Paint coatings have contributed greatly to the appearance of cars, and their colors and textures are very significant in considering car design and a products line-up. Recently, metallic-type paint coatings dominate the market and their flake pigments play a significant part in the paint appearance. To understand the mechanism of the paint appearance, it is necessary to clarify the optical characteristics of very small flake pigments, of which size is of an order of micrometers. First of all, an optical measurement system was set up to investigate the bidirectional reflectance of each flake pigment, and the measurements were made on micaceous iron oxide (MIO), flake pigments and aluminum ones. For MIO flake pigments, the particle size and the surface treatment were found to have a great influence on the bidirectional reflectance and the influence of the aspect ratio might be negligible. For aluminum flake pigments, on the other hand, it was revealed that the reflectance was larger than that of MIO pigments and that each sample had a different distribution. Mathematical model and its expressions for the bidirectional reflectance are investigated in order to clarify the factor, influence and mechanism of the reflection of the flake pigment itself. This study revealed the reproducibility and validity of the expressions of the bidirectional reflectance based on the measurements. In other words, it has been revealed that the bidirectional reflectance is mainly explained by the diffraction effect on the flake pigment size and that the distribution of the reflectance is changed by the diffusive reflection effect on the surface conditions, including roughness and shape. �@
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