A scattering lens zoom method based on optical transmission matrix

Abstract

The present invention relates to a scattering lens zoom method based on an optical transmission matrix. The method comprises the following steps: (1) obtaining prior data: given the position of a scattering lens reference surface, obtaining an optical transmission matrix that can achieve focusing on the reference surface; (2) establishing a light field inversion model: establishing a light field inversion model between a target surface and a reference surface, obtaining an inverted light field of the reference surface; selecting a portion of interest as a feature region based on the difference in light field intensity distribution; (3) fast-converging phase recovery iteration: obtaining the modulated light field phase through fast-converging phase recovery iteration, completing a zoom operation; (4) establishing a zoom model: loading the light field phase obtained by the zoom algorithm through a spatial light modulator to achieve beam focusing at a desired depth; changing the focus depth, repeatedly zooming to achieve light focusing at different depths, and establishing a scattering lens zoom model. The present invention is beneficial for improving the accuracy of zoom light field wavefront recovery and the focal intensity after zooming, and achieving fast spatial zooming.

Description

Technical Field

[0001] The present invention belongs to the technical field of scattering imaging, and in particular relates to a scattering lens zoom method based on an optical transmission matrix. Background Art

[0002] Scattering media are ubiquitous substances in nature, such as turbid atmosphere, smoke, and biological tissue. When a coherent light beam passes through a scattering medium, it is affected by random scattering. Particles in the medium alter the propagation direction of the photons, causing the transmission direction to deviate from the original input direction and become chaotic. This causes severe distortion of the wavefront, resulting in a granular intensity pattern. Only a speckle pattern is detected on the observation surface, making it difficult to observe or image the target. This has a significant impact on medical diagnosis, complex driving environments, fire rescue, and deep-sea exploration.

[0003] In computational optical imaging, the optical transfer matrix characterizes the transformation of the incident light field into the outgoing light field after it passes through a scattering medium. Combined with optimization methods such as reconstruction and image restoration algorithms, focusing can be achieved at any position and at any time. However, in traditional focusing through scattering media based on a transfer matrix, the focal intensity decreases significantly with even slight increases in distance, necessitating re-measurement of the transfer matrix to achieve effective focusing. Consequently, these traditional methods suffer from shortcomings such as shallow depth of focus, long time consumption, and low efficiency, making them unable to meet the requirements for rapid spatial zooming. To address this issue, a fast and effective scattering lens zoom method based on a transfer matrix is ​​proposed, which has application value in optical imaging and therapy through biological tissue. Summary of the Invention

[0004] The purpose of the present invention is to provide a scattering lens zoom method based on an optical transmission matrix, which uses angular spectrum diffraction inversion to establish a mathematical model of spatial position and combines iterative phase recovery technology to achieve a fast, time-saving and labor-saving zoom system.

[0005] To achieve the above object, the technical solution of the present invention is: a scattering lens zoom method based on an optical transmission matrix, comprising the following steps:

[0006] Step S1: Given the reference surface position of the scattering lens, a four-step phase-shift interferometry method is used to solve the optical transmission matrix that can achieve focusing on the reference surface;

[0007] Step S2: changing the expected focus depth, deriving a light field inversion model between the target surface and the reference surface according to the light wave propagation law in free space, and obtaining the reference surface inversion light field;

[0008] Step S3: dividing the reference surface into regions according to the intensity distribution difference of the inverted light field of the reference surface, and selecting the portion of interest as the feature region;

[0009] Step S4: using the characteristic region as an amplitude constraint, performing a fast-converging phase recovery iteration with the optical transmission matrix as a forward transformation and the mean square optimization operator as an inverse transformation to obtain the phase of the modulated light field;

[0010] Step S5: Loading the obtained light field phase through a spatial light modulator to achieve light beam focusing at a desired depth;

[0011] Step S6: Change the focus depth and repeat steps S2-S5 to achieve light focusing at different depths, thereby establishing a scattering lens zoom model.

[0012] In one embodiment of the present invention, step S1 is specifically implemented as follows:

[0013] Step S11: constructing a scattering lens zoom optical path system based on an optical transmission matrix, wherein the scattering lens zoom optical path system based on the optical transmission matrix includes: a laser, an attenuator, a beam expander and homogenizer, a polarizer, a liquid crystal spatial light modulator, a filter, an objective lens, a scattering medium, a detector, a displacement platform, and a computer. The detector is moved to a specified position via the displacement platform. The computer is connected to the detector to collect a speckle image. The computer is connected to the liquid crystal spatial light modulator to control the liquid crystal spatial light modulator to generate a desired modulated light field.

[0014] Step S12: Given a scattering lens reference surface Z o , fix the detector position, use the pure phase modulation liquid crystal spatial light modulator to simultaneously generate reference light and control light, and generate N groups of Hadamard basis as the basis vector of measurement;

[0015] Step S13: Keep the phase of the reference light unchanged, and shift the phase of the control light by 0, π / 2, π, and 3π / 2 respectively. According to the modulated light field of the given phase, the detector is used to collect the speckle image formed by the interference of the reference light and the control light, and the corresponding output light intensity I is obtained. 0 , I π / 2 , I π and I 3π / 2 ;

[0016] Step S14: Based on the mathematical relationship of the speckle images obtained by the four-step phase shift, the observation matrix is ​​obtained by solving the equation; wherein the light intensity formula of the m-th output channel is:

[0017]

[0018] Where s m It represents the complex amplitude of the light field generated in the mth channel of the detector after the reference light passes through the scattering medium. For s m The conjugate transpose of represents the nth input light field, determined by the Hadamard basis, Represents a matrix element of the observation matrix;

[0019] Step S15: Filter the observation matrix to obtain the optical transmission matrix T of the scattering lens zoom optical path system based on the optical transmission matrix.

[0020] In one embodiment of the present invention, step S2 is specifically implemented as follows:

[0021] Step S21: Change the expected focus depth by controlling the displacement platform to move the detector from the reference surface position Z o Move to the expected target surface position Z i ;

[0022] Step S22: Based on the laser wavelength λ and the distance Z between the reference surface and the target surface i -Z o The corresponding coordinate system spatial frequency f on the frequency domain spectrum x and f y The transfer function H is established, and the light field inversion formula between the target surface and the reference surface is derived based on the angular spectrum diffraction theory:

[0023] E2=F -1 [F(E3)·H -1 ]

[0024] Where E2 is the reference surface inversion light field, E3 is the target surface output light field, and H -1 Find the inverse matrices for the angular diffraction transfer function, F and F -1 represent Fourier transform and inverse Fourier transform respectively;

[0025] Step S23: setting the expected target surface output light field E3 according to the zoom requirement, and calculating the reference surface light field data using the light field inversion formula.

[0026] In one embodiment of the present invention, in step S3, the reference surface is divided into regions based on the difficulty of restoring the reference surface pattern. Specifically, after obtaining the inverted light field data of the reference surface, the intensity values ​​that are far below the noise level are eliminated. This part is easily submerged by noise during light field restoration, thereby affecting accuracy.

[0027] In one embodiment of the present invention, in step S3, the portion of interest is selected, that is, the region with an intensity value higher than the noise level in the middle of the inverted light field of the reference surface is selected. This region has the greatest impact on the target surface light field and is selected as the feature region.

[0028] In one embodiment of the present invention, step S4 is specifically implemented as follows:

[0029] Step S41, performing singular value decomposition of the transmission matrix and filtering to construct a mean square optimization operator W;

[0030] Step S42: generating a random initial phase;

[0031] Step S43: start iteration, normalize the input phase and amplitude to obtain a complex amplitude input light field;

[0032] Step S44: The input light field is transformed by the optical transmission matrix T and then acts on the scattering lens system to obtain a reference surface light field;

[0033] Step S45: retain the reference surface light field phase distribution, and use the characteristic region as an amplitude constraint condition to calculate and obtain a new constrained reference surface light field;

[0034] Step S46: The constrained reference surface light field is subjected to inverse transformation using the mean square optimization operator W and then acts on the system to obtain a new input light field;

[0035] Step S47: extract the phase information of the new input light field and use it as the input light field phase for the next iteration, and calculate the relative intensity change rate of the focus area of ​​the target surface;

[0036] Step S48: repeat steps S43-S47. When the relative rate of change is less than the threshold, the iteration stops and the final phase of the modulated light field is obtained, thereby establishing a fast-converging iterative phase recovery algorithm.

[0037] In one embodiment of the present invention, in step S5, the obtained light field phase is converted into a grayscale image in the range of 0-255, and the grayscale image is loaded onto the spatial light modulator to generate the expected modulated light field. After passing through the scattering lens system, the light beam is focused at the expected depth, and the detector is moved to the target surface position to observe the focusing effect.

[0038] In one embodiment of the present invention, in step S6, light focusing at different depths is achieved by calculating the transmission matrix of the scattering lens zoom optical path system based on the optical transmission matrix according to the prior data of the reference surface, establishing a connection between the reference surface light field and the modulated light field, and establishing a connection between the light field of the target surface to be focused and the light field of the reference surface through the light field inversion model, indirectly obtaining the modulated light field corresponding to the focused light field of the target surface at different depths, and establishing a scattering lens zoom model.

[0039] The present invention also provides a scattering lens zoom software calculation system based on an optical transmission matrix, comprising a memory, a processor, and computer program instructions stored in the memory and capable of being executed by the processor. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0040] The present invention also provides a computer-readable storage medium on which computer program instructions that can be executed by a processor are stored. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0041] Compared with the existing technology, the present invention has the following beneficial effects: the present invention provides a scattering lens zoom method based on the optical transmission matrix, which can achieve rapid focusing of target surfaces at different depths by only measuring the optical transmission matrix of a reference surface position. This method can reduce the amount of calculation and background noise, speed up data processing, improve inversion accuracy and focus intensity, and does not require additional feedback from the detector. It is simple and easy to implement, and closed-loop control can be achieved through a computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Flowchart of a scattering lens zoom algorithm based on a transfer matrix in a preferred embodiment of the present invention;

[0043] Figure 2 Schematic diagram of the structure of a scattering lens zoom system based on a transmission matrix in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0045] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0046] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0047] like Figure 1 As shown, this embodiment provides a scattering lens zoom method based on a transmission matrix, comprising the following steps:

[0048] Step S1: Given a scattering lens reference surface Z o , the detector position is fixed, and in the single-arm interferometer optical path, a pure phase modulation liquid crystal spatial light modulator is used to simultaneously generate reference light and control light. Within the circular incident light spot, the rectangular part controlled by the modulator accounts for 65% of the area, and the interference reference light area accounts for 35%. N groups of Hadamard bases are generated as the basis vectors of the measurement;

[0049] Step S2: Keep the phase of the reference light unchanged, and shift the phase of the control light by 0, π / 2, π, and 3π / 2 respectively to set the output light field. According to the modulated light field with a given phase, a detector is used to collect the speckle image formed by the interference of the reference light and the control light, and the corresponding output light intensity I is obtained. 0 , I π / 2 , I π and I 3π / 2 ;

[0050] Step S3: Based on the mathematical relationship of the speckle image obtained by the four-step phase shift, the observation matrix is ​​obtained. The light intensity formula of the m-th output channel is:

[0051]

[0052] Where s m It represents the complex amplitude of the light field generated in the mth channel of the detector after the reference light passes through the scattering medium. For s m The conjugate transpose of represents the nth input light field, determined by the Hadamard basis, Represents a matrix element of the observation matrix.

[0053] Step S4: filter the observation matrix to obtain the scattering lens system transmission matrix T;

[0054] Step S5, performing singular value decomposition on the transmission matrix and filtering to construct a mean square optimization operator W;

[0055] Step S6: Change the expected focus depth by controlling the displacement platform to move the detector from the reference surface position Z o Move to the expected target surface position Z i ;

[0056] Step S7: Based on the laser wavelength λ and the distance Z between the reference surface and the target surface i -Z o The corresponding coordinate system spatial frequency f on the frequency domain spectrum x and f y The transfer function H is established, and the light field inversion formula between the target surface and the reference surface is derived based on the angular spectrum diffraction theory:

[0057] E2=F -1 [F(E3)·H -1 ]

[0058] Where E2 is the reference surface inversion light field, E3 is the target surface output light field, and H -1 Find the inverse matrices for the angular diffraction transfer function, F and F -1 represent Fourier transform and inverse Fourier transform respectively;

[0059] Step S8, setting the expected target surface output light field E3 according to the zoom requirement;

[0060] Step S9: Calculate the reference surface light field data using the light field inversion formula and analyze the intensity distribution difference;

[0061] Step S10: Divide the reference surface into regions, remove the intensity value regions that are easily submerged by noise, and select the characteristic region with an intensity value higher than the noise level in the middle of the inverted light field of the reference surface as the amplitude constraint condition. This region has the greatest impact on the target surface light field.

[0062] Step S11, generating a random initial phase;

[0063] Step S12: start iteration, normalize the input phase and amplitude to obtain a complex amplitude input light field;

[0064] Step S13, the input light field is transformed by the optical transmission matrix T and then acts on the scattering lens system to obtain the reference surface light field;

[0065] Step S14: retain the reference surface light field phase distribution, and use the selected known feature area as the amplitude constraint condition to replace the original amplitude of the reference surface to calculate and obtain a new constrained reference surface light field;

[0066] Step S15: The constrained reference surface light field is subjected to inverse transformation using the mean square optimization operator W and then acts on the system to obtain a new input light field;

[0067] Step S16: extracting the input light field phase information and using it as the input light field phase for the next iteration;

[0068] Step S17, calculating the relative rate of change of intensity of the focus area of ​​the target surface;

[0069] Step S18, repeating steps S12-S17, when the relative change rate is less than the threshold, the iteration stops, and the final modulated light field phase is obtained;

[0070] Step S19: Convert the light field phase obtained by the phase recovery iterative algorithm into a grayscale image in the range of 0-255, load the grayscale image onto the spatial light modulator to generate the desired modulated light field, and focus the light beam at the desired depth after passing through the scattering lens system. Move the detector to the target surface position to observe the focusing effect.

[0071] Step S20: repeat steps S6-S19 to achieve focusing of target surfaces at different depths and establish a scattering lens zoom model.

[0072] like Figure 2As shown, this embodiment implements the above-mentioned method using a scattering lens zoom system based on a transmission matrix. The system mainly includes a light source, a light field modulation, and a zooming section. Specifically, the system comprises: a laser, an attenuator, a beam expander and homogenizer, a polarizer, a liquid crystal spatial light modulator, a filter, objective lenses (O1, O2), a scattering medium, a detector, a displacement platform, and a computer. The light source uses monochromatic light generated by a continuous laser. The power is attenuated by the attenuator to prevent excessive power from damaging other optical components. The system then undergoes beam expansion, homogenization, and collimation amplification. The output parallel light is incident on the light field modulation section. The polarization state is adjusted by the polarizer, and the spatial light modulator performs wavefront modulation. After filtering, the output uniform parallel light beam is focused by objective lens O1 onto the scattering medium. The scattered light is collected by objective lens O2 and enters the zooming section, where a detector collects a speckle image. The detector is adjusted to a specified position by the displacement platform. The computer is used to program and run a phase recovery iterative algorithm. It is connected to the detector to collect the speckle image and to the spatial light modulator to generate the desired modulated light field, achieving the desired focusing requirements on the target surface at different desired depths, thus achieving a fast and effective spatial zoom effect.

[0073] The present invention also provides a scattering lens zoom software calculation system based on an optical transmission matrix, comprising a memory, a processor, and computer program instructions stored in the memory and capable of being executed by the processor. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0074] The present invention also provides a computer-readable storage medium on which computer program instructions that can be executed by a processor are stored. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0075] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0076] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0077] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0078] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A scattering lens zoom method based on an optical transmission matrix, characterized in that: The following steps are involved: Step S1: Given the reference surface position of the scattering lens, a four-step phase-shift interferometry method is used to solve the optical transmission matrix that can achieve focusing on the reference surface; Step S2: changing the expected focus depth, deriving a light field inversion model between the target surface and the reference surface according to the light wave propagation law in free space, and obtaining the reference surface inversion light field; Step S3: dividing the reference surface into regions according to the intensity distribution difference of the inverted light field of the reference surface, and selecting the portion of interest as the feature region; Step S4: using the characteristic region as an amplitude constraint, performing a fast-converging phase recovery iteration with the optical transmission matrix as a forward transformation and the mean square optimization operator as an inverse transformation to obtain the phase of the modulated light field; Step S5: Loading the obtained light field phase through a spatial light modulator to achieve light beam focusing at a desired depth; Step S6: changing the focus depth, repeating steps S2-S5 to achieve light focusing at different depths, thereby establishing a scattering lens zoom model; Step S1 is specifically implemented as follows: Step S11: constructing a scattering lens zoom optical path system based on an optical transmission matrix, wherein the scattering lens zoom optical path system based on the optical transmission matrix includes: a laser, an attenuator, a beam expander and homogenizer, a polarizer, a liquid crystal spatial light modulator, a filter, an objective lens, a scattering medium, a detector, a displacement platform, and a computer. The detector is moved to a specified position via the displacement platform. The computer is connected to the detector to collect a speckle image. The computer is connected to the liquid crystal spatial light modulator to control the liquid crystal spatial light modulator to generate a desired modulated light field. Step S12: Given a scattering lens reference surface Z o , fix the detector position, use the pure phase modulation liquid crystal spatial light modulator to simultaneously generate reference light and control light, and generate N groups of Hadamard basis as the basis vector of measurement; Step S13: Keep the phase of the reference light unchanged, and shift the phase of the control light by 0, π / 2, π, and 3π / 2 respectively. According to the modulated light field of the given phase, the detector is used to collect the speckle image formed by the interference of the reference light and the control light, and the corresponding output light intensity I is obtained. 0 , I π / 2 , I π and I 3π / 2 ; Step S14: Based on the mathematical relationship of the speckle images obtained by the four-step phase shift, the observation matrix is ​​obtained by solving the equation; wherein the light intensity formula of the m-th output channel is: Where s m It represents the complex amplitude of the light field generated in the mth channel of the detector after the reference light passes through the scattering medium. For s m The conjugate transpose of represents the nth input light field, determined by the Hadamard basis, t mn Represents a matrix element of the observation matrix; Step S15: Filter the observation matrix to obtain the optical transmission matrix T of the scattering lens zoom optical path system based on the optical transmission matrix; Step S2 is specifically implemented as follows: Step S21: Change the expected focus depth by controlling the displacement platform to move the detector from the reference surface position Z o Move to the expected target surface position Z i ; Step S22: Based on the laser wavelength λ and the distance Z between the reference surface and the target surface i -Z o The corresponding coordinate system spatial frequency f on the frequency domain spectrum x and f y The transfer function H is established, and the light field inversion formula between the target surface and the reference surface is derived based on the angular spectrum diffraction theory: E2=F -1 [F(E3)·H -1 ] Where E2 is the reference surface inversion light field, E3 is the target surface output light field, and H -1 Find the inverse matrices for the angular diffraction transfer function, F and F -1 represent Fourier transform and inverse Fourier transform respectively; Step S23: setting the expected target surface output light field E3 according to the zoom requirement, and calculating the reference surface light field data using the light field inversion formula; In step S3, the interesting part selection is to select the intensity value area in the middle of the inverted light field of the reference surface that is higher than the noise level. This part has the greatest impact on the target surface light field and is selected as the feature area.

2. The scattering lens zoom method based on the optical transmission matrix according to claim 1, characterized in that: In step S3, the reference surface is divided into regions based on the difficulty of restoring the reference surface pattern. Specifically, after obtaining the inverted light field data of the reference surface, the intensity values ​​far below the noise level are eliminated. This part is easily submerged by noise during light field restoration, thereby affecting accuracy.

3. The scattering lens zoom method based on optical transmission matrix according to claim 1, characterized in that: Step S4 is specifically implemented as follows: Step S41, performing singular value decomposition of the transmission matrix and filtering to construct a mean square optimization operator W; Step S42: generating a random initial phase; Step S43: start iteration, normalize the input phase and amplitude to obtain a complex amplitude input light field; Step S44: The input light field is transformed by the optical transmission matrix T and then acts on the scattering lens system to obtain a reference surface light field; Step S45: retain the reference surface light field phase distribution, and use the characteristic region as an amplitude constraint condition to calculate and obtain a new constrained reference surface light field; Step S46: The constrained reference surface light field is subjected to inverse transformation using the mean square optimization operator W and then acts on the system to obtain a new input light field; Step S47: extract the phase information of the new input light field and use it as the input light field phase for the next iteration, and calculate the relative intensity change rate of the focus area of ​​the target surface; Step S48: repeat steps S43-S47. When the relative rate of change is less than the threshold, the iteration stops and the final phase of the modulated light field is obtained, thereby establishing a fast-converging iterative phase recovery algorithm.

4. The scattering lens zoom method based on optical transmission matrix according to claim 1, characterized in that: In step S5, the obtained light field phase is converted into a grayscale image in the range of 0-255, and the grayscale image is loaded onto the spatial light modulator to generate the expected modulated light field. After passing through the scattering lens system, the light beam is focused at the expected depth, and the detector is moved to the target surface position to observe the focusing effect.

5. The method for zooming a scattering lens based on an optical transmission matrix according to claim 1, wherein: In step S6, light focusing at different depths is achieved by calculating the transmission matrix of the scattering lens zoom optical path system based on the optical transmission matrix according to the prior data of the reference surface, establishing a connection between the reference surface light field and the modulated light field, and establishing a connection between the light field of the target surface to be focused and the light field of the reference surface through the light field inversion model, indirectly obtaining the modulated light field corresponding to the focused light field of the target surface at different depths, and establishing a scattering lens zoom model.

6. A scattering lens zoom software calculation system based on optical transmission matrix, characterized in that: The method comprises a memory, a processor, and computer program instructions stored in the memory and capable of being executed by the processor. When the processor executes the computer program instructions, the method steps according to any one of claims 1 to 5 can be implemented.

7. A computer-readable storage medium storing computer program instructions that can be executed by a processor, wherein when the processor executes the computer program instructions, the method steps according to any one of claims 1 to 5 can be implemented.

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