Brightness, discriminability and the "crispening effect".
Subjects adjusted the luminances, L, of 16 or 25 circles, all visible at the same time on a computer monitor, to make equal-interval brightness series. The background was black, white or grey. The luminance steps between adjacent circles behaved like the luminance discrimination thresholds of Whittle, P. [(1986) Vision Research, 26, 1677-1691)]. They showed a sharp minimum at the background luminance, Lb: the "Crispening Effect". They followed Weber's Law with respect to L when L was small, but with respect to delta L (= magnitude of L-Lb) near Lb. The Crispening Effect was abolished by a thin outline or a hue difference between circles and background.
Whittle
P
P
Department of Experimental Psychology, Cambridge, England.
D003118:Color Perception / Q000502:physiology; D003117:Color Vision Defects / Q000503:physiopathology; D015350:Contrast Sensitivity / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology*; D006801:Humans; D008027:Light; D008297:Male; D010783:Photometry; D012684:Sensory Thresholds / Q000502:physiology