Hierarchical motion estimation with spatial transforms

Spatial transformations motion estimation techniques have been proposed to address the inability of the conventional block matching to compensate for complex motion. Due to the relative high complexity of these approaches, fast motion search techniques are compulsory for practical implementations. In this paper we propose a hierarchical approach to spatial transformations motion estimation that significantly improves the prediction and complexity figures of the conventional methods. On the one hand we significantly reduce the complexity associated with the search techniques by initialising motion vectors at higher levels leaving only small displacement refinements for the more computational intensive lower levels. On the other hand we use the hierarchical differential motion structure to replace a large displacement fast search with small displacement fast searches at each level to overcome the fast methods inaccuracy with large motion. We demonstrate the validity of the approach both for quadrilateral matching motion estimation and warping motion estimation.