Directional Zero-Phase 2D IIR Filter Design Using Chebyshev- Padé Approximation

In this paper we propose a design method for a class of 2D linear filters, namely directional zero-phase IIR filters. Such filters are useful in detecting lines with a given angular orientation in an image. The design is achieved in the frequency domain and starts from 1D digital filters with given specifications. A zero-phase 1D filter is derived, whose frequency response is real and approximates to a certain accuracy the magnitude of the initial 1D prototype, using a convenient change of variable and a Chebyshev- Padé rational approximation. As prototype filters, we use elliptic and inverse Chebyshev filters, which are very efficient. Design examples are presented and some simulation results on image processing are finally shown.