Signal-adapted multiresolution transform for image-coding

Wavelet-type multiresolution transforms have recently been introduced in digital image coding, and have been shown to offer some advantages over classical block transform techniques such as the discrete cosine transform (DCT). This correspondence is mainly concerned with the problem of designing suitable multiresolution transforms that are adapted to the given image signal, in the sense that they maximize the coding gain at each resolution level. A simple alternating optimization algorithm is derived for solving this problem in the framework of the lattice realization of para-unitary quadrature mirror filters (QMF). The resulting image coding scheme is discussed in some detail, and its performance is compared with the DCT (JPEG) technique and with some non-adapted multiresolution transforms.