Optimum brightness level and simplified characterization of CRT color monitors

The nonlinear relationship between luminance and DAC count could be characterized with the simplified model, if optimum brightness level is set. In this study, we propose a technique to set the optimum level of brightness, in which offsets for RGB channels can be assumed to zero, and determine the gamma coefficients from log–log data without nonlinear optimization. The optimum brightness level could be found by measuring a few tones of neutral for the combination of 3 levels of brightness and 2 levels of contrast. This technique has two advantages. It does not require measurements for 0 DAC count, and does not require nonlinear optimization in finding the gamma coefficient of the display system. Two CRT monitors by different manufacturers have been tested. As the result, all monitors could be set to their optimum state with a different combination of brightness and contrast. In that state, the gamma coefficient for each channel could be determined from two measuring data and the tone reproduction characteristics of the RGB channel could be characterized with the simplified equation, neglecting offset and gain. The accuracy of characterization was better than 0.5 ΔE*_ab for 125 colors for a monitor having good channel independence. © 2000 John Wiley & Sons, Inc. Col Res Appl, 25, 408–415, 2000     

Fabrication of brightness optimizer for CRT color monitors

In CRT monitor characterization accuracy is largely affected by the brightness setting on the monitor. At the optimum brightness level, which adjusts the offsets of RGB channels to nearly zero, CRT monitors have a simple relationship between DAC count and luminance so characterization can be achieved accurately. However, since the optimum brightness levels of CRT monitors are different from one another monitor users, have to make adjustments to the monitor themselves. In this study, a simple device named, brightness optimizer, is fabricated to determine the optimum brightness level objectively. This method uses change of curvature in tone reproduction curves plotted in log‐log scale, according to the changes of brightness level. In this article, the configuration of the brightness optimizer and the measurement processes are described. The repeatability and the accuracy in the measurement of the optimum brightness level for three different CRT monitors are also evaluated. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 468–472, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10199     

Media‐dependent color appearance modeling based on artificial neural networks

In this study, we tried to consider various color appearance factors and device characterization together by visual experiment to simplify the across‐media color appearance reproduction. Two media, CRT display (soft‐copy) and NCS color atlas (hard‐copy), were used in our study. A total of 506 sample pairs of RGB and HVC, which are the attributes of NCS color chips, were obtained according to psychophysical experiments by matching soft copy and hard copy by a panel of nine observers. In addition, a set of error back‐propagation neural networks was used to realize experimental data generalization. In order to get a more perfect generalizing effect, the whole samples were divided into four parts according to different hues and the conversion between HVC and R_HVCG_HVCB_HVC color space was implemented. The current results show that the displays on the CRT and the color chips can match well. In this way, a CRT‐dependent reproduction modeling based on neural networks was formed, which has strong practicability and can be applied in many aspects. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 218–228, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20209     

Visual color matching under various viewing conditions

In this article, we provide colorimetry data for which it was judged that the colors between different media matched under various viewing conditions. Painted color patches, a monitor, and printed color patches were used in the color matching experiments, in which we compared the appearances of the painted color patch and the monitor, or the monitor and the printed color patch, using the method of constant stimuli. The nine types of viewing conditions we used could be envisaged to occur when comparing different device outputs indoors. The experimental data obtained were compared with corresponding colors predicted with the use of five types of color appearance model, including color appearance formulae. We found that when the viewing conditions were the same for the different media, there was good agreement between the experimental data and the CIECAT94 model. And by adjusting the brightness induction and the chromatic induction factors, it was possible to improve conformity for the lightness and the chromaticity. Moreover, it was possible to improve the white point shift, which cannot be adjusted with the use of optimized parameters by introducing incomplete adaptation. By optimizing the parameters and introducing incomplete adaptation, it is possible to make the mean color difference ΔE between the corresponding color and the color matching point less than 10 CIELAB units for all of the viewing conditions.     

Dependence between apparent color and extractable color in paprika

The color properties of 96 paprika samples were evaluated by tristimulus reflectance measurements. The extractable color (ASTA units) of all these samples was also determined. The linear correlation between individual CIELAB parameters and extractable color was very poor. Several color indices used with other foods were shown to be of insufficient accuracy for predicting the extractable color in paprika. A new color index for paprika (PACI) is proposed based on the CIELAB coordinates L* (lightness), a* (red‐blue), and h (hue angle), and it is calculated as “1000a*/(L*+h)”. This new index showed a high correlation with the logarithm of extractable color (r = 0.9662) and was able to distinguish between sample groups of different ASTA units. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 93–97, 1999     

Visual determination of hue suprathreshold color‐difference tolerances using CRT‐generated stimuli

Suprathreshold hue color‐difference tolerances were measured at four color centers using CRT‐generated stimuli. The tolerances, defined using CIELAB, were measured using two different methods of presentation. In the Absolute Experiment, the stimuli were presented at luminance levels that matched those of the previous object‐color experiments, so that the CRT stimuli were nearly metameric to the originals. In the Relative Experiment, the white point of the monitor was defined as L* = 100 at a corresponding chromaticity to the object‐color viewing environment, but at a lower luminance level. The results from these two experiments followed the same general trends; however, they were significantly different from each other for three of the four color centers. The same trends were seen in the object‐color results, although neither CRT experimental condition produced tolerances that were conclusively more similar to the object‐color results than the other. The feasibility of the use of the CRT has been demonstrated. It is likely that parametric effects of stimulus presentation are the cause of the differences in results among the different experiments, as opposed to differences in the mode of appearance. These parametric effects can be studied more quickly and economically using a computer‐controlled CRT display. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 164–176, 1999     

Color constancy,color‐mixing ability,and color inference

In the laboratory, the performance of color constancy has always been unstable. The variables posed by the subjects themselves tend to be neglected. In this study, a simple color‐mixing test was used to sort subjects into three groups. They were also provided with hue and brightness in a fixed color order as guidance during experimental tasks in an attempt to observe any changes in cognitive skills among subjects of varying color‐mixing abilities under changed illuminations. Three hypotheses were proposed: (1) Matching hypothesis: people remember and apply the spatial locations of color surrounds to the target color to achieve color constancy; (2) Comparing hypothesis: people identify the relative difference between color surrounds to achieve color constancy; and (3) Reasoning hypothesis: people compare the color surrounds and refer to color knowledge accumulated in the past to achieve color constancy through reasoning. The experimental results were as follows if the Comparing hypothesis is taken into account, (a) when hue guidance is hidden the subjects' identification rate (IR) performance supported the Reasoning hypothesis; (b) when hue guidance was shown, the IR performance of subjects in all three groups supported the Matching hypothesis. Based on these results, this study offers two recommendations: (a) color surrounds with a fixed relative location should be avoided because spatial location memory leading to people using matching skills and (b) subjects should be screened based on their color‐mixing ability because significant differences in color constancy performance exist between people with varying levels of color‐mixing ability. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

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.     

Correlations between color attributes and children's color preferences

This study examined the role of color attributes (lightness and saturation) on children's color preferences for interior room colors. It also investigated children's most preferred colors among each of the five major hue families in the Munsell color system using scale‐models. Previous color preference studies have typically been done with small color chips or papers, which are very different from seeing a color applied on wall surfaces. A simulation method allowed for investigating the value of color in real contexts and controlling confounding variables. Forty‐five color samples were displayed on scale‐models to 63 children ages 7–11 years old. This study identified children's most preferred colors among each of the five major hue families in Munsell color system. It also demonstrated that saturation was positively correlated with children's preferences in the red, green, blue, and purple hue families. In the yellow hue family, interestingly, lightness has a positive correlation with preferences. Children's gender differences were found in that girls prefer red and purple more than boys. These findings lead to color application guidelines for designers to understand better color and eventually to create improved environments for children and their families. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 452–462, 2014     

Interobserver variability and color representation systems

A systematic method of analyzing the colorimetric behavior of a set of observers is proposed. The differences between each observer and a standard one are analyzed with different procedures in two color‐representation systems. It is apparent that these differences strongly depend on the color‐representation system in which they are analyzed. Results obtained in this work indicate that comparison between two observers should be carried out by applying an optimized operator. This operator minimizes the differences between the color‐representation systems associated with the observers that are compared. The proposed method should be applied when color‐matching properties of a set of observers, or when color matching obtained with different colorimetric instruments, are compared. © 2002 Wiley Periodicals, Inc. Col Res Appl, 28, 15–24, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.     

An algorithm for the selection of high‐contrast color sets

Nominal color coding is the aesthetic and functional use of color to convey qualitative information in graphical environments. The specification of high‐contrast color sets is a fundamental step in this process. We formulate the color‐coding problem here as a combinatorial optimization problem on graphs and present an algorithm that performs well and does not require that the function used to code the similarity between colors be a distance function. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 132–138, 1999     

Complexity of the color appearance of objects with nonuniform illumination

An inversion relationship is clarified between lightness and brightness, and also between chroma and colorfulness under nonuniform illumination with different illuminance levels (high and low) within the same visual field. Brightness (or colorfulness) of object color with low lightness (or chroma) under high illuminance level is perceived higher than that of another object color with high lightness (or chroma) under low illuminance level. Two color images are given for showing the inversion phenomena on brightness–lightness and colorfulness–chroma between object colors under different illuminance levels. These color images are useful for making researchers on color understand the differences in concept between brightness and lightness, and also between colorfulness and chroma. In particular, the concept of colorfulness is important, but difficult to understand. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 372–377, 2007     

Optimal employment of color attributes to achieve saliency in icon matrix designs

With the wide use of smart devices, through which information is presented in vast quantities, objective guidelines are needed to enable designers to choose appropriate colors for information display. The purpose of this study is to determine which colors are the most eye‐catching in displays that employ icon matrices and thereby provide empirical grounds for strengthening the visual information structure of interface designs. Three attributes of color, which include hue, tone, and color combinations, are examined to optimize the color saliency in information displays. An eye‐tracking study was conducted to evaluate saliency objectively by analyzing fixations of visual attention. Based on the hue‐saturation‐brightness color system, a 5‐by‐5 matrix of 25 color patches was adopted to generate 21 color stimuli. Part I of the study focused on hue and indicated that warm colors are perceptually more eye‐catching relative to cool and neutral colors. Part II of the study investigated tonal influences and revealed that highly saturated colors provoked the greatest visual magnetism against a black background across all hue groups, although there was an alternative tendency for a blue hue. Contrary to expectations, no distinctive patterns were observed among brightness groups. With regard to color combination, Part III of the study provided empirical verification that high contrast between a foreground and a background generates a more dominant conspicuity. The results of the present study can be applied in designing electronic interfaces that display icon matrices to create effective communication by guiding visual attention and increasing aesthetic satisfaction. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 429–436, 2015     

Separate processing of chromatic and achromatic contrast in color constancy

In a preceding study we measured human color constancy in experimental conditions in which simulated illuminants and surface colors were varied in the chromatic domain only. Both illumination level and sample reflectance were fixed in that study. In the present study we focus on the achromatic dimension, both with respect to luminance contrast (Experiment 1) and overall illumination (Experiment 2). Sample‐to‐background contrast was varied over a two log unit range that covered both luminance decrements and increments. Illumination level was varied either for the short‐wave‐sensitive (S) cones only or for all three cone types simultaneously. Data predictions on the basis of a cone‐specific response function, derived in our preceding study, indicate that this model has difficulty in accommodating the results obtained with varying luminance contrast. However, a modified version of the response function, incorporating separate processing of color and luminance contrast, correctly predicts the data from both the present and the previous study. We also show that over a limited stimulus range our earlier response function is mathematically equivalent to Jameson and Hurvich's model of brightness contrast. The latter model, cast into a trichromatic format, performs equally well or better than our original response function, but is less accurate than our modified model. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 172–185, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20105     

On attributes of achromatic and chromatic object‐color perceptions

Adapting luminance dependencies of various color attributes of object colors (lightness, brightness, whiteness‐blackness, whiteness‐blackness strength, chroma, and colorfulness) were clarified under white illumination with various adapting illuminances. The correlation between the perceptions of lightness and brightness and those of whiteness‐blackness and whiteness‐blackness strength is also clarified for achromatic object colors. The difference between the increase of brightness and that of whiteness‐blackness contrast (the effect studied by Stevens and Jameson—Hurvich) by raising their adapting illuminance is resolved without any contradiction. It is also shown that the nonlinear color‐appearance model developed by the author and his colleagues is able to explain the complex characteristics of all the above color attributes of object colors by making minor modifications to it. In addition, two kinds of classifications of various color attributes are given; one is based on the similarity of perception level, and the other on the degree of adapting illuminance dependency. © 2000 John Wiley & Sons, Inc. Col Res Appl, 25, 318–332, 2000     

Comparison of color vision models based on spectral color representation

Recent break‐throughs in retinal imaging have raised new questions for color vision research, and the existing color vision models should be re‐evaluated. Many color vision models are based on an assumption that there are no differences in the detection phase, neither in the spatial configuration nor in the spectral sensitivities of cells. In this article, we have run experiments with four different color vision models. This evaluation gives us more knowledge about the essential properties of the models. We show how the tested color vision models are able to replicate the behaviour of human color vision by evaluating their performance in Farnsworth‐Munsell 100‐Hue color vision test. Also, the wavelength discrimination power of each model is presented and the properties of color spaces spanned by models are examined using samples from Munsell Book of Color. Our experiments show that there are large differences in the properties of different models. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 341–350, 2009     

Color‐emotion associations,designing color schemes for urban environment‐architectural settings

Color in urban design has become an important issue, each city may present different colors which help to define and describe its architectural features. In the study, color in urban design with architectural setting is studied, façade colors are analyzed with a specific emphasis on the following research questions; “Can color schemes be designed in respect to color‐emotion associations? ” and “Are color‐emotion associations affective while designing architectural setting‐urban environment?.” Non‐color experts, 170 people, from different European and non‐European countries were asked to match the most appropriate adjectives with the given street views in accordance to their color schemes. In the first step, the effect of color is identified in relation to architectural environment‐urban setting, second the relative effect of color is studied as a component of the material. A categorical specification on color cognition and linguistic level of representation is attempted. The results can be a starting point to highlight the importance of preparing color schemes in regard to color‐emotion associations. Abstract color schemes may also provide us an idea about image setting, especially at design process stage. In the study, keywords are linked as environment‐response pairs; such as quiet, calming, lively, exclusive, reserved, and natural. Human psychophysical structure such as “warm‐cool,” “heavy‐light” in regard to visualizing certain colors are evaluated and described in terms of building materials.     

Visual assessment of light source color quality

The color quality of the lit visual environment can be improved by optimizing light source spectral power distributions. For a comprehensive optimization, it is important to identify the relationship among the perceptual properties of color quality. In this work, a colorful still life or tabletop arrangement was constructed from real artificial objects. Thirty observers with normal color vision scaled nine different properties of color quality under three light sources, incandescent, fluorescent and white LED. Six factors were extracted from the correlations among the obtained visual color quality scales. Factors were assigned the following labels: memory, preference, brightness, fidelity, gamut and difference. Mean factor values were computed for each light source. Significant differences were found in case of preference, brightness and fidelity: for preference, INC was rated better than CFL and LED was rated better than CFL, for brightness, LED was better than INC and LED was better than CFL and for fidelity, INC was better than CFL and INC was better than LED. The brightness factor was consistent among the observers. Three clusters of observers were found for preference and fidelity. The memory, gamut and difference factors showed large interobserver variability. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2013     

Considerations on the calibration of color displays assuming constant channel chromaticity

To calibrate a CRT color monitor, several assumptions are often made about its performance, one of the most accepted being constanel channel chromaticity. However, when the measurements are taken in a extended field of CRT screen, where it is assumed that only one primary phosphor is excited, the relative spectral radiance of the other primary phosphors that are contained in that field also contributes, if the background luminance is not zero. This contribution is greater at low levels of RGB channel stimulation and would invalidate the results obtained with calibration methods based on the hypothesis of constancy of chromaticity coordinates of RGB channels. We have studied this effect on the calibration of the CRT color monitor and, as a result, we propose a calibration that takes this effect into account. to evaluate the accuracy of the method, we have calculated color differences between the chromaticity that we wanted to reproduce and the one displayed with the CIELUV color-difference formula, and the color tolerances with the line element of MacAdam ellipses.     

Color preference affected by mode of color appearance

Most color preference research focuses on colors in an object color mode. In our daily life, however, colors are perceived not only as an object color mode but also as other modes, such as unnatural object color and light source color modes. To explore the effect of the color appearance mode on color preference, we examined the relationship between color preference and the mode of color appearance. Thirty‐three color chips were chosen from the Munsell notation varying in hues and chromas. The color chips were presented in different color appearance modes by changing the subject's room illuminance and the color chip room illuminance. The experimental results showed that the brightest and most saturated colors were preferred. It was found that the subject preferred color in a light source color mode and unnatural object color mode to color in an object color mode. Moreover, we found that hue had a small effect on color preference in the light source color mode. We also investigated the relationship between color preference and the perceived color attributes (perceived chromaticness, whiteness, and blackness). In a supplementary experiment, elementary color naming was conducted. The results showed that the perceived chromaticness, perceived whiteness, and perceived blackness play a role for the determination of color preference for different color appearance modes. We, consequently, suggest that color preference is dominated not only by color attributes but also by the mode of color appearance. © 2009 Wiley Periodicals, Inc. Col Res Appl, 2010