Distinctness of perceived three-dimensional form induced by modulated illumination: effects of certain display and modulation conditions.

The present study concerns the distinctness of the 3-D shape induced on flat displays by space-modulated illumination ("shape from shading"). The displays that we used varied in structure, hue contrast, lightness contrast, and in the number of reflectance edges present. The modulations of the illumination were a square-wave grating, a gradual modulation (a blurred grating), and an "O'Brien modulation," which combines an edge and a gradient. The displays were compared, using the paired comparison method, as to the distinctness of the perceived 3-D form. The results showed that the structure and chromatic color of the display were important factors facilitating the distinctness of the induced 3-D shape under all the modulation conditions. The results are discussed in relation to the "vector model" for color constancy, proposed in earlier papers.