The bidirectional scattering-surface reflectance distribution function (BSSRDF) is the function that describes the variation of the radiance of the elementary areas of a surface with respect to the ...directionally incident radiant flux on that surface. Measurements of the BSSRDF are important for characterizing the translucency of objects and for obtaining those optical parameters affecting volume scattering. However, to date, no traceable measurements of this function are available, since, likely due to its technical complexity, no standard measurement procedure has been established. We have developed a primary facility for measuring the BSSRDF based on a gonio-spectrophotometer with spatial resolution in the collection, spectral resolution in the irradiation, and angular resolution both for irradiation and collection directions. The BSSRDF of twelve homogeneous and translucent samples (with controlled values for the mean diameter of the scattering particles and their concentration) have been measured with relative uncertainties below 3% inside the irradiated area. Some results are shown and commented. This primary facility will allow the BSSRDF scale to be transferred to other instruments.
Abstract
The bidirectional scattering-surface reflectance distribution function (BSSRDF) describes the radiance originated by the volume scattering and the surface reflectance of any position on the ...surface of a sample, when it is directionally irradiated at any other position. The present state of the technology for appearance rendering requires a more detailed physical description of translucent objects by traceable measurements of the BSSRDF. This work presents two primary facilities developed for traceable BSSRDF measurements by different measuring approaches. Their results on the same translucent samples have been compared and the achieved BSSRDF scale has been transferred to a commercial measuring system. This study highlights the problems of the different measuring instrument designs and provides the scientific community with more knowledge on the measurement of the BSSRDF, which will be crucial for future works on material appearance.
Abstract In recent years, a growing demand for the capability of performing accurate measurements of the bidirectional transmittance distribution function (BTDF) has been observed in industry, ...research and development, and aerospace applications. However, there exists no calibration and measurement capabilities-entry for BTDF in the database of the Bureau International des Poids et Mesures and to date no BTDF comparison has been conducted between different national metrology institutes (NMIs) or designated institutes (DIs). As a first step to a possible future key comparison and to test the existing capabilities of determining this measurand, two interlaboratory comparisons were performed. In comparison one, five samples of three different types of optical transmissive diffusers were measured by five NMIs and one DI. By specific sample choice, the focus for this study lay more on orientation-dependent scatter properties. In comparison two, where one NMI, one DI, one university, and three industrial partners investigated their measurement capabilities, the dependence on the orientation was not assessed, but two additional samples of the same material and different thickness were measured. Results of the two comparisons are presented, giving a good overview of existing experimental solutions, and showing specific sample-related problems to be solved for improved future BTDF measurements.
An erratum is presented to correct the measurement equation used for the calculation of the BSSRDF in our manuscript Opt. Express29 (21), 34175 (2021)10.1364/OE.439108. This correction affects ...slightly the results showed in Figs. 7 and 8 of the primary manuscript, so they are replaced by Fig. S1 and Fig. S2, respectively, of the current erratum. The discussion on the results of Fig. 7 of the primary manuscript is completely valid also for the new results, but a slightly different discussion is given on the new results showed in Fig. S2. Nevertheless, the conclusions of the original manuscript are not affected at all.
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