"Autoexposure for three-dimensional shape measurement with a digital-light-processing projector," Opt. Eng. (2011)

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L. Ekstrand* and S. Zhang, "Autoexposure for three-dimensional shape measurement with a digital-light-processing projector," Opt. Eng. 50(12) 123603, 2011; doi: 10.1117/1.3662387

Automatically adapting the camera exposure time is crucial for industrial applications where minimum human intervention is usually desirable. However, it is very challenging to realize such a capability for a conventional fringe projection system where only a finite increment of the exposure time is allowed due to its digital fringe generation nature. We study the generation of sinusoidal fringe patterns by properly defocusing binary ones, which permits the use of an arbitrary exposure time. This provides the potential to adapt the exposure time automatically. We present the principle of an automatic exposure technique and show some experimental results.

"Three-dimensional profilometry with nearly focused binary phase-shifting algorithms," Opt. Lett. (2011)

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L. Ekstrand* and S. Zhang, "Three-dimensional profilometry with nearly focused binary phase-shifting algorithms," Opt. Lett. 36(23) 4518-4520, 2011  (Cover feature); doi: 10.1364/OL.36.004518

This Letter investigates the effects of different phase-shifting algorithms on the quality of high-resolution three-dimensional (3-D) profilometry produced with nearly focused binary patterns. From theoretical analyses, simulations, and experiments, we found that the nine-step phase-shifting algorithm produces accurate 3-D measurements at high speed without the limited depth range and calibration difficulties that typically plague binary defocusing methods. We also found that the use of more fringe patterns does not necessarily enhance measurement quality.

"Optimal pulse width modulation for sinusoidal fringe generation with projector defocusing: Reply to comments," Opt. Lett. (2011)

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Y. Wang* and S. Zhang, "Optimal pulse width modulation for sinusoidal fringe generation with projector defocusing: Reply to comments," Opt. Lett. 36(6), 809-809, 2011; doi: 10.1364/OL.36.000809

We found that there were some inaccurate comments in the Comment by Ayubi and Ferrari.

"3D shape measurement technique for multiple rapidly moving objects," Opt. Express, (2011)

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Y. Wang*, S. Zhang, and J. H. Oliver, "3D shape measurement technique for multiple rapidly moving objects," Opt. Express,  19(9), 8539-8545, 2011; doi: 10.1364/OE.19.008539

Recently proposed binary defocusing techniques have led to ultrafast speed 3D shape measurement, but they are generally limited to measurement of a single object at a time. Introducing additional gray coded patterns for point-by-point phase unwrapping could permit simultaneous multiple-object measurement. However, when the objects are moving rapidly, the displacement between the first captured pattern and the last can be significant, and pose challenges related to the precisely designed gray codes. This paper presents a new phase unwrapping strategy that combines the conventional spatial phase unwrapping with the gray code to resolve motion related phase unwrapping problems. A system with a speed of 5,000 Hz was developed to verify the performance of the proposed technique.

High-resolution, high-speed three-dimensional shape measurement using projector defocusing," Opt. Eng., 2011

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[28] Y. Gong* and S. Zhang, "High-resolution, high-speed three-dimensional shape measurement using projector defocusing," Opt. Eng., 50(2), 023603, 2011; doi: 10.1117/1.3534798

We present a high-resolution, high-speed three-dimensional (3-D) shape measurement technique that can reach the speed limit of a digital fringe projection system without significantly increasing the system cost. Instead of generating sinusoidal fringe patterns by a computer directly, they are produced by defocusing binary ones. By this means,with a relatively inexpensive camera, the 3-D shape measurement system can double the previously maximum achievable speed and reach the refreshing rate of a digital-light-processing projector: 120

"High-resolution three-dimensional profilometry with binary phase-shifting methods," Appl. Opt., (2011)

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S. Zhang, "High-resolution three-dimensional profilometry with binary phase-shifting methods," Appl. Opt., 50(12), 1753-1757, 2011; doi: 10.1364/AO.50.001753

This paper presents a novel pixel-level resolution 3D profilometry technique that only needs binary phase-shifted structured patterns. This technique uses four sets of three phase-shifted binary patterns to achieve the phase error of less than 0.2%, and only requires two sets to reach similar quality if the projector is slightly defocused. Theoretical analysis, simulations, and experiments will be presented to verify the performance of the proposed technique.

"Superfast multifrequency phase-shifting technique with optimal pulse width modulation," Opt. Express, (2011)

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Y. Wang* and S. Zhang, "Superfast multifrequency phase-shifting technique with optimal pulse width modulation," Opt. Express, 19(6), 5143-5148, 2011(Image of the week of March 21, 2011, OSA Optics InfoBase); doi: 10.1364/OE.19.005149

The technique of generating sinusoidal fringe patterns by defocusing squared binary structured ones has numerous merits for high-speed three-dimensional (3D) shape measurement. However, it is challenging for this method to realize a multifrequency phase-shifting (MFPS) algorithm because it is difficult to simultaneously generate high-quality sinusoidal fringe patterns with different periods. This paper proposes to realize an MFPS algorithm utilizing an optimal pulse width modulation (OPWM) technique that can selectively eliminate high-order harmonics of squared binary patterns. We successfully develop a 556 Hz system utilizing a three-frequency algorithm for simultaneously measuring multiple objects.