1. A method for estimating global motion between a reference image or a portion thereof and a current image or a portion thereof, the method comprising steps of: computing translation invariant representations of the reference image or the portion thereof and the current image or the portion thereof, wherein the translation invariant representations preserve non-translational motion effects present in the reference image or the portion thereof and the current image or the portion thereof; from the translational invariant representations, determining a coarse estimation of the effect of the non-translational motion between the reference and the current image or the portions thereof; and determining a coarse estimation of the effect of translational motion from the coarse estimation of the effect of the non-translation motion and the current image or the portion thereof, wherein the effect of the non-translation motion and the effect the translation motion together constitute a coarse estimate of the global motion.