Real-time three-dimensional shape measurement based on color binary fringe projection

Abstract. A real-time three-dimensional (3-D) shape measurement based on single-shot color binary fringe (CBF) projection is proposed. In the traditional 3-D shape measurement methods based on binary fringe projection, the duty cycle of the binary fringe is always set to 1/2, so as to approximate the sinusoidal fringe by defocusing projection. In the proposed method, the binary fringe with a duty cycle of 1/3 is introduced. It is found that although the duty cycle is not 1/2, a nearly unbroken sinusoidal fringe pattern can be extracted from the captured fringe pattern by a filtering operation in the spatial frequency domain. In order to realize real-time 3-D shape measurement, a composite CBF was designed, in which three monochromatic binary fringes share the same duty cycle of 1/3 but misaligned 1/3 periods one by one are encoded in red (R), green (G), and blue (B) channels. When this composite CBF is projected onto the measured object, only one color-deformed pattern (CDP) needs to be captured and three monochromatic sinusoidal deformed patterns with a phase-shifting of 2π  /  3 one another can be extracted from the single-shot captured CDP. So the 3-D shape of the measured object can be reconstructed with three-step phase measuring profilometry. The experimental results show the feasibility and validity of the proposed method. It can either effectively avoid the color overlapping in traditional color sinusoidal fringe or avoid the grayscale nonlinearity of sinusoidal fringe caused by the effect of gamma.