Luminance-based specular gloss characterization (original) (raw)
Related papers
Image Contrast Measure as a Gloss Material Descriptor
Lecture Notes in Computer Science, 2017
Bidirectional reflectance distribution function provides a physical description of material appearance. In particular, it helps to describe the gloss. We suggest that, at least, one attribute of gloss: Contrast gloss (luster), may be described directly from an image by using local image contrast measurement. In this article, we investigate the relation between image contrast measures, gloss perception and bidirectional reflectance distribution function based on the Ward's α model parameter. Although more investigation is required to provide stronger conclusions, it seems that image related contrast measures may provide an indication of gloss perception.
Development of an image-based gloss measurement instrument
Journal of Coatings Technology and Research
This paper reports on the development of a measurement instrument to perform gloss measurements using an image-based detector. The image-based gloss meter was built according to the specifications of the optical layout of a specular gloss meter in a 60°m easurement geometry, as described in ASTM D523-14. The photodiode detector was thereby substituted with a CMOS detector. The optical layout of the system was designed and validated by the use of ray tracing software. A series of 16 matte to high-gloss test samples, with nominal gloss values ranging between 3 and 90 gloss units, was used to compare specular gloss measurements obtained with the developed instrument and a commercial specular gloss meter. An average and maximum deviation of only 1.2 and 2.7 gloss units, respectively, was obtained, confirming the suitability of the system to perform standard specular gloss measurements. The potential benefits of the image-based approach were then studied. By way of example, the optical characterization of orange peel and contrast gloss by the use of the system was discussed, corroborating the fact that the proposed instrument offers important opportunities for a more global characterization of the total gloss impression.
Effects of Shape, Roughness and Gloss on the Perceived Reflectance of Colored Surfaces
Frontiers in Psychology, 2020
This study examined perceptual differentiation of specular from diffuse shading for the recovery of surface color and gloss. In Experiment 1, we parametrically varied the mesoscale relief height of globally planar surfaces, specular sharpness and the orientation of the surface relative to the light source. We obtained psychophysical matches for perceived color saturation and value (HSV), but also considered whether the main effects could be influenced by color space used when transforming data to perceptually-uniform CIE LCH space. Results revealed strong interactions between perceived color attributes and the lighting conditions, the structure of specular reflections, and surface relief. Declines in saturation were observed with increasing specular roughness (using an HSV color representation), but no similar decline was observed in chroma (using a CIE LCH color representation). Experiment 2 found strong negative correlations between perceived gloss and specular roughness. Perceived gloss also depended on mesoscopic relief height and orientation of the surface relative to the light source. Declines in perceived gloss moderately accounted for the variability in color saturation and value matches obtained in Experiment 1. We found information about perceived specular coverage could further improve the model's accountability of perceived color saturation and lightness (Experiment 3). These findings together suggest that perceived color saturation and color value depends on the visual system's ability to distinguish the underlying diffuse shading from specular highlights in images.
Statistical correlates of perceived gloss in natural images
It is currently debated whether the perception of gloss is linked to the statistical parameters of the retinal image. In particular, it has been suggested that gloss is highly correlated with the skewness of the lumi-nance histogram. However, other psychophysical work with artificial stimuli has shown that skewness alone is not enough to induce the perception of gloss. Here, we analyzed many images of natural surfaces to search for potential statistical correlates of perceived gloss. We found that skewness indeed correlates with gloss when using rendered stimuli, but that the standard deviation, a measure of contrast, correlates better with perceived gloss when using photographs of natural surfaces. We verified the important role of contrast by manipulating skewness and contrast within images. Changing the contrast in images significantly modulates perceived gloss, but manipulating the skewness of the luminance histogram had only a small effect.
Highlight shapes and perception of gloss for real and photographed objects
Journal of Vision, 2016
Gloss perception strongly depends on the threedimensional shape and the illumination of the object under consideration. In this study we investigated the influence of the spatial structure of the illumination on gloss perception. A diffuse light box in combination with differently shaped masks was used to produce a set of six simple and complex highlight shapes. The geometry of the simple highlight shapes was inspired by conventional artistic practice (e.g., ring flash for photography, window shape for painting and disk or square for cartoons). In the box we placed spherical stimuli that were painted in six degrees of glossiness. This resulted in a stimulus set of six highlight shapes and six gloss levels, a total of 36 stimuli. We performed three experiments of which two took place using digital photographs on a computer monitor and one with the real spheres in the light box. The observers had to perform a comparison task in which they chose which of two stimuli was glossiest and a rating task in which they rated the glossiness. The results show that, perhaps surprisingly, more complex highlight shapes were perceived to produce a less glossy appearance than simple highlight shapes such as a disk or square. These findings were confirmed for both viewing conditions, on a computer display and in a real setting. The results show that variations in the spatial structure of ''rather simple'' illumination of the ''extended source'' type highlight influences perceived glossiness.
Quantification of gloss perception as a function of stimulus duration
2007
The mechanism and temporal characteristics of gloss perception are not entirely clear. In addition, the formulation for predicting gloss perception from photometric values has not been established. In the present study, we conducted an experiment to measure several temporal characteristics of gloss perception in order to clarify the mechanism. All stimuli were rendered as computer graphics with Phong and Lambert models to provide gloss perception to human observers. We measured perceptual glossiness with a magnitude estimation method and perceptual diffuse/specular reflectance of test stimuli with a matching method under several stimulus conditions, such as reflectance coefficients and stimulus duration. The results showed that the perceptual specular component and perceptual glossiness increase with decreasing stimulus duration. Finally, we proposed a formulation to predict perceptual glossiness as a function of stimulus duration.
Contextual effects in human gloss perception
Electronic Imaging, 2018
The well-known simultaneous contrast effect describes how surrounding surfaces influence lightness perception. Similar contextual effects are ubiquitous in the lightness literature. Contextual effects in gloss perception however, have not yet been studied intensively. Here, we describe two distinct studies that investigate the role of spatial interactions between different glossy materials. In a first study we produced real surfaces that contain two different materials and compared perceived gloss in two conditions: in isolation and in context with a second material. Our results provide strong evidence that the context largely influences perceived gloss. Gloss ratings of identical materials differed depending on the presentation mode. In a second study we wished to quantify the strength of these contextual effects using Maximum likelihood conjoint measurement. We used glossy versions of the simultaneous contrast display and again found strong influences of albedo and gloss of the surroundings on perceived gloss and lightness. Both studies hint towards a profound influence of the context on perceived gloss. Investigating spatial interactions between materials within a scene has largely been studied in the lightness literature but only received moderate attention in the gloss literature. Our results provide confirmatory evidence that perceived gloss is shaped by other materials in the scene.
Brazilian Dental Science
Objective: To evaluate the visual perception of surface gloss of resin composite under different illuminants by different observers. Material and methods: twelve cylindrical specimens (6mm x 1mm) were fabricated using a nanofilled resin composite (Z350, A2E shade) in order to compare different observers and to determine the limit of perceptibility of surface gloss. Bovine tooth specimen with similar dimensions was obtained for the comparison of different illuminants. Polishing of resin specimens was performed resulting in 6 groups, presenting surface gloss values at 10, 25, 40, 55, 70, and 85 GU (gloss units), measured by glossmeter (NOVOCURVE). Fifteen individuals were selected: 5 lay-person, 5 undergraduate students, and 5 dental professionals. Participants observed the specimens in a light booth (Gti lightbox) under three different illuminants, and rated the possible combinations between resin specimens or with the bovine enamel specimen (85GU). Data obtained were analyzed by PROBIT non-linear regression analysis (α=0.05). Results: Differences were observed among types of illuminants (p=0.042) and ΔGU (p=0.004), with no interaction between factors (p=0.139). The fluorescent light presented lower surface gloss perceptibility values in relation to incandescent light. There was no influence by type of observers (p=0.598). The surface gloss perception limit was 17.6 GU under the presented tested conditions. Conclusion: the illuminant type influenced perception of gloss, with lower percentage of perceptibility for fluorescent light, while such perceptibility was not influence by different observers. Influência de diferentes iluminantes e observadores na percepção do brilho superficial da resina composta