Automatic out-of-focus polarization imaging system and method for target detection

Abstract

The invention relates to an automatic out-of-focus polarization imaging system and method for target detection, and the method comprises the steps: obtaining the feature information of a target scene, determining an optimal focusing position through the combination of a coarse tuning and fine tuning focusing strategy, and then determining an optimal out-of-focus position through employing a coarse tuning and fine tuning adjustment strategy and an optimization function value based on the optimal focusing position. According to the method, the optimal target area can be obtained by performing anomaly detection on the polarization map of the optimal defocus position, the interference of background clutters is effectively suppressed on the premise that the requirements of low algorithm time complexity and high focusing position search speed are met, and a target detection result in a complex environment is more accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of polarization imaging, and in particular to an automatic defocus type polarization imaging system and method for target detection. Background Art

[0002] As one of the four basic properties of light waves, polarization is closely related to the surface features of objects such as contour, texture, roughness and water content, and inherent properties such as refractive index, emissivity and extinction coefficient. By combining the polarization information that characterizes the physical and chemical properties of materials with two-dimensional intensity imaging technology, polarization imaging technology can effectively improve the contrast of images and enhance the detection and recognition capabilities of targets under complex backgrounds through the polarization difference between the target and the background. At present, in the process of polarization imaging detection, the imaging system obtains no less than three clear polarization channel images through accurate focusing, and combines the deconstruction of polarization characteristic parameters (such as Stokes vector, degree of polarization and polarization angle) and multi-parameter image fusion to achieve target detection. Although this technical solution has significant application advantages in some scenarios, due to the principle limitations of signal filtering and attenuation and the current application status of poor adaptive adjustment capabilities, there are still problems such as low target and background differentiation in complex working environments such as ground reconnaissance. Specifically, it is manifested in the following two aspects: 1) The polarization imaging system relies on manual focusing and human eye judgment during operation, which has the disadvantages of cumbersome operation, low efficiency and strong subjectivity. Especially under harsh outdoor conditions, it is difficult to quickly determine the appropriate focus position through the screen display, which causes the collected image to lose target detail feature information; 2) The deconstruction of polarization degree and polarization angle usually involves nonlinear operations, which makes it more sensitive to noise and prone to large solution errors. Although image quality enhancement can be achieved by relying on the back-end noise reduction algorithm, the information loss caused by the constraints of the front-end system is difficult to make up.

[0003] At present, for the application of imaging systems such as visible light and long-wave infrared, relevant technical solutions have proposed methods such as focus position search and autofocus. For example, Chinese patent publication No. [CN103327245A] proposes an autofocus method for an infrared imaging system, and Chinese patent publication No. [CN118354202A] proposes a fast autofocus method for an infrared thermal imager with temperature compensation. Although these solutions can automatically realize the search for a clearly focused position, they have not yet considered the application in polarization imaging systems. There are still deficiencies in combining the characteristics of polarization feature analysis and realizing automatic defocusing strategies guided by high-precision target detection. In addition, in terms of polarization image processing and target detection, many technical solutions focus on methods such as original image denoising and defocused blurred image restoration, aiming to reduce the noise in the image and the blur caused by defocus. For example, Chinese patent publication No. [CN116703771A] proposes a polarization image denoising method based on four-dimensional block matching based on polarization constraints. Through methods such as four-dimensional block matching and filtering, efficient removal of noise in polarization images and accurate recovery of target polarization information are achieved. Although this technical solution can achieve image quality enhancement by relying on the back-end algorithm, the information loss caused by the constraints of the front-end system is difficult to make up for. The potential value of the out-of-focus blurred images generated during the focusing process is often ignored. New technical solutions are still to be proposed in terms of using blurred degraded images to reduce noise interference and improve detection accuracy.

[0004] Therefore, in order to solve the above problems, improve the adaptability of the polarization imaging system in different working scenarios, and meet the application needs of efficient detection of targets in complex environments, it is urgent to explore the application advantages of defocus blur in the field of target detection. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to realize fast, accurate and automatic search for the best focus position of a polarization imaging system and high-precision detection of a target.

[0006] The present invention provides an automatic defocus type polarization imaging method for target detection, comprising: Step 1: collect the polarization camera at different polarization angles at the initial focal depth position. Polarization image, calculate the Stokes parameter image at the initial focal depth position and the average gradient ; Step 2, presetting the direction, coarse adjustment step and fine adjustment step of the polarization camera's automatic focusing, the polarization camera performs coarse adjustment and fine adjustment based on the initial focal depth position, and compares the average gradient values ​​after coarse adjustment and fine adjustment to obtain the optimal positive focus position of the polarization camera; Step 3: Calculate the Stokes parameter image of the polarization camera at the optimal positive focus position , from the Stokes parameter image Stokes first parameter image in Select the target area and the background area, and calculate the optimization function values ​​of the target area and the background area ; Step 4, presetting the direction, coarse adjustment step length and fine adjustment step length of the polarization camera automatic focusing, the polarization camera performs coarse adjustment and fine adjustment based on the optimal positive focus position, and compares the optimization function values ​​after coarse adjustment and fine adjustment to obtain the optimal defocus position of the polarization camera; Step 5: The polarization camera collects the images at different polarization angles at the optimal defocus position. Polarization image, calculate the Stokes parameter image at the optimal defocus position ; Step 6: Stokes parameter image Stokes second parameter image in and Stokes third parameter image Perform anomaly detection and detect the optimal target area.

[0007] Compared with the prior art, the present application has the following advantages: by acquiring the characteristic information of the target scene, the optimal focus position is determined by combining the coarse adjustment and fine adjustment focusing strategies, and then the optimal defocus position is determined based on the optimal focus position by using the coarse adjustment and fine adjustment adjustment strategies and optimization function values. By performing anomaly detection on the polarization diagram of the optimal defocus position, the optimal target area can be obtained. The method of the present application effectively suppresses the interference of background clutter while satisfying the requirements of low algorithm time complexity and fast focus position search speed, and the target detection results in complex environments are more accurate.

[0008] In a possible implementation, the Stokes parameter image at the initial focal depth position is calculated in step 1. and the average gradient Specifically include: Step 101: Calculate the polarization intensity value of each polarization image based on the polarization imaging principle , the calculation formula is: ; In the formula, Represents the polarization angle of the polarization camera; represents the Stokes first parameter image, represents the Stokes second parameter image; represents the Stokes third parameter image; Step 102: based on the polarization intensity value , construct a linear system of equations to solve the Stokes parameter image , the calculation formula is: ; In the formula, Indicates the number of polarization images collected; represents the Stokes fourth parameter image; Step 103, based on the Stokes parameter image Calculate polarization image , the calculation formula is: ; Step 104, calculate the first Stokes parameter image The average gradient of , the calculation formula is: ; In the formula, Represent the first Stokes parameter images respectively The number of rows and columns of pixels in the Represents the coordinates of the pixel.

[0009] In a possible implementation manner, the step 2 specifically includes: Step 201, preset the step length of coarse adjustment to ; Preset parameters , The initial value of is 1; Step 202: The polarization camera is forward-focused to Depth of focus position, calculation Stokes first parameter image and average gradient value at focal depth ; Then, the polarization camera is focused forward to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Step 203, determine whether If yes, then go to step 204, if no, then , proceed to step 206; Step 204, determine whether If yes, it means that the current focusing direction is wrong, and the process goes to step 205; if no, the polarization camera returns to the initial focal depth position. , and return to step 202; Step 205: the polarization camera returns to the initial focal depth position. The polarization camera is reversely focused based on the initial focal depth position. Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Then, the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Return to step 203; Step 206, determine whether If yes, it means the current focus direction is correct. , and return to step 202; if not, then , The corresponding focal depth position is the suboptimal focal depth position. The polarization camera is adjusted to the suboptimal focal depth position, and the average gradient value corresponding to the suboptimal focal depth position is calculated. , and proceed to step 207; Step 207, preset fine-tuning step length , preset parameters , The initial value of is 1; Step 208: The polarization camera is forward-focused to the suboptimal focal depth position. Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Then, the polarization camera is focused forward to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Step 209, determine whether If yes, go to step 210; if no, then , proceed to step 212; Step 210, determine whether If yes, it means the current focusing direction is wrong, and the process goes to step 211; if no, the polarization camera returns to the suboptimal focal depth position. , return to step 208; Step 211, the polarization camera returns to the suboptimal focal depth position. , the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth position and the average gradient ; Then, the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Return to step 209; Step 212, determine whether If yes, it means the current focus direction is correct. , and return to step 208; if not, then , The corresponding focal depth position is the optimal positive focus position, and the polarization camera is adjusted to the optimal positive focus position.

[0010] In a possible implementation, the optimization function values ​​of the target area and the background area are calculated in step 3. , the calculation formula is: ; In the formula, represents the target area expectation, represents the background area expectation, represents the target region covariance, represents the background area covariance.

[0011] In one possible implementation, the target area is expected to The calculation formula is: ; In the formula, Represents the total number of pixels in the target area, Indicates the target area The pixel value of a pixel; Background area expectations The calculation formula is: ; In the formula, Represents the total number of pixels in the background area, Indicates the background area The pixel value of a pixel; Target region covariance The calculation formula is: ; Background area covariance The calculation formula is: ; In the formula, is the vector transpose symbol, Indicates Pixels and background area expectation The transpose of the difference.

[0012] In a possible implementation manner, step 4 specifically includes: Step 401: Preset the step length of coarse adjustment , preset parameters , The initial value of is 1; Step 402: The polarization camera is forward-focused to the optimal positive focus position. Depth of focus position, calculation Stokes first parameter image at and optimize the function value ; Then, the polarization camera is focused forward based on the optimal positive focus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Step 403, determine whether If yes, then go to step 404, if no, then , proceed to step 406; Step 404, determine whether If yes, it means the current focusing direction is wrong, and the process goes to step 405; if no, the polarization camera returns to the optimal positive focus position. , return to step 402; Step 405: the polarization camera returns to the optimal positive focus position. The polarization camera is reversely focused based on the optimal positive focus position. Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Return to step 403; Step 406, determine whether If yes, it means the current focus direction is correct. , and return to step 402; if not, then , The corresponding focal depth position is the suboptimal defocus position. The polarization camera is focused to the suboptimal defocus position, and the optimization function value corresponding to the suboptimal defocus position is calculated. , proceed to step 407; Step 407: Preset the fine-tuning step size , preset parameters , The initial value of is 1; Step 408: The polarization camera is forward-focused to the suboptimal defocus position. Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is focused forward to Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Step 409, determine whether If yes, then go to step 410; if no, then , proceed to step 412; Step 410, determine whether If yes, it means the current focusing direction is wrong, and the process goes to step 411; if no, the polarization camera returns to the suboptimal defocus position. , return to step 408; Step 411, the polarization camera returns to the suboptimal defocus position. , the polarization camera is reversed to focus based on the suboptimal defocus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is reversed to focus based on the suboptimal defocus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Return to step 409; Step 412, determine whether , if yes, then the current focus direction is correct, , return to step 408; if not, then , The corresponding focal depth position is the optimal defocus position, and the polarization camera is focused to the optimal defocus position.

[0013] In a possible implementation, the RX anomaly detection method is adopted in step 7, and the RX anomaly detection operator is: ; In the formula, represents the pixel to be detected; is the expectation for the background area; represents the background covariance matrix.

[0014] An automatic defocus polarized light imaging system for target detection comprises an imaging lens, an automatic focusing component, a polarizing device, an imaging detector, a driving control module, and an image acquisition and processing module; the imaging lens is connected to the imaging detector, and the automatic focusing component is arranged on the imaging lens to drive and adjust the zoom ratio and focus of the imaging lens; the polarizing device is located between the imaging lens and the imaging detector, and is used to separate and extract polarization information of incident light, and the axis of the imaging lens, the axis of the polarizing device, and the optical axis of the imaging detector are coaxially arranged; the polarizing device is electrically connected to the imaging detector, and is used to receive the light signal passing through the imaging lens and the polarizing device, and convert it into an electrical signal to acquire a polarized image of a target scene; the image acquisition and processing module is electrically connected to the imaging detector, and is used to control the automatic defocus polarized imaging method for target detection to generate a driving control signal of the automatic focusing component; the image acquisition and processing module is electrically connected to the driving control module, and the driving control module is connected to the automatic focusing component, and is used to send the driving control signal to the driving control module, generate the driving control signal of the automatic focusing component, and drive the automatic focusing component to focus the imaging lens.

[0015] In a possible embodiment, the automatic focusing assembly includes a focusing motor, a mounting base and a rotating base, the rotating base is arranged around the outer wall of the imaging lens, the rotating base is linked with the optical lens group, and is used to drive the optical lens group to move; the outer peripheral wall of the rotating base is provided with gear teeth, the mounting base is fixed on the outer wall of the optical lens, the focusing motor is fixed on the mounting base, the output end of the focusing motor is connected to a focusing gear, the focusing gear is meshed with the gear teeth on the outer peripheral wall of the rotating base, and the focusing motor is electrically connected to a drive control module.

[0016] In a possible implementation, the imaging lens includes an optical lens group for imaging; the imaging lens includes an ultraviolet lens, a visible light lens and an infrared lens; wherein the connection type of the visible light lens is a C-type interface or a CS-type interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is an application scenario of Example 1 of the present invention, using a scaled-down vehicle model experimental scene diagram against a jungle grassland background, wherein: Figure 1 (a) is the visible light image of the target scene and the enlarged image of the scaled vehicle model. Figure 1 (b) is the wide-band infrared intensity image of the target scene; Figure 2 The comparison image of the target detection results of the optimal in-focus position and the optimal out-of-focus position in Example 1 of the present invention; Figure 3 The ROC curve and box plot results corresponding to the optimal focus position and the optimal defocus position in Example 1 of the present invention; wherein, Figure 3 (a) is a schematic diagram of the ROC curve corresponding to the optimal focus position and the optimal defocus position. Figure 3 (b) is a schematic diagram of the box plot results corresponding to the optimal focus position and the optimal defocus position; Figure 4 This is a schematic diagram of the structure of Embodiment 2 of the present invention; Figure 5 Schematic diagram of the structure of the polarization device and the imaging detector in Example 2 of the present invention; Figure 6 This is a system framework diagram of Example 2 of the present invention.

[0018] Description of reference numerals: 1. Imaging lens; 2. Automatic focusing assembly; 2.1 Focusing motor; 2.2. Mounting base; 2.3. Rotating base; 2.4. Gear teeth; 2.5. Focusing gear; 3. Polarization device; 4. Imaging detector; 5. Drive control module; 6. Image acquisition and processing module. DETAILED DESCRIPTION

[0019] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0020] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0021] In the embodiments of the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0022] The present application is further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0023] This implementation uses a scaled vehicle model against a jungle grassland background as an example. For the actual field experiment scene, please refer to Figure 1 , Figure 1 (a) is the visible light image of the target scene and the enlarged image of the scaled vehicle model. Figure 1 (b) is a wide-band infrared intensity image of the target scene, where background clutter interference factors include grass, bare land, etc. Figure 1 (a) and Figure 1 The red box in (b) shows a scaled-down vehicle model. The imaging system uses the polarization camera provided in Example 2. The experimental weather conditions are sunny and cloudy, and the temperature is 28° C. During the field polarization information collection experiment, the target and the imaging system remain stationary.

[0024] See also Figure 1 to Figure 3 As shown, the embodiment of the present application discloses an automatic defocus type polarization imaging method for target detection, comprising: Step 1: Use a polarization camera to collect the initial focal depth at different polarization angles. Polarization image, calculate the Stokes parameter image at the initial focal depth position and the average gradient The Stokes parameter image (Stokes parameter) in this embodiment is an image used to characterize the polarization characteristics of the light field. A set of Stokes parameter images includes four parameters, namely, the Stokes first parameter image , Stokes second parameter image , Stokes third parameter image and Stokes fourth parameter image , which is used to describe the polarization state of light waves and to generate images, where the Stokes parameter of each pixel reflects the polarization characteristics of the pixel.

[0025] The Stokes parameter image at the initial focal depth position is calculated in step 1 and the average gradient Specifically include: Step 101: collect four polarization images at different polarization angles at the current focal depth of the polarization camera, and calculate the polarization intensity value of each polarization image based on the polarization imaging principle. , the calculation formula is: ; In the formula, Represents the polarization angle of the polarization camera; Step 102, based on the polarization intensity value , construct a linear equation system to solve the Stokes parameter image, the calculation formula is: ; In the formula, represents the number of polarization images collected; in this embodiment, ; Step 103: Calculate the polarization degree image based on the Stokes parameter image , the calculation formula is: ; Step 104: Select Stokes parameter image The Stokes first parameter image in , and calculate the first Stokes parameter image The average gradient of ; Average gradient value The calculation formula is: ; In the formula, Represent the first Stokes parameter images respectively The number of rows and columns of pixels in the Represents the coordinates of the pixel.

[0026] The average gradient value in this embodiment is used to quantitatively evaluate the defocus amount of the polarization camera. The larger the first Stokes parameter image The better the clarity, the smaller the defocus.

[0027] Step 2: preset the direction, coarse adjustment step and fine adjustment step of the polarization camera's automatic focusing. The polarization camera performs coarse adjustment and fine adjustment based on the initial focal depth position. The optimal positive focus position of the polarization camera is obtained by comparing the average gradient values ​​after coarse adjustment and fine adjustment.

[0028] The step 2 specifically includes: Step 201, preset the step length of coarse adjustment to ; Preset parameters , The initial value of is 1; Step 202: The polarization camera is forward-focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Then, the polarization camera is focused forward to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Step 203, determine whether If yes, then go to step 204, if no, then , proceed to step 206; Step 204, determine whether If yes, it means that the current focusing direction is wrong, and the process goes to step 205; if no, the polarization camera returns to the initial focal depth position. , and return to step 202; Step 205: the polarization camera returns to the initial focal depth position. The polarization camera is reversely focused based on the initial focal depth position. Depth of focus position, calculation Stokes first parameter image at focal depth and the average gradient ; Then, the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Return to step 203; Step 206, determine whether If yes, it means the current focus direction is correct. , and return to step 202; if not, then , The corresponding focal depth position is the suboptimal focal depth position. The polarization camera is adjusted to the suboptimal focal depth position, and the average gradient value corresponding to the suboptimal focal depth position is calculated. , and proceed to step 207; Step 207, preset fine-tuning step length , preset parameters , The initial value of is 1; Step 208: The polarization camera is forward-focused to the suboptimal focal depth position. The focal depth position of Stokes first parameter image at the focal depth position and the average gradient ; Then, the polarization camera is focused forward to The focal depth position of Stokes first parameter image at the focal depth position and the average gradient ; Step 209, determine whether If yes, go to step 210; if no, then , proceed to step 212; Step 210, determine whether If yes, it means the current focusing direction is wrong, and the process goes to step 211; if no, the polarization camera returns to the suboptimal focal depth position. , return to step 208; Step 211, the polarization camera returns to the suboptimal focal depth position. , the polarization camera is reversely focused to The focal depth position of Stokes first parameter image at the focal depth position and the average gradient ; Then, the polarization camera is reversely focused to The focal depth position of Stokes first parameter image at the focal depth position and the average gradient ; Return to step 209; Step 212, determine whether If yes, it means the current focus direction is correct. , and return to step 208; if not, then , The corresponding focal depth position is the optimal positive focus position, and the polarization camera is adjusted to the optimal positive focus position.

[0029] Step 3: The polarization camera collects the data at the optimal positive focus position. Polarization image, calculate the Stokes parameter image of the polarization camera at the optimal positive focus position , from the Stokes parameter image Stokes first parameter image in Select the target area and background area, and calculate the optimization function value of the target area and background area ; Optimize function value The calculation formula is: ; In the formula, represents the target area expectation, represents the background area expectation, represents the target region covariance, represents the background area covariance.

[0030] The target area is expected to The calculation formula is: ; In the formula, Represents the total number of pixels in the target area, Indicates the target area The pixel value of a pixel; Background area expectations The calculation formula is: ; In the formula, Represents the total number of pixels in the background area, Indicates the background area The pixel value of a pixel; Target region covariance The calculation formula is: ; Background area covariance The calculation formula is: ; In the formula, is the vector transpose symbol, Indicates Pixels and background area expectation The transpose of the difference.

[0031] When the optimization function value of the target area and the background area is larger, the difference between the corresponding feature vectors is smaller, and the probability of the target area being detected from the background area is greater.

[0032] Step 4, presetting the direction, coarse adjustment step and fine adjustment step of the polarization camera automatic focusing, the polarization camera performs coarse adjustment and fine adjustment based on the optimal positive focus position, and compares the optimization function values ​​after coarse adjustment and fine adjustment to obtain the optimal defocus position of the polarization camera.

[0033] The step 4 specifically includes: Step 401: Preset the step length of coarse adjustment , preset parameters , The initial value of is 1; Step 402: The polarization camera is forward-focused to the optimal positive focus position. Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is focused forward based on the optimal positive focus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Step 403, determine whether If yes, then go to step 404, if no, then , proceed to step 406; Step 404, determine whether If yes, it means the current focusing direction is wrong, and the process goes to step 405; if no, the polarization camera returns to the optimal positive focus position. , return to step 402; Step 405: the polarization camera returns to the optimal positive focus position. The polarization camera is reversely focused based on the optimal positive focus position. Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Return to step 403; Step 406, determine whether If yes, it means the current focus direction is correct. , and return to step 402; if not, then , The corresponding focal depth position is the suboptimal defocus position. The polarization camera is focused to the suboptimal defocus position, and the optimization function value corresponding to the suboptimal defocus position is calculated. , proceed to step 407; Step 407: Preset the fine-tuning step size , preset parameters , The initial value of is 1; the focusing direction to obtain the suboptimal defocus position is the positive direction; Step 408: The polarization camera is forward-focused to the suboptimal defocus position. Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is focused forward to Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Step 409, determine whether If yes, then go to step 410; if no, then , proceed to step 412; Step 410, determine whether If yes, it means the current focusing direction is wrong, and the process goes to step 411; if no, the polarization camera returns to the suboptimal defocus position. , return to step 408; Step 411, the polarization camera returns to the suboptimal defocus position. , the polarization camera is reversed to focus based on the suboptimal defocus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is reversed to focus based on the suboptimal defocus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Return to step 409; Step 412, determine whether , if yes, then the current focus direction is correct, , return to step 408; if not, then , The corresponding focal depth position is the optimal defocus position, and the polarization camera is focused to the optimal defocus position.

[0034] Step 5: The polarization camera collects the best defocus position. Polarization image, calculate the Stokes parameter image at the optimal defocus position .

[0035] Step 6: Stokes parameter image Stokes second parameter image in and Stokes third parameter image Anomaly detection is performed to obtain the optimal target area. This specific embodiment adopts the RX anomaly detection method, and the RX anomaly detection operator is: ; In the formula, represents the pixel to be detected; is the expectation for the background area; represents the background covariance matrix.

[0036] In this embodiment, the forward focusing of the focal depth position of the polarization camera means adjusting the polarizer adjustment ring of the polarization camera in a clockwise direction; the reverse focusing means adjusting the polarizer adjustment ring of the polarization camera in a counterclockwise direction.

[0037] See also Figure 2 The Stokes first parameter image of the target scene corresponding to the optimal focus position and the optimal defocus position , polarization image ，As well as the anomaly detection operator image, it can be seen that the detection operator image corresponding to the traditional optimal defocus position is difficult to effectively extract the target features from the background interference, and the detection effect is poor; by actively defocusing the polarization image The background area in the image is suppressed, while the target features are highlighted, and the target area and the background area are clearly divided; the detection operator image corresponding to the method proposed in the present invention can fully suppress the background clutter interference and highlight the target features, and the visual effect and target detection effect are the best; See also Figure 3 In order to further verify the practicality, effectiveness and advancement of the method of the present invention, the receiver operating characteristic curve (ROC) and box plot are used to quantitatively evaluate the performance of target detection. Among them, the area under the ROC curve (AUC) is used to quantitatively evaluate the performance of target detection with different polarization angle combinations. The larger the AUC area, the better the detection effect.

[0038] See also Figure 3 (a) It can be seen that under the condition of a certain detection rate, the target detection result corresponding to the method of the present invention has a lower false alarm probability and a maximum AUC value, and the detection effect is the best. In the box plot, the height of the box represents the suppression of background interference by different polarization channel configurations; the spacing of the boxes represents the separation of the background and anomalies by the algorithm. The larger the spacing, the more conducive it is to the separation of targets or anomalies. Figure 3 (b) It can be seen that the target box corresponding to the target detection result of the method of the present invention has the largest compression degree and the best background suppression. At the same time, the height difference between the boxes is the largest, and it has better background anomaly separation. Example 2

[0039] See also Figures 4 to 6 As shown, an automatic defocus type polarized light imaging system for target detection includes an imaging lens 1, an automatic focusing component 2, a polarization device 3, an imaging detector 4, a drive control module 5, and an image acquisition and processing module 6; The imaging lens 1 includes an optical lens group 1.1 for imaging. The working range of the imaging lens 1 in this embodiment is the infrared band, and a fixed focus is adopted according to the target scene. The specific parameters are: focal length 50mm, F number 1.0, field of view angle 12.42°×9.95°; the imaging lens 1 is connected to the imaging detector 4, and is used to focus the light field information reflected or radiated by the target scene onto the imaging detector 4; The automatic focusing assembly 2 is arranged on the imaging lens 1, and is used to drive and adjust the movement of the optical lens group 1.1 to adjust the zoom ratio and focus of the imaging lens 1; The polarizer 3 is located between the imaging lens 1 and the imaging detector 4, and is used to separate and extract the polarization information of the incident light; the axis of the imaging lens 1, the axis of the polarizer 3 and the optical axis of the imaging detector 4 are coaxially arranged; in this embodiment, based on the target scene requirements, the polarizer 3 is a micro-polarization column device integrated in the focal plane row of the imaging detector 4; the working band of the imaging detector 4 is a long-wave infrared detector, and its spectral response range is 8~14μm, the imaging resolution is 640×480, and the frame rate is 25Hz; Furthermore, the automatic focusing assembly 2 includes a focusing motor 2.1, a mounting base 2.2 and a rotating base 2.3. The rotating base 2.3 is arranged on the outer wall of the imaging lens 1, and the rotating base 2.3 is linked with the optical lens group 1.1 to drive the optical lens group 1.1 to move; gear teeth 2.4 are provided on the outer peripheral wall of the rotating base 2.3, the mounting base 2.2 is fixed on the outer wall of the optical lens, the focusing motor 2.1 is fixed on the mounting base 2.2, and the output end of the focusing motor 2.1 is connected to a focusing gear 2.5, and the focusing gear 2.5 is meshed with the gear teeth 2.4 on the outer peripheral wall of the rotating base 2.3. The focusing motor 2.1 is electrically connected to the drive control module 5, and the focusing motor 2.1 is a DC brushless motor.

[0040] The polarization device 3 is electrically connected to the imaging detector 4, the image acquisition and processing module 6 is electrically connected to the imaging detector 4 and the drive control module 5, and the drive control module 5 is electrically connected to the automatic focusing component 2; when acquiring the target scene image, the imaging detector 4 receives the light signal passing through the imaging lens 1 and the polarization device 3, and converts it into an electrical signal; the image acquisition and processing module 6 obtains the polarization images at different polarization angles, performs the analysis and detection of Example 1, generates a drive control signal according to the analysis result and sends it to the drive control module 5, and the drive control module 5 converts the drive control signal into an electrical signal of the rotation angle corresponding to the focusing motor 2.1, and controls the focusing motor 2.1 to rotate the corresponding angle.

[0041] In addition, the imaging lens 1 includes an optical lens group 1.1 for imaging; the imaging lens 1 includes an ultraviolet lens, a visible light lens and an infrared lens; wherein the connection type of the visible light lens is a C-type interface or a CS-type interface.

[0042] In the description of the embodiments of the present application, it should be noted that in the description of the present application, terms such as "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is only for the convenience of description, and does not indicate or imply that the device or component must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present application.

[0043] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0044] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. An automatic defocus polarization imaging method for target detection, characterized in that: include: Step 1: collect the polarization camera at different polarization angles at the initial focal depth position. Polarization image, calculate the Stokes parameter image at the initial focal depth position and the average gradient ; Step 2, presetting the direction, coarse adjustment step and fine adjustment step of the polarization camera's automatic focusing, the polarization camera performs coarse adjustment and fine adjustment based on the initial focal depth position, and compares the average gradient values ​​after coarse adjustment and fine adjustment to obtain the optimal positive focus position of the polarization camera; Step 3: Calculate the Stokes parameter image of the polarization camera at the optimal positive focus position , from the Stokes parameter image Stokes first parameter image in Select the target area and background area, and calculate the optimization function value of the target area and background area ; Step 4, presetting the direction, coarse adjustment step length and fine adjustment step length of the polarization camera automatic focusing, the polarization camera performs coarse adjustment and fine adjustment based on the optimal positive focus position, and compares the optimization function values ​​after coarse adjustment and fine adjustment to obtain the optimal defocus position of the polarization camera; Step 5: The polarization camera collects the images at different polarization angles at the optimal defocus position. Polarization image, calculate the Stokes parameter image at the optimal defocus position ; Step 6: Stokes parameter image Stokes second parameter image in and Stokes third parameter image Perform anomaly detection and detect the optimal target area.

2. The automatic defocus polarization imaging method for target detection according to claim 1, characterized in that: The Stokes parameter image at the initial focal depth position is calculated in step 1 and the average gradient Specifically include: Step 101: Calculate the polarization intensity value of each polarization image based on the polarization imaging principle , the calculation formula is: ； In the formula, Represents the polarization angle of the polarization camera; represents the Stokes first parameter image, represents the Stokes second parameter image; represents the Stokes third parameter image; Step 102: based on the polarization intensity value , construct a linear system of equations to solve the Stokes parameter image , the calculation formula is: ； In the formula, Indicates the number of polarization images collected; represents the Stokes fourth parameter image; Step 103, based on the Stokes parameter image Calculate polarization image , the calculation formula is: ； Step 104, calculate the first Stokes parameter image The average gradient value , the calculation formula is: ； In the formula, Represent the first Stokes parameter images respectively The number of rows and columns of pixels in the Represents the coordinates of the pixel.

3. The automatic defocus polarization imaging method for target detection according to claim 1, characterized in that: The step 2 specifically includes: Step 201, preset the step length of coarse adjustment to ; Preset parameters , The initial value of is 1; Step 202: The polarization camera is forward-focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Then, the polarization camera is focused forward to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Step 203, determine whether If yes, then go to step 204, if no, then , proceed to step 206; Step 204, determine whether If yes, it means that the current focusing direction is wrong, and the process goes to step 205; if no, the polarization camera returns to the initial focal depth position. , and return to step 202; Step 205: the polarization camera returns to the initial focal depth position. The polarization camera is reversely focused based on the initial focal depth position. Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Then, the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Return to step 203; Step 206, determine whether If yes, it means the current focus direction is correct. , and return to step 202; if not, then , The corresponding focal depth position is the suboptimal focal depth position. The polarization camera is adjusted to the suboptimal focal depth position, and the average gradient value corresponding to the suboptimal focal depth position is calculated. , and proceed to step 207; Step 207, preset fine-tuning step length is , preset parameters , The initial value of is 1; Step 208: The polarization camera is forward-focused to the suboptimal focal depth position. Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Then, the polarization camera is focused forward to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Step 209, determine whether If yes, go to step 210; if no, then , proceed to step 212; Step 210, determine whether If yes, it means the current focusing direction is wrong, and the process goes to step 211; if no, the polarization camera returns to the suboptimal focal depth position. , return to step 208; Step 211, the polarization camera returns to the suboptimal focal depth position. , the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth position and the average gradient ; Then, the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and the average gradient ; Return to step 209; Step 212, determine whether If yes, it means the current focus direction is correct. , and return to step 208; if not, then , The corresponding focal depth position is the optimal positive focus position, and the polarization camera is adjusted to the optimal positive focus position.

4. The automatic defocus polarization imaging method for target detection according to claim 1, characterized in that: In step 3, the optimization function values ​​of the target area and the background area are calculated. , the calculation formula is: ； In the formula, represents the target area expectation, represents the background area expectation, represents the target region covariance, represents the background area covariance.

5. The automatic defocus polarization imaging method for target detection according to claim 4, characterized in that: Target area expectations The calculation formula is: ； In the formula, Represents the total number of pixels in the target area, Indicates the target area The pixel value of a pixel; Background area expectations The calculation formula is: ； Target region covariance The calculation formula is: ； Background area covariance The calculation formula is: ； In the formula, is the vector transpose symbol, Indicates Pixels and background area expectation The transpose of the difference.

6. The automatic defocus polarization imaging method for target detection according to claim 1, characterized in that: The step 4 specifically includes: Step 401: Preset the step length of coarse adjustment , preset parameters , The initial value of is 1; Step 402: The polarization camera is forward-focused to the optimal positive focus position. Depth of focus position, calculation Stokes first parameter image at and optimize the function value ; Then, the polarization camera is focused forward to the optimal positive focus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Step 403, determine whether If yes, then go to step 404, if no, then , proceed to step 406; Step 404, determine whether If yes, it means the current focusing direction is wrong, and the process goes to step 405; if no, the polarization camera returns to the optimal positive focus position. , return to step 402; Step 405: the polarization camera returns to the optimal positive focus position. The polarization camera is reversely focused based on the optimal positive focus position. Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is reversely focused to Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Return to step 403; Step 406, determine whether If yes, it means the current focus direction is correct. , and return to step 402; if not, then , The corresponding focal depth position is the suboptimal defocus position. The polarization camera is focused to the suboptimal defocus position, and the optimization function value corresponding to the suboptimal defocus position is calculated. , proceed to step 407; Step 407: Preset the fine-tuning step size , preset parameters , The initial value of is 1; Step 408: The polarization camera is forward-focused to the suboptimal defocus position. Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is focused forward based on the suboptimal defocus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Step 409, determine whether If yes, then go to step 410; if no, then , proceed to step 412; Step 410, determine whether If yes, it means the current focusing direction is wrong, and the process goes to step 411; if no, the polarization camera returns to the suboptimal defocus position. , return to step 408; Step 411, the polarization camera returns to the suboptimal defocus position. , the polarization camera is reversed to focus based on the suboptimal defocus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Then, the polarization camera is reversed to focus based on the suboptimal defocus position Depth of focus position, calculation Stokes first parameter image at the focal depth and optimize the function value ; Return to step 409; Step 412, determine whether , if yes, then the current focus direction is correct, , return to step 408; if not, then , The corresponding focal depth position is the optimal defocus position, and the polarization camera is focused to the optimal defocus position.

7. The automatic defocus polarization imaging method for target detection according to claim 1, characterized in that: In step 6, the RX anomaly detection method is adopted, and the RX anomaly detection operator is: ； In the formula, represents the pixel to be detected; is the expectation for the background area; represents the background covariance matrix.

8. An automatic defocusing polarized light imaging system for target detection, characterized in that: The invention comprises an imaging lens (1), an automatic focusing component (2), a polarizing device (3), an imaging detector (4), a driving control module (5), and an image acquisition and processing module (6); the imaging lens (1) is connected to the imaging detector (4); the automatic focusing component (2) is arranged on the imaging lens (1) to drive and adjust the zoom ratio and focus of the imaging lens (1); the polarizing device (3) is located between the imaging lens (1) and the imaging detector (4) to separate and extract polarization information of incident light; the axis of the imaging lens (1), the axis of the polarizing device (3) and the optical axis of the imaging detector (4) are coaxially arranged; the polarizing device (3) is electrically connected to the imaging detector (4) to receive polarization information of incident light. The optical signal passing through the imaging lens (1) and the polarization device (3) is converted into an electrical signal to collect a polarization image of the target scene; the image acquisition and processing module (6) is electrically connected to the imaging detector (4) to generate a driving control signal of the automatic focusing component (2) by performing the automatic defocusing polarization imaging method for target detection according to any one of claims 1 to 7; the image acquisition and processing module (6) is electrically connected to the driving control module (5), and the driving control module (5) is electrically connected to the automatic focusing component (2) to send the driving control signal to the driving control module (5) to generate a driving control signal of the automatic focusing component (2) to drive the automatic focusing component (2) to focus the imaging lens (1).

9. The automatic defocus polarized light imaging system for target detection according to claim 8, characterized in that: The automatic focusing assembly (2) comprises a focusing motor (2.1), a mounting base (2.2) and a rotating base (2.3); the rotating base (2.3) is arranged around the outer wall of the imaging lens (1); the rotating base (2.3) is linked with the optical lens group (1.1) and is used to drive the optical lens group (1.1) to move; gear teeth (2.4) are provided on the outer peripheral wall of the rotating base (2.3); the mounting base (2.2) is fixed on the outer wall of the optical lens; the focusing motor (2.1) is fixed on the mounting base (2.2); the output end of the focusing motor (2.1) is connected to a focusing gear (2.5); the focusing gear (2.5) is meshed with the gear teeth (2.4) on the outer peripheral wall of the rotating base (2.3); and the focusing motor (2.1) is electrically connected to a drive control module (5).

10. The automatic defocus type polarized light imaging system for target detection according to claim 8, characterized in that: The imaging lens (1) comprises an optical lens group (1.1) for imaging; the imaging lens (1) comprises an ultraviolet lens, a visible light lens and an infrared lens; wherein the connection type of the visible light lens is a C-type interface or a CS-type interface.

Images