Adaptive nonstationary DPCM image coding with variable blocksize

This study investigates the design and performance of a spatial domain image encoding scheme that adapts to the localized statistical structure of an image. An adaptive differential pulse code modulation (DPCM) image coding system operates on an image that has been preprocessed into segments of variable size, square blocks. Each block is separately encoded by a DPCM system whose parameters have been obtained based upon an underlying nonstationary image model fitted to the block. The source coding performance of the adaptive DPCM algorithm proposed in this study has been found to result in an improvement of 2.5 dB, or greater, compared to that obtained using a nonadaptive, conventionally designed DPCM encoder/decoder pair when operating at low bit rates (i.e., 3 bits/pixel or less). Reconstructed images obtained in this study are of perceptually higher-quality due to the adaptive encoding system design being based on the more realistic assumption of nonstationary statistics. Specifically, experiments have revealed that reconstructed edges within local regions of the image are sharper providing an overall improvement in a viewers subjective assessment of global image quality.