Parallel structures for rank order and stack filters

Rank order filters are nonlinear filters which choose an output based on the rank within a window of sample inputs determined by sorting the inputs. Rank order filters are a subset of the class of stack filters which are also nonlinear. A systematic method for applying block processing, which transforms single-input single-output structures to parallel-input parallel-output structures for non-recursive rank order and stack filters is presented. This method takes advantage of shared substructures within the block structure to efficiently generate a block filter whose complexity can be up to one-half the size of the original filter structure times the block size. This method can also be applied to two-dimensional non-recursive rank order filters