Method for positioning the center of a laser spot and test system

Abstract

The application provides a laser spot center positioning method and a test system. The method comprises the following steps: acquiring a laser spot image; performing spot edge-preserving boundary denoising preprocessing on the acquired laser spot image; determining the spot area of the preprocessed laser spot image; calculating the radius according to the spot area and constructing a disk mask; performing traversal and template matching on the laser spot image by using the mask to determine the maximum energy center point of the spot in the laser spot image. The laser spot center positioning method and the test system greatly save the spot quality test experiment cost, effectively realize real-time positioning of the laser spot center at a long distance, and have excellent robustness and accuracy in center detection of near-field spots and far-field irregular spots, improve the spot performance inspection precision, thereby guiding the index design of the product, and shortening the research and development cycle and cost of similar products.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser technology, in particular to a laser spot center positioning method and a test system. BACKGROUND

[0002] The long-range adaptive laser spot center positioning is a very difficult problem. In the near distance spot axis, the energy center can be easily extracted because of the energy aggregation and regular shape of the spot. However, with the increase of the distance, the laser is transmitted in the long-distance atmosphere, and the spot is dispersed and separated into irregular shapes due to the atmospheric effects such as atmospheric turbulence, thermal blooming and particle scattering, so that the accurate target energy center cannot be obtained by the boundary fitting method, and there is a deviation.

[0003] The laser spot center positioning is widely used, and can improve the spot performance test accuracy of the long-range laser infrared composite detection system, the long-range laser ranging system, the long-range laser cutting and the long-range laser irradiation system, and the registration accuracy of the laser and the image center.

[0004] The detection of the near-field spot mainly uses the geometric center method, the mass center method, the weighted interpolation method, the least square circle fitting method, the feature point recognition and the spatial center moment, and the spot segmentation accuracy is required to be high, otherwise the scattered pixel values of the boundary will be weighted into the calculation of the spot center, so that the calculated spot center is deviated. In the detection and center positioning process of the far-field spot, the spot is dispersed and separated into irregular shapes, and the above methods cannot achieve the ideal effect in real-time or stability. SUMMARY

[0005] The technical problems to be solved by the present application are how to ensure that the algorithm can find the energy center of the spot with different distances, different spot sizes and different regularities, how to improve the laser spot center positioning accuracy, and how to improve the stability of the continuous multi-frame laser spot center positioning. The present application provides a laser spot center positioning method and a test system.

[0006] The laser spot center positioning method according to the embodiment of the present application comprises:

[0007] acquiring a laser spot image;

[0008] performing spot boundary-preserving denoising preprocessing on the acquired laser spot image;

[0009] determining the spot area of the preprocessed laser spot image;

[0010] calculating the radius according to the spot area and constructing a disk mask;

[0011] using the mask to perform traversal and template matching on the laser spot image to determine the maximum energy center point of the spot in the laser spot image.

[0012] According to some embodiments of the present application, a bilateral filtering based spot denoising algorithm is used for spot boundary preserving denoising preprocessing.

[0013] In some embodiments of the present application, determining the spot area of the preprocessed laser spot image comprises:

[0014] The preprocessed image obtained through preprocessing is subtracted from the laser spot image to obtain an enhanced image through image enhancement;

[0015] A binary image is generated through threshold segmentation of the enhanced image in combination with the Otsu algorithm and morphological filtering;

[0016] The spot area is calculated based on the binary image.

[0017] According to some embodiments of the present application, the image enhancement adopts one of the following methods: gamma stretching, DDE enhancement and adaptive histogram.

[0018] In some embodiments of the present application, the acquired laser spot image is continuous laser spot video frame data.

[0019] According to some embodiments of the present application, the acquired laser spot image is acquired from a spot formed by laser emission from a laser light source to a target at a distance ranging from 1 meter to 100 km.

[0020] The laser spot center positioning test system according to the embodiments of the present application comprises:

[0021] A laser emission source for emitting laser light;

[0022] A target for receiving laser light;

[0023] An acquisition unit for acquiring a laser spot image on the target;

[0024] A processing device for performing center positioning on the acquired laser spot image by using the laser spot center positioning method as described above.

[0025] According to some embodiments of the present application, the target is a movable target and is height adjustable.

[0026] In some embodiments of the present application, the processing device is a portable computer storing a program for running the method for determining the laser spot center positioning.

[0027] According to some embodiments of the present application, the acquisition unit is one of the following: a CCD camera, a CMOS camera, a visible light acquisition unit, a low-illumination acquisition unit, a low-light acquisition unit, an infrared acquisition unit and an ultraviolet acquisition unit.

[0028] In summary, the laser spot center positioning method and test system greatly saves the cost of spot quality test experiment, and effectively realizes real-time positioning of the laser spot center at a long distance. The method has excellent robustness and accuracy in center detection of near-field spots and far-field irregular spots, improves the spot performance test precision of systems including airborne and shipborne laser weapons, airborne photoelectric radars, ground air defense laser irradiation, laser ranging and laser striking, thereby guiding the index design of the products, and shortening the development cycle and funds of similar products. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A flow chart of the laser spot center positioning method according to the embodiment of the application is shown in FIG. 1.

[0030] Figure 2 A flow chart of the laser spot center positioning method according to the embodiment of the application is shown in FIG. 1.

[0031] Figure 3 A schematic diagram of the laser spot center positioning test system according to the embodiment of the application is shown in FIG. 2.

[0032] Figure 4 A gray scale distribution of a 16-bit original image before gamma stretching according to the embodiment of the application is shown in FIG. 3.

[0033] Figure 5 A gray scale distribution of an 8-bit enhanced image after gamma stretching according to the embodiment of the application is shown in FIG. 4.

[0034] Figure 6 A schematic diagram of a disk mask according to the embodiment of the application is shown in FIG. 5.

[0035] Figure 7 A schematic diagram of disk mask traversal convolution according to the embodiment of the application is shown in FIG. 6.

[0036] Figure 8 A schematic diagram of near-field spot center detection according to the embodiment of the application is shown in FIG. 7.

[0037] Figure 9 A schematic diagram of far-field spot center detection according to the embodiment of the application is shown in FIG. 8.

[0038] Figure 10 A schematic diagram of near-field spot center offset according to the embodiment of the application is shown in FIG. 9.

[0039] Figure 11 A schematic diagram of far-field spot center offset according to the embodiment of the application is shown in FIG. 10.

[0040] Figure 12 A work flow chart of the laser spot center positioning test system according to the embodiment of the application is shown in FIG. 11.

[0041] REFERENCE NUMERALS:

[0042] The test system 100,

[0043] The laser emission source 10, the target 20, the acquisition unit 30, and the processing device 40. DETAILED DESCRIPTION

[0044] To further clarify the technical means and effects taken by the present application to achieve the intended purpose, the present application is described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0045] The description of the method flow in the specification of the present application and the steps of the flowchart in the drawings of the present application do not necessarily strictly follow the step numbers, and the method steps can change the execution order. Moreover, certain steps can be omitted, multiple steps can be combined into one step for execution, and / or one step can be divided into multiple steps for execution.

[0046] As Figure 1 shown, the laser spot center positioning method according to the embodiment of the present application comprises:

[0047] S100, acquiring a laser spot image;

[0048] S200, performing spot edge-preserving denoising preprocessing on the acquired laser spot image;

[0049] S300, determining the spot area of the preprocessed laser spot image;

[0050] S400, calculating the radius and constructing a disk mask according to the spot area;

[0051] S500, using the mask to perform traversal and template matching on the laser spot image to determine the maximum energy center point of the spot in the laser spot image.

[0052] According to the laser spot center positioning method of the embodiment, the laser spot center positioning is realized through key steps such as image bright spot region enhancement, adaptive mask generation, and finding extreme values to determine the energy center, thereby improving the precision and stability of the laser spot center positioning.

[0053] According to some embodiments of the present application, in step S200, a spot denoising algorithm based on bilateral filtering is used for spot edge-preserving denoising preprocessing.

[0054] In some embodiments of the present application, in step S300, determining the spot area of the preprocessed laser spot image comprises:

[0055] S310, performing image enhancement on the difference between the preprocessed image obtained by preprocessing and the laser spot image to obtain an enhanced image;

[0056] S320 combines the Otsu algorithm with morphological filtering to perform threshold segmentation on the enhanced image and generate a binarized image;

[0057] S330 calculates the spot area based on a binarized image.

[0058] According to some embodiments of the present invention, in step S310, the image enhancement employs one of the following methods: gamma stretching, DDE enhancement, and adaptive histogram.

[0059] In some embodiments of the present invention, in S100, the acquired laser spot image is continuous laser spot video frame data.

[0060] According to some embodiments of the present invention, the acquired laser spot image is collected from a laser spot formed by a laser source emitting laser light towards a target at a distance ranging from 1 meter to 100 km.

[0061] like Figure 3 As shown, the laser spot center positioning test system 100 according to an embodiment of the present invention includes: a target 20, a data acquisition unit 30, and a processing device 40.

[0062] In this system, the laser emission source 10 emits laser light, the target 20 receives laser light, and the acquisition unit 30 acquires an image of the laser spot on the target 20. The processing device 40 uses the laser spot center positioning method described above to center the acquired laser spot image.

[0063] According to some embodiments of the present invention, the target 20 is a movable target 20 and its height is adjustable.

[0064] In some embodiments of the present invention, the processing device 40 is a portable computer storing a program for running a method to determine the center location of a laser spot.

[0065] According to some embodiments of the present invention, the acquisition unit 30 is one of the following: a CCD camera, a CMOS camera, a visible light acquisition unit, a low-light acquisition unit, a low-light acquisition unit, an infrared acquisition unit, and an ultraviolet acquisition unit.

[0066] In summary, the laser spot center positioning method and testing system 100 proposed in this invention significantly reduces the cost of spot quality testing and effectively achieves real-time positioning of the laser spot center at long distances. Furthermore, this method exhibits excellent robustness and accuracy in center detection of both near-field and far-field irregular spots, improving the accuracy of spot performance testing for systems including airborne and shipborne laser weapons, airborne optoelectronic radar, ground-based air defense laser illumination, laser ranging, and laser strike systems. This guides the design of specifications for such products and shortens the development cycle and reduces costs.

[0067] The laser spot center positioning method and testing system 100 according to the present invention are described in detail below with reference to the accompanying drawings. Its application areas include, but are not limited to, laser irradiation, photoelectric radar, laser cutting, and laser ranging systems on airborne, shipborne, spaceborne, vehicle-mounted, and ground-based carriers for spot performance testing and spot calibration. It is important to understand that the following description is merely exemplary and should not be construed as a specific limitation of the present invention.

[0068] Combination Figure 2 and Figure 12 As shown, the laser spot center positioning method includes:

[0069] A1, input continuous laser spot video frame data for acquisition and storage;

[0070] A2 uses a spot denoising algorithm based on bilateral filtering to perform spot boundary preservation denoising processing;

[0071] A3, after subtracting the filtering result from the original image, gamma stretching is performed to enhance the image. Then, the Otsu algorithm and morphological filtering, i.e. maximum inter-class variance, are combined to perform threshold segmentation to generate a binarized image and calculate its spot area.

[0072] A4. Calculate the radius based on the area obtained in step A3 and construct an adaptive-sized disk mask. Use the mask to traverse and match templates on the spot image.

[0073] A5, finds the maximum energy of the light spot under a certain aperture and finally returns to the center point, improving the high-precision positioning of the target at long distance;

[0074] A6, the algorithm generates and saves the positioning information and stability accuracy of historical frame images of the light spot while obtaining the real-time energy center of the light spot.

[0075] like Figure 3 As shown, the laser spot center localization test system 100 consists of a height-adjustable moving target 20, a near-infrared CCD camera covering the laser band, and a portable computer running a spot center localization algorithm. Figure 3 This is a schematic diagram of a long-range laser spot center detection system. After locating the center of the laser spot in the near field, a target 20 is placed at a distance, and the laser is directed onto the target 20. A near-infrared CCD detector (0.78~3µm) is used to analyze the laser spot. Since it responds to laser beams within a relevant optical spectral range, a near-infrared detector is used to analyze the formed laser spot, thereby acquiring images for spot center detection.

[0076] The laser spot center positioning and testing system 100 first performs edge-preserving denoising processing on the spot through bilateral filtering, performs image enhancement on the filtered result by subtracting the original image and performing gamma stretching, calculates the spot area using a binary image after threshold segmentation, constructs a disk mask with an adaptive size according to the area, performs template matching on the spot image using the mask, finds the maximum energy of the spot under a certain aperture, and finally returns the center point, so that the target remote positioning result is more accurate. Figure 2 The specific remote spot center detection flowchart.

[0077] The spot image filtering selects bilateral filtering for image enhancement processing. First, high-frequency components are extracted through filtering and noise points are filtered out, and the high-frequency information is superimposed on the original image. Image enhancement is performed on the superimposed image to achieve spot enhancement and improve the details of the main gray scale range. Figure 4 、 5 This facilitates the use of the maximum inter-class variance for spot separation in the next step.

[0078] Bilateral filtering is a classic image filtering method improved from Gaussian filtering. Equation 1 is the function of Gaussian filtering. For the Gaussian function, it is a function that uses spatial distance as a weight coefficient. The spot center is determined by convolution of the Gaussian kernel and the original image. The closer the center, the greater the weight. In equation 2, bilateral filtering not only considers spatial information, but also considers target gray scale information. The closer the gray value to the center point, the greater the weight. The spatial information and gray scale information are multiplied to determine the weight. Equation 3 is the bilateral filtering weight formula.

[0079] (1);

[0080] (2);

[0081] (3);

[0082] The method of first binarizing the enhanced image and then determining the spot area is adopted. Specifically:

[0083] The image to be detected only has a spot and a background, which is a binary classification problem. After enhancing the spot boundary through bilateral filtering, adaptive binary segmentation can be achieved through the inter-class variance method.

[0084] The maximum inter-class variance method for threshold segmentation divides a picture into two parts . By setting a threshold T, the part less than the threshold T is defined as the background , and the part greater than the threshold T is defined as the foreground . The gray scale contained by the background is , The gray scale contained by the foreground is The probability of being defined as foreground for all pixels of each gray level is The probability of each class appearing can be calculated by equation 4 and The total probability of foreground and background is equation 5~6 respectively, and the average gray level of each class is and as follows equation 7~8.

[0085] (4);

[0086] (5);

[0087] (6);

[0088] (7);

[0089] (8);

[0090] Where is the average gray level of the whole image, as follows

[0091] (9);

[0092] The variance of foreground and background can be obtained by equation 10~11, for this make the intra-class variance of two classes satisfy the maximum inter-class variance, that is maximum in equation 12, at this time it shows that the foreground and background variance is maximum, the probability of pixel error classification is smaller, so as to determine the segmentation threshold T, to achieve adaptive threshold segmentation, realize image binarization. Finally, according to the binarized image to determine the area of the light spot.

[0093] (10);

[0094] (11);

[0095] (12);

[0096] To improve the positioning accuracy of the light spot center, a disk mask is constructed, which is specifically:

[0097] A circular mask can be constructed by area, and the circular mask is used to convolve the light spot image to extract features. At this time, the maximum value in the feature map is the maximum energy center, and returning the maximum value is the maximum energy point. The following is the radius formula:

[0098] (13);

[0099] ConstructFigure 6 The disk mask is shown and is used to slide convolution on the original drawing, as shown in Figure 7 The sliding convolution is shown in the schematic diagram, the mask is traversed from the upper left corner to the entire image, and is convolved with the original drawing, when the mask completely covers the corresponding size of the light spot, the energy of the covered range is maximum at this time, and the maximum value in the convolution image corresponds to the position of the energy center.

[0100] Figure 12 It is a flowchart of a far and near range adaptive laser spot center positioning algorithm of the application, and the specific implementation steps are:

[0101] Step S1, a moving target is placed at the position where the far-range light spot reaches, and the height and position are adjusted so that the far-range light spot reaches the target;

[0102] Step S2, the input continuous laser spot video frame data is collected and stored, the peak value frame image of each light spot is calculated by laser emission frequency and CCD frame frequency, and the adaptive laser spot center positioning algorithm is executed;

[0103] Step S3, a light spot edge-preserving denoising algorithm based on bilateral filtering is used for light spot edge-preserving denoising processing;

[0104] Step S4, the filtered result is subtracted from the original drawing, and then image enhancement is realized through gamma stretching, and then a binary image is generated after threshold segmentation by combining the Otsu algorithm and morphological filtering, and the light spot area is calculated;

[0105] Step S5, the area obtained in steps S1-S4 is used to calculate the radius to construct a disk mask of adaptive size, and the mask is used for traversal and template matching of the light spot image;

[0106] Step S6, the maximum energy of the light spot under a certain radius is found, and the center point is finally returned, and the target long-range high-precision positioning is improved;

[0107] Step S7, the algorithm generates and saves the positioning information and stable accuracy of the light spot historical frame image while obtaining the real-time light spot energy center.

[0108] In step S1, other materials or objects that enhance the display of laser light spots can be added in addition to the color card, the distance of the far-field light spot is not unique and can be within 1 km to 100 km or within 1 m for the experiment, and the size of the target is not unique.

[0109] The CCD camera style and waveband used in step S2 are not unique, including but not limited to CCD cameras, CMOS cameras, visible light, low illumination, low light, infrared, ultraviolet, and other acquisition units.

[0110] The bilateral filtering denoising processing adopted in step S3 includes but is not limited to Gaussian filtering, median filtering, guide filtering, box filtering and nonlinear local filtering.

[0111] The image enhancement used in step S4 includes but is not limited to gamma stretching, DDE enhancement and adaptive histogram algorithm.

[0112] In conclusion, the long-distance spot center detection system used in the application is an indirect spot energy form acquisition system, the laser spot does not directly enter the light-sensitive acquisition device, neither large-scale CCD detector nor complex energy scaling optical system is needed, the required materials can be easily purchased and the price is low, which greatly reduces the system cost.

[0113] Although it is an indirect spot energy form acquisition system, because the target in the spot is far away, the CCD acquisition unit is close to the target and the angle is as small as possible, the accuracy and efficiency of spot acquisition can be ensured.

[0114] The long-range adaptive laser spot center positioning algorithm and test system 100 provided by the application is a necessary key step for all products and systems that need spot detection and center positioning, and the method is suitable for not only near-field spot center detection but also remote laser spot center detection and calibration (such as Figure 8 、 Figure 9 ) several kilometers away. The system stores the spot center of the historical frame and displays the spot center and the spot center of the historical frame in real time.

[0115] Compared with other methods, the long-range adaptive laser spot center positioning algorithm and test system 100 provided by the application has extremely high detection stability of the laser spot center: through energy center analysis of 30 continuous impact spots, it is found that the algorithm in the present application has a smaller outlier in the near field, the difference is within 1 pixel, the center offset of the circle fitting method is 2 pixels, and the centroid method also has good experimental effect. Figure 10 and Figure 11 The spot center offset amount under different distance scenes is shown.

[0116] The far and near range adaptive laser spot center positioning algorithm adopts the size of the disk circular mask dynamically generated based on the collected light spot, which is different from the method of finding the shape center or the centroid by using the fixed size radius shape.

[0117] Through the description of the specific embodiments, the technical means and effects adopted by the present application to achieve the predetermined purposes can be more deeply and specifically understood. However, the accompanying drawings are only provided for reference and illustration, and are not used to limit the present application.

Claims

1. A method of locating the center of a laser spot, characterized by, The method comprises: acquiring a laser spot image; performing spot edge-preserving denoising preprocessing on the acquired laser spot image; determining the spot area of the preprocessed laser spot image; calculating the radius according to the spot area and constructing a disk mask; performing traversal and template matching on the laser spot image using the mask to determine the maximum energy center point of the spot in the laser spot image. The method for determining the spot area of the preprocessed laser spot image comprises: performing image enhancement on the difference between the preprocessed image obtained through preprocessing and the laser spot image to obtain an enhanced image; generating a binary image through threshold segmentation of the enhanced image in combination with the Otsu algorithm and morphological filtering; calculating the spot area based on the binary image.

2. The method of claim 1, wherein, The spot edge-preserving denoising preprocessing is performed using a spot denoising algorithm based on bilateral filtering.

3. The method of claim 1, wherein, The image enhancement is performed using one of the following methods: gamma stretching, DDE enhancement, and adaptive histogram.

4. The method of claim 1, wherein, The acquired laser spot image is continuous laser spot video frame data.

5. The laser spot center positioning method according to any one of claims 1-4, characterized in that, The acquired laser spot image is collected from a spot formed by a laser light source emitting laser light to a target at a distance ranging from 1 meter to 100 km.

6. A laser spot center positioning test system, characterized in that, The method comprises: a laser emitting source for emitting laser light; a target for receiving laser light; an acquisition unit for acquiring a laser spot image on the target; a processing device for center positioning of the acquired laser spot image using the laser spot center positioning method according to any one of claims 1-5.

7. The laser spot center location test system of claim 6, wherein, The target is a movable target, and the height is adjustable.

8. The laser spot center location test system of claim 6, wherein, The processing device is a portable computer storing a program for running the laser spot center positioning method.

9. The laser spot center location test system of claim 6, wherein, The acquisition unit is one of the following: a CCD camera, a CMOS camera, a visible light acquisition unit, a low-illumination acquisition unit, a low-light acquisition unit, an infrared acquisition unit, and an ultraviolet acquisition unit.

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