DISPLACEMENT VECTORS DERIVED FROM 2ND-ORDER INTENSITY VARIATIONS IN IMAGE SEQUENCES

A local approach for interframe displacement estimates is developed by minimization of the squared differences between a second-order Taylor expansion of gray values from one frame and the observed gray values within the same window from the next frame. If the second-order terms in the Taylor expansion are significant, a system of two coupled nonlinear equations for the two unknown components of the displacement vector can be derived. In the special case of 'gray value corners,' these equations can be simplified to facilitate a closed form solution. An iterative refinement procedure is developed to extend these estimates for image regions which do not exhibit exactly the properties of 'gray value corners'. The minimization approach is generalized in such a way that the approach of Horn and Schunck, can be recognized as a special case of this generalized form which should be applicable even across occluding edges. It thus appears to be an interesting model for the local computation of optical flow.