Coding LED lighting source and active hyperspectral imaging system

Abstract

The invention discloses a coding LED illumination light source and an active hyperspectral imaging system, and effectively overcomes the defects of insufficient luminous flux and low signal-to-noise ratio in the current active hyperspectral imaging system based on the LED illumination light source. The system comprises an LED control module, an LED light-emitting module, a heat dissipation module, a focusing and dodging module, an imaging lens, an image detector, a computer and the like. The method is characterized in that coding illumination is carried out through a plurality of LEDs with different wavelength combinations based on a spectrum calculation principle, the illumination intensity of the active hyperspectral imaging system is multiplied, and the signal-to-noise ratio and the sampling speed of the system are improved. The invention provides a novel active hyperspectral imaging mode which can effectively meet the application requirements in different scenes such as high-resolution microscopic hyperspectral imaging and video-level high-speed hyperspectral imaging.

Description

Technical Field

[0001] The present invention relates to a coded LED illumination light source and an active hyperspectral imaging system, which are applicable to multiple fields such as food safety, industrial inspection, chromaticity measurement, biomedical detection, etc. Background Art

[0002] Hyperspectral imaging has witnessed vigorous development in recent years. It enriches traditional imaging methods and can provide unprecedented detailed features of objects. As a high-dimensional perception method, it plays an increasingly important role in fields such as precision agriculture, food safety inspection, environmental monitoring, and medical imaging. Traditional hyperspectral imaging technologies use various spectral splitting elements for spectral acquisition, including gratings, prisms, liquid crystal tunable filters, linear variable filters, etc. Such technologies have problems such as poor stability, long scanning time, and large volume. In the configuration of this traditional method, the quality of the spectral splitting element determines the performance of the imaging spectrometer. In order to obtain high-resolution spectral data, large-size and high-precision grating devices are often required, which further increases the device cost. In addition, in this type of hyperspectral imaging equipment, there is a mutual restriction relationship between spectral resolution and optical flux. The higher the spectral resolution, the lower the optical flux, thereby reducing the signal-to-noise ratio of the equipment and severely limiting the use of this equipment in low-light and dark environments. Currently, this hyperspectral imager is mainly applied in fields such as satellite monitoring.

[0003] In addition, the active hyperspectral imaging system based on LEDs has received extensive attention in recent years due to its advantages such as small volume, low price, and fast scanning speed. A typical active hyperspectral imaging system based on LEDs includes multiple LEDs with different central wavelengths. By sequentially turning on each LED and using a black-and-white camera to capture the images of the object under the illumination of each LED band, a multi-band hyperspectral image can be obtained. This type of active hyperspectral imaging system eliminates cumbersome steps such as the movement of mechanical structures and image registration, reduces the terminal computing overhead, and thus can conveniently and quickly obtain hyperspectral image data.

[0004] However, for existing LED active illumination systems, although the LED response speed is very fast, due to the narrow spectral bandwidth of a single LED, when collecting spectra by sequentially turning on LEDs, if the reflectance / transmittance of the sampled object is low, this illumination method faces the problem of insufficient single-channel optical flux. If the exposure time is extended to increase the optical flux, the imaging speed will be reduced; if the exposure time is not extended, the signal-to-noise ratio of the image in this band will decrease and the restoration accuracy will be reduced. Summary of the Invention

[0005] The present invention proposes a coded LED lighting technology and an active hyperspectral imaging system. By using a number of LEDs with different wavelength combinations for coded lighting each time and combining computational spectral imaging technology, the restoration of hyperspectral images is achieved, completely solving the problem of insufficient light flux in traditional active hyperspectral imaging systems based on LEDs, realizing high-speed hyperspectral imaging with high signal-to-noise ratio, and meeting the requirements of hyperspectral imaging in low-light and dynamic scenarios.

[0006] The coded LED lighting source applied to the active hyperspectral imaging system is composed of an LED control module, an LED lighting module, a heat dissipation module, and a focusing and homogenizing module. The LED lighting module contains several LED beads with different central wavelengths. During single illumination, the LED control module controls several LED beads with different wavelength combinations to light up simultaneously to achieve coded lighting. Among them, the selection method of the LED beads participating in coded lighting is as follows: Suppose there are LED beads with different central wavelengths, and each LED bead can be numbered 1, 2... , and the total number of illumination times is ; The LED control module stores an integer matrix with values of 0 and 1, called the coding matrix, whose length is , where the number of rows represents different illumination times, the number of columns represents different numbered beads, and the numbers 0 and 1 represent the states of the LED beads, 0 represents off, and 1 represents on; During illumination, the LED control module controls whether the corresponding numbered LED beads light up according to the state numbers in this matrix; Any two row vectors in the coding matrix are different.

[0007] Among them, in the LED lighting module, each LED bead is connected to a driving chip, and the driving chip can be controlled by the LED control module. By controlling the output current intensity or pulse width, the light intensity of the LED bead at this central wavelength can be controlled; The LED control module is connected to the LED lighting module and the heat dissipation module through data lines.

[0008] Among them, the heat dissipation module includes a temperature sensor and a radiator. Among them, the radiator is attached to the lower side of the LED lighting module through a heat-conducting adhesive, and the temperature sensor is attached to the LED lighting module to monitor its temperature and transmit this temperature information to the LED control module. The LED control module controls the operation of the heat dissipation module according to this signal, so that the LED lighting module is always at a normal operating temperature.

[0009] Among them, the focusing and homogenizing module is located above the LED lighting module and is composed of two achromatic convex lenses. The distance between the first achromatic convex lens and the LED lighting module is greater than its focal length, which is used to converge the LED light beam to the imaging plane; The distance between the second achromatic convex lens and this plane is exactly its focal length.

[0010] Active hyperspectral imaging system based on coded LED lighting source, which includes an LED lighting source, an objective lens, a tube lens, an image detector, and a computer. The computer is respectively connected to the LED lighting source and the image detector.

[0011] The corresponding spectral image acquisition and restoration method is as follows: The LED lighting source and its corresponding spectral image acquisition and restoration method are as follows: The computer applies synchronous signal triggers to the LED lighting source and the image detector respectively to trigger the LED lighting source to work, and at the same time the image detector acquires images; Different combinations of drive signals are sequentially applied to the LED lighting source, and the image detector acquires different image data; The spectral response of the LED lighting source under different drive signals is pre-calibrated, and finally the spectral image is restored through a calculation restoration method. The relationship between the image data acquired by the image detector and the spectral image to be measured is shown in the following formula: , where represents the output signal of a single pixel of the image detector under different drive voltages, represents different wavelengths, is the calibrated emission spectrum of the LED under the th illumination, that is, the response matrix, is the incident spectrum, is the number of spectral channels, is the total number of wavelength channels, is the spectral intensity at the wavelength channel; Solving the above equation can restore the hyperspectral image information from the intensity information of each pixel of the image detector.

[0012] Furthermore, in this solution, the central wavelength and quantity of the LED lamp beads can be selected according to the spectral resolution and working band, aiming to completely cover the working band. When working in different bands, devices such as a condenser and homogenizer module suitable for that band need to be selected.

[0013] Furthermore, in this solution, the luminous intensity and spectrum of the LED lamp beads need to be pre-calibrated in advance so that the entire LED lighting source has a relatively flat spectrum in the working band.

[0014] Furthermore, in this solution, at least 2 LED lamp beads with different central wavelengths need to participate in the illumination each time for the LED lamp bead illumination method to achieve a higher luminous flux.

[0015] Furthermore, in this solution, during a single illumination, the LED lamp beads participating in the illumination can be determined through an optimization algorithm, aiming to ensure that in different illumination rounds, the emission spectral lines of the participating LED lighting sources are as orthogonal as possible to ensure the accuracy of spectral restoration.

[0016] The beneficial effects of the present invention are as follows: The encoded LED illumination source and its active spectral imaging system proposed by the present invention overcome the disadvantages of insufficient light flux and low signal-to-noise ratio in the current active hyperspectral imaging system based on LEDs. Based on the principle of computational spectroscopy, by using the method of encoding illumination with LED lamp beads, the illumination intensity of such active hyperspectral imaging systems is effectively improved, and the signal-to-noise ratio and sampling speed are increased. Description of the Drawings

[0017] Figure 1 Schematic diagram of an encoded LED illumination source applied to an active hyperspectral imaging system.

[0018] Figure 2 Schematic diagram of a calibration system for an encoded LED illumination source applied to an active hyperspectral imaging system.

[0019] Figure 3 Schematic diagram of an active hyperspectral imaging system based on an encoded LED illumination source system.

[0020] Figure 4 Schematic diagram of an encoding matrix based on a random 0-1 matrix.

[0021] Figure 5 Emission spectra of 12 LED lamp beads measured experimentally.

[0022] Figure 6 Spectral restoration effect using the light source of the present invention.

[0023] Figure 7 Schematic diagram of another calibration system for an encoded LED illumination source applied to an active hyperspectral imaging system.

[0024] Figure 8 Schematic diagram of another active hyperspectral imaging system based on the encoded LED illumination source system of the present invention.

[0025] Figure 9 Schematic diagram of an encoding matrix based on a Hadamard matrix.

[0026] Description of the Reference Numerals

[0027] LED control module 1, LED light-emitting module 2, heat dissipation module 3, focusing and homogenizing module 4, LED lamp bead 21, lit LED lamp bead 211, extinguished LED lamp bead 212, drive chip 22, temperature sensor 31, radiator 32, first achromatic convex lens 41, second achromatic convex lens 42, spectrometer 5, object to be measured 6, objective lens 7, tube lens 8, image detector 9, computer 10, LED illumination source 11, mirror 12, semi-transparent and semi-reflective mirror 13, imaging module 14. Detailed Embodiments

[0028] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0029] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0030] The coded LED illumination light source and its active hyperspectral imaging system proposed by the present invention will be described below with reference to the accompanying drawings.

[0031] Embodiment 1: As Figure 1 shown, a coded LED illumination light source 11 applied to an active hyperspectral imaging system is composed of an LED control module 1, an LED light emitting module 2, a heat dissipation module 3, and a focusing and homogenizing module 4. Before hyperspectral imaging, spectral calibration is performed on the LED illumination light source 11. As Figure 2 shown is a calibration system of the present invention. In the system, the LED illumination light source 11 passes through the objective lens 7 and the tube lens 8, and then is received by the spectrometer 5. The computer 10 is connected to the LED control module 1, reads the state numbers of the coding matrix row by row, and controls several different combinations of LED beads 21 to light up according to the coding matrix; at the same time, the spectrometer 5 is used to obtain the light emission spectrum of the light source under this coded illumination; repeat times, and the times of spectral responses constitute a measurement matrix . The number of rows of this measurement matrix is the total number of illumination rounds, and the number of columns is the number of spectral sampling channels of this system.

[0032] As Figure 3 shown is a hyperspectral imaging system based on the LED illumination light source 11. Among them, the computer 10 is respectively connected to the LED control module 1 and the image detector 9. The LED illumination light source 11 irradiates the light beam onto the object to be measured 6. The object to be measured is located at the focal plane of the objective lens 7, and the transmitted light passes through the objective lens 7 and the tube lens 8 and is imaged on the image detector 9. During measurement, the computer 10 reads the state numbers of the coding matrix row by row, and according to the coding matrix ( Figure 4 ), controls several different combinations of LED beads 21 to light up. At the same time, the image detector 9 is used to capture the images of the object under different illumination conditions. Among them, the coding matrix taking values 0 and 1 is generated by the principle of a random integer matrix. Through rounds of coded illumination, An encoded spectral image. The intensities of individual pixels in the image under this measurement constitute the response matrix .

[0033] Using the response matrix Spectral and image restoration can be performed by the least squares algorithm. Without loss of generality, considering a single pixel of the image detector 9, the principle of hyperspectral imaging restoration is described as follows: , where, is the intensity value of a single pixel under the th illumination, is the emission spectrum of the LED under the th illumination, that is, the response matrix, is the incident spectrum, is the number of spectral channels, is the total number of wavelength channels, is the spectral intensity at the wavelength channel.

[0034] Solving several unknowns of this linear equation system, which is the spectral data of each image pixel. As Figure 5 shown are the emission spectral data of 12 LEDs measured in the experiment, Figure 6 is the spectral restoration effect achieved by using the encoded illumination of these 12 LEDs.

[0035] Example 2: Before hyperspectral imaging, spectral calibration is performed on the LED illumination source 11. As Figure 7 shown is another calibration system of the present invention. In the system, the LED illumination source 11 passes through the semi-transparent and semi-reflective mirror 13, passes through the objective lens 7 to reach the mirror 12, and then the reflected light passes through the objective lens 7, the semi-transparent and semi-reflective mirror 13, and the tube lens 8, and then is received by the spectrometer 5. The computer 10 is connected to the LED control module 1, reads the status numbers of the encoding matrix row by row, and controls several different combinations of LED beads 21 to light up according to the encoding matrix; meanwhile, the spectrometer 5 is used to obtain the emission spectrum of the light source under this encoding illumination; repeat times, and the spectral responses constitute the measurement matrix . The number of rows of this measurement matrix is the total number of illumination rounds, and the number of columns is the spectral sampling channel number of this system.

[0036] As Figure 8Shown is a hyperspectral imaging system based on the LED lighting source 11. Among them, the computer 10 is respectively connected to the LED control module 1 and the image detector 9. The LED lighting source 11 irradiates the light beam onto the object to be measured 6 through the semi-transparent and semi-reflective mirror 13 and the objective lens 7. The object to be measured is located at the focal plane of the objective lens 7. The transmitted light passes through the objective lens 7 and the tube lens 8 and is imaged on the image detector 9. During measurement, the computer 10 reads the state numbers of the coding matrix row by row. According to the coding matrix, it controls several different combinations of LED beads 21 to light up. At the same time, the image detector 9 is used to capture the images of the object under different lighting conditions. Among them, the coding matrix is generated by the Hadamard matrix ( Figure 9 )). Through rounds of coded illumination, coded spectral images can be obtained. The intensity of a single pixel in the image under this measurement constitutes the response matrix.

[0037] Using the response matrix , spectral and image restoration can be performed through the least squares algorithm. Without loss of generality, considering a single pixel of the image detector 9, the hyperspectral imaging restoration principle is described as follows: , where is the intensity value of a single pixel under the th illumination, is the emission spectrum of the LED under the th illumination, that is, the response matrix, is the incident spectrum, is the number of spectral channels, is the total number of wavelength channels, is the spectral intensity under the th wavelength channel.

[0038] Solving several unknowns of this linear equation system, this is the spectral data of each image pixel point.

[0039] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An encoded LED illumination light source applied to an active hyperspectral imaging system, which is composed of an LED control module (1), an LED light-emitting module (2), a heat dissipation module (3), and a focusing and light homogenizing module (4), and is characterized in that: The LED lighting module (2) includes a number of LED beads (21) with different central wavelengths; during single illumination, the LED control module (1) controls a number of LED beads (21) with different wavelength combinations to be lit simultaneously to achieve coded illumination; among them, the selection method of the LED beads (21) participating in the coded illumination is as follows: There are LED beads (21) with different central wavelengths, and each LED bead (21) can be numbered 1, 2... , and the total number of illumination times is ; the LED control module (1) stores a random integer matrix with values of 0 and 1, which is called a coding matrix, and its length is , where the number of rows represents different illumination times, the number of columns represents LED beads with different numbers, and the numbers 0 and 1 represent the states of the LED beads (21), 0 represents off, and 1 represents on; during illumination, the LED control module (1) controls whether the corresponding numbered LED beads (21) are lit according to the number of states in the coding matrix; any two row vectors in the coding matrix are different.

2. The encoded LED illumination light source applied to an active hyperspectral imaging system according to claim 1, wherein: In the LED light-emitting module (2), each LED lamp bead (21) is connected to a driving chip (22). The driving chip (22) can be controlled by the LED control module (1). By controlling the output current intensity or pulse width, the light-emitting intensity of the LED lamp bead (21) at the central wavelength can be controlled. The LED control module (1) is connected to the LED light-emitting module (2) and the heat dissipation module (3) through data lines.

3. The encoded LED illumination light source applied to an active hyperspectral imaging system according to claim 1, wherein: The heat dissipation module (3) includes a temperature sensor (31) and a radiator (32). Among them, the radiator (32) is connected under the LED light-emitting module (2) through a thermal conductive adhesive. The temperature sensor (31) is attached to the LED light-emitting module (2) to monitor its temperature and transmit the temperature information to the LED control module (1). The LED control module (1) controls the operation of the heat dissipation module (3) according to this signal, so that the LED light-emitting module (2) is always at a normal operating temperature.

4. The coded LED illumination light source applied to the active hyperspectral imaging system according to claim 1, wherein: The focusing and light homogenizing module (4) is located above the LED light-emitting module (2) and is composed of a first achromatic convex lens (41) and a second achromatic convex lens (42). The distance between the first achromatic convex lens (41) and the LED light-emitting module (2) is greater than its focal length, which is used to converge the LED light beam to the imaging plane. The distance between the second achromatic convex lens (42) and this plane is exactly its focal length.

5. An active hyperspectral imaging system based on the encoded LED illumination light source according to claim 1, characterized in that: It includes an LED illumination light source (11), an imaging module (14), an image detector (9), and a computer (10). The computer (10) is respectively connected to the LED illumination light source (11) and the image detector (9) to output control signals. The imaging module (14) is responsible for focusing on the scene to be measured so that a clear image is formed on the image detector (9). The image detector (9) is responsible for collecting the encoded image of the scene to be measured after being illuminated by the LED illumination light source (11).

6. The active hyperspectral imaging system based on a coded LED illumination source according to claim 5, wherein: The LED illumination light source (11) and its corresponding spectral image acquisition and restoration method are as follows: The computer (10) applies synchronous signal triggers to the LED illumination light source (11) and the image detector (9) respectively to trigger the LED illumination light source (11) to work, and at the same time the image detector (9) collects images. Different combinations of driving signals are applied to the LED illumination light source (11) in sequence, and the image detector (9) collects different image data. The spectral response of the LED illumination light source (11) under different driving signals is pre-calibrated, and finally the spectral image is restored by a calculation method. The relationship between the image data collected by the image detector and the spectral image to be measured is shown by the following formula: ， Among them represents the output signal of a single pixel of the image detector under different driving voltages, represents different wavelengths, is the th emission spectrum of the LED under illumination obtained by calibration, that is, the response matrix, is the incident spectrum, is the number of spectral channels, is the total number of wavelength channels, is the spectral intensity under the wavelength channel; solving the above equation can recover the hyperspectral image information from the intensity information of each pixel of the image detector.

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