Digitizing translucent object appearance by validating computed optical properties.

The optical properties available for an object are most often fragmented and insufficient for photorealistic rendering of the object. We propose a procedure for digitizing a translucent object with sufficient information for predictive rendering of its appearance. Based on object material descriptions, we compute optical properties and validate or adjust this object appearance model based on comparison of simulation with spectrophotometric measurements of the bidirectional scattering-surface reflectance distribution function (BSSRDF). To ease this type of comparison, we provide an efficient simulation tool that computes the BSSRDF for a particular light-view configuration. Even with just a few configurations, the localized lighting in BSSRDF measurements is useful for assessing the appropriateness of computed or otherwise acquired optical properties. To validate an object appearance model in a more common lighting environment, we render the appearance of the obtained digital twin and assess the photorealism of our renderings through pixel-by-pixel comparison with photographs of the physical object.

Primary facility for traceable measurement of BSSRDF: erratum.

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.

Primary facility for traceable measurement of the BSSRDF.

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.