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Lighting for texture

Fourier analysis is applied to two cyclic variables, the distribution of incident illumination around the circumference of a cylinder, and the luminance pattern of a regular optical grating. In each case it is useful to consider different harmonics independently. Recent studies of grating perception have suggested the action of neural mechanisms which must also mediate the effect of lighting on the perception of surface corrugations. The ability of a lighting system to reveal a finely corrugated texture is shown to depend mainly on the angle of incidence of the illumination vector. This angle, known as the angle of asymmetry of the lighting, may be indicated directly by a simple grease-spot device. The same criterion also applies to random depth textures.