The inspection of a sputum smear through the microscope is an important means to diagnosis of cytology. In other words, this implies that the smear examination is the key to quality control in medicine. Since a microscopic image possessed with a complicated background has poor contrast and the object pixels consist of a small part of the whole image, it is more difficult for us to separate the object from the random background. In this paper, we propose a method for contrast stretching and linear structure enhancement based on local statistical features. We use gray level value of edge-direction instead of the gray mean value of local region. Theoretical and experimental results indicate that this method is more efficient than the method suggested by Lee both in the aspects of rejecting the random noise and enhancing the contrast.