Design of linear phase, circularly symmetric two-dimensional recursive digital filters

A method is presented for the design of two-dimensional circularly symmetric recursive digital filters possessing linear-phase characteristics and approximately equiripple magnitude response. The filter format is octagonally symmetric and inherently stable. The denominator and the numerator of the transfer function are designed separately. The denominator is used to approximate the linear-phase specifications, while the numerator is used to approximate the overall magnitude characteristics. This method is suitable for both low-pass and bandpass filter design. The computation involved is simple and requires only a short computational time. The resultant filter format is also suitable for modular implementation