一种指示表表盘中心高精度定位方法

A high precision method for locating dial center of pointer meter

指示表表盘中心定位是智能读数识别的关键和前提,传统基于区域的视觉检测方法精度和可靠性欠佳.本文基于指示表结构特征并从形状识别角度出发,提出一种指示表表盘中心高精度定位方法.利用差影法从两幅指示表图像提取指针目标,使用傅里叶-极坐标变换估计指针方向;再沿指针方向进行两次灰度方向投影获得指针中心线在纵轴上的截距参数;从而根据指针中心线对应的直线方程确定出表盘中心坐标.本文方法检测过程无需进行阈值分割、细化等预处理操作,获得的表盘中心实质上相当于指针回转中心。因而方法简单科学、结果准确可靠,能够为其他定位方法的精度评价提供近似基准数值,也可为机器视觉智能读数识别提供可靠的技术支持.

The positioning of the dial center of pointer meter is the key and prerequisite for intelligent meter reading recognition.The traditional region-based visual detection methods have such shorcomings as poor accuracy and reliability.Based on the structure features of pointer meters and the principles of shape recognition,this paper proposes a high-precision method for locating the dial center.First,the pointer target is extracted from two frames of meter images with the background difference method,and the pointer direction is estimated by the Fourier-polar transform.Then,the intercept parameters of pointer centerlines on the vertical axis are obtained by two times of gray directional projections along the pointer's directions.Thus the dial center coordinates are determined from the equations of the pointer centerlines.The detecting process of the proposed method does not require image preprocessing operations such as threshold segmentation and thinning,and the dial center detected by this method is essentially equivalent to the rotating center of the pointer.Therefore,this method is simple and scientific,and the results are accurate and reliable.The proposed method can provide not only an approximate standard value for the accuracy evaluation of other locating methods but also reliable technical support for the intelligent reading recognition with machine vision.