徳永 留美

In this study, we propose a method to estimate oxygen saturation by selecting the best bands from video images captured by a multiband camera. Oxygen saturation is one of the most important bioindicators for measuring human health. For example, when a person contracts COVID-19, which is currently prevalent, oxygen uptake does not work properly and oxygen saturation drops without the person being aware of it, which may lead to severe symptoms. Monitoring oxygen saturation is very important so that the person receives treatment before such a situation occurs. The commonly used contact sensor is uncomfortable because of its pressure and it is difficult to wear on a daily basis, so non-contact estimation of oxygen saturation is desirable. To estimate oxygen saturation using a contact sensor, the difference in the absorption coefficients of oxidized hemoglobin and deoxidized hemoglobin is used. Using the same principle, it is possible to estimate oxygen saturation without contact using the signals from two channels obtained by an RGB camera. Currently, many smartphones are equipped with infrared cameras for face recognition, and increasingly more models are equipped with multi-camera systems consisting of RGB and infrared cameras. In such cases, it is difficult to take advantage of the multiple bands because the optimal combination of bands for oxygen saturation estimation varies depending on the imaging environment and the subject. In this study, to select the optimal combination of bands from multi-band video images, we used a Monte Carlo simulation of light scattering on the skin to simulate pulse waves during oxygen saturation changes while measuring the signals with a multi-band camera. We further propose a method to select the most accurate combination for estimating the oxygen saturation based on the features obtained from the pulse wave.

Previous claims of the number of color categories and corresponding basic color terms in modern Mandarin Chinese remain irreconcilable, mainly due to the shortage in objectively evaluating the basicness of color terms with statistical significance. Therefore the present study applied k-means cluster analysis to investigate native Mandarin Chinese speakers' color naming data of 330 color chips similar to those used in World Color Survey. Results confirmed that there are 11 basic color categories among modern Mandarin speakers in Taiwan, one corresponding to each basic color term. Results also showed that observers overwhelmingly agreed in their use of Mandarin color terms, including those that had yielded ambiguous results in previous studies (gray, brown, pink, and orange). There is significant cross-language similarity when comparing the distribution of color categories in the World Color Survey chart with American English and Japanese data. The motif analysis and group mutual information analysis suggest that Mandarin color terms used in Taiwan describe very similar categories and are, hence, similarly precise in communicating color information as those in Japanese and American English. These results show that three languages of fundamentally different cultures and histories have very similar basic color terms.

Despite numerous prior studies, important questions about the Japanese color lexicon persist, particularly about the number of Japanese basic color terms and their deployment across color space. Here, 57 native Japanese speakers provided monolexemic terms for 320 chromatic and 10 achromatic Munsell color samples. Through k-means cluster analysis we revealed 16 statistically distinct Japanese chromatic categories. These included eight chromatic basic color terms (aka/red, ki/yellow, midori/green, ao/blue, pink, orange, cha/brown, and murasaki/purple) plus eight additional terms: mizu ("water'')/light blue, hada ("skin tone'')/peach, kon ("indigo'')/dark blue, matcha ("green tea'')/yellow-green, enji/maroon, oudo ("sand or mud'')/mustard, yamabuki ("globeflower'')/gold, and cream. Of these additional terms, mizu was used by 98% of informants, and emerged as a strong candidate for a 12th Japanese basic color term. Japanese and American English color-naming systems were broadly similar, except for color categories in one language (mizu, kon, teal, lavender, magenta, lime) that had no equivalent in the other. Our analysis revealed two statistically distinct Japanese motifs (or color-naming systems), which differed mainly in the extension of mizu across our color palette. Comparison of the present data with an earlier study by Uchikawa & Boynton (1987) suggests that some changes in the Japanese color lexicon have occurred over the last 30 years.

Colour constancy needs to be reconsidered in light of the limits imposed by metamer mismatching. Metamer mismatching refers to the fact that two objects reflecting metameric light under one illumination may reflect non-metameric light under a second; so two objects appearing as having the same colour under one illuminant can appear as having different colours under a second. Yet since Helmholtz, object colour has generally been believed to remain relatively constant. The deviations from colour constancy registered in experiments are usually thought to be small enough that they do not contradict the notion of colour constancy. However, it is important to determine how the deviations from colour constancy relate to the limits metamer mismatching imposes on constancy. Hence, we calculated metamer mismatching's effect for the 20 Munsell papers and 8 pairs of illuminants employed in the colour constancy study by Logvinenko and Tokunaga and found it to be so extensive that the two notions-metamer mismatching and colour constancy-must be mutually exclusive. In particular, the notion of colour constancy leads to some paradoxical phenomena such as the possibility of 20 objects having the same colour under chromatic light dispersing into a hue circle of colours under neutral light. Thus, colour constancy refers to a phenomenon, which because of metamer mismatching, simply cannot exist. Moreover, it obscures the really important visual phenomenon; namely, the alteration of object colours induced by illumination change. We show that colour is not an independent, intrinsic attribute of an object, but rather an attribute of an object/light pair, and then define a concept of material colour in terms of equivalence classes of such object/light pairs. We suggest that studying the shift in material colour under a change in illuminant will be more fruitful than pursuing colour constancy's false premise that colour is an intrinsic attribute of an object.