Proc. SPIE. 10846, Optical Sensing and Imaging Technologies and Applications
KEYWORDS: Image fusion, 3D image reconstruction, Image processing, High power lasers, Diagnostics, High dynamic range imaging, Laser cutting, Charge-coupled devices, System integration, Laser systems engineering
The schlieren method was the most common method for measuring the far-field focal spot in high power laser facility. The reconstruction of far-field focal spot was used by manual and autocorrelation matching method usually. Although the problem of the automatic reconstruction of focal spot was solved by the autocorrelation matching method, it searched the best matching point in the whole region of the mainlobe cutting image, which would greatly reduce the efficiency of the reconstruction of far-field focal spot. To solve this problem, a fast method for searching the best matching point based on steepest descent method was proposed in this paper. Firstly, the mainlobe image and sidelobe image were cut into the mainlobe cutting image and sidelobe cutting image, which were named as cutzb and cutpb respectively, and the size of cutting images was 300*300.Then a new image that a circle the same size as the schlieren ball was dug from cutzb image was named as cutzb', while cutzb' and cutpb were converted into two column vectors respectively, and the SAM values of the two vectors are calculated. Secondly, calculated the gradients of 8 neighborhoods of current pixel, the next searching position was the neighborhood located in the direction of the largest gradient (the largest decrease) of 8 neighborhoods while using the steepest descent method. After all the SAM values of the two vectors that met requirement were searched. The upper left corner of mainlobe cutting image was the best matching point when the SAM value was minimal. Finally, according to the best matching point, the far-field focal spot was merged by the mainlobe image and sidelobe image, and the weighted average method was applied to fuse the stitching area of the merged image. The experimental results show that the method can not only realize the automatic reconstruction of the measurement of far-field focal spot while using the schlieren method, but also greatly improve the efficiency of the reconstruction of the far-field focal spot, and realize the accurate measurement of the far-field focal spot in the high dynamic range.
In order to realize the effective detection of surface structure targets in hyperspectral images, an improved target detection algorithm was proposed in this paper presents to solve the CEM algorithm problems which the large object extraction efficiency is low .First, the image was preprocessed, including end-member extraction, SAM classification. Second, after the ship pixels were subtracted from all pixels, the correlation matrix of pure background pixels was constructed to detect ship target. Third, the biggest write region was found as sea region by mathematical morphology. Finally, the false target pixels were removed from all target pixels using the characteristics which ship targets were surrounded in seawater, so the final ship targets were selected in the end. Experimental results show that the final max ratio between the energy of detection target and the energy of background increased greatly, the target signal is enhanced and the background signal is suppressed by the improved algorithm.
In order to obtain the far-field distribution of high dynamic range laser focal spot, the mathematical model of schlieren method to measure the far-field focal spot was proposed, and the traditional schlieren reconstructed algorithm was optimized in many aspects in this paper. First of all, the mathematical model which used to measure the far-field focal spot was created, the amplificatory coefficient <i>K</i> of the main lobe intensity and amplificatory coefficient <i>b</i> of the laser spot area were selected ; Secondly, the two important parameters were calibrated and the accurate main lobe spot and side lobe spot were captured by the integrated diagnostic beam fast automatic alignment system; Finally, the schlieren reconstructed algorithm was optimized by circle fitting method to calculate side lobe image center and weighted average method to fuse the joint image edge, and the error of traditional schlieren reconstruction method for side lobe center was reduced and the obvious joint mark of reconstructed image was eliminated completely. The method had been applied in a certain laser driver parameter measurement integrated diagnostic system to measure far-field laser focal spot. The experimental results show that the method can measure the far-field distribution of high dynamic range laser focal spot exactly on the condition that the parameter of mathematical model is calibrated accurately and the reconstructed algorithm of schlieren measure is optimized excellently.
In order to obtain the exact center of an asymmetrical and semicircular aperture laser spot, a method for laser spot detection method based on circle fitting was proposed in this paper, threshold of laser spot image was segmented by the method of gray morphology algorithm, rough edge of laser spot was detected in both vertical and horizontal direction, short arcs and isolated edge points were deleted by contour growing, the best circle contour was obtained by iterative fitting and the final standard round was fitted in the end. The experimental results show that the precision of the method is obviously better than the gravity model method being used in the traditional large laser automatic alignment system. The accuracy of the method to achieve asymmetrical and semicircular laser spot center meets the requirements of the system.