A two-layer coding approach with a spatial pyramid to achieve compatibility has been known to have several advantages. The first layer can have optimal performance. Rate control can be distributed between layers. However, the compression performance and the overall complexity at the high resolution layer suffer because of the requirement of compatibility. Therefore, good compatibility prediction is a crucial factor for a spatial scalability approach. In the paper, the authors focus on obtaining the best compatibility prediction, assuming that a spatially upsampled block and a motion compensated block are available. A spatio-temporal averaging technique has been shown to provide improvement. With a linear regression analysis, further improvement in prediction is shown. Better compatibility prediction can be obtained by assigning the spatio-temporal weights adaptively for individual pixels. The authors found that a pel-adaptive recursive estimation using Kalman filters gives a good compatibility prediction. The new difference signal has the statistical property of white Gaussian noise. The additional complexity is moderate and the bits for sending side information is insignificant. The resultant picture quality of the approach approximates the picture quality of the noncompatible single-layer approach.
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