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Two-dimensional recursive filters are useful only if stable, that is, if their outputs remain bounded for bounded inputs. The stability of a recursive filter depends on the phase spectrum of its denominator array. A two-dimensional generalization of the discrete Hilbert transform leads to a scheme producing stability with nominal distortions of the filter's desired amplitude spectrum. The method is therefore an attractive alternate to a least-squares procedure recently described by Shanks et al.
Date of Publication: July 1973