Traceable determination of the Sparkle and Graininess measurands and first-time generation of related measurements scales

In the finalized project BiRD JRP 16NRM08 (https://www.birdproject.eu), funded by the EU program EURAMET EMPIR Call 2016 – „Metrology Research for Pre‐ and Co‐normative projects“, basic research was carried out on such measurands which determine the appearance of products. These are, amongst color and its angle-dependent distribution also gloss, sparkle, and graininess. The term sparkle describes the specific appearance of surfaces which can be observed under directed illumination by reflection of point-like scattering centers and is similar to the appearance of sparkling stars in the night-sky. This effect is generated e.g. by high-reflective microparticles, which are embedded in the lacquer coat of a surface. Well-known examples are metallic automobile coatings. Graininess describes the appearance of such surfaces when illuminated diffusely [1]. Although the sparkle-effect is widely applied in industrial production, there is no standardized and commonly accepted definition of the related measurand. Few commercial systems generate device-dependent quantities by using non-disclosed evaluation procedures. To improve this situation, within the course of the BiRD-project the technical working group CIE JTC 12 [2] was founded, in which measurands for sparkle and graininess and measurement procedures to determine them were defined. Based on these provisions a comparison between four national metrology institutes was carried out, in which the technical realizations and the appropriateness of the measurand’s definition were tested [3]. Despite some variability in measurement apparatus’ very satisfactory results were gained in the objective determination of the sparkle measurands. The same holds true for sphere-based determinations of graininess. Using results from also conducted psycho-visual experiments on the same samples, it was possible to compare the visual appearance with the objective results [4]. The excellent correlation shows that appropriate measurands were selected. Therefore, for the first time, traceable measurements are presented and corresponding sparkle- and graininess-scales are available, which will serve as a basis for further investigations and standardization work.


Contact:

WG 4.51 Reflection and Transmission    
A. Schirmacher,     Alfred.Schirmacher@ptb.de
T. Quast,     Tatjana.Quast@ptb.de


[1]    Effektpigmente: Eine Herausforderung für die optische Messtechnik, Egbert Buhr,     Alfred Schirmacher, Andreas Höpe, in: Das Jahr des Lichts, PTB Mitteilungen 125,     Heft 4, 39 - 44 (2015)

[2]    CIE JTC 12 (D2/D1/D8) „The measurement of sparkle and graininess “ ,     (http://cie.co.at)

[3]    An insight into the present capabilities of national metrology institutes for measuring sparkle, A. Ferrero, N. Basic, J. Campos, M. Pastuschek, E. Perales, G. Porrovecchio, M. Smid, A. Schirmacher, J.L. Velázquez, F.M. Martínez-Verdú, 2020 Metrologia 57 065029, doi.org/10.1088/1681-7575/abb0a3

[4]    Preliminary measurement scales for sparkle and graininess, A. Ferrero, E. Perales, N. Basic, M. Pastuschek, G. Porrovecchio, A. Schirmacher, J.L. Velázquez, J. Campos, F.M. Martínez-Verdú, M. Smid, P. Linduska, T. Dauser, and P. Blattner, Optics Express 7589, Vol. 29, No. 5 / 1 March 2021, doi.org/10.1364/OE.411953