Neutral beam infrared image distortion correction based on vanishing point detection
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摘要: 传统的霍夫变换、Cannylines直线检测算法、霍夫概率变换方法在图像上的直线检测效果不佳,存在检测线段不连续不正确的问题,因而,利用Sobel滤波对红外图像横轴和纵轴两个方向分别进行锐化,通过线段检测(LSD)算法实现线段特征检测,进而经线段聚类拟合获得图像中完整的直线,通过对直线交点计算获得消失点,最后依据透视关系计算得到校正图像。实验结果表明,该方法可以实现对中性束红外图像的自动有效校正。Abstract: The key parameters of the neutral beam, such as beam uniformity and beam divergence angle, can be obtained by analyzing the infrared images generated by the beam bombarding the target surface. Due to the camera setup angle, the IR images show geometric distortion, which affects the accurate analysis of the beam parameters. Therefore, so the images should be corrected for the distortion. The traditional Hough transform, canny lines algorithm, and probabilistic Hough transform methods are not effective in detecting straight lines on this image, and there is a problem of detecting discontinuous and incorrect line segments. In this paper, Sobel filter is used to sharpen the infrared image in the horizontal and vertical directions respectively and line segment feature is detected by line segment detector (LSD) algorithm. Then complete straight lines are obtained in the image by clustering and fitting the line segments according to the geometric and angular relationships between them. Vanishing points is calculated by the intersection points of the lines. Finally, the corrected image is obtained based on the perspective relationship. Experiment results prove that this method can achieve automatic and effective correction of neutral beam infrared images and it lays a basis for obtaining key parameters of the beam.
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表 1 线段聚类算法
Table 1. Line segment clustering algorithm
algorithm line segment clustering algorithm based on line segment relation input the sample set D = {L1,L2,…,Lm}, L means coordinate values of two endpoints of a line segment output coordinates of vanishing points 1: R = $ \varnothing $ 2: for i = 1,2,…,m do 3 C=$ \varnothing $ 4: for j = 1,2….,m do 5: calculate $ h $ between Li and Lj 6: calculate $ \Delta \theta $ between Li and Lj 7: if $ h $<threshold and $ \Delta \theta $<threshold then 8: C=C $ \cup $ Lj 9: remove Lj from D 10: R=R $ \cup $ C 11: remove Li from D 12: take the two sets from R with the largest number of line segments. 13: use the least square method to fit the two lines in Step 12. 14: calculate the intersection of two lines. That is the vanishing point. 表 2 直线检测方法比较
Table 2. Comparison of linear detection methods
the degree
of
continuousthe number of
lines detected
in x-directionthe effective number
of lines detected
in x-directionthe number of
lines detected
in y-directionthe effective number
of lines detected
in y-directionrun
time/sHough transform 1 3 3 0 0 0.021 probabilistic Hough transform 0 105 98 11 0 0.014 Cannylines 0 53 44 31 24 3.08 our algorithm 1 5 5 5 5 4.61 -
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