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Sarah Elliott, Dingcai Cao; Scotopic hue percepts in natural scenes. Journal of Vision 2012;12(9):873. doi: 10.1167/12.9.873.
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The color appearance of an object under scotopic illuminating conditions varies depending on the context. Objects generally appear bluish-green when viewed in isolation, but can appear red or orange when seen with another object in view (Pokorny et al., 2006). The perceived hue of a test ring viewed under scotopic light levels changes with contrast, number, and spacing of inducer rings (Elliott & Cao, VSS2010). This study explored if 1) relational scotopic hue percepts occur in natural scenes and 2) whether hue percepts depend on contrast and spatial frequency relations within the images. Twenty-four natural images were chosen from the McGill Calibrated Colour Image Database. The images were calibrated and presented using only the B phosphor of a CRT (subtending 24°, mean luminance of -3.89 log photopic or -3.13 scotopic cd/m2). Following 25 min of dark adaptation, ten observers reported perceived hue and saturation using a hue scaling method for a 4° region (selected to highlight specific objects or uniform regions). Hue percepts were reported in 29% to 96% of the trials, depending on the image. The magnitude and polarity of contrast between the region and mean image luminance played a large role in reported hues. Hue percepts were reported more often for images with a mean contrast magnitude >14% within the region compared to images with a mean region contrast magnitude ≤14%. Reddish [yellowish] hues were reported only when region contrast was lower [higher] than the mean image luminance, which shows clear support for relational hues percepts in natural scenes. Memory color also contributed to hue percepts for some images, in which the object was clearly identifiable and had a strong daylight color associated with it. The role of spatial frequency content was unclear due to variability in the amplitude spectra across images.
Meeting abstract presented at VSS 2012
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