Brightness and sparkle appearance of goniochromatic samples

Abstract

n 2013 the European Metrology Research Program (EMRP) funded the research project, "Multidimensional Reflectometry for industry, xD-Reflect", to investigate the macroscopic optical properties related to visual appearance of modern surfaces and to develop and improve methodologies, tools and measurement devices able to provide a better description of material characteristics. One of the planned task developed several subjective tests on visual descriptors of gloss, sparkle, graininess, colour and their combined influences with reference to the measured values of reference samples. INRIM performed investigation on subjective descriptors of brightness and sparkle and their relationship with geometrical conditions of view, illuminating source characteristics, measured Radiometric Bidirectional Reflectance Distribution Function (BRDF), colorimetric attributes (CIE L*a*b*) and sparkles. This paper deals with the definition of subjective Brightness and Sparkle scales considering achromatic samples of goniochromatic materials, under LED and not LED lighting source. Key points of this study are the use of a soft metrology approach, with strong metrological characterization of the test behaviour (i.e.radiance and illuminance distribution, BRDF and sparkles of the samples), and the use of a large subject group (about 100 subject attended the test)

Graininess appearance of goniochromatic samples in lighting cabinets

“…Corn flakes shapes, with their sharp profile produce a larger spatial scattering of the reflected light that is more identified with brightness than graininess/sparkling. The two different performances of the lighting booths are coherent with those of a previous research on sparkling evaluation under LED and Fluorescent lighting made by the authors obviously considering directional light [13].…”