Ridler and Calvard’s, Kittler and Illingworth’s and Otsu’s methods for image thresholding

There are close relationships between three popular approaches to image thresholding, namely Ridler and Calvard’s iterative-selection (IS) method, Kittler and Illingworth’s minimum-error-thresholding (MET) method and Otsu’s method. The relationships can be briefly described as: the IS method is an iterative version of Otsu’s method; Otsu’s method can be regarded as a special case of the MET method. The purpose of this correspondence is to provide a comprehensive clarification, some practical implications and further discussions of these relationships.