Share Email Print
cover

Proceedings Paper

Phase unwrapping for flaw detection: is it necessary?
Author(s): Benjamin A. Bard
Format Member Price Non-Member Price
PDF $14.40 $18.00
cover GOOD NEWS! Your organization subscribes to the SPIE Digital Library. You may be able to download this paper for free. Check Access

Paper Abstract

The phase-stepping technique is becoming a common enhancement to digital shearography and holography systems used in NDE. Capturing a series of phase-stepped images, rather than just a pair, allows the calculation of surface deformation at every pixel; data from a equispaced, spatially dense set rather than a sparse collection of nonuniformly spaced points. Phase maps are calculated modulo 2(pi) . If surface deformations are of sufficiently high amplitude, the phase will appear 'wrapped'. The next logical step is to 'unwrap' the phase and make it continuous again. For flaw detection purposes, however, this difficult step should be questioned; it is sometimes not only unnecessary, but deleterious to the flaw detection process. Further image processing steps must sometimes be applied to the unwrapped phase in order to expose flaws once readily visible in the wrapped phase map. These steps, only applicable to an unwrapped phase map, can also serve to uncover some flaws not previously visible in the wrapped phase map. Finally, effective data visualization plays an important role in conveying information role in conveying information embedded in the wrapped phase map. Finally, effective data visualization plays an important role in conveying information embedded in the wrapped or unwrapped phase maps. This paper introduces these issues and gives several examples, wrapped and unwrapped, with varying excitation type, material, flaw type, and image processing.

Paper Details

Date Published: 31 March 1998
PDF: 11 pages
Proc. SPIE 3397, Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware II, (31 March 1998); doi: 10.1117/12.305048
Show Author Affiliations
Benjamin A. Bard, The Pennsylvania State Univ. (United States)


Published in SPIE Proceedings Vol. 3397:
Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware II
Glenn A. Geithman; Gary E. Georgeson, Editor(s)

© SPIE. Terms of Use
Back to Top