Showing papers by "Brian A. Wandell published in 1985"

Color measurement and discrimination

Abstract: Theories of color measurement attempt to provide a quantative means for predicting whether two lights will be discriminable to an average observer. All color measurement theories can be characterized as follows: suppose lights a and b evoke responses from three color channels characterized as vectors, v(a) and v(b); the vector difference v(a) - v(b) corresponds to a set of channel responses that would be generated by some real light, call it *. According to theory a and b will be discriminable when * is detectable. A detailed development and test of the classic color measurement approach are reported. In the absence of a luminance component in the test stimuli, a and b, the theory holds well. In the presence of a luminance component, the theory is clearly false. When a luminance component is present discrimination judgements depend largely on whether the lights being discriminated fall in separate, categorical regions of color space. The results suggest that sensory estimation of surface color uses different methods, and the choice of method depends upon properties of the image. When there is significant luminance variation a categorical method is used, while in the absence of significant luminance variation judgments are continuous and consistant with the measurement approach.

A method of, and apparatus for, determining colour

Abstract: A method is disclosed to separate the effect of the ambient lighting from the effects of surface reflectance to better analyse the surface properties of materials. The method uses the data sensed by a plurality of sensor classes to define a finite dimensional approximation of a surface reflectance function at each image point, and a finite dimensional approximation of the ambient light.