Precise perimeter measurement for planar object

A novel measurement scheme for an object’s surface boundary perimeter is proposed. This scheme consists of four steps. Firstly, a photoelectric image measurement system is devised to obtain a target image of a detected object. Secondly, a multi-scale active contour is applied in the defocusing and focusing image sequence to converge to the target’s contour edge. Thirdly, a novel centroid-self-calibration technology is applied, which measures the pixel’s size equivalence with a dual-frequency laser. Finally, for the convergent active contour, its true contour length is computed as the detected object’s true perimeter. An experiment on a circular aperture’s perimeter measurement indicates that this scheme’s measurement repetition error decreases to 0.40%.