A new algorithm for two-dimensional object inspection using string matching

In this paper, a string matching scheme is proposed to inspect two-dimensional objects for dimensional and shape verification in industrial environment. This approach consists of two stages. First, the procedures of determining the invariant starting point for boundary tracing and locating the cornerpoints of a curved object for polygon approximation are derived. To speed up the process, an optimization-based unconstrained line search method is used to locate the cornerpoints of the polygon image of a curved object. These cornerpoints are then recorded as feature string. At last, the feature string for each tested object are utilized to find the exact correspondence to one of several model objects. In contrast to conventional matching methods, which requires translation and rotation of the tested image before matching, the proposed method proves to be computationally efficient for real-time applications.