Please use this identifier to cite or link to this item: http://hdl.handle.net/1822/48273

TitleExploring combined dark and bright field illumination to improve the detection of defects on specular surfaces
Author(s)Forte, Paulo M. F.
Felgueiras, Paulo Eduardo Reis
Ferreira, Flávio Pedro Gonçalves Fernandes
Sousa, M. A.
Pereira, Eduardo J. Nunes
Bret, Boris P. J.
Belsley, M.
KeywordsDefect detection
Specular surfaces
Automatic optical inspection
Bright-field illumination
Dark-field illumination
Structured light
Issue date1-Jan-2017
PublisherElsevier
JournalOptics and Lasers in Engineering
Abstract(s)An automatic optical inspection system for detecting local defects on specular surfaces is presented. The system uses an image display to produce a sequence of structured diffuse illumination patterns and a digital camera to acquire the corresponding sequence of images. An image enhancement algorithm, which measures the local intensity variations between bright- and dark-field illumination conditions, yields a final image in which the defects are revealed with a high contrast. Subsequently, an image segmentation algorithm, which compares statistically the enhanced image of the inspected surface with the corresponding image for a defect-free template, allows separating defects from non-defects with an adjusting decision threshold. The method can be applied to shiny surfaces of any material including metal, plastic and glass. The described method was tested on the plastic surface of a car dashboard system. We were able to detect not only scratches but also dust and fingerprints. In our experiment we observed a detection contrast increase from about 40%, when using an extended light source, to more than 90% when using a structured light source. The presented method is simple, robust and can be carried out with short cycle times, making it appropriate for applications in industrial environments. (C) 2016 Elsevier Ltd. All rights reserved.
TypeArticle
URIhttp://hdl.handle.net/1822/48273
DOI10.1016/j.optlaseng.2016.08.002
ISSN0143-8166
Peer-Reviewedyes
AccessRestricted access (UMinho)
Appears in Collections:CDF - FAMO - Artigos/Papers (with refereeing)

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