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CN-122016049-A - Scanning hyperspectral imaging device and method based on linear gradient filter

CN122016049ACN 122016049 ACN122016049 ACN 122016049ACN-122016049-A

Abstract

The invention discloses a scanning hyperspectral imaging device and method based on a linear gradient filter. The device sequentially comprises an imaging objective lens, a gradient filter assembly, a telecentric imaging lens group and a camera along the incidence direction of an optical path, and when the device works, the one-dimensional linear displacement platform drives the gradient filter assembly to perform linear scanning motion in the direction perpendicular to the optical axis, so that light rays in an imaging view field are transmitted through bandpass filter areas with different central wavelengths on the gradient filter in a time-sharing mode. The monochromatic or narrowband light after filtering is projected onto the photosensitive target surface of the camera through the telecentric imaging lens group, and multiple frames of spectral images with different wave bands are continuously collected. And after the acquired sequence images are processed and reconstructed, a hyperspectral three-dimensional data cube containing space information and spectrum information is formed. The invention has the advantages of high imaging speed, high light flux, compact system structure, low cost and the like, and is suitable for hyperspectral data acquisition scenes with higher real-time requirements.

Inventors

  • HE SAILING
  • Zou Xiaer

Assignees

  • 浙江大学

Dates

Publication Date
20260512
Application Date
20260413

Claims (10)

  1. 1. A scanning hyperspectral imaging device based on a linear gradient filter, comprising: An imaging objective lens, a graded filter component, a telecentric imaging lens group and a camera which are sequentially arranged along the incidence direction of the light path; the gradual change filter plate component is arranged on a one-dimensional linear displacement platform, and the displacement platform drives the gradual change filter plate component to perform linear scanning movement in a direction perpendicular to the optical axis of the system; The graded filter plate component has the characteristic of central wavelength transmittance which linearly changes along the surface space position and is used for splitting an incident light beam; the telecentric imaging lens group is used for projecting the split light beams onto a photosensitive target surface of the camera so as to ensure that the principal ray is parallel to the optical axis for incidence and ensure the consistency of spectral characteristics of each position of the filter; The camera continuously collects images at a high frame rate in the scanning process, and each frame of image corresponds to one scanning position of the gradual change filter component and a corresponding spectrum band; The one-dimensional linear displacement platform is provided with a position feedback sensor and is used for feeding back the current position of the gradual change filter component in real time, so that the mapping relation between the scanning position and the central wavelength is established.
  2. 2. The apparatus of claim 1, further comprising a bandwidth adjustment mechanism for effecting continuous fine tuning of the synthesized spectral bandwidth by adjusting the relative position or transmission characteristics of the filters within the graded filter block assembly; The gradual change filter assembly comprises a linear gradual change long-wave pass filter and a linear gradual change short-wave pass filter which are arranged in parallel and laminated along the direction of an optical axis, the linear change directions of the linear gradual change long-wave pass filter and the linear gradual change short-wave pass filter are consistent, the peak transmittance is not lower than 90%, a band-pass window with adjustable bandwidth is formed by adjusting the relative position, and the bandwidth adjusting mechanism is used for adjusting the relative position of the linear gradual change long-wave pass filter and the linear gradual change short-wave pass filter, so that continuous fine adjustment of the bandwidth within a range of 5 nm-50 nm is realized.
  3. 3. The apparatus of claim 1, wherein the graded filter component is a monolithic linear graded bandpass filter having a transmission center wavelength that varies linearly and continuously along a geometric axis of the filter, a wavelength graded range of 400 nm to 1000 nm, a full width at half maximum (FWHM) of 10 nm to 20 nm, and a peak transmittance of not less than 80%.
  4. 4. The apparatus of claim 1, wherein the telecentric imaging lens group is an object-side telecentric lens or a double telecentric lens, the object plane position of which matches the center position of the graded filter member to ensure that the incident chief ray is parallel to the optical axis, and the optical system error of the lens group is controlled within λ/10.
  5. 5. The device of claim 1, wherein the camera is a high frame rate area array detector and is electrically connected with the one-dimensional linear displacement platform through a synchronous control unit, and the camera triggers acquisition at a preset frame rate in the scanning process, so that accurate synchronization of image acquisition and filter position is realized; The one-dimensional linear displacement table comprises a precise electric sliding table and a position feedback sensor, wherein the sensor is used for feeding back the current position of the gradual change filter component in real time and supporting wavelength positioning and data reconstruction.
  6. 6. The device according to claim 2, wherein the bandwidth adjusting mechanism adjusts the relative position or transmission characteristic of each filter in the graded filter plate assembly to achieve fine adjustment of the synthesized spectrum bandwidth, the adjustment range is 5 nm to 50 nm, and the adjustment step is less than or equal to 10 μm.
  7. 7. The apparatus of claim 1, wherein the spectral scaling process of the hyperspectral data comprises: (i) Removing the imaging objective lens, and irradiating the device by using a wide-field standard characteristic spectrum light source; (ii) Extracting pixel width coordinates w of characteristic spectral lines from an image corresponding to the position x of each one-dimensional linear displacement table, and establishing a wavelength function relation lambda (x, w) =a·x+b·w+c by using a least square method in combination with a known standard wavelength lambda 0 ; (iii) The data reconstruction process comprises the steps of calculating the actual center wavelength corresponding to each pixel of each frame of image according to a wavelength function lambda (x, w), carrying out space alignment and splicing on an image sequence based on a calculation result, setting a fixed spectrum coordinate grid, reconstructing spectrum information of all pixel points to the grid through an interpolation algorithm, and generating a hyperspectral three-dimensional data cube.
  8. 8. The apparatus of claim 7, wherein the establishing of the wavelength function λ (x, w) further comprises performing a multi-frame averaging process on the sequence of scaled images to reduce noise and improve fitting accuracy, and the fitting residual is less than or equal to 2 nm.
  9. 9. The device of claim 1, wherein the device is suitable for tissue blood oxygen imaging, short wave infrared drug identification, agricultural remote sensing, food safety detection, or industrial sorting applications.
  10. 10. A method of hyperspectral data acquisition using the apparatus as claimed in claim 7 or 8 comprising the steps of: S1, introducing light rays of a target scene into a light path through an imaging objective lens; S2, controlling a one-dimensional linear displacement table to drive the gradual change filter assembly to perform linear scanning in the direction perpendicular to the optical axis, wherein the speed is 5-50 mm/S; S3, synchronously acquiring a series of two-dimensional narrow-band images penetrating through the filter plate by the camera at a preset frame rate of more than or equal to 60 fps in the scanning process, wherein each frame of image corresponds to a scanning position x and a central wavelength lambda; S4, recording a scanning position x corresponding to each frame of image, and determining a center wavelength corresponding to each frame of image according to the linear dispersion characteristic of the gradient filter and a wavelength function lambda (x, w); and S5, carrying out space alignment and spectrum interpolation reconstruction on the acquired image sequence to generate a hyperspectral three-dimensional data cube containing space and spectrum information, wherein the spectrum dimension step length is less than or equal to 5 nm.

Description

Scanning hyperspectral imaging device and method based on linear gradient filter Technical Field The invention belongs to the technical field of spectrum imaging, and particularly relates to a scanning type high-flux rapid hyperspectral imaging device based on a linear gradient filter (Linear Variable Filter, LVF) and a corresponding hyperspectral data acquisition and reconstruction method. Background The hyperspectral imaging technology is used as a detection means integrating image information and spectrum information, and can acquire two-dimensional space morphology and one-dimensional spectrum characteristics of a target object under continuous narrow wave bands, so that the deep analysis and the accurate identification of the components of the target substance are realized. With the development of sensor technology and photoelectric materials, hyperspectral imaging has moved from laboratory research to a plurality of practical application fields such as agricultural remote sensing, industrial automatic detection, food safety sorting and biomedical diagnosis. However, how to realize high luminous flux, high acquisition speed and low system cost while ensuring high spatial resolution is always a core appeal in the technical field of hyperspectral detection. In the fields of agriculture and food safety, the hyperspectral imaging technology can capture the tiny spectral change of crops, so that early warning is carried out at the early stage of occurrence of plant diseases and insect pests and when the plant diseases are not recognized by naked eyes. By analyzing the reflectivity of a specific wave band, the system can accurately evaluate the chlorophyll content, the water content and the nitrogen fertilizer level of vegetation, and provide data support for accurate fertilization and irrigation. On the food processing line, the technology can realize non-contact detection of the internal quality of agricultural products, such as sugar degree classification of fruits, mildew screening of grains and component analysis of meat products, and greatly improves the detection efficiency and accuracy. In the field of industrial detection and resource recovery, hyperspectral imaging is a core tool for complex component identification by virtue of the advantage of 'map-in-one'. In the process of manufacturing the lithium battery, the technology can be used for detecting the uniformity of a pole piece coating and identifying surface defects, in the process of recycling waste resources, aiming at engineering plastics (such as PE, PP, PET and the like) with similar colors and different chemical components, the traditional machine vision is difficult to distinguish, and the hyperspectral imaging can realize the automatic separation with extremely high purity according to the unique spectral fingerprint. In addition, the technology also has irreplaceable application potential in the fields of textile component identification and cultural relic restoration. In the biomedical and pharmaceutical fields, hyperspectral imaging provides a new idea for noninvasive diagnosis. Because different tissues and lesion areas have different absorption and scattering properties for light of specific wavelengths, the technology can be used for assisting early screening of skin cancers, blood oxygen saturation monitoring in operation and accurate definition of tumor edges. In the production of medicines, the distribution uniformity and impurity content of active ingredients can be monitored in real time by carrying out hyperspectral scanning on tablets or powder, so that the quality of medicines is ensured to meet the standard. However, the above-mentioned fields place extremely high demands on the real-time performance and luminous flux of the imaging device, and it is often difficult for the existing imaging apparatus to strike a balance between high performance and low cost. Currently, the main hyperspectral imaging schemes on the market have obvious technical limitations in practical application. The time-sharing imaging technology represented by a Liquid Crystal Tunable Filter (LCTF) can rapidly switch the wave bands through an electric control mode, but the peak transmittance of the system is extremely low due to the principle of polarization interference, and the light energy utilization rate is usually less than 20%, so that the exposure time of the system in a weak light environment is required to be greatly prolonged, the detection capability of a dynamic target is greatly limited, and meanwhile, the core device has the advantages of complex manufacturing process, high acquisition cost and difficult large-scale popularization in an industrial production line. Another common push-broom spectral imaging technique uses slits and dispersive elements (such as gratings or prisms) to split light, and the presence of physical slits severely attenuates the light flux entering the detector despite the high spectral resolution, and in additi