A lapped transform progressive image coder
Several block-transform-based embedded image coders have been proposed recently in literature. The innovation here is to replace the wavelet transform in the EZW or SPIHT progressive image coding framework by popular block transforms such as the DCT or lapped transforms which can offer finer frequency spectrum partitioning and better energy compaction. However, most of the block transform coders above have not been able to compete with the wavelet-based ones on a consistent basis. In this paper, we present a fully progressive coding scheme based on appropriately-designed generalized lapped orthogonal/biorthogonal transforms (GenLOT or GLBT) coupled with several levels of wavelet decomposition of the DC band if needed. The uniform band block transform can be implemented in parallel fashion with fast, robust, and efficient lattice structures. Keying only on the transform stage, we are able to obtain the highest performance embedded coder up to date. This result shows that lapped transforms, when carefully designed, are capable of providing superior reconstructed image quality compared to wavelets, both objectively and subjectively.