一种新颖的基于哈德码变换的码字搜索算法

针对图像矢量量化编码的复杂性，提出了一种新颖的快速最近邻码字搜索算法。该算法首先计算出每个码字和输入矢量的哈德码变换，然后为输入矢量选取范数距离最近的初始匹配码字，利用多控制点的三角不等式和两条有效的码字排除准则，把不匹配的码字排除，最后选取与输入矢量最匹配的码字。实验结果表明，新算法相比于其他算法，在保证编码质量的前提下，码字搜索时间和计算量均有了明显降低。

Novel codeword search algorithm based on Hadamard transform

With the aim of overcoming the encoding complexity, a novel and fast neighbor codeword search algorithm for vector quantization in the Handamard transform domain was presented. In the proposed algorithm, firstly the Hadamard transform was applied to all the codewords in the codebook and the input vector. Then the initial match codeword was selected from the codeword whose norm was nearest to the norm of input vector on Hadamard transform. Furthermore, the triangle inequalities with multiple control vectors and the two elimination criteria were utilized to reject mismatch codewords. Finally, the best-match codeword to the input vector was found. Experimental results show that the proposed algorithm has greatly reduced codeword search time and computational complexity under the precondition of good restored image quality.