An efficient scheme is given for transmitting high-resolution still images based on a lower-resolution CCITT H.261 codec. Two transmission schemes based on a subsampling approach are studied in terms of image quality, transmission delay, and compatibility with H.261. It is found that the sequential frame-repeat scheme provides a good compromise among the different criteria. In addition, a simple progressive-reconstruction procedure for the decoded subimages is described. Simulation results show that the visual effects of such a reconstruction procedure are quite pleasing.
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