Little is known about how color signals and cone- and rod-based luminance signals contribute to perceived contrast in the mesopic range. In this study the perceived contrast of colored, mesopic stimuli was matched with that of spatially equivalent achromatic stimuli. The objective was to develop a metric for perceived contrast in the mesopic range in terms of an equivalent achromatic luminance contrast, referred to here as effective contrast. Stimulus photopic luminance contrast, scotopic luminance contrast, and chromatic difference from the background all contributed to effective contrast over the mid-mesopic range, but their contributions were not independent and varied markedly with background luminance. Surprisingly, color made a significant contribution to effective contrast from 10 to approximately 0.003 cd m^-2. A model describing this relationship is introduced (R2=0.89) and compared with predictions of mesopic luminance contrast obtained from a number of models proposed as systems of mesopic photometry.
© 2005 Optical Society of America
(330.0330) Vision, color, and visual optics : Vision, color, and visual optics
(330.1720) Vision, color, and visual optics : Color vision
(330.4060) Vision, color, and visual optics : Vision modeling
(330.4300) Vision, color, and visual optics : Vision system - noninvasive assessment
(330.5510) Vision, color, and visual optics : Psychophysics
Helen C. Walkey, John L. Barbur, J. Alister Harlow, Antony Hurden, Ian R. Moorhead, and Julie A. F. Taylor, "Effective contrast of colored stimuli in the mesopic range: a metric for perceived contrast based on achromatic luminance contrast," J. Opt. Soc. Am. A 22, 17-28 (2005)