Design of a gonio-spectro-photometer for optical characterization of gonio-apparent materials

Abstract

Gonio-apparent surfaces, characterized by large variations in optical properties with small variations in detection or illuminating directions, have a huge appeal for industrial product for aesthetic reasons. This work is dedicated to the design of a gonio-spectrophotometer (OptiMines goniometer) adequate for analyzing the light reflecting behavior of these challenging surface aspects. Such optical characterizations are useful data for realistic rendering of such surfaces in computer graphics but also for new product development and quality control in industrial manufacturing. To reach the four degrees of freedom necessary to cover the entire reflecting hemisphere, the designed geometrical setup favors movements of the sample so that illuminating and detection arms only carry one degree of freedom each. Having only one degree of freedom on each optical arm enables an easy installation of precise optical systems that leads to a very high directional accuracy for small arm dimensions. High directional accuracy is essential for fine analysis of gonio-apparent surfaces in order to prevent signal averaging with out-of-direction beam, in particular when the property change is abrupt. The analysis of both diffuse and gonio-apparent materials demonstrates the performance in surface metrology provided by this new device.

Characterization of the gonioapparent character of colored anodized titanium surfaces

“…The BRDF measurements are performed in two steps: the first one consists of a direct measurement of the light flux F source of the source, and the second one consists of a measurement of the light flux F sample reflected by the observed sample. The experimental expression of the BRDF is then given by the following equation 13 :…”

“…It relies on a goniospectrophotometer specifically designed to investigate gonioapparent and specular surfaces. 13 In this work, we performed angular-dependent color characterizations of anodized titanium samples, with three different surface finishes from "as received" (denoted "rough" in the following) to mirror polished. In the following sections, we will first describe the anodizing process and the different surface properties.…”

Global color estimation of special-effect coatings from measurements by commercially available portable multiangle spectrophotometers

“…To completely characterize the color of these coatings under any illuminant and for any illumination/viewing geometry, the spectral bidirectional reflectance distribution function (BRDF) [4] has to be measured at adequate measurement geometries to provide all information required to determine the variation of the spectral reflectance with respect to the geometry. Some sophisticated instruments to measure the spectral BRDF in an almost unlimited number of in-and out-of-plane geometries have been recently developed [5][6][7][8][9][10][11][12][13][14]. However, industrial applications need more compact and fast systems for colorimetric characterization, and commercially available instruments have a limited number of measurement geometries, following guidelines from some international standards (ASTM, DIN, CIE, etc.).…”

Rapid determination of the photometric bidirectional scatter distribution function by use of a near-field goniophotometer

“…computer graphics 2-3 , remote sensing [4][5] , appearance characterization [6][7] and lighting design [8][9] . In result, many BRDF and BTDF measuring instruments *Frederic.leloup@kuleuven.be; phone +32 9 265.87.13; fax +32 9 225.62.69; www.lichttechnologie.be have been reported in the literature 10 .…”

“…The major drawback of these type of devices is however that, due to the fact that they have been optimized to be time efficient, other features become generally more restricted (e.g. just the ability to perform measurements in reflectance or transmittance mode only) 7 .…”