Unique hue data for colour appearance models. Part III: Comparison with NCS unique hues

In this study, Swedish Natural Color System (NCS) unique hue data were used to evaluate the performance of unique hue predictions by the CIECAM02 colour appearance model. The colour appearance of 108 NCS unique hue stimuli was predicted using CIECAM02, and their distributions were represented in a CIECAM02 a_c–b_c chromatic diagram. The best‐fitting line for each of the four unique hues was found using orthogonal distance regression in the a_c–b_c chromatic diagram. Comparison of these predicted unique hue lines (based on the NCS data) with the default unique hue loci in CIECAM02 showed that there were significant differences in both unique yellow (UY) and unique blue (UB). The same tendency was found for hue uniformity: hue uniformity is worse for UY and UB stimuli in comparison with unique red (UR) and unique green (UG). A comparison between NCS unique hue stimuli and another set of unique hue stimuli (obtained on a calibrated cathode ray tube) was conducted in CIECAM02 to investigate possible media differences that might affect unique hue predictions. Data for UY and UB are in very good agreement; largest deviations were found for UR. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 256–263, 2015     

Unique hue data for colour appearance models. Part II: Chromatic adaptation transform

Unique hue settings of 185 observers under three room‐lighting conditions were used to evaluate the accuracy of full and mixed chromatic adaptation transform models of CIECAM02 in terms of unique hue reproduction. Perceptual hue shifts in CIECAM02 were evaluated for both models with no clear difference using the current Commission Internationale de l'Éclairage (CIE) recommendation for mixed chromatic adaptation ratio. Using our large dataset of unique hue data as a benchmark, an optimised parameter is proposed for chromatic adaptation under mixed illumination conditions that produces more accurate results in unique hue reproduction. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2013     

Accuracy of approximations for CIELAB chroma and hue difference computation

The transformation in CIELAB from differences in the L^*, a^*, b^* coordinates to those in lightness, chroma, and hue, ΔL^*, ΔC_ab^*, ΔH_ab^*, can be approximated by a rotation in 3-space. Expressions for the error in the approximation of chroma and hue differences are developed. Significant errors are introduced if either the hue angle or chroma difference between reference and sample colors are large. A computed example illustrates the use of the analysis. © 1997 John Wiley & Sons, Inc. Col Res Appl, 22, 61–64, 1997.     

Cognitive comparison of unique and intermediate hues

Eight panels were prepared using the most highly chromatic Natural Colour System (NCS) samples for each hue. Each panel consisted of a test hue and two reference hues, the samples representing either mean unique hues (uH) R, Y, B, or G as determined in earlier experiments or intermediate hues half way between them, (iHs) Or, Pp, YG, and BG. Subjects were asked to determine whether they considered it possible to match the test hue with the reference hues. A total of 45 color‐normal subjects participated in the study in three separate trials with at least 24 h gap between consecutive trials. The results, with very few exceptions, showed that a match was considered possible for the four iHs based on a mixture of adjacent pairs of uHs, while the majority did not believe uHs could be matched based on amounts of adjacent iHs. Statistical analysis of the test results indicates that responses for the two sets of panels were significantly different (P ～ 0, df = 539). The results provide support for Hering's uHs concept. However, a number of subjects believed that a mixture of adjacent iHs can result in a match of the reference uHs. Potential causes may include the use of experimental mean unique and intermediate hues and learned facts of colorant mixture. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 264–269, 2015     

Note calibrating low‐scattering samples using Kubelka–Munk model

Two calculation forms are presented for calibrating a Kubelka–Munk (KM) translucent layer using white and black backgrounds. The equations, derived from the hyperbolic and exponential forms of the KM equations and replacing variables a and b with c = S/K and d = bc, give results identical to the usual method, but avoid near‐zero divisions in the low‐scattering limit. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 399–401, 2016     

Optimum solution of the CIECAM02 yellow–blue and purple problems

Brill [Color Res Appl 2006;31:142‐145] and Brill and Süsstrunk [Color Res Appl 2008;33:424‐426] found that CIECAM02 has the yellow–blue and purple problems and gave partial solutions to them. In this article we model the optimum solution to the yellow–blue and purple problems simultaneously as a constrained non‐linear optimization problem. An optimum solution resulting in a new CAT02 matrix is numerically obtained. This new matrix satisfies the nesting rule and performs better than the Hunt‐Pointer‐Estévez (HPE) matrix in predicting both corresponding colours and colour appearance data sets. Specifically, it was found that the new and HPE matrices performed significantly different on nine (out of 21) corresponding colour data sets and on all corresponding colours data sets as a whole. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 491–503, 2015     

A shade guide model based on the color distribution of natural teeth

The objectives were to determine the color distribution of natural teeth sorted by the parameters of Value, Chroma, and hue angle measured with a colorimeter, and to suggest a shade guide model. The color of maxillary and mandibular 12 anterior teeth was measured with a tristimulus colorimeter for 47 subjects (n = 564). The color of teeth was grouped initially by Value (CIE L*) by the interval of 3.3 units. After then, within each main group, the color of teeth was subgrouped by Chroma by the interval of 3.3 units. Chroma was calculated as C*_ab = (a*2 + b*2)^1/2. Since the hue angles were in the first or fourth quadrant, subgroups were further sorted by the first or fourth quadrant hue angles. Hue angle was calculated as h° = arctan (b*/a*). Mean color difference (ΔE*_ab) between the color of an individual tooth and the mean color of each main group was 2.5–3.3, which was lower than acceptable limit (ΔE*_ab < 3.3), and that in each subgroup was 0.9–3.1. The number of subgroups was 22, which was comparable to those of conventional shade guides. A shade guide model based on the color distribution of natural teeth sorted by Value in six main groups, three or four subgroups within each main group sorted by Chroma, and further sorted by hue angle (first or fourth quadrant values) was suggested. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 278–283, 2007     

Does hue affect the perception of grayness?

Although gray is defined as an achromatic color sensation varying only in lightness, in practice, grayness can be tinged by any hue within a limited range of chroma. Given the fact that preferred perceived white and black are slightly chromatic, the hypothesis tested in this study is that the preferred perceived object gray is also slightly chromatic. Two psychophysical experiments were carried out to test this hypothesis. A total of 56 color normal subjects assessed 27 different gray patches that varied mainly in hue, in three separate trials. Subjects selected a subset of samples (10 in the first experiment and five in the second experiment) that were considered “most gray” resulting in 168 selected sets of samples. Subjects then ranked their selected subset of samples from most to least gray. A total of 1225 assessments were thus obtained (750 assessments in the first experiment and 465 in the second experiment). Results from both experiments were in good agreement and indicate that greenish blue grays in the range of 190° to 235° of CIELAB hue angle were selected as most gray, thus indicating that the perception of grayness is influenced by hue. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 374–382, 2015     

Hue uniformity and the CIELAB space and color difference formula

The hue uniformity of the CIELAB system is investigated using a hue circle of Munsell colors at value 6 and chroma 14 and experimentally determined hue coefficient data. CIELAB hue differences for equal Munsell hue increments are found to vary up to nearly a factor 4, and hue coefficients differ from the experimentally determined ones by up to 40% at certain wavelengths. Dominant wavelengths assigned by the CIELAB system to individual Munsell hues are found to vary up to 35 nm from those of the Munsell Renotations. Four other color space systems are compared with widely differing but comparable results. The CIE 2° color-matching functions are adapted to result in a set of opponent-color functions accurately representing the Munsell Hue and Chroma data. A call is made for the experimental determination of the “standard hue observer” as a step toward an improved color space/color-difference formula. © 1998 John Wiley & Sons, Inc. Col Res Appl, 23, 314–322, 1998     

Test/retest and inter‐test agreement of color aptitude measures

The color discrimination capacity of color vision normal observers can be assessed using color aptitude tests (CATs), although data on the test/retest reliability and inter‐test agreement of such tests using appropriate statistical measures is limited. In this study, 32 color vision normal observers twice performed each of five CATs, being the Farnsworth‐Munsell 100 hue test, HVC Color Vision Skills Test, inter‐Society Color Council Color Aptitude Test, the Nagel Anomaloscope (Nagel), and a custom designed two‐color discrimination test. Two methods of determining the Nagel matching range were used based on the initially accepted matching range or on repeated measures. The test/retest performance of each test was determined using the method outlined by Bland and Altman[Lancet 1986;1:307–310] and the inter‐test agreement was analyzed using the same method, after converting test scores into z score units. No test was found to have a significant systematic alteration in test performance between test and retest. Test/retest performance was generally poor, indicating that tests can only reliably classify observers into very broad performance bands. All tests failed to show inter‐test agreement, and our data indicate a primary reason for this: as test/retest performance is generally poor, inter‐test agreement must also be poor as no test can agree more with another test than it agrees with itself. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 224–231, 2015     

On the relationship between wavelength and perceived hue

Unlike in the case of sound where there is a compressed but straightforward relationship between frequency of sound waves and the perceived pitch, in the case of color the relationship is highly nonlinear, as first pointed out by Ostwald in 1916. In this article, the relationship between the perceptual Munsell hue scale and the related dominant wavelengths of the color chips involved is investigated. A hypothesis is proposed according to which the immediate cause of the nonlinearity can be found in the relative activation of the kinds of chromatically opponent functions shown to exist in neurons of the lateral geniculate nuclei. However, at this time, the relationship is only correlational, given the lack of deeper understanding of the relationship between the physiological operation of the color vision system and conscious experiences of color. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011;     

Influence of ageing on the gloss,color, and structure of colored ABS

The results of examination of the influence of ageing by UV rays on the gloss, color, and morphology of injection molded parts made of ABS terpolymer with addition of coloring agents in the form of powder and its masterbatch (granulate) based on ABS and PS media are presented in this article. It has been shown that the UV radiation contributes to decrease in the value of gloss and increase in the luminance of moldings and also changes values of parameters a and b, describing the change in parts color, in the direction of red and yellow, which is connected with the degradation of polymer ABS and coloring agents. Ageing process leads to structural changes in polymer, depending on the type of coloring agent. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 392–398, 2016     

Changes in colour appearance of a large display in various surround ambient conditions

This article focuses on the change in colour appearance of a large display arising from various illumination conditions. Nine experimental phases were conducted according to different surround conditions including dark, indoor, and outdoor conditions. Each of the presented test colours was assessed by 10 observers using a magnitude estimation method. The surrounds used in all phases were divided into two groups: excluding and including veiling glare. Additionally, the effect due to different sizes of both stimuli and surround was investigated. Diverse visual effects were examined and reported. Finally, the visual colour appearance data were used to test the CIECAM02 colour appearance model. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Feasibility of recycled newspaper as cellulose source for regenerated cellulose membrane fabrication

An environmental friendly regenerated cellulose membrane (RCM) was successfully prepared via NaOH/urea aqueous solution system by utilizing recycled newspaper (RNP) as the cellulose source. The morphological and chemical structure of resulting membrane were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD) spectroscopy, and thermogravimetric analysis (TGA). Results from FTIR and XRD verified that the transparent RCM possesses cellulose II structure. SEM observation revealed that the transparent RCM consist of homogeneous dense symmetric membrane structure and composed of a skin layer with mean roughness parameter R_a, obtained from AFM analysis of 29.53 nm. Pure water flux, water content, water contact angle, porosity, and pore size of the resulting membrane were also measured. This study promotes the potential of the cellulose‐based membrane obtained from low cost cellulose source for application in filtration and separation system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42684.     

Are chroma tolerances dependent on hue‐angle?

Relationships between suprathreshold chroma tolerances and CIELAB hue‐angles have been analyzed through the results of a new pair‐comparison experiment and the experimental combined data set employed by CIE TC 1–47 for the development of the latest CIE color‐difference formula, CIEDE2000. Chroma tolerances have been measured by 12 normal observers at 21 CRT‐generated color centers L*₁₀ = 40, C*_ab,10 = 20 and 40, and h_ab,10 at 30° regular steps). The results of this experiment lead to a chroma‐difference weighting function with hue‐angle dependence W_CH, which is in good agreement with the one proposed by the LCD color‐difference formula [Color Res Appl 2001;26:369–375]. This W_CH function is also consistent with the experimental results provided by the combined data set employed by CIE TC 1–47. For the whole CIE TC 1–47 data set, as well as for each one of its four independent subsets, the PF/3 performance factor [Color Res Appl 1999;24:331–343] was improved by adding to CIEDE2000 the W_CH function proposed by LCD, or the one derived by us using the results of our current experiment together with the combined data set employed by CIE TC 1–47. Nevertheless, unfortunately, from the current data, this PF/3 improvement is small (and statistically nonsignificant): 0.3 for the 3657 pairs provided by CIE TC 1–47 combined data set and 1.6 for a subset of 590 chromatic pairs (C*_ab,10>5.0) with color differences lower than 5.0 CIELAB units and due mainly to chroma. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 420–427, 2004; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/col.20057     

Introducing Wpt (Waypoint): A color equivalency representation for defining a material adjustment transform

The basis of this research is the manipulation of sensor excitation values to account for differences in observer or illuminant when spectral data are unknown. This touches on several related topics: color constancy, chromatic adaptation, and white balancing. The central premise is that these concepts make use of some form of intermediate color equivalency representation or waypoint system that makes comparison and color transformations possible. Differences between these concepts are related to the kind of color equivalency representation system used and how transformations are made into and out of it. A new sensor excitation normalization method was derived that has been optimized to predict changes in material color as Wpt (pronounced Waypoint) coordinates, which can be used to form a material adjustment transform. The prediction of such changes is also known as least dissimilar color matching. This is contrasted with a chromatic adaptation transform, which is optimized to predict corresponding color changes. As such a distinction is made between adaptation (which is based on corresponding color) and adjustment (which is based on other criteria). © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 535–549, 2015     

Gloss evaluation and prediction of achromatic low‐gloss textured surfaces from the automotive industry

In this article, we investigate the benefit of including texture information in models of gloss perception of low‐gloss textured achromatic plastic surfaces from the automotive industry. 4 models are compared: two gloss prediction models including texture information, one using data from reflectometry (M1) and one using data from goniophotometry (M2), and two models using data from reflectometry (M3) or goniophotometry (M4) alone. Both texture‐corrected models (M1‐M2) outclass the uncorrected intensity‐based models, mainly because they are made texture invariant. Although the texture‐corrected reflectometer‐based prediction (M1) correlates rather well with sensory data, a more consistent fit is obtained by mixing textural to goniophotometric data (M2). This can be explained by the fact that contrast gloss is better than multiangle specular gloss at reflecting the observer's gloss evaluation strategy. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 154–164, 2016     

Colour words and their uses

Popular usage of colour words as parts of speech obey certain rules according to whether they are population dependent and whether use demands a degree of colour vision. The word green refers to that colour most of us see, recognize and categorize as being of the colour called green. But, colours and colour words are to do with emotion as well as perception. What can we learn from the greatest writers, artists and musical composers; how do they, for example, regard green? From them we learn that we perceive colours with our ears as well as our eyes and, in an emotional sense, a colour word means or is associated with just what the writer intends. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 111–113, 2015     

Automatic detection of layout of color yarns of yarn‐dyed fabric. Part 2: Region segmentation of double‐system‐Mélange color fabric

To detect the layout of color yarns automatically, a novel projection‐based fabric segmentation method is proposed to segment the double‐system‐mélange color fabric into several regions, which can be seen as single‐system‐mélange color fabrics. This method consists of five main steps: (1) yarn skew detection, (2) fabric image projecting, (3) projection curve smoothing, (4) variance curve calculating, and (5) curve peak confirmation. Based on the acquisition fabric image, the skew angles of warp and weft yarns are detected by Hough transform first. The projection curves of L, a, and b channels in Lab color model are generated and smoothed by Savitzky–Golay filter. The variance curves of L, a, and b are then calculated, and the peaks corresponding to the regional boundaries in each curve are detected. The regional boundaries are confirmed by synthesizing the curve peaks of L, a, and b. The experimental and theoretical analysis proves that the proposed method can segment the double‐system‐mélange color fabric into regions with satisfactory accuracy and good robustness. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 626–635, 2016     

A hue rectangle and its color metrics in a modified opponent‐colors system

In the proposed modified opponent‐colors system, the hue regular rectangles show the chromatic coordinates of any chromatic colors better than hue circles. In the hue rectangles equihue and equichroma loci are shown together with equigrayness loci. In the color perception space of the modified opponent‐colors system, a city‐block metric must be used instead of a Euclidean one for distance. The reason for this is described in detail. The proposed color perception space constitutes a regular octahedron. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 171–179, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10046