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.