关键词: 指针式仪表, 读数识别, 帧差分, 质心提取

Abstract: For machine vision based calibration systems of pressure gauges with pointers, a scheme based on the frame difference method and the angle method is presented for automatic reading recognition of index instruments. A method that uses the extreme points in detected regions to determine the centroids of pointers is also proposed to solve the problem of centroid deviation for incompletely detected pointers. First, the center of the dial plate is determined and the region of the dial plate is segmented using Hough circle detection. Then the pointer region is detected using the three-frame-difference method. The pointer centroid is located by selecting the two points closest to the diagonal vertexes of the minimum rectangle enclosing the pointer region from the extreme points in eight directions. Finally, the deflection angle of the pointer is computed and the pointer reading is recognized via connecting the pointer centroid and the center of the dial plate. Experimental results reveal that the regional extreme points based pointer centroid location can simply and effectively correct the centroid deviation for incompletely detected pointers. The overall scheme can accurately recognize the readings of pressure gauges with pointers.

Key words: pointer instrument, reading recognition, frame difference, centroid extraction