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Applied Optics

Applied Optics


  • Vol. 41, Iss. 17 — Jun. 10, 2002
  • pp: 3461–3468

Improved method for isochromatic demodulation by RGB calibration

Juan Antonio Quiroga, Ángel Garcı́a-Botella, and José Antonio Gómez-Pedrero  »View Author Affiliations

Applied Optics, Vol. 41, Issue 17, pp. 3461-3468 (2002)

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The red-blue-green (RGB) calibration technique consists in constructing an a priori calibration table of the isochromatic retardation versus the triplet of RGB values obtained with a RGB CCD camera. In this way a lookup table (LUT) is built in which the entry is the corresponding RGB triplet and the output is the given retardation. This calibration (a radiometric quantity) depends on the geometric and chromatic parameters of the setup. Once the calibration is performed, the isochromatic retardation at a given point of the sample is computed as the one that minimizes the Euclidean distance between the measured RGB triplet and the triplets stored in the LUT. We present an enhanced RGB calibration algorithm for isochromatic fringe pattern demodulation. We have improved the standard demodulation algorithm used in RGB calibration by changing the Euclidean cost function to a regularized one in which the fidelity term corresponds to the Euclidean distance between RGB triplets; the regularizing term forces piecewise continuity for the isochromatic retardation. Additionally we have implemented a selective search in the RGB calibration LUT. We have tested the algorithm with simulated as well as real photoelastic data with good results.

© 2002 Optical Society of America

OCIS Codes
(100.2000) Image processing : Digital image processing
(120.4290) Instrumentation, measurement, and metrology : Nondestructive testing
(120.5630) Instrumentation, measurement, and metrology : Radiometry

Original Manuscript: September 5, 2001
Revised Manuscript: February 4, 2002
Published: June 10, 2002

Juan Antonio Quiroga, Ángel Garcı́a-Botella, and José Antonio Gómez-Pedrero, "Improved method for isochromatic demodulation by RGB calibration," Appl. Opt. 41, 3461-3468 (2002)

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