Abstract: It is a tricky problem for threshold techniques to decide an optical threshold automatically.An automatic threshold
selection method based on gray system theory is proposed in this paper to calculate the optical threshold without manual intervention.
By analyzing the degraded gray-level histogram，the samples（seed points） around medial of the peaks are obtained.
Then the novel method applies GM（1，1） model to predict the trend of the seed points.Finally，the intersection is calculated， which acts as the optimal threshold.15 images are segmented by the proposed method compared with traditional methods（i.e. Otsu，Kapur） and two improved methods in references[3] and [4].The segmentation results are evaluated by area error rate. The average error rate is 19.37% on a data set with diverse segment complexity.The results show that the proposed method
can segment objects from images effectively.