Chroma,chromatic luminance,and luminous reflectance. Part I: Basic research and illustration of relations

Chromatic luminance carries both wavelength and radiance of light, is the source of all psychophysical dimensions and all color attributes, and is a key to understand their relations. It has long attracted research, hindered in the past by flawed definitions of colorimetric purity (p_c), remedied in a recent article. This article investigates relations between luminous reflectance Y (i.e., total luminance, chromatic plus achromatic), chromatic luminance (calculated from Y per p_c), and chroma/colorfulness. Relations are clarified, illustrated by formulas and graphs including three‐dimensional schemas of luminance Y, chromatic luminance, and color solids. A useful new term, relative chromatic luminance, is introduced. Munsell chroma is shown to resemble inverted log luminance much more closely than inverted log colorimetric purity as claimed by previous researchers. The relationship is used in Part II to model chroma, colorfulness, and brightness. © 2008 Wiley Periodicals, Inc. Col Res Appl, 34, 45–54, 2009.     

Analysis of cross‐cultural color emotion

This study investigates the relationship between color perceptual attributes and color emotions, as well as the influence of different cultural backgrounds. Totally 214 color samples were evaluated on 12 emotion variables by subjects from seven different region groups in the psychophysical experiment. By factor analysis, it was found that three factors were sufficient to represent 80 “region‐emotion” variables. For each variable, there is no distinct difference among different region groups. The 12 emotion variables could be divided into four categories, namely, activity index, potency index, definition index, and temperature index. Factor scores were further calculated to study the determinants on each factor. The analysis showed that the three factors were mainly related to chroma, lightness, and hue, respectively. It was concluded that chroma and lightness were the most important factors on color emotion, whereas the influences of hue and cultural background were very limited. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 223–229, 2007     

Differences in attributes between color difference and color appearance (chroma and hue) for near‐neutral colors

Chroma‐step perception and its corresponding color difference in the same hue direction are the different attributes on color perception. The differences between them are different for different hues. Hue‐appearance step and its corresponding color difference along the same hue circle also have completely different concepts. The causes of the above two facts are clarified. The information based on various experiments and theoretical considerations are given for supporting the facts. In addition, it is clarified that the relationship on color‐appearance step and color difference has completely different characteristics between the quantitative (chroma) and the qualitative (hue) attributes of object colors. The importance of chromatic strength (CS) on hue is clarified in each of the three color attributes hue, value, and chroma. © 2004 Wiley Periodicals, Inc. Col Res Appl, 30, 42–52, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20073     

Investigating the personality associations evoked by single colors: An exploratory study

Despite the crucial role of color appearance in forming first impressions, it is still not clear how color evokes personality associations—that is, a color‐personality association (CPA). This study aims to propose a method for quantifying the relationships between color attributes and CPAs for single colors. Specifically, we first collected the CPAs of five traits evoked by single colors (i.e., extraverted–introverted, moody–unemotional, agreeable–disagreeable, organized–disorganized, and wide interests–narrow interests) in a carefully controlled experiment. Then, multiple linear regression (MLR) analyses were adopted to predict these CPAs based on three color attributes (lightness, chroma, and hue). Our results showed that (1) the personality associations could be evoked by colors and perceived consistently by observers; (2) the relationships between the color attributes and the CPAs could be well quantified by separately conducting MLR analyses in different regions of hue (i.e., red, green, blue, and yellow regions); and (3) both lightness and chroma were significant predictors in almost all predictive models and they might have different relative importance or directions of effect when predicting the CPAs in different regions of hue, even for the same trait. This study improves the understanding of how color evokes personality associations and takes the first step toward developing the method for predicting the CPAs for multicolor combinations. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 388–396, 2017     

Effect of chromatic components on facial skin whiteness

Although the color measurement of facial skin becomes more common in dermatology and cosmetics, little is known about the relationship between subjective color perception and colorimetric values in facial skin. In this study, the possible relationships among perceived whiteness and the metric lightness, chroma and hue angle of Japanese females' facial skin color were investigated. First, the perceived brightness of the facial skin of Japanese females was evaluated visually and compared with metric lightness, chroma and hue angle, and the effect of hue and chroma on the perceived brightness was discussed. Second, a psychophysical experiment on the whiteness of the facial images and synthesized skin color plate images was conducted for examining the effect of hue and chroma on the perceived whiteness more precisely and independently. The results of two experiments showed that in regard to the facial skin color of the Japanese female, metric lightness disagrees with perceived whiteness or brightness in a narrow lightness range. The reddish facial skin color appeared brighter or whiter than that of a yellowish one in high lightness regions, and the low‐chroma facial skin color appeared brighter or whiter than a high‐chroma one. However, in the color plate images, a change in perceived whiteness by hue could not be confirmed, and the change in perceived whiteness by chroma was weaker than that from facial images. These results indicated that a higher‐level process of face recognition affected whiteness perception, and the criterion of facial skin whiteness was determined by facial skin color distribution. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011;     

Effect of purity on hue (Abney effect) in various conditions

The effect of purity on hue has been reported severally (including Munsell and NCS data on constant hue loci) over 100 years but without general agreement. For example, the number of hue shift nulls in the data vary from 2 to 6. Hence, despite this effect's commonality it lacks reliable data for modeling underlying mechanisms or color appearance. The purity of a stimulus may be decreased by adding white (as in Abney's experiment), by adding black, or by adding gray such that luminance, or alternatively lightness, remains constant. This article gives new data for CRT stimuli for illuminant D65 for all four conditions but mainly for equal luminance, for 31 observers and 13 test dominant wavelengths. Further, samples were observed in two temporal conditions: either simultaneously as pairs (the contrast mode) or singly (the no‐contrast mode). Three types of samples were tested: (1) equal luminance 30 cd/m² for all dominant wavelengths, (2) equal lightness for all dominant wavelengths, and (3) zero‐gray colors, requiring different luminances for different dominant wavelengths. In all the above conditions, the resultant hue shifts graphed a robust bimodal curve (two peaks in cyan and red, two troughs in blue and green) across the hue cycle, similar to Munsell and NCS data except the definite peak in cyan.© 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 25–39, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20286     

Color determinants of surface stratification

Although color plays a crucial role in the demarcation of surfaces in the visual field, its role in depth perception is not well understood. Certain special effects of color on depth perception that arise from optical factors such as chromatic aberration (chromostereopsis) have been studied, but less is known about the role of perceptual factors of color in determining depth relations. The present study explores the role that the different attributes of color such as hue, chroma, and lightness play in the stratification of surfaces in depth. In two experiments, subjects manipulated specific dimensions of colors (hue, chroma, lightness, and whiteness) while making judgments of coplanarity of either two or more abutting surfaces. The results demonstrate that for surfaces to appear coplanar, their lightness has to be proportional to the natural (intrinsic) lightness of the hues. No meaningful effects of chroma, whiteness, or blackness were found in depth stratification. The results suggest a primary role of the natural lightness of hues in depth perception.     

Chroma,chromatic luminance,and luminous reflectance. Part II: Related models of chroma,colorfulness, and brightness

Part I of this article found, inter alia, that chroma resembles log inverted luminance. This article develops three math models of Munsell chroma and associated colorfulness from (1) inverted luminous reflectance Y, (2) inverted chromatic luminance, and (3) inverted chromatic luminance combined (over the mid‐spectrum 480–580 nm) with the unimodal curve for spectral absorptance of M cones. The first two models are simple but of limited accuracy and demonstrate that inverted luminance (of any form) cannot fully account for varying relative chroma around the hue cycle, particularly the minor minimum and maximum about 490 and 520 nm (which also feature in B:L functions). The third model is rather complex but very accurate, apparently the only accurate model of Munsell chroma or other experimentally based scales of relative chromaticness in the literature. It adjusts to any level of luminance or purity, as demonstrated for several levels. Three models of brightness (B:L ratio) for 2⁰ field aperture colors are given, based on either Munsell chroma or log inverted chromatic luminance. The former provides two accurate and simple models of the CIE B:L function: (1) log chroma = B:L ratio ±0.1, and (2) (chroma/k)^x = B:L ratio ±0.1. The latter also predicts B:L for nonspectral colors and those of lower purities, e.g., object colors. The results finally solve the relationship between brightness and chroma and demonstrate that B:L ratio (a contrast in constant luminance) arises directly from chroma (also a form of contrast in constant luminance), or the reverse. © 2008 Wiley Periodicals, Inc. Col Res Appl, 34, 55–67, 2009.     

Research on color harmony of building façades

In this study, the 28 primary colors and 11 complementary colors suggested by Chang et al in their investigation on building colors in Wanhua District of Taipei City were taken as color samples. The two-color combination mode was adopted to obtain 308 simulation photos, and two-color harmony was discussed from the perspective of visual evaluation using psychophysical tests. This study explored building façade color harmony in the CIELAB color space, and the relationship between the color attributes (hue, lightness, and chroma) and the color harmony, and between the differences of the color attributes and color harmony. It found that a high lightness of a building's primary color is associated with a high level of building color harmony, while the color harmony is reduced when the color falls in the green or blue sector in the CIELAB color space; a greater lightness difference between building façade colors is associated with a higher level of building color harmony, while the colors are disharmonized when they tend to the blue sector in the CIELAB color space. The contribution of this study is to summarize the principles for the application of building color harmony in urban renewal, and proposed suggestions on building color harmony in the urban renewal process.     

Predictions of Munsell values with the same perceived lightness at any specified chroma irrespective of hues—Determination of any tonal colors

Simple formulas are proposed for predicting the Munsell value of colors with the same tone (the same values for whiteness‐blackness, perceived lightness, and chroma irrespective of hue). The formulas can be used for any tone. In other words, the method can determine the Munsell value with the same perceived lightness at any specified chroma irrespective of hue. The chromatic strength (CS) function is only used for the derivations. The formulas are very simple, and can be used not only in the colorimetry but also in the color design field. The concept described in this study is that a common CS function can be used for transforming each of the three color attributes (hue, lightness, and chroma) from their uniform color space metric to their corresponding color appearance space attribute. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

Color appearance modeling of bicolor striped woven fabrics considering neighboring color effects

In this article, the effect of the spatial and colorimetric attributes of neighboring color on color appearance shift in bicolor striped woven fabrics is investigated. A total of 240 test/neighboring woven color combinations were constructed in four different striped paradigms. Each test color in the combinations was visually assessed by 12 observer panels with the use of the magnitude estimation method estimating the magnitude of perceptual color attributes lightness, colorfulness, and hue. The visual estimates obtained were analyzed statistically by employing correlation and simple regression methods, and, as a result, the following significant neighboring color effects were detected and individually defined: (1) neighboring color's size, lightness, colorfulness, and hue on test color's lightness, (2) neighboring color's colorfulness and hue on test color's colorfulness, and (3) neighboring color's hue on test color's hue. Furthermore, through multiple regression analysis, color appearance models by which the lightness, colorfulness, and hue of bicolor woven fabrics can be predicted were derived. The predictive performance of the models was evaluated by calculating the difference between the visually estimated and the predicted color appearances, using ΔL*, ΔC*, Δh°, and ΔE_CMC(2:1). Among all the derived models, the model producing the smallest mean error was chosen as a final model, and its great accuracy in color appearance predictions was verified through further statistical evaluation. It is envisaged that the findings of this research are of benefit to design textile products with bicolor striped woven fabrics to have desired color appearances. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 512–521, 2017     

Proposal of an opponent‐colors system based on color‐appearance and color‐vision studies

A new theoretical color order system is proposed on the basis of various studies on color appearance and color vision. It has three orthogonal opponent‐colors axes and an improved chromatic strength of each hue. The system has color attributes whiteness w, blackness bk, grayness gr, chroma C, and hue H. A method is given for determining Munsell notations of any colors on any equi‐hue planes in the system. A method is also given for determining grayness regions and grayness values on hue‐chroma planes in the system. It is concluded that colors with the same color attributes [w, gr, bk, C] but with different hues in the theoretical space have approximately the same perceived lightness, the same degree of vividness (“azayakasa” in Japanese), and also the same color tone. The tone concept, for example used in the Practical Color Coordinate System (PCCS), is clarified perceptually. The proposed system is a basic and latent color‐order system to PCCS. In addition, the concept of veiling grayness by a pure color with any hue is introduced. Further, relationships are clarified between generalized chroma c(gen) and grayness. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 135–150, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10234     

Color appearance of a large homogenous visual field

In this article, the color appearance of a large (85°) homogeneous self‐luminous visual stimulus was studied in a psychophysical experiment. Large stimuli were displayed on a plasma display panal (PDP) monitor. The large stimuli were viewed with a fixed viewing time (2 s). They were compared with 2° and 10° stimuli presented on a grey background on a CRT monitor. The so‐called “color size effect” was found to be significant. The color stimulus was perceived to be lighter when it was large compared with the 2° and 10° situation. But we did not find the general increase of chroma claimed in previous literature. We found only small hue changes. A model of the color appearance of large‐field stimuli is presented in terms of the CIELAB L*, a*, and b* values of the corresponding 2° and 10° stimuli. © 2007 Wiley Periodicals, Inc. Col Res Appl, 33, 45–54, 2008     

Considering the surround in device-independent color imaging

When viewing images, the relative luminance of the surround has a profound impact on the apparent contrast of the image. For this reason, photographic transparencies intended for projection in a darkened room are produced with an objective contrast substantially higher than that necessary for optimum reproduction as prints viewed in an illuminated surround. the dark surround causes the image elements to appear lighter and this effect is stronger for darker colors resulting in a loss in perceived contrast. This effect is also of great importance in deviceindependent color imaging since resultant images might be observed in a wide variety of media and viewing conditions. Research on psychophysical scaling of brightness and lightness and the effects of background and surround relative luminance on lightness and chroma is reviewed. the importance of this research for device-independent color imaging systems is described along with the prediction of these effects using the RLAB color-appearance model. Finally, experiments testing the use of RLAB and other color-appearance models in cross-media color reproduction applications are described.     

Whiteness,chromaticness, and blackness symmetries for CIELAB,with a numerical example

Whiteness, chromaticness, and blackness are defined for CIELAB. These NCS‐like color attributes offer an alternative to lightness and chroma for describing color. Their hue‐preserving symmetries are derived for tristimulus color space. A numerical example provides what theory predicts are visually uniform sequences of colors with constant lightness, whiteness, chromaticness, or blackness. Numerical approximation is unnecessary. Such sets of symmetric colors in one hue are visually interesting, and useful for computer aided design. The appropriateness of such attributes for CIELAB is briefly discussed. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Computational color combination analysis of Papilionidae butterflies as aesthetic objects

In this study, our aim is to clarify the color combination rules of the human-preferred Papilionidae butterflies as aesthetic objects. A set of 118 butterfly images, including color polyphenism from the 47 Papilionidae species that are generally preferred by humans, was selected. These images were classified using hierarchical cluster analysis based on similarities of lightness, chroma, and hue attributes in CIELAB space, determined using histogram intersection. Then, the color distributions and combinations in each cluster were analyzed using a Gaussian mixture model and the color combination types defined in the present study. Accordingly, we obtained the following main color combination rules of human-preferred Papilionidae: (a) dominant low lightness and contrasting lightness components, (b) dominant low chroma and similar chroma components, and (c) dominant orange to yellow-green hue and similar hue components. These rules partly agree with the robust harmony principles found in previous research. We infer that the cognitive effects concerning the processing fluency through these color combination rules influence human aesthetic responses.     

Emotional response to color across media

In this study, the characteristics of emotional responses to color are explored in two empirical studies. In particular, the relationship between color attributes and emotional dimensions—valence, arousal, and dominance—is analyzed. To account for the cognitive quantity of color, 36 color stimuli were selected following hue and tone categorizations and based on the CIELAB LCh system. In one experiment, the colors were presented on A5‐size glossy paper whereas the identical colors were displayed on CRT monitors in the other experiment. In both experiments, the subjects assessed the emotional responses to each color stimulus using a Self‐Assessment‐Manikin (SAM), which consists of three rows of five pictograms illustrating the three dimensions of emotion, respectively. The empirical results provide evidence that the patterns of affective judgment of colors can be profiled in terms of the three dimensions of emotion (Reliability coefficient, Cronbach's alpha > 0.7). All three attributes of colors, i.e. hue, Chroma, and Lightness, influenced the emotional responses (repeated measurement One‐way ANOVA, P < 0.05), and especially, Chroma was always positively correlated with each of the three emotional dimensions (r > 0.60 P < 0.01). Moreover, the results indicate that emotional responses to color vary more strongly with regard to tone than to hue categories. Comparing the SAM ratings between the two experiments, a systemic explanation has yet to be found to conclude that there is a media effect on the emotional responses to colors. Furthermore, the process of affective judgment of colors and the limit of color as an emotion elicitor are discussed. © 2009 Wiley Periodicals, Inc., Col Res Appl, 2010.     

A comparison of constant stimuli and gray‐scale methods of color difference scaling

Two psychophysical techniques, the method of constant stimuli and the gray‐scale comparison method, were used to determine color tolerances for three different color centers in the hue, chroma, and lightness directions in CIELAB color space. The same color‐difference pairs were used as the stimuli in both experiments. Although the results followed the same trends, they were different for the two techniques. Based on comparison of the validity and precision of the results, as well as the ease of implementation, use, and analysis, the method of constant stimuli is the preferable method. © 2002 Wiley Periodicals, Inc. Col Res Appl, 28, 36–44, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.     

Distance metrics for very large color differences

Small, supra-threshold color differences are typically described with Euclidean distance metrics, or dimension-weighted Euclidean metrics, in color appearance spaces such as CIELAB. This research examines the perception and modeling of very large color differences in the order of 10 CIELAB units or larger, with an aim of describing the salience of color differences between distinct objects in real-world scenes and images. A psychophysical experiment was completed to compare directly large color-difference pairs designed to probe various Euclidean and non-Euclidean distance metrics. The results indicate that very large color differences are best described by HyAB, a combination of a Euclidean metric in hue and chroma with a city-block metric to incorporate lightness differences.