A hyperspectral imaging method using a meta-lens

Abstract

The present invention relates to the technical field of hyperspectral imaging, and specifically provides a hyperspectral imaging method of a meta-lens, which controls a focusing platform to drive a camera, and gradually moves from an ideal focal length position corresponding to the longest imaging band to an ideal focal length position corresponding to the shortest imaging band. Each time it moves to an ideal focal length position corresponding to a band, the camera is controlled to shoot, and an image formed by the meta-lens corresponding to the ideal focal length position is obtained, the ideal focal length position is recorded, and a micro-spectrometer is controlled to obtain the spectral component of the band. Based on the ideal focal length position corresponding to each band obtained, the image formed by the meta-lens and the spectral component, a hyperspectral image containing multiple spectral band information is obtained. The imaging method of the present invention does not require complex structural support, and improves spatial resolution and spectral resolution.

Description

Technical Field

[0001] The present invention relates to the technical field of hyperspectral imaging, and specifically provides a meta-lens hyperspectral imaging method. Background Art

[0002] Hyperspectral imaging (HSI) is a powerful technology that is used in various fields such as agriculture, environmental monitoring, surveillance and medical imaging. Existing hyperspectral imaging technologies include push-broom imaging, sweep imaging, snapshot imaging, tunable filter imaging and interferometric imaging.

[0003] In push-broom imaging, the sensor continuously scans the scene line by line as the platform (such as an aircraft or satellite) moves, with each line corresponding to a different wavelength, capturing a hyperspectral data set. Because different materials reflect, absorb, or emit light differently at different wavelengths, materials in the scene can be identified and characterized. However, push-broom imaging is complex, requires precise synchronization between the sensor and the platform motion, is prone to motion blur and distortion, and has poor spatial resolution. Swipe imaging operates in a similar manner to push-broom imaging, but instead of continuously scanning the entire scene, it captures only one spatial line at a time, redirecting light into different spectral bands through scanning mirrors or prisms. Similar to push-broom imaging, swipe imaging is complex, requires precise synchronization, is susceptible to motion-related issues, and has limitations in spatial resolution and spectral range. Snapshot imaging allows simultaneous capture of all spectral bands through specialized optics or spectral filters that separate the incoming light into its component wavelengths, which are then captured by a detector array. The complexity of the optics and detector arrays for snapshot imaging can make snapshot systems expensive and have poor spatial resolution and spectral range. The imaging system of tunable filter imaging uses tunable filters to selectively filter light of different wavelengths. By filtering a range of wavelengths, hyperspectral data can be captured. It can be based on technologies such as liquid crystal tunable filters or acousto-optic tunable filters. Compared with other technologies, the spectral range and resolution of tunable filter imaging are limited, and due to the slow response speed of tunable filters, it cannot be used in dynamic scenes. Interferometric imaging usually uses interferometers such as Fabry-Perot interferometers or Michelson interferometers to separate the incident light into its component wavelengths. However, the complex structure makes its optical device difficult to align and calibrate, and the spectral resolution and sensitivity are limited.

[0004] In view of the shortcomings of the existing technology, it is necessary to propose a hyperspectral imaging method with a simpler structure and higher spatial and spectral resolution. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a metalens hyperspectral imaging method, which utilizes the dispersion properties of the metalens itself, captures images at different ideal focal lengths with a camera and establishes an objective function to solve the ideal hyperspectral image. The overall structure is simple and the spatial resolution and spectral resolution are improved.

[0006] The meta-lens hyperspectral imaging method provided by the present invention comprises:

[0007] S1: In the meta-lens The ideal focal length position corresponding to each band is collected by the camera The image formed by the metalens ; and record the focus position corresponding to each image ;

[0008] S2: obtained by micro-spectrometer The proportion of the spectral components corresponding to each band in the total spectral energy ;

[0009] S3: Based on the imaging principle of meta-lens, the objective function for solving the ideal hyperspectral image is established:

[0010] ;

[0011] in, Meta-lens The label of any band in the bands, Indicates band The convolution matrix constructed by the corresponding point spread function, Indicates the focus position Images taken at Any one of Representation and Image The corresponding ideal hyperspectral image to be solved is, represents the intensity of scattered light after the meta-lens, represents the threshold value, represents the penalty function;

[0012] S4: Based on image , Focus position The proportion of the spectral components to the total spectral energy Solve the objective function and obtain the ideal hyperspectral image.

[0013] Preferably, the camera is arranged on a focusing platform, and the focusing platform can drive the camera to move.

[0014] Preferably, image The collection method is:

[0015] Through the focusing platform, the camera is driven to gradually move from the ideal focal length position corresponding to the longest wavelength band of the meta-lens imaging to the ideal focal length position corresponding to the shortest wavelength band of the meta-lens imaging. , both use cameras to capture an image of the meta-lens , get the image .

[0016] Preferably, the penalty function is the ridge regression penalty function: .

[0017] Preferably, the intensity of the scattered light scattered by the meta-lens is The calculation method is:

[0018] ;

[0019] in, Represents the diffraction efficiency of the metalens.

[0020] Preferably, the meta-lens imaging principle expression is:

[0021] ;

[0022] in, represents an independent and identically distributed Gaussian noise vector with zero mean.

[0023] Preferably, the signals between the camera and the meta-lens are always synchronized.

[0024] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0025] The meta-lens hyperspectral imaging method provided by the present invention utilizes the dispersion properties of the meta-lens itself, and solves the ideal hyperspectral image by taking images at different ideal focal length positions with a camera and establishing an objective function. Structurally, only a focusing platform, a camera that can move with the focusing platform, and a micro-spectrometer are required. The overall structure is simple, the layout difficulty is low, the cost is low, and the lack of a complex structure can make the application scenarios of the overall system unrestricted and more flexible. The signals between the camera and the meta-lens are always synchronized to ensure that the camera responds promptly and accurately, improve the efficiency of the camera in acquiring images, and reduce the possibility of image data redundancy. According to the objective function, the ideal hyperspectral image is obtained by calculation, and the spatial resolution and spectral resolution are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flow chart of a method for obtaining an ideal hyperspectral image according to an embodiment of the present invention;

[0027] Figure 2is a schematic diagram of the dispersion properties of a meta-lens provided according to an embodiment of the present invention;

[0028] Figure 3 It is a schematic diagram of the structure of an image acquisition device provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0031] like Figure 1 As shown, the embodiment of the present invention provides a hyperspectral imaging method of a meta-lens, which can be used in various hyperspectral imaging occasions, such as drone-to-ground hyperspectral imaging occasions, biomedical hyperspectral imaging occasions, ground-based telescope-to-air target hyperspectral imaging, etc. The imaging method specifically includes:

[0032] S1: Metalens is an optical element based on metamaterials, which has different dispersion properties from traditional refractive lenses, and its refractive index increases with the increase of wavelength. Figure 2 As shown, the dispersion property will cause light of different wavelengths to focus at different positions in the meta-lens.

[0033] The embodiment of the present invention is provided with a focusing platform in structure, and a camera capable of collecting images is provided on the focusing platform. The focusing platform is a platform system for adjusting the focal length or focus, and can enable the object or imaging target to be clearly imaged on the focal plane by precisely controlling the position of the lens or imaging element.

[0034] The camera is set on a focusing platform, and the focusing platform is used to drive the camera to move along a predetermined trajectory. During the movement of the camera, the signal synchronization between the camera and the metalens is always maintained. Signal synchronization can ensure that the information exchange between the camera and the metalens is timely and accurate. The camera captures images immediately after reaching the ideal focal length position, which improves efficiency and reduces image data redundancy.

[0035] In the full field of view of the super-lens, there are Bands, The wavelength corresponding to each band is recorded as , the embodiment of the present invention uses express The label of any band in the bands, any band Each corresponds to an ideal focal length position. In the embodiment of the present invention, represents any ideal focal length position, The ideal focal length position corresponding to each band is recorded as , band The corresponding focus position is Control the focusing platform to drive the camera from the ideal focal length position corresponding to the longest imaging band Gradually move to the ideal focal length corresponding to the shortest imaging band , each time an ideal focal length position is reached , both use cameras to capture an image of the meta-lens The complete imaging process was performed times, obtained The image is recorded as The ideal focal position is recorded at each imaging Corresponding focus position , i.e. in the focus position Get the image .

[0036] S2: The embodiment of the present invention also has a micro-spectrometer, and the field of view of the micro-spectrometer is the same as that of the metalens. The micro-spectrometer is a device that measures the intensity of different wavelength positions of spectral lines through a photoelectric detector. Its dispersion system can independently select the required wavelength and perform intensity measurement. There are a variety of micro-spectrometers available on the market, for example, the Hamamatsu C12880MA micro-spectrometer or other micro-spectrometers that meet the needs can be selected.

[0037] Through the micro-spectrometer, corresponding to the longest imaging band to the shortest imaging band, all spectral components in the full field of view of the meta-lens are obtained, and the proportion of each spectral component to the total spectral energy is calculated, which is recorded as , .

[0038] S3: Get image After that, you need to Restore the hyperspectral image and convert the image It can be understood as a kind of observation data. According to the imaging principle of meta-lens, the image satisfy:

[0039] ;

[0040] in, Indicates band The convolution matrix constructed by the corresponding point spread function is a known quantity, which is obtained by the ideal focal length position recorded in S1. Corresponding focus position It can be obtained. Representation and Image The corresponding ideal hyperspectral image to be solved has some scattered light because the diffraction efficiency of the meta-lens cannot reach 100%. represents the intensity of scattered light after the meta-lens, represents an independent and identically distributed Gaussian noise vector with zero mean.

[0041] According to the above formula, the objective function for solving the ideal hyperspectral image is established as follows:

[0042] ;

[0043] in, Represents the threshold value, which is a non-negative real number and can be selected by cross-validation method. It is an existing technology. represents the penalty function, which is some kind of prior.

[0044] S5: Solve the objective function in S4 to obtain the ideal hyperspectral image , the specific solution process is as follows:

[0045] For a given meta-lens, its diffraction efficiency is are known parameters, so we can solve :

[0046] ;

[0047] Then the objective function is a known quantity.

[0048] To simplify the description, the embodiment of the present invention uses a common ridge regression penalty function, namely , transform the objective function into:

[0049] ;

[0050] in, Indicates the current parameters The objective function value of .

[0051] Will right The derivative is:

[0052] ;

[0053] in, Indicates The serial number of the band, Represents the derivative operation in mathematical calculations. Indicates The ideal hyperspectral image of the bands, Indicates The band is The convolution matrix constructed from the point spread function of the focus position.

[0054] make , we can get:

[0055] ;

[0056] Transform the listing:

[0057] ;

[0058] After the transformation again, the solution formula for the ideal hyperspectral image is obtained:

[0059] ;

[0060] After obtaining the solution formula for the ideal hyperspectral image, it is iterated to reconstruct the ideal hyperspectral image from a series of images obtained at different ideal focal lengths. , The wavelength corresponding to the band , the diffraction efficiency of the meta-lens , Threshold and the point spread function ( , ) is substituted into the above solution formula of ideal hyperspectral image and iterated.

[0061] First, according to the formula Calculate the scattered light intensity C of the meta-lens and then initialize the estimate of the ideal hyperspectral image:

[0062] ;

[0063] Set the number of iterations to , according to the formula:

[0064] ;

[0065] Will The initial value is 1. The initial value is 1, and each iteration The value increases by 1. The value increases by 1, and the ideal hyperspectral image estimate of each band is continuously updated through an iterative process until the predetermined number of iterations is reached. , get the ideal hyperspectral image estimate .

[0066] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Those skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0067] The above specific implementations of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A meta-lens hyperspectral imaging method, characterized in that: include: S1: In the meta-lens The ideal focal length position corresponding to each band is collected by the camera The image formed by the metalens ; and record the focus position corresponding to each image ; S2: obtained by micro-spectrometer The proportion of the spectral components corresponding to each band in the total spectral energy ; S3: Based on the imaging principle of meta-lens, the objective function for solving the ideal hyperspectral image is established: ； in, Meta-lens The label of any band in the bands, Indicates band The convolution matrix constructed by the corresponding point spread function, Indicates the focus position Images taken at Any one of Representation and Image The corresponding ideal hyperspectral image to be solved is, represents the intensity of scattered light after the meta-lens, represents the threshold value, represents the penalty function; S4: Based on the image , Focus position The proportion of the spectral components to the total spectral energy The objective function is solved to obtain an ideal hyperspectral image.

2. The method for hyperspectral imaging using a meta-lens as claimed in claim 1, wherein: The camera is arranged on a focusing platform, and the focusing platform can drive the camera to move.

3. The hyperspectral imaging method of the meta-lens as claimed in claim 2, characterized in that: The image The collection method is: The focusing platform drives the camera to gradually move from the ideal focal length position corresponding to the longest wavelength band of the meta-lens imaging to the ideal focal length position corresponding to the shortest wavelength band of the meta-lens imaging. , both use the camera to capture an image formed by the meta-lens , get the image .

4. The meta-lens hyperspectral imaging method according to claim 1, wherein: The penalty function is the ridge regression penalty function: .

5. The meta-lens hyperspectral imaging method according to claim 1, characterized in that: The intensity of the scattered light scattered by the meta-lens is The calculation method is: ； in, Represents the diffraction efficiency of the metalens.

6. The meta-lens hyperspectral imaging method according to claim 1, wherein: The imaging principle of the meta-lens is expressed as follows: ； in, represents an independent and identically distributed Gaussian noise vector with zero mean.

7. The meta-lens hyperspectral imaging method according to claim 1, characterized in that: The signals between the camera and the meta-lens are always synchronized.

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