Low-Level Image Cues in the Perception of Translucent Materials

Abstract

When light strikes a translucent material (such as wax, milk or fruit flesh), it enters the body of the object, scatters and reemerges from the surface. The diffusion of light through translucent materials gives them a characteristic visual softness and glow. What image properties underlie this distinctive appearance? What cues allow us to tell whether a surface is translucent or opaque? Previous work on the perception of semitransparent materials was based on a very restricted physical model of thin filters [Metelli 1970; 1974a,b]. However, recent advances in computer graphics [Jensen et al. 2001; Jensen and Buhler 2002] allow us to efficiently simulate the complex subsurface light transport effects that occur in real translucent objects. Here we use this model to study the perception of translucency, using a combination of psychophysics and image statistics. We find that many of the cues that were traditionally thought to be important for semitransparent filters (e.g., X-junctions) are not relevant for solid translucent objects. We discuss the role of highlights, color, object size, contrast, blur, and lighting direction in the perception of translucency. We argue that the physics of translucency are too complex for the visual system to estimate intrinsic physical parameters by inverse optics. Instead, we suggest that we identify translucent materials by parsing them into key regions and by gathering image statistics from these regions.

Scattering-aware texture reproduction for 3D printing

“…7) could subjectively improve our results even further. In general, the perception of heterogeneous translucency is largely an open topic [Fleming and Bültho 2005;Fleming et al 2004;Gkioulekas et al 2013a] and deserves a dedicated treatment.…”

Understanding the role of phase function in translucent appearance

“…We did not use the checkerboard for the backlighting case, as we judged that in that case there was enough contrast with the background due to strong brightness changes at the border of the foreground object (see "Lucy + Dining room" in Figure 4). Overall, our scenes were designed to feature image cues that have been related to the perception of translucency by others [Fleming and Bülthoff 2005;Motoyoshi 2010] or that we ourselves believe to be related. These cues include fine geometric detail, specular highlights, sharp edges, intensity gradients, color bleeding effects, and strong backlighting.…”

“…For the reasons described in Sections 4.1, we chose the σ s and σ t values of marble for generating the stimuli for psychophysical analysis. We also selected the Campus and Dining room lighting environments, corresponding to sidelighting and backlighting conditions, which have been demonstrated to be important for translucency [Fleming and Bülthoff 2005].…”

On the appearance of translucent edges

“…This internal scattering can create a variety of image effects, depending on an object's shape and material; its distance from the observer; and the composition of the lighting around it. Common human experience suggests that these image effects contain useful material information, and there is psychophysical evidence that humans can discriminate subtle differences in translucent appearance, recognize translucent material categories, and make inferences about physical scattering parameters [2,11,13,27].…”