Imaging Systems

Two-step triangular-pattern phase-shifting method for three-dimensional object-shape measurement

[+] Author Affiliations
Peirong Jia

University of Ottawa, Department of Mechanical Engineering, Ottawa, Ontario, Canada, K1N 6N5

Jonathan Kofman

University of Waterloo, Department of Systems Design Engineering, Waterloo, Ontario, Canada, N2L 3G1

Chad English

Neptec Design Group Ltd., 302 Legget Drive, Kanata, Ontario, Canada, K2K 1Y5

Opt. Eng. 46(8), 083201 (August 13, 2007). doi:10.1117/1.2768616
History: Received June 05, 2006; Revised February 05, 2007; Accepted February 12, 2007; Published August 13, 2007
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Existing phase-shifting measurement methods involve processing of three acquired images or computation of functions that require more complex processing than linear functions. This paper presents a novel two-step triangular-pattern phase-shifting method of 3-D object-shape measurement that combines advantages of earlier techniques. The method requires only two image-acquisition steps to capture two images, and involves projecting linear grayscale-intensity triangular patterns that require simpler computation of the intensity ratio than methods that use sinusoidal patterns. A triangular intensity-ratio distribution is computed from two captured phase-shifted triangular-pattern images. An intensity ratio-to-height conversion algorithm, based on traditional phase-to-height conversion in the sinusoidal-pattern phase-shifting method, is used to reconstruct the object 3-D surface geometry. A smaller pitch of the triangular pattern resulted in higher measurement accuracy; however, an optimal pitch was found, below which intensity-ratio unwrapping failure may occur. Measurement error varied cyclically with depth and may partly be due to projector gamma nonlinearity and image defocus. The use of only two linear triangular patterns in the proposed method has the advantage of less processing than current methods that process three images, or methods that process more complex functions than the intensity ratio. This would be useful for high speed or real-time 3-D object-shape measurement.

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© 2007 Society of Photo-Optical Instrumentation Engineers

Citation

Peirong Jia ; Jonathan Kofman and Chad English
"Two-step triangular-pattern phase-shifting method for three-dimensional object-shape measurement", Opt. Eng. 46(8), 083201 (August 13, 2007). ; http://dx.doi.org/10.1117/1.2768616


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