Spectral coding imaging system

Abstract

The utility model is suitable for the technical field of spectral imaging, and specifically relates to a spectral coding imaging system. The spectral imaging system provided by the utility model comprises spectral acquisition and spectral super-resolution reconstruction of an upper computer. An image detector with a surface integrated deterministic filtering structure is used for spectrum acquisition and is responsible for spectrum coding of a scene to be detected. And the spectrum reconstruction module realizes spectrum super-resolution and space image reconstruction aiming at the spectrum coding value. The device has the advantages of simple structure, low cost, high flux and the like, and can realize tunable reconfiguration wavelength resolution according to actual application scene requirements.

Description

Technical Field

[0001] The utility model belongs to the technical field of spectral imaging, and particularly relates to a spectral encoding imaging system based on a deterministic filter structure. Background Art

[0002] The spectral imaging system based on deterministic filtering can encode the spectral signals of a target to be measured by integrating a filter structure on the surface of an image sensor, form a two-dimensional compressed image containing spectral information, and then reconstruct a hyperspectral image through decoding.

[0003] For traditional push-broom spectral imaging systems, the time resolution is low and they are not suitable for real-time scenarios; the FP cavity line array scanning overcomes the disadvantages such as large volume of traditional push-brooms, but the time resolution is poor; snapshot spectral imaging realized based on pixel-level array filter arrays integrated with array detectors is a future trend. However, since array filters generally adopt thin-film FP cavity structures, the channel encoding efficiency does not exceed 5%, restricting their applications; the array metasurfaces developed in recent years have the ability of single-pixel channel multispectral encoding. However, the device fabrication process is complex, and challenges are encountered in terms of consistency and stability, as well as energy utilization efficiency.

[0004] Therefore, those skilled in the art urgently need to develop a spectral imaging system that is simple to manufacture, low in cost, high in energy utilization efficiency, and high in spatial resolution, time resolution, and spectral resolution, which is crucial for the future development of spectral imaging chips in applications such as smart agriculture and military. Summary of the Invention

[0005] The purpose of the utility model is to provide a spectral encoding imaging system that can modulate the spectral signals of a target to be measured, form a two-dimensional compressed image containing spectral information, and reconstruct a hyperspectral image after decoding.

[0006] To achieve the above purpose, the system of the utility model includes a target to be measured, an imaging lens for imaging the object light emitted by the target to be measured, a deterministic filter structure for encoding the target to be measured to obtain an encoded measurement value, and an image detector that converts the encoded measurement value information into a grayscale signal and then performs decoding and reconstruction through a spectral super-resolution reconstruction module to construct a complete hyperspectral three-dimensional data cube, which are arranged in sequence along the light transmission direction;

[0007] The deterministic filter structure is composed of several encoding units arranged in a matrix, each encoding unit corresponds to its own image detector, and the transmittance curve of each encoding unit is obtained through the following method;

[0008] Step 1.1: Adjust the central wavelength of the monochromatic light output by the motorized monochromator to the minimum operating wavelength of the image detector;

[0009] Step 1.2: The monochromatic light passes through the integrating sphere and collimator and is incident on the deterministic filter structure in the form of parallel light. The encoded monochromatic light forms a grayscale electrical signal on the surface of the image detector, and the response signal intensity of the monochromatic light is obtained.

[0010] Step 1.3: Adjust the central wavelength of the monochromatic light output by the motorized monochromator with a fixed step size d, keep the incident intensity of the monochromatic light unchanged, and repeat Step 1.2 until the central wavelength of the monochromatic light output by the monochromator reaches the maximum working wavelength of the image detector, and obtain the response signal intensity change curve of the image detector of this encoding unit to the incident monochromatic light.

[0011] Step 1.4: Change the spectral light signal of the motorized monochromator, and repeat Steps 1.1 to 1.3 to obtain the transmittance curves of each encoding unit of the deterministic filter structure 3.

[0012] The wavelength encoding characteristic of the encoding unit of the deterministic filter structure has a high throughput of greater than or equal to 60%.

[0013] The correlation between the transmittance curves corresponding to adjacent pixels of each encoding unit of the deterministic filter structure is between 0 and 0.5.

[0014] Compared with the prior art, the beneficial technical effects of the present utility model are as follows:

[0015] First, the system integrates a deterministic filter structure on the surface of the image detector, including multiple encoding units. Each filter unit has different spectral transmittance curves, which are two-dimensionally continuously variable in spatial structure. In terms of spectral characteristics, it has a high spectral transmittance contrast at the pixel feature size.

[0016] Second, compared with the traditional method of designing the deterministic filter structure according to the curve, the present utility model uses a motorized monochromator, an integrating sphere, a collimator, and an image detector to obtain the pixel-level spectral transmittance curve of the deterministic filter structure, directly measure the actual spectral transmittance curve, and the result is more accurate. As the measurement matrix in the algorithm reconstruction. Afterward, by accurately measuring the spectral characteristics of each pixel, there is no need to design a dedicated filter for different applications, avoiding the problem of precise alignment at the pixel level.

[0017] Third, the characteristic of precise resolution adjustment improves the adaptability of the system. The system can independently select the size of the filter unit according to requirements to achieve spectral super-resolution at different magnifications, and has a high encoding flexibility. The characteristic of precise resolution adjustment improves the adaptability of the system. Description of the Drawings

[0018] Figure 1 is the structural schematic diagram of a spectral imaging system based on a deterministic filter structure provided by the present utility model;

[0019] Figure 2 Schematic diagram for calibrating the spectral response curve of a deterministic filter structure provided by the present utility model;

[0020] Figure 3 Schematic diagram for dividing coding units provided by the present utility model;

[0021] Figure 4 Schematic diagram for spectral super-resolution reconstruction in an embodiment of the present utility model; Detailed implementation manners

[0022] To make the objectives, advantages and features of the present utility model clearer, a spectral imaging system based on a deterministic filter structure proposed by the present utility model will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0023] As Figure 1 shown, the system of the present utility model includes a target to be measured 1, an imaging lens 2, a deterministic filter structure 3 and an image detector 4 arranged in sequence along the optical transmission direction. The imaging lens 2 is used to image the object light emitted by the target to be measured 1 on the deterministic filter structure 3. The deterministic filter structure 3 is composed of a plurality of coding units arranged in a matrix, and each coding unit corresponds to its own image detector 4. The image detector 4 converts the coded measurement values obtained by coding each coding unit of the deterministic filter structure 3 into gray-scale signals and then decodes and reconstructs them through a spectral super-resolution reconstruction module to construct a complete hyperspectral three-dimensional data cube.

[0024] As Figure 2 shown, the transmittance curves of the respective coding units of the deterministic filter structure 3 of the present utility model are obtained by the following method;

[0025] Step 1.1: Adjust the central wavelength of the monochromatic light output by the motorized monochromator 5 to the minimum operating wavelength of the image detector 4;

[0026] Step 1.2: The monochromatic light passes through the integrating sphere 6 and the collimator 7 and is incident on the deterministic filter structure 3 in the form of parallel light. The coded monochromatic light forms a gray-scale electrical signal on the surface of the image detector 4 to obtain the response signal intensity of the monochromatic light;

[0027] Step 1.3: Adjust the central wavelength of the monochromatic light output by the motorized monochromator 5 with a fixed step d, keep the incident intensity of the monochromatic light unchanged, and repeat Step 1.2 until the central wavelength of the monochromatic light output by the monochromator 5 reaches the maximum operating wavelength of the image detector 4 to obtain the response signal intensity change curve of the image detector 4 of this coding unit to the incident monochromatic light;

[0028] Step 1.4: Change the spectral light signal of the motorized monochromator 5 and repeat Steps 1.1 to 1.3 to obtain the transmittance curves of the respective coding units of the deterministic filter structure 3.

[0029] The monochromator 5 of the present utility model is arranged on the incident light path of the integrating sphere 6, and then passes through the collimator 7 and the deterministic filter structure 3. The integrating sphere 6 is used to scatter the monochromatic light so that the monochromatic light is uniformly incident on the deterministic filter structure 3, and after encoding, an electrical signal is generated on the image detector 4. The wavelength of the monochromatic light is sequentially changed in steps of d to obtain the light intensity encoding values in different bands, and the spectral transmittance curve of the pixel level of the deterministic filter structure is obtained through extraction.

[0030] In the calibration optical path of the spectral transmittance curve of the deterministic filter structure of the spectral imaging system, an integrating sphere and a collimator are arranged to ensure the uniformity and collimation of the incident light, and improve the accuracy and reliability of the measurement. This design effectively overcomes the problems of uneven illumination and optical path deviation in the traditional method, and ensures the accurate determination of the spectral transmittance curve of the deterministic filter structure.

[0031] As Figure 3 shown, the deterministic filter structure includes a plurality of coding units. Different unit channels have different spectral transmittance curves and low internal correlation. The specification sizes of the channels of the plurality of coding units are the same and are uniformly arranged, and their length and width are integer multiples of the pixel size of the image sensor. The deterministic filter structure and the image sensor are fixed together by physical pasting. The channels of the coding units are combined in a fixed order with different spectral transmittance curves and arranged periodically in n*n to achieve mosaic snapshot imaging.

[0032] In this embodiment, the image detector is a CMOS detector. Taking the division of 5*5 coding units as an example, the construction principle of the measurement matrix is described. The monochromatic light passes through Figure 2 the optical path shown, and the detector converts it into a gray value. Each coding unit corresponds to form a matrix of 25*(λmax - λmin) / d. According to the above recombination method, each coding unit has a measurement matrix centered on itself.

[0033] See Figure 4 , the spectral super-resolution reconstruction process of this embodiment includes the following steps:

[0034] Step 1: Obtain the transmittance curve of the deterministic filter structure 3 for optical signals in different spectral bands;

[0035] Step 1.1: Adjust the central wavelength of the monochromatic light output by the motorized monochromator 5 to the minimum operating wavelength of the image detector 4;

[0036] Step 1.2: The monochromatic light passes through the integrating sphere 6 and the collimator 7 and is incident on the deterministic filter structure 3 in a parallel light manner. The encoded monochromatic light forms a gray electrical signal on the surface of the image detector 4, and the response signal intensity of the monochromatic light is obtained;

[0037] Step 1.3: Adjust the central wavelength of the monochromatic light output by the motorized monochromator 5 at a fixed step size d, keep the incident intensity of the monochromatic light unchanged, and repeat Step 1.2 until the central wavelength of the monochromatic light output by the monochromator 5 reaches the maximum working wavelength of the image detector 4, so as to obtain the curve of the change in the response signal intensity of the image detector 4 of this coding unit to the incident monochromatic light;

[0038] Step 1.4: Change the spectral light signal of the motorized monochromator 5, and repeat Steps 1.1 to 1.3 to obtain the transmittance curves of each coding unit of the deterministic filter structure 3.

[0039] Step 2: Divide the coding units (5*5), and construct the measurement matrix Φi(λ) according to the transmittance curves obtained in Step 1;

[0040] Step 2.1: Each coding unit of the deterministic filter structure 3 is arranged periodically;

[0041] Step 2.2: According to the transmittance curves of the deterministic filter structure for different spectral light signals obtained in Step 1, use the curve values of each channel of the coding unit as each row of the measurement matrix in turn to construct the measurement matrix;

[0042] Step 2.3: Repeat Step 2.2 to obtain the measurement matrices corresponding to each coding unit of all the deterministic filter structures 3 in turn.

[0043] Step 3: Encode the spectral information S(λ,x,y) at the spatial position (x,y) of the target spectrum to be measured received by the 5*5 different channels in each coding unit of the deterministic filter structure. The image detector converts the modulated spectral information S(λ,x,y) of the target spectrum to be measured into a gray-scale signal Yi(x,y). There is the following relationship:

[0044]

[0045] λmin and λmax are respectively the lower and upper limits of the spectral range. Φi(λ) is the spectral transmittance curve of the i-th deterministic filter structure, i = 1, 2,..., 25, and D(λ) is the spectral response curve of the image detector. These 25 light intensity values constitute a set of encodings of the original spectral signal S(λ,x,y).

[0046] Step 4: According to the spectral information of the target spectrum to be measured, perform sparse representation on S(λ), and use the greedy algorithm based on compressive sensing to obtain the optimization equation:

[0047]

[0048] Among them, Φi(λ) is the measurement matrix composed of the spectral transmittance of the coding unit, with 25 rows and N columns;

[0049] D(λ) is the matrix after discretizing the spectral response curve of the image detector into an N*1 matrix;

[0050] Ψ is the sparse basis matrix, α is the sparse coefficient, and Yi is the matrix of the electrical signal intensity received by the image detector for one of the encoding units. Yi = (Y1, Y2, …, Y n ).

[0051] Step 5: According to the greedy algorithm, solve the sparse coefficient and super-resolution reconstruct the spectral S(λ, x, y) of the target to be measured for one encoding unit.

[0052] Step 6: Repeat Step 2 - Step 5 to successively solve the spectral S(λ, x, y) of the target to be measured for all divided encoding units, thereby constructing a complete hyperspectral three-dimensional data cube and completing the super-resolution reconstruction of the spectrum.

Claims

1. A spectrally coded imaging system, characterized in that: The invention comprises targets to be measured (1) arranged in sequence along the light transmission direction, an imaging lens (2) for imaging the object light emitted by the targets to be measured (1), a deterministic filter structure (3) for encoding the targets to be measured (1) to obtain a coded measurement value, and an image detector (4) for converting the coded measurement value information into a grayscale signal and then decoding and reconstructing it through a spectral super-resolution reconstruction module, thereby constructing a complete hyperspectral three-dimensional data cube; The deterministic filter structure (3) is composed of a plurality of coding units arranged in a matrix, each coding unit corresponds to a respective image detector (4), and the transmittance curve of each coding unit is obtained by the following method; Step 1.1, adjusting the central wavelength of the monochromatic light output by the electric monochromator (5) to the minimum operating wavelength of the image detector (4); Step 1.2, the monochromatic light passes through the integrating sphere (6) and the collimator (7) and is incident on the deterministic filter structure (3) in the form of parallel light, and the encoded monochromatic light forms a grayscale electrical signal on the surface of the image detector (4), and the response signal intensity of the monochromatic light is obtained; Step 1.3, adjusting the central wavelength of the monochromatic light output by the electric monochromator (5) with a fixed step length d, keeping the incident intensity of the monochromatic light unchanged, repeating step 1.2 until the central wavelength of the monochromatic light output by the monochromator (5) reaches the maximum working wavelength of the image detector (4), and obtaining a response signal intensity change curve of the image detector (4) of the encoding unit to the incident monochromatic light; Step 1.4, changing the spectral light signal of the electric monochromator (5), repeating steps 1.1 to 1.3, and obtaining the transmittance curve of each coding unit of the deterministic filter structure (3).

2. The spectrally coded imaging system according to claim 1, characterized in that: The wavelength encoding characteristics of the encoding unit of the deterministic optical filtering structure (3) have a high throughput greater than or equal to 60%.

3. The spectrally coded imaging system according to claim 1, characterized in that: The correlation of the transmittance curves corresponding to adjacent pixels of each coding unit of the deterministic filter structure 3 is between 0 and 0.5.

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