Characterization of byko-spectra effect light booth for digital simulation in a rendering tool

CIE 2019, Washington DC, June 14 to 22, 2019. -- http://washington2019.cie.co.atDigital simulation by rendering of gonio-apparent coatings is nowadays a very active hot topic for optical metrology, colour science, computer graphics, and visual perception. Since this type of coatings changes visual attributes such as colour and texture, depending on illumination and viewing geometry, rendering three-dimensional objects covered by these coatings is a technological challenge. The encoding and representation of gonio-appearance in computer graphics platforms is usually done by 3D rendering software packages, and by applying theoretical optical models of the interaction between light and matter. A first step to get visual fidelity is to simulate the illumination scene. For this purpose, a directional light booth is simulated in a new rendering software developed by the AkzoNobel Technology Group Color. This new software is based on a multi-spectral physics-based approach to represent the BRDF when rendering three dimensional objects. For the illumination scene we selected the Byko-spectra effect multi-directional light booth (BYK-Gardner). This light booth is particularly suitable for this task, since it was designed such as to optimize the visibility of sparkle and other texture effects in gonio-apparent automotive coatings. The lighting environment for the rendering tool is specified in terms of the IES/EULUMDAT format. This enables the user to specify the luminous intensity distribution from lamps and reflective areas surrounding the object that needs to be rendered. Unfortunatly, IES/EULUMDAT files of the light tubes inside the Byko-spectra effect light booth were not available from the manufacturer. Therefore, the aim of this work is to delvelop a methodology to include the light emission characteristics of the light tubes, in order to be able to consider the bidirectional reflectance for any geometry of the coatings to be rendered. This methodology is based on measured illuminance levels inside the light booth