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     

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;     

Quantifying colour appearance. part V. simultaneous contrast

Experiments were carried out to investigate the effect of simultaneous contrast on colour appearance by varying the lightness, colourfulness, and hue of an induction field surrounding a test colour. A total of 814 test/surround combinations were displayed on high-resolution colour displays. Each was assessed by a panel of five to six observers using a magnitude estimation technique. the results indicate that colours presented on a computer display are affected by simultaneous contrast in a similar way to surface colours. All three colour appearance parameters studied (i.e., lightness, colourfulness, and hue) are affected and these effects are summarized. In general, the results support and add to the findings of the other studies. the Hunt colour appearance model was tested and gave a somewhat poor prediction to this data set. Further modifications are required to improve its performance. © 1995 John Wiley & Sons, Inc.     

Additivity of colour harmony

An additive approach to predict harmony for three‐colour combinations is proposed in this article. It is hypothesised that a three‐colour combination can be seen as a combination of three colour pairs, each generating a harmonious/disharmonious feeling that can be quantified by a two‐colour harmony model the authors previously derived; the average of these three harmony values can then determine the overall harmony. To establish whether this hypothesis was valid, two psychophysical experiments were conducted in the United Kingdom and the United States. Experiment 1 used 6545 three‐colour wheels as the stimuli, presented individually on a calibrated cathode ray tube display. Under the same viewing conditions, Experiment 2 used 111 interior images as the stimuli. In each experiment, 20 British and 31 American participated as the observers. An additional test was undertaken, with 64 observers taking part, to address the issue of large sample size as encountered in Experiment 1, using 90 colour wheels selected randomly from those used in Experiment 1. The experimental results show close agreement between the observers' response and the harmony value predicted by the proposed method, with a correlation coefficient of 0.71 for the 6545 colour wheels, 0.93 for the 111 interior images and 0.88 for the additional 90 colour wheels. The results support the additive approach as a simple but robust method for predicting harmony in any three‐colour combinations, which may also apply to combinations generated by any number of colours. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

Impact of matching field size on color matching (functions) accuracy

Accurate colorimetry starts with accurate color matching functions (CMFs). Due to changes in the macular pigment and cone pigment optical densities at different retinal locations, different CMFs are required for different stimulus field sizes. To characterize the accuracy of the CIE recommendation for the use of 2° and 10° standard CMFs and the field-size dependent CIEPO06 model, in this study, a series of achromatic matching experiments were performed with 2°, 4°, 6°, 8°, and 10° bipartite fields using spectrally narrowband primaries. Using the CIEPO06 model, optimal field sizes were estimated that minimize the chromaticity differences between the spectrally narrowband observer matches and the spectrally broadband achromatic target. It was found that the optimal field size estimated using the CIEPO06 model is close to half the actual bipartite field size in most cases, except for the 2° field. The discrepancy between the 10° bipartite field in Stiles & Burch's experiments and our optimal field size (6.54°) was assumed to be due to different individual color comparison strategies. However, the results of experiments requiring specific observer gaze positions did not support this assumption and the reason for the discrepancy remains unclear. Confirming our earlier results, the primary set (636, 521, 447 nm) was again found to be largely insensitive to changes in CMFs and to provide the most accurate matches under various fields of view. The inter- and intra-observer variability ellipses for 2° matches are larger than those for 10°, consistent with Brown's finding for color discrimination ellipses. The magnitude of the intraobserver variability was similar for all field sizes, except for 2° field size, where matching errors were larger for some primary sets.     

Spectral power distributions for the CIE stimuli

The CIE reference colour stimuli, X, Y, and Z, were derived by constructing a triangle outside the R,G,B triangle and outside the area bounded by the spectrum locus and the purple line. By this means, all colours, including monochromatic ones, have positive tristimulus values. The colour‐matching functions are the relative quantities of these stimuli required to be mixed additively to match the equal energy monochromatic colours. The stimuli are not realizable as light sources, and the CIE has not specified their spectral power distributions. There is an infinite number of spectral power distributions whose properties meet the prerequisites for X (X = 100, Y = 0, Z = 0), Y (0, 100, 0), and Z (0, 0, 100), and two possible sets have been calculated by different methods. These curves could be used as primary red, green, and blue lights in additive mixing to produce synthetic reflectance curves, which are useful in the specification of on‐screen colours, and as a means of producing colour constant standards. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 478–482, 2001     

Colour appearance of room colours

Psychophysical experiments were conducted to investigate the colour appearance changes between small colour patches and real room colours. The results clearly showed that colours appear lighter and more colourful for room colours. A method based on CIECAM02 was developed to quantify the colour size effect. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Michel‐Eugène Chevreul: From laws and principles to the production of colour plates

Michel‐Eugène Chevreul (1786–1889) did major scientific work in the fields of chemistry and colour and pioneered the study of simultaneous contrast. His book De la loi du contraste simultané des couleurs (The Principles of Harmony and Contrast of Colours) was published in 1839. Here, his studies pertained to simultaneous contrast, when two or more colours seen contiguously are influenced in brightness and/or in hue, and on successive contrast, when afterimages modify colour perception. He also investigated the mixed contrast that appeared in tapestries in which a mixture of colours was obtained by the plying of yarn or by hatching. Later, he reported on the influence exerted on vision by coloured objects in circular motion around an axis perpendicular to their plane (1879). Many examples and numerous experimental checks documented in his books supported his demonstration of contrast. Of particular interest are the colour plates attached to the books. Another significant work by Chevreul was a three‐dimensional colour classification system (1864), after which he manufactured a colour atlas showing colour circles and monochrome lightness scales. Data are presented from recent measurements of Chevreul's atlas circles and plates, and there is a discussion of his choice of complementary colours. © 2002 John Wiley & Sons, Inc. Col Res Appl, 27, 4–14, 2002     

Colour preference for Taiwanese floral pattern fabrics

A psychophysical experiment was carried out to investigate factors affecting colour preference for Taiwanese floral pattern fabrics, as a case study of object colour preference. A total of 175 test images of Taiwanese fabrics were used as the stimuli presented on a calibrated computer display. The images were generated on the basis of 5 existing Taiwanese fabrics, each manipulated into 35 images by changing the fabric colour. The 35 colours were selected to cover the most frequently used colours for existing Taiwanese fabrics. The 175 test images were assessed by 76 Taiwanese observers in terms of 9 semantic scales, including Taiwanese style/non‐Taiwanese style, Japanese style/non‐Japanese style, splendid/plain, traditional/modern, active/passive, warm/cool, heavy/light, like/dislike and harmonious/disharmonious. The experimental results reveal two underlying factors: “Splendidness” and “Harmony.” The like/dislike response was found to highly correlate with harmonious/disharmonious, but have poor correlation with Taiwanese style/non‐Taiwanese style. The study also reveals several factors affecting colour preference for Taiwanese fabrics, including the interaction effect of colour and pattern, observer's general liking for the object, and the effect of user experience. These findings can help develop a more robust, comprehensive theory of object colour preference. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 43–55, 2016     

The UNL trichromatic colorimeter

The UNL trichromatic colorimeter was designed to perform color‐matching experiments under a range of stimulus conditions. The colorimeter can be set up with a conventional 10° structure‐free bipartite viewing field (either horizontally or vertically bisected) but can also be configured for field sizes as large as 102° (wide) × 50° (high), and depth cues can be introduced into the viewing field. This article documents the construction and performance of the apparatus, including the structural components, light sources, optics, filters, and instrumentation. Maxwell method CMFs measured at a homogeneous 10° horizontally bisected field are reported with results that compare favorably with CMFs reported by Thornton under similar stimulus conditions. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 209–220, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20109     

Large‐field color matching functions

Color‐matching functions (CMFs) were derived with the Maxwell method for 10 subjects using two field conditions: (1) horizontally bisected circular 10° and (2) vertically bisected rectangular 102° (wide) × 50° (high). The primary set was composed of 453–533–601 nm components with a mean full‐width at half maximum of 18.3 nm; the reference field was illuminated with daylight fluorescent lamplight. Field size had a significant effect on the shape of the resulting CMFs. Under the large‐field conditions subjects were less sensitive to shorter wavelengths as characterized with the b? function and had higher sensitivities to the longer wavelengths as characterized with the r? function. © 2005 Wiley Periodicals, Inc. Col Res Appl, 31, 18–29, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20170     

Effect of observer metamerism on colour matching of display and surface colours

We studied the individual variability of asymmetric metameric colour matching between computer displays and object colour stimuli in conditions typical for the surface colour industries. Using two different computational techniques, we assessed the contribution of observer metamerism to this variability. In the studied conditions of spatially separated computer display and surface colour stimuli, this contribution was found to be insignificant for all colours but neutrals. In the chromaticness plane, the range of matches made by different observers practically coincides with the range of matches made by an individual observer. Consequently, we conclude that in the task of matching spatially separated display and surface colours, the range of matches made by a group of observers cannot be determined from variations in their colour‐matching functions, and thus the paradigm of the Standard Deviate Observer is shown to be inapplicable to the studied conditions. We suggest that individual variability in these conditions is governed by mechanisms of chromatic discrimination, and can be modeled by advanced colour difference formulae with suitably adjusted parametric coefficients. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 346–359, 2008     

Why higher resolution graphics cards are needed in colour vision research

The colour resolution of a 14‐bit and an 8‐bit per channel graphics card were evaluated and compared with the just noticeable difference between colours (varying only in luminance) for: (1) a standard observer (based on the CIE 1976 L*u*v* colour space) and (2) real observers in a colour discrimination task. The results of this study show that an 8‐bit per channel graphics card seems adequate for colour discrimination experiments where stimuli only vary in luminance. However, considering that the resolution of the graphics card should be equal to the Nyquist rate, an 8‐bit per channel card turns out to be inadequate. For colour discrimination experiments where stimuli only vary in chromaticity, there is an undersampling of the colour space with respect to MacAdam ellipses when using 8‐bit per channel graphics cards. The extremely fine colour resolution of a 14‐bit per channel graphics card overcomes these problems. Its use allows more accurate measurements of achromatic and chromatic discrimination thresholds and avoids experimental (spatial or luminance) artefacts, such as bandings that can occur on achromatic or chromatic gradients. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

A general metric for the magnitude of observer metamerism

Observer metamerism is defined as a property of a pair of spectrally different stimuli having the same colour sensation for an individual (reference) observer. Frequently, samples in this pair no longer match if the observer is changed. In this article, a linear approximation formula is developed that predicts a metameric effect caused by small changes in the observer's colour‐matching functions. This approximation formula enables a general metric of observer metamerism, the observer metamerism potential, to be defined that is independent of any particular deviated observer but still provides a close link to ‘observer‐metameric’ colour difference. Numerical experiments were conducted to investigate the correlation between the observer metamerism potential and the maximum of 53 metameric colour differences caused by the change from the colour‐matching functions of CIE standard 10° observer to the colour‐matching functions of 49 Stiles and Burch's real 10° test observers. The proposed general metric, together with a previous metric proposed by the present authors, the illuminant metamerism potential, could be taken as a quantitative measure of the performance of spectral approximation methods.     

Colour in folklore and tradition—The principles

Human beings use colour to manipulate their personal appearance and environment. A large part of this usage falls within the area of oral tradition and ritual that have been handed down within families, tribes or geographical areas. The resulting images are part of our culture; they are activities that give us feelings of belonging and of doing the ‘right thing’. Two surveys were designed to learn more of these very human activities. The first centered on Britain and Ireland; the other was international. Three major driving forces were found for the use of colour in folklore and symbolism—economic, historical and social. The Principle of Adaptation of Physical Resources accounts for the choice of mourning colours of most countries. Colour usage in death echoes the three approaches to mourning of sadness, joy (for the life of the dead), and fear of the spirits of the dead. The Principle of Adaptation of Ideas accounts for regional variations in colour folklore. This embodies a Darwinian‐type principle of behavior, that is, “to survive within a community a belief must have relevance to that community.” A major principle of folk medicine involving colour is the Principle of curing like with like. There are four Principles of Colour Selection in folklore—by the contrast displayed, as a transfer from the perceived or actual usefulness of the colour, by association, and by availability. Green above all colours has especial significance both in the UK and Ireland. In everyday language it is the Principle of Singularity that controls use of colour words as symbols. The biological mechanism permitting these many and contrasting uses of colour depends on the fact that colour is a perception, not the property of an object. That is, a colour can ‘mean’ whatever we wish it to ‘mean’. © 2003 Wiley Periodicals, Inc. Col Res Appl, 29, 57–66, 2004; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/col.10212     

Ultra‐large color difference and small subtense

Color difference calculations are usually applied to match or tolerance of small differences between large (>2°) visual fields. In contrast, we examine here the application of ultra‐large color differences to enhance conspicuousness and discriminability of small (1° subtense or smaller) visual targets, e.g., in visual information displays. We show that CIEDE2000, and color difference metrics based on the OSA Uniform Color Space and CIECAM02 are superior to CIELAB and CIELUV. Considering gray scale only, we show that Whittle's JND metric of achromatic contrast is as good as L* for this purpose, while also modeling contrast polarity and “crispening.” Furthermore, using this JND metric, we replicate Highnote's finding that elongation of small targets affects their apparent contrast. We discuss the perceived fading of color differences when targets become smaller, and suggest practical methods to mitigate the adverse effect on color conspicuousness and discriminability. © 2009 Wiley Periodicals, Inc., Col Res Appl, 2010.     

Colour changes of heat‐treated woods of red‐bud maple,European hophornbeam and oak

Colour evolution and colour changes were analyzed from small specimens of three heat treated wood species using the CIE L*a*b* colour space. Upon heat exposure, the wood substance became darker of species; this was accompanied by a steady reduction in lightness. As treatment conditions (e.g., time and temperature) increase, various shades of yellow were favoured for the surface of red‐bud maple wood (Δb = 1.22–9.79). For European hophornbeam wood, increased times at elevated temperatures make a blue (?b) colour the better choice. The total colour difference (ΔE) of the surfaces of wood substrates appear to be well correlated with the treatment temperature and time. The FTIR spectra suggest that the level of modification was insufficient for removing the major cell wall constituents of the wood substrates. All heat‐treated samples showed much less stability against colour difference in outdoor conditions. For red‐bud maple, the greatest improvement was achieved for samples that were treated at 150°C for 2 h (ΔE = 3.12). However, heat‐treated oak wood hadmuch less stability of colour difference for treatment conditions of 150°C for 10 h. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010.     

Comparison of real colour gamuts using a new reflectance database

A large set of data, comprising the spectral reflectances of real surface colours, has been accumulated. The data comprise 16 groups with different materials and include 85,879 measured spectra. From these data, CIELAB colorimetric coordinates were calculated under CIE illuminant D50 and the CIE 1931 standard colorimetric (2°) observer. Several published colour gamuts including those developed by Pointer and ISO reference colour gamut [ISO Graphic Technology Standard 12640‐3:2007] were compared using the present data set. It was found that the Pointer gamut is smaller than the new real data in most of the colour regions. The results also showed that the ISO reference colour gamut is larger than the new real accumulated data in most regions. The present finding indicates that there is a need to derive a new colour gamut based on the newly accumulated data for common applications. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 442–451, 2014     

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     

Rod contribution to large-field color matching

The linear algebraic features of foveal colorimetry do not apply to 10° degree colorimetric fields. A light presented as a foveal 2° field stimulates the three classes of cone photoreceptors, and a light presented as a 10° field stimulates the cone and rod photoreceptors. While no more than three primary lights are required to match either of these lights, large-field color matches with three primaries do not obey Grassmann's laws of linearity because the relative contribution of the rod signal to a color match changes with retinal illuminance. A three-primary set of color-matching functions (CMFs) affected by rodintrusion, therefore, cannot serve as the basis for colorimetry. Stiles and Burch removed the effects of rod activity from their 10° color-matching data to create a set of CMFs that have the same linear algebraic features as foveal, 2° colorimetry. They did this by selecting the primaries appropriately, making the matches at high retinal illuminance levels, and removing the small residual effects with numerical techniques. the resulting CMFs formed the major portion of the CIE 1964 10° Standard Observer. These CMFs describe color matches at the level of the cone-photoreceptor and, therefore, can be generalized to predict color matches with any set of primaries, but they cannot account for the effects of rod activity in the matching sample. If two colorimetric fields differ in the amount of rod activity they produce, calculations with the 1964 Standard Observer may predict their metamerism inaccurately. This article summarizes Stiles and Burch's methods for removing the effect of rods, gives examples of the implications for colorimetry, and suggests procedures for preventing the adverse effects of rod activity in applied situations. It also shows that three recently published sets of 10° CMFs may be influenced by the effects of rod activity. © 1994 John Wiley & Sons. Inc.