On the oscillatory roots of one and two dimensional median type filters

In this paper we analyze the root structures of the standard median (SM) filters, the recursive median (RM) filters and of the new FIR Median Hybrid (FMH) filters which contain nonrecursive (FIR) substructures. It is shown that with infinite length signals the SM and the RM filters have many oscillatory binary roots. With finite signal lenght the roots of the SM and the RM filters may depend very much on the first and the last values of the sample sequence which are appended to the beginning and the end of the signal. In these situations the new FMH filters are shown to behave better than the SM and the RM filters. If the length of the filter is changed properly almost all the abnormal root structures can be avoided.