Efficient two step edge based partial distortion search for fast block motion estimation

In video coding, block based full search motion estimation algorithm has been widely used, but it suffers from high computational requirements. In order to reduce the computations, this paper proposes a novel edge based partial distortion search (EPDS) algorithm which reduces the computation of each distortion measure by using partial distortion search. In this algorithm, the entire macroblock (MB) is divided into different sub-blocks and the calculation order of partial distortion is determined based on the edge strength of sub-blocks. This algorithm adaptively changes the early termination threshold for every accumulated partial sum of absolute difference. In the proposed method, only selected numbers of search points are considered for candidate motion vectors. An efficient early termination method, which is based on the dynamic threshold, is also proposed to decide whether a search point has met the rate-distortion (RD) cost criterion so that the best search point can be determined early. Simulation results show that the proposed method offers a remarkable improvement in computational speed when compared to full search (FS) and normalized partial distortion search (NPDS) algorithms. The proposed method is 115 times faster than FS, 10 times faster than NPDS and 2 times faster than the dual halfway stop NPDS (DHS-NPDS) on an average. PSNR degradation of the proposed algorithm is negligible and in the region of 0.01 dB. The proposed method can be easily applied to many mobile video application areas such as digital cameras and DMB (Digital Multimedia Broadcasting) phones.