ENHANCED SEARCH STRATEGIES FOR HIERARCHICAL MOTION ESTIMATION

Motion estimation in flat regions of video sequences and/or in regions of low energy in a certain spatial direction shall be improved. Thus, there is provided a method for estimating motion between successive frames by estimating a first motion vector (v1) using a measurement window (mw) and search range in a first level of hierarchy, defining a second measurement window and search range for a second level of hierarchy, the second measurement window and search range being smaller than the first measurement window and search range, providing an energy dependent value for the second measurement window comparing the energy dependent value with a threshold value and determining as resultant motion vector: a) either the sum of the first motion vector and a second motion vector estimated within the second measurement window, if the energy dependent value exceeds the threshold value or b) the first motion vector if the energy dependent value does not exceed the threshold value. Moreover, the energy of the image signal differences in the measurement window in horizontal, vertical, diagonal or other directions may be determined, and if the energy is low in a certain direction and large in the orthogonal one, the vector component will be frozen in the direction of low energy and left unchanged, while continuing motion estimation only in the other direction of larger energy.