 error is optionally DCT 1. If VAR(DBD) < VAR(MD) then interframe + motion encoded. Both modes provide options that affect the compensation (Inter + MC) coding is selected. In performance and video quality of the system. The this case, the motion vector data (MVD) is trans- motion estimate method, mode selection criteria, and mitted. Table 7.4-5 indicates that there are three block transmission criteria are not specified although the Inter + MC modes that allow for the transmission of ITU has published reference models [21, 22] that make the prediction error (DMD) with or without DCT particular implementation recommendations. The encoding of some or all of the four coding algorithm used in the ITU-T Reference Model 8 8 X 8 basic blocks. (RM8) [22] is summarized in three steps, and is followed 2. "VAR input" is defined as the variance of the input by an explanation of its important encoding elements. macroblock. If VAR input < VAR(DMD) and VAR 1. The motion estimator creates a displacement vector input < VAR(MD) then the intraframe mode (Intra) for each macroblock. The motion estimator generally is selected. Intraframe mode uses DCT encoding of operates on the 16 X 16 pixel luminance macroblock. all four 8 X 8 basic blocks. The displacement vector is an integer value between 3. If VAR(MD) < VAR(DMD) then interframe mode +15, which is the maximum size of the search (Inter) is selected. This mode indicates that the neighborhood. The motion estimate is scaled by motion vector is zero, and that some or all of the 8 X 8 a factor of 2 and applied to the C1 and Cb component prediction error (MD) blocks can be DCT encoded. macroblocks. 2. The compression mode for each macroblock is se- The transform coefficient coded block pattern (CBP) lected using a minimum error criteria that is based parameter is used to indicate whether a basic block is upon the displaced macroblock difference (DMD), reconstructed using the corresponding basic block from the previous frame, or if it is encoded and transmitted. In DMD(i,j,k) = b(i,j,k