Comments on "Subband coding of images using asymmetrical filterbanks

In the above paper Egger and Li (see ibid., vol.4, p.478-85, Apr. 1995) presented a set of two-channel filterbanks, asymmetrical filterbanks (AFB's), for image coding applications. The basic properties of these filters are linear-phase, perfect reconstruction, asymmetric lengths for dual filters, and maximum regularity. In this correspondence, we point out that the proposed AFB's are not new in the sense that the proposed construction is equivalent to the factorization of Lagrange halfband filters, which has been reported by other researchers. In addition, we correct an error in the formulation of constructing AFBs in their paper.