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Proceedings Paper

Extended dynamic range imaging in shearography
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Paper Abstract

Extended dynamic range (EDR) imaging is a post-processing technique commonly associated with photography. A set of images of the same scene which are recorded by the camera using different shutter settings are integrated into a single higher dynamic range image. Image processing software is used to identify pixels in the image which are correctly exposed, underexposed or overexposed and pixels with the optimum intensity are rescaled with respect to their exposure time and fused to form the EDR image. An intensity rescaling processing is then required as the EDR images generated generally exceed the contrast ratio of conventional displays and printers. In optical metrology, speckle interferometry and holography techniques require a well-modulated intensity signal to extract the phase information and of these techniques, shearography is most sensitive to different object surface reflectivities as it uses self-referencing from a sheared image. In this paper the authors demonstrate real-time EDR imaging in shearography extending an 8-bit camera to 16-bits. Experimental results from a difficult surface reflectivity sample, a wooden panel painting containing gold and dark earth colour paint, are presented. A pre-processing step that could be incorporated in the image capture routine was identified and implemented. This allowed the existing library of 8-bit image processing routines to be used without modification.

Paper Details

Date Published: 25 April 2008
PDF: 8 pages
Proc. SPIE 7000, Optical and Digital Image Processing, 700010 (25 April 2008); doi: 10.1117/12.781949
Show Author Affiliations
Roger M. Groves, Univ. Stuttgart (Germany)
Giancarlo Pedrini, Univ. Stuttgart (Germany)
Wolfgang Osten, Univ. Stuttgart (Germany)

Published in SPIE Proceedings Vol. 7000:
Optical and Digital Image Processing
Peter Schelkens; Touradj Ebrahimi; Gabriel Cristóbal; Frédéric Truchetet, Editor(s)

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