摘要
车牌倾斜校正是车牌识别系统中的一关键技术,校正效果将直接影响到后续字符分割和识别的效果.为此,提出了一种快速有效的混合倾斜车牌校正方法.水平倾斜校正时,先进行Sobel垂直边缘检测算子提取字符的有效数据点,构造有效数据点矩阵,然后进行矩阵奇异值分解,利用特征向量矩阵导出车牌水平倾斜角度的表达式;垂直倾斜校正时,首先通过Sobel垂直和水平边缘检测有效去除边框及上下左右噪声干扰区域,然后通过形态学腐蚀提取有效反映字符水平错位的有效数据点,其次将这些有效数据点水平投影分成七个字符区域,求取每个区域错切变换后的最佳列坐标质心对应其区域垂直倾斜角,最后取区域垂直倾斜角的均值作为车牌的最佳垂直倾斜角.对大量复杂背景下的倾斜车牌进行实验,并做了精确度、运行时间、抗干扰性分析,实验结果表明:提出的混合倾斜校正方法精确度高、运行时间短、抗干扰性强.
Slant Correction of vehicle License plate is a key technology in vehicle license recognition system, because effectiveness of Slant Correction ultimately have a direct bearing on result of Segmentation and Recognition of Character in subsequent part. Consequently, this paper puts forward a fast and effective correction algorithm of mixed slant vehicle License plate. Horizontal Tilt Correction： firstly, extract effective data points of characters based on the method of Sobel edge detection and build effective data point matrix, then make a SVD of matrix. Simultaneously through the feature vector matrix, a expression of horizontal tilt angle will be deduced; Vertical Tilt Correction： firstly, effectively remove License plate frame and the up and down or so noise interference area by the way of vertical and horizontal edge detection of Sobel. Afterwards, by means of morphological corrosion do extract effective data points of characters, which can effectively reflect horizontal dislocation of characters. Secondly, these effective data points should be divided into seven area of characters in this way of horizontal projection of effective data points, and then each area should be made a shear transform, meanwhile, which will make sure that the optimal centroid of column coordinates of each area corresponds to vertical tilt angle of the area. At l^t, take the mean of vertical tilt angle of all area for the optimal vertical tilt angle ＇of vehicle license plate. In this paper, experiment for large complex background tilt vehicle license plate had been made. In addition, through the accuracy, operation time and anti-jamming analysis of the e^xperimental results, a conclusion ultimately have been drawn that the proposed hybrid tilt correction methods is of high precision, short runtime and excellent robustness.
出处
《数学的实践与认识》
CSCD
北大核心
2012年第19期87-95,共9页
Mathematics in Practice and Theory
基金
中国博士后科学基金(20100481307)
山西省自然科学研究基金(200901 1018-3)
关键词
SOBEL边缘检测
字符有效数据点
矩阵SVD分解
形态学腐蚀
列坐标质心
sobel edge detection
effective data points of characters
svd of matrix
morphological corrosion
centroid of column coordinates
