Thermography autofocus applied in air leak location

Abstract

A thermography autofocus system based on stepping motor control is designed for air leak location. DFF (Depth From Focus) is adopted to realize the autofocus of thermography. Firstly, a focusing target is designed, and then the horizontal temperature distribution of its thermal image is operated by using energy gradient function as the evaluation function of edge detection, finally the hill climbing method is used to achieve the optimal focusing position. The theoretical analysis and experimental results show that the adopted control scheme and evaluation function can obtain a very good focusing effect and effectively overcome the virtuality of images caused by the position difference of the tested object.