Three-level median filters for digital mammography

A class of non-linear filters, consisting of median filters in a three-level (tree-like) structure, is proposed for mammographie image processing which has more robust characteristics for noise suppression and image detail preservation than single median filters. The tree-structured filters combine the output of subfilters which are based on median operations with linear and curved windows so as to preserve a mammographic feature in one direction. Four variations of the three-level filter were applied to normal and abnormal mammographic images and the results were compared to a single median filter based on simulated noise criteria.