All visual sensors, biological and artificial, are finite in resolution by necessity. As a result, the effective reflectance of surfaces in a scene varies with magnification. A reflectance model for matte surfaces is described that incorporates the effect of macroscopic surface undulations on image brightness. The model takes into account complex physical phenomena such as masking, shadowing, and interreflections between points on the surface, and it predicts the appearance of a wide range of natural surfaces. The implications of these results for human vision, machine vision, and computer graphics are demonstrated with both real and rendered images of three-dimensional objects. In particular, objects with extremely rough surfaces produce silhouette images devoid of shading, precluding visual perception of the object's shape.
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