期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：2007
卷号：XXXVI-5/C53
出版社：Copernicus Publications
摘要：Measurements, optical simulations, samples realization of gilded surfaces were made for studying the visual appearance and the sub- strate color in.uence of gilded surfaces mainly encountered in sculpture. The presented study concerns the characterization of the extrinsic and intrinsic parameters useful for the optical simulation of the visual properties of the gilded surfaces. Thus, geometrical and optical data have been acquired. These measurements on several cross-sections give the characteristic thickness of a sample, very useful for the spectral simulations. The mean geometrical parameters are completed by laser profilometry measurements made on the prepared samples. We have obtained the optical characteristics of pure gold (bulk sample) and some alloys of gold by spectroscopic ellipsometry and obtained very detailed complex indices of refraction. It appeared that the gold-leaf were about 2μm thick. Such a thickness allows a fraction of the incident light to be transmitted through the gold-leaf and to reach the gold-size. That weak spectral transmissivity is then coupled with the scattering of the incident light due to the small cracks or holes appearing in the so mechanically fragile gold-leaf. Thus, fundamental mechanisms of light-matter interaction are simultaneously present as optical transmissivity by the metallic film, surface plasmons and very small holes, macroscopic holes and cracks. The spectrophotometric measurements also give access to a statistical estimation of the holes and diameters densities extracted from SEM or optical microscopy imaging. These quantitative in- formations are obtained by comparison between bulk and gold-leaf re.ectance factors at normal and oblique incidence. The computed images based on the measured optical properties on all the materials of the sculptures are obtained thanks to an adapted model from Cook-Torrance's one. As a side effect, a surface plasmon resonance contribution is added for understanding the spectral transmissivity through the gold leaf. The specular re.ection on the rough metallic interface is also enriched by the volume scattering originating in the pigmented layer made by the gold-size. That scattering contribution is modeled by the phenomenological Kubelka-Munk formulas. Then rendering is finally made with our spectral ray-tracer called Virtuelium(C ALLET and Z YMLA , 2006)
