Skeleton is a kind of important geometric characteristic of image. How to fast acquire the non-distorted skeleton of image with different shape and size is the precondition for those applications such as shape analysis

characteristic extraction or pattern recognition. Morphologic thinning algorithms based on mathematical morphology are effective thinning approaches to obtaining skeletons of image

which use some pre-defined structure elements with definite shape to operate on the image

only some shifting and logical operations are needed. But the traditional sequential morphological thinning algorithm has the disadvantage that its convergence speed is too slow and using only one structure element to carry out the thinning in every interation may produce distorted skeletons. A new thinning algorithm named fast shape preserving morphological thinning algorithm is advanced in this paper. The algorithm uses four types of structure elements of different direction simultaneously to operate on the image with the hitting operation. The union set of the hitting result is taken as the foundation of whether the outer pixels are exfoliated

thus it can cause the image to converge to its skeleton in every direction fast and symmetrically. The test result of an image of Chinese characters with various fonts enunciates that this algorithm can obtain symmetrical

regular and non-distorted skeletons of the Chinese characters

and its convergent speed is four times more than the speed of sequental morphological thinning algorithm.