The impact of ‘crispening’ upon the perceived contrast of textures

TitleThe impact of ‘crispening’ upon the perceived contrast of textures
Publication TypeChart
Year of Publication2015
AuthorsKane D, Bertalmío M
Image Source ProgramThe Optical Society of America
Abstract

We investigate the role of lightness perception in determining the perceived contrast of simple textures. It is known that the background luminance of a display affects the relationship between onscreen-luminance and perceived lightness. This effect can be approximated by a power-law with an exponent that increases with the background luminance level (Bartleson & Breneman, 1967; Bartleson, 1975; Stevens & Stevens, 1963). Moreover, recent work has demonstrated that an adaptive lightness model is critical to understanding the perceived contrast of natural textures (Kane & Bertalmío, Submitted). However, a simple power-law cannot account for the effect of ‘crispening’, whereby subjects are more sensitive to luminance variations around the background luminance (Whittle, 1992). In this study we empirically estimated subject’s luminance-to-lightness functions via a bisection paradigm (Munsell, Sloan, & Godlove, 1933) for five background luminance levels from 0 to 100%. The results reveal complex functions with clear evidence of ‘crispening’. We then computed the point-of-subjective-equality (PSE) for the contrast of a reference and test patches with a mean luminance of 25% and 75% respectively, using the background luminance conditions from experiment one. The PSE’s as a function of background luminance exhibit a peak and a trough around the mean luminance of the test and reference, respectively. We find that subjects’ PSE can only be modeled by first passing the stimulus through the empirically estimated lightness functions before estimating contrast. Future work will investigate whether the demonstrated impact of ‘crispening’ generalizes to more complex stimuli, and stimuli that subtend a greater angle.