Dynamic 3D shape reconstruction under complex reflection and transmission conditions using multi-scale parallel single-pixel imaging

Depth measurement and three-dimensional(3D)imaging under complex reflection and transmission conditions are challenging and even impossible for traditional structured light techniques,owing to the precondition of point-to-point triangulation.Despite recent progress in addressing this problem,there is still no efficient and general solution.Herein,a Fourier dual-slice projection with depth-constrained localization is presented to separate and utilize different illumination and reflection components efficiently,which can significantly decrease the number of projection patterns in each sequence from thousands to fifteen.Subsequently,multi-scale parallel single-pixel imaging(MS-PSI)is proposed based on the established and proven position-invariant theorem,which breaks the local regional assumption and enables dynamic 3D reconstruction.Our methodology successfully unveils unseen-before capabilities such as(1)accurate depth measurement under interreflection and subsurface scattering conditions,(2)dynamic measurement of the time-varying high-dynamic-range scene and through thin volumetric scattering media at a rate of 333 frames per second;(3)two-layer 3D imaging of the semitransparent surface and the object hidden behind it.The experimental results confirm that the proposed method paves the way for dynamic 3D reconstruction under complex optical field reflection and transmission conditions,benefiting imaging and sensing applications in advanced manufacturing,autonomous driving,and biomedical imaging.

High-speed and high-efficiency three-dimensional shape measurement based on Gray-coded light

Fringe projection profilometry has been increasingly sought and applied in dynamic three dimensional(3D)shape measurement.In this work,a robust,high-efficiency 3D measurement based on Gray-coded light is proposed.Unlike the traditional method,a tripartite phase unwrapping method is proposed to avoid the jump errors on the boundary of code words,which are mainly caused by the defocusing of the projector and the motion of the tested object.Subsequently,the time overlapping coding strategy is presented to greatly increase the coding ef-ficiency,decreasing the projected number in each group from seven(i.e.,3+4)to four(i.e.,3+1)for one restored 3D frame.The combination of two proposed techniques allows the reconstruction of a pixel-wise and unambiguous 3D geometry of dynamic scenes with strong noise using every four projected patterns.To the best of our knowledge,the presented techniques for the first time preserve the high anti-noise ability of a method based on the Gray code while overcoming the drawbacks of jump errors and low coding efficiency.Experiments have demonstrated that the proposed method can achieve robust,high efficiency 3D shape measurement of high speed dynamic scenes even polluted by strong noise.

Superfast and large-depth-range sinusoidal fringe generation for multi-dimensional information sensing

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)].