The L2-norm pyramid has already been investigated as a promising data structure for the fast search of vector quantization (VQ) encoding in the previous work. Because the distortion at the top level is always tested first when using such a conventional L2-norm pyramid, the top level is most important. In order to enhance the capability of achieving a rejection decision at the top level, a modification is introduced into the conventional L2-norm pyramid in this letter by using both the mean and the variance of a vector simultaneously to replace the L2-norm of the vector for distortion computation at the top level. Two issues are made clear as 1) why this modification is beneficial to the distortion test is proved and 2) why only the top level of a conventional L2-norm pyramid should be modified is interpreted as well. Experimental results confirmed that the performance of VQ encoding by using the modified L2-norm pyramid can be improved obviously.
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