Analysis Of Structured Light 3d Reconstruction Method Based On Carré Algorithm

The modern processing and manufacturing technology is developing in the direction of high accuracy,high speed and low cost.Optical three-dimensional(3D)shape measurement technology has widely applied to modern industrial measurement because of its characteristics of high efficiency,wide measurement range,non-contact,and high automation.As a typical representative of optical 3D measurement,Digital phase shifting structured light technology has become a popular research topic in related fields.Based on the existing digital phase shifting technology,this paper modifies the conventional phase shifting algorithm and analyzes the error of the modified algorithm to improve the measurement efficiency.Firstly,this paper introduces and compares the phase-shifting algorithms and phase unwrapping algorithms.Carré algorithm is a classic phase shifting measurement method due to its advantage in resisting the error caused by inaccurate phase step.The conventional Carré algorithm only calculates the wrapped phase,so multiple frequencies are used to unwrap the phase so as to obtain the absolute phase,which increases the number of patterns and decreases the measuring speed.So a modified Carré algorithm which use fewer patterns with high-accuracy is proposed in this paper.The phase step in modified Carré algorithm is encoded as a linear variable and used to unwrap the wrapped phase.Then the unwrapped phase is converted to depth information with calibrated system parameters.With the linear phase step,the wrapped phase and absolute phase are obtained simultaneously from only 4 patterns.The proposed method is non-sensitive to the errors in phase step,the same as the conventional Carré algorithm.Several experiments demonstrate its performance in high accuracy,high efficiency and robustness.Then,aiming at the nonlinear error caused by the Gamma distortion of the projector,this paper analyze the error in the modified Carré algorithm and obtain the corresponding analytical formula of the phase error and phase step error.After simulating the errors and utilizing its periodic characteristics,an inverse error compensation method is proposed.The proposed method only needs four additional fringe patterns to compensate the phase error and phase step error at the same time pixel by pixel.Finally,a monocular structured light measurement system is built.We compare the3 D reconstruction results before and after error compensation and quantitatively analyze the error.Experimental results verify the methods proposed in this paper can effectively improve the measurement accuracy and speed.