An innovative object-centred approach for the visual inspection of textured
ceramic tiles has been developed for the acquisition of product quality co
ntrol data. A demonstrator system has been constructed for the analysis of
complex surfaces, surfaces which possess detailed three-dimensional topogra
phic features, which are concealed by coincident regular or random chromati
c patterns. The technique is able to isolate mixed topographic and chromati
c surface features in order to allow for subsequent separate analysis. Surf
ace topography is captured as an array of perturbed surface normals, known
as a surface bump map, while the surface reflectance is isolated as a separ
ate albedo image. Synthetically rendered images of the bump map description
allow surface topography to be viewed off-line under user defined virtual
illumination conditions, and in isolation from the surface albedo. Topograp
hic features defined by the bump map description may be subject to analysis
in terms of perturbation thresholding, or integrated to recover their thre
e-dimensional relief. The technique has application for the quality inspect
ion of a wide range of manufactured and processed surfaces, uses a low-cost
fixed lighting configuration, requires no initial training, is largely pos
e invariant, and has been tested on a representative range of real tile sam
ples. Experimental results are presented in the paper. (C) 2000 Elsevier Sc
ience B.V. All rights reserved.