Method for extracting froth velocity of coal slime flotation based on image feature matching
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摘要: 煤泥浮选泡沫图像局部静态特征相似,一些较为复杂的工况判断需要用到浮选泡沫图像的动态特征,而现有的针对煤泥浮选泡沫速度动态特征的提取方法存在准确性、实时性和稳定性不足问题。针对上述问题,提出了一种基于图像特征匹配的煤泥浮选泡沫速度特征提取方法。首先,采用限制对比度自适应直方图均衡化(CLAHE)和三维块匹配滤波(BM3D)对浮选泡沫图像进行预处理,以提高图像质量,突出图像的边缘细节特征。其次,采用加速KAZE(AKAZE)算法对浮选泡沫特征进行特征点检测。然后,在利用暴力匹配(BF)对泡沫图像特征进行粗匹配的基础上,采用基于网格的运动统计(GMS)算法快速可靠地区分正确与错误的特征匹配。最后,根据特征匹配结果计算煤泥浮选泡沫速度,并以此为测量值,利用卡尔曼运动估计方法对得到的测量值进行迭代修正,得到更稳定的煤泥浮选泡沫速度特征。实验结果表明:① AKAZE−GMS算法较好地解决特征点簇集的同时又尽量保留了更多数量的特征点,这是因为预处理后图像受噪声影响降低、对比度增强、边缘特征更突出。② 与SIFT(尺度不变特征转换)、SURF(加速稳健特征)、AKAZE算法相比,AKAZE−GMS算法匹配对分布更为均匀,保留了更多正确的匹配对,匹配精度达99.99%,且运行时间仅需3.73 s。③ 直接经过特征匹配结果计算得到的泡沫速度测量值波动幅度较大,测量值经过卡尔曼运动估计修正后的速度估计值较为平稳,更符合真实工况。Abstract: The local static characteristics of coal slime flotation foam image are similar. The dynamic characteristics of flotation foam image are needed for judging some complex working conditions. The existing extraction method for the dynamic features of the froth velocity of coal slime flotation has the problems of insufficient accuracy, real-time performance and stability. In order to solve the above problems, a feature extraction method of froth velocity in coal slime flotation based on image feature matching is proposed. Firstly, the contrast limited adaptive histogram equalization (CLAHE) and block-matching and 3D filtering(BM3D) are used to preprocess the flotation froth image to improve the quality of the image and highlight the edge details of the image. Secondly, the accelerated-KAZE (AKAZE) algorithm of accelerated features in nonlinear scale space is used to detect the feature points of flotation froth features. Thirdly, on the basis of rough matching of froth image features by brute-force matching (BF), a grid-based motion statistics (GMS) algorithm is used to quickly and reliably distinguish correct and wrong feature matching. Finally, the method calculates the slime foam velocity according to the feature matching results. The foam velocity is taken as the measured value. The Kalman motion estimation method is used to iteratively modify the measured values to obtain more stable foam velocity characteristics of coal slime flotation. The experimental results show the following points. ① The AKAZE-GMS algorithm can solve the problem of feature point clustering well and keep more feature points as much as possible. This is because the preprocessed image is less affected by noise, has better contrast, and has more prominent edge features. ② Compared with SIFT (scale-invariant feature transform), SURF (speeded up robust features) and AKAZE, the AKAZE-GMS algorithm has a more uniform distribution of matching pairs, retains more correct matching pairs. The method achieves a matching accuracy of 99.99%. The running time is only 3.73 s. ③ The measured value of froth velocity directly calculated from the feature matching results fluctuates greatly. The velocity estimated value of the measured value corrected by Kalman motion estimation is more stable, which is more consistent with the real working condition.
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表 1 匹配精度及运行时间
Table 1. Matching accuracy and running time
算法 总匹配对 正确匹配对 正确率/% 时间/s SIFT 556 540 97.12 15.74 SURF 308 301 97.73 12.84 AKAZE 736 732 99.46 9.76 AKAZE−GMS 2585 2584 99.99 3.73 表 2 不同算法提取速度特征统计分析
Table 2. Statistical analysis of speed features extracted by different algorithms
像素/s 算法 测量值 卡尔曼运动估计
修正后测量值速度均值 标准差 速度均值 标准差 SIFT 9.356 5 7.314 7 12.419 2 5.153 3 SURF 12.309 8 7.602 8 12.311 6 1.408 7 AKAZE 12.752 5 7.008 0 12.318 7 1.383 0 AKAZE−GMS 10.974 2 5.045 6 11.181 3 1.188 2 -
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