Glossiness can be increased by adding chromatic information to the object images. However, the mechanisms that create color-induced glossiness enhancement are unclear. In this study, we psychophysically measured the glossiness of object images to which various hue chromaticities were added to elucidate the perceptual and image factors that explain the color-induced glossiness enhancement effect. Two types of coloring conditions were tested: the both-colored (BC) condition, in which both specular and diffuse components were colored with the same chromaticity, and the diffuse-colored (DC) condition, in which only diffuse components were colored while specular components remained achromatic. The results showed that glossiness enhancement was more prominent in the BC than in the DC condition, and the dependency of glossiness enhancement on the stimulus color direction was similar to that of the Helmholtz-Kohlrausch (H-K) effect. Furthermore, we performed a regression analysis with a linear mixed model based on image features and an additional experiment in which an H-K effect-based increase in perceived brightness was imitated on achromatic stimuli by manipulating luminance. The results demonstrated that the H-K effect-based brightness enhancement in the highlight regions explains the glossiness enhancement effect well. These results suggest that the H-K effect, especially around the highlight region, is a dominant factor that creates the color-induced glossiness enhancement, although other color-related factors could also be partly involved.
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 compared the color-discrimination thresholds and supra-threshold color differences (STCDs) obtained in complete chromatic adaptation (gray) and incomplete chromatic adaptation (red). The color-difference profiles were examined by evaluating the perceptual distances between various color pairs using maximum likelihood difference scaling. In the gray condition, the chromaticities corresponding with the smallest threshold and the largest color difference were almost identical. In contrast, in the red condition, they were dissociated. The peaks of the sensitivity functions derived from the color-discrimination thresholds and STCDs along the L–M axis were systematically different between the adaptation conditions. These results suggest that the color signals involved in color discrimination and STCD tasks are controlled by separate mechanisms with different characteristic properties.
Understanding visual perception of materials is critical for informing image-based approaches to real-time rendering. This poster presents a new cue to translucency that can be efficiently modeled using graphical rendering.
When we enter a dark place like a tunnel from a bright exterior, our visual sensitivities take some time to adapt to the lower light level. However, there have been few reports about how quickly our sensitivities of luminance and chromaticity discrimination recover in this situation. This study aimed to quantify the time course of discrimination sensitivity for luminance and chromaticity directions after an abrupt decrease in background luminance. In each trial, the background luminance dropped from 100 cd/m² to 1 cd/m². Then, one target and three reference stimuli with different colors were presented under four stimulus onset asynchrony (SOA) conditions. The observer was asked to discriminate the target stimulus from the reference stimuli. The results showed that discrimination sensitivity was lowest right after the background luminance change and gradually improved with SOAs. However, sensitivity recovery differed across color directions, with the most improvement in luminance, followed by S, and negligible change in L-M. There was a statistically significant difference between +S and ±(L-M) sensitivities, indicating that the sensitivity recovery after the sudden background luminance change differed between chromaticity directions. Based on the comparison with previous studies, we speculate that both adaptation and masking may contribute to the temporal change of discrimination sensitivities.
Organic electroluminescent lighting (OLED) is expected to become one of the next generation lighting devices. In this research, we investigated the impression of a space illuminated by either flat-type LED lighting panels or OLED panels by changing the area of the illumination. The experiment was conducted with a small box in which miniature furniture was placed. Subjects rated the impression of the room for 20 adjective items in five steps while observing the model of the living room. From the results of the rated values, we found that the space illuminated by the surface-emitting type illumination will increase the impression of “brightness” and “uniformity” as the area of illumination increases. Moreover, OLED lighting was found superior in many items, such as warm and soft. From the results of factor analysis, several factors were extracted, such as “amenity”, “activeness”, and “personality”. INTRODUCTION In recent years, Organic Electro-Luminescence (OLED) lighting has been attracting attention as a next-generation illuminant. This type of lighting has several important features including a wide range of illumination, thickness, and flexibility. The researches dealing with OLED in practical use, however, have just started and it is essential to explore various aspects of OLEDs before it enters the market. One of the biggest differences between OLED and other lighting devices is that OLED is a surface-emitting light source. When installed as a ceiling light, it is possible to place many OLED panels right next to each other to occupy a large area of a ceiling. Compared with conventional point or line light sources such as incandescent and fluorescent lamps, the setting of area light sources can cast shadows of the objects in a completely different way. As a result, OLED may mediate a different impression of the space. The purpose of this research is to find the effects of the relative ratio of the light source to the ceiling on the impression of the space under its illumination. Moreover, a flat-panel type LED lighting panel, which looks similar to an OLED panel, has recently entered the market. In order to find the differences in LED and OLED under a similar way of lighting, we repeated the same experiments for both light sources to find any potential effects of the light source on the impression of a space. PA 17
Impacts of lower- and higher- luminance components on the material perception Textures of objects underneath the glossy finish resides in the lower part of the luminance histogram of object images, while specular reflections reside in the higher part. We psychophysically investigated which of these luminance components contributes more to material perception. The stimuli were photographs of various material samples from stone, wood, leather, and fabric categories. In addition, we created two types of luminance-modulated images: low- and high-luminance preserved images (LLP and HLP images). The LLP images were created by compressing the luminance contrast in the higher half of the original photographs by 1/5, and vice versa. The LLP and HLP images were presented randomly on the right and left of the original image at the center, and observers were asked to choose which modified image gave material impression closer to the original image. In the results, there were large differences between sample categories in selection ratios of HLP images, suggesting that the contribution of lower- and higher-luminance components to material perception differed among sample categories. We further investigated relations between the choice and spatial frequency subband components of image statistics. We found that the LLP and HLP were chosen in fabric/leather samples and wood/stone samples, respectively, when the images contain richer high spatial frequency components. This is probably because higher/lower luminance components of images included characteristic patterns of each material. These results suggest that the lower-luminance components possibly play an important role in the material perception for the samples with fine selfshading patterns like fabric and leather.
Human lightness (albedo) perception is not necessarily accurate. Previous studies have shown that humans perceive object lightness based on the surface area excluding specular highlights, though this highlight removal performance varies depending on the surface reflective properties and shapes. The purpose of this study was to examine the image features that determine the ability to remove highlights for lightness perception by focusing on the effects of spatial frequency of surface undulations in psychophysical experiments. The stimuli were computer-graphics images of plate-like objects, in which the undulations of real plastic samples were reproduced. There were many conditions in the spatial frequency and amplitude of the undulations, the surface roughness, and illumination maps as experimental parameters. In each trial, a plane-like object (test stimulus) and a matte sphere (reference stimulus) were presented side-by-side on a display. The observer adjusted the lightness of the reference stimulus so that the perceived lightness was matched between them. The results showed that, roughly speaking, the perceived lightness was determined mainly based on the mean luminance of the test stimulus. However, the perceived lightness was lower than that expected from the mean luminance prediction especially on low roughness stimuli, suggesting the contributions of highlight removal. Thus, we defined the difference in the perceived lightness on the test stimulus from that on flat planes as the highlight-removal index. This index moderately correlated with the image luminance contrast from the stimulus images, especially when filtered by the contrast sensitivity function (CSF). However, when the CSF-filtered luminance contrast was smaller than a certain level, the highlight-removal index was fixed at zero even though the undulations on all test stimuli could be easily perceived. These results suggest that perceptual highlight removal for lightness perception requires much more detailed luminance patterns than those for shape perception.
It has been reported that the colorimetric color match sometimes does not ensure the visual color match between different medias such as a display and a print. One of the reasons is that the color matching functions (CMFs) used in the colorimetric systems (CIE1931 standard observer) do not necessarily represent the observers' CMFs owing to the individual differences. Although we have constructed a device for measuring the individual CMFs, the validity of these measured CMFs has not been fully evaluated. When metameric match is completed by an observer, color difference calculated with his CMFs should be smaller than those calculated with CIE1931 CMFs. In our preliminary experiment, we carried out the color matching experiment between a LCD display and a color chart. Mean color difference (ΔE*ab) calculated with individual CMFs and with CIE1931 were 5.51 and 6.02, respectively. However, the effects of the compensation of individual differences were not so distinct. One of the reasons is that the stimuli used in this experiment had broadband spectral distributions. If we use a stimulus with narrowband spectral distributions, the effects would be further highlighted as the differences in CMFs reveal more clearly. In order to verify this hypothesis, we constructed a stimulus generator with LEDs, and conducted color matching experiments between LED light and a LCD display. In the presentation, we will report our experimental results and effects of compensation of CMFs, which might lead to a “customized” color management system.
