Blind pixel detection method of infrared focal plane polarization detector

Abstract

The invention discloses a blind pixel detection method of an infrared focal plane polarization detector, which belongs to the technical field of infrared polarization imaging and comprises the following steps: acquiring infrared polarization data after non-uniform correction; stokes vectors of the collected data at different temperatures are calculated; setting a threshold value, respectively judging the stokes vector sum, judging the stokes vector sum as a blind pixel when the stokes vector is smaller than a lower threshold value or larger than an upper threshold value, marking on a blind pixel table, and setting the threshold value according to a criterion; the Stokes vector of the current pixel is judged point by point, and three blind pixel tables are generated; and performing'or 'operation on the three blind pixel tables to obtain a complete blind pixel table containing intensity blind pixels and polarization blind pixels. According to the method, the blind pixel detection problem of the infrared focal plane polarization detector is effectively solved, the steps are simple and effective, and a solid foundation is laid for subsequent popularization and application of the infrared focal plane polarization detector.

Description

Technical Field

[0001] This invention relates to the field of infrared polarization imaging technology, and specifically to a blind element detection method for an infrared focal plane polarization detector. Background Technology

[0002] As a cutting-edge infrared imaging device, the infrared focal plane polarization detector can simultaneously acquire multi-dimensional information such as the polarization (degree of polarization, polarization angle, etc.) and intensity of a target, effectively increasing the information content of infrared images. Natural terrain scenes are often characterized by high complexity and roughness, resulting in small differences in infrared radiation between natural terrain scenes and the target being detected. Traditional infrared equipment struggles to achieve ideal detection and identification results. Research shows that there are significant differences in the polarization radiation characteristics between natural terrain scenes and man-made objects. Based on this difference, it is possible to detect and identify man-made targets within natural terrain scenes. Therefore, infrared polarization imaging technology has technological advantages and application value in detecting hidden, camouflaged, and dimly lit targets.

[0003] Infrared focal plane array detectors commonly suffer from blind pixel problems due to factors such as manufacturing processes, materials, and circuit structures. In the national standard GB / T 17444-2013, blind pixels are also referred to as invalid pixels, including dead pixels and overheated pixels. Dead pixels are those with a responsivity less than half the average responsivity, while overheated pixels are those with a noise voltage greater than twice the average voltage. With advancements in technology and changes in application environments and scenarios, the methods for identifying blind pixels are constantly being updated. However, in infrared focal plane polarization detectors, the addition of micro-nano optical mechanisms that generate polarization effects introduces an invalid pixel that affects polarization calculations. This invalid pixel exhibits normal intensity response but cannot produce a correct polarization response; therefore, it is called a polarization blind pixel. For infrared focal plane polarization detectors, the detection and replacement of polarization blind pixels are just as important as those for intensity blind pixels. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide a blind element detection method for an infrared focal plane polarization detector, addressing the issue that existing blind element detection methods cannot detect infrared polarization blind elements. This invention introduces a detection method suitable for infrared polarization blind elements by combining the characteristics of polarization detectors, effectively improving the efficiency of blind element detection and replacement, and laying a solid foundation for the application and promotion of infrared polarization imaging technology.

[0005] The present invention adopts the following technical solution:

[0006] A blind element detection method for an infrared focal plane polarization detector includes the following:

[0007] Step 1: Acquisition of Infrared Polarization Data

[0008] Infrared polarization data was acquired by rotating the polarizer while adjusting the blackbody to different temperatures at a fixed integration time. The data has undergone infrared non-uniformity correction processing, including:

[0009] The blackbody temperatures are set to a first temperature and a second temperature, respectively, wherein there must be a certain temperature difference between the first temperature and the second temperature, and the first temperature is lower than the second temperature;

[0010] The polarizer needs to be rotated at fixed intervals for at least half a revolution to obtain infrared polarization data at different polarization angles at the first and second temperatures, which have been non-uniformly corrected.

[0011] Infrared polarization data can be short-wave, mid-wave, long-wave, and other infrared band data, and the data source can be cooled or uncooled infrared focal plane polarization detector components.

[0012] Step 2: Determine the upper and lower thresholds

[0013] Determine the Stokes vector corresponding to the infrared polarization data, and use it as... To obtain the upper and lower thresholds for each component of the criterion, including:

[0014] Calculate the Stokes vector corresponding to each set of infrared polarization data using the following formula:

[0015] ;

[0016] in, , , and The polarization angles of the polarized infrared focal plane detectors are respectively... , , and The grayscale values ​​of four adjacent pixels.

[0017] For each component in the Stokes vector, its upper and lower thresholds are calculated according to the following formula:

[0018] ;

[0019] in, The mean of all Stokes components. ; denoted as the standard deviation of each Stokes component.

[0020] Step 3: Obtain three blind tables

[0021] Stokes vectors of infrared polarization data respectively , and Make a judgment when the Stokes vector , and If any value is less than the lower threshold or greater than the upper threshold, the pixel is determined to be a blind pixel, and three blind pixel tables corresponding to the three Stokes vectors are obtained, including:

[0022] Each Stokes component of each group of infrared polarization data is judged point by point. If it is less than its corresponding lower threshold or greater than its corresponding upper threshold, then this position is marked as a blind cell.

[0023] Since two sets of infrared polarization data were collected at the first and second blackbody temperatures respectively under the same integration time, and each set of infrared polarization data corresponds to three Stokes components, a total of six blind element tables were obtained under the same integration time. By performing an OR operation on the blind element tables at the first and second temperatures respectively, three blind element tables corresponding to the three Stokes components at different blackbody temperatures were finally obtained.

[0024] Step 4: Obtain the complete blind table

[0025] By performing an OR operation on the three blind element tables, a complete blind element table for the infrared focal plane polarization detector can be obtained.

[0026] It is worth mentioning that since blind element detection was performed on all three Stokes vectors, and these three vectors are the basis for calculating parameters such as intensity, degree of polarization and polarization angle, the blind element table obtained after blind element detection includes both intensity blind elements and polarization blind elements.

[0027] Furthermore, the above-mentioned blind cell detection method is based on the following device:

[0028] The infrared focal plane polarization detector assembly, polarizer, blackbody of corresponding wavelength, and data acquisition system are placed coaxially. The polarizer is a linear polarizer and the polarization angle can be adjusted manually or electrically.

[0029] Note: The Stokes vector , and They are respectively:

[0030] S0 represents the total intensity of light, which is directly related to the energy of light.

[0031] S1 is the intensity difference between the horizontal and vertical polarization components, reflecting the horizontal / vertical polarization tendency of light;

[0032] S2 is the polarization intensity difference between the +45° and -45° (or 135°) directions, describing the oblique linear polarization state.

[0033] The beneficial effects of this invention are:

[0034] (1) The present invention calculates the Stokes vector of polarized light and determines the threshold for the determination of blind elements, so that this method can detect intensity blind elements and polarization blind elements;

[0035] (2) This invention uses infrared polarization response data with different temperatures and different starting angles for calculation and blind element determination. It takes into account various situations in the actual use of infrared focal plane polarization detectors and obtains a more complete blind element table, which is conducive to the subsequent promotion and application of infrared focal plane polarization detectors. Attached Figure Description

[0036] Figure 1 This is a flowchart of a blind element detection method for an infrared focal plane polarization detector according to the present invention;

[0037] Figure 2 This is a schematic diagram of the superpixel arrangement formed by the four polarization detection directions in the infrared focal plane polarization detector involved in this invention.

[0038] Figure 3 This is an experimental optical path diagram of a blind element detection method for an infrared focal plane polarization detector according to the present invention. In the diagram: 1-plane source blackbody, 2-polarizer, 3-infrared focal plane polarization detector assembly, 4-data acquisition system.

[0039] Figure 4 This is a complete blind element table for an infrared focal plane polarization detector obtained using the blind element detection method of the present invention. Detailed Implementation

[0040] To further illustrate the technical means and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] The following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. The descriptions of the method flow and the steps marked in the flowcharts in this specification are not necessarily strictly executed according to the step numbers; the execution order of the steps can be adjusted depending on the specific application. Furthermore, depending on the usage requirements, certain steps can be omitted, multiple steps can be combined, or a single step can be broken down into multiple steps.

[0042] This invention provides a blind element detection method for an infrared focal plane polarization detector, the process of which is as follows: Figure 1 As shown, the specific steps include the following:

[0043] Step 1: Acquisition of infrared polarization data. The infrared polarization data is acquired by rotating the polarizer while adjusting the blackbody to different temperatures at a fixed integration time, and the data has been processed for infrared non-uniformity correction.

[0044] Step 2, determine the Stokes vector corresponding to the infrared polarization data, and use... The upper and lower thresholds of each component are obtained as criteria;

[0045] Step 3: Analyze the Stokes vectors of the infrared polarization data respectively. , and The Stokes vector is judged to be a blind cell if it is less than the lower threshold or greater than the upper threshold, and three blind cell tables corresponding to the three Stokes vectors are obtained.

[0046] Step 4: Perform an OR operation on the three blind element tables to obtain the complete blind element table for the infrared focal plane polarization detector.

[0047] The above steps will be described in detail below with reference to the embodiments:

[0048] Step 1: Acquisition of infrared polarization data. The infrared polarization data is acquired by rotating the polarizer while adjusting the blackbody to different temperatures at a fixed integration time, and the data has been processed for infrared non-uniformity correction.

[0049] In this embodiment, a micro-polarizer array can be integrated onto a conventional infrared mercury cadmium telluride array detector. The arrangement of the micro-polarizer array is as follows: Figure 2 As shown, the directions of deviation are respectively , , and Four pixels make up a The superpixels generate a linearly polarized response to incident radiation. It is understood that the selected etching angle and micro-polarizer arrangement are merely exemplary and do not limit the pixel etching angle and micro-polarizer arrangement of the infrared focusing plane polarization detector in this invention.

[0050] In this embodiment, the experimental apparatus used to implement the present invention is as follows: Figure 3 As shown, it includes an infrared focal plane polarization detector assembly 3, a polarizer 2, a blackbody 1, and a data acquisition system 4.

[0051] First, the infrared focal plane polarization detector assembly 1 is placed on the optical platform, and the polarizer 2 is placed between the blackbody 1 and the polarization detector assembly 3, with the centers of the polarization detector assembly 3, the polarizer 2 and the blackbody 1 kept on the same axis; the polarizer 2 is a linear polarizer, and the polarization angle can be adjusted manually or electrically.

[0052] The surface source blackbody 1 is set to a first temperature and a second temperature, respectively. The polarizer 2 is adjusted by rotating at fixed intervals of at least half a revolution to obtain infrared polarization data at different polarization angles at the first and second temperatures. In this embodiment, the first temperature and the second temperature are respectively set to... and The polarizer angles are respectively set to , , and One hundred images were acquired for each temperature condition and polarization angle, resulting in eight sets of data. The 100 images within each set were averaged to eliminate temporal noise, thus obtaining the averaged high-temperature image. , , , and low temperature images , , , A total of eight images were generated, recording the response of each pixel on the infrared polarization focal plane to different polarization radiation. It is understood that the selected first temperature, second temperature, and polarizer angle are merely illustrative and not limiting, and can be adjusted and set according to actual usage requirements.

[0053] Step 2: Determine the Stokes vector corresponding to the infrared polarization data, and use... The upper and lower thresholds of each component are obtained as criteria.

[0054] In this embodiment, the eight Stokes vectors corresponding to the eight mean images obtained in the previous step are calculated according to the following formula:

[0055] ;

[0056] in, , , and The polarization angles of the polarized infrared focal plane detectors are respectively... , , and The grayscale values ​​of the four adjacent pixels can be determined according to... Figure 2 The schematic diagram of the detector polarization superpixel arrangement shown extracts grayscale values ​​corresponding to the polarization angles from eight mean images. It is understood that the Stokes vector calculation formula used is merely exemplary and does not constitute a limitation; it can be adjusted and modified according to actual usage requirements.

[0057] In this embodiment, the mean and standard deviation of the eight Stokes vectors are calculated according to the following formula:

[0058] ;

[0059] in, and The dimensions of the Stokes vector graphic; , This represents the Stokes vector corresponding to the mean image. It is understood that the formulas used to calculate the Stokes vector mean and standard deviation are merely illustrative and not limiting, and can be adjusted and modified according to actual usage requirements.

[0060] In this embodiment, the threshold values ​​for each group of Stokes components are expressed as follows:

[0061] ;

[0062] It is understood that the threshold calculation formula used is merely exemplary and does not constitute a limitation; it can be adjusted and modified according to actual usage needs.

[0063] Step 3: Analyze the Stokes vectors of the infrared polarization data separately. , and The Stokes vector is judged to be a blind cell if it is less than the lower threshold or greater than the upper threshold, and three blind cell tables corresponding to the three Stokes vectors are obtained.

[0064] In this embodiment, the eight sets of Stokes vectors are judged separately. If the following formula is satisfied, the position is determined to be a blind cell, and the corresponding position is marked on the blind cell table:

[0065] or ;

[0066] It is worth noting that when performing blind pixel determination on the eight sets of Stokes vectors, they need to be divided into a first temperature group and a second temperature group according to the blackbody problem. That is, the first and second temperature groups each have four sets of Stokes vectors corresponding to four bias angles and their thresholds. Within each temperature group, blind pixel determination is performed sequentially on the four sets of Stokes vectors, and the blind pixel table is iterated sequentially to obtain two sets of six blind pixel tables for the first and second temperatures. The two sets of blind pixel tables are then ORed sequentially to finally obtain three blind pixel tables corresponding to the three Stokes vectors. It is understood that the method used to generate the blind pixel tables is merely exemplary and does not constitute a limitation; it can be adjusted and modified according to actual usage requirements.

[0067] Step 4: Perform an OR operation on the three blind element tables to obtain the complete blind element table for the infrared focal plane polarization detector.

[0068] In this embodiment, considering that the formula for calculating the degree of polarization includes three Stokes vectors, three blind element tables corresponding to the three Stokes vectors are generated respectively. These three blind element tables are then ORed to include all the calculation parameters that may cause polarization blind elements, thus forming a complete blind element table for an infrared focal plane polarization detector.

[0069] Considering that the infrared focal plane polarization detector primarily converts the acquired infrared polarized radiation into intensity, polarization angle, and degree of polarization in subsequent applications, a Stokes vector is introduced to determine polarization blind elements based on the calculation formula. Infrared polarization data is acquired using a relatively simple experimental setup, and then calculations are performed according to the method and steps proposed in this invention to obtain a complete blind element table. The innovation of this invention lies in using the calculation of the Stokes vector of polarized light and the determination of a threshold for blind element determination. This allows the method to detect both intensity and polarization blind elements, achieving a superior blind element detection effect.

Claims

1. A method for detecting blind elements in an infrared focal plane polarization detector, characterized in that, The method comprises the following steps: Step 1, acquisition of infrared polarization data; Step 2, determine the Stokes vector corresponding to the infrared polarization data, and acquire the upper and lower thresholds of each component as the criterion ; Step 3: Analyze the Stokes vectors of the infrared polarization data respectively. , and Make a judgment when the Stokes vector , and If any value is less than the lower threshold or greater than the upper threshold, the pixel is determined to be a blind pixel, and three blind pixel tables corresponding to the three Stokes vectors are obtained. Step 4, performing OR operation on the three blind element tables to obtain a complete blind element table of the infrared focal plane polarization detector.

2. The method of claim 1, wherein the method further comprises: The infrared polarization data in step 1 is acquired by rotating a polarizer when a black body is set to different temperatures under a fixed integration time, and has been subjected to infrared non-uniform correction processing.

3. The method of claim 2, wherein the step of detecting the defective pixel is performed by the steps of: determining a difference between the first and second signals; and determining whether the difference is greater than a predetermined threshold. Specifically, the method comprises the following steps: The black body temperature is set to a first temperature and a second temperature, wherein a certain temperature difference is required between the first temperature and the second temperature, and the first temperature is lower than the second temperature. The polarizer is rotated at least half a circle at a fixed interval to obtain infrared polarization data at different polarizing angles under the first temperature and the second temperature after non-uniform correction.

4. The method of claim 2, wherein the step of detecting the defective pixel is performed by using a method of detecting a defective pixel of an infrared split focal plane polarized detector, the method comprising the steps of: The infrared polarization data is any infrared waveband data of short wave, medium wave or long wave, and the data source is a refrigeration type or non-refrigeration type infrared focal plane polarization detector assembly. ​ 5. The method of claim 1, wherein the method further comprises: Step 2 comprises: The Stokes vector corresponding to each group of infrared polarization data is calculated according to the following formula: ； wherein, , , and are the gray scale values of four adjacent pixels with polarization angles of , , and respectively. For each component in the Stokes vector, its upper and lower threshold values are calculated according to the following formula: ； wherein is the mean value of each Stokes component, ; is the standard deviation of each Stokes component.

6. The method of claim 1, wherein the method further comprises: Step 3 specifically comprises: Each Stokes component of each group of infrared polarization data is judged point by point, and if it is less than the corresponding lower threshold value or greater than the corresponding upper threshold value, the position is marked as a blind element. Since two groups of infrared polarization data are acquired under the same integration time when the black body temperature is set to the first temperature and the second temperature, each group of infrared polarization data corresponds to three Stokes components, so six blind element tables are obtained under the same integration time. The blind element tables under the first temperature and the second temperature are subjected to OR operation, respectively, so that three blind element tables corresponding to the three Stokes components under different black body temperatures are finally obtained, which contain intensity blind elements and polarization blind elements.

7. The method of claim 1-6, wherein, Step 4 specifically comprises: The three Stokes vectors have been subjected to blind element detection, and the three vectors are the basis for calculating intensity, degree of polarization and polarization angle. The complete blind element table obtained contains both intensity blind elements and polarization blind elements.

8. The method of claim 1-6, wherein, The method is performed by using a blind element detection device, which comprises an infrared focal plane polarization detector assembly (3), a polarizer (2), a surface source black body (1) corresponding to a wavelength, and a data acquisition system (4). The polarizer (2) is placed between the surface source black body (1) and the external focal plane polarization detector assembly (3), and the centers of the external focal plane polarization detector assembly (3), the polarizer (2) and the surface source black body (1) are kept on the same axis.

9. The method of claim 8, wherein the step of detecting the defective pixel comprises the steps of: determining a difference between the first and second signals; and determining whether the difference is greater than a predetermined threshold. The polarizer is a linear polarizer, and the polarizing angle thereof can be adjusted by manual or electric means.

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