ned to minimize the source entropy. The VLC is is transmitted along with the VLC encoded motion applied to a serial bit stream that is generated by vectors MVk. The decoder can reconstruct the current scanning the transform coefficient block. The scan- frame Ik using the previously reconstructed frame Ik-1 ning pattern should be chosen with the objective of (stored in the decoder), the current frame motion vec- maximizing the performance of the VLC. The tors, and the prediction error. The motions vectors MVk MPEG encoder for instance, describes a zigzag operate on Ik-1 to generate the current prediction frame scanning pattern that is intended to maximize Pk. The encoded prediction error Eke is decoded to transform zero coefficient run lengths. The H.261 produce the reconstructed prediction error . The VLC is designed to encode these run lengths using prediction error is added to the prediction to form the a variable length Huffman code. current frame Ik. The functional elements of the gener- alized model are described here in detail. The feedback loop sequentially reconstructs the encoded spatial and prediction error frames and stores the results Spatial operator - This element is generally a unitary in order to create a prediction for the current image sub- two dimensional linear transform, but in principle block. The elements required to do this are the inverse can be any unitary operator that can distribute most quantizer, inverse spatial operator, delayed frame of the signal energy into a small number of memory, motion estimator, and motion compensator. coefficients, i.e., decorrelate the signal data. Spatial transformations are successively applied to small Inverse operators - The inverse operators Q and T-1 are applied to the encoded current frame Ike or image blocks in order to take advantage of the high the current prediction error Eke in order to recon- degree of data correlation in adjacent image pixels. struct and store the encoded frame for the motion The most widely used spatial operator for image an