Profilometry of discontinuous solids by means of co-phased demodulation of projected fringes with RGB encoding

J. M. Padilla; M. Servin; G. Garnica

doi:10.1117/12.2184821

21 June 2015 Profilometry of discontinuous solids by means of co-phased demodulation of projected fringes with RGB encoding

J. M. Padilla, M. Servin, G. Garnica

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Proceedings Volume 9528, Videometrics, Range Imaging, and Applications XIII; 95280A (2015) https://doi.org/10.1117/12.2184821
Event: SPIE Optical Metrology, 2015, Munich, Germany

Abstract

Here we describe a 2-projectors and 1-camera setup for profilometry of discontinuous solids by means of co-phased demodulation of projected fringes and red, green, and blue (RGB) multichannel operation. The dual projection configuration for this profilometer is proposed to solve efficiently specular regions and self-occluding shadows due to discontinuities, which are the main drawbacks for a 1-projector 1-camera configuration. This is because the regions where shadows and specular reflections are generated, and the fringe contrast drops to zero, are in general different for each projection direction; thus, the resulting fringe patterns will have complementary phase information. Multichannel RGB operation allows us to work simultaneously with both projectors and to record independently the complementary fringe patterns phase-modulated by the 3D profile of the object under study. In other words, color encoding/decoding reduces the acquisition time respect to one-at-a-time grayscale operation and, in principle, enables the study of dynamic phenomena. The co-phased demodulation method implemented in this work benefits from the complex (analytic) nature of the output signals estimated with most phase demodulation methods (such as the Fourier method, and temporal phaseshifting algorithms). This allowed us to straightforwardly generate a single phase-map well-defined for the entire area of interest. Finally we assessed our proposed profilometry setup by measuring a fractured spherical cap made of (uncoated) expanded polystyrene. The results were satisfactory but in the authors’ opinion this must be considered a preliminary report.

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J. M. Padilla, M. Servin, and G. Garnica "Profilometry of discontinuous solids by means of co-phased demodulation of projected fringes with RGB encoding", Proc. SPIE 9528, Videometrics, Range Imaging, and Applications XIII, 95280A (21 June 2015); https://doi.org/10.1117/12.2184821

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KEYWORDS

Demodulation

RGB color model

Fringe analysis

Modulation

Profilometers

Solids

Projection systems

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