Colour memory for various sky,skin, and plant colours: Effect of the image context

In memory‐matching techniques, the remembered colour might differ from the original colour even if the viewing situation is the same. Our aim was to point out whether these so‐called memory shifts are significant in the everyday situations of viewing photos depicting sky, skin, or plant, or viewing standalone uniform colour patches of sky, skin, or plant colours. In many cases, significant memory shifts have been found. Considering only one type of object (sky or skin or plant), memory shifts turned out to be systematic in the sense that they were directed toward specific intervals of hue, chroma, and lightness. This tendency was more explicit for photos than for standalone colour patches. A method to quantify prototypical colours and their tolerance bounds was suggested. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 278–289, 2001     

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     

The usability of the CIE colour‐matching functions in the case of CRT monitors

During the past years, several papers have been published that question the use of the CIE colour‐matching functions in the case of metameric samples. Visually matching samples produced on CRT (Cathode Ray Tube) monitors are metameric to most colour stimuli created by illuminating reflecting materials. As CRT monitors are often used in colour design applications, it seemed important to check how well CIE colorimetry will predict such colour matches. To investigate this problem, we set up an experiment in which painted samples were matched with samples produced on a CRT monitor. The colour of incandescent lamp irradiated Munsell samples were visually matched to the mixture of the RGB primaries of a CRT monitor. Both the reflected colour stimuli of the Munsell samples and the emitted stimuli of the monitor were measured spectroradiometrically. Our results imply that there is an observer‐dependent variability among the matches, but we could not find a major difference between the tristimulus data of the hard copy and soft copy presentations that would indicate errors in the CIE colour‐matching functions. The measurement accuracy, quantization errors of the monitor, and the achieved accuracy of the colour matches are treated in this study. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 436–441, 2001     

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     

Lightness and hue contrast effects in surface (fabric) colours

Simultaneous contrast effects on lightness and hue in surface colours were investigated. Test colours, surrounded by induction colours, were matched by colours surrounded by neutral gray. The matching colours were selected from a series of samples that varied in either lightness or hue respectively. The lightness experiments were carried out by a panel of 20 observers on 135 test/induction colour combinations. The hue experiments were conducted on 51 test/induction colour combinations by a panel of eight observers. The lightness of the test colour was found to decrease linearly with the lightness of the induction colour, regardless of the hue of the induction colour. The magnitude of the lightness contrast effect in fabric colours was found to be about one‐quarter of that found in CRT display colours in a previous study. The hue contrast effect found in this study followed the opponent‐colour theory. Two distinctly different regions could be identified when the hue difference was plotted against hue‐angle difference between the induction colour and the test colour. The slope of the line in the region where the hue of the induction colour is close to the test colour was much larger than the slope in the other region, indicating that the hue contrast effect was more obvious when the induction colour was close to the test colour. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 55–64, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20285     

Testing LED lighting for colour discrimination and colour rendering

Light‐emitting diode (LED) technology offers the possibility of obtaining white light, despite narrow‐band spectra. In order to characterize the colour discrimination efficiency of various LED clusters, we designed a classification test, composed of 32 caps equally distributed along the hue circle at about 3 ΔE* _ab‐unit intervals. Forty normal colour observers were screened under four different LED test light sources adjusted for best colour rendering, and under one control incandescent light of the same colour temperature. We used commercially available red, green, blue, and/or amber LED clusters. These yielded a poor colour rendering index (CRI). They also induced a significantly higher number of erroneous arrangements than did the control light. Errors are located around greenish‐blue and purplish‐red shades, parallel to the yellow‐axis direction, whereas when the distribution of light covers the full spectrum, the LED clusters achieve satisfactory colour discrimination efficiency. With respect to the lights we tested, the colour discrimination is correlated with the CIE CRIs as well as with a CRI based on our sample colours. We stress the fact that increasing the chroma of samples by lighting does not necessarily imply an improvement of colour discrimination. © 2008 Wiley Periodicals, Inc. Col Res Appl, 34, 8–17, 2009.     

Adaptation and colour matching of display and surface colours

In an asymmetric colour matching experiment, eleven observers adjusted computer displays to colour‐match surface samples in a viewing booth. We found systematic discrepancies between the observers' judgments and the predictions of the CIE 1964 Standard Colorimetric Observer. The features of the discrepancies are consistent with previous reports on adaptation in colour matching and on failures of colorimetric additivity, but have never been confirmed to be significant in practical colorimetry. We attribute the discrepancies to post‐receptoral adaptation mainly of the blue‐yellow chromatic channel, and report a framework of an adaptation transform based on the MacLeod‐Boynton chromaticity diagram which can compensate for them without abandoning traditional colorimetry and the use of tristimulus values. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 182–193, 2009     

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     

Color memory matching: Time effect and other factors

The methods of simultaneous and successive, or memory, color matching have been compared for 10 color reference samples distributed in two groups each performed by 50 observers (25 men and 25 women). Our results, obtained with a total of two hundred Munsell color chips arrayed on ten gray cardboard panels, indicate that: (a) while by simultaneous matching the mean color differences obtained are, in most cases, lower than 1 CIELAB unit, those obtained by memory are generally higher; (b) the worst remembered colors are yellow, light green, blue, and pink, and the best remembered color is orange; (c) the influence of the delay time (15 s, 15 min, and 24 h) is significant for the remembered mean color (p < 0.03); (d) we find significant men-women differences for the remembered mean color (p < 0.05). © 1998 John Wiley & Sons, Inc. Col Res Appl, 23, 234–247, 1998     

Color matching experiment for highlighting interobserver variability

Human color vision differs from person to person, not only when color deficiencies occur but also within color‐normal populations. Investigating individual variability in normal color vision is beneficial both for clinical purposes and for quantifying observer metamerism. Researchers have used color matches such as Rayleigh matches, Moreland matches, the D&H color rule, and various combinations of different media for such investigations. However, none of them were originally aimed at investigating the interobserver variability in color‐normal populations, but rather were aimed at screening for color‐deficiencies. The objective of this study was, therefore, to design and carry out a color matching experiment where observer variability appeared as large as possible to detect the interobserver differences in the color‐normal population. Color matching was simulated under different combinations of reference spectrum and matching primaries using ColorChecker patches, different display/projector primaries, and the Stiles and Burch 49 observers. The simulation results showed: (1) The choice of spectra for the matching primaries had a significant effect on observer variability, (2) observer variability was large for near‐neutral reference colors, and (3) observer variability in the lightness direction was small relative to chromatic variability. The color matching experiment highlighting interobserver variability was designed based on these three findings and carried out for 61 color‐normal observers. Typical interobserver variability was 9.2 mean color difference from the mean (MCDM) using CIEDE2000 (spanning about 40 CIELAB units), which was much larger than any previous experiment. The obtained color matching data are useful for derivation, validation, and analysis of color matching functions. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 530–539, 2016     

Evaluation of the crispening effect using CRT‐displayed colour samples

In this study, the crispening effect was clearly observed when 38 neutral‐coloured sample pairs with only lightness differences were assessed under 5 neutral backgrounds of different lightness values. The sample pairs are CRT‐based colours, and they are selected along the CIELAB L* axis from 0 to 100. The magnitude of colour difference of each pair is 5.0 CIELAB units. The visual assessment results showed that there is a very large crispening effect. The colour differences of the same pair assessed under different backgrounds could differ by a factor of up to 8 for a sample pair with low lightness. The perceived colour difference was enlarged when the lightness of a sample pair was similar to that of the background. The extent of crispening effect and its quantification are discussed in this investigation. The performances of five colour‐difference equations were also tested, including the newly developed CIEDE2000. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 374–380, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20045     

Colour matching experiments with RGB‐LEDs

CIE colorimetry breaks down when lights produced by narrow band RGB‐LEDs are matched with broad‐band lights. A colour matching experiment was set up and matches in a number of parts of the chromaticity diagram have been made, to determine the magnitude of the discrepancy. Differences between visual and instrumental matches increase as one moves in the chromaticity diagram from yellowish white lights toward greenish and bluish lights. CIE TC 1‐36 recently suggested newly defined cone fundamentals: Applying a transformation of these to a space similar to the CIE XYZ space enables a much better prediction of the matches to be made. The difference between the visual match and its instrumental prediction decreases by a factor of two or even more. The use of a cone fundamental based colorimetric system is recommended for LED colorimetry. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 108–112, 2008     

Color memory in children

The methods of simultaneous and memory color matching have been studied for a set of five Munsell color samples by 50 children, 25 boys and 25 girls (ranging in age from 9 to 11 years). By comparison between this group and one of 50 young adult observers, we can deduce the following: (a) In children, as in young adults, the mean CIELAB total color difference, ΔE*_ab, in simultaneous color matching is lower than the ΔE*_ab by memory color matching. (b) Children matched reference test worse than young adults for orange, bluish green (only boys and men) and yellow green (only girls and women). (c) While men remember, independently of age and delay time, violet reference test worse than women (P = 0.02), boys remember, independently of delay time, reference test worse than girls for orange (P = 0.026) and pink (P = 0.049). (d) In short‐term memory, boys remember the reference test better than girls for bluish green (P = 0.022); girls remember yellow green reference test worse than women (P = 0.034). (e) Chroma is the perceptual color attribute that best explains sex differences, although that depends upon the reference color test considered. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 372–380, 2008     

Colour and tolerance of preferred skin colours on digital photographic images

Skin‐tone has been an active research subject in photographic colour reproduction. There is a consistent conclusion that preferred skin colours are different from actual skin colours. However, preferred skin colours found from different studies are somewhat different. To have a solid understanding of skin colour preference of digital photographic images, psychophysical experiments were conducted to determine a preferred skin colour region and to study inter‐observer variation and tolerance of preferred skin colours. In the first experiment, a preferred skin colour region is searched on the entire skin colour region. A set of nine predetermined colour centers uniformly sampled within the skin colour ellipse in CIELAB a*b* diagram is used to morph skin colours of test images. Preferred skin colour centers are found through the experiment. In a second experiment, a twice denser sampling of nine skin colour centers around the preferred skin colour center determined in the first experiment are generated to repeat the experiment using a different set of test images and judged by a different panel of observers. The results from both experiments are compared and final preferred skin colour centers are obtained. Variations and hue and chroma tolerances of the observer skin colour preference are also analysed. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2013     

Color memory in elderly adults

The methods of simultaneous and successive color matching have been compared for a set of five Munsell color samples by 50 older adult observers, 25 men and 25 women (ranging in age from 64 to 80 years). From comparison between this population and one of 50 younger adult observers, 25 men and 25 women (in the 20–27 age range), we can deduce, in general, the following: (a) In the elderly adults the mean CIELAB total color difference (ΔE*_ab) in simultaneous color matching is lower than the ΔE*_ab by memory color matching. (b) While younger adults matched well the color of all the reference tests, the elderly adults matched poorly both greens and orange. (c) Younger adults remember the original color better than do the older adults (P = 0.007), depending on gender and delay time. (d) Although with simultaneous matching, the observer's gender does not determine significant differences, by memory, men matched the color of reference test more poorly than did women (P = 0.0), independently of age, color and delay time, especially for bluish green, violet, and pink. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 458–467, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20258     

A pattern matching method for large‐scale multipurpose process scheduling

This article proposes a novel pattern matching method for the large‐scale multipurpose process scheduling with variable or constant processing times. For the commonly used mathematical programming models, large‐scale scheduling with long‐time horizons implies a large number of binary variables and time sequence constraints, which makes the models intractable. Hence, decomposition and cyclic scheduling are often applied to such scheduling. In this work, a long‐time horizon of scheduling is divided into two phases. Phase one is duplicated from a pattern schedule constructed according to the principle that crucial units work continuously, in parallel and/or with full load as possible, exclusive of time‐consuming optimization. Phase two involves a small‐size subproblem that can be optimized easily by a heuristic method. The computational effort of the proposed method does not increase with the problem size. The pattern schedule can be not only used for production/profit maximization but also for makespan estimation and minimization. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

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     

Colour matching using LEDs as primaries

In our metameric experiment, the colour of a filtered incandescent lamp was matched with the additive mixture of three LEDs in a Lummer–Brodhun‐type visual photometer. Two sets of primaries were used, one had their dominant wavelengths at 467, 533, and 600 nm; the other set had dominant wavelengths at 478, 552, and 635 nm. These values correspond approximately to the characteristic wavelengths of the Prime and Non‐Prime Colour spectral regions defined by W. A. Thornton. 1 Both the light of the incandescent lamp and that of the LED clusters were seen monocularly in a centrally divided bipartite field at a visual angle of 2°. The luminance of the matching fields was in the order of 20 cd/m² to provide sufficient gamut for the LED mixture. Ten young observers with normal colour vision participated in the experiment. The emission spectra of the viewing fields were measured with an array‐type spectroradiometer, and two sets of colour‐matching functions were used to calculate the chromaticity of the matching stimuli: the CIE 1931 standard colorimetric observer and the Judd–Vos modification of the colour‐matching functions. We found that the Judd–Vos modification of the CIE 1931 standard observer represents more accurately the real observers in the evaluation of our results. No systematic differences between the use of the two sets of LEDs were detected in contradiction to Thornton's findings. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 360–364, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20044     

A computer‐assisted colour selection system based on aesthetic measure for colour harmony and fuzzy logic theory

An aesthetic measure based approach for constructing a colour design/selection system is proposed in this article. In this model, an image data base for the relationships between the psychological preference of customers and clothing colour tones is built using the membership functions of a fuzzy set, and an aesthetic measure calculation method based on colour harmony is also proposed. In addition, a skin colour detection theory is proposed to construct a skin colour detection program to detect the skin colour of a customer, which is then taken as the major colour in matching the skin, polo shirt, and(or) pant colours to select the best colour combination. Integrating the skin colour detection theory, colour harmony theory, aesthetic measure method, and fuzzy set theory, a program is constructed to build an aesthetic measure based colour design/selection system. With the aid of this system, one can get proper cloth colours to match his/her skin colour and image requirement by starting with inputting one's colour photo, catching image with a camera, or inputting R, G, B values of his/her skin. The theoretical results for the ranks of clothing colours proposed by the system are examined with the experimental results and the result shows they are very close, suggesting that the proposed colour selection system is acceptable. Although the selection of clothing colours is taken as an example to specify the methodology, it can also be used to develop a system for other products. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 411–423, 2008