COMPLEX, LINEAR-PHASE FILTERS FOR EFFICIENT IMAGE-CODING

With the exception of the Haar basis, real-valued orthogonal wavelet filter banks with compact support lack symmetry and therefore do not possess linear phase, This has led to the use of biorthogonal filters for coding of images and other multidimensional data, There are, however, complex solutions permitting the construction of compactly supported, orthogonal linear phase QMF filter banks, By explicitly seeking solutions in which the imaginary part of the filter coefficients is small enough to be approximated to zero, real symmetric filters can be obtained that achieve excellent compression performance.