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An efficient algorithm is proposed to reduce the computational complexity of block matching motion estimation by using the characteristics of spatial correlation. The proposed algorithm is to skip the motion vector search of inside macroblocks surrounded by identical motion vectors. Experimental results show that the proposed algorithm reduces computational complexity by 52.5% compared to conventional motion estimation at the cost of negligible performance degradation.
Introduction: To reduce the temporal redundancy of video sequences, block matching motion estimation has been adopted in various video coding standards such as ISO=IEC MPEG-1, MPEG-2, MPEG-4 and ITU-TH.263 [1]. In those applications, motion estimation has a large effect on overall computational complexity. Many algorithms have been developed to reduce the search space of motion vectors [2]. Based on the fact that there is little motion difference among spatially neighbouring macroblocks, the neighbouring motion vectors are utilised to reduce the candidate locations to be searched for a macro- block [3] or to approximate the motion vector without exploiting the search space [4].In[4], the motion vector of a macroblock is approximated by the median value of three motion vectors of the left, upper, and upper right macroblocks if the resulting distortion is not larger than the median distortion of the neighbouring macro- blocks. Such a block-by-block approximation has a limitation in reducing the computational complexity although it reflects the motion behaviour of macroblocks.
In this Letter, we propose a low complexity motion estimation algorithm that uses the spatial correlation to further skip the motion vector search by conditionally identifying a group of macroblocks being moved together. The proposed algorithm reduces computational complexity while maintaining the quality of motion estimation.
Proposed algorithm: Motion vectors in an image frame are smoothly varying and discontinuous only at the boundaries of objects moving in different directions or with different velocities, which means that a considerable number of contiguous macroblocks have identical motion vectors in real image sequences. If the boundary of the...