Changes In Color Appearance Research Articles

Zero-dimensional halide hybrid bulk glass exhibiting reversible photochromic ultralong phosphorescence

Dynamically responsive materials, capable of reversible changes in color appearance and/or photoemission upon external stimuli, have attracted substantial attention across various fields. This study presents an effective approach wherein switchable modulation of photochromism and ultralong phosphorescence can be achieved simultaneously in a zero-dimensional organic-inorganic halide hybrid glass doped with 4,4´-bipyridine. The facile fabrication of large-scale glasses is accomplished through a combined grinding-melting-quenching process. The persistent luminescence can be regulated through the photochromic switch induced by photo-generated radicals. Furthermore, the incorporation of the aggregation-induced chirality effect generates intriguing circularly polarized luminescence, with an optical dissymmetry factor (glum) reaching the order of 10–2. Exploiting the dynamic ultralong phosphorescence, this work further achieves promising applications, such as three-dimensional optical storage, rewritable photo-patterning, and multi-mode anti-counterfeiting with ease. Therefore, this study introduces a smart hybrid glass platform as a new photo-responsive switchable system, offering versatility for a wide array of photonic applications.

Utilising spectral lighting simulation technique for evaluating transmitted daylight through glazing: Exploring the non-visual effects and colour appearance

Modern humans spend more time indoors than their ancestors. In indoor environments, windows are the primary building elements that provide access to daylight and views. The advancement of the building industry has introduced new glazing and coating technologies for windows. Electrochromic glazing, in particular, has gained popularity in recent decades. These glazings’ tint varies with light exposure and electrical voltage, affecting the spectral power distribution of transmitted daylight. The growing knowledge of the impacts of light on sleep and health encourages an evaluation of the non-visual effects of daylight transmitted through glazing. Therefore, the aim of this paper is to investigate the non-visual effects of transmitted daylight through one clear and one smart glazing and evaluate the colour appearance variations. However, conventional visualisation tools are inadequate for this purpose, necessitating the use of alternative techniques that consider the spectral power distribution of light. To accomplish this, the Radiance-based Lark spectral lighting simulation tool was utilised. The non-visual effects were analysed by examining the responses of the five photoreceptors (Short-, Medium-, Long-wavelength cones, Rods, and ipRGCs) to light using the CIE spectral sensitivity functions. Additionally, the changes in colour appearance were assessed using six attributes: lightness, hue, chroma, vividness, depth, and clarity. The results demonstrate the effect of the studied glazing on non-visual light stimulation and colour appearance while presenting the challenges, applicability, and limitations of spectral simulation techniques. The proposed method yields promising results and can be a valuable tool for evaluating the effects of glazing on humans.

Relationship between color appearance evaluation and categorical color responses of small stimuli in central and near peripheral visual fields

AbstractThe appearance of color stimuli can be measured psychophysically using two major techniques: (1) elementary color naming and (2) categorical color naming. On the relation between the two naming techniques, a network model (published 20 years ago) autonomously labels colors without retrieving color names from a database and has the flexibility to adapt to individual differences or observing environments. However, this network model has not been recently applied in this context as few works have focused on two types of color naming experiments using the same observers and conditions, mainly because most studies focused either on continuous changes in color appearance or on categorical color perception and did not need to employ both techniques. In our previous study, new datasets of hue and saturation judgments with whiteness and blackness evaluations were obtained. The evaluation of these datasets included elementary color naming and categorical color naming using 11 basic color terms (BCTs) with 0.5°‐diameter stimuli presented at the center and 12 locations along the horizontal and vertical meridians in the visual field for three observers. The feasibility of applying the model to our new datasets in the center and near periphery has to be examined before utilizing the model for various applications. Gain factor values for each categorical color response (CCR) were individually optimized, and the same combination of gain factors were used for all locations for each observer. The results of the chi‐square goodness‐of‐fit test indicated that the response distribution estimated by the model (color names and “undefined”) was not significantly different from the experimental data obtained in 35 out of 39 conditions. The overall average of the correct estimation was 77%. The high estimation obtained from the same gain factor values is indicative of an invariant relationship between the two naming techniques, with up to 20° eccentricity. It also shows the model's plausibility in explaining individual differences among normal observers.

Photoinduced Aryl Transfer from Imidazolyl-Quinoline π-Conjugated Systems.

Aryl transfer between heteroatoms was photochemically available through radical initiation followed by a bimolecular reaction. However, such an excited-state reaction has rarely been reported through a photoinduced intramolecular pathway in the π-conjugated systems. Herein, we found, for the first time, a clean photoinduced intramolecular aryl shift for imidazolyl-quinoline derivatives 2NQ (imidazophenanthrene) and 4NQX (imidazophenanthroline), of which the photoproducts are thermally reversible. Upon light irradiation of the studied compounds in solution, an appreciable blue fluorescence along with a gradual change in color appearance was observed, the photoluminescence and photoconversion quantum yields of which were shown to be competitive in the same excited state. We were able to harness the photoconversion quantum yields of the NQ compounds with facile electronic modifications. These, in combination with time-resolved studies on the NQ compounds, gave an oxygen-insensitive aryl transfer rate within 1-100 ns. The anomalously slow intramolecular reaction rates were further proven to be associated with the ∼5.0 kcal/mol transition free energy. The photoproducts NQ_rs were isolated, identified by X-ray analyses, and also shown to demonstrate anti-Vavilov reverse reactions back to the NQ compounds in the higher-lying excited state. The discovery of photoinduced intramolecular aryl transfer paves a new pathway in the synthetic field, which may also be extended and far-reaching to solar-chemical storage under an appropriate design strategy.

Time-course analysis of change in display color-appearance based on ambient light change

This study investigates the time course of changes in display color appearance according to changes in ambient lighting. Psychophysical experiments were conducted to observe brightness under lighting transitions in illuminance and the perceived white point under lighting transitions in correlated color temperatures. The result shows that significant change in the color appearance occurs immediately after ambient lighting changes. In addition, the initial change in color appearance depends on the lighting transition characteristics. The continuous change in color appearance was observed when ambient lighting was changed to brighter or lower CCT. On the other hand, a significant abrupt change at the initial stage of adaptation was observed when ambient lighting was changed to darker or higher CCT.

Content Fidelity of Deep Learning Methods for Clipping and Over-exposure Correction

Exposure problems, due to standard camera sensor limitations, often lead to image quality degradations such as loss of details and change in color appearance. The quality degradations further hiders the performances of imaging and computer vision applications. Therefore, the reconstruction and enhancement of uderand over-exposed images is essential for various applications. Accordingly, an increasing number of conventional and deep learning reconstruction approaches have been introduced in recent years. Most conventional methods follow color imaging pipeline, which strongly emphasize on the reconstructed color and content accuracy. The deep learning (DL) approaches have conversely shown stronger capability on recovering lost details. However, the design of most DL architectures and objective functions don’t take color fidelity into consideration and, hence, the analysis of existing DL methods with respect to color and content fidelity will be pertinent. Accordingly, this work presents performance evaluation and results of recent DL based overexposure reconstruction solutions. For the evaluation, various datasets from related research domains were merged and two generative adversarial networks (GAN) based models were additionally adopted for tone mapping application scenario. Overall results show various limitations, mainly for severely over-exposed contents, and a promising potential for DL approaches, GAN, to reconstruct details and appearance.

Color appearance of small stimuli presented in central and near peripheral visual fields

AbstractThis study investigates the change in the color appearance of a small stimulus with a diameter of 0.5° presented at various locations along the vertical and horizontal meridians in the visual field. To determine the color appearance, the hue and saturation judgment method and the categorical color naming method were used. The results obtained using these two methods at 0° exhibit the same quality of color appearance as that of a stimulus with a diameter of about 2° reported in previous studies. A more rapid decrease in perceived saturation and hue shift toward yellow in reddish and greenish stimuli are indicated in the hue and saturation judgment, whereas early distinction of “red” and persistence of “yellow” and “blue” responses are observed in the categorical color naming method. Despite the evident change in color appearance for each stimulus, the relationship between the responses obtained by the two methods for all stimuli was approximately the same across the visual field examined here. The unique hue component needed to elicit the color name of “yellow,” “green,” or “blue” is nearly constant along the eccentricity. However, the hue component of “red” is significantly higher than that of the other primary colors, especially at 0°, which suggests the specificity of that color.

An investigation into the variability of skin colour measurements

AbstractThis study aimed to investigate the variability of skin colour measurements for two kinds of extensively used instruments, telespectroradiometers (TSR) and spectrophotometers. A Konica Minolta CM700d spectrophotometer and a PhotoResearch PR650 telespectroradiometer were used to measure the forehead and the cheekbone of 11 subjects. The variability was evaluated using different measurement parameters including measurement aperture size and pressure on the facial locations for the spectrophotometer, and measurement distance for the telespectroradiometer. The mean colour difference from the mean was used to define the short‐term repeatability; the CIELAB colour difference and colour appearance changes in each perceptual CIELAB attribute between each of two instrument settings were used to evaluate the inter‐instrument agreement. The results show that, for the TSR, different measurement distances have identical repeatability but the colour shifts were significant; for the spectrophotometer, the large aperture size of the target masks gave the most repeatable results and the aperture size had more influence on the colour shifts than the measurement pressure. In addition, to investigate the effect of ethnicity and body location on measurement variability, skin colours from additional 151 subjects were measured. The differences between the measurements for different body locations were, in general, larger than the instrument repeatability and the inter‐instrument agreement.

Object color naturalness and attractiveness with spectrally optimized illumination.

Previous analyses have shown that optimizing illuminants' spectral power distributions for object reflectance can yield energy savings in excess of 40% by reducing the light lost to absorption. Here, commercially available LEDs and real objects, instead of theoretical spectra and test sample colors, are investigated. Simulations show that energy savings of up to 15% are possible when illuminating common objects with mixtures of narrowband LEDs, compared to illumination by reference phosphor-coated white LEDs, without inducing changes in color appearance. Experiments show that higher energy savings are achievable without degrading object appearance. Object optical properties impact the success of this approach.

Quantifying the watercolor effect: from stimulus properties to neural models.

Visual illusions are perceptions that violate our expectations with respect to what we understand about the physical stimulus, for example, surfaces of identical spectral composition that appear to be of different colors. Such phenomena are thought to reveal mechanisms, biases, priors or strategies that the brain uses to interpret the visual environment. In natural viewing, we perceive all surfaces within a context of surrounding light and nearby objects, and this context affects their appearance. Change in color appearance due to the surrounding light is called color induction and can be of type contrast, when appearance of a test region shifts in chromaticity away from that of the surround and assimilation when the shift is toward that of the surround. Pinna et al. (Pinna, 1987; Pinna et al., 2001) demonstrated a long-range, color assimilation phenomenon called the Watercolor Effect (WCE) that provides an interesting example for studying such processes. The WCE occurs when a wavy, dark, chromatic contour delineating a figure is flanked on the inside by a lighter chromatic contour on a bright background. The lighter color spreads into the entire enclosed area so that the interior surface is perceived as filled in with a uniform color. Previous studies reported also a weak coloration effect exterior to the contour (Cao et al., 2011; Devinck et al., 2005). The WCE is distinguished from other assimilation illusions due by to its spatial extent; the phenomenon has been reported to be observed over distances of up to 45 deg (Pinna et al., 2001). Here, we review and discuss stimulus configurations, based on different procedures, that induce the WCE and their implications for a neural model of this phenomenon.

Modelling of chromatic contrast for retrieval of wallpaper images

AbstractColour remains one of the key factors in presenting an object and, consequently, has been widely applied in retrieval of images based on their visual contents. However, a colour appearance changes with the change of viewing surroundings, the phenomenon that has not been paid attention yet while performing colour‐based image retrieval. To comprehend this effect, in this article, a chromatic contrast model, CAMcc, is developed for the application of retrieval of colour intensive images, cementing the gap that most of existing colour models lack to fill by taking simultaneous colour contrast into account. Subsequently, the model is applied to the retrieval task on a collection of museum wallpapers of colour‐rich images. In comparison with current popular colour models including CIECAM02, HSI and RGB, with respect to both foreground and background colours, CAMcc appears to outperform the others with retrieved results being closer to query images. In addition, CAMcc focuses more on foreground colours, especially by maintaining the balance between both foreground and background colours, while the rest of existing models take on dominant colours that are perceived the most, usually background tones. Significantly, the contribution of the investigation lies in not only the improvement of the accuracy of colour‐based image retrieval but also the development of colour contrast model that warrants an important place in colour and computer vision theory, leading to deciphering the insight of this age‐old topic of chromatic contrast in colour science. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 361–373, 2015

Color shifts caused by perceived structure-from-motion

When a figure is segmented from a chromatic background using stereoscopic depth, only weak shifts in color appearance are found (Shevell & Miller, 1996). When, however, a figure is segmented from ground by percepts of transparent layers, shifts in color appearance are large (Wollschlager & Anderson, 2009). Color appearance, therefore, may depend critically on the specific perceptual attributes that segment an object from its chromatic background. This study shows that changes in color appearance due to chromatic adaptation depend on a cortical neural representation at the level of three-dimensional object perception. Shifts in the color appearance of an equilateral-triangle test (0.125 deg in area) were measured using a red/green hue cancellation technique following adaptation to a larger reddish background [L/(L+M) = 0.75, S/(L+M) = 0.2]. The test was perceptually segmented from the background using structure-from-motion so the overall percept was a separate triangular test field on a distinct background. The background was sprinkled with small dots (same chromaticity but slightly higher luminance) that were (i) stationary, (ii) randomly located on each successive frame, or (iii) presented so they were perceived to move coherently over time to create the percept of a 3D sphere. An important feature of the experimental design was that retinal adaptation within 1 deg of the test field was constant in all conditions. When the dot motion created the percept of a 3D sphere, the color shift induced by the background was reduced for three observers, compared to the stationary-dots condition. Randomly relocating dots on each frame also caused some reduction in the influence of the background, but significantly less reduction than when the dots gave the percept of a 3D sphere. In sum, central neural mechanisms of object perception significantly alter the color-appearance changes caused by a given chromatic adapting light. Meeting abstract presented at VSS 2013

Colour constancy across the life span: evidence for compensatory mechanisms.

It is well known that the peripheral visual system declines with age: the yellowing of the lens causes a selective reduction of short-wavelength light and sensitivity losses occur in the cone receptor mechanisms. At the same time, our subjective experience of colour does not change with age. The main purpose of this large-scale study (n = 185) covering a wide age range of colour-normal observers (18–75 years of age) was to assess the extent to which the human visual system is able to compensate for the changes in the optical media and at which level of processing this compensation is likely to occur. We report two main results: (1) Supra-threshold parafoveal colour perception remains largely unaffected by the age-related changes in the optical media (yellowing of the lens) whereas our ability to discriminate between small colour differences is compromised with an increase in age. (2) Significant changes in colour appearance are only found for unique green settings under daylight viewing condition which is consistent with the idea that the yellow-blue mechanism is most affected by an increase in age due to selective attenuation of short-wavelength light. The data on the invariance of hue perception, in conjunction with the age-related decline in chromatic sensitivity, provides evidence for compensatory mechanisms that enable colour-normal human observers a large degree of colour constancy across the life span. These compensatory mechanisms are likely to originate at cortical sites.

Colorimetric properties and stability of 3D prints

PurposeThe purpose of this paper is to evaluate and discuss colour properties, stability and lightfastness after accelerated exposure in xenon‐arc light apparatus, of 3D ink jet prints produced by using 3D colour printing process.Design/methodology/approach3D colour prints were produced using ZCorporation 3D printing method. The samples were divided into groups according to the finishing process applied (untreated, finished with different infiltrants). Colorimetric properties were measured using spectrophotometer. Samples were placed into xenon‐arc based weathering apparatus (Xenotest), using the preset glass filtered sunlight, standard indoor conditions. Colour stability was evaluated as change in colour after repeating the spectrophotometer measurements and comparing spectral and specific colorimetric values of initial and exposed samples.FindingsBased on methodology used, the analysis has shown the changes in colour appearance of differently finished 3D prints, which were mostly attributed to chroma and lightness variations. The colour stability of samples studied noticeably varied and is dependent on colour, percentage of ink coverage and finishing method. Issues of colour and stability of 3D ink jet prints could become important as 3D printing emerges into new application areas, in which the object properties will need to be maintained for a certain amount of time.Research limitations/implicationsThe research is comparative and is limited to the specific materials and procedures used.Originality/valueThe paper describes aspects of colour 3D printing for which the published research and literature data are still, for the most part, lacking. Colour measurements methodology and evaluation of stability described could be of value for further research and for users of the technology.

Investigation of colour size effect for colour appearance assessment

AbstractThree psychophysical experiments were conducted to investigate the colour appearance changes between different sizes under various media or viewing conditions. The results are highly consistent that when increase stimulus size, the colour will appear to be lighter and more colourful with little change in hue. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 201–209, 2011;

Color appearance and compensation in the near periphery

The spectral sensitivity of the visual system varies markedly between the fovea and surrounding periphery owing in part to the rapid fall in macular pigment density with eccentricity. We examined how colour appearance changes between the fovea and near periphery (88) by measuring achromatic loci and the loci of unique and binary hues. Chosen colours remained much more similar at the two locations than predicted by the change in spectral sensitivity. Compensation for white may reflect long-term gain changes within the cones that equate sensitivity for the local average stimulus in the fovea and periphery. However, adjusting only to the average stimulus cannot correct for all of the effects of a spectral sensitivity change, and predicts differences in colour percepts between the fovea and periphery that were not observed. The similarities in hue percepts at 0 and 88 thus suggest that additional processes help compensate colour appearance to maintain constancy in the near periphery. We model the results of previous studies to show that similar adjustments are implied by age-related changes in lens pigment, and to show that these adjustments are consistent with previous measurements of peripheral colour appearance based on hue cancellation.

Colour appearance and compensation in the near periphery

The spectral sensitivity of the visual system varies markedly between the fovea and surrounding periphery owing in part to the rapid fall in macular pigment density with eccentricity. We examined how colour appearance changes between the fovea and near periphery (8°) by measuring achromatic loci and the loci of unique and binary hues. Chosen colours remained much more similar at the two locations than predicted by the change in spectral sensitivity. Compensation for white may reflect long-term gain changes within the cones that equate sensitivity for the local average stimulus in the fovea and periphery. However, adjusting only to the average stimulus cannot correct for all of the effects of a spectral sensitivity change, and predicts differences in colour percepts between the fovea and periphery that were not observed. The similarities in hue percepts at 0 and 8° thus suggest that additional processes help compensate colour appearance to maintain constancy in the near periphery. We model the results of previous studies to show that similar adjustments are implied by age-related changes in lens pigment, and to show that these adjustments are consistent with previous measurements of peripheral colour appearance based on hue cancellation.

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

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

AbstractThis 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

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.