Direct design of approximately linear phase (ALP) 2-D IIR digital filters

A fast design method is presented for approximately linear phase (ALP) 2-D IIR digital filters composed of a parallel connection of two allpass subfilters. The technique exploits the fact that the filter transform function depends on the phase of each subfilter. A closed form expression is derived for the phase and the filter coefficients of each subfilter are obtained by solving a set of overdetermined linear simultaneous equations.