Visual hulls from single uncalibrated snapshots using two planar mirrors

Two mirrors are used to create five views of an object: a view onto the object, two reflections and two reflections of reflections. The five views are captured in a single snapshot. Epipolar geometry of the object’s five silhouettes is determined directly from the image without knowing the poses of the camera or the mirrors. The epipolar geometry provides constraints on the pose of each silhouette, allowing the pose of each silhouette to be computed in a common reference frame using only the silhouette outlines. Once the pose associated with each silhouette has been computed, a five-view visual hull of the object can be computed from the five silhouettes. By capturing several images of a rigid object in different poses, sets of five silhouettes can be combined into a single silhouette set in which the pose of each silhouette is known in a common reference frame. This allows visual hulls of an arbitrary number of views to be computed if more than one image is used. The method is applied to an ornamental cat, and experimental results are shown.

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