溝上 陽子

© 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.

© Optics Photonics International Congress 2019. We evaluated the colour performance of the latest self-emissive displays based on the CIELAB colour volume metric. The white reference point was set at (1) white with a 25% window, (2) absolute value, (3) white with a 100% window. None of the reference whites resulted perfectly satisfactorily on its own, but the combination of these results was reasonable. The CIELAB volume metric with the appropriate normalization can be a great tool for evaluating the latest self-emissive display.

© Springer Nature Switzerland AG 2019. The recent development of new solid-state lamps including OLED lighting offered a wide variety of lighting conditions through controlling the spectral power distribution and the spatial distribution of light. The appearance of an object surface is largely influenced by lighting conditions and object materials. Variable control of lighting condition would be useful to offer an optimal material impression. We have investigated the possibility whether the subjective evaluation, comparing material appearance under different lighting distribution with that under natural illumination, is able to determine a lighting condition for an appropriate material appearance. We tested viewing condition consisted of three spotlight sizes and three illuminance levels. Participants chose one viewing condition in which the material appearance of fruits and vegetable food samples was closest to those impression learned from observing and holding freely in a reference natural illumination. In addition, they evaluated impressions of stimuli in each condition by the twelve questionnaires of seven-point scales. The result showed higher tendencies to select the wide spotlight size condition with higher diffuseness of illumination rather than narrower spotlight conditions, suggesting that diffuseness of illumination influences object material appearance. Results of seven-point scales showed differences between samples, but little differences among lighting distribution. It was thus suggested the possibility to provide an optimal lighting condition to offer material appearance similar to material impression learned with visual and tactile information in natural illumination.

Most color simulators for color deficiencies are based on the tristimulus values and are intended to simulate the appearance of an image for dichromats. Statistics show that there are more anomalous trichromats than dichromats. Furthermore, the spectral sensitivities of anomalous cones are different from those of normal cones. Clinically, the types of color defects are characterized through Rayleigh color matching, where the observer matches a spectral yellow to a mixture of spectral red and green. The midpoints of the red/green ratios deviate from a normal trichromat. This means that any simulation based on the tristimulus values defined by a normal trichromat cannot predict the color appearance of anomalous Rayleigh matches. We propose a computerized simulation of the color appearance for anomalous trichromats using multispectral images. First, we assume that anomalous trichromats possess a protanomalous (green shifted) or deuteranomalous (red shifted) pigment instead of a normal (L or M) one. Second, we assume that the luminance will be given by L + M, and red/green and yellow/blue opponent color stimulus values are defined through L-M and (L + M) - S, respectively. Third, equal-energy white will look white for all observers. The spectral sensitivities of the luminance and the two opponent color channels are multiplied by the spectral radiance of each pixel of a multispectral image to give the luminance and opponent color stimulus values of the entire image. In the next stage of color reproduction for normal observers, the luminance and two opponent color channels are transformed into XYZ tristimulus values and then transformed into sRGB to reproduce a final image for anomalous trichromats. The proposed simulation can be used to predict the Rayleigh color matches for anomalous trichromats. We also conducted experiments to evaluate the appearance of simulated images by color deficient observers and verified the reliability of the simulation. (c) 2018 Optical Society of America

It has been suggested that skin color changes not only with advancing age but also with the times. The purpose of this study was to investigate changes in Japanese women's facial skin color over 25 years, as well as the changes in skin pigmentation that affect skin color. First, skin color changes in terms of Munsell color values were investigated. A total of 3181 Japanese women residing in the greater Tokyo area were enrolled, and datasets were collected using spectrophotometers, designated as the 1991, 2001, 2005, and 2015 data. The mean Munsell hue, value, and chroma were calculated for each measurement year. Next, the concentrations of melanin and hemoglobin were calculated from spectral data, to investigate changes in skin pigmentations. Finally, Monte Carlo simulations were performed to verify that the suggested changes in skin pigmentations brought about skin color changes. As a result, skin color significantly changed toward high lightness, low saturation, and high yellowness from the 1991 data to the 2001 data. From the 2005 to 2015 data, the skin color distribution shifted toward lower saturation and increased redness. In addition, the concentration of hemoglobin decreased significantly from the 1991 data to the 2001 data, while the melanin concentration decreased significantly from the 2005 data to the 2015 data.

We investigated the applicability of the CIELAB color gamut volume metric to the latest self-emissive displays. Where to set the reference white is the key. The luminance of maximum white, full-screen white and absolute value are appropriate. The weighted average can give the criteria of the display color performance.

肌の色は，年齢・健康状態・顔印象などの判断に関わる重要な要素であり，その知覚特性を明らかにすることは非常に重要である．先行研究で，人は肌の赤みの変化に対して高い感度を示すという特性や，赤みがかった肌の方がより明るく見えるといった特性が報告されている．これらのことから，人は肌を認識した上で，肌特有の色知覚をしている可能性が考えられる．そこで本研究では，特に肌色の色分布と色弁別の関係性に注目した．日本人女性694名の肌を測定して得られたCIELAB値に対して主成分分析を行い，第1主成分と第2主成分によって構成される肌色特有の色平面を構築した．そして，肌画像と肌色単色画像をその平面上の8方向に変調し，肌色の弁別閾値を調べた．また，その変調方向と肌の色の主な色素成分であるメラニン・ヘモグロビン量の変化との対応関係を調べた．実験の結果，人はヘモグロビンの増加に伴う色変化に対して弁別能が高い可能性が示唆された．

There has been debate about how and why color constancy may be better in three-dimensional (3-D) scenes than in two-dimensional (2-D) scenes. Although some studies have shown better color constancy for 3-D conditions, the role of specific cues remains unclear. In this study, we compared color constancy for a 3-D miniature room (a real scene consisting of actual objects) and 2-D still images of that room presented on a monitor using three viewing methods: binocular viewing, monocular viewing, and head movement. We found that color constancy was better for the 3-D room; however, color constancy for the 2-D image improved when the viewing method caused the scene to be perceived more like a 3-D scene. Separate measurements of the perceptual 3-D effect of each viewing method also supported these results. An additional experiment comparing a miniature room and its image with and without texture suggested that surface texture of scene objects contributes to color constancy.

人間の視覚は加齢に伴い変化することが知られている．変化の1つとして白内障が挙げられる．白内障になると視界にかすみが生じ，結果として視界の彩度が低下する.高橋らの研究では，かすみが生じた瞬間に彩度低下を補正する効果の存在を明らかにした．しかしこの研究で使用した画像は1種類であり，結果の一般性についての検証が不十分であった．本研究では，かすみに対する順応時間と彩度知覚の関係について，より詳細に検証した．実験では，眼前にフォギーフィルタを設置後，0秒から180秒の間で設定時間ごとにテスト刺激を各2秒間呈示し，被験者の応答を記録した．彩度を段階的に変調させた各テスト刺激に対し，「自然に見える」と「色あせて見える」境界（低彩度側）と「自然に見える」と「色鮮やかに見える」境界（高彩度側）を測定することで，画像の鮮やかさが自然に見える範囲を求めた．その結果，瞬間的な補正効果が先行研究と同様に得られた．さらに，かすみがある場合，かすみがない場合に比べて自然に見える範囲が増加した．時間的な変化では，高彩度側はフィルタありの場合の見えに近づき，低彩度側はより彩度が低い画像も自然に見えるようになった．

Background: Facial skin pigmentation is one of the most prominent visible features of skin aging and often affects perception of health and beauty. To date, facial pigmentation has been evaluated using various image analysis methods developed for the cosmetic and esthetic fields. However, existing methods cannot provide precise information on pigmented spots, such as variations in size, color shade, and distribution pattern. The purpose of this study is the development of image evaluation methods to analyze individual pigmented spots and acquire detailed information on their age-related changes. Methods: To characterize the individual pigmented spots within a cheek image, we established a simple object-counting algorithm. First, we captured cheek images using an original imaging system equipped with an illumination unit and a high-resolution digital camera. The acquired images were converted into melanin concentration images using compensation formulae. Next, the melanin images were converted into binary images. The binary images were then subjected to noise reduction. Finally, we calculated parameters such as the melanin concentration, quantity, and size of individual pigmented spots using a connected-components labeling algorithm, which assigns a unique label to each separate group of connected pixels. Results: The cheek image analysis was evaluated on 643 female Japanese subjects. We confirmed that the proposed method was sufficiently sensitive to measure the melanin concentration, and the numbers and sizes of individual pigmented spots through manual evaluation of the cheek images. The image analysis results for the 643 Japanese women indicated clear relationships between age and the changes in the pigmented spots. Conclusion: We developed a new quantitative evaluation method for individual pigmented spots in facial skin. This method facilitates the analysis of the characteristics of various pigmented facial spots and is directly applicable to the fields of dermatology, pharmacology, and esthetic cosmetology.

顔の肌色は，肌色に対する嗜好やそれに伴う化粧行動などに影響を受け，時代によって変化することが示唆されている．1990年代初頭と比較し，2000年代初頭の日本人女性の肌色は，明度が上昇，彩度が低下，色相が黄みへ変化したことが確認されているが，2000年以降の変遷については明らかにされていない．その背景には，多くの女性の肌色データの収集が困難なことに加え，同一測色計の維持の難しさがある．本研究の目的は，異なる分光測色計を用いて得られた肌色データを比較可能とするための補正式を構築し，日本人女性の肌色分布の長期的な変遷について明確化することである．まず，異なる分光測色計を用いて肌の同一部位を測定し，その差異を確認した上で，肌の分光反射率の補正式を構築した．さらに，2005年と2015年に約2000名の日本人女性の頬部を測色し，補正式を適用した1990年代初頭のデータ，2001年代初頭のデータと比較することで，約25年間の肌色分布の変遷を明らかにした．2000年以降，日本人女性の肌色分布は低彩度・赤みへシフトしたことが確認された．

Recently, the demand for printed wood grain has been growing. The elements of wood grain of natural wood and printed wood grain are different. These differences result in the differences in characteristics of their corresponding spatial frequencies, and would influence the identification of natural and printed wood grain. In our study, we analyzed the spatial frequency of wood samples. Results showed that a more noticeable the difference in the samples was seen in the high spatial frequency region. We also visually evaluated the discriminability between natural and printed wood grain for various viewing distances. The results demonstrated that it was difficult to distinguish between natural and printed wood grain at long distances, whereas, it was easy at short distances. This suggests that the differences in the high spatial frequency and the presence or absence of half tone has an effect on the distinguishability in natural and printed wood grain samples.

The shape of image luminance histograms is related to material perception. We investigated how the luminance histogram contributed to improvements in the perceived quality of wood images by examining various natural wood and adhesive vinyl sheets with printed wood grain. In the first experiment, we visually evaluated the perceived quality of wood samples. In addition, we measured the colorimetric parameters of the wood samples and calculated statistics of image luminance. The relationship between visual evaluation scores and image statistics suggested that skewness and kurtosis affected the perceived quality of wood. In the second experiment, we evaluated the perceived quality of wood images with altered luminance skewness and kurtosis using a paired comparison method. Our result suggests that wood images are more realistic if the skewness of the luminance histogram is slightly negative.

色を定量的に扱う際，人間の視覚特性を考慮することが大切である。CIE表色系は，色覚の感度特性に基づく色の表現と捉えることができる。しかし，等色関数は等色実験により求められており，錐体の分光感度とは一致していない。近年，錐体の分光感度を直接用いた，視覚生理に基づくより正確な色の表現も提案されている。一方，色覚メカニズムは環境に適応するように進化しており，森林と果物の色の違いや季節変化等，環境の色特性が色覚の形成に影響を与えていると考えられる。環境の色と色覚メカニズムの密接なかかわりは進化や発達の面だけではない。私たちの視覚は短期的な環境の明るさや色の変化に対しても適応し，安定した見えを保つことができる。色の恒常性や，環境の彩度低下を補正して知覚する特性は，これらの色覚の適応性，柔軟性を示す例と言える。 色の見えの評価には，表色値のみでなくこれらの適応メカニズムの影響も考慮する必要がある。