利用改进Faster-RCNN识别小麦条锈病和黄矮病

    Recognizing stripe rust and yellow dwarf of wheat using improved Faster-RCNN

    • 摘要: 条锈病和黄矮病是严重威胁小麦生产的重大病害,病害的早期识别对病害防控具有重要意义。现有病害识别模型对相似表型症状识别困难,对早期病害的识别准确度低。为此,该研究构建了一种改进的快速区域卷积神经网络(Faster Regions with CNN Features,Faster-RCNN)的病害识别方法。该方法采用卷积核拆解和下采样延迟策略优化了深度残差网络(Deep Residual Neural Network,ResNet-50),用优化后的ResNet-50作为主干特征提取网络以增强所提取特征的表达力,同时简化模型的参数;并采用ROI (Region of Interest)Align改进ROI迟化层以降低特征量化误差,提升识别的精度。在自建的涵盖200余种不同发病时期、不同抗感性的小麦叶部图像数据集上进行试验,结果表明:改进的Faster-RCNN识别方法比其他SSD (Single Shot Multi-Box Detector)、YOLO(You Only Look Once)和Faster-RCNN网络模型的平均精度均值(mean Average Precision,mAP)分别提升了9.26个百分点、7.64个百分点和14.97个百分点。对小麦条锈病、黄矮病、健康小麦和其他黄化症状小麦识别的平均精度均值可达98.74%;对小麦条锈病和黄矮病轻、重症识别的平均精度均值可达91.06%。同时,模型损失函数值降低更快,整体性能表现更优。进一步开发小麦病害智能识别系统部署研究模型,使用微信小程序进行田间小麦病害的识别。在最大并发100的条件下,小程序平均返回时延为5.02 s,识别返回成功率为97.85%,对两种小麦病害及其细分轻重症识别的平均准确率为93.56%,能够有效满足实际应用需求,可用于指导病害的科学防控。

       

      Abstract: Wheat stripe rust and wheat yellow dwarf have posed a great threat to the yield and quality of wheat. An accurate identification has important implications for the prevention and control of wheat diseases. However, the phenotypic symptoms are similar to the infected leaves of wheat stripe rust and wheat yellow dwarf. Particularly, drought, nutrient deficiency, and bacterial disease can lead to the chlorosis and yellowing of plant leaves. In addition, the infected leaves are also similar to the healthy ones, due to the indistinct phenotypic symptoms in the early stage of diseases. It is difficult to quickly and accurately distinguish them by the existing identification. In this study, an improved Faster Regions with CNN Features (Faster-RCNN) was proposed for disease identification. There were two improvement strategies. Firstly, three 3×3 grouping convolution and down-sampling delays were employed to optimize the Deep Residual Neural Network (ResNet-50), which was designed as the backbone feature extraction network, in order to enhance the fine feature extraction of the entire network. Secondly, the region of interest (ROI) alignment was employed to reduce the feature error caused by double quantization, instead of ROI pooling. As such, the subtle differences were recognized after alignment. Transfer learning was selected to improve the training speed of the model. The data augmentation was then utilized to reduce the over-fitting, in order to further enhance the recognition performance and generalization ability. The image data set of disease leaf was collected from more than 200 wheat varieties with different resistance and susceptibility to the diseases, covering various symptoms at different disease stages. A series of experiments were carried out to evaluate the improved strategy. The performance indicators were selected to verify the model, such as loss function convergence curve and mean average precision (mAP). The experimental results showed that the mAP of the improved Faster-RCNN reached 98.74% for the wheat stripe rust and wheat yellow dwarf. Moreover, the early identification of disease infection was strengthened to predict the diseases as early as possible. The dataset contained 683 and 630 mild symptom images of these two diseases, respectively. The mAP reached 91.06% for the mild and severe symptom identification of two diseases. A comparison was made on the mainstream deep learning models, such as the SSD, YOLO, and RCNN series, under the same experimental conditions. Specifically, there were 9.26, 7.64, and 16.57 percentage points higher than the SSD, YOLO, and RCNN, respectively. Meanwhile, the loss function decreased significantly, while the model performed better than before. Finally, the intelligent recognition system was developed for wheat disease. Consequently, the average return delay was 5.024s under the maximum concurrent access of 100, and the success rate of recognition reached 97.85%. Anyway, the improved system can rapidly and accurately recognize wheat diseases via a WeChat applet. The finding can also greatly contribute to the control of wheat diseases.

       

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