Effect of Geometric Sharpness on Translucent Material Perception

Abstract

When judging optical properties of a translucent object, humans often look at sharp geometric features such as edges 4 and thin parts. Analysis of the physics of light transport shows that these sharp geometries are necessary for scientific 5 imaging systems to be able to accurately measure the underlying material optical properties. In this paper, we examine 6 whether human perception of translucency is likewise affected by the presence of sharp geometry, by confounding our 7 perceptual inferences about an object's optical properties. We employ physically accurate simulations to create visual 8 stimuli of translucent materials with varying shapes and optical properties under different illuminations. We then use these 9 stimuli in psychophysical experiments, where human observers are asked to match an image of a target object by adjusting 10 the material parameters of a match object with different geometric sharpness, lighting geometry, and 3D geometry. We 11 find that the level of geometric sharpness significantly affects perceived translucency by the observers. These findings 12 generalize across a few illuminations and object shapes. Our results suggest that the perceived translucency of an object 13 depends on both the underlying material optical parameters and 3D shape. We also conduct analyses using computational 14 metrics including (luminance-normalized) L2, structural similarity index (SSIM), and Michelson contrast. We find that these 15 image metrics cannot predict perceptual results, suggesting low level image cues are not sufficient to explain our results. 16

Visual discrimination of optical material properties: a large-scale study

“…One possibility is that the diagnostic features for translucent perception lie in the edge/corner of a translucent object and our rugged objects included much information to judge translucency. More recently, Xiao et al (2020) investigated the effect of geometry on translucency perception. In their experiments, they changed the smoothness of the object edges.…”

Crystal or jelly? Effect of color on the perception of translucent materials with photographs of real-world objects

“…First, the physical process of translucency is complex, involving surface reflection and subsurface scattering (see Gkioulekas, Xiao, Zhao, Adelson, Zickler, & Bala, 2013 ; Xiao, Walter, Gkioulekas, Zickler, Adelson, & Bala, 2014 for detailed description of physical model of subsurface scattering and translucency perception). Previous work shows that physical material properties, lighting, shape, and context all affect the appearance of translucent objects ( Chowdhury, Marlow, & Kim, 2017 ; Fleming & Bülthoff, 2005 ; Gigilashvili, Shi, Wang, Pedersen, Hardeberg, & Rushmeier, 2021 ; Gigilashvili, Thomas, Hardeberg, & Pedersen, 2021 ; Marlow & Anderson, 2021 ; Marlow, Kim, & Anderson, 2017 ; Motoyoshi, 2010 ; Nagai, Ono, Tani, Koida, Kitazaki, & Nakauchi, 2013 ; Sawayama, Dobashi, Okabe, Hosokawa, Koumura, Saarela, et al, 2019 ; Tamura, Higashi, & Nakauchi, 2018 ; Xiao et al, 2014 ; Xiao, Zhao, Gkioulekas, Bi, & Bala, 2020 ), and it still remains unknown how humans extract intrinsic translucent material properties from images. Second, there are many different kinds of translucent materials in real life.…”

“…Using rendered images, most previous works have measured translucent appearance using a single task (e.g. asking observers to rate the apparent translucency, asking observers to judge which of the two images seems to be more translucent, or matching the images based on the perceived translucency by using a slider to adjust one particular physical parameter) ( Motoyoshi, 2010 ; Nagai et al, 2013 ; Xiao et al, 2020 ). Such measurements may not fully reflect how humans perceive and recognize translucent materials in the real world.…”

“…Nearly all previous work in translucency perception has used monochromatic images ( Motoyoshi, 2010 ; Nagai et al, 2013 ; Xiao et al, 2020 ). The use of monochromatic images in translucency perception is largely due to the lack of high-quality renderings of physically plausible colored images of translucent appearance.…”

The translucency of human teeth and its relation to esthetic restorative materials

“…On the other hand, it has been demonstrated that changing the direction of lighting was associated with a significant impact on the translucency consistency of the human teeth as in some cases, failure was noticed. 18,19 A previous investigation compared the parallel and perpendicular directions of the transmitted light intensities concerning the proximal surface of the tooth to investigate the light fluxes-related directional dependence. 20 The authors have estimated mean values of 2.88, and 0.86 for the parallel and perpendicular transmitted intensities of light for dentin and enamel, respectively.…”