Wu Zhoujie, Guo Wenbo, Zhang Qican
Opt Express. 2019 Aug 5;27(16):22631-22644. doi: 10.1364/OE.27.022631.
The measuring technique combining a phase-shifting algorithm and Gray-code light has been widely used in three-dimensional (3D) shape measurement for static scenes because of its high robustness and anti-noise ability. However, in the high-speed measurement, phase unwrapping errors occur easily on the boundaries of adjacent Gray-code words because of the defocus of the projector, the motion of the objects and the non-uniform reflectivity of the surface. To overcome this challenge, a high-speed 3D shape measurement method based on shifting Gray-code light has been proposed in this paper. Firstly, the average intensity of three captured phase-shifting fringe images are used as a pixel-wise threshold to binarize the Gray codes and to eliminate most phase unwrapping errors caused by the non-uniform reflectivity, ambient light variations, and the defocus of projector. Then, the shifting Gray-code (SGC) coding strategy is proposed to avoid the remaining errors of phase unwrapping on the edge of the code words. In this strategy, no additional patterns are projected, and two sets of decoding words with staggered boundaries are built in the temporal sequences for one wrapped phase. Finally, the simple, efficient, and robust phase unwrapping can be achieved in the high-speed dynamic measurement. This proposed method has been applied to reconstruct 3D shape of randomly collapsing objects in a large depth range, and the experimental results demonstrate that it can reliably obtain high-quality shape and texture information at 310 frames per second.
结合相移算法和格雷码光的测量技术因其高鲁棒性和抗噪声能力，已在静态场景的三维（3D）形状测量中得到广泛应用。然而，在高速测量中，由于投影仪的散焦、物体的运动以及表面反射率的不均匀性，相邻格雷码字的边界容易出现相位展开误差。为了克服这一挑战，本文提出了一种基于移位格雷码光的高速3D形状测量方法。首先，将采集到的三幅相移条纹图像的平均强度用作逐像素阈值，对格雷码进行二值化处理，并消除由反射率不均匀、环境光变化和投影仪散焦引起的大部分相位展开误差。然后，提出了移位格雷码（SGC）编码策略，以避免码字边缘的相位展开剩余误差。在该策略中，不投射额外的图案，并且在一个包裹相位的时间序列中构建两组具有交错边界的解码字。最后，在高速动态测量中可以实现简单、高效且鲁棒的相位展开。该方法已应用于在大深度范围内重建随机坍塌物体的3D形状，实验结果表明，它可以在每秒310帧的速度下可靠地获得高质量的形状和纹理信息。
