CN115393441B - A high-precision extraction and positioning method of light spots based on liquid crystal optical closed-loop system - Google Patents

Abstract

The invention relates to a high-precision spot extraction and positioning method based on a liquid crystal optical closed-loop system, comprising the following steps: S1: filtering the collected original diffraction spot image; S2: thresholding and outputting the processed spot image Image; S3: carry out opening operation to the image output in S2; S4: carry out horizontal scanning and longitudinal scanning to the image after opening operation, find the area where target spot is located; S5: according to the area where target spot is located obtained in S4 , extract the edge contour line of the target spot saturation plane area in the processed image in S2, and perform Gaussian cross-section fitting on the extracted edge contour line, obtain the distribution expression of the edge pixel points, and use the expression as the objective function Carrying out the least squares fitting, and obtaining the center coordinates of the spot by calculation, compared with other extraction and positioning methods, the present invention has a faster calculation speed under the premise of ensuring high precision.

Description

A high-precision extraction and positioning method of light spots based on liquid crystal optical closed-loop system

technical field

The invention relates to the technical field of space laser communication, in particular to a method for high-precision extraction and positioning of light spots based on a liquid crystal optical closed-loop system.

Background technique

A typical wireless laser communication system mainly includes a terminal transmitting and receiving system and an APT beam control system. At the transmitting end, the signal to be sent is encoded by the encoder and then sent to the modulator. The modulation circuit converts the encoded data into a corresponding voltage signal. The modulated signal is loaded on the semiconductor laser after passing through the automatic power control system. A modulated light beam is emitted through an optical transmit antenna with a very small beam spread. At the receiving end, the optical receiving antenna collects the signal light in free space. After the beam passes through the beam splitting system, part of the beam is transmitted to the APT system, and the other part of the beam is transmitted to the signal receiving detector. The APT system uses the beam position error as feedback to realize the capture, alignment and tracking functions of the beam; on the other hand, the optical signal is converted into an electrical signal through the photoelectric detection system, and the baseband signal is restored through the demodulation circuit, and finally the original signal is output through the decoder. In the traditional APT system, the position of the beam is adjusted by using piezoelectric ceramics to drive the Fast Steering Mirror (FSM). In the traditional piezoelectric ceramic drive method, the bandwidth of this mechanical servo control method can only reach the order of tens to hundreds of hertz. In order to solve this problem, researchers have proposed a non-mechanical servo control method, which is suitable for larger bandwidth magnitude, larger vibration amplitude and higher frequency range.

The closed-loop system of liquid crystal spatial light modulator is a typical non-mechanical servo control system. The liquid crystal spatial light modulator has an electronically controlled birefringence effect, and the beam can be deflected by changing the voltage. The simplified model of the system composed of the liquid crystal spatial light modulator is shown in Figure 1. After the laser beam passes through the laser, polarizer, and beam splitter, and travels a certain distance in space, the beam hits the liquid crystal spatial light modulator. After the beam passes through the liquid crystal spatial light modulator, it will produce Bragg diffraction effect, and multiple diffraction spots After being accepted by the CCD camera, the horizontal "line" is arranged in the image. Extract and locate the +1st-order diffraction spot with the largest energy to obtain its spatial position; then feed back the spatial position to the servo system, so that the voltage applied to the liquid crystal spatial light modulator changes, and then changes the position of the spot to align it with the wireless laser communication system receiver. The diffraction spot image collected by the CCD camera is shown in Figure 2. A series of light spots are arranged horizontally in the image, and the light spots around the +1 order diffraction spot gradually become smaller as the distance increases.

Regarding the extraction of a specific spot from multiple spots, there is a lack of relevant literature at home and abroad. According to the energy characteristics of the extracted light spot required by the closed-loop system of the liquid crystal spatial light modulator, it can be known that the target light spot to be extracted has the maximum energy. The spot with the largest energy occupies the largest sum of gray levels and the largest area in the image captured by the CCD. Therefore, the common methods are to extract the connected domain and then select the largest connected domain, and to extract the target edge contour and then select the longest contour. However, extracting the largest connected domain requires 2 traversals to mark each connected domain in the image, and then select it, and it is also difficult in hardware implementation. Extracting the longest edge profile also requires extracting the spot profiles one by one and then comparing them to obtain the maximum spot.

The beam in the wireless laser communication system belongs to the laser, and the predecessors have proposed many methods for the extraction of the laser spot for reference. One is the method based on the gray value, among which the gray centroid method and the Gaussian surface fitting method are more representative; the other is the method based on the edge, the more common ones are the circle fitting method, the ellipse fitting method, the Hough Transformation method and its improvement method. In this paper, there are burrs and irregular edges in the laser spot profile. When using the edge-based method to calculate the center, it is inevitable to introduce error points in the residual item; at the same time, because the energy distribution of the laser spot conforms to the Gaussian distribution, the method based on the gray value can be very fast. It fits the energy distribution characteristics well. Among them, the Gaussian surface fitting method can best fit the characteristics of Gaussian distribution. However, because the laser energy is too high, the light spots captured by the CCD camera have a gray value saturation phenomenon in the central area, and the simple Gaussian surface fitting cannot collect enough sample points, which will introduce errors, and the calculation of this method is too large, which will lead to greater delay. time.

Contents of the invention

Therefore, the technical problem to be solved by the present invention is to overcome the defect that the simple Gaussian surface fitting in the prior art cannot collect enough sample points, which will introduce errors and the method will introduce a larger delay time if the amount of calculation is too large, so as to provide High-precision extraction and positioning method of light spot based on liquid crystal optical closed-loop system.

A method for high-precision extraction and positioning of light spots based on a liquid crystal optical closed-loop system, comprising the following steps:

S1: Carry out median filter processing to the original diffraction spot image collected by CCD;

S2: performing threshold segmentation on the spot image processed by the median filter by an iterative method and outputting the image;

S3: carry out opening operation to the image output in S2;

S4: horizontal scanning and vertical scanning are carried out to the image after the opening operation, to find the connected region with the largest horizontal and vertical span, that is, the region where the target spot is located;

S5: According to the area where the target spot is located obtained in S4, extract the edge contour line of the target spot saturation plane area in the image after median filtering in S2, and perform Gaussian section line fitting to the extracted edge contour line, edge pixels The point distribution expression is:

；

;

Among them: x and y are the horizontal and vertical coordinates of the pixel in the image, x ₀ and y ₀ are the spatial positions of the vertices of the Steinian surface, δ _x and δ _y are the variance of the Gaussian surface function, and A is the amplitude;

Use the above expression as the objective function to perform least square fitting to find x ₀ and y ₀ , and (x ₀ , y ₀ ) are the center coordinates of the desired spot.

Further, the iterative method in the step S2 performs threshold segmentation and the specific steps are:

S2.1: select an initial threshold T ₀ ;

S2.2: Utilize the threshold T0 to divide the image into two parts, and the image gray levels of the two parts are R1 and R2 respectively;

S2.3: Calculate the mean value of R1 and the mean value of R2, denoted as μ ₁ and μ ₂ respectively;

；S2.4: Select a new threshold T, and

;

S2.5: If the absolute value of the difference between T and T0 is less than the preset value, then T is the final threshold, otherwise set T ₀ =T and repeat steps S2.2-S2.5.

Further, the specific steps of scanning the image horizontally in the step S4 are:

S4.1.1: Scan the first line of the image, record the number of points with a pixel value of 1 in this line, and push it into the stack;

S4.1.2: traverse all rows, and repeat the step of scanning the first row in step S4.1.1 for other rows;

S4.1.3: Read out the elements in the stack one by one, and record the order of reading;

S4.1.4: Find the sequence that can continuously read out the longest non-zero value, and the readout sequence of the sequence corresponds to the row position of the main light spot.

Further, the specific steps of vertically scanning the image in the step S4 are:

S4.2.1: Scan the first column of the image, record the number of points with a pixel value of 1 in this column, and push it into the stack;

S4.2.2: traverse all columns, and repeat the step of scanning the first column in step S4.2.1 for other rows;

S4.2.3: Read out the elements in the stack one by one, and record the order of reading;

S4.2.4: Find the sequence that can continuously read out the longest non-zero value, and the readout sequence of the sequence corresponds to the column position of the main light spot.

Further, the initial threshold T ₀ is an average value of the maximum gray value and the minimum gray value in the image.

Further, the preset value is 0.1.

An electronic device includes a memory and a processor, the memory stores a computer program, and the processor implements the steps of any one of the methods described above when executing the computer program.

A computer-readable storage medium is used for storing computer instructions, and when the computer instructions are executed by a processor, the steps of any one of the methods described above are implemented.

The technical solution of the present invention is suitable for spot extraction in a closed-loop system based on liquid crystal space light. Compared with other extraction and positioning methods, it has a faster calculation speed under the premise of ensuring high precision, and is logically more suitable for hardware environments. accomplish.

Description of drawings

In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the specific embodiments or prior art. Obviously, the accompanying drawings in the following description The drawings show some implementations of the present invention, and those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a simplified model diagram of a system composed of a liquid crystal spatial light modulator;

Figure 2 is a diffraction spot image;

Figure 3 is a schematic diagram of the spot extraction results;

Figure 4 is a three-dimensional diagram of the energy distribution of the +1 order diffraction spot;

Figure 5 is the outline of the peak of the +1-level spot.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Apparently, the described embodiments are some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" etc. The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, or in a specific orientation. construction and operation, therefore, should not be construed as limiting the invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and should not be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that unless otherwise specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection. Connected, or integrally connected; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediary, and it can be the internal communication of two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention in specific situations.

In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as there is no conflict with each other.

A method for high-precision extraction and positioning of light spots based on a liquid crystal optical closed-loop system, comprising the following steps:

S1: Perform median filter processing on the original diffraction spot image collected by the CCD to eliminate the influence of single-pixel noise and achieve the effect of filtering;

S2: performing threshold segmentation on the spot image processed by the median filter by an iterative method and outputting the image;

S3: open operation is carried out to the image output in S2; In the light spot image that obtains with iterative method, there are still a series of burrs around the light spot, which is unfavorable for subsequent accurate extraction of light spots, so the present invention adds after threshold segmentation The operation of opening operation eliminates the burr edges around the spot without significantly changing the area of the spot;

S4: The basic idea of the light spot extraction in the present invention is to use the light spots to present a horizontal distribution, and the target light spot has the characteristics of the highest energy and the largest area, so the image after the opening operation is scanned horizontally and vertically to find the horizontal and vertical For the connected area with the largest span, after two scans, find the coordinate range with the largest span in the two directions, which is the location of the target spot. The result of spot extraction is shown in Figure 3;

The spot to be extracted in the present invention is a laser spot, and the ideal laser spot energy distribution presents a Gaussian distribution, but after the diffraction spot in this system is collected by a CCD camera, due to the saturation of the photosensitive element of the CCD camera, the pixel values in the center of the spot are all Displayed as maximum pixel value. As shown in Figure 4, it can be seen from the figure that the energy of the diffraction spot is cut off at the peak to form a plane due to saturation.

The spot in Figure 3 can be positioned using the Gaussian surface fitting method, and the functional formula of the spot energy distribution is as follows:

（1），

(1),

In the above formula, ƒ(x, y) represents the energy of the spot, which is the gray value of the pixel in the image, x and y are the horizontal and vertical coordinates of the pixel in the image, and x ₀ and y ₀ are the vertices of the Si surface The spatial position, δx and δy are the variance of the Gaussian surface function, and A is the amplitude;

However, the accuracy of the reduction of sample points will be lower than the extraction effect of the complete spot, and the Gaussian surface fitting method needs to bring in a large number of sample points. For this reason the present invention is aimed at this situation, has proposed the fitting method of Gaussian section line, the pixel value at the top plane place in Fig. Curve, the spatial position of each point on the closed curve is different, but the gray value is 255. This method has high precision and greatly reduces the number of sample points required for fitting, while taking into account both precision and efficiency, specifically as in step S5;

S5: According to the area where the target light spot is located in S4, extract the edge contour line of the target light spot saturation plane area in the image after median filtering in S2, specifically: traverse the space area where the target light spot is located, and search for a value less than 255 The adjacent pixel value of the pixel is 255, and the extracted contour is shown in Figure 5;

Gaussian section line fitting is performed on the extracted edge contour, and the distribution expression of edge pixels is:

（2），

(2),

A, δx, δy, x ₀ and y ₀ are undetermined parameters, and formula (2) is used as the objective function to perform least square fitting to find x ₀ and y ₀ , (x ₀ , y ₀ ) is the desired Spot center coordinates.

In order to facilitate the calculation, we express the formula (2) in logarithmic form, and get the formula (3), as follows:

（3），

(3),

Formula (3) can be expressed in the form of quadratic polynomial after further transformation, as shown in formula (4). Converting a function into a polynomial form of expression has many advantages, especially after the derivative and partial derivative of the function are obtained, the result is still in the form of a polynomial, which is conducive to the combination of items and simplifies the calculation process;

（4），

(4),

The expressions of a, b, c, d and e are shown in the following formula (5):

（5），

(5),

a, b, c, d and e are the unknowns to be solved, and after they are calculated, the center coordinates (x ₀ , y ₀ ) of the light spot can be calculated according to the formula (5).

The least squares solution is used to minimize the sum of squares of the residual, and the expression of the sum of squares of the residual is shown in formula (6):

（6），

(6),

The summation range in the above formula is a circle of pixels around the saturated part of the light spot, which is the outline obtained in Figure 5. x and y are the spatial positions of the peripheral pixels, which are brought in as known data.

According to the minimum value condition, calculate the partial derivative of each variable and make it 0, and then perform the transposition to obtain the equation group (7), as follows:

（7），

(7),

Equation (7) can be further written in the form of matrix, as shown in formula (8):

（8），

(8),

The matrix expressions of B, K, and C are shown in formulas (9), (10) and (11), respectively, as follows:

（9），

(9),

（10），

(10),

（11），

(11),

The values of a series of parameters a, b, c, d and e can be obtained by using the spatial coordinates of the intercepted edge pixels and the expression (9), and finally the center coordinates of the spot (x ₀ , y ₀ ).

In the step S2, the iterative method performs threshold segmentation and the specific steps are:

S2.1: select an initial threshold T ₀ ;

S2.2: Utilize the threshold T ₀ to divide the image into two parts, and the image gray levels of the two parts are R1 and R2 respectively;

S2.3: Calculate the mean value of R1 and the mean value of R2, denoted as μ ₁ and μ ₂ respectively;

；S2.4: Select a new threshold T, and

;

S2.5: If the absolute value of the difference between T and T ₀ is less than the preset value, then T is the final threshold, otherwise set T ₀ =T and repeat steps S2.2-S2.5.

The specific steps of horizontally scanning the image in the step S4 are:

S4.1.1: Scan the first line of the image, record the number of points with a pixel value of 1 in this line, and push it into the stack;

S4.1.2: traverse all rows, and repeat the step of scanning the first row in step S4.1.1 for other rows;

S4.1.3: Read out the elements in the stack one by one, and record the order of reading;

S4.1.4: Find the sequence that can continuously read out the longest non-zero value, and the readout sequence of the sequence corresponds to the row position of the main light spot.

The specific steps of vertically scanning the image in the step S4 are:

S4.2.1: Scan the first column of the image, record the number of points with a pixel value of 1 in this column, and push it into the stack;

S4.2.2: traverse all columns, and repeat the step of scanning the first column in step S4.2.1 for other rows;

S4.2.3: Read out the elements in the stack one by one, and record the order of reading;

S4.2.4: Find the sequence that can continuously read out the longest non-zero value, and the readout sequence of the sequence corresponds to the column position of the main light spot.

The initial threshold T ₀ is the mean value of the maximum gray value and the minimum gray value in the image.

The preset value is 0.1.

The present invention also includes an electronic device, including a memory and a processor, the memory stores a computer program, and the processor implements the steps of any one of the methods described above when executing the computer program.

The present invention also includes a computer-readable storage medium for storing computer instructions, and when the computer instructions are executed by a processor, the steps of any one of the methods described above.

The memory in the embodiments of the present application may be a volatile memory or a nonvolatile memory, or may include both volatile and nonvolatile memories. Among them, the non-volatile memory can be read only memory (read only memory, ROM), programmable read only memory (programmable ROM, PROM), erasable programmable read only memory (erasable PROM, EPROM), electrically erasable Programmable read-only memory (electrically EPROM, EEPROM) or flash memory. Volatile memory can be random access memory (RAM), which acts as external cache memory. By way of illustration and not limitation, many forms of RAM are available, such as static random access memory (static RAM, SRAM), dynamic random access memory (dynamic RAM, DRAM), synchronous dynamic random access memory (synchronous DRAM, SDRAM ), double data rate synchronous dynamic random access memory (double data rate SDRAM, DDRSDRAM), enhanced synchronous dynamic random access memory (enhanced SDRAM, ESDRAM), synchronous connection dynamic random access memory (synchlink DRAM, SLDRAM) and Direct memory bus random access memory (direct rambusRAM, DR RAM). It should be noted that the memory of the methods described herein is intended to include, but not be limited to, these and any other suitable types of memory.

In the above embodiments, all or part of them may be implemented by software, hardware, firmware or any combination thereof. When implemented using software, it may be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer instructions are loaded and executed on the computer, the processes or functions according to the embodiments of the present application will be generated in whole or in part. The computer can be a general purpose computer, a special purpose computer, a computer network, or other programmable devices. The computer instructions may be stored in or transmitted from one computer-readable storage medium to another computer-readable storage medium, for example, the computer instructions may be transmitted from a website, computer, server or data center Transmission to another website site, computer, server, or data center by wired (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.). The computer-readable storage medium may be any available medium that can be accessed by a computer, or a data storage device such as a server or a data center integrated with one or more available media. The available medium may be a magnetic medium (for example, a floppy disk, a hard disk, a magnetic tape), an optical medium (for example, a high-density digital video disc (digital video disc, DVD)), or a semiconductor medium (for example, a solid state disk (solid state disc, SSD)) etc.

In the implementation process, each step of the above method can be completed by an integrated logic circuit of hardware in a processor or an instruction in the form of software. The steps of the methods disclosed in connection with the embodiments of the present application may be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules in the processor. The software module can be located in a mature storage medium in the field such as random access memory, flash memory, read-only memory, programmable read-only memory or electrically erasable programmable memory, register. The storage medium is located in the memory, and the processor reads the information in the memory, and completes the steps of the above method in combination with its hardware. To avoid repetition, no detailed description is given here.

It should be noted that the processor in the embodiment of the present application may be an integrated circuit chip, which has a signal processing capability. In the implementation process, each step of the above-mentioned method embodiments may be completed by an integrated logic circuit of hardware in a processor or instructions in the form of software. The above-mentioned processors may be general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components . Various methods, steps, and logic block diagrams disclosed in the embodiments of the present application may be implemented or executed. A general-purpose processor may be a microprocessor, or the processor may be any conventional processor, or the like. The steps of the method disclosed in connection with the embodiments of the present application may be directly implemented by a hardware decoding processor, or implemented by a combination of hardware and software modules in the decoding processor. The software module can be located in a mature storage medium in the field such as random access memory, flash memory, read-only memory, programmable read-only memory or electrically erasable programmable memory, register. The storage medium is located in the memory, and the processor reads the information in the memory, and completes the steps of the above method in combination with its hardware.

The invention is suitable for spot extraction in a closed-loop system based on liquid crystal space light. Compared with other extraction and positioning methods, the invention has faster calculation speed under the premise of ensuring high precision.

Apparently, the above-mentioned embodiments are only examples for clear description, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (8)

1. A light spot high-precision extraction positioning method based on a liquid crystal light closed-loop system is characterized by comprising the following steps:

s1, performing median filtering processing on an original diffraction spot image acquired by a CCD (charge coupled device);

s2, performing threshold segmentation on the light spot image subjected to median filtering by an iteration method and outputting the image;

s3, performing open operation on the image output in the S2;

s4, performing transverse scanning and longitudinal scanning on the image subjected to the opening operation, and searching a connected region with the largest transverse and longitudinal spans, namely a region where the target light spot is located;

s5, according to the area where the target light spot is obtained in the S4, extracting an edge contour line of a target light spot saturated plane area in the image subjected to median filtering in the S2, specifically: traversing the spatial region where the target light spot is located, finding out the pixel point with the pixel value of 255 adjacent to the pixel point smaller than 255, and performing Gaussian sectional fitting on the extracted edge contour line, wherein the distribution expression of the edge pixel point is as follows:

wherein: x and y are the horizontal and vertical coordinates of the pixel points in the image, x ₀ And y ₀ Is the spatial position of the vertex of the sigmoid, delta _x And delta _y Is the variance of the Gaussian surface function, and A is the amplitude;

A、δx、δy、x ₀ and y ₀ For undetermined parameters, performing least square fitting by taking a distribution expression of edge pixel points as a target function to obtain x ₀ And y ₀ ，x ₀ ，y ₀ The coordinate of the light spot center is obtained;

expressing the distribution expression of the edge pixel points in a logarithmic mode, wherein the logarithmic expression is as follows:

expressing the logarithmic expression in the form of a quadratic polynomial, wherein the quadratic polynomial is specifically as follows:

ln ²⁵⁵ ＝ax ² +by ² +cx+by+e，

wherein the expressions of a, b, c, d and e are specifically as follows:

a. b, c, d and e are unknowns to be solved, and then the central coordinate x of the light spot is solved according to the expression of a, b, c, d and e ₀ ，y ₀ ；

And solving by using least squares to minimize the sum of squares of the residuals, wherein the expression of the sum of squares of the residuals is as follows:

Q＝∑(ax ² +by ² +cx+dy+e-ln ²⁵⁵ ) ² ，

the summation range in the residual square sum expression is a circle of pixel points at the periphery of the saturated part of the light spot, and x and y are the spatial positions of the peripheral pixel points and are taken as known data to be brought in;

according to the minimum condition, calculating the partial derivative of each variable and making the partial derivative be 0, and then performing item shifting to obtain an equation set, wherein the equation set is as follows:

writing the equation set into an expression form of a matrix, wherein the matrix is specifically as follows:

BK＝C

BK＝C，

wherein the matrix expressions of B, K and C are respectively as follows:

the values of parameters a, B, c, d and e are solved by using the intercepted space coordinates of the edge pixel points and the matrix expression of B, and finally the central coordinate x of the light spot is solved according to the expressions of a, B, c, d and e ₀ ，y ₀ 。

2. The method according to claim 1, wherein the iterative threshold segmentation in step S2 specifically comprises the steps of:

s2.1 selecting an initial threshold T ₀ ；

S2.2 Using threshold T ₀ Dividing an image into two parts, wherein the gray scales of the two parts are R1 and R2 respectively;

s2.3 calculating the mean value of R1 and R2, respectively denoted as mu ₁ And mu ₂ ；

S2.4, selecting a new threshold value T, and

s2.5 if T and T ₀ If the absolute value of the difference is smaller than the preset value, T is the final threshold value, otherwise T is enabled ₀ T and repeat steps S2.2-S2.5.

3. The method according to claim 1, wherein the step S4 of scanning the image laterally comprises the following specific steps:

s4.1.1: scanning a first line of the image, recording the number of points with pixel values of 1 in the line, and pressing the points into a stack;

s4.1.2: traversing all the rows, and repeating the step of scanning the first row in the step S4.1.1 for other rows;

s4.1.3: reading elements in the stack one by one, and recording the reading sequence;

s4.1.4: the sequence with the longest non-zero values that can be read out continuously is found, and the reading order of the sequence corresponds to the row position of the main spot.

4. The method according to claim 1, wherein the step S4 of longitudinally scanning the image comprises the following specific steps:

s4.2.1: scanning a first column of the image, recording the number of points with the pixel value of 1 in the column, and pressing the points into a stack;

s4.2.2: traversing all columns, repeating the step of scanning the first column in step S4.2.1 for other rows;

s4.2.3: reading elements in the stack one by one, and recording the reading sequence;

s4.2.4: the longest sequence of non-zero values that can be read out continuously is found, the read-out order of the sequence corresponding to the column position of the main spot.

5. Method according to claim 2, characterized in that said initial threshold T is ₀ Is the average of the maximum and minimum gray values in the image.

6. The method according to claim 2, characterized in that said preset value is 0.1.

7. An electronic device comprising a memory and a processor, the memory storing a computer program, wherein the processor, when executing the computer program, performs the steps of the method according to any of claims 1-6.

8. A computer-readable storage medium storing computer instructions, which when executed by a processor implement the steps of the method of any one of claims 1 to 6.

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