The many benefits of putting stack filters into disjunctive or conjunctive normal form

Stack filters are nonlinear filters used for image processing (examples: median filters, order statistics). In the translation-invariant case a stack filter is determined by a positive Boolean function b. Many important properties of stack filters (idempotency, co-idempotency, order relations) can be tested in polynomial time if the DNF and/or CNF of b are known.