low temperature chamber to -40℃, then adjust the integration time of the cooled infrared thermal imager to integration time INT1, and collect the raw image data of the infrared thermal imager as low-temperature data. Then set the temperature of the high and low temperature chamber to -20℃, and collect the raw image data of the infrared thermal imager at the same integration time INT1 as high-temperature data. Calculate the correction parameters based on the collected high-temperature and low-temperature data and save them. The integration time INT1 is the integration time of the infrared thermal imager at the lower limit of the low temperature in the sub-range, -40℃. Specifically, the integration time is adjusted according to the output characteristics of the thermal imager at the lower limit of the low temperature in the temperature range. When the average value of the image output by the thermal imager is half of the maximum value of the thermal imager output, the corresponding integration time is the integration time of the thermal imager in that sub-range. Alternatively, data at other temperatures within the [-40, -20] range can be collected for calibration at the same integration time INT1.

[0030] Step 4: For the sub-interval [-20, 0], set the temperature of the high and low temperature chamber to -20℃, then adjust the integration time of the cooled infrared thermal imager to integration time INT2, and collect the raw image data of the infrared thermal imager as low-temperature data. Then, set the temperature of the high and low temperature chamber to 0℃, and collect the raw image data of the infrared thermal imager at the same integration time INT2 as high-temperature data. Calculate the correction parameters based on the collected high-temperature and low-temperature data, and save them. The integration time INT2 is the integration time of the infrared thermal imager at the lower limit of the low temperature in the sub-interval of -20℃. Similarly, data at other different temperatures within the [-20, 0] interval can also be collected for calibration at the same integration time INT2.

[0031] Step 5: For the sub-interval [0,20], set the temperature of the high and low temperature chamber to 0℃, then adjust the integration time of the cooled infrared thermal imager to integration time INT3, and collect the raw image data of the infrared thermal imager as low-temperature data. Then, set the temperature of the high and low temperature chamber to 20℃, and collect the raw image data of the infrared thermal imager at the same integration time INT3 as high-temperature data. Calculate the correction parameters based on the collected high-temperature and low-temperature data, and save them. The integration time INT3 is the integration time of the infrared thermal imager at the lower limit of the low temperature of 0℃ in the sub-interval. Similarly, data at other different temperatures within the [0,20] interval can also be collected for calibration at the same integration time INT3.

[0032] Step 6: For the sub-interval [20,40], set the temperature of the high and low temperature chamber to 20℃, then adjust the integration time of the cooled infrared thermal imager to integration time INT4, and collect the raw image data of the infrared thermal imager as low-temperature data. Then, set the temperature of the high and low temperature chamber to 40℃, and collect the raw image data of the infrared thermal imager at the same integration time INT4 as high-temperature data. Calculate the correction parameters based on the collected high-temperature and low-temperature data, and save them. The integration time INT4 is the integration time of the infrared thermal imager at the lower limit of the low temperature of 20℃ in the sub-interval. Similarly, data at other different temperatures within the [20,40] interval can also be collected for calibration at the same integration time INT4.

[0033] Step 7: For the sub-interval [40, 60], set the temperature of the high and low temperature chamber to 40℃, then adjust the integration time of the cooled infrared thermal imager to integration time INT5, and collect the raw image data of the infrared thermal imager as low-temperature data. Then, set the temperature of the high and low temperature chamber to 60℃, and collect the raw image data of the infrared thermal imager at the same integration time INT5 as high-temperature data. Calculate the correction parameters based on the collected high-temperature and low-temperature data, and save them. The integration time INT5 is the integration time of the infrared thermal imager at the lower limit of the low temperature of 40℃ in the sub-interval. Similarly, data at other different temperatures within the [40, 60] interval can also be collected for calibration at the same integration time INT5.

[0034] Step 8: Restore the temperature of the high and low temperature chamber to room temperature (25℃), then save the temperature range and corresponding integration time to the cooled infrared thermal imager. After saving, power off the infrared thermal imager.

[0035] Step 9: Power on again. The infrared thermal imager uses the integration time corresponding to the sub-interval of the ambient temperature detected by the temperature sensor to perform imaging, and uses the parameters of the sub-interval to calibrate the imaging.

[0036] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for non-uniformity correction of a cooled infrared thermal imager for a wide temperature interval, characterized in that, The working environment temperature range of the refrigeration infrared thermal imager is divided into multiple subintervals; the refrigeration infrared thermal imager is placed in a temperature chamber, and imaging at different temperatures is respectively performed in the subintervals; wherein the refrigeration infrared thermal imager uses the same integration time to perform imaging in the same subinterval; wherein the integration time is the integration time corresponding to the low temperature limit of the subinterval; the correction parameters of the subinterval are obtained according to the imaging data in the subinterval; The refrigeration infrared thermal imager selects the integration time corresponding to the subinterval during correction to perform imaging according to the working environment temperature of the refrigeration infrared thermal imager, and corrects the imaging result by using the correction parameters of the subinterval; The working temperature range of the refrigeration infrared thermal imager is equally divided to obtain multiple subintervals; The temperature difference of the subinterval is 20 DEG C. The parameter correction is performed in the following manner: Correction gain parameter: Correcting the bias parameter: The corrected image is Y(i,j)=G(i,j)X(i,j)+O(i,j) where (i,j) e (T,W), T and W are the height and width of the image, respectively; X(i,j) is the pixel value of the i-th row and j-th column pixel of the image; the subscripts L and H represent the image data at temperatures L and H, respectively; where < Y(i,j) > is the mean value of the pixels of the image, G(i,j) is the gain parameter, O(i,j) is the offset parameter, and Y(i,j) is the corrected image.

2. The method for non-uniformity correction of a cryogenic infrared thermal imager for a wide temperature range according to claim 1, characterized in that, Imaging is respectively performed at the low temperature limit and the high temperature limit of the subinterval.

3. The method for non-uniformity correction of a cryogenic infrared thermal imager for wide temperature range according to claim 1, characterized in that, The integration time is: at the temperature point of the low temperature limit of the subinterval, the integration time of the refrigeration infrared thermal imager when the pixel mean value of the output image is half of the maximum value.

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