A unified projection method for fast search of vector quantization

Vector quantization (VQ) is a famous asymmetric signal compression method. In VQ, the search process to find the winner for an input vector is extremely time consuming due to a lot of k-dimensional Euclidean distance computations. This property of VQ constrains its practical applications to some extent. In order to speed up the search process of VQ, a unified projection method is proposed in this letter to reject a candidate code vector by a lighter computational burden. This method is universal because it can unify several types of previous works through suitably selecting a projection axis. Furthermore, two criteria for how to select an optimal projection axis for a code vector are proven mathematically, which are most important because they demonstrate the direction for a potential improvement to the search efficiency of VQ. Experimental results of VQ encoding show that the proposed method is very search effective.