Range gating laser radar image reconstruction method

Abstract

The invention provides a range-gated laser radar image reconstruction method, and solves the technical problems that the edge of an imaging target of an existing range-gated laser radar is fuzzy, the environmental noise interference is serious, and the range resolution is poor. The method comprises the following steps: acquiring a plurality of radar slice images, sequentially taking each frame as a target frame preprocessing image after preprocessing, performing difference on the target frame preprocessing image and front and back adjacent frames, performing binaryzation, and performing AND operation to obtain a target frame distance information enhancement image; and performing AND operation on the target frame distance information enhanced image and the target frame preprocessed image to obtain an optimized target frame radar slice image, multiplying the optimized target frame radar slice image with a corresponding detection distance to obtain a target frame distance matrix, performing iteration and superposition to obtain a detection target object matrix, and performing pseudo-color processing to reconstruct a detection target object distance image. The method can be widely applied to the technical field of laser radar imaging.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser radar imaging, and more particularly relates to a range-gated laser radar image reconstruction method. BACKGROUND

[0002] Laser radar is a technology for realizing shape detection of a target object by using pulsed laser as a transmitting source, receiving reflected echo signal intensity of a laser beam on the target object, and obtaining the distance between the target object and the laser according to the time-of-flight method. The target object detection with higher resolution at a farther distance is realized by using the characteristics of short laser wavelength, narrow pulse width, smaller divergence angle, and higher pulse energy.

[0003] The range-gated technology realizes the reception of echo signals of a specific distance by precisely controlling the transmitting time of pulsed laser and the opening time of a gated detector, and is an important method for suppressing the laser backscattering effect. However, when the target object has a large volume, the sampling area needs to cover the entire target object. In order to not increase the opening time of the gated range, the time width of the range-gated range is generally much larger than the delay step length of the multiple continuous step slice images of the detector, resulting in that each slice image has a time overlapping part between the previous and subsequent images, and thus the background noise of the target object is increased.

[0004] The existing range-gated laser radar image reconstruction technology mainly uses the centroid algorithm and the binary algorithm to separate the target object and the background, and obtain the distance features of the target object. However, the binary algorithm is only suitable for images with high contrast between the target object and the background, and the threshold value needs to be determined according to the specific conditions of each slice image, and thus it is difficult to be used for quickly processing multiple slice images to realize the reconstruction of the distance image of the target object. The centroid method depends on the intensity of the target echo signal, and the target object and the background noise are not easy to distinguish, the distance resolution is limited, and the clarity of the reconstructed image is low. SUMMARY

[0005] The purpose of the embodiments of the application is to provide a range-gated laser radar image reconstruction method to solve the technical problems of blurred edges of the imaging target, serious environmental noise interference, and poor distance resolution in the prior art.

[0006] To achieve the above purpose, the embodiments of the application provide a range-gated laser radar image reconstruction method, which comprises the following steps: A plurality of radar slice images at different distances are acquired, and after preprocessing, each frame is sequentially taken as a target frame preprocessed image starting from the second frame, and difference is performed on the target frame preprocessed image and the adjacent frames to obtain a target frame preprocessed image and a target frame postprocessed image, and after binaryzation, the target frame preprocessed image and the target frame postprocessed image are subjected to AND operation to obtain a target frame distance information enhanced image. The target frame distance information enhancement map is ANDed with the target frame preprocessed image to obtain an optimized target frame radar slice image, and the distance corresponding to the radar slice image is multiplied to obtain a target frame distance matrix. Iteration is performed until all target frame distance matrices are obtained, and a detection target object matrix is obtained after superposition. The detection target object distance image is reconstructed by pseudo-color processing.

[0007] Preferably, the binarization process respectively includes: binarizing the target frame pre-difference image and the target frame post-difference image respectively with zero as a threshold to obtain a target frame binarized pre-difference image and a target frame binarized post-difference image.

[0008] Preferably, for each pixel intensity value of the pixel intensity matrix of the optimized target frame radar slice image, the pixel intensity value is multiplied by the distance corresponding to the radar slice image to obtain a target frame distance matrix.

[0009] Preferably, the formula for obtaining the optimized target frame radar slice image is: ; In the formula, is the optimized target frame radar slice image, is the target frame distance information enhancement map, is the target frame preprocessed image.

[0010] Preferably, the formula for obtaining the target frame distance matrix is: ; In the formula, is the target frame distance matrix, is the optimized target frame radar slice image, is the distance corresponding to the i-th frame radar slice image.

[0011] Preferably, the formula for obtaining the detection target object matrix is: ; In the formula, is the detection target object matrix, and N is the number of frames of the radar slice image, is the target frame distance matrix.

[0012] Preferably, the target frame distance information enhancement map is obtained by ANDing the target frame binarized pre-difference image and the target frame binarized post-difference image, and the formula is: ; In the formula, is the target frame distance information enhancement map, is the target frame binarized pre-difference image, is the target frame binarized post-difference image.

[0013] Preferably, the preprocessing means: denoising a plurality of radar slice images to obtain denoised radar slice images.

[0014] Preferably, the denoising is median filtering, mean filtering or Gaussian filtering.

[0015] Preferably, the pseudo-color processing is JET color mapping, piecewise linear mapping or rainbow mapping.

[0016] The application has the beneficial effects that: the application provides a range-gated laser radar image reconstruction method, a plurality of radar slice images of different distances are obtained through continuous stepping of a range-gated gate in a range-gated laser radar, background noise influence caused by the range-gated gate being wider than the time delay step length of the laser radar is overcome, and the picture quality is improved; target distance information is strengthened through inter-frame difference and binarization operation to obtain a target frame distance information strengthening image, and background noise is effectively suppressed; an optimized target frame radar slice image is obtained through AND operation of the target frame distance information strengthening image and a target frame preprocessed image, real target edges are highlighted, and blurring is reduced; then, a target frame distance matrix is obtained through multiplication of the optimized target frame radar slice image and the corresponding distance of the radar slice image; finally, an iterative calculation target frame distance matrix is obtained, superimposed, a detection target object matrix is obtained, and a high-precision detection target object distance image is reconstructed after pseudo-color processing, and the distance resolution and anti-interference performance are significantly improved.

[0017] In summary, the application significantly improves the anti-noise ability, optimizes the distance resolution performance, and effectively enhances the clarity and authenticity of the target edges. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 The overall flowchart of a range-gated laser radar image reconstruction method provided by an embodiment of the application is shown in the figure. Figure 2 In the figure, (a) is a target frame pre-processing image, (b) is a target frame pre-processing image, and (c) is a target frame post-processing image. Figure 3 In the figure, (a) is a target frame pre-processing image, (b) is a target frame pre-processing image, and (c) is a target frame post-processing image. Figure 4The optimized target frame radar slice image provided by an embodiment of the present application; Figure 5 The target object distance image provided by an embodiment of the present application; Figure 6 The comparative diagram for detecting an indoor 8-17 m scene by using the present application, wherein (a) is a schematic diagram of an indoor scene photographed by a camera, and (b) is a distance-gated laser radar distance image of the indoor scene; Figure 7 The comparative diagram for detecting a 20 cm interval target at a position of 10.9 m in a water pipe by using the present application, wherein (a) is a schematic diagram of an interval target in water photographed by a camera, and (b) is a laser radar distance image of the interval target. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0021] Please refer to Figure 1 The distance-gated laser radar image reconstruction method provided by an embodiment of the present application comprises the following steps. S1: Obtain a plurality of radar slice images at different distances, and after preprocessing, sequentially take each frame as a target frame preprocessed image starting from the second frame.

[0022] The gating distance, step number and step length of the distance-gated laser radar are set, N frames of radar slice images at different distances are obtained by continuous stepping, and the N frames of radar slice images at different distances obtained are preprocessed, and sequentially take each frame as a target frame preprocessed image starting from the second frame.

[0023] In an optional embodiment, after obtaining N frames of radar slice images, the present application is preprocessed to obtain N frames of preprocessed radar slice images, and three consecutive preprocessed radar slice images (i.e. i-1 frame, i frame and i+1 frame) are selected, the i-1 frame preprocessed radar slice image is taken as a target frame preprocessed image, as shown in (a) of FIG. 1; Figure 2 the i frame preprocessed radar slice image is taken as a target frame preprocessed image, as shown in (b) of FIG. 1; Figure 2 and the i+1 frame preprocessed radar slice image is taken as a target frame preprocessed image, as shown in (c) of FIG. 1. Wherein, the value range of i is 1 Figure 2 Specifically, the preprocessing in the present application refers to denoising processing, and the N frames of radar slice images obtained are denoised by using a median filtering method.

[0024] It is worth noting that this application does not limit the denoising method, and any denoising method such as deep learning, graph neural network, median filtering, mean filtering, Gaussian filtering, etc. can be used for denoising.

[0025] S2: Differentiate the target frame preprocessed image with the previous and next adjacent frames to obtain a target frame front differential image and a target frame back differential image, perform binarization processing on them respectively to obtain a target frame front differential image and a target frame back differential image, and perform an AND operation on them to obtain a target frame distance information enhancement map.

[0026] Preprocess the target frame image Preprocess the image before the target frame Perform differential to obtain the differential image before the target frame , the specific formula is as follows: ; Where, is the difference image before the target frame, Preprocess the image for the target frame, Preprocess the image before the target frame.

[0027] Then, the target frame front difference image is taken with zero as the threshold Perform binarization processing to obtain the difference image before binarization of the target frame , the results are as follows Figure 3 As shown in (a), the specific formula is as follows: ; Where, is the differential image before binarization of the target frame, is the difference image before the target frame.

[0028] Next, the target frame is preprocessed After preprocessing the image with the target frame Perform differential and obtain the differential image after the target frame The specific formula is as follows: ; Where, Target frame post-difference image, Preprocess the image for the target frame, Preprocess the image for the target frame.

[0029] After that, the target frame is subjected to differential image processing with zero as the threshold. Perform binarization processing to obtain the differential image after binarization of the target frame , the results are as follows Figure 3 As shown in (b), the specific formula is as follows: ; In the formula, is the difference image of the target frame after binarization, is the difference image of the target frame.

[0030] Finally, the difference image of the target frame before binarization and the difference image of the target frame after binarization perform logical AND operation to obtain the target frame distance information enhancement map , the final result is shown in Figure 3 (c), the formula is as follows: ; In the formula, is the target frame distance information enhancement map, is the difference image of the target frame before binarization, is the difference image of the target frame after binarization.

[0031] S3: Perform logical AND operation between the target frame distance information enhancement map and the target frame preprocessed image to obtain the optimized target frame radar slice image, multiply the distance corresponding to the different distance radar slice image to obtain the target frame distance matrix, iterate until all target frame distance matrices are obtained, superimpose to obtain the detection target object matrix, and perform pseudo-color processing to reconstruct the detection target object distance image.

[0032] Perform logical AND operation between the target frame distance information enhancement map and the target frame preprocessed image to obtain the optimized target frame radar slice image , the result is shown in Figure 4 , the formula is as follows: ; In the formula, is the optimized target frame radar slice image, is the target frame distance information enhancement map, is the target frame preprocessed image.

[0033] Multiply each pixel intensity value of the pixel intensity matrix of the optimized target frame radar slice image with the distance corresponding to the different distance radar slice image to obtain the target frame distance matrix , the formula is as follows: ; In the formula, is the target frame distance matrix, is the optimized target frame radar slice image, is the distance corresponding to the i-th frame radar slice image.

[0034] Target 1 <i<N的目标帧预处理图像进行迭代直至第N帧目标帧预处理图像,以获得每一帧雷达切片图像对应的目标帧距离矩阵 .

[0035] Next, the distance matrix of all target frames is obtained Superposition is performed to obtain the detection target object matrix The specific formula is as follows: ; Where, is the detection target object matrix, N is the number of frames of radar slice image, is the target frame distance matrix.

[0036] Then, the detection target object matrix Perform pseudo color processing, and the final result is as follows Figure 5 As shown in the figure, the range image of the detected target object is reconstructed. Among them, the pseudo color processing can be selected from JET color mapping, piecewise linear mapping, rainbow mapping, etc. There is no restriction on the choice of pseudo color processing here, and you can choose it according to the actual situation.

[0037] Specific embodiment 1: An imaging experiment of an indoor scene.

[0038] See also Figure 6 , is a schematic diagram of an experiment using a range-gated lidar image reconstruction method of this application to detect indoor scenes at a distance of 8-17m, wherein, Figure 6 (a) is an indoor scene captured by a camera. During the detection process, a range-gated laser radar was used to continuously step images of scenes between 8 and 17 meters. The step time interval was 0.25 ns, corresponding to a step length of 3.75 cm, and 240 radar slice images of the target object were obtained at equal intervals. The radar slice images of the target object were reconstructed using this application and pseudo-color processed, and finally the range image of the indoor scene detected by the range-gated laser radar was obtained. The results are shown in the figure. Figure 6 As shown in (b), based on the color characteristics of the range image, the distance information between the target object and the lidar can be accurately obtained.

[0039] Specific embodiment 2: An imaging experiment of an underwater spaced target.

[0040] See also Figure 7 , is a schematic diagram of an experiment using a range-gated lidar image reconstruction method to detect targets at 20 cm intervals at a distance of 10.9 m in water, wherein: Figure 7The middle (a) is a 20cm interval target in water photographed by a camera. During the detection process, a range-gated laser radar is used to continuously step imaging in the range of 9m-13m in water, the step time interval is 0.25ns, corresponding to the step length of 2.81cm in water, and 142 frames of equally spaced target object slice images are obtained.

[0041] Due to the strong backscattering of plankton and suspended particles in water, the radar slice image has strong environmental noise. The target object slice image is reconstructed and pseudo-color processed using the present application, and finally the range image of the range-gated laser radar detecting the interval target in water is obtained, as shown in the middle (b). Figure 7 According to the color characteristics of the range image, the distance information between the detected interval target and the laser radar can be accurately obtained, and the range resolution and lateral resolution are very high.

[0042] Those skilled in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are realized in hardware or software depends on the specific application and design constraints of the technical solution. The skilled person can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0043] The above-described embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A range-gated lidar image reconstruction method, characterized in that: The following steps are involved: Acquire several radar slice images at different distances. After preprocessing, starting from the second frame, take each frame as the target frame preprocessing image, perform difference with the adjacent frames to obtain the target frame front difference image and target frame back difference image. After binarization, perform AND operation on each frame to obtain the target frame distance information enhancement map. The target frame distance information enhancement map is ANDed with the target frame preprocessed image to obtain an optimized target frame radar slice image, which is multiplied by the distance corresponding to the radar slice image to obtain a target frame distance matrix. This is iterated until all target frame distance matrices are obtained, and the detected target object matrix is ​​obtained after superposition. Pseudo-color processing is performed to reconstruct the detected target object distance image.

2. The range-gated laser radar image reconstruction method according to claim 1, wherein: The binarization process includes: performing binarization processing on the target frame before and after differential images with zero as a threshold value to obtain the target frame before and after binarization differential images.

3. The range-gated laser radar image reconstruction method according to claim 1, wherein: For each pixel intensity value of the pixel intensity matrix in the optimized target frame radar slice image, the pixel intensity value is multiplied by the distance corresponding to the radar slice image to obtain the target frame distance matrix.

4. The range-gated laser radar image reconstruction method according to claim 1, wherein: The formula for obtaining the optimized target frame radar slice image is: ； Where, is the optimized target frame radar slice image, is the target frame distance information enhancement map, Preprocess the image for the target frame.

5. The range-gated laser radar image reconstruction method according to claim 1, wherein: The formula for obtaining the target frame distance matrix is: ； Where, is the target frame distance matrix, is the optimized target frame radar slice image, is the distance corresponding to the i-th radar slice image.

6. The range-gated laser radar image reconstruction method according to claim 1, wherein: The formula for obtaining the detection target object matrix is: ； Where, is the detection target object matrix, N is the number of frames of radar slice image, is the target frame distance matrix.

7. The range-gated laser radar image reconstruction method according to claim 2, wherein: The target frame distance information enhancement map is obtained by performing an AND operation on the target frame difference image before binarization and the target frame difference image after binarization. The formula is: ； Where, is the target frame distance information enhancement map, is the differential image before binarization of the target frame, is the difference image after binarization of the target frame.

8. The range-gated laser radar image reconstruction method according to claim 1, wherein: The preprocessing includes: performing denoising on the radar slice images at several different distances to obtain denoised radar slice images.

9. The range-gated laser radar image reconstruction method according to claim 8, wherein: The denoising is performed by median filtering, mean filtering or Gaussian filtering.

10. The range-gated laser radar image reconstruction method according to claim 1, wherein: The pseudo color processing is JET color mapping, piecewise linear mapping or rainbow mapping.

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