A qualitative description of thermochromism in color measurements

The color of an object depends on the temperature of the object. This phenomenon is known as the thermochromic effect, and it is already noticeable at room temperature if the temperature varies just a few centigrades. Red and orange samples are especially sensitive to temperature variation and may cause difficulties in precise color measurement. In this article we show how the phenomenon is based on physical processes and does not only reflect the instability of red color pigments. We derive simple formulas that are shown to be able to explain the published experimental data. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 271–275, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10062     

Match prediction of highly fluorescent colors

Color formulation of fluorescent materials is not feasible with the usual methods used for nonfluorescent colors. Realizing the need for certain textiles that are dyed with fluorescent colorants, a technique was developed based on using certain dual-monochromator measurements of the spectra of fluorescent colorants. to accomplish this formulation, a new spectral quantity independent of illuminant was developed for all fluorescent colorants. This is termed RELEX, which describes the relative excitation of the colorant. When this quantity is weighted by the spectral power distribution for a specific illuminant and factored for absorption by all ingredients in a mixture of colorants, the proper fluorescent emission is obtained, which can be added to the spectral reflected radiance factor, β_s, for that mixture. Consequently, match prediction can be done for spectral radiance factor, β_T, curves of fluorescent materials using an iterative estimation algorithm.     

热致可逆变色涂料的发展

概述了热致可逆变色涂料及可逆变色涂料微胶囊化的发展应用。     

PP/橡胶合金热致变色原因的探讨

采用熔融共混法制备了几种聚丙烯(PP)/橡胶合金,并用沸水进行浸泡。结果发现,PP/三元乙丙橡胶(EPDM)合金与PP/聚烯烃热塑性弹性体(POE)合金热水浸泡时发生变色,而PP/乙丙橡胶(EPR)合金不变色。采用X射线衍射仪(XRD)、差示扫描量热仪(DSC)对PP/橡胶合金的热致变色原因进行探讨。结果表明:热水浸泡时PP发生二次结晶是热致变色的主要原因。     

三芳甲烷苯酞类可逆热致变色材料

综述了三芳甲烷苯酞类可逆热致变色材料的组成及研究现状,有47篇参考文献.     

硬脂酸镍与焦性没食子酸的热致变色反应研究

本文报道了硬脂酸镍（NiSt2）和焦性没食子酸（Pyrogallicacid，PGA）的热致变色现象，研究了热敏涂层的显色密度随加热温度和时间的变化关系．结果表明，涂层密度随温度的升高和时间的延长而增大．通过溶解度实验和吸收光谱的分析，推测了热致变色的可能产物是NiSt2和PGA生成的某种分子化合物，该分子化合物随浓度的增加可能形成某种分子聚集体，在可见光区产生新的吸收峰．     

Metrology,documentary standards,and color specifications for fluorescent materials

Some aspects of the metrology of fluorescence are reviewed. ASTM Committee E-12 on Appearance has written two documentary standards on the instrumental measurement of fluorescent colors. Test Method E 1247 provides two procedures for detecting small amounts of fluorescence that might affect the measurement or use of nominally nonfluorescent materials. Practice E 991 deals with the measurement of specimens meant to be viewed under standard natural daylight, and that, therefore, must be illuminated by a good instrument daylight simulator. Two procedures are given for assessing the suitability of the simulator, and the required instrument geometry is specified. A future ASTM standard is under consideration that would describe methods for correcting the data obtained with another instrument source to the data that would have been obtained with standard daylight illumination. Two groups of standard specifications exist for fluorescent colors used for signaling or safety enhancement. One defines suitable chromaticities for both red and orange colors [among others], but ignores the fact that these colors cannot always be obtained with good lightfastness by use of existing pigments. the other group provides instead a red-orange specification for which specimens with good lightfastness can be obtained. the relative merits of the two groups are discussed.     

Optimal fluorescent colors

This article poses and discusses a maximization problem: for a given chromaticity, and in a given illumination, how light a fluorescent color is possible. The article does not present a solution, but does offer a conjecture that for many illuminants and many chromaticities the greatest lightness is achieved by a simple form of bispectral function. The output is in two points plus a tail, so we call it a “PPT” function. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 85 – 91, 2007     

The representation of colors in spherical space

Color scaling experiments have established that perceived colors are distributed on the surface of a hypersphere in spherical space. A formal mathematical model of the color space is defined. Color differences as estimated by an observer are equal to the chord distance between corresponding points on the surface in spherical space. In one mathematical model are united: brightness, saturation, and hue as expressed in the empirical Munsell and NCS systems; complementary colors; large color differences; and contrast effects that are not represented in other models. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 113–124, 2008.     

Colorimetry of durable fluorescent retroreflective materials

The development of durable daylight fluorescent retroreflective sheetings has led us to investigate some of the factors that influence color measurement of these materials. the colorimetry of retroreflective materials is particularly sensitive to measurement geometry. the added aspect of fluorescence increases the spectral uncertainties, making appearance measurements even more difficult. the visual properties used to describe fluorescent retroreflective materials should include chromaticity, lightness, peak spectral radiance factor, nighttime color, and color stability on exposure. A number of test methods exist for these measurements; however, practical experience in applying these methods to fluorescent materials shows significant variation in the resulting measured values. Colorimetric measurements on commercial instruments using 45/0 (0/45) geometry, a simulated D65 illuminant, and the CIE 2° standard observer yield results that are inadequate for precise quality control of durable fluorescent retroreflective materials. the uncertainty can be reduced by the use of transfer standards, provided that the standard is similar to the sample in both hue and fluorescent emission. Ultimately, the wide availability of commercial 2-monochromator spectrocolorimeters will be required. © 1995 John Wiley & Sons, Inc.     

Quantitative representation of floral colors

Human and insect pollinator perceived floral colors of 81 species of angiosperms (flowering plants) from Trivandrum (Kerala, India) was represented using the CIE 1976 L*a*b* color space and color hexagon, respectively. The floral color difference among human perceived red, yellow, and blue‐hued flowers and that of each flower from its respective pure hue was calculated using the CIE ΔE 2000 formula. Human perceived floral color difference values were consistently higher than 3.5, indicating the uniqueness of floral colors. Flowers perceived red and yellow by humans were dominant and of comparable proportions. Insect pollinators perceive most of the flowers as blue‐green. Quantitative representation of human and pollinator perceived floral colors would be invaluable to understand the information broadcasted by flowers. It can form the basis of flower grading in the floriculture industry and underpin objectivity in evolving the framework for national pollinator strategies.     

Color appearance and color connotation models for unrelated colors

The purpose of this research is to investigate the color appearance and color connotation of unrelated colors. To investigate color appearance (i.e., brightness, colorfulness, and hue) for unrelated colors, 22 observers have answered their color appearance for 50 unrelated color stimuli using the magnitude estimation method. Perceptual data obtained by the experiment is compared with the color attributes data estimated by unrelated‐color appearance models, CAM97u and CAM02u. It is found that both models perform reasonably well but the performance of CAM02u is better than that of CAM97u. For investigating color connotation for unrelated colors, 32 observers have judged their color connotation for the 50 unrelated color stimuli using the 10 color connotation scales (i.e., “Warm – Cool,” “Heavy – Light,” “Modern – Classical,” “Clean – Dirty,” “Active – Passive,” “Hard – Soft,” Tense – Relaxed,” “Fresh – Stale,” “Masculine – feminine,” and “like – Dislike”), and semantic differential method is used for measurement. It is found that the color connotation models developed for related colors perform poorly for unrelated colors. Experimental results indicate that brightness attribute is confusing to estimate and does not affect color connotation significantly for unrelated colors. Based on the psychophysical data, new models for “Warm‐Cool”, “Heavy‐Light”, “Active‐Passive” and “Hard‐Soft” were proposed using CAM02u hue, brightness, and colorfulness. Color connotations for unrelated colors are classified into three categories, which “Color solidity,” “Color heat,” and “Color purity.” © 2013 Wiley Periodicals, Inc. Col Res Appl, 40, 40–49, 2015     

Exploring compatible facility colors and associated colors for outdoor recreational spaces

Many studies have demonstrated that people associate customary colors to buildings and facilities, and these colors significantly influence people's evaluations of the environment. However, whether customary colors also exist in the environments where building facilities have been installed is rarely discussed. Using correspondence analysis, this study explored the colors associated with five different outdoor recreational spaces (theme parks, national parks, recreational farms, riverside parks, and historic heritage sites) and fitted facility colors. The study acquired a valid sample of 103 college students and demonstrated that people judge colors in recreational spaces according to past experience and their impressions of the spaces. Hue, value, and saturation are not independent factors for color consideration; a color with a specific value and saturation is particularly suitable for some spaces. In addition, the color associated with an environment and the compatible color for facilities are not exactly the same. The possible factors that influence different environment colors and future research directions were also discussed. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 424–432, 2016     

Color measurement of a ruby

The impurity transition element chromium Cr³⁺ in ruby can be excited to high energy levels by absorbing visible light. When the excited Cr³⁺ returns to ground state through an intermediate energy level, the ruby emits red light as fluorescence. The fluorescence of ruby is actually caused by visible light, not by ultraviolet. The color of ruby is attributed to both the absorption and the fluorescence. The spectrum of a natural ruby under visible light is directly measured by a dual integrating sphere spectrometer. The measured spectrum includes both the spectral reflectance and the fluorescence caused by visible light. This study confirmed that the red fluorescence of ruby is indeed caused by visible light, not by ultraviolet radiation. In addition, average color of the ruby is calculated from the measured spectrum, and true color grade is also obtained by the artificial intelligent software of the spectrometer. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 328–333, 2013     

Perceived illumination measured

We consider a method of measurement of apparent illumination using the perceptual phenomenon of fluorescence to which we give a psychophysical explanation based on the hypothesis of direct relation of perception of self-luminosity to the apparent illumination of the scene observed by the viewer. We report results of three experimental studies: (1) measurements of apparent illumination when a flat mondrian in the darkness is observed; (2) measurements of apparent illumination in a “rich” 3D scene; (3) testing linearity of the subjective illumination space. Based on the obtained data, we confirm the basic hypothesis of a relation between the self-luminosity phenomenon and the perceived illumination, and show that the suggested method of measurement of apparent illumination gives reliable and accurate (errors were in the range 4–10%) values of its chromatic components. Apparent illumination in the case of a mondrian observed in the darkness is found unstable, which can be expected given that the context of such a scene is insufficient for obtaining a unique solution for all the components of the photometric problem. In the second experiment, we show that the measurement results remain constant when the context of a “rich” 3D scene is changed and that they follow the changes in illumination conditions. In the third experiment, we study the composition of different illuminations and show that the simple relation f = f₁ + f₂ holds for the measurement of the illumination (f) when two other illuminations (f₁, f₂) are applied simultaneously. © 1998 John Wiley & Sons, Inc. Col Res Appl, 23, 159–168, 1998     

Maximum number of discriminable colors in a region of uniform color space

Continuing a discussion by Kuehni, this note examines the problem of fitting as many as possible colors in a 1‐JND radius sphere such that each pair of colors is separated by at least 1 JND. Kuehni announced nine. A first estimate yields a maximum of 13, but this is too many because colors populating adjacent spheres will be too close to each other. Accordingly, I derive the maximum number, , of discriminable colors per unit volume of color space, and then formally compute from this number packing density a number of colors inside the unit sphere. That estimate, nearly 6, will undoubtedly erode when discrete color points are chosen within the unit sphere. Kuehni's estimate of 9 is too high. © 2016 Wiley Periodicals, Inc. Col Res Appl, 2016     

Suprathreshold color-difference ellipsoids for surface colors

The RIT-DuPont visual color-difference data [Color Res. Appl. 16, 297–316 (1991)] have been used to estimate contours of equal color-differences (ellipsoids) at 19 color centers, in CIELAB and x, y, Y/100 color spaces. The ellipsoid fits are better in the CIELAB space than in x, y, Y/100, since the design of the RIT-DuPont experiment emphasized directional balance in CIELAB. The ellipsoids estimated are hardly tilted with respect to L* or Y/100, and they appear to be in overall good agreement with those reported for object colors in recent publications. From the characteristics and accuracy of the RIT-DuPont experiment, the current ellipsoids can be considered highly reliable and representative of color discrimination under the observational conditions employed, these closely following the “reference conditions” recently suggested by the CIE for industrial color-difference evaluation [Color Res. Appl. 20, 399–403 (1995)]. © 1997 John Wiley & Sons, Inc. Col Res Appl, 22, 148–155, 1997     

Describing natural colors with Munsell and NCS color systems

The Munsell Color System and the Natural Color System are widely used but they have some limitations due to the manufacturing process and sampling choices. To estimate quantitatively these limitations we compared the colors of natural scenes with the colors represented by these systems under a wide range of illuminants. Spectral data from the two systems and from natural scenes were used in the analysis. It was found that a considerable portion of natural colors are not accounted by these systems, mainly colors with low lightness levels. Under D65 the Munsell Color System color volume corresponds to 72% of the Natural Color System color volume which in turn represents only 53% of the natural scenes color volume. If individual colors are considered, less than half are contained within these systems. To obtain a complete match to the natural colors contained by the color systems thresholds of 7 and 5 CIELAB units would be required for Munsell Color System and Natural Color System, respectively. Variations with the illuminant are generally modest showing that both system work similarly across different illuminations. Although these Color Systems have limitations in describing low lightness colors they perform quite well for medium to high levels of lightness.