Colour constancy of vat prints on cotton fabrics

Colour constancy of prints with vat dyes on cotton fabrics was investigated by computing the CMCCON02 colour inconstancy index with the key element CAT02 for chromatic adaptation transform. The results show that the highest changes in colour appearance can be expected when the average daylight is replaced with fluorescent light. If D65 daylight is replaced with some other type of daylight, such as D50 or D55, only minor colour deviations occur which do not substantially change the colour appearance of the prints. The analysis of the influence of the lightness and chromaticity of prints shows that the chromaticity of the samples significantly affects their colour constancy. The change of appearance of the prints with lower chroma because of changed illumination conditions is less probable. The influence of a dye blend composition was also investigated. On average, multi‐coloured dye blends have proved to be more colour constant.     

Quantifying colour appearance. Part I. Lutchi colour appearance data

The work described here forms part of a research project entitled Predictive Perceptual Colour Models. The aim of this project is to develop a colour appearance model capable of predicting changes of colour appearance under various different viewing conditions. This will provide industry with a quantitative measure for assessing the quality of colour reproduction and enable more rapid and accurate proofing simulations in the graphic art industry. A large-scale experiment has been carried out in which colour appearance was assessed under a wide range of viewing conditions. The parameters studied were (1) D65, D50, white fluorescent, and tungsten light sources, (2) luminance levels of about 40 and 240 cd/m², (3) five background conditions: white, grey, black, grey with white border, and grey with black border, and (4) two media: luminous colours (displayed on a high-resolution colour monitor) and nonluminous colours (presented in a viewing cabinet). Each colour was assessed by a panel of six or seven observers using a magnitude estimation method. In total, 43,332 estimations were made, and these form the LUTCHI Colour Appearance Data. Data analysis has been carried out to examine the reliability of the experimental results and to understand the effects of the various viewing parameters studied. (Part II of this article describes how the LUTCHI Colour Appearance Data has been used to test the performance of various colour spaces and models.     

A colour-difference formula for surface colours under illuminant A

The available experimental data for small colour differences between surface colours under illuminant A have been analysed in a manner similar to that used earlier for the comparable results under daylight. Chromaticity discrimination ellipses were calculated from the results for each colour centre. The size of the ellipses varied with chromaticity in an irregular manner suggesting that the visual results for the different centres were effectively on different scales. New experiments, carried out using a grey scale method for the visual assessments, allowed the relative sizes of ellipses to be adjusted. After adjustment the size of the ellipses varied much more systematically with chromaticity. Similar adjustments allowed all the results to be combined together and used to develop a new colour-difference formula suitable for assessments under illuminant A. Values of ΔE from the new formula gave a better fit to the visual results than those from other formulae. Earlier formulae were intended to be used with results for daylight. Using chromatic adaption formulae to transform the illuminant A results to illuminant D₆₅ improved the agreement, but the results were still not as good as those obtained with the new formula.     

Colour appearance rating of familiar real objects

The determination of the long‐term memory colours of objects has been the subject of investigation for many years. Colour acceptance boundaries have been determined from the visual assessments of objects under variable illumination or by presenting manipulated images of objects on a calibrated computer display. However, a systematic and quantitative rating of the colour of real objects with respect to memory colour is not available at this moment. In this article, nine familiar real objects with colours distributed around the hue circle were positioned in a specially designed LED illumination box. For each object, approximately hundred real illumination spectra were synthesized in a random order keeping the luminance of the object approximately constant. Observers were asked to rate, on a five‐point scale, the similarity of the perceived object colour to their idea of what the object looked like in reality. By avoiding specular reflections, the observer was unable to identify any clues as to the colour of the illumination. For each object, similarity ratings showed a good intraobserver and interobserver agreement. The ratings of all the observers were pooled and successfully modeled in IPT colour space by a bivariate Gaussian distribution. It was found that the chromaticity corresponding to the highest rating tended to be shifted toward higher chroma in comparison with the chromaticity calculated under D65 illumination. The bivariate distributions could be very useful in applications where the quantitative evaluation of the colour appearance of an object stimulus is required, such as in the evaluation of the colour rendering capabilities of a light source. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 192–200, 2011;     

The Concept of Colourfulness and its Use for Deriving Grids for Assessing Colour Appearance

A technique of subjective magnitude estimation has been used to assess a set of pseudosurface colours, each having a luminance factor of 0.2. Three adaptation conditions corresponding to daylights D₆₅ and D₅₀ and tungsten light S_A were used. The experimental technique and data analysis represent an improvement on that previously reported. The concept of colourfulness, as opposed to chroma or saturation, has been introduced with considerable success. The loci of constant hue and colourfulness were derived in u',v' chromaticity space and the results compared with predictions obtained using the Bartleson adaptation equations.     

Sky-Blue Pink*

The appearance of colours is affected by both instantaneous and gradual adaptations. Instantaneous adaptation can result in a projected white light looking both sky-blue and pink when seen as shadows in superimposed orange and green light. Gradual adaptation can contribute markedly to the colour constancy of illuminants in the tungsten-light to daylight range. In colour photographic reflection prints and projected transparencies, naming and scaling techniques have been used to determine the chromaticities of subjective grey-points and preferred and acceptable reproductions of blue sky, green grass, and Caucasian skin. The use of haploscopic matching to determine, and Von Kries types of transformation to predict, equivalent stimuli for different adaptations is discussed: it is suggested that colour scaling is preferable to haploscopic matching because haploscopic results have been shown to be dependent on the matching technique adopted; it is also argued that, because adaptation cannot be adequately represented by a Von Kries type of transformation, equivalent stimuli are better defined by means of grids of lines of constant hue and saturation for various adaptation conditions.     

On the colours dichromats see

Dichromatic colour vision is commonly believed to be a reduced form of trichromatic colour vision (referred to as the reductionist principle). In particular, the colour palette of the dichromats is believed to be a part of the colour palette of the trichromats. As the light‐colour palette differs from the object‐colour palette, the dichromatic colour palettes have been derived separately for light‐colours and object‐colours in this report. As to light‐colours, the results are in line with the widely accepted view that the dichromatic colour palettes contain only two hues. However, the dichromatic object‐colour palettes have proved to contain the same six component colours which constitute the trichromatic object‐colour palette (yellow, blue, red, green, black and white). Moreover, all the binary and tertiary combinations of the six component colours present in the trichromatic object‐colour palette also occur in the dichromatic object‐colour palettes. Yet, only five of the six component colours are experienced by dichromats as unitary (unique) object‐colours. The green unitary colour is absent in the dichromatic object‐colour palettes. The difference between the dichromatic and trichromatic object‐colour palettes arises from the fact that not every combination of the component‐colour magnitudes occurs in the dichromatic object‐colour palettes. For instance, in the dichromatic object‐colour palettes there is no colour with the strong green component colour. Furthermore, each achromatic (black or white) component colour of a particular magnitude is combined with the only combination of the chromatic components. In other words, the achromatic component colours are bound with the chromatic component combinations in dichromats. © 2012 Wiley Periodicals, Inc. Col Res Appl, 39, 112–124, 2014     

The Specification of Colour Appearance. I. Concepts and Terms

Concepts necessary for the specification of the appearance of colours are described, and the corresponding colour terms collected. Psychometric and psychoquantitative terms are listed that correlate with the perceptual and psychophysical terms used. The perceptual term colourfulness is proposed to denote the attribute of a visual sensation according to which an area appears to exhibit more or less chromatic colour; for a given chromaticity, as the luminance increases, colourfulness generally increases. For related colours, the CIE 1976 Colour Spaces are used to systematize some psychometric variables that are independent of absolute luminance level, including metric saturation, metric purity, and metric chroma, and formulae are given for calculating their amounts. (In Part II, to appear in the next issue, the effects of changes in viewing conditions will be discussed).     

Colour gamuts arising from absorber–dielectric–metal optical resonators

Structural coloration is a quickly growing field, encompassing physical and photonic processes such as interference, diffraction, and scattering. In this study, we investigated the optical effects in the visible wavelength range, and in particular, the colour gamuts achievable with absorber–dielectric–metal sandwich structures. These chemical‐free layered structures are highly tunable, easily scaled, optical cavities that are capable of generating remarkable colours whose properties are determined completely by material and structural parameters. We employed experimental and numerical strategies to demonstrate that each absorber spans a unique colour gamut, i.e. a subset of the full chromaticity space. While gamut overlap is observed between different absorber types, the gamut areas unique to each absorber occur at different hues of high excitation purity. A comprehensive understanding of how these colour gamuts develop and how different materials may be combined to expand larger subsets of the chromaticity space is required in order to maximize the variety of colours achievable with this system and elevate it into a ‘structural coloration technology’.     

Evaluation of daylight simulators. Part 1; Colorimetric and spectral variations

This paper describes the development of daylight simulators and various standards for specifying the quality of daylight simulators. The spectral power distributions of 15 D65 simulators and 58 D50 simulators were accumulated from UK and USA industrial laboratories, respectively. The lamp variations between the investigated simulators were examined in terms of colorimetric values and spectral results for different lamp types and manufacturers. The colorimetric results include luminance, chromaticity coordinates, chromaticity deviation relative to the CIE daylight illuminant, correlated colour temperature, colour rendering index and metamerism index for the visible range. The spectral results were calculated in terms of relative spectral power distributions and spread of relative power at each reported wavelength. Spectral analysis was conducted for the D65 and D50 broad-band fluorescent lamps. The quality of these investigated simulators was evaluated based on the relevant CIE recommendation and ISO standards.     

Age effects on colour emotion,preference, and harmony

Two psychophysical experiments were carried out to investigate whether or not colour emotion responses would change with the advance of the viewer's age. Two forms of stimuli were used: 30 single colours (for Experiment 1) and 190 colour pairs (for Experiment 2). Four word pairs, warm/cool, heavy/light, active/passive, and like/dislike, were used to assess colour emotion and preference in Experiment 1. In Experiment 2, harmonious/disharmonious was also used in addition to the four scales for Experiment 1. A total of 72 Taiwanese observers participated, including 40 (20 young and 20 older) for Experiment 1 and 32 (16 young and 16 older) for Experiment 2. The experimental results show that for single colours, all colour samples were rated as less active, less liked, and cooler for older observers than for young observers. For colour combinations, light colour pairs were rated as less active and cooler for older observers than for young observers; achromatic colour pairs and those consisting of colours in similar chroma were rated as cooler, less liked and less harmonious for older observers than for young observers. The findings may challenge a number of existing theories, including the adaptation mechanism for retaining consistent perception of colour appearance across the lifespan, the modeling of colour emotion based on relative colour appearance values, and the additive approach to prediction of colour‐combination emotion. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011     

Memory for the color of non‐monochromatic lights

The aim of this work was to explore the limits of memory for the hue of coloured illumination using nonspectral colours. Eighty‐four undergraduate optometry students with normal colour vision as assessed by the Ishihara 38 plate test, were given 10 s to memorize the hue of a luminous surface (luminance 120 cd m^?2), subtending 22 by 18 degrees in an otherwise unlit room. The sample hue was one of 12 samples with chromaticity spaced evenly every 30 degrees around a hue circle in the CIE UCS diagram. The circle, radius 0.06, was centered at the chromaticity of D65 (u′ = 0.198, v′ = 0.468). The hue was displaced randomly by between 40 and 100 degrees, and the participants were required to use one of two keys to return the hue to its original appearance. The keys changed CIE 1976 hue angle (h_uv) by 1 degree, one in a clockwise and the other in a counterclockwise direction, but left the CIE 1976 saturation (s_uv) and the luminance unchanged. Each participant saw the to‐be‐memorized hue once only and made subsequent adjustments without seeing it again. Four adjustments were made immediately, four after 1 h, and a further four after 1 week. The second and the fourth in each set of four were preceded by a clockwise displacement of hue angle and the remaining two by an anticlockwise displacement. The CIE 1976 UCS chromaticity of the standard and the chromaticity of the very first adjustment performed immediately after the presentation of the standard were separated by 0.0210 (s.d. 0.0178) averaged across hues. One hue (purple) was more readily nameable than the others and was more accurately reproduced. There was no evidence of stable individual differences in observers' memory: observers' accuracy in reproducing one colour was not significantly correlated with their accuracy in reproducing another. Adjustments made after an interval of 1 h were worse than those undertaken immediately, but no better than those performed after 1 week. The variability of hue memory under these conditions was similar to the variability of coloured surfaces under common sources of illumination. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 11–15, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20281     

Colour combination effects in experimental rooms*

This article deals with the way colours in a room affect each other through contrast effects and reflections. The study presented is based on the visual observations of the colour appearance of three inherent colours in a sequence of experimental situations. My point of departure was a yellow, blue, and red room. The room had distinctly different colour appearances of the same inherent colours when observed at different locations. The effects of both contrasts and reflections were evident. However, reflection effects seemed to dominate the situation. In a study of small experimental rooms, different combinations of the same three inherent colours were systematically tested. Comparisons were made to examine the differences in colour appearance between monochromatic rooms and multicoloured rooms with varying colour schemes. The illumination was kept stable. In the cases studied, it was obvious how the colours in the two‐coloured rooms became more alike or “neutralized each other.” The contrast strengthening between abutting areas on the same level had distinct significance for colour appearance and perception of space. However, not in such a way that the perceived colour differences became larger in the two‐coloured room than between each monochromatic rooms. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 230–242, 1999     

A study of colour emotion and colour preference. Part III: Colour preference modeling

In this study three colour preference models for single colours were developed. The first model was developed on the basis of the colour emotions, clean–dirty, tense–relaxed, and heavy–light. In this model colour preference was found affected most by the emotional feeling “clean.” The second model was developed on the basis of the three colour‐emotion factors identified in Part I, colour activity, colour weight, and colour heat. By combining this model with the colour‐science‐based formulae of these three factors, which have been developed in Part I, one can predict colour preference of a test colour from its colour‐appearance attributes. The third colour preference model was directly developed from colour‐appearance attributes. In this model colour preference is determined by the colour difference between a test colour and the reference colour (L*, a*, b*) = (50, ?8, 30). The above approaches to modeling single‐colour preference were also adopted in modeling colour preference for colour combinations. The results show that it was difficult to predict colour‐combination preference by colour emotions only. This study also clarifies the relationship between colour preference and colour harmony. The results show that although colour preference is strongly correlated with colour harmony, there are still colours of which the two scales disagree with each other. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 381–389, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20047     

Effect of grey component replacement processing and varnishing on the light fastness of colours on cardboard prints

The visual appearance of packaging is one of its most important features. Electromagnetic irradiation causes a change in colour and often leads to colour fading (ie, to diminished visual appearance of a printed product). This research study aimed to determine the combined effect of grey component replacement image processing and varnishing on the protection of prints' appearance when exposed to accelerated ageing. For that purpose, two test charts were printed in a lithographic press and coated with water-based and ultraviolet-curable varnish before exposing them to xenon light. The prepared prints were evaluated by determining the tone values and colour difference, as well as the rub and abrasion resistance. In addition, Fourier Transform–infrared-attenuated total reflectance spectra were recorded to detect possible chemical changes caused by the (AcA). The results showed that the investigated period of (AcA) caused significant differences in the tone values of yellow, while the other primary colours proved to be more resistant. The water-based varnish provided better protection than the ultraviolet-curable varnish. The grey component replacement image processing diminished the colour difference caused by (AcA) on all the prepared print samples, and was particularly detected in tertiary colours containing the mid-range tone values of yellow (34%-68%). Both varnishes improved the rub resistance of aged prints, but only ultraviolet-curable varnish improved the abrasion resistance of both the unaged and the aged prints. In conclusion, applying varnish to prints ensured enhanced rub and abrasion resistance and diminished the colour change caused by (AcA). Finally, improved resistance to colour change was achieved by processing images with the grey component replacement method.     

An investigation of colour appearance for unrelated colours under photopic and mesopic vision

Data were obtained for the colour appearance of unrelated colours under photopic and mesopic conditions. The effects of changes in luminance level and stimulus size were investigated. The method used was magnitude scaling of brightness, colourfulness, and hue. Two stimulus sizes (10° and 0.5°) and four starting luminance levels (60, 5, 1, and 0.1, cd/m²) were used. The results at 0.1 cd/m² had large variations, so data were obtained for two additional stimulus sizes (1° and 2°) at this luminance level. Ten observers judged 50 unrelated colours. A total of 17,820 estimations were made. The observations were carried out in a completely darkened room, after 20 min adaptation; each test colour was presented on its own. Brightness and colourfulness were found to decrease with decreases of both luminance level and stimulus size. The CAM97u model predicted brightness more accurately than CIECAM02 but gave worse performance in predicting colorfulness. For hue, CAM97u and CIECAM02 both gave satisfactory predictions. Using the brightness correlate from CAM97u, a new colour‐appearance model based on CIECAM02 was developed specifically for unrelated colours under photopic and mesopic conditions, with parameters to allow for the effects of luminance level and stimulus size. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011;     

Individual differences in human colour vision as derived from stiles & Burch 10° colour matching functions

Individual differences between the 49 Stiles & Burch observers have been analyzed using the object‐colour space put forth recently (J of Vision 2009;9:1–23). A set of rectangular reflectance spectra has been used as a common frame of reference for representing object colours for all the observers. Being metameric to one of these rectangular reflectance spectra, every reflectance spectrum can be geometrically represented as a point in the three‐dimentional space. The interindividual differences reveal themselves in that, for various observers, the same reflectance spectrum maps to different points in this space. It has been found that on average such differences do not exceed the differences in object‐colour appearance induced by an illumination shift from daylight to the fluorescent daylight simulator F1. Such small individual variations have been accounted for by the fact that the cone spectral tuning curves have a special form that mitigates the individual differences in cone spectral positioning. © 2012 Wiley Periodicals, Inc. Col Res Appl, 2013     

Chromic textiles: Colour fastness properties and irreversible colour change behaviour of textiles screen printed with thermochromic,photochromic and hydrochromic colourants

The objective of this work was to study how ultraviolet (UV) light exposure, washing and rubbing can influence colour and dynamic qualities of chromic textiles, and to explore how the results attained can be applied by designers for the development of colour changing palettes. The experimental work was conducted with 74% polyamide and 26% elastane elastics screen printed with thermochromic, photochromic and hydrochromic pigments in diverse colours. Initially, colourfastness properties of each pigment type versus colour were assessed. Although washing and rubbing can interfere in samples' colours by becoming lighter at different degrees, the results attained highlight the poor stability to lighting of thermochromic and photochromic pigments, which also present changes between hues along exposure time. For conventional textile applications, poor colour fastness commonly represents a limitation. This work proposes that the way textile colours and behaviour are permanently affected by the studied conditions can be interpreted as a creative variable in the design process. Research samples with a combination of pigments were developed and tested with a combination of cycles of different fastness tests, namely one washing cycle for every 4 h of UV light exposure, totalling 48 h and 12 washing cycles. Results demonstrate the possibility of creating interactive surfaces capable of displaying a wide range of colours that evolve to static within different hues, over stimuli conditions.     

A comparison of colour appearance for surface colours between outdoor and indoor environments

Psychophysical experiments of colour appearance, in terms of lightness, colourfulness, and hue, were conducted outdoors and indoors to investigate whether there was any difference in colour appearance between outdoor and indoor environments. A panel of 10 observers participated in the outdoor experiment, while 13 observers took part in the indoor experiment. The reference white had an average luminance of 12784 cd/m² in the outdoor experiment and 129 cd/m² in the indoor experiment. Test colours included 42 colour patches selected from the Practical Coordinate Color System to achieve a reasonable uniform distribution of samples in CIECAM02. Experimental results show that for both outdoor and indoor environments, there was good agreement between visual data and predicted values by CIECAM02 for the three colour appearance scales, with the coefficient of variation values all lower than 25 and the R² values all higher than 0.73, indicating little difference in the three dimensions of colour appearance between indoor and outdoor viewing conditions. Experimental data also suggest that the observers were more sensitive to variation in lightness for grayish colours than for highly saturated colours, a phenomenon that seems to relate with the Helmholtz-Kohlrausch effect. This phenomenon was modeled for predicting perceived lightness (J′) using the present experimental data. The new J′ model was tested using three extra sets of visual data obtained both outdoors and indoors, showing good predictive performance of the new model, with an average coefficient of variation of 14, an average R² of 0.88, and an average STRESS index of 14.18.