Abstract
In the search for reduction of the unacceptably high bit rates of PCM digital images, vector quantization seems to have the edge: its theoretical distortion is lower than that of other block coding methods at comparable bit rates. However, to obtain high quality pictures, when used as a stand-alone process, a vector quantizer requires a codebook of large size and is excessively computational intensive. For the dynamic range of the original images, 0 to 255, it is doubtful that a single optimal and universal codebook of manageable size can be obtained. Hence, to reduce the dynamic range of the signals encoded using VQ, we propose a method that uses Adaptive Delta Modulation with one stage look ahead as a preprocessor in conjunction with vector quantization of the appropriately defined error signals. Using such a scheme, it is shown that good quality composite color video images can be obtained using 1.5 to 2.0 bits per pixel and codebooks which are small and universal.
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