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Proceedings Paper

Industrial surface inspection by wavelet analysis
Author(s): Thomas Kreis; Lars Rosenboom; Werner Jüptner
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Paper Abstract

Wavelet analysis is a processing method for the description of single- or multi-dimensional signals in multiple scales and therefore well suited for describing technical surfaces with variable resolution. Here optically measured height data of technical surfaces are wavelet-transformed along two dimensions with two different objectives: One is the representation with only a few coefficients in the sense of an efficient data compression, the other is the reliable detection of defects, which can be regarded as a pattern recognition task. A systematic comparison of various wavelet families results in the choice of the biorthogonal pseudo-coiflets for representing the surfaces, and differentiating wavelets like Burt-Adelson-wavelet or short-range Daubechies-wavelets for solving the defect detection problem. It is shown that the representation can be improved by not using the most significant wavelet-values - which can be interpreted as low-pass filtered coefficients, but to maintain those with the largest weights. Thus the variance between the original surface and that reconstructed from the representation data is minimized by a factor up to 4. Defect detection is best performed with separate transformation in two orthogonal directions with subsequent superposition. The procedures obtained here are applied to surfaces like a coin-surface, a copper-mirror surface, and a lacquered surface.

Paper Details

Date Published: 27 May 2011
PDF: 8 pages
Proc. SPIE 8082, Optical Measurement Systems for Industrial Inspection VII, 808234 (27 May 2011); doi: 10.1117/12.889112
Show Author Affiliations
Thomas Kreis, Bremer Institut für angewandte Strahltechnik GmbH (Germany)
Lars Rosenboom, Bremer Institut für angewandte Strahltechnik GmbH (Germany)
Werner Jüptner, Bremer Institut für angewandte Strahltechnik GmbH (Germany)

Published in SPIE Proceedings Vol. 8082:
Optical Measurement Systems for Industrial Inspection VII
Peter H. Lehmann; Wolfgang Osten; Kay Gastinger, Editor(s)

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