laces the reconstruction levels at the centroids of the implemented in three stages. The first stage estimates adjacent input quantization steps. This minimizes the objective motion (motion estimation) between the total absolute error within each quantization step based previously reconstructed frame and the current frame. upon the input distribution. The second stage creates the current frame prediction Vector quantizers decompose the input into a length n (motion compensation) using the motion estimates and vector. An image for instance, can be divided into M X N the previously reconstructed frame. The final stage dif- blocks of n pixels each, or the image block can be trans- ferentially encodes the prediction and the actual current formed into a block of transform coefficients. The frame as the prediction error. Therefore, the receiver resulting vector is created by scanning the two di- reconstructs the current image only using the VLC mensional block elements into a vector of length N. A encoded motion estimates and the spatially and VLC vector X is quantized by choosing a codebook vector encoded prediction error. representation X that is its "closest match." The closest Motion estimation and compensation are common match selection can be made by minimizing an error techniques used to encode the temporal aspect of a video measure, i.e., choose X = Xi such that the MSE over all signal. As discussed earlier, block based motion com- codebook vectors is minimized, pensation and motion estimation techniques used in video compression systems are capable of the largest X = Xi : min MSE(X, = reduction in the raw signal bit rate. Typical imple- mentations generally out-perform pure spatial encodings (7.4.9) by a factor of three or more. The interframe redundancy The index i of the vector Xi denotes the codebook contained in the temporal dimension of a digital image sequence accounts for the impressive signal compression entry that is used by the receiver to decode the vector. capability that can be achieved by video e