The textural appearance of materials encountered in our daily environment depends on two directions, the irradiation and viewing direction. We investigate the bidirectional grey level histograms of a large set of materials, obtained from a texture database. We distinguish important categories, relate the various effects to physical mechanisms, and list material attributes that influence the bidirectional histograms. We use a model for rough surfaces with locally diffuse and/or specular reflection properties, a class of materials that commonly occurs, to generate bidirectional histograms and obtain close agreement with experimental data. We discuss several applications of bidirectional texture functions and histograms. In particular, we present a new approach to texture mapping based on bidirectional histograms. For 3D texture, this technique is superior to standard 2D texture mapping at hardly any extra computational cost or memory requirements.
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