Absolute three-dimensional shape measurement with a known object

This paper presents a novel method for absolute three-dimensional (3D) shape measurement that does not require conventional temporal phase unwrapping. Our proposed method uses a known object (i.e., a ping-pong ball) to provide cues for absolute phase unwrapping. During the measurement, the ping-pong ball is positioned to be close to the nearest point from the scene to the camera. We first segment ping-pong ball and spatially unwrap its phase, and then determine the integer multiple of 2π to be added such that the recovered shape matches its actual geometry. The nearest point of the ball provides zmin to generate the minimum phase Φmin that is then used to unwrap phase of the entire scene pixel by pixel. Experiments demonstrated that only three phase-shifted fringe patterns are required to measure absolute shapes of objects moving along depth z direction.