溝上 陽子

Gloss is associated significantly with material appearance, and observers often focus on gloss unevenness. Gloss unevenness is the intensity distribution of reflected light observed within a highlight area, that is, the variability. However, it cannot be analyzed easily because it exists only within the highlight area and varies in appearance across the reflection angles. In recent years, gloss has been analyzed in terms of the intensity of specular reflection and its angular spread, or the bidirectional reflectance distribution function (BRDF). In this study, we develop an apparatus to measure gloss unevenness that can alter the angle with an angular resolution of 0.02°. Additionally, we analyze the gloss unevenness and BRDF in terms of specular reflection. Using a high angular resolution, we measure and analyze high-gloss materials, such as mirrors and plastics, and glossy materials, such as photo-like inkjet paper and coated paper. Our results show that the magnitude of gloss unevenness is the largest at angles marginally off the center of the specular reflection angle. We discuss an approach for physically defining gloss unevenness based on the BRDF.

Abstract Explicit evaluation methods and suppression techniques for reflected glare have not been clarified in museum lighting. The purpose of this study is to elucidate the occurrence mechanism of reflected glare and to make use of its knowledge for future exhibitions in museums. In this paper, for the first step, we focused on the several factors, which were assumed to have an influence on the intensity of the reflected glare, such as the balance between ambient light levels for an exhibition room and target light levels for paintings, the Munsell value of paintings, and the amount of varnish coating. We conducted a subjective experiment in which the reflected glare on the replica paintings was evaluated by subjects aged in their 20s in an experimental room that was assumed to be an actual exhibit space. Based on the results of this experiment, we confirmed that the degree of reflected glare in museums could be roughly estimated from luminance distribution, reflectance, and glossiness of the paintings.

One strategy for aiding color deficiencies is to use three narrow passbands to filter the light spectrum to increase the saturation of colors. This filtering is analogous to the narrow emission bands used in wide gamut lighting or displays. We examined how perception adapts to the greater color gamut area produced by such devices, testing color-normal observers and simulated environments. Narrowband spectra increased chromatic contrasts but also increased contrast adaptation, partially offsetting the perceived contrast enhancements. Such adaptation adjustments are important for understanding the perceptual consequences of exposure to naturally or artificially enhanced color gamut areas for both color-deficient and color-normal observers.

Gloss is an essential visual property of objects. It is still controversial how well gloss constancy works under different light distributions. In this paper, we conducted three experiments of different light distributions to investigate whether the stable discrimination and gloss constancy of paper occurred with different glossiness levels at the different light source distances and illuminances. The results suggest instability of paper discrimination and gloss perception when both light source distance and illuminance change. Then we tested two additional conditions. One is setting the distance the same and manipulating the illumination. The other is setting the illuminance constant and manipulating the distance, respectively. We further verify that illuminance and specular reflection can affect material and gloss perception, regardless of the width of the highlight region changed by light source distance.

The appearance of an object depends on its material, shape, and lighting. In particular, the diffuseness of the illumination has a significant effect on the appearance of material and surface texture. We investigated a diffuseness condition suitable for reproducing surface appearance using computer graphics. First, observers memorized the appearance and impression of objects by viewing pre-observation images rendered using various environment maps. Then they evaluated the appearance of the objects in test images rendered under different levels of diffuseness. As a result, moderate diffuseness conditions received a higher evaluation than low diffuseness conditions. This means that low or very high diffuseness unfamiliar in daily life is unsuitable for reproducing a faithful and ideal surface appearance. However, a particular material is difficult to memorize and evaluate its appearance. The results suggest that it is possible to define a diffuseness that adequately reproduces the appearance of an object using computer graphics.

Human skin color is one of the most common colors that we see and perceive in everyday life. Previous research on skin color distribution in young Japanese women has revealed that yellowish skin has higher lightness than reddish skin. Furthermore, reddish skin appears brighter than yellowish skin when both have the same lightness (Yoshikawa et al., 2012). Despite these findings, it is unclear how brightness perception of facial skin color is influenced by the diversity of skin colors and observers. The present study investigated the perception of facial skin color among observers in three Asian countries. A young Japanese female face was used, and test faces of four skin color shades were prepared, corresponding to the average skin colors of Japanese, Thai, Caucasian, and African individuals. A test image (with constant lightness but different hue angles) and a scale image (with the original hue but varying lightness) were presented side-by-side on a color-calibrated tablet display, and observers adjusted the brightness of the facial skin of the scale image to match that of the test image. The findings indicated that Japanese observers showed a trend in which reddish skin was perceived as brighter than yellowish skin; however, Thai and Chinese observers did not show this trend. This implies the potential influence of ethnicities or environments on brightness perception of facial skin.

© 2020 Wiley Periodicals, Inc. In this article, we present an evaluation method for the skin color distribution in the face area. Unlike previous methods that extract a specific area, our method subdivides the entire face into small regions and analyzes detailed, per-frame textures. Our evaluation method for skin color distribution is based on facial feature points and includes segmentation that takes into account the facial skeleton and muscle orientation. The use of facial feature points enables a comparison at relatively equal positions on the face without depending on the shape or size of the individual's face. Our evaluation method is versatile, and as an application, we clarified age-specific features and seasonal variations of facial color distribution. As a result of applying this evaluation method to the facial images of women aged 20 to 78 years, we confirmed that the lightness of the face decreased as age increased. In particular, the decrease in lightness was remarkable in the region along the cheekbone, from the temple to the center of the cheek. Furthermore, we analyzed the seasonal changes of melanin distribution in the face area. This showed that the melanin index increased particularly in the cheekbone area in the summer when the influence of ultraviolet rays became large. Our novel methodology and the data presented in this article will be useful in various fields, such as dermatology, cosmetics, and computer vision.

© 2019 Elsevier Ltd We perceive the stable surface color of objects even if the reflected light changes depending on illumination color. This perceptual property is known as color constancy. To understand color constancy in real life it is essential to conduct experiments within real three-dimensional (3-D) space. Color constancy is generally better and more stable for 3-D stimuli compared with two-dimensional (2-D) stimuli. Color, shape, and material properties are not represented precisely in a 2-D environment, such as images or patterns. Thus, there is missing information that may influence our recognition of objects and scenes. The critical factors for color constancy have not be conclusively identified. However, the combination of various cues present within the object and environment, and the recognition of space, illumination and objects, should contribute to establishing good and stable color constancy.