Motion Estimation Using a Complex -

This paper describes a new motion estimation algorithm which is potentially useful for both computer vision and video compression applications. It is hierarchical in structure, using a separable 2-d Discrete Wavelet Transform (DWT) on each frame to eeciently construct a multiresolution pyramid of subimages. The DWT is based on a complex-valued pair of 4-tap FIR lters with Gabor-like characteristics. The resulting Complex DWT (CDWT) eeectively implements an analysis by an ensemble of Gabor-like lters with a variety of orientations and scales. The phase diierence between the subband coeecients of each frame at a given subpel bears a predictable relation to a local translation in the region of the reference frame subtended by that subpel. That relation is used to estimate the displacement eld at the coarsest scale of the multiresolution pyramid. Each estimate is accompanied by a directional conndence measure in the form of the parameters of a quadratic matching surface. The initial estimate eld is progressively reened by a coarse-tone strategy, in which ner scale information is appropriately incorporated at each stage. The accuracy, eeciency, and robustness of the new algorithm are demonstrated in comparison testing against hierarchical implementations of intensity gradient-based and fractional-precision block matching motion estimators.