Hierarchical Integer Pixel and Adaptive Fractional Pixel Motion Estimation

Motion estimation (ME) plays an important role in digital video compression, since it can significantly affect the image quality, the encoding speed and the compression ratio. ME is very computationally demanding part of the encoder. To reduce computational complexity and to maintain the good image quality, integer pixel and fractional pixel ME methods are proposed in this paper. For integer pixel ME, a hierarchical search strategy is proposed. This strategy method consists of symmetrical cross search pattern, multi square grid pattern, large and small diamond search patterns. To reduce the computational time and not to fall into the local minimum, these search patterns place search points symmetrically and evenly in the overall search area. After integer pixel ME, the adaptive fractional pixel ME method is performed. This fractional pixel ME method decides the search pattern adaptively according to the block size. Experimental results show that the speedup improvement of the proposed method over unsymmetrical cross multi hexagon grid search (UMHexagonS) and full search (FS) can be about 1.2~ 5.2 times faster. Compared to image quality of FS, the proposed method shows an average PSNR drop of 0.01 dB while showing an average PSNR gain of 0.02 dB in comparison to that of UMHexagonS.