Effects of surrounding brightness on visual search for safety colors

The present article reports the investigation of the effects of surrounding brightness on a visual search for three safety colors: red, orange, and yellow. Images of visual stimuli consisting of an array of colored circles placed on a large visual field (a visual angle of 40°) were displayed on an 80‐in. screen with a DLP projector. Experiment I examined the search efficiency under three levels of background luminance that were equivalent to the three target luminances. The results showed that the search efficiency for the orange target decreased as the number of distractors increased, under each of the background luminance levels, whereas the efficiency scarcely decreased for the red and yellow targets. Although a reduction in background luminance increased the search efficiency for the orange target, it is suggested that the effect of background luminance is smaller than the effect of the target color in search efficiency. Experiment II examined the search efficiency under three conditions of low levels of incident illuminance, which were matched with a linear regression to the luminance of color chips of safety colors measured twilight conditions. The results showed that the search efficiency for the orange target decreased as the number of distractors increased under each of the different illuminance conditions, whereas the efficiency scarcely decreased for red and yellow targets. Furthermore, as illuminance decreased, the search time for the orange target was more greatly impacted than for red or yellow. These results imply that the recognition of orange tends to be influenced by the surrounding brightness. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 400–409, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20152     

Color and visual complexity in abstract images: Part II

There are a limited number of studies examining color, visual complexity, and visual interest together, and one of the recent studies that tried to bring a new understanding to the association between color, visual complexity, and visual interest was the first part of the current study. Most of the well‐known color studies researching the effects of color on psychology, physiology, emotion, mood, attention, well‐being, visual complexity, and visual interest used isolated color patches that might be lacking in reflecting the dominating factors. Thus, the aim of this study was to find the relationship between visual complexity, visual interest, and color difference (ΔE) values of colors in abstract images, and it was hypothesized that, as the average ΔE value of colors in an abstract image increases, visual interest and visual complexity will increase until reaching a threshold where visual interest and visual complexity start to decrease. In order to test the hypothesis, a new abstract image was generated and colored. The generated abstract image was rated by 120 undergraduate students from the Faculty of Art, Design and Architecture. As the results of the study indicated, there was an inverted U‐curve relationship between average ΔE values and both visual interest and visual complexity in abstract images.     

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     

Color rendering,a reassessment

The deficiencies of the CIE method of measuring and specifying colour rendering properties of light sources are discussed. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 197–206, 1999     

Color constancy from invariant wavelength ratios. III: Chromatic adaptation theory,model and tests

A theory of chromatic adaptation is derived from Parts I and II, and presented in terms of relative wavelength, purity, and radiant power, leading directly to a predictive model of corresponding hue, chroma, and lightness. Considering that even simple animals have effective color vision and color constancy, the aim was to develop a simple model of complete adaptation. The model is tested against well‐known data sets for corresponding colors in illuminants D65, D50, and A, and for small and large visual fields, and performs comparably to CIECAM02. Constant hue is predicted from Part I's mechanism of color constancy from invariant wavelength ratios, where constant hues shift wavelength linearly with reciprocal illuminant color temperature. Constant chroma is predicted from constant colorimetric purity. Constant lightness is predicted from chromatic adaptation of spectral sensitivity represented by power ratios of complementary colors (rather than cone responses which lack spectral sharpening). This model is the first of its type and is not formatted for ease of computation. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Color constancy from invariant wavelength ratios: I. The empirical spectral mechanism

The wavelengths of several constant hues over four illuminants (D95, D65, D50, A) are derived from several sets of published data. In the plane of wavelength and reciprocal illuminant color temperature (MK^?1), the wavelengths of constant hues plot straight approximately parallel lines whose mean slope is about 87°. Parallel lines give invariant wavelength ratios, hence constant hues in this plane are near‐invariant wavelength ratios across illuminants. As recently demonstrated, the complementary wavelengths to a constant hue (across illuminants) represent the complementary constant hue; these complementary wavelengths also plot a near‐parallel line to the first constant hue. To confirm and further define the constant slope of these lines, it is shown that complementary wavelength pairs, per CIE data, can only plot parallel straight lines at the angle of 87° ± 1. In summary, near‐parallel sloping lines represent constant hues at near‐invariant wavelength ratios. This mechanism of color constancy is shown to relate to the well‐known theory of relational color constancy from invariant cone‐excitation ratios. In the visual process, the latter ratios are presumably the source of the former (invariant wavelength ratios). © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 238–249, 2008     

Color determination in olive oils

Color characterization of olive oil may be of great importance to the industry. To determine the color of a solution, it is necessary to accurately measure a series of tristimulus coordinates for which several methods exist. This study analyzes the errors in the calculation of tristimulus values of olive oil color based on methods, by using several selected ordinates and an increasing number of weighted ordinates, and how these errors affect the values of the chromatic parameters defined in the various chromatic systems. The above analysis shows that the use of a large number of ordinates will lead to better results in the color definition of oils. For its determination, we have used the CIE 1931, CIELUV 1976 and CIELAB 1976 spaces; the latter yields the best results.     

Hue and warm‐cool feeling as the visual resemblance criteria for iso‐CCT judgment

The hue perception and ‘warm‐cool’ feelings were investigated, in response to various lighting settings, following the adaptation to either 3500K or 5000K to compare which one—between conventional iso‐Correlated Color Temperature (CCT) and a new one based on CIE u'v′ color space—is more compatible with the visual perception. Twenty participants evaluated hue and warm‐cool feelings for 48 test lighting settings, by observing an empty gray booth. The results showed that yellow‐blue and ‘warm‐cool’ feelings are closely located around the Planckian locus, while red‐green roughly follows the line orthogonal to the Planckian locus in CIE u'v′ color space, at both 3500 K and 5000 K settings. This suggests that u'v′ color space correlates better with human perception.     

Color constancy from invariant wavelength ratios: An algorithm to simplify the chromatic adaptation model

In a recent article on color constancy, the chromatic adaptation model was of a novel type comprising three components separately calculated—hue, chromaticness, and lightness. The constant hue component was a simple calculation of predicted wavelength but the other two components were less direct. This article provides an algorithm to simplify the model's calculation. Calculation is far simpler and more intuitive than conventional models using complex 3 × 3 matrix transforms with their various and contentious adaptation primaries and potential disadvantages (e.g., in brightness and color gamut). The model is shown to be at least as accurate as six other (conventional) models and does not require high math skill. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 468–476, 2016     

Color discrimination subject to illuminant and color transition

Due to technological influence on the production process there are variations of the chromaticity coordinates that may cause visible differences of the perceived color of LEDs of the same production batch. To minimize the negative impact of such variations for the user the manufacturers carry out colorimetric measurements of LEDs and sort them into tolerance groups of similar chromaticity coordinates. The corresponding groups are defined by their respective center point surrounded by a quadrangular tolerance limit whereas the tolerance limits are based on tolerance ellipses gained in the 1940s by MacAdam. However, due to another scientific target of MacAdam's experiments, applying his ellipses as a base for grouping the chromaticity coordinates has to be questioned. With a view toward a method for grouping according to chromaticity coordinates for white LEDs with phosphor conversion, the results of research with test subjects regarding their discrimination and magnitude perception of chromatic differences are presented. In this research three chromaticities with the correlated color temperatures of 2700, 4000, and 6500 K and variations of color transitions are investigated, which match realistic luminaire designs for practical applications. The empirically determined thresholds are expanded according to the transformation to different chromatic adaptation conditions as per von Kries that are then compared to the results by MacAdam and the influence on adaptation is being discussed. A new concept for the calculation of tolerance limits for LED binning is presented. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 457–467, 2016     

Color appearance of afterimages compared to the chromatic adaptation to illumination

The color appearance of negative afterimages was measured by the elementary color naming method, and the results were compared with those obtained by the two‐room technique. Twenty adapting stimuli were presented on a display sequentially. Subjects first assessed the color appearance of the stimuli. After looking at the adapting stimulus for 10 seconds, the subjects assessed color of the afterimage. Apparent hue of the afterimage was in general not opponent color to the adapting color. The relation between the adapting stimuli and the afterimages was analyzed by the angle difference Δθ, when apparent hues are expressed by the angles of the points on the polar diagram of the opponent color theory. The relation relationship of Δθ to the angle of the adapting color θ_ing was quite similar to the results obtained by the two‐room technique, implying that the chromatic adaptation shown by the afterimage also occurs in the brain rather than in the retina.     

The new deviate visual functions improving the instrumental estimation on the visual color difference for the metamers with about 1° field size

Although the CIE1931 and 1964 color matching functions have been used in color specification for decades, many researchers, from Allen in 1970 to Hu and Houser in 2006, have found that there still exists a great visual mismatch on the discrimination of color difference as in terms of the CIE color matching functions. Hence, some significant error would be made on color specification due to employing the CIE1931 and 1964 color matching functions. Therefore, six color difference formulae developed from different experimental methods are used to derive various deviate visual functions (DVFs) respectively, and to investigate the effect of these DVFs on the performance of the color difference formulae tested in estimating visual color difference. The results indicate that the performance of the color difference formulae in estimating color difference is significantly improved by the deviate visual functions derived in this study. The CIE94 color difference formula has the best performance in predicting the total visual color difference (ΔV_T) using the DVFs and DVFIIs having the mean values 29 and 27 in PF/4 unit, respectively, while the CMC(l:c) the worst the ones 37 and 38. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 115–127, 2009     

Color constancy from invariant wavelength ratios. II. The nonspectral and global mechanisms

Given the spectral mechanism of color constancy (Part I of this series), the remaining nonspectral mechanism is formulated here in Part II by the constraint of correlation with known spectral illuminant–invariant functions, i.e., invariant wavelength ratios between constant hues, which plot straight parallel lines in the plane of wavelength and reciprocal illuminant color temperature (MK^?1). The same is assumed to apply to nonspectral constant hues in the same plane and dominant wavelength scale extended to cover the nonspectrals (see accompanying article “Relative wavelength metric for the complete hue cycle …”). To simplify analysis, stimuli are optimal aperture colors; their monochromatic stimuli lie between 442 and 613 nm, common boundaries with optimal compound stimuli (nonspectrals). It is shown that the wavelengths and invariant ratios of spectral constant hues can be formulated exactly (±0.5%) from the ratios of an harmonic period, which shifts wavelength with MK^?1. The formula implies this color‐constant hue cycle is isomorphic across illuminants and allows prediction of nonspectral constant hues. To identify these colorimetrically, their spectral complementary wavelengths are specified for various illuminants. This completes theglobal color constancy mechanism for the illuminant color temperature range 2800 to 25,000 K. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Color tolerance prediction for recycled paper based on consumers' awareness

Consumers' tolerance of the color of recycled paper was evaluated by the visual assessment of such paper by 30 Japanese university students. The assessment was performed to measure color tolerance using 266 color samples in eight conditions specifying the situation of paper as (1) “either paper is recycled or not recycled,” (2) “whether you will buy/use,” and (3) “use for office paper or for workbook paper.” The responses of the subjects were sorted out quantitatively in terms of the colorimetric values of color samples and then correlated with International Organization for Standardization (ISO) brightness and CIE whiteness. Both the ISO brightness and CIE whiteness were found to be dependent on hue factors and also to be restricted for use in direct representation of the consumers' responses to paper quality. Since the consumers' evaluation of paper quality is due to visual whiteness, we propose a new equation to predict the consumers' tolerance of paper color, in which the equation contains two factors concerning the color distance from the white point and the hue impact. The new tolerance equation was confirmed to predict the consumers' tolerance successfully, particularly when the consumers are aware that the paper is recycled. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011     

The relationship between visual acuity and color contrast in the OSA uniform color space

OSA uniform color space was used to study the relationship between visual acuity and OSA color contrast. Visual acuity is characterized by 50% minimal separable visual angle using Landolt-C. The OSA color contrast is characterized by the distance between colors in OSA color space. Twenty subjects with normal color vision were tested on 342 test sheets printed with colored Landolt-Cs and background. These results demonstrated that MSVA is approximately inverse log-linearly related to OSA color contrast (R² = 80.4%). Although luminance contrast (R² = 54.2%) is more salient than chromatic contrast (R² = 16.4%), both contrasts can induce very high visual acuity provided that they are sufficiently high. There is also evidence of an additive interaction between chromatic contrast and luminance contrast. Based on these findings, the OSA uniform color space and its color difference formula can be used as a scale for quantifying color contrast to accurately predict the size of colored text or symbols. © 1996 John Wiley & Sons, Inc.     

Comparison of different monoptic and dichoptic color‐matching functions

The objective of this article is to analyze different color matching functions (CMFs) obtained with three (650, 530, and 460 nm) and four primary colors (650, 565, 513, and 460 nm), using both monoptic and dichoptic central vision. This strategy helps to clarify (i) lack of additivity of brilliance; (ii) shift in maximum sensitivity peaks of CMFs when experimental conditions change; (iii) variations in luminance for the same reason; (iv) strong metamerism of the mixtures; and (v) differences of chromatic opponence between monoptic and dichoptic vision. The results obtained reflect two important facts: marked stability of the visual system, which allows the experimental conditions analyzed to be solved with an equal degree of success, and plasticity based especially on the balance of retinal illumination, which was maintained at an average of 40 trolands. The results obtained bring to mind an assertion made by MacAdam to the effect that the law of additivity when applied to luminance is not applied to measurements of brightness. Perceptively, brightness is not additive, and so CMFs should not be considered as significant functions in computing tristimulus values R, G, and B. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 416–426, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.     

Colour,contrast and gestalt theories of perception: The impact in contemporary visual communications design

Visual communications design, which generally relates to design projects with specific communication objectives, includes most forms of graphic and digital design that have a commercial or an educational purpose. The effectiveness of such design projects rests on how well the embedded communications objectives are met from the perspective of the target audience. In advertising as in education, various post‐campaign evaluation techniques are used to measure effectiveness. The challenge for designers is to create designs that are aesthetically appropriate and visually engaging for the target audience, but which are also functionally‐legible and support the encoding of communication messages so that these are effectively decoded as intended. This is particularly important given that the effectiveness of visual communications is not guaranteed in the visually‐cluttered environment of the 21st century. Of the design elements available to the designer of visual communications, colour and contrast play key roles in visual perception, and the strategic use of these can contribute to the effectiveness of visual communications design. Examining the roles that colour and contrast within the context of Gestalt theories of perception provides additional insight into the ways in which these design elements can be harnessed to improve the effectiveness of visual communications design. © 2013 Wiley Periodicals, Inc. Col Res Appl, 40, 85–92, 2015     

Study of balance of images using visual weight

The purpose of this research is to analyze the factors that create a sensation of balance or unbalance when a color image is observed depending on the light transmitted, reflected, and/or emitted by the objects that appear in it. This study is carried out by calculating the center of gravity (CG) of each image. The weight and the CG are obtained by calculating the force resulting from the different visual weights that make up the visual image and its position on this. When the visual CG and the geometric center coincide, it is recognized that the image is balanced. The action that acts on the balance of the lightness of an image is labeled as the visual weight. The visual weight of a figure is defined from the amount of visible light coming from it and the space occupied by this in the visual image. The colors show us the amount of light coming from a figure, while the shape provides us with information about the space that it occupies. The study explores how the qualities of appearance of three‐dimensional objects affect visual weight and how it can vary due to changes in light, motion of objects or the perspective of the image. Since these calculations can be very complex, we have developed the software called “PesoVisual” that automatically performs these operations on digital color images. Similarly, this software enables the analysis of the variability of the visual image. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 175–187, 2016     

sRGB颜色空间与显示器呈色

sRGB颜色空间是显示器呈色遵循的一个标准颜色空间,具有一定的颜色控制规律。出厂时的显示器在白场色温、光通道阶调曲线和色域等方面不一定与sRGB相符。校准技术可调整显示器的白场和阶调曲线,并与sRGB标准相符合,但不能根本上改变色域。环境光照对显示器的呈色构成影响。实验结果表明,对一般的显示器,当其屏幕表面的光照度达100lx以上时,会明显压缩光通道的暗色调颜色层次,并在该颜色部位减小色域。