A distance error compensation method for laser range-gated three-dimensional imaging

Abstract

The present invention relates to the technical field of photoelectric detection and laser three-dimensional imaging, and specifically discloses a distance error compensation method for laser distance-gated three-dimensional imaging. A distance error compensation method for laser distance-gated three-dimensional imaging comprises: step S01: imaging a target using a laser radar system to obtain a sequence image of the target; step S02: processing the sequence image to obtain a pixel point grayscale curve diagram, obtaining the distance of all pixel points according to the relationship between the target energy and the laser flight time, and obtaining a three-dimensional image of the target; step S03: the laser radar system includes an electro-optical crystal, analyzing the inhomogeneity generated by the electro-optical crystal to obtain a compensation matrix of the three-dimensional image; step S04: compensating the three-dimensional image of the target according to the compensation matrix to obtain a compensated three-dimensional image.

Description

Technical Field

[0001] The invention relates to the technical field of photoelectric detection and laser three-dimensional imaging, and in particular to a distance error compensation method for laser distance-gated three-dimensional imaging. Background Art

[0002] 3D imaging LIDAR systems can obtain the distance and three-dimensional images of the target of interest, so they are widely used in space target detection, land landscape mapping, underwater target detection, and unmanned driving. For 3D imaging LIDAR, in order to ensure that certain key performance indicators of LIDAR are not reduced while reducing the cost as much as possible, many researchers have proposed many different LIDAR solutions to replace the original high-cost detectors. In many 3D imaging LIDAR systems, the use of high-speed optical switches and low-bandwidth, low-cost CCD and CMOS detectors is a common solution to achieve high resolution and high distance accuracy.

[0003] For common range-gated active three-dimensional imaging laser radars using array imaging devices, ICCD cameras with built-in high-speed shutters and high gain are generally used as imaging devices. However, the imaging process of ICCD cameras has disadvantages such as multiple electro-optical conversions, low quantum efficiency and low lateral resolution caused by pixel coupling, and high price. Therefore, compared with the common use of ICCD in general range-gated laser radar systems, the biggest advantage of using EMCCD and SCMOS as imaging devices is that SCMOS has better signal-to-noise ratio, better lateral resolution, longer service life and stronger resistance to mechanical impact in non-extremely weak light conditions. However, compared with the shutter of ICCD cameras, SCMOS cameras themselves do not have high-speed shutters and can only obtain grayscale information, so an optical switch composed of electro-optical crystals and polarizers is needed to slice the image so that the grayscale value of the image can correspond to a certain distance information. Electro-optical crystals can be used as optical switches because of their own conoscopic interference effect, but the distribution of the conoscopic interference rings generated by electro-optical crystals is uneven, resulting in the grayscale value of the image formed by the SCMOS camera deviating from the grayscale value corresponding to the ideal switch.

[0004] Therefore, there is an urgent need for a method that can meet the needs of three-dimensional imaging and attitude measurement of targets such as drones in various complex environments, ensure the spatial resolution, effective range and distance accuracy of the experimental system, and reduce costs. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a distance error compensation method for laser distance-gated three-dimensional imaging. It is used to correct the systematic error of the distance image obtained by the distance-gated laser three-dimensional imaging work of the electro-optical modulated crystal as an optical switch. After correction, the overall distance error of the system is significantly improved. It can meet the needs of three-dimensional imaging and attitude measurement of targets such as drones in various complex environments, ensure the spatial resolution, effective range and distance accuracy of the experimental system, and reduce costs at the same time.

[0006] The technical solution adopted by the present invention is: a distance error compensation method for laser range-gated three-dimensional imaging, comprising:

[0007] Step S01: using a laser radar system to image a target and obtain a sequence of images of the target;

[0008] Step S02: Processing the sequence of images to obtain a pixel grayscale curve diagram, obtaining the distances of all pixels according to the relationship between target energy and laser flight time, and obtaining a three-dimensional image of the target;

[0009] Step S03: the laser radar system includes an electro-optical crystal, and the inhomogeneity generated by the electro-optical crystal is analyzed to obtain a compensation matrix of a three-dimensional image;

[0010] Step S04: compensating the three-dimensional image of the target according to the compensation matrix to obtain a compensated three-dimensional image.

[0011] Preferably, the step S02 further comprises: plotting the pixel points in the sequence of images in the order of the gating time to obtain a grayscale curve diagram of the pixel points, thereby obtaining the relationship between the grayscale value and the gating time.

[0012] Preferably, in step S02, the distance between the pixels is:

[0013] ;

[0014] ;

[0015] ;

[0016] Where c is the speed of light, n is the refractive index, is the initial frame delay time, is the mean of the image sequence numbers, is the initial delay step, is the gray value of each pixel in the i-th image, is the delay time corresponding to the i-th image, is the delay time, For delayed stepping, For the The distance corresponding to the secondary image.

[0017] Preferably, in step S03, the compensation matrix is:

[0018] ;

[0019] Where C is the compensation matrix, is the transmittance matrix, is the actual optical switch transmittance matrix, is the total non-uniformity coefficient.

[0020] Furthermore, the total non-uniformity coefficient is:

[0021] ;

[0022] in, is the inhomogeneity caused by the different incident light angles on the crystal. It is the non-uniformity coefficient of light intensity caused by the imperfect pulse voltage.

[0023] Furthermore, the inhomogeneity caused by different incident light angles on the crystal is:

[0024] ;

[0025] in, is the zenith angle of the incident light on the crystal surface, is the azimuth angle of the incident light on the crystal surface, is the half-wave voltage of the crystal, is the polarization direction of the incident light, The phase difference corresponding to the half-wave voltage.

[0026] Furthermore, the non-uniformity coefficient of the light intensity caused by the imperfect pulse voltage is:

[0027] ;

[0028] in, is the zenith angle of the incident light on the crystal surface, is the azimuth angle of the incident light on the crystal surface, is the half-wave voltage of the crystal, is the polarization direction of the incident light, The phase difference corresponding to the half-wave voltage is: is the light intensity corresponding to the half-wave voltage, is the light intensity distribution of the integral image generated on the primary imaging CCD, is the phase difference corresponding to one imaging.

[0029] Preferably, in step S02, the relationship between the target energy and the laser flight time includes:

[0030] ;

[0031] in, is the energy received by the detector, is the laser pulse power, is the optical switching function, z is the target distance, and c is the speed of light.

[0032] Furthermore, the laser pulse power is:

[0033] ;

[0034] in, is the expression of laser pulse power, is the laser power at time t, Is the pulse width.

[0035] Furthermore, the optical switch function is:

[0036] ;

[0037] in, is the delay time, For duration.

[0038] Beneficial effects of the above technical solution:

[0039] (1) A distance error compensation method for laser distance-gated three-dimensional imaging is provided, which is used to correct the systematic error of the distance image obtained by distance-gated laser three-dimensional imaging using an electro-optical modulated crystal as an optical switch. After correction, the overall distance error of the system is significantly improved.

[0040] (2) It can meet the needs of three-dimensional imaging and attitude measurement of targets such as drones in various complex environments, ensure the spatial resolution, effective range and distance accuracy of the experimental system, and reduce costs.

[0041] (3) The compensation method provided by the present invention can effectively suppress the error existing when the pulse voltage source applied to the crystal is not an ideal pulse waveform, the peak waveform stability is poor, and the sequence image weighted average method is used to restore the distance depth. It can also effectively suppress the non-uniformity of the conic interference effect itself when the crystal is used as an optical switch, and the error that will exist at the edge of the field of view. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A flow chart of the distance error compensation method for laser distance-gated three-dimensional imaging provided by the present invention;

[0043] Figure 2 An imaging timing diagram of a laser radar system provided for one embodiment of the present invention;

[0044] Figure 3 A laser and optical switch convolution energy diagram of a laser radar system provided for one embodiment of the present invention;

[0045] Figure 4 An image sequence diagram of a laser radar system provided by one embodiment of the present invention;

[0046] Figure 5 A pixel grayscale curve diagram of a laser radar system provided by an embodiment of the present invention;

[0047] Figure 6 A conoscopic interference pattern when V=0 provided by one embodiment of the present invention;

[0048] Figure 7 A crystal conoscopic interference pattern at a half-wave voltage provided by one embodiment of the present invention;

[0049] Figure 8 An image of a voltage applied to a crystal detected by an oscilloscope provided in accordance with an embodiment of the present invention;

[0050] Fig. 9 This is an effect diagram of imaging compensation of the distance error compensation method provided by the present invention;

[0051] Fig.10 The three-dimensional point cloud image is restored from the slice image before compensation;

[0052] Fig.11 The three-dimensional point cloud image is restored from the compensated slice image;

[0053] Fig.12 is the depth map obtained by strobed imaging before compensation;

[0054] Fig.13 The depth map is obtained from the compensated depth image. DETAILED DESCRIPTION

[0055] The following is a further detailed description of the implementation methods of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than an exhaustive list of all the embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0056] The terms "first", "second", etc. (if any) in the specification and claims are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way are interchangeable where appropriate so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products, or devices.

[0057] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0058] Embodiment 1

[0059] like Figure 1 The present invention provides a distance error compensation method for laser distance gating three-dimensional imaging, which specifically includes the following steps:

[0060] In order to analyze the distance error of three-dimensional imaging, this embodiment first constructs a laser radar system with an electro-optical crystal as an optical switch, including a SCMOS camera, a polarizer, an analyzer, an electro-optical crystal, a narrow-band filter, a collimator, a receiving optical system, a pulse laser, a microlens array, a beam expander, a delay signal generator, and a computer. Among them, the polarization directions of the polarizer and the analyzer are perpendicular to each other, and together with the crystal, they constitute a crystal optical switch, and the light path can be turned on and off by changing the external voltage of the crystal. The laser is a 532nm band pulse solid laser with low repetition frequency, high pulse energy, and narrow pulse width.

[0061] When the LiDAR system is working, a high-power pulsed laser The pulse width transmitted to the target of interest at any time is When the pulsed laser is homogenized and expanded, the voltage applied to the LN crystal is zero when the pulsed laser travels back and forth between the target and the receiving system. At this time, the optical switch composed of the polarizer, LN crystal, and analyzer is in the off state to prevent atmospheric backscattering and non-target scattered light. After that, when the target's laser pulse reflected light returns to the receiving system, it is first filtered out by the narrowband filter NBF to remove stray light from other bands. Then, under the control of the high-precision delay signal generator, a high-precision voltage source is added to the two ends of the crystal for a duration of The pulse voltage has a voltage value equal to the half-wave voltage of the crystal. At this time, the crystal optical switch is in the open state, and the reflected light of the target is received by the SCMOS camera. After this process is completed, the system completes an imaging of the target. The corresponding slice depth of field is:

[0062] (1)

[0063] Where c is the speed of light, is the duration, Is the pulse width.

[0064] It can be seen that the crystal optical switch is only turned on for a very short time, so that the image obtained by the SCMOS camera, which originally could not obtain distance information, corresponds to a certain distance information. A series of distance slice images can be obtained. Through the temporal relationship and energy relationship between different slices, the distance information of each point on the image can be calculated, and then a three-dimensional image of the target of interest can be obtained.

[0065] The laser radar imaging process is quantitatively analyzed. Assuming that the laser pulse is an ideal rectangular pulse and the crystal optical switch is an ideal rectangular window, the effect of the interaction between the two is as follows: Figure 2 and Figure 3 shown.

[0066] The laser pulse is:

[0067] (2)

[0068] in, is the laser power at time t. When the laser is an ideal pulse function, is a constant.

[0069] The function of the optical switch is:

[0070] (3)

[0071] in, is the delay time, For duration.

[0072] The expression of the gating distance is:

[0073] (4)

[0074] Where c is the speed of light, is the delay time.

[0075] The gating distance represents the minimum distance at which a laser pulse can be completely received by the receiving system. In an imaging process, the energy received by the camera is the convolution of the laser pulse function and the optical switch function. The expression of the energy received by the camera is:

[0076] (5)

[0077] It can be seen that the energy received by the camera The function realizes the association between echo energy and target distance, which is called distance-energy relationship. Within the dynamic range of the camera, the echo energy and the pixel grayscale of the image are linearly related, so the grayscale value of the camera pixel and the target distance are also linearly related. Figure 3 It can be seen that only one imaging cannot obtain a one-to-one correspondence between camera pixels and distance, and slices at different distances are affected by atmospheric attenuation and laser divergence to different degrees. Multiple slice images are needed to determine the distance of the target.

[0078] In order to obtain the distance information of the target, the range-gated laser radar system changes the gating time according to a fixed delay step to obtain a sequence of images of the target. Figure 4 As shown in the figure, A represents a specific pixel of the detector. The gray value of point A is plotted according to the order of the gating time, and the gray value of point A is obtained. Figure 5 The grayscale curve of pixel A in the figure shows the target echo energy at this pixel. Figure 5 L represents the gray value corresponding to A, and the horizontal axis corresponds to different gating times. The relationship between target energy and laser flight time (TOF) is established through a specific algorithm to achieve ranging.

[0079] According to the principle of range gating imaging, the distance corresponding to the i-th image in the sequence of images is:

[0080] (6)

[0081] in, is the delay time corresponding to the i-th image, is the delay time, Delayed stepping.

[0082] The mean of the image numbers is:

[0083] (7)

[0084] In the formula, is the gray value of each pixel in the i-th image. Then the distance corresponding to each pixel can be obtained:

[0085] (8)

[0086] Here, n is the refractive index.

[0087] When the distance to the target point is determined, the spatial position of the target point can be obtained based on the geometric relationship between the target image, the imaging optical system, and the target. The three-dimensional coordinate conversion is performed on the acquired coordinates of each target point, and then the three-dimensional image of the target is obtained through display processing.

[0088] An optical switch system composed of an electro-optic crystal and a polarizer is used for slicing so that the grayscale value of the image corresponds to a certain distance information. When the voltage applied to the electro-optic crystal is 0, the central interference level of the conoscopic interference pattern generated by the light passing through the optical switch is a dark spot, and the optical switch is in the closed state; when the voltage applied to the electro-optic crystal is a half-wave voltage, the conoscopic interference pattern generated by the light passing through the optical switch is a bright spot, and the shutter is in the open state. The distribution of the conoscopic interference rings generated by the electro-optic crystal is uneven, resulting in a deviation between the grayscale value of the image formed by the back-end SCMOS camera and the grayscale value corresponding to the ideal switch, resulting in an error in the calculated image sequence mean.

[0089] The inhomogeneity of the crystal is the main source of the distance error. In this embodiment, an LN crystal is selected as the optical switch, and the inhomogeneity of the LN crystal is analyzed to obtain error compensation.

[0090] When the light passing direction is along the crystal optical axis, the crystal phase difference delay caused by the electro-optical effect is:

[0091] (9)

[0092] in, is the refractive index of ordinary light in the crystal, is the electro-optic coefficient of the crystal, L and d are the length and thickness of the crystal in the light transmission direction, V is the external voltage of the crystal, and λ is the wavelength of light.

[0093] The corresponding crystal light intensity is:

[0094] (10)

[0095] in, is the zenith angle of the light incident on the electro-optical crystal, is the azimuth of the incident light, V is the applied voltage of the crystal, is the polarization direction, is the phase of the modulated light when the voltage is V.

[0096] It can be seen that the ordinary refractive index of the crystal is , electro-optic coefficient , length and thickness L, d are all constant after the crystal is determined, so the light intensity of the crystal is , , V are functions of variables. The factors affecting the light intensity inhomogeneity of the crystal optical switch are also mainly derived from , 、V.

[0097] The impact of inhomogeneity is divided according to the source of influence, and the total inhomogeneity coefficient is , which represents the difference between the actual normalized light intensity received by a certain pixel on the detector and the normalized light intensity of the corresponding pixel at the center of the field of view on the detector, that is, the difference between the transmittance corresponding to the pixel at the center of the field of view and the transmittance corresponding to any other pixel. , The different generated inhomogeneity coefficients are defined as , represents the difference in transmittance of the crystal optical switch due to the conoscopic interference effect. The non-uniformity coefficient caused by the imperfect applied voltage V of the crystal is , which represents the difference between the transmittance of the actual non-ideal gate pulse voltage applied to the crystal and the transmittance of the ideal pulse gate voltage applied, then the total non-uniformity coefficient It is the sum of the results of two factors:

[0098] (11)

[0099] The inhomogeneity caused by different incident light angles on the crystal Conduct analysis.

[0100] At a known phase difference and polarization direction , the interference light intensity formula of the crystal is expressed as:

[0101] (12)

[0102] The interference pattern of the crystal under ideal conditions is simulated and calculated, and the simulation results are as follows: Figure 6 As shown, Figure 6 (a) Interference light intensity distribution; (b) Effect of polarization direction on light intensity ; (c) Effect of phase difference on light intensity ; (d), (e), and (f) are the expansion of the 1° field of view in the center of (a), (b), and (c), respectively. From (d), it can be seen that the image uniformity is good in the center, and the image uniformity is poor in the edge area of ​​the field of view at azimuth angles of 45°, 135°, 225°, and 315°. By analyzing the simulation data, (d) has a field of view angle of When the internal light intensity is less than 0.07, the electro-optic modulation is considered to be in the "off" state.

[0103] During the simulation, the voltage across the crystal is set to half-wave voltage. The simulation results are as follows: Figure 7 As shown, Figure 7(a) Interference light intensity distribution in the crystal conoscopic interference pattern under half-wave voltage; (b) The influence of polarization direction on the interference light intensity ; (c) Effect of phase difference on light intensity ; (d), (e), and (f) are enlargements of the 1° field of view angle area of ​​(a), (b), and (c), respectively.

[0104] Figure 7 In (d), the light intensity within the field of view angle of 1° is greater than 0.87, and the electro-optic modulation is considered to be in the "on" state at this time. However, the aberration at the edge of the field of view is large. According to the interference light intensity formula, the source of the non-uniformity error is analyzed. Figure 6 In the middle (e), the light intensity varies from 0.95 to 1; Figure 7 The intensity of the light in the middle (f) varies from 0.86 to 1. Therefore, the polarization direction within the 1° field of view is Little impact on light intensity.

[0105] When the voltage applied to the crystal is 0, the electro-optic modulation is in the "off" state, and the phase difference between the center and the edge within the 1° field of view is small, and the impact on imaging can be ignored. When the electro-optic modulation is in the "on" state, the polarization direction The error caused is very small, so the interference light intensity can be approximately expressed as the expression of phase difference:

[0106] (13)

[0107] When the voltage applied to the crystal is a half-wave voltage, the electro-optic modulation is in the "on" state. Within the entire optical switch field of view, the ideal interference light intensity value is 1. At this time, the phase difference of each point imaged on the detector should be , then at each point outside the center of the field of view, the corresponding light intensity non-uniformity coefficient is:

[0108] (14)

[0109] The non-uniformity caused by the applied voltage V The imaging result of the distance-gated laser radar using an electro-optical crystal is the result of the convolution of the laser pulse echo and the electro-optical crystal optical switch gating. In order to calculate the inhomogeneity of the pulse voltage, an oscilloscope is used to measure the pulse voltage applied to the electro-optical crystal. Preferably, the pulse voltage width of the external voltage source used in this embodiment is preset to 100ns.

[0110] Make the oscilloscope measure the waveform of the pulse voltage Figure 8As shown. The actual measured pulse width of the pulse voltage is about 100ns. The conoscopic interference pattern generated by the crystal is a function of voltage. Different voltages correspond to different conoscopic interference patterns. Without considering the laser pulse waveform, when a half-wave pulse voltage is applied to the electro-optic crystal, the light intensity distribution generated on the CCD is:

[0111] (15)

[0112] in, is the light intensity distribution of the integral image generated on the primary imaging CCD, is the voltage value of the i-th sampling point on the oscilloscope, The voltage applied to the crystal is When the light intensity corresponding to the crystal conoscopic interference pattern is The voltage is The normalized light intensity of the laser pulse received by the crystal at this time.

[0113] remember is the half-wave voltage of the crystal, Represents the conoscopic interference light intensity distribution corresponding to the half-wave voltage, and the light intensity non-uniformity coefficient caused by the imperfect pulse voltage is:

[0114] (16)

[0115] Taking into account the conoscopic interference effect of the LN crystal itself and the influence of the uneven external pulse voltage, the total unevenness coefficient generated by the electro-optical crystal optical switch is obtained as follows:

[0116] (17)

[0117] It can be seen that due to the existence of these two kinds of inhomogeneities, there is a distance error in laser three-dimensional imaging using electro-optical crystals as optical switches.

[0118] When the laser pulse is completely received by the ideal optical switch, the corresponding transmittance matrix is For all matrix, Represents the transmittance at the center of the field of view. The theoretical calculation of the inhomogeneity matrix is ​​expressed as:

[0119] (18)

[0120] in, is the theoretical calculation inhomogeneity matrix, represents a matrix of all 1s, To obtain the maximum value function, is the extinction ratio matrix, is the total non-uniformity coefficient.

[0121] (19)

[0122] Where C is the compensation matrix, is the transmittance matrix, is the actual optical switch transmittance matrix, is the total non-uniformity coefficient.

[0123] The image captured by the laser radar experimental system is compensated to obtain an image that compensates for the inhomogeneity of the crystal optical switch.

[0124] Accuracy simulation results evaluation

[0125] Verification was carried out in two experimental scenarios. In the first set of experimental scenarios, a pure white flat panel was placed 22 meters in front of the receiving optical system, and the white flat panel was imaged to verify the compensation algorithm. The effect diagram of imaging compensation is as follows Fig. 9 As shown. Fig. 9 As can be seen in (a), since the physical principle of the crystal as an optical switch is the conoscopic interference effect of the crystal, only the area of ​​about 301×301 pixels in the center of the field of view can achieve uniform imaging. Figures (c) and (d) are comparison diagrams of the imaging effects of the 601×601 pixel area in the center of the crystal before and after compensation. From the image effects before and after compensation, it can be seen that in the pixel area taken, the uniformity of the grayscale image of the target imaging is significantly improved, which shows the accuracy of the compensation method provided by the present invention.

[0126] The slice images before and after compensation are used for three-dimensional reconstruction to obtain Fig.10 and Fig.11 The distance depth map of the flat target obtained by the system before and after compensation is as follows: Fig.12 and Fig.13 It can be seen that due to the influence of the inhomogeneity of the crystal optical switch, the calculated value of the distance depth in the upper left and lower right parts of the image restored using the original slice image is generally smaller than the true value, while in the lower left and upper right sides of the image, the calculated value of the distance depth is generally larger than the true value, and there are obvious isolated points in the edge part of the point cloud image. The accuracy of the image restored using the compensated slice image is significantly improved in the corner part, and the number of isolated points in the edge part of the point cloud image is significantly reduced. This result verifies the accuracy of the compensation method.

[0127] The distance accuracy of the image within the 10mrad field of view is calculated, and the expression for calculating the mean square error of the distance depth map is as follows:

[0128] (20)

[0129] in, is the standard deviation of the distance depth, p is the total number of pixels, n (100 shots) is the number of imaging times, For the Line The distance depth corresponding to the column pixel point, The target distance actually measured is set to 22.05 meters. Fig.12 and Fig.13 The corresponding standard deviations of distance depth are 3.0cm and 2.27cm respectively. The main reasons for the ranging error are as follows: first, the pulse voltage source applied to the crystal is not an ideal pulse waveform, and its peak waveform stability is poor. In this case, there will be errors when the weighted average method of the sequence image is used to restore the distance depth; second, the principle of the crystal as an optical switch is the conoscopic interference effect of the crystal. The conoscopic interference effect itself is non-uniform, and there will be large errors at the edge of the field of view; third, the jitter time of the crystal pulse voltage triggered by the delay signal generator (TDG) is 0.25ns, corresponding to a ranging error of 3.75cm; fourth, the shot noise of Scmos will also cause a certain distance error. After compensation by the compensation algorithm, the influence of reasons one and two is significantly suppressed, and the standard deviation of the system distance depth is significantly improved.

[0130] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A distance error compensation method for laser range-gated three-dimensional imaging, characterized in that ,,include: Step S01: using a laser radar system to image a target and obtain a sequence of images of the target; Step S02: Processing the sequence of images to obtain a pixel grayscale curve diagram, obtaining the distances of all pixels according to the relationship between target energy and laser flight time, and obtaining a three-dimensional image of the target; Step S03: the laser radar system includes an electro-optical crystal, and the inhomogeneity generated by the electro-optical crystal is analyzed to obtain a compensation matrix of a three-dimensional image; Step S04: compensating the three-dimensional image of the target according to the compensation matrix to obtain a compensated three-dimensional image; In step S02, the distance between the pixels is: Where c is the speed of light, n is the refractive index, t0 is the initial frame delay time, is the mean of the image sequence number, Δt is the initial delay step, L i is the gray value of each pixel in the i-th image, τ i is the delay time corresponding to the i-th image, τ D is the delay time, Δτ is the delay step, and r is the distance corresponding to the i-th image; In step S03, the compensation matrix is: Among them, C is the compensation matrix, Z is the transmittance matrix, Z′ is the actual optical switch transmittance matrix, and μ is the total non-uniformity coefficient.

2. The distance error compensation method for laser range-gated three-dimensional imaging according to claim 1, characterized in that: The step S02 further includes: plotting the pixel points in the sequence of images according to the order of the gating time to obtain a pixel grayscale curve diagram, thereby obtaining the relationship between the grayscale value and the gating time.

3. The distance error compensation method for laser range-gated three-dimensional imaging according to claim 1, characterized in that: The total non-uniformity coefficient is: μ=κ+ρ; Among them, κ is the non-uniformity caused by the different angles of incident light on the crystal, and ρ is the non-uniformity coefficient of light intensity caused by the imperfect pulse voltage.

4. The distance error compensation method for laser range-gated three-dimensional imaging according to claim 3, characterized in that: The inhomogeneity caused by different incident light angles on the crystal is: Among them, α is the zenith angle of the incident light on the crystal surface, β is the azimuth angle of the incident light on the crystal surface, and V π is the half-wave voltage of the crystal, φ(α,β) is the polarization direction of the incident light, θ(α,β,V π ) is the phase difference corresponding to the half-wave voltage.

5. The distance error compensation method for laser range-gated three-dimensional imaging according to claim 3, characterized in that: The non-uniformity coefficient of light intensity caused by the imperfect pulse voltage is: Among them, α is the zenith angle of the incident light on the crystal surface, β is the azimuth angle of the incident light on the crystal surface, and V π is the half-wave voltage of the crystal, φ(α,β) is the polarization direction of the incident light, θ(α,β,V π ) is the phase difference corresponding to the half-wave voltage, I(α,β,V π ) is the light intensity corresponding to the half-wave voltage, I(α,β,V mean ) is the light intensity distribution of the integral image generated on the primary imaging CCD, θ(α, β, V mean ) is the phase difference corresponding to one imaging.

6. The distance error compensation method for laser range-gated three-dimensional imaging according to claim 1, characterized in that: In step S02, the relationship between the target energy and the laser flight time includes: Among them, Q(z) is the energy received by the detector, P(t) is the laser pulse power, G(t) is the optical switching function, z is the target distance, and c is the speed of light.

7. The distance error compensation method for laser range-gated three-dimensional imaging according to claim 6, characterized in that: The laser pulse power is: Where P(t) is the expression of laser pulse power, P is the laser power at time t, τ p Is the pulse width.

8. The distance error compensation method for laser range-gated three-dimensional imaging according to claim 6, characterized in that: The optical switch function is: Among them, τ D is the delay time, τ g For duration.

Images