Chromatic Background Research Articles

Surrounding and background shades effect on color adjustment of single-shade composites.

This study evaluated the effects of surrounding and background shades on the color adjustment potential (CAP) and visual color match of two single-shade composites, Vittra APS Unique and Charisma Diamond One. Cylinder-shaped specimens were constructed, consisting of either single-shade composites alone (simple) or composites surrounded by the Forma material at shades A1 or A3 (dual). Simple specimens using only the Forma at the specified shades were also prepared. Color measurements of simple specimens were taken against a gray background using a spectrophotometer. For dual specimens, the color of the inner composite was measured against a gray or chromatic (the same shade as the outer composite) background. Color differences (ΔE00) between the single-shade composites and the A1/A3 composite were calculated. CAP was determined by comparing data from simple and dual specimens. Four experienced dentists scored the color match (perfect to unacceptable) for each specimen using a viewing booth illuminated by an illuminant D65. Data were analyzed with repeated-measures ANOVA and the Kruskal-Wallis test. The results showed that both single-shade composites showed the lowest color discrepancies when they were compared to A1 and A3. Using a chromatic background only significantly affected the CAP when the outer composite was A3. The visual analysis showed poor color matches between the single-shade and control chromatic composites, except for Charisma Diamond One surrounded by A1. In conclusion, the CAP values of the evaluated single-shade composites were impacted by both surrounding shade and background color, and the color match of these materials tended to be poor.

The role of interface distance and underlying substrate on the color adjustment potential of single-shade composites.

This study assessed how the distance from the composite interface and the underlying chromatic substrate affect the color adjustment potential (CAP) of two single-shade composites. Cylinder-shaped specimens were created using Vittra APS Unique (VU), Charisma Diamond One (DO), and a shaded (A3) composite. Some single-shade specimens were surrounded by the A3 composite, forming dual specimens. Color measurements of simple specimens were taken against a gray background using a spectrophotometer. All specimens were positioned at a 45° angle in a viewing booth under illuminant D65, and images were captured with a DSLR camera against gray or A3 backgrounds. Image colors were measured using image processing software and converted to CIELAB coordinates. Color differences (ΔE00 ) between the single-shade composites and the A3 composite were calculated. CAP was determined by comparing data from simple and dual specimens. No clinically significant differences were observed between color measurements obtained from images and the spectrophotometer. CAP was higher for DO compared to VU and increased as the distance from the composite interface decreased and when specimens were positioned against an A3 background. The color adjustment potential increased with decreased distance from the composite interface and against a chromatic background. Achieving satisfactory color match in restorations using single-shade composites is crucial, and selecting an appropriate underlying substrate is essential. The color adjustment gradually decreases from the restoration margins towards its center.

A five-primary Maxwellian-view display for independent control of melanopsin, rhodopsin, and three-cone opsins on a fine spatial scale.

Independent spatiotemporal control of the stimulation of the five photoreceptor classes requires a display with as many primary lights to probe their isolated spatial and temporal responses. No such system exists with suitable performance properties. We present a system to construct a five-primary display from commercially available three-primary digital light processing projectors. It optimizes the set of five primary lights required to maximize the achievable contrast of a single photoreceptor class in a silent substitution protocol, including where the background chromaticity is first specified. From these chosen five primaries, we describe a method to convert complex three-primary (RGB) images to five-primary representations with complete specification of the photoreceptor excitations at each pixel. Key to enabling this multiple display system with a single HDMI connection is a novel control protocol implemented in a deterministic field-programmable gate array controller that splits the data into five video streams to allow nearly synchronous presentation of primary image data through multiple displays. Each pixel is controlled over 9.5 bits for each primary over a single frame for measurement of threshold-level vision. In addition to a large contrast gamut, the Maxwellian view offers high retinal illumination to support the investigation of five opsin-based responses to complex spatiotemporal images with a truly silent substitution protocol, while avoiding the confounding effects of uncontrolled photoreceptor excitations as occurs in four-primary systems. The customizable primaries facilitate this display translation to species with different photoreceptor spectral responses, and the optics are designed for integration into microscopes for use as a stimulus generator in physiological experiments.

Chromatic discrimination in fixed saturation levels from trichromats and subjects with congenital color vision deficiency

Color vision tests use estimative of threshold color discrimination or number of correct responses to evaluate performance in chromatic discrimination tasks. Both approaches have advantages and disadvantages. In the present investigation, we compared the number of errors during color discrimination task in normal trichromats and participants with color vision deficiency (CVD) using pseudoisochromatic stimuli at fixed saturation levels. We recruited 28 normal trichromats and eight participants with CVD. Cambridge Color Test was used to categorize their color vision phenotype, and those with a phenotype suggestive of color vision deficiency had their L- and M-opsin genes genotyped. Pseudoisochromatic stimuli were shown with target chromaticity in 20 vectors radiating from the background chromaticity and saturation of 0.06, 0.04, 0.03, 0.02, 0.01, and 0.005 u’v' units. Each stimulus condition appeared in four trials. The number of errors for each stimulus condition was considered an indicator of the participant's performance. At high chromatic saturation, there were fewer errors from both phenotypes. The errors of the normal trichromats had no systematic variation for high saturated stimuli, but below 0.02 u’v' units, there was a discrete prevalence of tritan errors. For participants with CVD, the errors happened mainly in red-green chromatic vectors. A three-way ANOVA showed that all factors (color vision phenotype, stimulus saturation, and chromatic vector) had statistically significant effects on the number of errors and that stimulus saturation was the most important main effect. ROC analysis indicated that the performance of the fixed saturation levels to identify CVD was better between 0.02 and 0.06 u’v’ units reaching 100%, while saturation of 0.01 and 0.005 u’v’ units decreased the accuracy of the screening of the test. We concluded that the color discrimination task using high saturated stimuli separated normal trichromats and participants with red-green color vision deficiencies with high performance, which can be considered a promising method for new color vision tests based in frequency of errors.

Influence of Stimulus Size on Simultaneous Chromatic Induction.

Chromatic induction is a major contextual effect of color appearance. Patterned backgrounds are known to induce strong chromatic induction effects. However, it has not been clarified whether the spatial extent of the chromatic surrounding induces a chromatic contrast or assimilation effects. In this study, we examined the influence of the width of a center line and its flanking white contour on the color appearance when the line was surrounded by chromatic backgrounds. A strong color shift was observed when the center line was flanked by white contours with the L/M- and S-cone chromatic backgrounds. There was a difference between the optimal widths of the center line and the contour for the shift in color appearance for the L/M-cone chromaticity (0.9 and 1.1–1.7 min, respectively) and the S-cone chromaticity (8.2–17.5 and 0.9–2.5 min, respectively). The optimal width of the center line for the L/M-cone was finer than the resolution-limit width of the chromatic contrast sensitivity and coarser than that of the luminance contrast sensitivity. Thus, the color appearance of the center line could be obtained by integrating broad chromatic information and fine luminance details. Due to blurring and chromatic aberrations, the simulated artifact was large for the darker center line and S-cone background, thus suggesting that the artifact could explain the luminance dependency of the induction along the S-cone chromaticity. Moreover, the findings of this study reveal that the dominant factor of the color shift is neural instead of optical.

Modeling chromatic contrast sensitivity across different background colors and luminance

In this research we compare chromatic contrast sensitivity models for two separate datasets and for the pooled dataset. They were obtained from two studies employing a very similar experimental paradigm. The data represent threshold visibilities of chromatic Gabor patterns varying in spatial frequency, background chromaticity, direction of color modulation and luminance, at constant stimulus size. Using the extended data set, we reconfirm our previously reported finding that a model based on coloropponent contrast signals is an improvement over a cone contrast model. However, when linear background scaling in classic cone contrast is replaced by nonlinear background scaling, an improvement of almost similar size is obtained. The results of this study can be of interest for the development of vision models employing the processing of spatio-chromatic information.

Behavioural thresholds of blue tit colour vision and the effect of background chromatic complexity

Vision is a vital attribute to foraging, navigation, mate selection and social signalling in animals, which often have a very different colour perception in comparison to humans. For understanding how animal colour perception works, vision models provide the smallest colour difference that animals of a given species are assumed to detect. To determine the just-noticeable-difference, or JND, vision models use Weber fractions that set discrimination thresholds of a stimulus compared to its background. However, although vision models are widely used, they rely on assumptions of Weber fractions since the exact fractions are unknown for most species. Here, we test; i) which Weber fractions in long-, middle- and shortwave (i.e. L, M, S) colour channels best describe the blue tit (Cyanistes caeruleus) colour discrimination, ii) how changes in hue of saturated colours and iii) chromatic background noise impair search behaviour in blue tits. We show that the behaviourally verified Weber fractions on achromatic backgrounds were L: 0.05, M: 0.03 and S: 0.03, indicating a high colour sensitivity. In contrast, on saturated chromatic backgrounds, the correct Weber fractions were considerably higher for L: 0.20, M: 0.17 and S: 0.15, indicating a less detailed colour perception. Chromatic complexity of backgrounds affected the longwave channel, while middle- and shortwave channels were mostly unaffected. We caution that using a vision model whereby colour discrimination is determined in achromatic viewing conditions, as they often are, can lead to misleading interpretations of biological interactions in natural – colourful – environments.

Evaluation of shade correspondence between current monolithic CAD/CAM blocks and target shade tab by considering the influence of cement shade and restorative material thickness.

It was aimed to evaluate shade matching between novel CAD/CAM blocks and the A2 target shade tab by considering the influence of cement shade and restorative material thickness on the chromatic background. A total number of 120 rectangular-shaped specimens were subtracted from four different prefabricated CAD/CAM blocks [Vita Enamic (VE), Lava Ultimate (LU), GC Cerasmart (GC), and Vita Mark II (VMII)]. These specimens had thicknesses of 0.5mm and 1.0mm. Three different shades (A2, opaque, and translucent) of dual-polymerized resin cement were chosen. The dentin shade (A3.5) restorative composite foundation was incrementally fabricated in a silicon mold. For control group, the A2 shade tab of the Vitapan classical shade guide was used. Different restorative material-cement-foundation assemblies were generated with optic gel. Color readings were performed by using a clinical spectrophotometer, and CIEDE2000 (ΔE00) formula was used to assess color differences. Data were statistically analyzed (α = 0.05). With increasing thickness, color difference values decreased. Higher mean ΔE00 units were observed in all restorative material sub-groups for 0.5mm thickness. In TR shade, no statistically significant difference was detected among the mean ΔE00 values of 0.5mm-thick restorative materials. Color differences in groups 1.0mm-opaque-LU and 1.0mm-opaque-GC indicated perceptible but clinically acceptable values (0.8˂ΔE00 ≤ 1.8). The highest and lowest ΔE00 units were observed in the 0.5mm-A2-VE group (ΔE00 = 7.07) and 1mm-opaque-GC group (ΔE00 = 1.46), respectively. Luting cement shade, restorative material type, and thickness significantly influenced the resultant color of restoration. Opaque cement on dentin foundation exhibited lower color differences.

Delayed cone-opponent signals in the luminance pathway.

Cone signals in the luminance or achromatic pathway were investigated by measuring how the perceptual timing of M- or L-cone-detected flicker depended on temporal frequency and chromatic adaptation. Relative timings were measured, as a function of temporal frequency, by superimposing M- or L-cone-isolating flicker on "equichromatic" flicker (flicker of the same wavelength as the background) and asking observers to vary contrast and phase to cancel the perception of flicker. Measurements were made in four observers on up to 35 different backgrounds varying in wavelength and radiance. Observers showed substantial perceptual delays or advances of L- and M-cone flicker that varied systematically with cone class, background wavelength, and radiance. Delays were largest for M-cone-isolating flicker. Although complex, the results can be characterised by a surprisingly simple model in which the representations of L- and M-cone flicker are comprised not only of a fast copy of the flicker signal, but also of a slow copy that is delayed by roughly 30 ms and varies in strength and sign with both background wavelength and radiance. The delays, which are too large to be due to selective cone adaptation by the chromatic backgrounds, must arise postreceptorally. Clear evidence for the slow signals can also be found in physiological measurements of horizontal and magnocellular ganglion cells, thus placing the origin of the slow signals in the retina-most likely in an extended horizontal cell network. Luminance-equated stimuli chosen to isolate chromatic channels may inadvertently generate slow signals in the luminance channel.

Project 1640 Observations of Brown Dwarf GJ 758 B: Near-infrared Spectrum and Atmospheric Modeling

Abstract The nearby Sun-like star GJ 758 hosts a cold substellar companion, GJ 758 B, at a projected separation of ≲30 au, previously detected in high-contrast multi-band photometric observations. In order to better constrain the companion’s physical characteristics, we acquired the first low-resolution (R ∼ 50) near-infrared spectrum of it using the high-contrast hyperspectral imaging instrument Project 1640 on Palomar Observatory’s 5 m Hale telescope. We obtained simultaneous images in 32 wavelength channels covering the Y, J, and H bands (∼952–1770 nm), and used data processing techniques based on principal component analysis to efficiently subtract chromatic background speckle-noise. GJ 758 B was detected in four epochs during 2013 and 2014. Basic astrometric measurements confirm its apparent northwest trajectory relative to the primary star, with no clear signs of orbital curvature. Spectra of SpeX/IRTF observed T dwarfs were compared to the combined spectrum of GJ 758 B, with χ 2 minimization suggesting a best fit for spectral type T7.0 ± 1.0, but with a shallow minimum over T5–T8. Fitting of synthetic spectra from the BT-Settl13 model atmospheres gives an effective temperature T eff = 741 ± 25 K and surface gravity dex (cgs). Our derived best-fit spectral type and effective temperature from modeling of the low-resolution spectrum suggest a slightly earlier and hotter companion than previous findings from photometric data, but do not rule out current results, and confirm GJ 758 B as one of the coolest sub-stellar companions to a Sun-like star to date.

Rod influence on chromatic discrimination away from chromatic and achromatic backgrounds

Rod influence on chromatic discrimination away from chromatic and achromatic backgrounds

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

Unperceived patterned chromatic backgrounds induce large shifts in color appearance

Unperceived patterned chromatic backgrounds induce large shifts in color appearance

Proton negative feedback synapses through H2 to H3 horizontal cells via blue cones are much more suppressed than through H1 horizontal cells by HEPES and chromatic background light

Proton negative feedback synapses through H2 to H3 horizontal cells via blue cones are much more suppressed than through H1 horizontal cells by HEPES and chromatic background light

The Effect of Luting Agents and Ceramic Thickness on the Color Variation of Different Ceramics against a Chromatic Background

The aim of this study was to assess the influence of various ceramic thicknesses and luting agents on color variation in five ceramic systems. Fifteen disc-shaped ceramic specimens (11 mm diameter; shade A3) were fabricated with each of the six veneering ceramics tested, with 1, 1.5, or 2 mm thickness (n=5). Resin composite discs (Z-250, shade C4) were used as bases to simulate a chromatic background. The cementation of the veneers was carried out with an opaque resin-based cement (Enforce, shade C4), a resin-based cement (Enforce, shade A3), or without cement (C4, control group). Color differences (ΔE*) were determined using a colorimeter. Three-way ANOVA was used to analyze the data, followed by a Tukey post-hoc test (α=.05). The L*a*b* values of the ceramic systems were affected by both the luting agent and the ceramic thickness (P<.05). In general, there was no difference between the control group and the group using the resin-based cement. The use of an opaque luting agent resulted in an increase of the color coordinates a*, b*, L*, producing differences in ΔE* values for all ceramics tested, regardless of the thickness (P<.05). For the 2-mm thick veneers, higher values in the color parameters were obtained for all ceramics and were independent of the luting agent used. The association of 2-mm thickness with opaque cement presented the strongest masking ability of a dark colored background when compared to a non- opaque luting agent and the other thicknesses tested.

A luminous efficiency function, VD65* (λ), for daylight adaptation: A correction

We recently proposed a 2° photopic luminosity function, VD65*(λ) [J Vis 2005;5:948–968], which improves upon the original CIE 1924 V(λ) function and its modifications, while being consistent with a linear combination of the Stockman and Sharpe [Vis Res 2000;40:1711–1737] long- and middle-wavelength-sensitive cone fundamentals [L(λ) and M(λ), respectively]. Its derivation was based on 25-Hz heterochromatic flicker photometric (HFP) data obtained from 40 observers of known genotype on a 1000 troland white (D65) background. However, as a result of an analysis of new luminous efficiency data obtained on an series of chromatic backgrounds [J Vis 2008;8:1–26], we now recognize that the 25-Hz flickering targets, though near-flicker-threshold, altered the mean chromaticity of the adapting background. Consequently, we have revised the original analysis, taking into account the changes in mean adapting chromaticity with target wavelength. Our reanalysis of the individual and mean data shows that the VD65*(λ) function for a D65 background should be redefined as 1.89L(λ) + M(λ) in quantal terms and as 1.98L(λ) + M(λ) in energy terms. The change in the L-cone weighting factor represents a change in luminous efficiency across the spectrum of ∼0.04 log unit. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011

Effect of Colored Lights and Illuminance Levels on Subjective Contrast between Chromatic Patches and Achromatic Backgrounds

This study aimed to investigate the effect of colored lights and illuminance levels on subjective contrast between chromatic patches and their achromatic backgrounds. It also aimed to examine whether the color difference in CIECAM02 explains the subjective contrast under each lighting condition. We defined the subjective contrast as the subjective and comprehensive differences between a patch and its background. We carried out an experiment under the conditions of combinations of six types of colored lights and five illuminance levels, in which subjects selected the combination of an achromatic patch and its achromatic background that had the same visual difference between a chromatic patch and its achromatic background. The color difference of the selected achromatic combination was defined as the equivalent color difference. The relation between the equivalent color difference and the color difference in CIECAM02 under each lighting condition was clarified. Under white, red, green, or yellow light and illuminance levels of 30 lux or more, subjective contrast was explained by the color difference in CIECAM02.

有彩色背景上に表示された有彩色文章の可読性の定量化

We measured the visibility of several type of chromatic text presented on a chromatic background on a liquid crystal (LC) display and extended the visibility index function (VIF) as a function of character luminance, background luminance, and character size to explain the current experimental results with a higher degree of accuracy. In addition to character luminance, background luminance, and character size, we analyzed the effect of different chromatic text and background colors under several saturation and hue conditions. The results show that the original VIF cannot predict the experimental data well under small luminance difference and large character conditions. Finally, a method was developed that showed that our improved VIF can precisely estimate the actual visibility of chromatic text presented under various conditions on a chromatic background.

The dependence of luminous efficiency on chromatic adaptation

We investigated the dependence of luminous efficiency on background chromaticity by measuring 25-Hz heterochromatic flicker photometry (HFP) matches in six genotyped male observers on 21 different 1000-photopic-troland adapting fields: 14 spectral ones ranging from 430 to 670 nm and 7 bichromatic mixtures of 478 and 577 nm that varied in luminance ratio. Each function was analyzed in terms of the best-fitting linear combination of the long- (L) and middle- (M) wavelength sensitive cone fundamentals of A. Stockman and L. T. Sharpe (2000). Taking into account the adapting effects of both the backgrounds and the targets, we found that luminous efficiency between 603 and 535 nm could be predicted by a simple model in which the relative L- and M-cone weights are inversely proportional to the mean cone excitations produced in each cone type multiplied by a single factor, which was roughly independent of background wavelength (and may reflect relative L:M cone numerosity). On backgrounds shorter than 535 nm and longer than 603 nm, the M-cone contribution to luminous efficiency falls short of the proportionality prediction but most likely for different reasons in the two spectral regions.

Color Perception in Children with Autism

This study examined whether color perception is atypical in children with autism. In experiment 1, accuracy of color memory and search was compared for children with autism and typically developing children matched on age and non-verbal cognitive ability. Children with autism were significantly less accurate at color memory and search than controls. In experiment 2, chromatic discrimination and categorical perception of color were assessed using a target detection task. Children with autism were less accurate than controls at detecting chromatic targets when presented on chromatic backgrounds, although were equally as fast when target detection was accurate. The strength of categorical perception of color did not differ for the two groups. Implications for theories on perceptual development in autism are discussed.