Modified M-band synthesis filter bank for fractional scalability of images

Subband image coding with classical wavelet transforms inherently provides dyadic scalability since the low-pass approximation band can be used as a half-sized version of the original image. The multiresolution approach further provides scalability factors that are powers of two, but no other factors can be easily reached. On the other hand, a hierarchical scheme based on M-bandtransforms will lead only to scalability factors that are powers of M. In this letter, we present how an M-band synthesis filter bank can be modified in order to directly reconstruct an output image of a resolution reduced by a factor M/P, where P is an integer lower than M. As the analysis filter bank is not modified, this technique allows the design of subband decoding schemes that support fractional scalability. With this feature, the same compressed bitstream can be directly decoded by different receivers at several resolutions, depending on their computational and bandwith capabilities.