Estimating Physical Camera Parameters based on Multi-Sprite Motion Estimation

Global-motion estimation algorithms as they are employed in the MPEG-4 or H.264 video coding standards describe motion with a set of abstract parameters. These parameters model the camera motion, but they cannot be directly related to a physical meaning like rotation angles or the focal-length. We present a two step algorithm to factorize these abstract parameters into physically meaningful operations. The first step applies a fast linear estimation method. In an optional second step, these parameters can be refined with a non-linear optimization algorithm. The attractivity of our algorithm is its combination with the multi-sprite concept that allows for unrestricted rotational camera motion, including varying of focal-lengths. We present results for several sequences, including the well-known stefan sequence, which can only be processed with the multi-sprite approach.