一种适合低信噪比投影栅的时空二维相移算法

提出了一种适合低信噪比投影栅的时空二维相移算法。首先设计四步相移正弦光栅条纹图,由DLP投影仪投影到待测物体表面,再由CCD相机采集受物体形貌调制的变形条纹图;然后对其中一幅变形条纹图进行傅里叶变换以确定抽样间隔,再对4幅相移条纹图用相移法求得条纹背景和调制幅度后,对每幅变形条纹图做归一化处理;对每幅相移条纹图在空间域进行下采样抽样和灰度插值,构建相移莫尔条纹图,得到多帧时空域相移条纹图;对多帧时空域相移条纹图按时空二维相移法处理求得莫尔相位,再将莫尔相位与抽样点相位叠加求和得到变形条纹图对应的相位数据;最后,以面膜作为样品进行了实验测量,结果表明,经典四步相移法重构的物体形貌出现明显失真,而本文方法能较好恢复物体的三维形貌。

A spatiotemporal phase-shifting profilometry applied for the low sig nal-noise ratio projection

A spatiotemporal phase-shifting profilometry is proposed in order to solve the problem of phase demodulation error for the low signal-noise ratio (SNR) fringe project ion in three-dimensional(3D) shape measurement.Firstly,four-step phase-shiftin g sinusoidal patterns designed by computer are projected onto the tested object by a digital-light-process (DLP) projector and the deformed fringe patterns are acquired by a CCD camera.The sampling pitch is determined by the Fourier tr ansform method.Normalized fringe patterns are obtained after the amplitude and backgrou nd intensities are determined by the phase-shifted method.Then multi-frame spatiotemporal phase-shifting Moire fringes are attained by the process of down-sampling with a sampling pitch and intensity interpolation in space domain for each four-step phase-shifted fringe image.Thus,the phase distribution of the Moire patterns can be calculated using two-dimensional spatiotemporal phase-shifting method.The phase distribution of the original deformed grating can be obtained b y adding the phase of the sampling point to that of the Moire pattern.Finally,the experiment for the facial mask is performed by fringe projection to verify the effectiveness of the proposed method.The results show that the reconstructed 3D shape shows visible distortion with the standard four-step phase-shif ting algorithm but remains fidelity with the proposed algorithm instead.