Abstract: In order to improve the proportion of target detection, a novel adaptive method of automatic threshold selection based on the method of Otsu thresholding is proposed. It takes the gray level statistics of the resultant target and background region as a criterion for discrimination if correct segmentation is obtained. Theoretical analysis shows that correct image segmentation can be obtained for a low contrast image with complex background using this method, no matter the proportion of the target is high or low. Moreover, the amount of computation and the processing time can be decreased greatly by setting a gray level selection threshold. Several experimental results are presented to support the validity of this method.