Application of a color-appearance model to vision through atmospheric haze

Environmental laws mandate the protection of visibility conditions in natio nal parks and wilderness areas from atmospheric haze, which occurs due to t he emissions of anthropogenic air pollutants. To calculate the improvement in visibility that results from the reduction of these air pollutants, it i s necessary to quantify the relationship of haze to the color appearance of objects being viewed through it. To this end, a field study was conducted in the Great Smoky Mountains National Park in eastern Tennessee. Color appe arance of objects was quantified by color matching with a special visual co lorimeter. The Hunt94 color-appearance model was used to compare these matc hes with simultaneous spectral measurements. In addition to the chromaticit y coordinates and luminance of the object, the Hunt94 model requires a numb er of parameters such as the chromaticity of the adapting light and chromat ic and brightness surround induction factors, which need to be determined f or the outdoor viewing conditions. This article describes how this was acco mplished. Although it accounts for differences in viewing conditions betwee n the colorimeter and daylight conditions, the Hunt94 model does not accoun t for the perceptual transparency effect of haze on outdoor color appearanc e. These results challenge the manner in which current air quality-visibili ty models are being utilized. (C) 1999 John Wiley & Sons, Inc.