Computationally efficient pseudo QMF filter bank for a multi-compatible HDTV codec

A review is presented of methods usable in a coding scheme to obtain compatible images (images with lower resolution) based on the discrete cosine transform (DCT), quadrature mirror filters (QMF), conjugate quadrature filters (CQF) and pseudo quadrature mirror filters (PQMF). Compared to QMF or CQF, PQMF gives better frequency selectivity for a much lower computational cost. The theory of PQMF is reviewed and new results are described, especially regarding computational cost, hardware implementation, and constraints on the length of the prototype filter used to generate the modulated filter bank. Both cases of NF even and NF odd, where NF is the prototype filter number of taps, are then checked, and optimal implementations using fast transforms (a classical DCT for NF odd and a type IV DCT for NF even) are explained for the encoder and the compatible decoders