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REFERENCES A shikhmin , M. and S hirley , P. 2000. An anisotropic phong brdf model. J. Graph. Tools 5, 2 (Feb.), 25–32. C ook , R. L. and T orrance , K. E. 1982. A reflectance model for computer graphics. ACM Trans. Graph. 1, 1, 7–24. Ď urikovič , R., K olchin , K., and E rshov , S. 2002. Rendering of japanese artcraft. In Short Presentations of EUROGRAPHICS Conference . Braunschweig, Germany, 131–138. M atusik , W., P fister , H., B rand , M., and M c M illan , L. 2003. A data-driven reflectance model. In SIGGRAPH ’03: ACM SIGGRAPH 2003 Papers

Abstract

Measurement of the appearance of an object consists of a group of measurements to characterize the color and surface finish of the object. This group of measurements involves the spectral energy distribution of propagated light measured in terms of reflectance and transmittance, and the spatial energy distribution of that light measured in terms of the bidirectional reflectance distribution function (BRDF). In this article we present the virtual gonio-spectrophotometer, a device that measures flux (power) as a function of illumination and observation. Virtual gonio-spectrophotometer measurements allow the determination of the scattering profile of specimens that can be used to verify the physical characteristics of the computer model used to simulate the scattering profile. Among the characteristics that we verify is the energy conservation of the computer model. A virtual gonio-spectrophotometer is utilized to find the correspondence between industrial measurements obtained from gloss meters and the parameters of a computer reflectance model.

References ACHUTHA, S. 2006. Brdf acquisition with basis illumination. M.S. thesis, Department of Computer Science, University of British Columbia, Vancouver, Canada. ASHIKHMIN, M. AND SHIRLEY, P. 2000. An anisotropic phong BRDF model. J. Graph. Tools 5, 2 (Feb.), 25-32. BAGHER, MAHDI, M., SOLER, C., AND HOLZSCHUCH, N. 2012. Accurate fitting of measured reflectances using a Shifted Gamma micro-facet distribution. Computer Graphics Forum 31, 4 (June). BJORCK, A. 1996. Numerical Methods for Least Squares Problems, 1 ed. SIAM: Society for Industrial and Applied

reenberg , D. P. 2001. A psychophysically-based model of surface gloss perception. In Proceedings SPIE Human Vision and Electronic Imaging ’01 . 291–301. M atusik , W., P fister , H., B rand , M., and M c M illan , L. 2003. A data-driven reflectance model. In SIGGRAPH ’03: ACM SIGGRAPH 2003 Papers . ACM, New York, NY, USA, 759–769. M ihálik , A. and Ď urikovič , R. 2011. Virtual gonio-spectrophotometer for validation of BRDF designs. Central European Journal of Physics 9 , 1334–1343. W estlund , H. B. and M eyer , G. W. 2001. Applying appearance standards to

Abstract

In industry, manual visual inspection is typically applied to assess surface imperfections on basic optical elements according to the standard DIN ISO 14997. This article proposes a machine vision setup to mimic the human tester's inspection process. It consists of multiple cameras and LED light sources. Both are arranged on the surface of a hemisphere with the optical element to be inspected at its center. By enabling individual LED sources on the hemisphere, any movement during acquisition can be omitted. Thus, the system is capable of acquiring a sparse pseudo BRDF (Bidirectional Reflectance Distribution Function) representation of imperfections. It is shown by experiments that this representation allows to discriminate between certain imperfections. Besides the mechanical setup, the image processing methodology and classification results are discussed. A comparison to results from manual inspection for 20 optical elements of the same geometry is also presented. Results indicate that a good agreement with the de-facto standard manual inspection method from industry can be obtained by the system.

and Editing”, Acm. T. Graphic., Vol. 25, (2006), pp. 735–745. http://dx.doi.org/10.1145/1141911.1141949 [13] S.R. Marschner: Inverse Rendering for Computer Graphics, Thesis (PhD), Cornell University, 1998. [14] W. Matusik, H. Pfister, M. Brand and L. McMillan: “A Datadriven Reflectance Model”, Acm. T. Graphic., Vol. 22, (2003), pp. 759–769. http://dx.doi.org/10.1145/882262.882343 [15] A. Ngan, F. Durand and W. Matusik: “Experimental Validation of Analytical BRDF Models”, In: ACM SIGGRAPH — Sketches and Applications, ACM Press, 2004, pp. 129–138. [16] G. Rosler

Abstract

Lack of training data is one of the main problems when realizing optical surface inspection systems. In the best case, provision of enough representative training samples is difficult and most of the time expensive. In some cases, it is not possible at all. Here we present an alternative method where the surface defects are simulated. Thereby, we focus on metal surfaces in the microscale where diffraction phenomena start to play a major role. Ray tracing and scalar diffraction approximation methods are applied and compared.