Reflectance and Shape from a Rotating Object

In this paper we show that the reflectance function of a rotating object illuminated under a collinear light source (where the light source lies on or near the optical axis) can be estimated from the image sequence of the object and applied to surface recovery. We first calculate the 3D locations of some singular points from the image sequence, and extract the brightness values of these singular points during the object rotation to estimate the surface reflectance function. Then we use the estimated reflectance function for surface recovery from the images of the rotating object. Two subprocedures are used in surface recovery. The first subprocedure computes the depth around a point of known depth and surface orientation by using first-order Taylor series approximation. The other computes the surface orientation of a surface point from its image brightness values in the two different images by applying the estimated reflectance function. Starting from surface points of known depth values and surface orientations and iteratively applying the two subprocedures, the surface depth and orientation are recovered simultaneously over the whole object surface. The experimental results on real image sequences of both matte and specular surfaces show that the technique is feasible and robust.