基于支持向量机的玉米根茬行图像分割

    Image segmentation of maize stubble row based on SVM

    • 摘要: 玉米根茬行的准确识别是实现玉麦轮作机器视觉式小麦自动对行免耕播种技术的前提。针对华北一年两熟区联合收获机玉米留茬收获后根茬行较难准确分割的问题,该研究以直立玉米根茬为研究对象,提出一种基于支持向量机(Support Vector Machine,SVM)的玉米根茬行分割方法。首先,利用主成分分析(Principal Components Analysis,PCA)对提取的目标(直立根茬)与背景(行间秸秆及裸露地表)的颜色和纹理特征进行分析,优选出21个特征,构成特征向量作为训练直立根茬SVM识别模型的输入;然后,根据图像坐标设置图像中间包含完整玉米根茬行的矩形区域为感兴趣区域(Region of Interest,ROI);最后,使用训练好的直立根茬SVM识别模型以25×25(像素)的窗口在ROI内滑动检测,采用阈值法分割根茬行并通过形态学处理优化得到最终的玉米根茬行二值图像。利用在农业农村部河北北部耕地保育农业科学观测实验站采集的100幅玉米根茬行图像进行试验,结果表明,本文方法对于不同行间秸秆覆盖量和不同光照条件下的根茬行分割表现出较好的准确性和鲁棒性,直立根茬平均识别准确率、平均分割准确率、平均召回率、平均分割准确率与平均召回率的加权调和平均值(F1avr值)分别为93.8%、93.72%、92.35%和93.03%,每幅图像的平均分割时间为0.06 s,具有较好的实时性。基于SVM的分割方法可实现联合收获机玉米留茬收获后根茬行图像的分割,为下一步检测玉米根茬行直线并将其作为导航基准线进行视觉导航的研究提供良好基础。

       

      Abstract: Abstract: Accurate identification of maize stubble row has widely dominated the automatic row-followed seeding using machine vision. However, it is difficult to segment the images of stubble row in the maize stubble field harvested by combine harvesters, due mainly to the indistinct chromaticity difference with naked land surface and maize residues. In this study, image segmentation was presented using a support vector machine (SVM), in order to realize precise and rapid segmentation of the maize stubble row. Firstly, principal component analysis (PCA) was used for dimensionality reduction and feature optimization of the dataset, where the specific features were selected to distinguish standing stubble, naked land surface, and maize residues. Especially, the 1 500 sample images of standing stubble, 1500 sample images of the naked land surface, and 1 500 sample images of maize residues were collected, while, 2 210 features containing 697 color features, and 1 513 texture features were obtained using sample images. Then, PCA was used to choose 21 color features of the standing stubble, naked land surface, and maize residues in the R, G, B, L, a, b, v, YIQ-V and YCbCr-Y components from the datasets. The selected color features were constructed into a 21-dimensional feature vector, which was used as the input of the standing stubble SVM recognition model. Secondly, the region of interest (ROI) was selected in the middle of the image with the integrated maize stubble row for the higher efficiency of image segmentation. Finally, the trained SVM recognition model was used for the slide detection of standing stubble within the ROI with a window of 25×25(pixel). If the currently detected window was standing stubble in slide detection, the grayscale value would be set to 255. The maize stubble row was segmented by a threshold when the slide detection was complete. The segmented binary image was then optimized using the morphological open operation processing with a disc-shaped structural element with a radius of 2 pixels. Furthermore, 100 test images were collected to verify the segmentation performance from the Scientific Observing and Experimental Station of Arable Land Conservation (North Hebei), Ministry of Agriculture and Rural Affairs in Zhuozhou City, China in October 2019. The capture size was divided into 4 classes, including 0, 1, 2, and 3 kg/m2, according to the quality of maize residues between rows. At the same time, each class included the front lighting on a sunny day, direct sunlight, backlight on a sunny and cloudy day. Moreover, the images of the 0 kg/m2 class also involved different shapes and surface moisture contents, due to the change of time and weather. The results revealed that the algorithm presented higher accuracy and robustness for the stubble row segmentation under various maize residues quality between rows and different lighting conditions. The average recognition accuracy of standing stubble was 93.8% in the SVM recognition model, whereas, those were 62.76% and 63.71% in the BPNN and ELM model, respectively. The average segmentation accuracy, average recall rate, and F1avr in the SVM recognition model were 93.72%,92.35% and 93.03%, respectively, whereas, those in the BPNN, ELM and genetic models were 61.88%, 86.94%, 72.3%, 62.92%, 88.75%, 73.63%, 90.13%, 51.36% and 65.43%, respectively. Additionally, the average processing time was 0.06 s for a 640×480(pixel) image using the SVM recognition models, indicating excellent real-time performance. Therefore, the SVM recognition model can widely be expected to realize better performance than others in the segmentation of the maize stubble row after the maize is harvested by the combine harvesters.

       

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