Two fast architectures for the direct 2-D discrete wavelet transform

In this paper, we propose two architectures for the direct two-dimensional (2-D) discrete wavelet transform (DWT), The first one is based on a modifie d recursive pyramid algorithm (MRPA) and performs a "nonstandard" decomposi tion (i.e., Mallet's tree) of an N x N image in approximately 2Na(2)/3 cloc k cycles (ccs), This result consistently speeds up other known architecture s that commonly need approximately Na ccs, Furthermore, the proposed archit ecture is simpler than others in terms of hardware complexity. Subsequently, we show how "symmetric"/"anti-symmetric" properties of linear -phase wavelet filter bases can be exploited in order to further reduce the VLSI area. This is used to design a second architecture that provides one processing unit for each level of decomposition (pipelined approach) and pe rforms a decomposition in approximately N-2/2 ccs, In many practical cases, even this architecture is simpler than general MRPA-based devices (having only one processing unit).