Crosstalk reduction of a color fringe projection system based on multi-frequency heterodyne principle

Color fringe projection systems for 3D shape measurement have been widely studied in academia because of the advantages of non-contact operation, full-field, and fast data processing. A color CCD camera and a DLP (Digital Light Processing) projector are mostly used. However, crosstalk between color channels of the camera and projector changes the sinusoidal shape of the obtained fringe patterns and then reduces the measurement accuracy. Several methods have been proposed to solve this problem, but they are either too complicated for calculating the color-coupling coefficients using a series of phase-shifting fringe patterns or unstable convergence due to the iterative technique used. This paper presents a simple method to reduce crosstalk between red, green and blue channels. Crosstalk between color channels can be seen as signal aliasing, so different wavelength in color channels can be used to keep them apart. Two wrapped phase maps are obtained by processing corresponding spectrum with FTP (Fourier transform profilometry) in each color channel. The unwrapped phase is calculated based on multi-frequency heterodyne principle. Simulated and experimental results show that the proposed method can significantly reduce the influence of crosstalk on phase calculation and improve the measurement accuracy of the color fringe projection system.