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Lightning Channel Image Recognition Based on Line Support Region
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摘要: 提出了一种基于线支持区域的闪电通道识别算法 (LLSR)，该算法首先应用对比度拉伸和高斯匹配滤波方法对闪电通道图像进行预处理，以增强闪电通道的对比度；然后自动检测出包含闪电通道的线支持区域，并用最小外接矩形包含这些区域；最后在各个矩形区域内分别使用最大类间方差Otsu阈值法进行分割，得到闪电通道识别结果。试验结果表明:LLSR具有良好的局部特性和自适应性，它不仅能自动提取低对比度闪电图像的通道，还能自动提取具有复杂背景闪电图像的通道，自动提取结果在视觉上与人眼观测结果一致。且定量评估结果表明:LLSR相比传统算法具有更好的分割精度。Abstract: Lightning channel coordinates in digital images are often manually extracted to analyze the development and morphology of lightning channels, but this method is not efficient and its result is often subjective. Therefore, more and more researchers start to investigate approaches to recognize lightning channel information automatically. In general, lightning channel images are complex and diverse because of low contrast, occlusion of clouds, and interference of other environmental factors, so most traditional lightning channel segmentation algorithms do not work well for such lightning images.A new lightning channel segmentation algorithm named LLSR is brought forward based on line support regions. First, Gauss matched filtering and contrast stretching method are applied to enhance the contrast of lightning channels, according to the gray distribution characteristics of cross section of lightning channels. Second, line support regions, which include lightning channels within a minimum enclosing rectangle, are extracted as foreground area by a line segment detection method. In addition, line support regions are expanded in both the main direction and its perpendicular direction. In general, a line support region contains a segment of a lightning channel. Furthermore, it has better contrast between lightning channel and background. Finally, Otsu thresholding method is applied in each line support region to extract lightning channels, because the gray level distribution of each line support region is bimodal. Therefore, lightning channels are segmented from complicated background.A dataset including various types of lightning channel images, are constructed and manually marked to evaluate the proposed algorithm LLSR. Compared with traditional algorithms, global thresholding method (GThres), local thresholding method (LThres), and Canny thresholding method (CThres), the proposed LLSR has higher precision for lightning channel segmentation, and it obtains a better balance between recall rate and false positive rate. Besides, experiment results show that traditional algorithms are not robust enough for all types of lightning images, but the new method demonstrates better generality. LLSR can recognize not only the lightning channels with low contrast but also the lightning channels with complicated background, and the segmentation result is visually consistent with human eyes.
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Key words:
- lightning image;
- channel identify;
- line support region;
- Otsu;
- thresholding algorithm
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图 1 图像预处理示例
(a) 闪电通道原图，(b) 对比度拉伸图像，(c) 高斯匹配滤波图像
Fig. 1 Example of image preprocessing results
(a) the original lightning channel image, (b) the image after contrast stretching, (c) the image after Gauss matched filtering
图 3 闪电通道线支持区域矩形扩展示例
(a) 扩展前，(b) 扩展后
Fig. 3 Examples of the rectangular expansion of lightning channel line support region
(a) before expansion, (b) after expansion
图 4 闪电通道图像中三个矩形区域及其对应的灰度直方图
(a) 闪电通道图像中3个区域示例, (b) 区域1的灰度直方图, (c) 区域2的灰度直方图, (d) 区域3的灰度直方图
Fig. 4 Three rectangular regions and their corresponding gray histogram
(a) example of three rectangular regions in lightning channel image, (b) gray histogram of region 1, (c) gray histogram of region 2, (d) gray histogram of region 3
图 5 闪电图像及其对应的人工标注图像示例
Fig. 5 Examples of lightning images and their corresponding manually marked images
表 1 不同σ取值对应的LLSR性能
Table 1 Performance of LLSR with different σ
σ Rrecall Ppre Fmeasure 0.7 0.5439 0.8182 0.6397 1.6 0.7347 0.7621 0.7352 2.3 0.7462 0.6655 0.6777 
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表 2 不同τ取值对应的性能表
Table 2 Performance of LLSR with different τ
τ/(°) Rrecall Ppre Fmeasure 14 0.6952 0.7635 0.7101 15 0.7042 0.7566 0.7116 18 0.7224 0.7390 0.7118 20 0.7290 0.7303 0.7106
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表 3 不同的算法性能表
Table 3 Performance for different algorithms
算法 Rrecall Ppre Fmeasure GThres 0.6252 0.6724 0.6227 LThres 0.8709 0.3090 0.4455 CThres 0.8834 0.2243 0.3534 LLSR 0.7224 0.7390 0.7118
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