This paper presents a method to unwrap phase pixel by pixel by solely using geometric constraints of the structured light system without requiring additional image acquisition or another camera. Specifically, an artificial absolute phase map, Φmin, at a given virtual depth plane z = zmin, is created from geometric constraints of the calibrated structured light system; the wrapped phase is pixel-by-pixel unwrapped by referring to Φmin. Since Φmin is defined in the projector space, the unwrapped phase obtained from this method is absolute for each pixel. Experimental results demonstrate the success of this proposed novel absolute phase unwrapping method.
One of the major challenges of employing a two-frequency (or two-wavelength) phase-shifting algorithm for absolute three-dimensional shape measurement is its sensitivity to noise. Therefore, three- or more-frequency phase-shifting algorithms are often used in lieu of a two-frequency phase-shifting algorithm for applications where the noise is severe. This paper proposes a method to use geometric constraints of digital fringe projection system to substantially reduce the noise impact by allowing the use of more than one period of equivalent phase map for temporal phase unwrapping. Experiments successfully verified the enhanced performance of the proposed method without increasing the number of patterns.
This paper presents a method to achieve high-speed and high-accuracy 3D surface measurement using a custom-designed mechanical projector and two high-speed cameras. We developed a computational framework that can achieve absolute shape measurement in sub-pixel accuracy through: 1) capturing precisely phase-shifted fringe patterns by synchronizing the cameras with the projector; 2) generating a rough disparity map between two cameras by employing a standard stereo-vision method using texture images with encoded statistical patterns; and 3) utilizing the wrapped phase as a constraint to refine the disparity map. The projector can project binary patterns at a speed of up to 10,000 Hz, and the camera can capture the required number of phase-shifted fringe patterns with 1/10,000 second, and thus 3D shape measurement can be realized as high as 10,000 Hz regardless the number of phase-shifted fringe patterns required for one 3D reconstruction. Experimental results demonstrated the success of our proposed method.
This paper presents a method that recovers high-quality 3D absolute coordinates point by point with only five binary patterns. Specifically, three dense binary dithered patterns are used to compute the wrapped phase; and the average intensity is combined with two additional binary patterns to determine fringe order pixel by pixel in phase domain. The wrapped phase is temporarily unwrapped point by point by referring to the fringe order. We further developed a computational framework to reduce random noise impact due to dithering, defocusing and random noise. Since only five binary fringe patterns are required to recover one 3D frame, extremely high speed 3D shape measurement can be achieved. For example, we developed a system that captures 2D images at 3,333 Hz, and thus performs 3D shape measurement at 667 Hz.
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