A fast three-step search algorithm with minimum checking points using unimodal error surface assumption

Fast motion estimation algorithms for compression of moving pictures are widely required for real-time video encoding instead of the full search (FS) block matching algorithm. It provides optimal error performance but requires enormous computation for calculating the motion vector. In many fast algorithms, the three-step search (TSS) has been used for real time video encoding and low bit-rate video communications because of the reduced computations, simplicity and reasonable performance. Other modified algorithms of the TSS have been studied for the speed of computation and the error performance for motion estimation. This paper proposes a new algorithm (fast three-step search) for further reduction in computational complexity using a unimodal error surface assumption (UESA) without serious degradation of the error performance. We show that the computational complexity is further reduced with additional subsampling of the matching block. It is also shown that the proposed algorithm (FTSS) is computationally efficient while keeping the same performance as that of the TSS.