Multi-slit optical path compensation device for improving imaging quality of linear scanning hyperspectral camera

Abstract

The invention discloses a multi-slit optical device for improving the imaging quality of a line-scanning hyperspectral camera, and the device comprises a multi-slit assembly which comprises a multi-slit structure, an optical path compensation structure, and a filtering structure. The multi-slit structure comprises at least two slits, and each slit is responsible for transmitting light in a certain wavelength range; the light filtering structure comprises at least two light filters, and each light filter corresponds to one slit in the multi-slit structure; light with different wavelengths penetrates through the different optical filters, and the wavelength range of the light is consistent with that of the corresponding slits. And the optical path compensation structure is used for compensating the offset of the focal plane in different wavelength intervals. According to the invention, by modifying the slit assembly in the line scanning hyperspectral camera, introducing the multi-slit assembly and carrying out physical compensation on light paths of different wavebands, light of different wavelengths can be simultaneously and clearly imaged on the sensor, so that the image quality of the whole working waveband is obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of optical imaging and spectral analysis technology, and specifically relates to a multi-slit optical device for improving the imaging quality of a line-scan hyperspectral camera. Background Technology

[0002] Hyperspectral imaging technology can simultaneously acquire two-dimensional spatial information and one-dimensional spectral information of a target, thereby obtaining the spatial distribution of its chemical composition. It has broad application prospects in remote sensing, smart agriculture, and industrial inspection. Hyperspectral imaging technology has the characteristics of a camera, which can sense the light at every spatial location in the shooting area and form a "photo"; at the same time, hyperspectral imaging also has the characteristics of a spectrometer, which can sense different wavelengths of light at each spatial point and form a "spectrum".

[0003] Line-scan (also known as spatial scanning) hyperspectral imaging is the mainstream hyperspectral imaging technology. In this approach, a hyperspectral camera acquires optical information along a narrow spatial band through optical modulation, then performs wavelength dispersion using a grating or prism, and finally performs spectral imaging on an optical sensor. Each image captured by a line-scan hyperspectral camera can obtain spatial and spectral information over a linear spatial range. By moving the camera or sample, information from different locations along the line can be obtained, and finally, these images are stitched together to form complete hyperspectral data.

[0004] A line-scan hyperspectral camera consists of an imaging lens (also known as an objective lens), an optical slit, a collimating lens group, a beam splitter (grating, prism, or prism), a converging lens group (also known as an objective lens), and an optical sensor. Light from the scene being photographed is modulated by the imaging lens and imaged on the slit plane; the slit only allows light in a thin line in the non-scanning direction to pass through, and is collimated by the collimating lens group; the collimated light is then split into monochromatic light of different wavelengths in the scanning direction by the beam splitter; finally, the image is formed on the optical sensor by the converging lens group.

[0005] Data captured by a hyperspectral camera is called a hyperspectral image or hyperspectral data cube, which is a three-dimensional data structure. Two of these dimensions are spatial (scanning axis x, non-scanning axis y), and one is wavelength (λ). Each data point in the data structure represents the light intensity at a certain wavelength at a spatial location within the phase amplitude. For a line-scan hyperspectral camera, each shot generates a two-dimensional image. By scanning and capturing the x-axis frame by frame, a complete three-dimensional photograph is finally formed.

[0006] In practical applications, in order to adapt to different observation needs and scenarios, the main body of a hyperspectral camera (including the slit and subsequent optical system) is often designed as an independent module, and users can select different imaging lenses according to their needs.

[0007] Hyperspectral cameras are typically paired with industrial lenses because these lenses offer a wide spectral response, covering the range from visible light to near-infrared (typically 400nm-900nm). However, due to the dispersive properties of optical materials, these lenses generally suffer from focal plane shift: light of different wavelengths cannot be focused onto the same image plane. In particular, the optimal focal plane positions for visible light (e.g., 400nm-700nm) and near-infrared light (e.g., 700nm-900nm) often differ significantly; sometimes, the focal plane for the blue light band (380~480 nm) also differs from that for the green and red light bands (480~780 nm).

[0008] For ordinary imaging cameras, this effect may not be significant, but for line-scan hyperspectral cameras that need to simultaneously and clearly image the same spatial line at all wavelengths, focal plane shift can lead to a serious problem: the imaging quality of a certain band (usually one of the visible or near-infrared) will always be degraded across the entire spectrum, resulting in blurred images and affecting the accuracy of subsequent spectral analysis.

[0009] Currently, methods to address chromatic aberration or focal plane shift typically involve using apochromatic lens groups or employing complex active focusing mechanisms. However, these solutions result in complex optical system designs, high costs, large sizes, and are not easily adapted to existing hyperspectral camera structures.

[0010] Therefore, there is an urgent need for a technical solution that is simple in structure, low in cost, and can effectively solve the focal plane shift problem of broadband line-scan hyperspectral cameras. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multi-slit optical device to improve the imaging quality of a line-scan hyperspectral camera. This invention modifies the slit components in the line-scan hyperspectral camera, introduces a multi-slit component, and physically compensates the optical paths for different wavelengths, enabling light of different wavelengths to be clearly imaged on the sensor simultaneously, thereby significantly improving the image quality across the entire operating wavelength range.

[0012] To achieve the above objectives, the technical solution of the present invention is as follows:

[0013] A multi-slit optical device for improving the imaging quality of a line-scan hyperspectral camera includes a multi-slit assembly, wherein the multi-slit assembly includes a multi-slit structure, an optical path compensation structure, and a filter structure.

[0014] The multi-slit structure includes at least two slits, each of which is responsible for transmitting light within a certain wavelength range.

[0015] The filtering structure includes at least two filters, each filter corresponding to one slit in the multi-slit structure; different filters transmit light of different wavelengths, and the range of wavelengths transmitted is consistent with the range of the corresponding slits;

[0016] The optical path compensation structure is used to compensate for focal plane offset in different wavelength ranges.

[0017] Optionally, the slits are parallel to each other and parallel to the non-scanning direction of the camera.

[0018] Optionally, the spacing between the slits shall be no less than 5 times the maximum operating wavelength of the hyperspectral camera.

[0019] Optionally, the optical path compensation structure compensates for the focal plane offset by:

[0020] in, and These are the average focal length of the i-th slit (through wavelength) and the average focal length of the target, respectively. Let be the offset of the i-th slit. The target average focal length must not be greater than the average focal length of any slit; in a preferred embodiment, the target average focal length is equal to the focal length of the wavelength range with the shortest average focal length.

[0021] Optionally, the optical path compensation structure is one (when there are two slits, and (At one time) or multiple optical media windows, the window materials may be the same or different, fixed together with the plane of the slit being compensated, completely covering the slit being compensated, and completely not covering other slits.

[0022] The thickness of the optical path compensation structure corresponding to the i-th compensated slit The following relationship must be satisfied:

[0023] in, The average refractive index of the material within the wavelength range to be compensated;

[0024] Optionally, the arrangement order of the multi-slit structure, optical path compensation structure, and filter structure along the light direction can be arbitrarily changed. Preferably, the optical path compensation structure is placed before the multi-slit structure.

[0025] Optionally, the hyperspectral camera system using the multi-slit assembly needs to perform the following processing on the acquired hyperspectral images:

[0026] Wavelength filtering: Apply pixel-wavelength mapping parameters to the wavelength axis of the raw hyperspectral data to retain pixel data within the working wavelength range and remove pixel data outside the wavelength range;

[0027] Spatial registration: Based on the spatial offset parameters, stitch together the images corresponding to each slit of the removed hyperspectral data.

[0028] Optionally, the pixel-wavelength mapping parameters are obtained by taking pictures of a series of light with known wavelengths using a hyperspectral camera and recording their pixel positions on the sensor to generate a pixel-wavelength mapping.

[0029] Optionally, the spatial offset parameter is obtained by taking a picture of a standard image calibration plate using a hyperspectral camera, then registering the images of the image intervals corresponding to each slit, and finding the number of misaligned pixels in each band in the scanning direction, which is the spatial offset parameter.

[0030] Compared with the prior art, the advantages of this invention are as follows:

[0031] The multi-slit optical device for improving the imaging quality of a line-scan hyperspectral camera proposed in this invention has the following advantages compared to a traditional single-slit line-scan hyperspectral camera:

[0032] 1. Improved image quality: By using physical optical path compensation, the focal plane shift problem of light of different wavelengths is fundamentally solved, ensuring that the hyperspectral camera can obtain clear images throughout the entire working band;

[0033] 2. Improved imaging lens adaptability: This multi-slit assembly can serve as a universal module, easily adapting to various industrial camera objective lenses with focal plane offset issues, thereby enhancing the overall flexibility and application range of hyperspectral cameras;

[0034] 3. Flexible cost-effectiveness options: Performance can be improved to varying degrees through a variety of materials and processes, allowing users to choose the most cost-effective solution based on their application's performance requirements and budget constraints;

[0035] 4. Simple structure and low modification cost: The core components of this invention are only a multi-slit plate with a light-filtering function and a piece of compensating glass. It does not require modification of the complex collimating lens, grating and focusing lens group inside the hyperspectral camera, nor does it require replacement of expensive apochromatic objectives, which greatly reduces the difficulty and cost of implementation;

[0036] 5. High reliability: It adopts pure passive optical compensation, with no moving parts, making the system stable, reliable and long-lasting. Attached Figure Description

[0037] Figure 1A schematic diagram of the optical path principle of a traditional hyperspectral camera;

[0038] Figure 2 A schematic diagram of the optical path principle of the multi-slit optical device for improving the imaging quality of a line-scan hyperspectral camera provided in the embodiments of this application (taking a double slit as an example).

[0039] Figure 3 This is a schematic diagram of a traditional single-slit assembly.

[0040] Figure 4 A schematic diagram of the structure of the multi-slit assembly provided in the embodiments of the application;

[0041] Figure 5 A visual diagram illustrating the data processing process;

[0042] Figure 6 This is a layered structure diagram of the multi-slit assembly in Example 1;

[0043] Figure 7 This is an exploded view of the multi-slit assembly in Example 2;

[0044] Figure 8 Layered structure diagram of the multi-slit assembly in Example 3

[0045] In the figure: 1. Multi-slit structure; 11. Slit; 2. Optical path compensation structure; 21. Optical medium window; 3. Filter structure; 31. Filter. Detailed Implementation

[0046] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0047] See Figure 1 The diagram shown illustrates the structure and optical path of an existing line-scan hyperspectral camera, which includes, in sequence, an imaging lens, an optical slit, a collimating lens group, a beam-splitting assembly, a converging lens group, and an optical sensor. Figure 3 As shown, the optical slit is a single slit. Because the infrared band has a focal plane shift compared to the visible band, a clear image cannot be formed on the sensor in the infrared band.

[0048] See Figure 2 The diagram shown is a schematic of the structure and optical path of the multi-slit optical device for improving the imaging quality of a line-scan hyperspectral camera provided in this embodiment. The core improvement lies in the slit assembly. The multi-slit assembly is located behind the imaging lens of the hyperspectral camera and in front of the collimating lens (in the direction of light, the closer to the light source is front, and the closer to the sensor is rear). It replaces the single-slit assembly of a traditional hyperspectral camera, allowing light of different wavelengths to pass through their respective slits. The additional optical structure compensates for the focal plane shift of different wavelengths of light, so that light of all wavelengths can be clearly imaged on the sensor at the same time, thereby significantly improving the image quality of the entire working band.

[0049] See Figure 4 As shown, the main body of the dual-slit assembly provided in this embodiment consists of three main structures: a multi-slit structure 1, an optical path compensation structure 2, and a filter structure 3.

[0050] The multi-slit structure 1 includes several slits 11, each allowing light to pass through different wavelength ranges within the operating wavelength range. The order of the transmitted wavelengths should correspond to the grating order selected in the hyperspectral system. Specifically, based on the wavelength separation direction on the optical sensor, slits that allow light to pass through shorter wavelengths are located on the shorter wavelength side of the wavelength separation, while slits that allow light to pass through longer wavelengths are located on the longer wavelength side. The filter structure 3 includes filters 31 in the same number as the slits 11, allowing light to pass through the corresponding wavelength range of the slits while blocking light of other wavelengths. The arrangement of the three main structures in the light direction can be arbitrarily changed; therefore, there are six possible arrangements of the three structures (from front to back): filter structure 3 - multi-slit structure 1 - optical path compensation structure 2, multi-slit structure 1 - filter structure 3 - optical path compensation structure 2, multi-slit structure 1 - optical path compensation structure 2 - filter structure 3, filter structure 3 - optical path compensation structure 2 - multi-slit structure 1, optical path compensation structure 2 - filter structure 3 - multi-slit structure 1, optical path compensation structure 2 - multi-slit structure 1 - filter structure 3. In some embodiments, the multi-slit assembly may also include a scratch-resistant structure (protective layer) and a mechanical fixing structure. In a preferred embodiment, the optical path compensation structure should be placed before the multi-slit structure to achieve the best compensation effect.

[0051] In one specific embodiment, the slits of the multi-slit structure 1 are parallel to each other and parallel to the non-scanning direction of the camera (consistent with the direction of a conventional hyperspectral camera); the length of the slit 11 should be greater than the field-of-view aperture size of the camera at that location (the same requirement as for a conventional hyperspectral camera); the number of slits should be minimized while meeting image optical quality requirements; in a preferred embodiment, the number of slits 11 should not exceed three; the position and spacing of the multiple slits 11 in the scanning direction can be determined according to specific application requirements, but for optimal image quality, the preferred solution is to reduce the spacing and position them close to the center of the camera's field of view; the spacing between slits 11 should not be less than 5 times the maximum working wavelength to prevent optical anomalies such as interference; for most hyperspectral optical systems, the preferred slit spacing is 500~2000 μm, and the multiple slits 11 are symmetrically distributed on both sides of the center point of the image plane; the slit spacing should not be too large to ensure that all working wavelengths can be projected onto the optical sensor; the width of the slits should be determined according to the actual imaging quality requirements; in a preferred embodiment, the slit width is 5~100 μm. The width of the slit can be uniform or inconsistent depending on the light intensity requirements of the actual application; the material and process of the slit should be selected according to the application requirements, and it can be a metal material or a glass material with a coating.

[0052] In one specific embodiment, the optical path compensation structure compensates for the focal plane offset by:

[0053] in, and These are the average focal length of the i-th slit (through wavelength) and the average focal length of the target, respectively. Let be the offset of the i-th slit. The target average focal length must not be greater than the average focal length of any slit; in a preferred embodiment, the target average focal length is equal to the focal length of the wavelength range with the shortest average focal length. .

[0054] The thickness of the optical path compensation structure corresponding to the i-th slit The following relationship must be satisfied:

[0055] in, The average refractive index of the material within the wavelength range to be compensated; in some embodiments, it may be difficult to accurately compensate for the thickness d, and the allowable tolerance of d can be determined according to the actual sharpness requirements to produce an optical path compensation structure that meets the tolerance standard.

[0056] The optical path compensation structure 2 consists of one (when there are two slits, and It consists of one or more optical medium windows 21. The materials of the optical medium windows 21 may be the same or different. The medium material is required to maintain a relatively consistent transmittance within the covered working wavelength range and have no significant absorption. The material can be glass, plastic, dielectric film, or surface deposition layer. In addition, it should be as close as possible to the plane of the slit being compensated and fixed together. The fixing method can be adhesive bonding, mechanical pressing, or surface coating. It needs to completely cover the slit being compensated and not cover other slits at all.

[0057] In one specific embodiment, a filter 31 is disposed behind the slit 11. The filter 31 completely covers the corresponding slit but does not cover other slits. The filter 31 allows the set wavelength band to pass through and blocks light of other wavelengths. The filter 31 can be a specific film layer coated on the slit plate or an additional independent filter. The filter should be as close as possible to the plane of the slit and fixed together. The fixing method can be adhesive bonding, mechanical pressing, or surface coating. The filtering method of the filter can be reflective or absorptive, and the type can be long-pass, short-pass, or bandpass. The material of the filter can be a dielectric film, doped glass, or synthetic plastic.

[0058] Replacing the single-slit assembly of a traditional hyperspectral camera with the multi-slit assembly of this embodiment will have two effects: a) There is a wavelength vacuum region between each band of the slit. b) Photos taken simultaneously by different slits are located at different positions on the image frame, with spatial differences between them. Therefore, post-processing of the image data is necessary to eliminate the influence of these two parts, such as... Figure 5 As shown, the specific processing steps include:

[0059] Wavelength filtering: Apply pixel-wavelength mapping parameters to the wavelength axis of the raw hyperspectral data, retain pixel data within the working wavelength range, and discard pixel data outside the wavelength range, thus identifying the region located in the wavelength vacuum. Some data will be discarded. Specifically, the pixel-wavelength mapping parameter is obtained by wavelength calibration of the camera, that is, by using a hyperspectral camera to photograph a series of light of known wavelengths and recording their pixel positions on the sensor, the pixel-wavelength mapping can be generated.

[0060] Spatial registration: For the discarded hyperspectral data, the images corresponding to each slit (each wavelength range) are stitched together according to the spatial offset parameter. Specifically, the spatial offset parameter is obtained through optical calibration, that is, a standard image calibration board is photographed using a hyperspectral camera, and then the images of the image ranges (each band) corresponding to each slit are manually or algorithmically registered to find the number of pixels misaligned between the two bands in the scanning direction, which is the spatial offset parameter.

[0061] The number of wavelength vacuum regions and spatial position differences is one less than the number of slits. The more slits there are, the more invalid pixels exist in the original data. Therefore, in practical design, a balance should be struck between optical image quality and the number of slits, and the number of slits should be minimized. In preferred embodiments, the number of slits is usually 2 to 3.

[0062] Wavelength calibration and image registration only need to be performed once after installing this multi-slit assembly and recording the calibration parameters; afterwards, when the camera is shooting, the previously calibrated parameters can be used for image post-processing, or written into the camera's digital signal processing firmware for automatic processing.

[0063] The following two application examples will further verify and illustrate the multi-slit optical device for improving the imaging quality of a line-scan hyperspectral camera provided in this application:

[0064] Example 1:

[0065] A hyperspectral instrument for hyperspectral photomicrography. It operates in the 400-900nm wavelength range and uses a 1 / 2” CMOS sensor. It requires a C-mount fixed-focus microscope objective and eyepiece assembly to achieve high-resolution imaging.

[0066] Tests revealed that the focal plane difference at the eyepiece exit is mainly between the visible light band (400~700 nm) and the infrared band (700~900 nm). The actual flange focal lengths for the two bands are 17.525 ± 0.005 mm and 17.568 ± 0.005 mm, respectively, with an average focal plane distance difference of approximately 0.04 mm. Based on actual photographic measurements, the difference needs to be reduced to within ±0.01 mm to meet the requirements for hyperspectral imaging quality.

[0067] To ensure that the original hyperspectral images captured are consistent with the color perception of the optical microscope, the same slit width of 10 μm is used for both the visible and infrared bands.

[0068] This embodiment is applied to a high-end hyperspectral instrument, which has high requirements for parameters such as slit size and correction accuracy, necessitating the use of high-precision manufacturing methods to produce the components. The specific implementation method is as follows:

[0069] a. Select 2 mm thick single-sided gold-plated K9 glass as the substrate and cut it into 12 mm * 7 mm rectangular blocks;

[0070] b. Using ion beam etching, two slits with a width of 10 μm and a length of 8 mm are etched along the long side of the substrate on the gold-plated surface. The two slits are 1 mm apart and symmetrically distributed on both sides of the center of the substrate, thus forming a multi-slit structure 1 with two slits, one of which is a visible light slit and the other is an infrared light slit.

[0071] c. Setting the target average focal length f0 = 17.600 mm, the calculated coating thickness for the infrared wavelength is... Therefore, a silicon dioxide coating with a thickness of about 0.07 mm is applied to the surfaces of the two gold-plated slits, which can protect the gold-plated surface and also form an optical path compensation structure in the infrared band 2.

[0072] d. Block one side of the slit and apply a secondary silicon dioxide coating to the coating surface on the other side (i.e., the visible light slit) to compensate for the optical path difference in the visible light band. The optical path difference to be compensated is... Subtracting the coating thickness already achieved in the previous step, this step requires an additional 0.09 mm of coating thickness.

[0073] e. Sequentially blocking one side of the visible light slit and one side of the infrared light slit, respectively depositing bandpass dielectric films with transmittance of 700 ~ 900 nm and 400 ~ 700 nm, forming filter structure 3, and finally forming a complete double-slit assembly, the overall result is as follows. Figure 6 As shown.

[0074] f. Based on the assembly requirements of the hyperspectral camera and the actual test results, determine the orientation of the multi-slit assembly; that is, one side of the filter structure 3 can be placed in front, forming the spatial sequence of filter structure 3-optical path compensation structure 2-multi-slit structure 1; or one side of the slit glass can be placed in front, forming the spatial sequence of multi-slit structure 1-optical path compensation structure 2-filter structure 3.

[0075] g. By performing wavelength and spatial calibration on this hyperspectral camera, the necessary parameters for wavelength selection and spatial registration are obtained, and the raw data is processed after data acquisition.

[0076] In this implementation, because the equipment is a hyperspectral microscope with high precision requirements, a glass surface coating method is used to realize the multi-slit assembly. The resulting assembly has the advantages of high precision, high integration, and modularity, while ensuring performance and stability, and also has the potential for mass production.

[0077] Example 2:

[0078] A hyperspectral camera device for industrial testing of avocado ripeness. It operates in the 500-850nm wavelength range and uses a 700,000-pixel standard definition camera with a 2 / 3” CMOS sensor. It requires a fixed-focus industrial telephoto lens.

[0079] Tests showed that the focal length of the lens to be adapted was 58.175 mm in the 500 ~ 750 nm band (hereinafter referred to as band 1), and the focal plane of the 750 ~ 850 nm band (hereinafter referred to as band 2) was 58.280 mm. The difference between the two was 0.105 mm, which is the main focal plane difference. According to actual measurements, the difference needs to be reduced to within ±0.040 mm to meet the hyperspectral imaging quality requirements.

[0080] In this embodiment, the width of the two slits is set to 50 μm, which is sufficient to meet the needs of industrial inspection.

[0081] This embodiment has lower requirements for slit width and correction accuracy, therefore a more economical implementation method is adopted. The specific implementation method is as follows:

[0082] a. The multi-slit structure 1 uses a 50 μm thick stainless steel plate as the base and is laser-cut into a 25.0 mm diameter disc according to the equipment assembly requirements;

[0083] b. The slits are 50 μm wide and 12 mm long, with a slit spacing of 2 mm. The visible light slit is located at the center of the optical axis and is formed by laser etching.

[0084] c. Setting the target average focal length to be the same as that of band 2, f0 = 58.280 mm, then band 2 does not require optical path compensation; only band 1 needs compensation. A tempered glass screen protector with a thickness of d = 0.2 mm is used as optical path compensation structure 2, with a refractive index of approximately n = 1.47. Calculations show that it can compensate approximately... The focal plane shift resulted in a final focal plane difference of 0.011 mm between the two bands, meeting the design requirements; the tempered film was processed into a "large semi-circular window piece cut from a circle with a diameter of 25.0 mm, and the cutting chord was offset from the center of the circle by 1.0 mm" using laser cutting.

[0085] d. The optical path compensation structure 2 is bonded to the slit through the silicone adhesive layer of its film material. Its outer edge coincides with the outer edge of the slit structure, and the cutting chord is parallel to the double slit and located in the middle of the double slit.

[0086] e. Use a 1.0 mm thick PMMA infrared long-pass filter 31 (750 ~ 1600 nm transparent) as the band 1 transparent filter, and use a 1.0 mm thick PMMA infrared short-pass filter 31 (below 750 nm transparent) as the band 2 transparent filter.

[0087] f. Use laser cutting to cut a PMMA infrared long-pass filter into a "small semi-circular window piece cut from a circle with a diameter of 25.0 mm, with the cutting chord offset from the center of the circle by 1.0 mm", and cut a PMMA infrared short-pass filter into a "large semi-circular window piece cut from a circle with a diameter of 25.0 mm, with the cutting chord offset from the center of the circle by 1.0 mm".

[0088] g. Two filters 31 are glued to the back of the slit structure using AB adhesive, with their outer edges coinciding with the outer edges of the slit structure. The cut chords are joined, parallel to the double slits and positioned in the center of the double slits, ultimately forming a complete double slit assembly. The overall result is as follows: Figure 7 As shown.

[0089] h. Based on the assembly requirements of the hyperspectral camera and the actual test results, determine the orientation of the multi-slit assembly; that is, one side of the optical path compensation structure 2 can be placed in front, forming the spatial order of optical path compensation structure 2-multi-slit structure 1-filter structure 31; or one side of the filter structure 31 can be placed in front, forming the spatial order of multi-filter structure 3-slit structure 1-optical path compensation structure 2.

[0090] i. By performing wavelength and spatial calibration on this hyperspectral camera, the necessary parameters for wavelength selection and spatial registration are obtained, and the raw data is processed after data acquisition.

[0091] In this implementation, because industrial inspection requires relatively low precision and the slits are wide, metal slits and a range of civilian optical materials were selected as the main components. This significantly reduced the cost of the double-slit assembly while meeting performance requirements, making it more readily adopted for price-sensitive industrial applications.

[0092] Example 3:

[0093] A high-definition hyperspectral imaging colorimeter is required, operating in the 380 ~ 760 nm (visible light band) wavelength range, using a 1” 2K resolution high-definition CCD sensor. A macro lens is needed for compatibility. Furthermore, the colorimeter must have a strong ability to detect color differences between the red and blue channels.

[0094] Since the requirement is for colorimetric measurements, referencing the CIE 1931 XYZ standard, the system is divided into three bands: blue (380nm ~ 490nm), green (490nm ~ 580nm), and red (580nm ~ 760nm), using a three-slit structure. Testing revealed that the average flange focal length for the lens to be adapted is 17.472 mm in the blue band, 17.526 mm in the green band, and 17.550 mm in the red band. Furthermore, based on actual measurements, the difference needs to be reduced to within ±0.010 mm to meet the requirements for hyperspectral imaging quality.

[0095] CCD sensors have relatively low sensitivity to red and blue light. By increasing the width of the two corresponding slits, the light flux of the three colors can be balanced, thereby improving the ability to perceive color differences in the red and blue channels.

[0096] The specific implementation method of this embodiment is as follows:

[0097] a. Select 2 mm thick single-sided gold-plated K9 glass as the substrate and cut it into rectangular blocks of 12.0 mm * 7.0 mm;

[0098] b. Using ion beam etching, three slits with a length of 8 mm are etched along the long side of the substrate on the gold-plated surface, allowing blue, green, and red light to pass through sequentially. The spacing between each pair of slits is 1 mm, and they are symmetrically distributed on both sides of the center of the substrate. The green light slit at the center of the substrate is 15 μm wide, and the red and blue light slits on both sides are 20 μm wide, forming a three-slit structure 1.

[0099] c. Dielectric film is deposited on the surface of the gold-plated slits. The three slits are coated with 380nm ~ 490nm, 490nm ~ 580nm and 580nm ~ 760nm bandpass dielectric films from top to bottom, respectively, to form a filter structure 3.

[0100] d. Set the target's average focal length to match the average focal length of the red band, f0 = 17.550 mm, and use a Schott D263M glass plate for optical path compensation; then, according to calculation, the optical path compensation thickness for the green wavelength is... A commonly used D263M glass sheet with a thickness of 0.05 mm was selected as an optical medium window 21. It was laser-cut into a rectangular block of 12.0 mm * 4.0 mm and bonded to the surface of the filter structure 3 with photocurable adhesive to cover the green and blue light slits and form a partial optical path compensation structure 2.

[0101] e. The optical path compensation thickness for blue light wavelength is After deducting the already compensated portion, an additional 0.097 mm compensation is needed. A commonly used 0.10 mm thick D263M glass sheet is selected as another optical medium window 21. It is laser-cut into 12.0 mm * 3.0 mm rectangular blocks and bonded to the surface of the filter structure 3 with photocurable adhesive, covering the blue light slit and forming a partial optical path compensation structure 2. The overall result is as follows: Figure 8 As shown;

[0102] f. Based on the assembly requirements of the hyperspectral camera and the actual test results, determine the orientation of the multi-slit assembly; that is, one side of the optical path compensation structure 2 can be placed in front, forming the spatial order of optical path compensation structure 2-filter structure 3-multi-slit structure 1; or one side of the slit glass can be placed in front, forming the spatial order of multi-slit structure 1-filter structure 3-optical path compensation structure 2.

[0103] g. By performing wavelength and spatial calibration on this hyperspectral camera, the necessary parameters for wavelength selection and spatial registration are obtained, and the raw data is processed after data acquisition.

[0104] In summary, the multi-slit optical device for improving the imaging quality of a line-scan hyperspectral camera proposed in this application has the following advantages compared to a traditional single-slit line-scan hyperspectral camera:

[0105] 1. Improved image quality: Through physical optical path compensation, the focal plane shift problem in broadband imaging is fundamentally solved, ensuring that the hyperspectral camera can obtain clear images throughout the entire operating band;

[0106] 2. Improved imaging lens adaptability: This multi-slit assembly can serve as a universal module, easily adapting to various industrial camera objective lenses with focal plane offset issues, thereby enhancing the overall flexibility and application range of hyperspectral cameras;

[0107] 3. Flexible cost-effectiveness options: Performance can be improved to varying degrees through a variety of materials and processes, allowing users to choose the most cost-effective solution based on their application's performance requirements and budget constraints;

[0108] 4. Simple structure and low modification cost: The core components of this invention are only a multi-slit plate with filtering function and a compensating glass. There is no need to modify the complex collimating lens, grating and focusing lens group inside the hyperspectral camera, nor is it necessary to replace the expensive apochromatic objective lens, which greatly reduces the difficulty and cost of implementation;

[0109] 5. High reliability: It adopts pure passive optical compensation, with no moving parts, making the system stable, reliable and long-lasting.

[0110] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera, characterized in that, The multi-slit assembly comprises a multi-slit structure, an optical path compensation structure and a filter structure. The multi-slit structure comprises at least two slits, each of which is responsible for transmitting light of a certain wavelength range. The filter structure comprises at least two filters, each of which corresponds to one slit in the multi-slit structure; different filters transmit light of different wavelengths, and the wavelength range transmitted is consistent with the corresponding slit. The optical path compensation structure is used to compensate for the displacement of the focal plane in different wavelength intervals.

2. The multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera according to claim 1, wherein, The slits are parallel to each other and parallel to the non-scanning direction of the camera.

3. The multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera according to claim 1 or 2, characterized in that, The distance between the slits is not less than 5 times the maximum working wavelength of the hyperspectral camera.

4. The multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera according to claim 1, wherein, The displacement of the focal plane compensated by the optical path compensation structure is: ； wherein, and are the average focal length and the target average focal length of the wavelength transmitted by the i-th slit, respectively; is the offset of the i-th slit. 。 5. The multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera according to claim 4, wherein, The optical path compensation structure is an optical medium window piece, which is fixed with the compensated slit plane and completely covers the compensated slit and does not cover other slits.

6. The multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera according to claim 5, wherein, a thickness of the optical path compensation structure corresponding to the i-th compensated slit satisfies the following relationship: ； wherein n is the average refractive index of the material in the wavelength range to be compensated.

7. The multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera according to claim 1, wherein, In the direction of the light, the optical path compensation structure is in front of the multi-slit structure.

8. The multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera according to claim 1, wherein, The hyperspectral camera system using the multi-slit assembly needs to process the collected hyperspectral images as follows: Wavelength screening: apply pixel-wavelength mapping parameters to the wavelength axis of the hyperspectral raw data, retain pixel data within the working wavelength range, and eliminate pixel data outside the wavelength range; Spatial registration; According to the spatial bias parameter, the images corresponding to each slit are spliced after the eliminated hyperspectral data.

9. The multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera according to claim 8, wherein, The pixel-wavelength mapping parameter is obtained by using the hyperspectral camera to shoot a series of light with known wavelengths and recording the pixel position on the sensor to generate a pixel-wavelength mapping.

10. The multi-slit optical device for improving the imaging quality of a pushbroom hyperspectral camera according to claim 8 or 9, characterized in that, The spatial bias parameter is obtained by using the hyperspectral camera to shoot a standard image calibration board and then registering the image intervals corresponding to each slit to find the number of pixels of the misalignment of each band in the scanning direction, which is the spatial bias parameter.

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