Explaining #theShoe based on the optimal color hypothesis: The role of chromaticity vs. luminance distribution in an ambiguous image

The image of #theShoe is a derivative image of #theDress which induces vastly different color experiences across individuals. The majority of people perceive that the shoe has grey leather with turquoise laces, but others report pink leather with white laces. We hypothesized #theShoe presents a problem of color constancy, where different people estimate different illuminants falling onto the shoe. The present study specifically aimed to understand what cues in the shoe image caused the ambiguity based on the optimal color hypothesis: our visual system knows the gamut of surface colors under various illuminants and applies the knowledge for illuminant estimation. The analysis showed that estimated illuminant chromaticity largely changes according to the assumed intensity of the illuminant. When the illuminant intensity was assumed to be low, a high color temperature was estimated. In contrast, assuming high illuminant intensity led to the estimation of low color temperature. A simulation based on a von Kries correction showed that the subtraction of estimated illuminants from the original image shifts the appearance of the shoe towards the reported states (i.e. gray-turquoise or pink-white). These results suggest that the optimal color hypothesis provides a theoretical interpretation to #theShoe phenomenon. Moreover, this luminance-dependent color-shift was observed in #theDress phenomenon, supporting the notion that the same trigger induces #theShoe.