A modified valley-emphasis method for automatic thresholding

Otsu method is a commonly used technique for image thresholding selection, which can provide satisfactory results for thresholding an image with a histogram of clear bimodal distribution. This method, however, fails if the histogram is unimodal or close to unimodal. Ng (Ng, H.F., 2006. Automatic thresholding for defect detection. Pattern Recognition Lett. 27 1644–1649) proposed a modified method, called as valley-emphasis method, which weighs the objective function of the Otsu method with the valley point of the histogram for defect detection. In this paper, a revised valley-emphasis thresholding method is presented using the neighborhood information of the valley point. Experiment results show that the proposed method has the proper segmentation results in defect detection and provides better segmentation results than that of valley-emphasis method and Otsu method.

► A novel thresholding method is proposed based on the valley-emphasis method.
► The new method weighs the objective function of the Otsu method with the neighborhood gray level of the threshold.
► The threshold of the presented method has small probabilities in its neighborhood area in the gray-level histogram.
► The proposed method has better segmentation results in some cases than that of valley-emphasis method and Otsu method.