Based upon studying the strategy for adaptive quantization suggested by MPEG-2 Test Model 5

a new quantizer is presented in this paper.Block-based visual activities are analyzed to exploit local perceptual characteristics in the macroblock.In order to decide the adaptive perceptual quantization factor

macroblock characteristic is identified by evaluating comprehensively each block’s local activity within this macroblock.Experiment results show that coding distortion is uniformly distributed across the image with the proposed quantizer

and picture quality is improved. In particular

block artifacts in flat area and distortion at edges on flat backgrounds are significantly reduced.