Range gating laser radar image reconstruction method based on improved centroid method

Abstract

The invention provides a range gating laser radar image reconstruction method based on an improved centroid method, and solves the technical problems that detection target signals and background noise are difficult to distinguish and reconstructed image distance information is distorted due to the fact that the intensity of existing laser radar echo signals is influenced by the difference of object surface reflectivity. The method comprises the following steps: acquiring a plurality of radar slice images, extracting the pixel intensity of a certain pixel point in the plurality of radar slice images, and drawing a pixel intensity value change trend chart; performing background judgment on the pixel intensity value change trend chart, and if the pixel intensity value change trend chart is a background, performing zero clearing on the centroid distance of a certain pixel point; otherwise, the target object is obtained, the centroid distance of a certain pixel point is calculated, iteration is carried out until all pixel points are calculated to obtain a centroid distance matrix, and pseudo-color processing is carried out to obtain a distance image of the reconstructed target object. 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 based on an improved centroid method. BACKGROUND

[0002] Laser radar is a technology that uses pulsed laser as a transmitting source, receives the reflected echo signal intensity of the laser beam on the target object, and obtains the distance between the target object and the laser according to the time-of-flight method to realize the detection of the shape of the target object. The characteristics of short wavelength, narrow pulse width, smaller divergence angle, and higher pulse energy of laser are used to realize the detection of target objects at a farther distance with higher resolution.

[0003] The range-gated technology realizes the reception of echo signals of specific distances by precisely controlling the transmission time of pulsed laser and the opening time of the gated detector, and is an important method for suppressing the backscattering effect of laser. However, when detecting a large target object, the sampling area needs to cover the entire target object. In order to not increase the opening time of the gating door, the time width of the range-gated door is generally much larger than the delay step length of the multiple continuous step slice images of the detector, resulting in a time overlap between each slice image and the previous and next several images, which increases the background noise of the target object.

[0004] The existing Chinese invention patent with the application number CN201910801487.6 proposes a range-gated laser radar imaging method based on adjacent frame difference, which obtains the effective distances corresponding to the front and rear edges of the ICCD gating door by performing difference operation on the adjacent two intensity images, and realizes fast imaging. However, this patent only considers single target scanning imaging in the imaging process, and does not consider the influence of the difference in reflectivity of the object surface on the echo signal intensity of the laser radar in a complex environment background, which makes it difficult to distinguish the detected target signal from the background noise, and the distance information of the reconstructed image is distorted. SUMMARY

[0005] The purpose of the embodiments of the present application is to provide a range-gated laser radar image reconstruction method based on an improved centroid method, to solve the technical problem that the echo signal intensity of the laser radar is affected by the difference in reflectivity of the object surface, which makes it difficult to distinguish the detected target signal from the background noise, and the distance information of the reconstructed image is distorted.

[0006] To achieve the above-mentioned purpose, the embodiments of the present application provide a range-gated laser radar image reconstruction method based on an improved centroid method, comprising the following steps: Obtain a plurality of radar slice images, extract the pixel intensity of a certain pixel point in the plurality of radar slice images, and draw a pixel intensity value trend graph; The background of the pixel intensity value trend graph is judged, if it is background, the centroid distance of a certain pixel point is cleared; otherwise, it is a target, the centroid distance of a certain pixel point is calculated, and iteration is performed until the centroid distance matrix of all pixel points is obtained, and the distance image of the reconstructed target object is obtained by pseudo-color processing.

[0007] Preferably, the process of obtaining the centroid distance comprises: extracting the centroid in the pixel intensity value trend graph to obtain the frame number of the centroid corresponding to the radar slice image, multiplying the resolution distance of adjacent two frames and adding the starting distance to obtain the centroid distance; The starting distance refers to the distance of the starting node of the radar slice image.

[0008] Preferably, the process of obtaining the centroid comprises: The maximum and minimum values of the pixel intensity in the pixel intensity value trend graph are obtained, the maximum and minimum values of the pixel intensity are equally divided to obtain a plurality of pixel intensity value gradients; The abscissa corresponding to the first and last time when the pixel intensity value is greater than the pixel intensity value gradient is obtained, and the median value is taken to obtain the distance frame approximation value; Iterate in turn until all distance frame approximation values are obtained, and then take the average to obtain the centroid.

[0009] Preferably, the process of background judgment comprises: The maximum and minimum values of the pixel intensity in the pixel intensity value trend graph are obtained, the range is calculated and a threshold is set; If the range is less than the threshold, a certain pixel point is background, and the centroid distance is set to zero; otherwise, a certain pixel point is a target, and the centroid distance of all pixel points is calculated.

[0010] Preferably, the formula of the pixel intensity value gradient is: ; In the formula, is the pixel intensity value gradient, is the maximum value of the pixel intensity, is the minimum value of the pixel intensity, is the total number of equal division, =1,2,…… , is the equal division.

[0011] Preferably, the formula of the centroid distance is as follows: ; In the formula, is the centroid distance corresponding to the pixel point (x, y), d0 is the starting distance, j is the frame number of the centroid corresponding to the radar slice image, is the resolution distance of adjacent frames of the distance gated laser radar.

[0012] Preferably, the pixel intensity in the pixel intensity value change trend graph is sorted by the bubble method to obtain the maximum value and the minimum value of the pixel intensity.

[0013] Preferably, the centroid in the pixel intensity value change trend graph is extracted by gradually approaching through dichotomy.

[0014] Preferably, the range formula is: ; In the formula, is the extreme value, is the maximum value in the pixel intensity change trend graph, is the minimum value in the pixel intensity change trend graph.

[0015] Preferably, the centroid distance of a certain pixel point is cleared, which means that the centroid distance is set to the initial distance.

[0016] The application has the beneficial effects that the application provides a distance-gated laser radar image reconstruction method based on an improved centroid method. First, the intensity value change trend graph is drawn by obtaining the pixel intensity of a certain pixel point in a plurality of radar slice images. The background is judged according to the intensity value change trend graph, the background of a certain pixel point is judged, the intensity change in the time sequence is considered instead of the intensity value at a single moment, the misjudgment caused by the reflectivity difference of the object surface is effectively avoided, and the background and the target are accurately distinguished. Then, the centroid distance of a certain pixel point for the background is cleared to avoid the interference of the background noise on the subsequent distance image generation. Subsequently, the centroid distance of the target corresponding pixel point is calculated based on the pixel intensity value change trend graph, and the centroid distance matrix of all pixel points is obtained through iterative processing. The actual centroid distance information is reflected according to the pixel intensity value change trend, which does not depend on a single reflectivity threshold judgment, reduces the distance information distortion caused by the reflectivity difference, and improves the accuracy of the reconstructed image. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. 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.

[0018] Figure 1 The overall flowchart of a distance-gated laser radar image reconstruction method based on an improved centroid method provided by an embodiment of the application is shown in the figure. Figure 2 The pixel intensity value change trend graph of a pixel point (290, 230) provided by an embodiment of the application is shown in the figure. Figure 3 A background judgment flowchart provided for an embodiment of the present application; Figure 4 A flowchart of extracting the centroid of the pixel intensity value trend graph provided for an embodiment of the present application; Figure 5 An indoor scene schematic diagram provided for an embodiment of the present application; Figure 6 An indoor scene differential method imaging schematic diagram provided for an embodiment of the present application; Figure 7 An indoor scene improved centroid method imaging schematic diagram provided for an embodiment of the present application; Figure 8 An outdoor scene schematic diagram provided for an embodiment of the present application; Figure 9 An outdoor scene differential method imaging schematic diagram provided for an embodiment of the present application; Figure 10 An outdoor scene improved centroid method imaging schematic diagram provided for an embodiment of the present application. DETAILED DESCRIPTION

[0019] In order to make the technical problems to be solved by the present application, technical solutions and beneficial effects more clearly understood, 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 not to limit the present application.

[0020] Please refer to Figure 1 A distance-gated laser radar image reconstruction method based on an improved centroid method provided for an embodiment of the present application, comprising the following steps: S1: Obtain a plurality of radar slice images, extract the intensity value of a certain pixel point in the plurality of radar slice images and draw a pixel intensity value trend graph.

[0021] The distance-gated laser radar starts stepping from the starting distance d0, steps at the same step value to obtain K consecutive frames of radar slice images at different distances, and the size of each radar slice image is Let the pixel point of the jth frame of radar slice image be , and the pixel intensity is represented as , wherein , , , M is the number of pixels of the radar slice image in the vertical direction, N is the number of pixels of the radar slice image in the horizontal direction, and K is the number of frames of the radar slice images obtained continuously.

[0022] In an optional embodiment, for the first pixel point in the radar slice image , traverse its pixel intensity in K frames of radar slice images at different distances ,in, , draw the pixel intensity value change trend graph. The pixel intensity value change trend diagram is as follows Figure 2 shown.

[0023] S2: Perform background judgment on the pixel intensity value change trend graph. If it is background, the centroid distance of a certain pixel point is cleared to zero; otherwise, it is a target and the centroid distance of a certain pixel point is calculated.

[0024] See also Figure 3 , which is a flowchart for background judgment. This application uses the bubble method to obtain the maximum value in the pixel intensity value change trend diagram corresponding to a pixel point (x, y) in the radar slice image. and minimum value , and calculate the range based on the maximum and minimum values. The specific formula is as follows: ; Where, is an extreme value, is the maximum value in the pixel intensity value change trend graph, It is worth noting that the present application does not limit the method of obtaining the maximum and minimum values, and the method can be selected according to the actual situation.

[0025] The threshold T is empirically set based on the background intensity outside the radar gating interval. , then the pixel For the background, set the corresponding centroid distance , the pixel The corresponding centroid distance is cleared to zero; if the extreme difference , then determine the pixel point As the target, the centroid of the pixel intensity value change trend graph is extracted using the bisection method to obtain the pixel point The corresponding centroid frame number j.

[0026] Specifically, the specific implementation process of the centroid method is as follows: Figure 4 The specific steps are as follows: First, get the pixel points The maximum value of pixel intensity in the pixel intensity value trend graph and minimum value ; Next, the maximum pixel intensity With minimum value difference Divide equally and get a pixel intensity value gradient, specifically as follows: ; In the formula, is a pixel intensity value gradient, is a pixel intensity maximum value, is a pixel intensity minimum value, is a total number of equal divisions, =1,2,… is the first equal division.

[0027] Then, the abscissa a corresponding to the first time when the pixel intensity value in the pixel point is greater than the pixel intensity value gradient , and the abscissa b when the pixel intensity value is last greater than the pixel intensity value gradient , are taken, and the median of the abscissa a and the abscissa b is taken as an approximate value of the frame number of the pixel point, and the formula is as follows: ; Finally, by analogy, the approximate values of the frame number of the pixel intensity value gradient corresponding to the pixel point are obtained, and the frame number of the pixel point centroid corresponding to the radar slice image is obtained by averaging, to obtain the frame number of the pixel point centroid in the pixel intensity trend graph.

[0028] In an optional embodiment, a certain pixel point is (290, 230), the resolution distance of the adjacent two frames is multiplied by the frame number of the pixel point centroid corresponding to the radar slice image, to obtain the centroid distance corresponding to the pixel point. , , wherein, is the resolution distance of the adjacent two frames of the laser radar.

[0029] S3: Iteratively calculate the centroid distance of all pixel points to obtain a centroid distance matrix, and perform pseudo-color processing to obtain a distance image of the reconstructed target object.

[0030] For each pixel point in the radar slice image, the centroid distance of the pixel point is calculated in turn, and a centroid distance matrix of the target image is formed, and the centroid distance matrix is subjected to pseudo-color processing, the distance range corresponding to the color bar is the step range of the laser radar, and the distance image of the detected target object is reconstructed.

[0031] Specific embodiment 1: Comparative experiment of reconstructed image of indoor scene once.

[0032] ​​Please refer to Figure 5 , is a schematic diagram of the indoor scene imaging by the algorithm of the present application. The star-shaped target is detected at a distance of 12 m in the indoor scene by using the range-gated laser radar. The star-shaped target is placed on a stool at a distance of 12 m in front of the radar transmitting end. The range-gated laser radar starts step imaging at a distance of 10 m. The step time is set to 0.25 ns. The resolution distance of adjacent two frames is 0.0375 m. A total of 186 slice images of continuous steps are obtained. Figure 5 , is a schematic diagram of the target scene, Figure 6 is a result image of image reconstruction of the target by using the difference method. As can be seen from the image, due to the different reflectivities of the white and black surfaces of the star-shaped target, the target is in the same distance plane as a whole, but the image reconstructed by the difference method cannot distinguish the distance information of the targets with different reflectivities. The detected indoor scene distance image obtained by using the algorithm of the present application is as shown in Figure 7 . As can be seen from the image, the reconstructed image of the target in the same distance plane basically keeps the same color. Based on the color characteristics of the distance image, the distance information between the measured target and the laser radar transmitting end can be accurately obtained, and the influence of the target surface reflection characteristics can be effectively avoided.

[0033] Specific embodiment 2: comparison experiment of a reconstructed image of an outdoor complex scene.

[0034] Please refer to Figure 8 , is a schematic diagram of the outdoor complex scene imaging by the algorithm of the present application. The range-gated laser radar is used to detect Figure 8 the unoccupied iron house at a distance of 80 m in the outdoor scene as shown in the figure. The system starts step imaging at a distance of 50 m. The step time is set to 0.25 ns. The resolution distance of adjacent two frames is 0.0375 m. A total of 1120 slice images of continuous steps are obtained. Due to the difference of the target reflection characteristics, there is a significant difference between the front and side echo signal intensities of the iron house. Figure 9 is a result of image reconstruction of the radar image by using the difference method. The side of the iron house is farther than the front, but limited by the weak echo signal, the distance image cannot accurately reflect the distance information of the target. The pseudo-color processed detected outdoor scene distance image obtained by using the image reconstruction method of the present application is as shown in Figure 10 . As can be seen from the image, the color of the front of the iron house gradually changes to the side with the distance, which is consistent with the change of the distance information of the target in the actual scene. The detected distance image obtained by using the algorithm of the present application can clearly obtain the target image and the corresponding distance information. The difference of the echo signal almost has no influence on the result.

[0035] Those skilled in the art can understand that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are realized in hardware or software manner 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.

[0036] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit the technical solutions; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced by equivalent replacements; 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 based on an improved centroid method, characterized in that: The following steps are involved: Acquire a plurality of radar slice images, extract the pixel intensity of a certain pixel point in the plurality of radar slice images, and draw a pixel intensity value change trend graph; Performing background judgment on the pixel intensity value change trend graph, and if it is background, clearing the centroid distance of the certain pixel point to zero; Otherwise, it is a target, and the centroid distance of the certain pixel point is calculated, and it is iterated until all pixel points are calculated to obtain a centroid distance matrix, and pseudo color processing is performed to obtain a reconstructed range image of the target object.

2. The range-gated laser radar image reconstruction method based on the improved centroid method according to claim 1, characterized in that: The process of obtaining the centroid distance includes: extracting the centroid from the pixel intensity value change trend graph, obtaining the frame number of the radar slice image corresponding to the centroid, multiplying the result by the resolution distance between two adjacent frames and adding the result to the starting distance to obtain the centroid distance; The starting distance refers to the distance from the starting node of obtaining the radar slice image.

3. The range-gated laser radar image reconstruction method based on the improved centroid method according to claim 2, characterized in that: The process of obtaining the centroid includes: Obtaining the maximum and minimum values ​​of pixel intensities in the pixel intensity value change trend graph, and dividing the difference between the maximum and minimum values ​​of the pixel intensities into equal parts to obtain a plurality of pixel intensity value gradients; Obtain the horizontal coordinates corresponding to the first and last times when the pixel intensity value is greater than the pixel intensity value gradient, and take the median to obtain the distance frame approximation; Iterate in sequence until all the distance frame approximations are obtained and then averaged to obtain the centroid.

4. The range-gated laser radar image reconstruction method based on the improved centroid method according to claim 1, characterized in that: The background judgment process includes: Obtaining the maximum and minimum values ​​of pixel intensities in the pixel intensity value change trend graph, calculating the range and setting a threshold; If the range is less than the threshold, the certain pixel point is the background and the centroid distance is set to zero; otherwise, the certain pixel point is the target and the centroid distance of all pixel points is calculated.

5. The range-gated laser radar image reconstruction method based on the improved centroid method according to claim 3, characterized in that: The formula for the pixel intensity value gradient is: ； Where, is the pixel intensity gradient, is the maximum pixel intensity, is the minimum pixel intensity, is the total number of equal parts, =1,2,…… , for the equal parts.

6. The range-gated laser radar image reconstruction method based on the improved centroid method according to claim 1, characterized in that: The formula for the centroid distance is as follows: ； Where, is the distance from the center of mass of the pixel point (x, y), d0 is the starting distance, j is the number of frames of the radar slice image corresponding to the center of mass, is the resolution distance of adjacent frames of the range-gated lidar.

7. The range-gated laser radar image reconstruction method based on the improved centroid method according to claim 3, characterized in that: The pixel intensities in the pixel intensity value change trend graph are sorted by a bubble method to obtain the maximum and minimum values ​​of the pixel intensities.

8. The range-gated laser radar image reconstruction method based on the improved centroid method according to claim 2, characterized in that: The centroid of the pixel intensity value variation trend graph is extracted by stepwise approximation using a binary method.

9. The range-gated laser radar image reconstruction method based on the improved centroid method according to claim 4, characterized in that: The range formula is: ； Where, is an extreme value, is the maximum value in the pixel intensity change trend graph, is the minimum value in the pixel intensity change trend graph.

10. The range-gated laser radar image reconstruction method based on the improved centroid method according to claim 2, characterized in that: Clearing the centroid distance of the certain pixel point to zero refers to setting the centroid distance to the starting distance.

Images