We study the motion estimation across three images by simultaneously enforcing the geometric constraint of trilinearity and the constant-brightness constraint. An iterative and hierarchical three-frame scheme is proposed to solve the geometry-consistent and appearance-consistent motion fields. It provides an uncalibrated approach to dense motion estimation, applicable to both 2-D and 3-D rigid scenes under perspective projection with unconstrained camera motion. Valid and consistent constraints are explored to alleviate the inherent aperture and over smoothing problems.