"Optimal pulse width modulation for sinusoidal fringe generation with projector defocusing," Opt. Lett., (2010)

[27] Y. Wang* and S. Zhang, " Optimal pulse width modulation for sinusoidal fringe generation with projector defocusing," Opt. Lett.,  35(24), 4121-4123, 2010; doi: 10.1364/OL.35.004121

Recently, a study showed that generating sinusoidal fringe patterns by properly defocusing binary ones can significantly simplify three-dimensional shape measurement system development and drastically improve its speed. However, when the fringe stripes are very wide, it is very difficult for this technique to achieve high-quality measurement. This Letter presents a method to improve this technique by selectively eliminating high-frequency harmonics induced by a squared binary pattern. As a result, better sinusoidal fringe patterns can be generated with a small degree of defocusing even for wide fringe stripes. Simulation and experiments will be presented to verify the performance of this proposed technique. 

"Ultrafast 3-D shape measurement with an off-the-shelf DLP projector," Opt. Express, (2010)

[26] Y. Gong* and S. Zhang, "Ultrafast 3-D shape measurement with an off-the-shelf DLP projector," Opt. Express 18(19), 19743-19754, 2010 (Cover Feature); doi: 10.1364/OE.18.019743

This paper presents a technique that reaches 3-D shape measurement speed beyond the digital-light-processing (DLP) projector’s projection speed. In particular, a “solid-state” binary structured pattern is generated with each micro-mirror pixel always being at one status (ON or OFF). By this means, any time segment of projection can represent the whole signal, thus the exposure time can be shorter than the projection time. A sinusoidal fringe pattern is generated by properly defocusing a binary one, and the Fourier fringe analysis means is used for 3-D shape recovery. We have successfully reached 4,000 Hz rate (80 μs exposure time) 3-D shape measurement speed with an off-the-shelf DLP projector

"Composite phase-shifting algorithm for 3-D shape compression," Opt. Eng.. (2010)

[24] N Karpinsky* and S Zhang, "Composite phase-shifting algorithm for 3-D shape compression," Opt. Eng. 49(6), 063604, 2010; doi:10.1117/1.3456632 

With recent advancements in 3-D imaging and computational technologies, acquiring 3-D data is unprecedentedly simple. However, the use of 3-D data is still limited due to the size of 3-D data, especially 3-D video data. Therefore, the study of how to store and transmit the 3-D data in real time is vital. We address a technique that encodes a 3-D surface shape into a single 24-bit color image. In particular, this image is generated by advanced computer graphics tools with two primary color channels encoded as sine and cosine fringe images, and the third channel encoded as a stair image to unwrap the phase obtained from the two fringe images. An arbitrary 3-D shape can then be recovered from a single image. We test 3-D shapes with differing levels of complexity along with various image formats. Experiments demonstrate that, without significantly losing the shape quality, the compression ratio can go up to 1:36.86, compared with the native smallest possible 3-D data representation method.

"Superfast phase-shifting method for 3-D shape measurement," Opt. Express, (2010)

[25] S. Zhang, D. van der Weide, and J. Oliver "Superfast phase-shifting method for 3-D shape measurement," Opt. Express18(9), 9684-9689, 2010. (Selected for July 6, 2010 issue of The Virtual Journal for Biomedical Optics); doi: 10.1364/OE.18.009684

Recently introduced DLP Discovery technology allows for tens of kHz binary image switching, which has great potential for superfast 3-D shape measurement. This paper presents a system that realizes 3-D shape measurement by using a DLP Discovery technology to switch binary structured patterns at very high frame rates. The sinusoidal fringe patterns are generated by properly defocusing the projector. Combining this approach with a phase-shifting method, we achieve an unprecedented rate for 3-D shape measurement: 667 Hz. This technology can be applied to numerous applications including medical science, biometrics, and entertainment.

"Flexible 3-D shape measurement using projector defocusing: extended measurement range," Opt. Lett., (2010)

[23] S. Zhang, "Flexible 3-D shape measurement using projector defocusing: extended measurement range," Opt. Lett. 35(7), 931-933, 2010 (Cover Feature); doi: 10.1364/OL.35.000934

A recently proposed flexible 3D shape measurement technique using a defocused projector [Opt. Lett. 34, 3080 (2009)] shows great potential because of its elimination of projector’s gamma calibration. However, it cannot handle step-height surfaces. I present here a technique to extend its measurement range to an arbitrary shape by integrating a binary coding method. A computational framework is also proposed to tackle the problems related to the defocusing.

"Recent progresses on real-time 3-D shape measurement using digital fringe projection techniques," Opt. Laser Eng., (2010)

[21] S. Zhang, "Recent progresses on real-time 3-D shape measurement using digital fringe projection techniques," Opt. Laser Eng., 48, 149-158, 2010 (Invited). (#2 most cited papers in the past five years 2006-2011, 2007-2012, 2008-2013; #1 most downloaded paper October-December, 2009; January-March, 2010; April-June, 2012; July-September, 2012; January - December 2012 Full Year; January-March, 2013; July-September 2013); doi: 10.1016/j.optlaseng.2009.03.008

Over the past few years, we have been developing techniques for high-speed 3D shape measurement using digital fringe projection and phase-shifting techniques: various algorithms have been developed to improve the phase computation speed, parallel programming has been employed to further increase the processing speed, and advanced hardware technologies have been adopted to boost the speed of coordinate calculations and 3D geometry rendering. We have successfully achieved simultaneous 3D absolute shape acquisition, reconstruction, and display at a speed of 30 frames/s with 300 K points per frame. This paper presents the principles of the real-time 3D shape measurement techniques that we developed, summarizes the most recent progresses that have been made in this field, and discusses the challenges for advancing this technology further.

"Digital sinusoidal fringe generation: defocusing binary patterns VS focusing sinusoidal patterns," Opt. Laser, (2010)

[22] S. Lei* and S. Zhang, "Digital sinusoidal fringe generation: defocusing binary patterns VS focusing sinusoidal patterns,"Opt. Laser Eng. 48, 561-569, 2010; doi: 10.1016/j.optlaseng.2009.12.002

There are two approaches to generate sinusoidal fringe patterns with a digital-light-processing (DLP) projector: defocusing binary patterns (DBP), and focusing sinusoidal patterns (FSP). This paper will compare the potential errors for both methods induced by the following factors: (1) degree of defocusing, (2) exposure time, (3) synchronization, and (4) projector’s nonlinear gamma. Experiments show that in most scenarios, the error for the DBP method is smaller than that of the FSP method. Therefore, generating a sinusoidal fringe image using a DBP method seems to be appealing.