We discuss a strategy for adaptive quantisation in an MPEG encoder, based on the properties of the human visual system. This method can be used to replace the adaptive quantisation stage of the well known MPEG Test Model 5 (TM5), which is a simple method that does not closely model human perception. Our quantiser takes into account spatial masking by distinguishing between smooth, edge and texture regions, since they are known to have different masking properties. We also discuss methods of incorporating motion and higher level perceptual factors into our quantiser. The results show an improvement in PSNR of between 0.6 and 2.0 dB for a wide range of sequences and bit rates, compared to the TM5 model. We observed a significant increase in subjective picture quality using our adaptive quantiser, particularly at low bit rates.
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