Patent ID: 7020305

Claim:
A method to estimate head motion between two images of a face, the method comprising operations of: identifying locations of a plurality of distinct facial features in the two images, the locations corresponding to a number of unknowns determined upon estimation of head motion, the number of unknowns being determined by a number of equations; converting the identified locations into a set of physical face parameters based on the symmetry of the distinct facial features, the set of physical face parameters reducing the number of unknowns as compared to the number of equations used to determine the unknowns; and estimating head motion from identified points in the two images, the identified points being based on the set of physical face parameters; and wherein the operation of estimating head motion comprise operations of: calculating an estimation objective function to determine an initial estimate of head rotation, the estimation objective function comprising a set of terms to estimate: (a) each of the set of physical face parameters. (b) a first head pose transform corresponding to the first image, and (c) a second head pose transform corresponding to the second image; placing an inequality constraint on a particular face parameter of the set of physical face parameters, such that the particular face parameter is constrained within a predetermined minimum and maximum value; converting the inequality constraint to an equality constraint using a penalty function; and adding the equality constraint to the initial estimate.