Abstract
Studies of perceptual transparency have mostly focused on the generation of the percept, with thin filters floating above a Lambertian background. However, in the natural world transparent objects are not just thin and see-through: they have a 3D shape, often possess specular highlights, and generate caustics, refractions and shadows and - if they absorb parts of the light spectrum - a tinted image of the background. Such objects interact with light very differently from matte, opaque objects and little is known about how the color of such objects – which is a mixture of the object’s material color, the illumination and colors of objects in the background – is perceived. Here, we investigate the perceived color of tinted, 3-D glass objects in a complex scene under a blue and a yellow illuminant. We conducted three asymmetric matching experiments in which observers either changed the color of a patch until it had the same color as the object; changed the color of a patch until it looked like the dye that was used to tin the object; and changed the color of a transparent 2-D filter on an achromatic Voronoi background until its color matched the object. Observers’ color matches correlated significantly with the mean chromaticity and luminance of the object. However, in the first two experiments, the mean luminance of matches was offset by ~40 L* units on average. The mean luminance in experiment 3 did not show a luminance offset and matches corresponded best to a distributed region of patches of mid- to low-luminance across the surface of the object, according to the CIEDE2000 metric. These results suggest that the color of a 3-D transparent object is not determined by a single region. Rather, an integration process presumably takes place, which could help reduce the bias from colors behind the transparency.
Acknowledgement: Funding was provided by the Alexander von Humboldt Foundation in the framework of the Sof’ja Kovalevskaja Award endowed by the German Federal Ministry of Education and Research