基于顶点与主体区域同步检测的精准车牌定位  

Accurate license plate location based on synchronous vertex and body region detection

作　　者：徐光柱[1,2] 刘高飞 匡婉 万秋波 马国亮 雷帮军[1,2] XU Guangzhu;LIU Gaofei;KUANG Wan;WAN Qiubo;MA Guoliang;LEI Bangjun(Hubei Key Laboratory of Intelligent Vision Monitoring for Hydropower Engineering(China Three Gorges University),Yichang 443002,China;College of Computer and Information Technology,China Three Gorges University,Yichang 443002,China;Traffic Police Detachment,Public Security Bureau of Yichang City,Yichang 443002,China)

机构地区：[1]湖北省水电工程智能视觉监测重点实验室(三峡大学),宜昌443002 [2]三峡大学计算机与信息学院,宜昌443002 [3]宜昌市公安局交通警察支队,宜昌443002

出　　处：《北京航空航天大学学报》2024年第2期376-387,共12页Journal of Beijing University of Aeronautics and Astronautics

基　　金：湖北省中央引导地方科技发展专项(2019ZYYD007);湖北省水电工程智能视觉监测重点实验室开放基金(2022SDSJ03)。

摘　　要：为应对非约束环境下的车牌精定位问题,提出一种基于顶点局部区域与主体区域同步检测策略的非约束性车牌定位算法。通过删减YOLOv5网络的输出结构,训练得到可同步检测车牌及顶点区域的车牌检测网络,在兼顾精度与计算速度的前提下,实现车牌顶点和主体区域的同步定位。针对一幅图中存在多个车牌区域及顶点区域存在少量漏检和误检的情况,分别设计了车牌顶点归类和单一缺失顶点预测后处理算法,借助顶点间的空间位置关系进行漏检目标预测和误检目标排查,有效改善了因场景复杂导致的个别顶点目标检测效果差的问题。所提算法在中国城市停车场数据集(CCPD)上的测试结果显示,平均精准率达99.25%,平均召回率达98.70%。所提算法不仅能够准确预测出车牌的4个顶点坐标,而且在中端GPU硬件平台上处理速度可达121帧/s,具有较好的应用价值。A novel unconstrained license plate accurate location algorithm is designed by simultaneously detecting the four local vertex regions and the body of a license plate and fusing the results to address the issue that the widely used rectangular bounding boxes in mainstream target detection methods cannot meet the license plate location accuracy requirement in many unconstrained environments where the license plate images are not commonly rectangle.At first,the four local rectangular sub-regions with centers on four vertices of a license plate were annotated as vertex-region objects according to the size of the plate’s contour-rectangle and the vertex coordinates.Then,a multi-class image dataset is built up in which the contour-rectangle region covering the whole license plate body is a class and the four kinds of vertex-region construct other four classes.In order to locate these five object classes efficiently,the output structure of the YOLOv5 network is modified by taking accuracy and efficiency into consideration and trained with the newly constructed multi-class dataset.Finally,vertex region grouping and single missing vertex forecasting are carried out as the post-processing to address the issue that there are multiple candidate license plates in an image and a few vertices region false or missing detection errors will happen in some unique instances.By exploiting the relationship among the vertexes,the post-processing can effectively recognize missing and false detection errors in some special complex scenarios and improve the whole system’s performance greatly.The proposed algorithm is evaluated on the Chinese city parking dataset(CCPD),and reaches an average positioning accuracy of 99.25%and an average recall rate of 98.70%.The performance certificates our method not only can accurately predict the coordinates of the four vertices but also can run at 121 frame/s on a moderate GPU hardware platform,which has great application potential.

关 键 词：深度学习 卷积网络 视觉目标检测 非约束车牌定位 车牌顶点检测 

分 类 号：TP391[自动化与计算机技术—计算机应用技术]