拐点不变量是局部不变量的一种，广泛应用于缺损目标识别。介绍了三种拐点提取方法，分割融合算法，Hough变换和广义拐点方法。它们具有旋转，平移，尺度不变形，利用它们对４类缺损目标图象进行识别，取得了较好的结果。

Corner feature is widely used in pattern recognition for it is invariant to scale, shift and rotation. This paper introduces three algorithms to extract corner feature, named splitting merging algorithm, the extended Hough transform algorithm and the extended corner algorithm. Among them the splitting merging algorithm is the easiest one to implement but is the most sensitive to noise. The extended Hough algorithm is much strong to noise and the last algorithm is much more suitable to describe the characteristics of practical contours. Result of computer simulation for recognizing four occluded objects by using these algorithms is given.