基于灰度拓展复合光栅的单帧三维测量方法

提出了一种基于灰度拓展的单帧正交复合光栅三维测量方法。由于受商用DLP最大灰阶动态范围256的标准限制，单帧复合光栅中的多张调制光栅共享256灰阶动态范围导致其对比度变小，其表征的三维物体的相位信息被压缩，解相过程出现相位断裂现象，测量误差增大。采用时分复用原理，将一具有766灰阶的正交复合光栅拆分为三幅不同的具有256灰阶的条纹图。依次序加载进循环播放的视频中投射至待测物体表面，当用曝光时间为3倍视频刷新周期的整数倍10 bit CCD采集时，就可采集到具有766灰阶动态范围的变形复合光栅像。通过滤波和灰度校准等计算后，物体的三维面形能够完整而精确的重建。经仿真和实验验证，所提方法打破了DLP256灰度投影的限制，有效提高了相移变形条纹的动态范围，增大了被测物体细节信息，避免了相位展开环节相位断裂而引起物体面形重构不完整的现象。

Single-shot 3D measurement using grayscale expanded composited grating

A single-shot 3D shape measurement using orthogonal composited grating based on grayscale expanding (OCGGE) was proposed. In the traditional orthogonal composited grating (OCG) profilometry, the modulated gratings in the orthogonal composited grating must share the same grayscale level since the maximal grayscale dynamic range of commercial Digital Light Processing (DLP) is limited in 256, that results in some phenomenon increasing the measuring error, including the weakened contrast of the modulated grating, the compressed phase information and the broken phase during the process of phase unwrapping. Based on the principle of time division multiplexing, one orthogonal composited grating was designed with 766 gray level and was spited into three different fringe patterns with 256 grayscales, then loaded these patterns in sequence to edit a video. When this video was played and projected onto the measured object continuously, by setting the exposure time as an integer times of the 3 times of the frame refresh cycle of the video for a 10bit CCD, a deformed pattern with 766 grayscales could be obtained. After the filtering and grayscale calibration, the object could be reconstructed accurately and completely. Both simulation and experiment results prove that the proposed method can break the limit of 256 grayscale projection and increase the dynamic range of the phase-shifting deformed patterns efficiently. And it can also enrich the detailed information of the measured object and avoid the incomplete surface reconstruction caused by phase break.