Relationship between pupillary size,brightness, and photoreceptor responses for unrelated self-luminous stimuli at low photopic light levels

Research on the correlation between the initial pupillary light reflex, the perceptual brightness, and the excitations of the photoreceptors was performed for unrelated self-luminous 10° stimuli at low photopic light levels (5 to 80 cd/m²). All stimuli were optically characterized using a spectroradiometer. For determining the pupillary diameter, an Eye Tracker was used. The perceived brightness was evaluated with the magnitude estimation method. Test stimuli were presented alternating with a reference stimulus and the Michelson contrast of the pupillary diameter between test and reference conditions was calculated. Six observers (three female and three male) participated, with ages between 30 and 39 years (with an average of 34.5 years). It was found that the coefficient of determination between the pupillary response and the perceived stimulus brightness was higher than the corresponding value for luminance, allowing the suggestion that brightness has a greater effect on pupillary size than luminance. Nevertheless, this is not the complete story: highly saturated red and blue stimuli both induce a high brightness perception but the pupil contraction induced by the blue stimuli is much greater than for the red stimuli. Pupillary diameter was also studied as a function of the relative excitations of the five photoreceptors. The effect of rod and ipRGC excitations on pupillary size variation seems to be larger than that of the other photoreceptors. However, for the working conditions prevailing in this research, it could be expected that rods are not very active and that the ipRGC response might be the major driving mechanism.     

Modulation of visual attention assessed using the Stroop task during the menstrual cycle: Comparison between the menstrual and ovulation phases

Women might have changes in perception and cognition of colours according to hormonal changes during the menstrual cycle. Colours are often associated with specific emotional facial expressions, but how these two factors interact with each other and differ according to the cycle has remained unclear. We investigated attentional interference between colours and emotional facial expressions for women in the menstrual compared to the ovulation phases by colour judgment based on the Stroop tasks. Participants identified the colours (either red, yellow, or blue) of three types of face stimuli (happy, neutral, or sad) and corresponding scrambled face stimuli by pressing buttons, and we recorded participants' reaction times. The results showed better performance in the menstrual phase than in the ovulation phase. An interference effect was not observed. However, in the scrambled face stimuli task, only the reaction time for happy scrambled face shape and red did not differ between the phases. Thus, participants might pay stronger attention to faces with colours in the menstrual phase than in the ovulation phase but weaker attention to scrambled face shapes in the menstrual phase.     

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 shifts in two different‐sized viewing conditions

This study assessed the effect of size on colour appearance, using a colour matching paradigm where two sizes were presented in a setting similar to a normal colour selection interface. Twelve colours sampling the entire range of the colour spectrum were chosen as target stimuli. The target stimuli consisted of either a large (30° by 50°) or a small (0.5° by 0.5°) test field displayed on a cathode ray tube (CRT). In the experiment, a set of small colour samples consisting of the target and its neighboring colours was presented on the screen. Fifty‐seven participants were asked to pick a colour from the sample set that appeared to exactly match the target. Results in CIECAM02 showed a consistent increase in the apparent brightness (Q) but some decrease in saturation (s) for the larger field. Hue shifts were observed to form a systematic pattern. We noticed a discernable trend showing that, for targets of bluish or purplish colour hues, the accuracy of colour matching is lower and colour difference is greater in the condition of the large viewing field. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

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     

Asymmetric colour matching: Memory matching versus simultaneous matching

We have compared corresponding pairs obtained by simultaneous matching (haploscopic matching) and by memory matching (after 10 min) using 34 reference tests selected from the Munsell Atlas (glossy), belonging to the four main hues 5Y, 5G, 5PB, and 5RP. These colours lie very close to the F₁ and F₂ axes in the SVF space, where we have analyzed our results. Illuminants D65 and A were used as reference and matching illuminants, respectively. Our results show for both kinds of matching a tendency to select more colourful colours than the original ones, with significant differences between matching and test colours, whereas hue does not seem to follow a definite pattern. This behavior is similar to that found in colour‐matching experiments without illuminant changes. The analogy does not hold for lightness, which in the present experiment does not seem to follow a clear pattern. The best matching colours lie along the red‐green axis and the worst matching colours along the blue‐yellow axis. © 2001 John Wiley & Sons, Inc. Col Res Appl, 26, 458–468, 2001     

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.     

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;     

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.     

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     

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.     

Psychophysical models of consumer expectations and colour harmony in the context of juice packaging

The aim of this study was to develop psychophysical models that predict the influence of pack colours on consumers' psychological responses of fruit juices, such as visually perceived expectations of freshness, quality, liking, and colour harmony. Two existing colour harmony models derived from experiments involving only uniform colour plaques were tested using the juice packaging experimental data. Both models failed to predict the visual results obtained. Nevertheless, two parameters relevant to chromatic difference and hue difference were somewhat associated with the visual results. This suggested that, among all colour harmony principles for uniform colours, only the equal‐hue and the equal‐chroma principles can be adopted to describe colour harmony of packaging used for juice. This has the implication that the principles of colour harmony may vary according to the context in which the colours are used. A new colour harmony model was developed for juice packaging, and a predictive model of freshness was derived. Both models adopted CIELAB colour attributes of the package colour and the fruit image colour to predict viewers' responses. Expected liking and juice quality can be predicted using the colour harmony model while expected freshness can be predicted using the predictive model of freshness. © 2013 Wiley Periodicals, Inc. Col Res Appl, 40, 157–168, 2015     

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     

Tactile colour pictogram to improve artwork appreciation of people with visual impairments

A recent development in tactile technology enables an improvement in the appreciation of the visual arts for people with visual impairment (PVI). The tactile sense, in conjunction with, or a possibly as an alternative to, the auditory sense, would allow PVIs to approach artwork in a more self‐driven and engaging way that would be difficult to achieve with just an auditory stimulus. Tactile colour pictograms (TCPs), which are raised geometric patterns, are ideographic characters that are designed to enable PVIs to identify colours and interpret information by touch. In this article, three TCPs are introduced to code colours in the Munsell colour system. Each colour pattern consists of a basic cell size of 10 mm × 10 mm to represent the patterns consistently in terms of regular shape. Each TCP consists of basic geometric patterns that are combined to create primary, secondary, and tertiary colour pictograms of shapes indicating colour hue, intensity and lightness. Each TCP represents 29 colours including six hues; they were then further expanded to represent 53 colours. Two of them did not increase the cell size, the other increased the cell size 1.5 times for some colours, such as yellow‐orange, yellow, blue, and blue‐purple. Our proposed TCPs use a slightly larger cell size compared to most tactile patterns currently used to indicate colour, but code for more colours. With user experience and identification tests, conducted with 23 visually impaired adults, the effectiveness of the TCPs suggests that they were helpful for the participants.     

Unique hue data for colour appearance models. Part I: Loci of unique hues and hue uniformity

Psychophysical experiments were conducted to assess unique hues on a CRT display for a large sample of colour‐normal observers (n = 185). These data were then used to evaluate the most commonly used colour appearance model, CIECAM02, by transforming the CIEXYZ tristimulus values of the unique hues to the CIECAM02 colour appearance attributes, lightness, chroma and hue angle. We report two findings: (1) the hue angles derived from our unique hue data are inconsistent with the commonly used Natural Color System hues that are incorporated in the CIECAM02 model. We argue that our predicted unique hue angles (derived from our large dataset) provide a more reliable standard for colour management applications when the precise specification of these salient colours is important. (2) We test hue uniformity for CIECAM02 in all four unique hues and show significant disagreements for all hues, except for unique red which seems to be invariant under lightness changes. Our dataset is useful to improve the CIECAM02 model as it provides reliable data for benchmarking. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

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 equal to half that of its adapting surround. Five observers scaled each of the colours three times in each of two adaptation conditions corresponding to daylight and tungsten light at 120 cd/m². Loci of constant hue and saturation were derived in u', v' chromaticity space for daylight and tungsten light. These grids enable the appearance of a colour to be specified from a knowledge of its chromaticity coordinates and they enable such effects as colour constancy and colour fidelity to be investigated in terms of perceived colour appearance.     

Age-related changes in the color appearance of broadband surfaces

Chromatic and achromatic components of 15 broadband surfaces were scaled by 15 younger (mean age = 21.3 yrs) and 15 older (mean age = 71.9 yrs) subjects. Colored surfaces were obtained from the OSA Uniform Color Scales and presented as 2°-diameter test stimuli that were freely viewed. Stimuli were presented in a grey (L = 0) ganzfeld-like hemisphere with an illuminant having a correlated color temperature of 6200 K. Five stimuli were presented at three lightness levels (L = ?4, 0 and +4). Each lightness level included samples chosen so that one pair plotted approximately along a tritan axis in MacLeod-Boynton receptor-excitation space and another pair plotted on an axis of constant S-cone stimulation. The appearance of each test stimulus was scaled using the hue terms red, green, yellow and blue, and in terms of the proportion of overall chromatic content. The results indicate that hue names were used similarly for the two groups of subjects, however, older subjects perceived all stimuli as having less chromatic content than demonstrated by younger observers. Differences between the two age groups in perceived chromatic content of the test stimuli progressively increased as the lightness and luminance levels of the test stimuli decreased. Results obtained from control experiments suggest that this difference between the two age groups is not due to the influence of senile miosis or lenticular senescence leading to variations in the illuminances and spectral compositions of the test lights reaching the retina. © 1993 John Wiley & Sons, Inc.     

Determination of constant Hue Loci for a CRT gamut and their predictions using color appearance spaces

A colorimetrically characterized computer-controlled CRT display was used to determine 24 loci of constant perceived hue for pseudo-object related stimuli, sampling the display's interior color gamut at constant lightness and the edge of its gamut at variable lightness. Nine observers performed three replications generating matching data at 132 positions. the constant hue loci were used to evaluate the correlation between perceived hue and hue angle of CIELAB, CIELUV, Hunt, and Nayatani color appearance spaces. the CIELAB, CIELUV, and Hunt spaces exhibited large errors in the region of the blue CRT primary, while the Nayatani and CIELUV spaces produced large errors in the region of the red primary for constant lightness stimuli. Along the edge of the CRT's color gamut (variable lightness stimuli), all the spaces had a similar trend, large errors in the cyan region. the differences in performance between the four spaces were not statistically significant for the constant lightness stimuli. For the variable lightness stimuli, CIELAB and CIELUV had statistically superior performance in comparison with the Nayatani space and equal performance in comparison with the Hunt space. It was concluded that for imaging applications, a new color appearance space needs to be developed that will produce small hue error artifacts when used for gamut mapping along loci of constant hue angle. © 1995 John Wiley & Sons, Inc.     

Quantifying colour appearance. part III. Supplementary LUTCHI colour appearance data

The experimental data from this study supplements the LUTCHI Colour Appearance Data as described in Part I of this paper. Two further experiments were carried out: one was to check conflicting results found previously, and another was to extend the range of luminance conditions used earlier. In addition, a brightness attribute was added to the original lightness, colourfulness, and hue scales for colour assessment. Experiment I results verified the uncertainties found previously in the comparison between luminous and nonluminous colours, and between the grey background results with and without a white border. Experiment II results revealed the changes in four perceived attributes under six quite different adapting luminances. The results were then used to test five uniform colour spaces and colour-appearance models used in Part II of this paper. Hunt's 91 model gave more accurate predictions of the experimental visual results, in comparison with the other spaces and models. Its predictive error for all attributes studied is within the accuracy of the typical observer.