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Katharina Zeiner, Marianne Maertens; Effects of changes in atmosphere on lightness perception. Journal of Vision 2013;13(9):1156. doi: 10.1167/13.9.1156.
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© ARVO (1962-2015); The Authors (2016-present)
The color of achromatic surfaces, i.e. their perceived reflectance, can only indirectly be inferred from the luminance image in the retina. Variations in illumination as well as different 'atmospheres' such as transparent media located between the object and our eyes may dramatically alter the luminance of one and the same object. Adelson (2000) proposed that in order to veridically perceive an object's reflectance regardless of the atmosphere through which it is seen, the visual system must invert, what he called atmospheric transfer functions (ATF), namely the functions which map reflectance to luminance values in different atmospheres. The inverted functions used by the visual system to infer lightness from luminance were called lightness transfer functions (LTF). To test twhether such an inversion adequately describes lightness perception, we measured ATFs and LTFs in checkerboards, which consisted of ten by ten checks with ten different, randomly assigned, surface reflectances. The checkerboards were rendered using Povray, and each of the ten different surface reflectances could be presented in one of a number of different 'atmospheres' including plain view, shadow, and different kinds of transparencies. The luminance range of the different reflectances spanned 16 to 398 cd/m[sup]2 [/sup]in plain view. To measure the LTFs observers adjusted a comparison patch such that it appeared as light as one of the ten test reflectances viewed in different atmospheres. We find LTFs that are indeed almost perfectly inverse functions of the ATFs as indicated by a close correspondence between reflectance and perceived reflectance (lightness). The LTFs of our observers in different atmospheres are linear and differ by a multiplicative (slope) and a subtractive (intercept) factor. A shadow affects the slope whereas transparencies affect both the slope and intercept of the transfer function. The colour of the transparency affects the intercept while the translucency affects the slope.
Meeting abstract presented at VSS 2013
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