Effect of geometric sharpness on translucent material perception

Abstract

When judging the optical properties of a translucent object, humans often look at sharp geometric features such as edges and thin parts. An analysis of the physics of light transport shows that these sharp geometries are necessary for scientific imaging systems to be able to accurately measure the underlying material optical properties. In this article, we examine whether human perception of translucency is likewise affected by the presence of sharp geometry, by confounding our perceptual inferences about an object's optical properties. We use physically accurate simulations to create visual stimuli of translucent materials with varying shapes and optical properties under different illuminations. We then use these stimuli in psychophysical experiments, where human observers are asked to match an image of a target object by adjusting the material parameters of a match object with different geometric sharpness, lighting, and three-dimensional geometry. We find that the level of geometric sharpness significantly affects perceived translucency by observers. These findings generalize across a few illumination conditions and object shapes. Our results suggest that the perceived translucency of an object depends on both the underlying material's optical parameters and the three-dimensional shape of the object. We also find that models based on image contrast cannot fully predict the perceptual results.

Translucency perception: A review

“…According to the literature, translucency can impact perceived macro-scale surface geometry of the objecttranslucent objects appearing less sharp (Chowdhury et al, 2017). Interestingly, Xiao et al (2020) have found the correlation the other way round tooexperimenting with different levels of surface relief and claiming that presence of sharp edges make materials appear less translucent. They partially attribute this to the local contrast generated by the shadows owing to high surface reliefs.…”

“…three objects are made of an identical material. If the proposal by Xiao et al (2020) generalizes well to all geometries, then the ranking from the most translucent to the least translucent should be the following: a cylinder, low-resolution Lucy, and a high-resolution Lucy. It is difficult to claim the latter definitively.…”

“…Xiao et al Xiao et al (2020) have shown that a sharp surface relief enhances perceived opacity and argue that this can be attributed to sharper and darker shadows generated by these areas, which on the one hand agrees with the previous findings (Fleming & Bülthoff, 2005;Motoyoshi, 2010) that blurriness and brightness (mean luminance) of the shadowed regions can play a role in translucency perception, but on the other hand, should be taken with care, as the sharp and fine details of the surface can also lead to interreflections and bright appearance, as this is the case for the Lucy in Figure 14. In another work (Xiao et al, 2014), they observed that the thin parts and fine details of the Lucy contribute most to translucent material discrimination, supporting similar observations by other researchers (Fleming & Bülthoff, 2005;Gkioulekas et al, 2015;Nagai et al, 2013).…”

“… Xiao et al. (2020 ) have shown that a sharp surface relief enhances perceived opacity and argue that this can be attributed to sharper and darker shadows generated by these areas, which on the one hand agrees with the previous findings ( Fleming & Bülthoff, 2005 ; Motoyoshi, 2010 ) that blurriness and brightness (mean luminance) of the shadowed regions can play a role in translucency perception, but on the other hand, should be taken with care, as the sharp and fine details of the surface can also lead to interreflections and bright appearance, as this is the case for the Lucy in Figure 14 .…”

The Role of Subsurface Scattering in Glossiness Perception

“…Image cues as well as the amount of light exiting the volume depend on the shape complexity and thickness of a given object. For instance, it has been shown that sharp geometric details of the object impact apparent translucency [74] and the other way round, translucency affects perception of geometric edge sharpness [6]. Sawayama et al [57] have reported that "sensitivity to translucent discrimination was high when the object has rugged surfaces."…”