Improved Accuracy in Initial Search Center Prediction to Fasten Motion Estimation in h.264/AVC

In this paper, a new two-step approach for enhancing the accuracy of initial search center (ISC) prediction in h.264 has been proposed which improves the speed of motion estimation in video encoding. Previous methods for estimating the ISC worked in a single step by finding the mean/median of motion vectors (MVs) of neighboring blocks of the current and reference frames. The major drawback of all the existing ISC techniques is that they consider the participation of all the neighboring blocks with equal probability without taking into account their correlation with the current block. The blocks which have least correlation or no correlation at all affect the accuracy of prediction and hence increase the chances of trapping the search in local minima. Moreover, in the existing ISC prediction techniques, participation of MVs of restricted neighboring blocks is considered, which further limits the prediction accuracy. To elevate these drawbacks, a new two-step approach has been presented. The first step of the method works by identifying some candidate blocks for ISC and the second phase refines the search to obtain best possible ISC. Use of all the surrounding blocks from spatial and temporal frame along with the refinement stage has improved the accuracy. Simulation results clearly show the enhancement in accuracy of ISC prediction, improvement in video quality in terms of peak signal-to-noise ratio (PSNR) and reduction in the number of search steps. Most recent approach in ISC prediction has shown an improvement of 11.7% as compared to standard median predictor, whereas the proposed technique shows an improvement of almost 50%. The reduction in search points is nearly 40%-50% compared to standard median predictor for fast-motion sequences. Also the proposed technique works equally well for fast, medium, slow, cif, qcif and HD video sequences as indicated in the results.