Approximation of the gonio radiance properties of gold-coated paper sheets by BRDF models

Yoshinori Akao*1, Norimichi Tsumura*2, Toshiya Nakaguchi*2 and Yoichi Miyake*2, 3

*1 National Research Institute of Police Science
6-3-1, Kashiwanoha, Kashiwa, Chiba 277-0882, Japan

*2 Department of Information and Image Sciences, Chiba University
1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

*3 Research Center for Frontier Medical Engineering, Chiba University
1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Japanese Journal of Forensic Science and Technology 12, 107-120 (2007)

Abstract
In this paper, we approximated gonio radiance properties of the surface reflection component of paper sheets by BRDF model, which is required in the digital image archive system recording the specimens of forensic document examination. Surface reflection component was selectively acquired by measuring the paper sheets processed with gold evaporation. Gonio radiance factor of three kinds of gold-coated paper sheets were approximated by TSL model, which is the linear combination of two BRDF models, Torrance-Sparrow model and Lambert model. Relative gonio properties of each sample were well depicted by TSL model, however a large deviation occurred in the specular reflection geometry for glossy paper. The RMSE between the measurement and the approximation by TSL model was under 2% of the range of measured value. The roughness parameter in Torrance-Sparrow model corresponded with the state of surface roughness, and also the ratio between Torrance-Sparrow model and Lambert model showed the difference of material characteristics between samples. Therefore TSL model was considered to be effective as a BRDF model approximating the gonio radiance properties of surface reflected light from paper sheets.


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