Experiments In Texture Perception
Final rept. 1 Jun 1974-30 Nov 1977
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF PSYCHOLOGY
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Visual textures may be described completely by their spatial frequency components. For one-dimensional textures whose luminance varies only along the X-axis of the display, the descriptive elements are gratings that have sinusoidal modulations of luminance. Although any arbitrary one-dimensional blurred texture may require a very large number of sinusoidal components for its complete physical description, only four components are needed to create a texture that appears equivalent to the human observer. Thus, the human visual system does not act like a spectral analyzer, but rather appears to process spatial frequency information by filtering operations similar to that performed in color vision. In the more general case, textures will have luminance distributions varying in two dimensions i.e. in both X and Y. If a two- dimensional texture is created with orthogonal luminance profiles whereby the axis orientations of X and Y are 90 deg apart, then the X and Y profiles are independent and four spatial frequencies will be needed for X and four for Y. The most general case of texture equivalence, where many orientations are present in a texture, has not yet been solved. However, preliminary experiments by M. Riley show that orientation equivalence can be attained by utilizing only four independent orientations. This constraint suggests an upper bound of sixteen on the number of fixed spatial frequencies required to create an equivalence to any two-dimensional texture pattern. However, where control over the maximum visual angle can be maintained, twelve spatial frequencies may suffice for practical purposes, especially if the basic waveform of the primary components can be pre-programmed.
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