An automatic exposure method and system for a differential absorption spectrometer

Abstract

This invention discloses an automatic exposure method and system for a differential absorption spectrometer, relating to the field of spectrometer technology. Based on a calibrated fast-exposure differential imaging spectroscopy system, parameters are set. Under the current light intensity, hyperspectral data output by the differential absorption spectrometer and three-channel values ​​output by a visual camera are simultaneously acquired. Based on the three-channel values ​​and the set parameters, the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity is obtained. The target pixel value of the hyperspectral data is substituted into the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity to obtain the target exposure time. The target exposure time is corrected, and the corrected target exposure time is set as the exposure time of the differential absorption spectrometer and fed back to the differential absorption spectrometer to obtain spectral data. This automatic exposure method and system can acquire hyperspectral data with a high signal-to-noise ratio.

Description

Technical Field

[0001] This invention relates to the field of spectrometer technology, and in particular to an automatic exposure method and system for a differential absorption spectrometer. Background Technology

[0002] In the field of spectral imaging technology, in order to ensure both data acquisition efficiency and spectral data quality, different exposure times need to be set according to the changes in light intensity in the actual application scenario.

[0003] Traditional automatic exposure methods are not suitable for spectrometer-type imaging systems, and usually require at least 3-4 images for exposure measurement, wasting the data acquisition time window. Automatic exposure values ​​can be obtained by taking multiple images using spectral data acquired by an imaging spectrometer, but this is no longer applicable to imaging spectrometers with mechanical shutters or in situations requiring higher acquisition efficiency.

[0004] Imaging system brightness adjustment parameters typically include three types: aperture size, exposure time, and imaging gain (i.e., magnification). Therefore, adjusting the brightness of the target image involves adjusting these three parameters.

[0005] Automatic exposure refers to the imaging system automatically adjusting its parameters to achieve a specified brightness standard for the target image. This standard is the target brightness evaluation algorithm, which typically includes three types: average brightness method, weighted average method, and brightness histogram method. The average brightness method calculates the average brightness of all pixels in the image, continuously adjusting exposure parameters to eventually reach the target brightness. The weighted average method assigns different weights to different areas of the image to calculate brightness. The brightness histogram method calculates image brightness by assigning different weights to the peak values ​​in the histogram.

[0006] The spectrometer imaging system acquires the spectral information of the target region. Target brightness can be evaluated (i.e., photometry) using the average brightness method, which obtains the average brightness information across the entire target region. When high brightness information for a specific characteristic band is needed, data from its corresponding inversion band can be obtained, thus specifying a band with higher brightness—this is the band-dependent automatic exposure imaging method. This method acquires the target light intensity through multiple exposures and calculates the target exposure time, shortening the photometry time by reading only a few lines of data from the detector.

[0007] Differential imaging spectrometers typically use spectral inversion in the 300-400nm band to obtain trace gas concentrations in the target region. To significantly improve acquisition efficiency and spectral data quality, a rapid, automatic exposure imaging method is required.

[0008] Existing photometric methods are not suitable for imaging spectrometers: (1) The photometric time is relatively long; usually, 3-4 full-view images need to be taken for photometric measurement before data acquisition, which wastes the data acquisition time window. (2) Band-correlated automatic exposure imaging methods still require multiple exposures during the acquisition window, and are not applicable to situations using mechanical shutters or situations requiring more efficient data acquisition. Summary of the Invention

[0009] Based on the technical problems existing in the background technology, the present invention proposes an automatic exposure method and system for a differential absorption spectrometer. It eliminates the need for photometry using a differential absorption spectrometer, saves the photometry cycle, makes full use of the data acquisition time window, can greatly improve the data acquisition efficiency of the equipment, realize rapid automatic exposure imaging, and extend the service life of the mechanical shutter.

[0010] The present invention proposes an automatic exposure method for a differential absorption spectrometer, comprising the following steps:

[0011] Step 1: Based on the calibrated fast-exposure differential imaging spectroscopy system, set the exposure time, aperture value, and fitting parameters of the visual camera, and simultaneously set the exposure time range [T] of the differential absorption spectrometer. min T cali Additionally, the original exposure time-pixel value curve corresponding to the differential absorption spectrometer is obtained;

[0012] Step 2: Under the current light intensity, simultaneously acquire the hyperspectral data output by the differential absorption spectrometer and the three-channel values ​​output by the visual camera. Based on the three-channel values ​​and the fitted parameters, calculate the differential absorption spectrometer's performance at exposure time T. cali The pixel values ​​are combined with the offset value corresponding to 0 seconds of exposure in the original exposure time-pixel value curve to obtain the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity.

[0013] Step 3: Substitute the target pixel value of the hyperspectral data into the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity to obtain the target exposure time T;

[0014] Step 4: Determine if the target exposure time T is within the exposure time range [T] min T cali Within this, the exposure time will be less than the minimum exposure time T. min The target exposure time T is set as T = T min It will be greater than the maximum exposure time T. cali The target exposure time T is set as T = T cali To correct the target exposure time T to the exposure time range [T] min T cali [Among];

[0015] Step 5: Set the corrected target exposure time T as the exposure time of the differential absorption spectrometer and feed it back to the differential absorption spectrometer to obtain spectral data.

[0016] Furthermore, the calibration process of the fast exposure differential imaging spectral system is as follows:

[0017] (a1) Determine the target light intensity range of the differential absorption spectrometer based on actual application scenarios [L] min L max [and the original exposure time-pixel value curves of the differential absorption spectrometer under different illuminations, L] min L is the minimum light intensity value. max This represents the maximum light intensity value.

[0018] (a2) Based on the noise level of the differential absorption spectrometer imaging, the noise zone 1 of the maximum output value of the differential absorption spectrometer is obtained, thereby setting the pixel value boundary conditions [DN] of the differential absorption spectrometer during the calibration stage. min DN max and exposure time range [T] min T cali ];

[0019] (a3) Based on the range of light intensity of the observed target [L] min L max Determine the exposure time-grayscale value relationship curve of the visual camera at different apertures, and set the effective grayscale value range of the visual camera image based on the Noise Zone2 of the visual camera. min Gr max ];

[0020] (a4) Set the exposure time T2 of the visible camera to be less than the maximum exposure time T. cali The exposure time-grayscale value relationship curves under different apertures with exposure time T2 were obtained, and the effective grayscale value range closest to the effective grayscale value range [Gr] was selected. min Gr max The aperture of the camera is the effective aperture, at which point the dynamic range of the camera is at its maximum.

[0021] (a5) Set the exposure time and aperture size of the visible camera based on the exposure time T2 and the effective aperture;

[0022] (a6) Based on the fact that the field of view of the visual camera covers the field of view of the differential absorption spectrometer, the field of view of the visual camera and the field of view of the differential absorption spectrometer are calibrated.

[0023] (a7) Based on the calibrated visual camera and differential absorption spectrometer, targets in practical application scenarios are photographed to obtain the light intensity range of multiple observed targets [L].min L max The data includes hyperspectral data output from the differential absorption spectrometer and three-channel values ​​output from the visual camera.

[0024] (a8) Based on the field of view in (a6), integrate the common field of view data and pixel value boundary conditions of the differential absorption spectrometer and the visual camera [DN]. min DN max and the effective grayscale value range [Gr] min Gr max By fitting the three-channel numerical and hyperspectral data, the relationship between the pixel values ​​of the differential absorption spectrometer and the pixel values ​​of the visual camera is obtained, and the fitting parameters are obtained, which are the calibration results.

[0025] Furthermore, in (a2), the pixel value boundary conditions of the differential absorption spectrometer during the calibration stage [DN] min DN max and exposure time range [T] min T cali The setup process for ] is as follows:

[0026] Set the maximum effective pixel value DN max The maximum effective pixel value DN is obtained when the value is less than 50% of the noise zone 1. max Corresponding to the maximum light intensity condition L max Maximum exposure time T cali ;

[0027] Combined with the minimum light intensity value L min The original exposure time-pixel value curve is used to obtain the exposure time T. cali At the minimum light intensity value L min The minimum effective pixel value DN corresponding to the time min ;

[0028] According to the maximum light intensity condition L max The original exposure time-pixel value curve below, its minimum effective pixel value DN min The corresponding time is set to the minimum exposure time T. min .

[0029] Furthermore, in (a3), the effective grayscale value range of the visible camera image [Gr] min Gr max The setup process for ] is as follows:

[0030] Set the maximum effective grayscale value Gr max The maximum effective gray value Gr was obtained at different apertures by measuring less than 50% of the noise zone 2 of the visible camera. max Corresponding to the maximum light intensity condition L maxMaximum exposure time T s ;

[0031] Combining the minimum light intensity value L at different apertures min The corresponding exposure time-grayscale value relationship curve yields the exposure time T. s At the minimum light intensity value L min The minimum effective gray value Gr corresponding to time min .

[0032] Furthermore, in (a8): the relationship between the pixel values ​​of the differential absorption spectrometer and the pixel values ​​of the visual camera is obtained by fitting the three-channel numerical and hyperspectral data, and the fitting parameters are obtained, wherein the formula for the relationship between the pixel values ​​of the differential absorption spectrometer and the pixel values ​​of the visual camera is as follows:

[0033]

[0034] Where N is the pixel value of the differential absorption spectrometer, α, β, γ, α′, β′, and γ′ are all fitting parameters, R, G, and B are the three-channel values ​​of the visual camera, and δ and δ′ are the balancing parameters.

[0035] Furthermore, in step two, based on the three-channel values ​​and the fitting parameters, and using the formula relating the pixel values ​​of the differential absorption spectrometer to the pixel values ​​of the visual camera, the exposure time T of the differential absorption spectrometer is calculated. cali The pixel values ​​below.

[0036] An automatic exposure system for a differential absorption spectrometer is provided, which realizes automatic exposure of the differential absorption spectrometer based on a calibrated fast exposure differential imaging spectroscopy system. The fast exposure differential imaging spectroscopy system includes a differential absorption spectrometer, a visual camera, and a processor.

[0037] The calibrated fast exposure differential imaging spectroscopy system performs the following process:

[0038] Step 1: Based on the calibrated fast-exposure differential imaging spectroscopy system, set the exposure time, aperture value, and fitting parameters of the visual camera, and simultaneously set the exposure time range [T] of the differential absorption spectrometer. min T cali Additionally, the original exposure time-pixel value curve corresponding to the differential absorption spectrometer is obtained;

[0039] Step 2: Under the current light intensity, the processor simultaneously acquires the hyperspectral data output by the differential absorption spectrometer and the three-channel values ​​output by the visual camera. Based on the three-channel values ​​and the fitted parameters, the differential absorption spectrometer calculates the exposure time T. caliThe pixel values ​​are combined with the offset value corresponding to 0 seconds of exposure in the original exposure time-pixel value curve to obtain the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity.

[0040] Step 3: The processor inputs the target pixel value of the hyperspectral data into the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity to obtain the target exposure time T;

[0041] Step 4: The processor determines whether the target exposure time T is within the exposure time range [T] min T cali Within this, the exposure time will be less than the minimum exposure time T. min The target exposure time T is set as T = T min It will be greater than the maximum exposure time T. cali The target exposure time T is set as T = T cali To correct the target exposure time T to the exposure time range [T] min T cali [Among];

[0042] Step 5: The processor sets the corrected target exposure time T as the exposure time of the differential absorption spectrometer and feeds it back to the differential absorption spectrometer to obtain spectral data.

[0043] The advantages of the automatic exposure method and system for a differential absorption spectrometer provided by this invention are as follows: It proposes a rapid automatic exposure imaging method and dual imaging system suitable for differential absorption spectrometers; the visual camera system is inexpensive and readily available, resulting in low overall cost; by prioritizing the exposure time-pixel value curve (T-DN curve) of the imaging spectrometer and combining it with the calculated spectral imaging pixel value (DN value) under the current light intensity, the exposure time corresponding to the desired DN value can be directly obtained, making the calculation efficient and fast; Furthermore, it proposes an automatic exposure calibration method for differential imaging spectrometers, combining practical application scenarios, acquiring RGB three-channel data from the differential absorption spectrometer and the visual camera, and obtaining fitting parameters through a piecewise function fitting method; by obtaining the fitting parameters through system calibration and combining the working principles of the imaging spectrometer and the visual camera imaging system, it proposes a method for plotting the exposure time-pixel value curve (T-DN curve) and the exposure time-grayscale value relationship curve (T-Gr curve), which can fully utilize the dynamic range of the two imaging systems and improve the system calibration accuracy. Meanwhile, the frame rate of the visual camera is higher than that of the imaging spectrometer, which enables real-time adjustment of the exposure time parameter of the differential absorption spectrometer, improving the data acquisition efficiency of the observation time window; moreover, it eliminates the need for multiple exposures, reducing the number of imaging operations for the differential absorption spectrometer, and significantly extending the shutter life for mechanical shutter imaging spectrometers. Attached Figure Description

[0044] Figure 1This is a schematic diagram of the structure of the fast exposure differential imaging spectroscopy system of the present invention;

[0045] Figure 2 This is a flowchart of the calibrated fast exposure differential imaging spectroscopy system in the application stage;

[0046] Figure 3 The diagram illustrates the exposure calculation method of a fast-exposure differential imaging spectroscopy system. (a) shows the T-DN curve of the differential absorption spectrometer imaging system; (b) shows the T-Gr curve of the visual camera imaging system; (c) shows the T-Gr curves of the visual camera imaging system at different aperture sizes under specific exposure times; and (d) shows the pixel values ​​of the spectrometer imaging system obtained by mapping the RGB channel pixel values ​​of the visual camera. Detailed Implementation

[0047] The technical solution of the present invention will now be described in detail through specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0048] To optimize the photometric time of the imaging spectrometer, this embodiment employs a dual-imaging system mode, which involves adding a standard RGB color camera to the differential absorption spectrometer. Currently, RGB cameras are inexpensive and offer excellent image quality, resulting in lower costs. A system block diagram is shown below. Figure 1 As shown in the figure, the differential absorption spectrometer acquires spectrometer data, and the visual camera acquires spectral data from the three RGB channels. The data receiving and processing computer (i.e., the processor) simultaneously receives hyperspectral data from the imaging spectrometer and color image data from the visual camera. In this embodiment, the imaging exposure time parameters of the differential absorption spectrometer are calculated in real time using the color image data from the visual camera, thereby realizing automated exposure of the differential imaging spectrometer.

[0049] It should be noted that this embodiment is divided into a calibration stage and an application stage. The calibration stage is used to determine system parameters, fitting parameters, etc.; the application stage uses the calibration results to directly calculate the target exposure time; the details are explained below.

[0050] like Figures 1 to 3 As shown, the automatic exposure method for a differential absorption spectrometer proposed in this invention includes the following steps in the application stage:

[0051] Step 1: Based on the calibrated fast-exposure differential imaging spectroscopy system, set the exposure time, aperture value, and fitting parameters of the visual camera, and simultaneously set the exposure time range [T] of the differential absorption spectrometer. min T caliAdditionally, the original exposure time-pixel value curve corresponding to the differential absorption spectrometer is obtained;

[0052] Step 2: Under the current light intensity, simultaneously acquire the hyperspectral data output by the differential absorption spectrometer and the three-channel values ​​output by the visual camera. Based on the three-channel values ​​and the fitted parameters, calculate the differential absorption spectrometer's performance at exposure time T. cali The pixel values ​​are combined with the offset value corresponding to 0 seconds of exposure in the original exposure time-pixel value curve to obtain the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity.

[0053] Step 3: Substitute the target pixel value of the hyperspectral data into the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity to obtain the target exposure time T;

[0054] Step 4: Determine if the target exposure time T is within the exposure time range [T] min T cali Within this, the exposure time will be less than the minimum exposure time T. min The target exposure time T is set as T = T min It will be greater than the maximum exposure time T. cali The target exposure time T is set as T = T cali To correct the target exposure time T to the exposure time range [T] min T cali [Among];

[0055] Step 5: Set the corrected target exposure time T as the exposure time of the differential absorption spectrometer and feed it back to the differential absorption spectrometer to obtain spectral data.

[0056] Through steps one through five, this embodiment proposes a rapid automatic exposure imaging method and a dual imaging system suitable for differential absorption spectrometers. The visual camera system is inexpensive, readily available, and has a low overall cost. By a priori plotting the exposure time-pixel value curve (i.e., the T-DN curve) of the imaging spectrometer, combined with the calculated spectral imaging pixel value (DN value) under the current light intensity, the exposure time corresponding to the desired DN value can be directly obtained, making the calculation efficient and fast. In addition, there is no need to use a differential absorption spectrometer for photometry, saving the photometry cycle, making full use of the data acquisition time window, which can significantly improve the data acquisition efficiency of the equipment, realize rapid automatic exposure imaging, and extend the service life of the mechanical shutter.

[0057] Before the application phase, after the fast exposure differential imaging spectroscopy system is calibrated, parameters such as aperture size and exposure time of the visual camera are fixed. The processor feeds back the exposure time to the differential absorption spectrometer based on the hyperspectral data output by the differential absorption spectrometer and the color image data output by the visual camera, so as to realize the automatic exposure of the differential absorption spectrometer.

[0058] During the calibration phase, the calibration process of the fast exposure differential imaging spectral system is shown in (a1) to (a8):

[0059] (a1) Determine the target light intensity range of the differential absorption spectrometer based on actual application scenarios [L] min L max [and the original exposure time-pixel value curves of the differential absorption spectrometer under different illuminations, L] min L is the minimum light intensity value. max This represents the maximum light intensity value.

[0060] Differential absorption spectrometers simultaneously acquire spatial and spectral information of the target region. Typically, the energy E received by the detector is linearly related to the exposure time of the differential absorption spectrometer. Therefore, the exposure time is linearly related to the pixel value (DN value), i.e., the T-DN curve. For a given differential absorption spectrometer, its T-DN curve is fixed; therefore, T-DN curves under different light intensities can be obtained, and they should exhibit a fan-shaped structure, such as... Figure 3 As shown in (a), L in (a) min L max These represent the minimum and maximum light intensity values ​​corresponding to the imaging target in the actual application scenario, and Bais is the imaging bias of the differential absorption spectrometer.

[0061] (a2) Based on the noise level of the differential absorption spectrometer imaging system, the noise zone 1 of the maximum output value of the differential absorption spectrometer is obtained, thereby setting the pixel value boundary conditions [DN] of the differential absorption spectrometer during the calibration stage. min DN max and exposure time range [T] min T cali ];

[0062] like Figure 3 In (a), Noise Zone 1 represents the noise limit set according to the noise level of the differential absorption spectrometer imaging system. That is, when the pixel value (DN value) of the imaging system enters Noise Zone 1, the presence of noise may render the value invalid. Therefore, the maximum effective DN value is set to be slightly smaller than Noise Zone 1, i.e., DN... max Maximum effective pixel value DN max Below 50% of the noise zone 1, i.e., DN max =NoizeNone1 min -NoiseZone1 width 0.5, NoizeNone1 min NoiseZone1 widthThese represent the lower boundary and width of the noise zone 1, respectively; at maximum light intensity L max The exposure time corresponding to the original exposure time-pixel value curve (i.e., the T-DN curve) is set to T. cali This refers to the exposure time when data is acquired during the calibration phase; combined with the minimum light intensity value L min The original exposure time-pixel value curve is used to obtain the exposure time T. cali At the minimum light intensity value L min The minimum effective pixel value DN corresponding to the time min ;[DN min DN max This refers to the pixel value boundary conditions of the differential absorption spectrometer during the calibration stage.

[0063] According to the maximum light intensity condition L max The original exposure time-pixel value curve below, its minimum effective pixel value DN min The corresponding time is set to the minimum exposure time T. min ;[T min T cali This refers to the exposure time range of the differential absorption spectrometer during the calibration stage.

[0064] (a3) Based on the range of light intensity of the observed target [L] min L max Determine the exposure time-grayscale value relationship curve of the visual camera at different apertures, and set the effective grayscale value range of the visual camera image based on the Noise Zone2 of the visual camera. min Gr max ];

[0065] Similarly, in the imaging system of a visual camera, under fixed exposure time and fixed light intensity, the relationship between the image grayscale value and the exposure time is also linear, i.e., the exposure time-grayscale value relationship curve (T-Gr curve). Here, the grayscale value is calculated from the values ​​of the three RGB channels using formula (1).

[0066] Gr=c1·R+c2·G+c3·B; (1)

[0067] Where Gr represents the grayscale value of the visual camera, R, G, and B are the three channel values ​​of the visual camera, namely the values ​​of the red, green, and blue channels, respectively, and c1, c2, and c3 are independent parameters. Preferably, c1 = 0.299, c2 = 0.587, and c3 = 0.114.

[0068] Following the same method as imaging spectrometers, the following can be obtained: Figure 3 The graphic in (b) refers to setting the maximum effective grayscale value Gr. maxSlightly smaller than the noise zone 2 of the visible camera, i.e., the maximum effective gray value Gr max Below 50% of the noise zone 2 of the visible camera, i.e., Gr max =NoizeNone2 min -NoiseZone2 width 0.5, NoizeNone2 min NoiseZone2 width The lower boundary and width of the noise zone 2 are used to obtain the maximum effective gray value Gr at different apertures. max Corresponding to the maximum light intensity condition L max Maximum exposure time T s Combined with the minimum light intensity value L under different apertures min The corresponding exposure time-grayscale value relationship curve yields the exposure time T. s At the minimum light intensity value L min The minimum effective gray value Gr corresponding to time min .

[0069] Figure 3 Gr in (b) max This represents the maximum effective grayscale value, which is slightly smaller than the Noise Zone 2. It is determined by the noise level and maximum output grayscale value of the visual camera's imaging system. Adjusting the aperture size to f / 1, f / 2, ..., f / N will yield the values ​​within the light intensity range [L]. min L max Similarly, by analyzing different exposure time-grayscale value regions (T-Gr regions) under [the specified conditions], the minimum effective grayscale value Gr can be obtained. min , [Gr min Gr max This refers to the effective grayscale range of a visual camera imaging system.

[0070] (a4) Set the exposure time T2 of the visible camera to be less than the maximum exposure time T. cali The exposure time-grayscale value relationship curves under different apertures with exposure time T2 were obtained, and the effective grayscale value range closest to the effective grayscale value range [Gr] was selected. min Gr max The aperture of the camera is the effective aperture, at which point the dynamic range of the camera is at its maximum.

[0071] To fully utilize the dynamic range of the visual camera and achieve real-time output of the exposure time, the exposure time of the visual camera must be shorter than the exposure time T of the differential absorption spectrometer during the calibration stage. cali If the value is T2, then T2 < T. caliUnder T2 conditions, exposure time-grayscale value relationship curves (T-Gr curves) can be obtained for different aperture sizes. The curve with the closest effective grayscale value range to [Gr] is selected. min Gr max The aperture is f / 2. Figure 3 As shown in (c), the dynamic range of the visible camera is at its maximum at this time.

[0072] (a5) Set the exposure time and aperture size of the visual camera based on the exposure time T2 and the effective aperture.

[0073] (a6) Based on the fact that the field of view of the visual camera covers the field of view of the differential absorption spectrometer, the field of view of the visual camera and the field of view of the differential absorption spectrometer are calibrated.

[0074] In the field of view of the visual camera, mark the differential absorption spectrometer Rect(lt, lb, rt, tb), where lt, lb, rt, and tb represent the upper left, lower left, upper right, and lower right coordinates of the local rectangular region of the field of view, respectively.

[0075] (a7) Based on the calibrated visual camera and differential absorption spectrometer, targets in practical application scenarios are photographed to obtain the light intensity range of multiple observed targets [L]. min L max The data includes hyperspectral data output from the differential absorption spectrometer and three-channel values ​​output from the visual camera.

[0076] (a8) Based on the field of view in (a6), integrate the common field of view data and pixel value boundary conditions of the differential absorption spectrometer and the visual camera [DN]. min DN max and the effective grayscale value range [Gr] min Gr max By fitting the three-channel numerical and hyperspectral data, the relationship between the pixel values ​​of the differential absorption spectrometer and the pixel values ​​of the visual camera is obtained, and the fitting parameters are obtained, which are the calibration results.

[0077] Under the above conditions, fully collect the light intensity range [L] min L max The hyperspectral data and color image data within the image are used to fit the pixel values ​​of the RGB channels of the visual camera to obtain the grayscale values ​​of the differential absorption spectrometer, such as... Figure 3 As shown in (d). The study found that the spectral composition of the imaging target affects the fitting parameters under different lighting conditions, mainly related to ultraviolet intensity. Therefore, a piecewise function can be used for fitting based on the relationship between the three channels of the visual camera:

[0078]

[0079] Where N is the pixel value of the differential absorption spectrometer, α, β, γ, α′, β′, and γ′ are all fitting parameters, R, G, and B are the three-channel values ​​of the visual camera, and δ and δ′ are both balance parameters.

[0080] Therefore, in practical applications, the pixel values ​​(DN values) of the differential absorption spectrometer can be obtained by combining the pixel values ​​of the R, G, and B channels acquired by the visual camera with formula (2), which corresponds to the differential absorption spectrometer at exposure time T in step two. cali The pixel values ​​at the specified light intensity, combined with the bias at exposure time T=0, yield the T-DN curve for that light intensity. Specifically, the bias bias is taken as a point on the straight line, and the exposure time T is... cali and exposure time T cali Using the pixel value corresponding to the given value as another point, draw a straight line; this straight line is the T-DN curve under that light intensity.

[0081] The target pixel value (DN) is calculated on the T-DN curve. tar The exposure time T is set at the value of the value, and the exposure time T is corrected based on step four. The corrected exposure time T is then fed back to the differential absorption spectrometer as the target exposure time T. The differential absorption spectrometer can then obtain high signal-to-noise ratio hyperspectral data based on the target exposure time T fed back by the processor.

[0082] This embodiment proposes an automatic exposure calibration method for differential imaging spectrometers. Based on practical application scenarios, it acquires RGB three-channel data from a differential absorption spectrometer and a visual camera, and obtains fitting parameters using a piecewise function fitting method. By obtaining the fitting parameters through system calibration and combining the working principles of the imaging spectrometer and visual camera imaging systems, it proposes a method for plotting the exposure time-pixel value curve (T-DN curve) and the exposure time-grayscale value relationship curve (T-Gr curve). This method can fully utilize the dynamic range of the two imaging systems and improve the system calibration accuracy.

[0083] In addition, the frame rate of the visual camera set in this embodiment is higher than that of the imaging spectrometer, which can realize real-time adjustment of the exposure time parameter of the differential absorption spectrometer and improve the data acquisition efficiency of the observation time window; moreover, it does not require multiple exposure imaging, reducing the number of imaging times of the differential absorption spectrometer, and can greatly improve the shutter life for mechanical shutter imaging spectrometers.

[0084] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An automatic exposure method for a differential absorption spectrometer, characterized in that, Includes the following steps: Step 1: Based on the calibrated fast-exposure differential imaging spectroscopy system, set the exposure time, aperture value, and fitting parameters of the visual camera, and simultaneously set the exposure time range [T] of the differential absorption spectrometer. min ,T cali Additionally, the original exposure time-pixel value curve corresponding to the differential absorption spectrometer is obtained; Step 2: Under the current light intensity, simultaneously acquire the hyperspectral data output by the differential absorption spectrometer and the three-channel values ​​output by the visual camera. Based on the three-channel values ​​and the fitted parameters, calculate the differential absorption spectrometer's performance at exposure time T. cali The pixel values ​​are combined with the offset value corresponding to 0 seconds of exposure in the original exposure time-pixel value curve to obtain the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity. Step 3: Substitute the target pixel value of the hyperspectral data into the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity to obtain the target exposure time T; Step 4: Determine if the target exposure time T is within the exposure time range [T] min ,T cali Within this, the exposure time will be less than the minimum exposure time T. min The target exposure time T is set as T = T min It will be greater than the maximum exposure time T. cali The target exposure time T is set as T = T cali To correct the target exposure time T to the exposure time range [T] min ,T cali [Among]; Step 5: Set the corrected target exposure time T as the exposure time of the differential absorption spectrometer and feed it back to the differential absorption spectrometer to obtain spectral data.

2. The automatic exposure method for a differential absorption spectrometer according to claim 1, characterized in that, The calibration process for the fast exposure differential imaging spectral system is as follows: (a1) Determine the target light intensity range of the differential absorption spectrometer based on actual application scenarios [L] min ,L max [and the original exposure time-pixel value curves of the differential absorption spectrometer under different illuminations, L] min L is the minimum light intensity value. max This represents the maximum light intensity value. (a2) Based on the noise level of the differential absorption spectrometer imaging, the noise zone 1 of the maximum output value of the differential absorption spectrometer is obtained, thereby setting the pixel value boundary conditions [DN] of the differential absorption spectrometer during the calibration stage. min ,DN max and exposure time range [T] min ,T cali ]; (a3) Based on the range of light intensity of the observed target [L] min ,L max Determine the exposure time-grayscale value relationship curve of the visual camera at different apertures, and set the effective grayscale value range of the visual camera image based on the Noise Zone2 of the visual camera. min Gr max ]; (a4) Set the exposure time T2 of the visible camera to be less than the maximum exposure time T. cali The exposure time-grayscale value relationship curves under different apertures with exposure time T2 were obtained, and the effective grayscale value range closest to the effective grayscale value range [Gr] was selected. min Gr max The aperture of the camera is the effective aperture, at which point the dynamic range of the camera is at its maximum. (a5) Set the exposure time and aperture size of the visible camera based on the exposure time T2 and the effective aperture; (a6) Based on the fact that the field of view of the visual camera covers the field of view of the differential absorption spectrometer, the field of view of the visual camera and the field of view of the differential absorption spectrometer are calibrated. (a7) Based on the calibrated visual camera and differential absorption spectrometer, targets in practical application scenarios are photographed to obtain the light intensity range of multiple observed targets [L]. min ,L max The data includes hyperspectral data output from the differential absorption spectrometer and three-channel values ​​output from the visual camera. (a8) Based on the field of view in (a6), integrate the common field of view data and pixel value boundary conditions of the differential absorption spectrometer and the visual camera [DN]. min ,DN max and the effective grayscale value range [Gr] min Gr max By fitting the three-channel numerical and hyperspectral data, the relationship between the pixel values ​​of the differential absorption spectrometer and the pixel values ​​of the visual camera is obtained, and the fitting parameters are obtained, which are the calibration results.

3. The automatic exposure method for a differential absorption spectrometer according to claim 2, characterized in that, In (a2), the pixel value boundary conditions of the differential absorption spectrometer during the calibration stage [DN] min ,DN max and exposure time range [T] min ,T cali The setup process for ] is as follows: Set the maximum effective pixel value DN max The maximum effective pixel value DN is obtained when the value is less than 50% of the noise zone 1. max Corresponding to the maximum light intensity condition L max Maximum exposure time T cali ; Combined with the minimum light intensity value L min The original exposure time-pixel value curve is used to obtain the exposure time T. cali At the minimum light intensity value l min The minimum effective pixel value DN corresponding to the time min ; According to the maximum light intensity condition L max The original exposure time-pixel value curve below, its minimum effective pixel value DN min The corresponding time is set to the minimum exposure time T. min .

4. The automatic exposure method for a differential absorption spectrometer according to claim 2, characterized in that, In (a3), the effective grayscale value range of the visual camera image [Gr] min Gr max The setup process for ] is as follows: Set the maximum effective grayscale value Gr max The maximum effective gray value Gr was obtained at different apertures by measuring less than 50% of the noise zone 2 of the visible camera. max Corresponding to the maximum light intensity condition L max Maximum exposure time T s ; Combining the minimum light intensity value L at different apertures min The corresponding exposure time-grayscale value relationship curve yields the exposure time T. s At the minimum light intensity value L min The minimum effective gray value Gr corresponding to time min .

5. The automatic exposure method for a differential absorption spectrometer according to claim 2, characterized in that, In (a8): The relationship between the pixel values ​​of the differential absorption spectrometer and the pixel values ​​of the visual camera is obtained by fitting the three-channel numerical and hyperspectral data. The fitting parameters are as follows: Where N is the pixel value of the differential absorption spectrometer, α, β, γ, α′, β′, and γ′ are all fitting parameters, R, G, and B are the three channel values ​​of the visual camera, and δ and δ′ are both balance parameters.

6. The automatic exposure method for a differential absorption spectrometer according to claim 5, characterized in that, In step two, based on the three-channel values ​​and the fitting parameters, and using the formula relating the pixel values ​​of the differential absorption spectrometer to the pixel values ​​of the visual camera, the exposure time T of the differential absorption spectrometer is calculated. cali The pixel values ​​below.

7. An automatic exposure system for a differential absorption spectrometer, characterized in that, Automatic exposure of a differential absorption spectrometer is achieved based on a calibrated fast exposure differential imaging spectroscopy system, which includes a differential absorption spectrometer, a visual camera, and a processor. The calibrated fast exposure differential imaging spectroscopy system performs the following process: Step 1: Based on the calibrated fast-exposure differential imaging spectroscopy system, set the exposure time, aperture value, and fitting parameters of the visual camera, and simultaneously set the exposure time range [T] of the differential absorption spectrometer. min ,T cali Additionally, the original exposure time-pixel value curve corresponding to the differential absorption spectrometer is obtained; Step 2: Under the current light intensity, the processor simultaneously acquires the hyperspectral data output by the differential absorption spectrometer and the three-channel values ​​output by the visual camera. Based on the three-channel values ​​and the fitted parameters, the differential absorption spectrometer calculates the exposure time T. cali The pixel values ​​are combined with the offset value corresponding to 0 seconds of exposure in the original exposure time-pixel value curve to obtain the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity. Step 3: The processor inputs the target pixel value of the hyperspectral data into the exposure time-pixel value curve of the differential absorption spectrometer under the current light intensity to obtain the target exposure time T; Step 4: The processor determines whether the target exposure time T is within the exposure time range [T] min ,T cali Within this, the exposure time will be less than the minimum exposure time T. min The target exposure time T is set as T = T min It will be greater than the maximum exposure time T. cali The target exposure time T is set as T = T cali To correct the target exposure time T to the exposure time range [T] min ,T cali [Among]; Step 5: The processor sets the corrected target exposure time T as the exposure time of the differential absorption spectrometer and feeds it back to the differential absorption spectrometer to obtain spectral data.

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