Enhanced fast encoding method for vector quantization by finding an optimally-ordered Walsh transform kernel

In a framework of vector quantization (VQ), the encoding speed is a key issue for its practical applications. To speed up the VQ encoding process, Walsh transform is introduced in the previous work to map vectors in a k-dimensional (k-D) spatial domain into k-D Walsh domain in order to exploit the energy-compaction property of an orthogonal transform. However, there still exist a serious problem in that previous work because it just simply used the most common sequency-ordered Walsh transform kernel, which is actually not very high efficient for fast VQ encoding. In order to solve the kernel order problem in VQ encoding this paper proposes an optimal order for Walsh transform kernel based on the energy distribution of a particular codebook at each dimension in a k-D Walsh domain, which requires that the dimension with a larger energy distribution be put forward to be as a lower dimension. Experimental results confirmed that the proposed method could reduce the computational cost to 85.9% ∼ 53.1% compared to the previous work so as to enhance its performance obviously.