This study aimed to determine the perceptibility and acceptability thresholds for the relative translucency parameter (RTP) of ceramic materials, using observer-based assessments under simulated clinical conditions. The null hypothesis was that no difference existed in RTP values for perceptibility and acceptability thresholds. Specimens of lithium disilicate in five translucency levels were fabricated into discs and anterior crowns. RTP was calculated using the CIEDE2000 color difference formula with black and white backings. Digital photographs of paired crowns on typodont models were presented to 30 dental clinicians in a controlled visual environment using a randomized Qualtrics survey. Observers judged translucency differences (perceptibility) and clinical appropriateness (acceptability). A repeated-measures logistic regression model was used to analyze observer responses. A significant relationship was found between Delta RTP (△RTP) and both perceptibility and acceptability judgments (p < 0.0001). Perceptibility thresholds were identified at -17.5, while acceptability thresholds were defined at 12.6. △RTP values exceeding 27 were consistently perceived as different, while values below 12 were often judged acceptable. The null hypothesis was rejected, confirming a statistical difference between perceptibility and acceptability judgments and their relationship to RTP. Clinically relevant RTP thresholds for translucency perception and acceptability were established. These findings validate RTP as a meaningful and quantifiable tool for assessing esthetic differences in translucency among restorative materials. The results have implications for material selection and clinical decision-making in prosthodontics.

It is well established that object shape perception significantly influences the perception of translucency. However, how object shape cues such as motion and binocular disparity affect the perception of translucency in rich environments, like virtual reality or real visual environments, remains unclear. This study aims to psychophysically measure the extent to which multiple object shape cues influence the perception of translucency. Additionally, we examined whether top-down factors, such as changes in cognitive attitude caused by the sequence of experiments, affect translucency perception. The results revealed that while motion and binocular disparity enhance translucency perception, this effect is confined to situations where shape cues are poor. Moreover, the effect became particularly pronounced when the experiments began with weak specular reflection stimuli, followed by the experiments using stimuli with specular reflection. In the case of translucent objects without specular reflection, strong shape information cannot be derived solely from shading patterns. These findings thus suggest that top-down factors related to shape modulate the influence of shape cues on translucency perception.

We propose a method of reproducing perceptual translucency in three-dimensional printing. In contrast to most conventional methods, which reproduce the physical properties of translucency, we focus on the perceptual aspects of translucency. Humans are known to rely on simple cues to perceive translucency, and we develop a method of reproducing these cues using the gradation of surface textures. Textures are designed to reproduce the intensity distribution of the shading and thus provide a cue for the perception of translucency. In creating textures, we adopt computer graphics to develop an image-based optimization method. We validate the effectiveness of the method through subjective evaluation experiments using three-dimensionally printed objects. The results of the validation suggest that the proposed method using texture may increase perceptual translucency under specific conditions. As a method for translucent 3D printing, our method has the limitation that it depends on the observation conditions; however, it provides knowledge to the field of perception that the human visual system can be cheated by only surface textures.

Previous studies have shown that information concerning object shape is important for the perception of translucency. This study aims to explore how the perception of semi-opaque objects is influenced by surface gloss. We varied specular roughness, specular amplitude, and the simulated direction of a light source used to illuminate a globally convex bumpy object. We found that perceived lightness and roughness increased as specular roughness was increased. Declines in perceived saturation were observed but were far smaller in magnitude with these increases in specular roughness. There were inverse correlations found between perceived gloss and perceived lightness, perceived transmittance and perceived saturation, and between perceived roughness and perceived gloss. Positive correlations were found between perceived transmittance and glossiness, and between perceived roughness and perceived lightness. These findings suggest that specular reflections influence the perception of transmittance and color attributes, and not just perceived gloss. We also performed follow-up modeling of image data to find that perceived saturation and lightness could be explained by the reliance on different image regions with greater chroma and lower lightness, respectively. We also found systematic effects of lighting direction on perceived transmittance that indicate there are complex perceptual interactions that require further consideration.

Humans constantly assess the appearance of materials to plan actions, such as stepping on icy roads without slipping. Visual inference of materials is important but challenging because a given material can appear dramatically different in various scenes. This problem especially stands out for translucent materials, whose appearance strongly depends on lighting, geometry, and viewpoint. Despite this, humans can still distinguish between different materials, and it remains unsolved how to systematically discover visual features pertinent to material inference from natural images. Here, we develop an unsupervised style-based image generation model to identify perceptually relevant dimensions for translucent material appearances from photographs. We find our model, with its layer-wise latent representation, can synthesize images of diverse and realistic materials. Importantly, without supervision, human-understandable scene attributes, including the object’s shape, material, and body color, spontaneously emerge in the model’s layer-wise latent space in a scale-specific manner. By embedding an image into the learned latent space, we can manipulate specific layers’ latent code to modify the appearance of the object in the image. Specifically, we find that manipulation on the early-layers (coarse spatial scale) transforms the object’s shape, while manipulation on the later-layers (fine spatial scale) modifies its body color. The middle-layers of the latent space selectively encode translucency features and manipulation of such layers coherently modifies the translucency appearance, without changing the object’s shape or body color. Moreover, we find the middle-layers of the latent space can successfully predict human translucency ratings, suggesting that translucent impressions are established in mid-to-low spatial scale features. This layer-wise latent representation allows us to systematically discover perceptually relevant image features for human translucency perception. Together, our findings reveal that learning the scale-specific statistical structure of natural images might be crucial for humans to efficiently represent material properties across contexts.

Humans constantly assess the appearance of materials to plan actions, such as stepping on icy roads without slipping. Visual inference of materials is important but challenging because a given material can appear dramatically different in various scenes. This problem especially stands out for translucent materials, whose appearance strongly depends on lighting, geometry, and viewpoint. Despite this, humans can still distinguish between different materials, and it remains unsolved how to systematically discover visual features pertinent to material inference from natural images. Here, we develop an unsupervised style-based image generation model to identify perceptually relevant dimensions for translucent material appearances from photographs. We find our model, with its layer-wise latent representation, can synthesize images of diverse and realistic materials. Importantly, without supervision, human-understandable scene attributes, including the object's shape, material, and body color, spontaneously emerge in the model's layer-wise latent space in a scale-specific manner. By embedding an image into the learned latent space, we can manipulate specific layers' latent code to modify the appearance of the object in the image. Specifically, we find that manipulation on the early-layers (coarse spatial scale) transforms the object's shape, while manipulation on the later-layers (fine spatial scale) modifies its body color. The middle-layers of the latent space selectively encode translucency features and manipulation of such layers coherently modifies the translucency appearance, without changing the object's shape or body color. Moreover, we find the middle-layers of the latent space can successfully predict human translucency ratings, suggesting that translucent impressions are established in mid-to-low spatial scale features. This layer-wise latent representation allows us to systematically discover perceptually relevant image features for human translucency perception. Together, our findings reveal that learning the scale-specific statistical structure of natural images might be crucial for humans to efficiently represent material properties across contexts.

We propose a method of reproducing perceptual translucency in three-dimensional printing. In contrast to most conventional methods, which reproduce the physical properties of translucency, we focus on the perceptual aspects of translucency. Humans are known to rely on simple cues to perceive translucency, and we develop a method of reproducing these cues using the gradation of surface textures. Textures are designed to reproduce the intensity distribution of the shading and thus provide a cue for the perception of translucency. In creating textures, we adopt computer graphics to develop an image-based optimization method. We validate the effectiveness of the method through subjective evaluation experiments using three-dimensionally printed objects. The results of the validation show that the proposed method using texture is effective in improving perceptual translucency.

The perception of translucency from surface gloss

In the cosmetics industry, fine particles suspended or dispersed in a medium are widely used. Optical properties of the medium can be an indicator for evaluating the performance of cosmetic product, such as the ultraviolet protection capacity of sunscreens and also its appearance. However, the relationship between the optical properties and the appearance of the product has not been clarified. In this study, dispersions of fine particles with titanium dioxide or zinc oxide were used as scattering medium to clarify the relation between their scattering properties and changes in visual perception. For visual perception, sensory tests with human panelists were performed using a custom-designed apparatus to inspect the samples and evaluate the two visual sensory quantities, “glossiness” and “translucency”. The sensory test employed Thurston’s one-pair comparison method, and a total of 18 panelists were asked to evaluate the samples. The sensory tests showed that the translucency became stronger as the scattering coefficient decreased. On the other hand, only the samples in the group with the highest scattering coefficient showed a slightly low glossiness. In contrast, the other samples showed little difference in glossiness due to the difference in scattering coefficients. The results of this study indicate that the appearance of cosmetics products can be influenced by controlling the scattering properties of the medium.

In this work we study the perception of suprathreshold translucency differences to expand the knowledge about material appearance perception in imaging and computer graphics, and 3D printing applications. Translucency is one of the most considerable appearance attributes that significantly affects the look of objects and materials. However, the knowledge about translucency perception remains limited. Even less is known about the perception of translucency differences between materials. We hypothesize that humans are more sensitive to small changes in absorption and scattering coefficients when optically thin materials are examined and when objects have geometrically thin parts. To test these hypotheses, we generated images of objects with different shapes and subsurface scattering properties and conducted psychophysical experiments with these visual stimuli. The analysis of the experimental data supports these hypotheses and based on post experiment comments made by the observers, we argue that the results could be a demonstration of a fundamental difference between translucency perception mechanisms in see-through and non-see-through objects and materials.

Translucent materials are ubiquitous in nature (e.g. teeth, food, and wax), but our understanding of translucency perception is limited. Previous work in translucency perception has mainly used monochromatic rendered images as stimuli, which are restricted by their diversity and realism. Here, we measure translucency perception with photographs of real-world objects. Specifically, we use three behavior tasks: binary classification of “translucent” versus “opaque,” semantic attribute rating of perceptual qualities (see-throughness, glossiness, softness, glow, and density), and material categorization. Two different groups of observers finish the three tasks with color or grayscale images. We find that observers’ agreements depend on the physical material properties of the objects such that translucent materials generate more interobserver disagreements. Further, there are more disagreements among observers in the grayscale condition in comparison to that in the color condition. We also discover that converting images to grayscale substantially affects the distributions of attribute ratings for some images. Furthermore, ratings of see-throughness, glossiness, and glow could predict individual observers’ binary classification of images in both grayscale and color conditions. Last, converting images to grayscale alters the perceived material categories for some images such that observers tend to misjudge images of food as non-food and vice versa. Our result demonstrates that color is informative about material property estimation and recognition. Meanwhile, our analysis shows that mid-level semantic estimation of material attributes might be closely related to high-level material recognition. We also discuss individual differences in our results and highlight the importance of such consideration in material perception.

Translucency is an optical and a perceptual phenomenon that characterizes subsurface light transport through objects and materials. Translucency as an optical property of a material relates to the radiative transfer inside and through this medium, and translucency as a perceptual phenomenon describes the visual sensation experienced by humans when observing a given material under given conditions. The knowledge about the visual mechanisms of the translucency perception remains limited. Accurate prediction of the appearance of the translucent objects can have a significant commercial impact in the fields such as three-dimensional printing. However, little is known how the optical properties of a material relate to a perception evoked in humans. This article overviews the knowledge status about the visual perception of translucency and highlights the applications of the translucency perception research. Furthermore, this review summarizes current knowledge gaps, fundamental challenges and existing ambiguities with a goal to facilitate translucency perception research in the future.

This data folder contains the following contents: - The raw data obtained from experiment. - The R analysis codes for the raw data. - The Matlab analysis codes for computational modeling. - The Python codes for generating stimuli.

Abstract Visual material perception is often studied with physically well-defined stimuli that lack ecological variety. Yet, even the visual variety found in our natural environment is limited when compared to artistic depiction. A similar object can be depicted in numerous different ways that all make visual sense. We studied the perception of translucency using 38 paintings of sea waves as experimental stimuli. It has previously been shown that translucency depends on the shape of the translucent object and on the light conditions. Both shape and light appear in many variations in depictions of seas. In the first experiment we explored the use of Thurstonian scaling and introduce the concept of Number of Distinguishable Levels (NDL). We found that the NDL ranged between 1.5 in a set with small waves to 4 in a set with large waves. While Experiment 1 took place in the lab, Experiment 2 was performed online and replicated the data from Experiment 1 qualitatively, although the NDL was lower in the online experiment. Furthermore, in this experiment we conducted Thurstonian scaling on a number of other attributes that possibly contribute to translucency perception, such as wavetip shading, surface reflections and realism. We found that many of these correlated significantly with translucency. In sum, this study advocates and demonstrates the use of uncontrolled stimuli, in our case paintings, to explore the wide variety of input the human visual system can process.

Purpose : The current study investigated the effect of different sintering protocols (long, speed and high- speed cycles) on translucency and fracture resistance of monolithic zirconia crowns. Materials and Methods: 30 monolithic zirconia crowns were CAD/CAM fabricated from translucent BruxZir zirconia blanks. The crowns were divided into three groups (n=10 each) according to the sintering protocols(temperature & speed); Group (I): samples sintered by long sintering cycle (1510°C , 120 min holding time and 8 hours total cycle time), Group (II): speed sintering ( 1540°C , 25 min holding time and 2 hours total cycle time) and Group (III): high-speed sintering (1580°C, 10 min holding time representing the total firing cycle).Translucency parameter (TP) and Contrast Ratio (CR) were measured using a spectrophotometer, then compressive load was applied till fracture in a universal testing machine. One representative disc sample (10mm diameter x 1 mm thickness) was fabricated and sintered according to the parameters of each group and analyzed by scanning electron microscope. Collected data were statistically analyzed. Results: Sintering speed had a statistically significant effect on (TP),(CR) and fracture resistance means. Long cycle showed the statistically significantly highest (TP) and lowest (CR) mean values. The high-speed cycle recorded the statistically significantly highest fracture resistance mean values. Conclusion: Shortening the sintering cycle significantly decreased translucency and increased fracture resistance of monolithic zirconia crowns. Regarding Translucency Perception Threshold ,speed cycle can be recommended for sintering of BruxZir monolithic zirconia crowns.

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.

Caustics projected onto the surface carry very interesting information regarding the material they are cast by. It has been observed in previous studies that caustics could be a widely used cue for translucency assessment by human subjects. We hypothesize that changing the reflectance properties of the surface an object is placed on, and removal of the caustic pattern might impact perceived translucency of the material. We conducted psychophysical experiments to investigate the correlation among caustics, environment colors and translucency perception, and found very interesting indications that materials appear less translucent under the conditions where caustics are absent.

This work takes a step towards understanding fundamental aspects of appearance change in cultural heritage. Particularly, we concentrate on the case study of the Hedal Madonna – a polychrome wood sculpture dated to the mid-1200s, and an important object of ecclesiastical art and Norwegian heritage. It is covered with a layered coating that gives rise to complex reflective properties and gives the sculpture a unique appearance. We studied the goniometric, spectral, and chromatic properties of mock-ups manufactured according to medieval techniques, and also carried out accelerated aging. We compared the properties of aged and original mock-ups, and found non-trivial changes in polychrome appearance. While the color of the mock-ups did not change significantly, we observed a noticeable change in their glossiness, presumably caused by structural degradation of the surface. We also found a difference in the goniometric properties of the polychrome material’s reflectance as a function of angle. Reflectance distributions that were originally symmetric with respect to angle became asymmetric. These findings will help to understand the original appearance of the Hedal Madonna, as well as aiding the design of appropriate conservation conditions for both the original statue and its recent reconstruction.

Translucency is one of the major appearance attributes. Apparent translucency is impacted by various factors including object shape and geometry. Despite general proposals that object shape and geometry have a significant effect on apparent translucency, no quantification has been made so far. Quantifying and modeling the impact of geometry, as well as comprehensive understanding of the translucency perception process, are a point of not only academic, but also industrial interest with 3D printing as an example among many. We hypothesize that a presence of thin areas in the object facilitates material translucency estimation and changes in material properties have larger impact on apparent translucency of the objects with thin areas. Computergenerated images of objects with various geometry and thickness have been used for a psychophysical experiment in order to quantify apparent translucency difference between objects while varying material absorption and scattering properties. Finally, absorption and scattering difference thresholds where the human visual system starts perceiving translucency difference need to be identified and its consistency needs to be analyzed across different shapes and geometries.

Effect of masticatory simulation on the translucency of different types of dental zirconia