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.

The binary defocusing technique has been widely used in high-speed three-dimensional (3D) shape measurement because it breaks the bottlenecks in high-speed fringe projection and the projector’s nonlinear response. However, it is challenging for this method to realize a two- or multi-frequency phase-shifting algorithm because it is difficult to simultaneously generate high-quality sinusoidal fringe patterns with different periods under the same defocusing degree. To bypass this challenge, we proposed a high-speed 3D shape measurement technique for dynamic scenes based on cyclic complementary Gray-code (CCGC) patterns. In this proposed method, the projected phase-shifting sinusoidal fringes kept one same frequency, which is beneficial to ensure the optimum defocusing degree for binary dithering technique. The wrapped phase can be calculated by phase-shifting algorithm and unwrapped with the aid of complementary Gray-code (CGC) patterns in a simple and robust way. Then, the cyclic coding strategy further extends the unambiguous phase measurement range and improves the measurement accuracy compared with the traditional Gray-coding strategy under the condition of the same number of projected patterns. High-quality 3D results of three complex dynamic scenes—including a cooling fan and a standard ceramic ball with a free-falling table tennis, collapsing building blocks, and impact of the Newton’s cradle—were demonstrated at a frame rate of 357 fps. This verified the proposed method’s feasibility and validity.

Jump errors easily occur on the discontinuity of the wrapped phase because of the misalignment between wrapped phase and fringe order in fringe projection profilometry (FPP). In this paper, a phase unwrapping method that avoids jump errors is proposed for FPP. By building two other staggered wrapped phases from the original wrapped phase and dividing each period of fringe order into three parts, the proposed generalized tripartite phase unwrapping (Tri-PU) method can be used to avoid rather than compensatorily correct jump errors. It is suitable for the phase unwrapping method assisted by fringe order with a basic wrapped phase and fringe order, no matter which method is used to recover them. The experimental results demonstrate the effectiveness and generality of the proposed method, which is simple to implement and superior to measure complex objects with sharp edges.

High-speed three-dimensional (3D) shape measurement has been continuously researched due to the demand for analyzing dynamic behavior in transient scenes. In this work, a time-overlapping structured-light 3D shape measuring technique is proposed to realize high-speed and high-performance measurement on complex dynamic scenes. Time-overlapping structured-light projection is presented to maximumly reduce the information redundancy in temporal sequences and improve the measuring efficiency; generalized tripartite phase unwrapping (Tri-PU) is used to ensure the measuring robustness; fringe period extension is achieved by improving overlapping rate to further double the encoding fringe periods for higher measuring accuracy. Based on the proposed measuring technique, one new pixel-to-pixel and unambiguous 3D reconstruction result can be updated with three newly required patterns at a reconstruction rate of 3174 fps. Three transient scenes including collapsing wood blocks struck by a flying arrow, free-falling foam snowflakes and flying water balloon towards metal grids were measured to verify the high performance of the proposed method in various complex dynamic scenes.

Among many multi-dimensional information sensing methods such as structured-light and single-pixel imaging technologies, sinusoidal fringe generation is general and crucial. Current methods of sinusoidal fringe generation force concessions in either the speed or the depth range. To mitigate this trade-off, we have simultaneously achieved both speed breakthrough and depth range enhancement by improving both the optical projection system and binary coding algorithm based on an off-the-shelf projector. Specifically, we propose a multifocal projection system and oblique projection method, which essentially eliminates the existence of a single focal plane in the conventional axisymmetric system and utilizes its anisotropy characteristics to achieve a superior filtering effect. Furthermore, the optimal pulse width modulation technique is introduced to modulate the square binary pattern for eliminating specific harmonics. To the best of our knowledge, the proposed method, for the first time, simultaneously achieved superfast (9524 frames per second) and large-depth-range (560 mm, about three times that of the conventional method) sinusoidal fringe generation with consistently high accuracy. Experimental results demonstrate the superior performance of the proposed method in multi-dimensional information sensing such as 3D, 4D, and [ x , y , z , t ; s (strain)].