Nonlinear filtering without aliasing errors

A scheme based on a combination of linear and nonlinear filters ensuring high detail-preservation, with no blurring and without giving rise to aliasing artifacts, is described. Nonlinear detail-preserving filters are combined with linear filters using a special frequency detector to switch the operation to a particular filter depending on the local signal content. In signal areas with rapidly varying high-frequency content, the linear filter is switched on to avoid aliasing distortions. In fast-changing signal areas, the nonlinear filter is switched on to avoid blurring edges. The high frequency signal components which may give rise to aliasing errors are effectively removed while edges and details remain intact. Results of tests on real and simulated images indicate that the new scheme unifies the best features of linear and nonlinear filters