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Volume: 33 | Article ID: art00006
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Study and simulations of speckle effects on BRDF measurements at very high angular resolution
  DOI :  10.2352/ISSN.2470-1173.2021.5.MAAP-140  Published OnlineJanuary 2021
Abstract

Goniospectrophotometer ConDOR designed by CNAM, France, measures BRDF at very high angular resolution (0.014°), comparable to that of human vision. This is achieved using a very collimated light beam and a dedicated Fourier lens. Interestingly, the BRDF of glossy surfaces measured at this resolution exhibits a granular aspect around the specular direction, like a rapid angular fluctuation, which is not detection noise as it is repeatable between successive measurements on the same sample. Based on our experiments using ConDOR as well as numerical simulations, we claim that this granular aspect comes from an optical effect called speckle, which occurs every time a sufficiently coherent light beam — which is inevitably the case when the incident solid angle is very narrow — strikes a rough surface. First elements of confirmation are given in this paper.

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Thomas Labardens, Pierre Chavel, Yvan Sortais, Mathieu Hébert, Lionel Simonot, Ana Rabal, Gaël Obein, "Study and simulations of speckle effects on BRDF measurements at very high angular resolutionin Proc. IS&T Int’l. Symp. on Electronic Imaging: Material Appearance,  2021,  pp 140-1 - 140-7,  https://doi.org/10.2352/ISSN.2470-1173.2021.5.MAAP-140

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