Abstract: Recently, a variable block size (VBS) motion estimation technique has been employed to improve the performance of the motion compensated transform coding (MCTC). This technique allows larger blocks to be used when smaller blocks provide little gain, saving the bit rates, especially for areas containing more complex motion. However, the employment of the VBS motion estimation technique addresses a new optimization issue for the motion compensated coding (MCC), since an increased bit rate should be allocated to the VBS motion vectors. That is, the rate allocation between the motion vector encoding and the displaced frame difference (DFD) coding is an important issue. Hence, in this paper, a rate-distortion (R-D) optimization between the hierarchical VBS motion estimation and DFD coding is described. First, to make the R-D search feasible, the hierarchical VBS motion structures age grouped into two-level model structures and an efficient R-D search method is proposed. Next, a solution for the control of the VBS motion information, based on Lagrange multiplier method, is introduced. Intensive computer simulation employing the MCTC technique shows that an overall improvement up to 1.0 dB, compared to the fixed block size motion estimation, is obtained.!16
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