Suprathreshold Color Differences Research Articles

Increasing magnitude of color differences amplifies category effects

Previous studies have identified differences in sensitivity characteristics between color discrimination and perception of suprathreshold color differences. However, it remains highly unclear how color difference sensitivity changes with increasing magnitudes of color difference along various color hues. This study aimed to quantify the sensitivity transition across various magnitudes of color differences and uncover the underlying mechanisms. Color discrimination sensitivities were measured using an adaptive staircase method for 32 isoluminant pedestal colors in the u'v' chromaticity diagram. For suprathreshold color differences, we employed the Maximum Likelihood Difference Scaling (MLDS) method to measure sensitivity to various color difference levels for the same 32 colors. Our findings confirmed the differences in sensitivity characteristics between discrimination and suprathreshold color difference perception. Furthermore, we observed increased sensitivities at many color category boundaries in suprathreshold color difference perception. By investigating the relation between the category effects and the color difference size levels through a model simulation, our findings suggest that the influence of color categories on the perception of color differences may become more pronounced as the magnitude of color differences increases.

Color durability of pigmented slurry surfacing after artificial aging tests simulating weathering and traffic

In the new vision of complete street, the use of colored pavements has been promoted in recent years to improve road user safety and to enhance the reorganization and aesthetic of the urban environment. But, besides several benefits these pavements undergo environmentally and traffic induced changes in appearance, faster than the traditional ones, a few months after installation. Thus, the laboratory-scale investigation analyzed the color durability of pigmented slurry seals, which were prepared using a clear synthetic emulsion and mineral pigments, subject to different artificial accelerated aging procedures. They simulated the exposition to sunlight at high temperature (QUV weathering tester), the aggression of chemical products (salt brine bath) used for winter maintenance operations and the dynamic actions of vehicle tires (loaded wheel tester). The analyses of color change measured with a spectrophotometer highlighted the extreme sensitivity of pigmented thin surfacing to physical and mechanical stresses. Specifically, the thermal and photo-oxidation of the binder film induced by the UV exposure at high temperature and its wear caused by the dynamic passage of rubber tire produced a large supra-threshold color difference on the samples’ surface. These results suggest how a correct mix-design, both in the materials choice and ingredients dosage, should be properly calibrated on the basis of the pavement end-use and of the prevailing climatic conditions to ensure color consistency throughout the pavement lifetime.

Using suprathreshold color-difference ellipsoids to estimate any perceptual color-difference

Relating instrumentally measured to visually perceived colour-differences is one of the challenges of advanced colorimetry. Lately, the use of color difference formulas is becoming more important in the computer vision field as it is a key tool in advancing towards perceptual image processing and understanding. In the last decades, the study of contours of equal color-differences around certain color centers has been of special interest. In particular, the contour of threshold level difference that determines the just noticeable differences (JND) has been deeply studied and, as a result, a set of 19 different ellipsoids of suprathreshold color-difference is available in the literature. In this paper we study whether this set of ellipsoids could be used to compute any color difference in any region of the color space. To do so, we develop a fuzzy multi-ellipsoid model using the ellipsoids information along with two different metrics. We see that the performance of the two metrics vary significantly for very small, small, medium and large color differences. Therefore, we also study how to adapt two metric parameters to optimize performance. The obtained results outperform the currently CIE-recommended color-difference formula CIEDE2000.

Contributions of luminance and S-cone signals to color discrimination and supra-threshold color difference in color-deficient observers

Contributions of luminance and S-cone signals to color discrimination and supra-threshold color difference in color-deficient observers

Dissociation of equilibrium points for color-discrimination and color-appearance mechanisms in incomplete chromatic adaptation.

We compared the color-discrimination thresholds and supra-threshold color differences (STCDs) obtained in complete chromatic adaptation (gray) and incomplete chromatic adaptation (red). The color-difference profiles were examined by evaluating the perceptual distances between various color pairs using maximum likelihood difference scaling. In the gray condition, the chromaticities corresponding with the smallest threshold and the largest color difference were almost identical. In contrast, in the red condition, they were dissociated. The peaks of the sensitivity functions derived from the color-discrimination thresholds and STCDs along the L-M axis were systematically different between the adaptation conditions. These results suggest that the color signals involved in color discrimination and STCD tasks are controlled by separate mechanisms with different characteristic properties.

Performance of select color-difference formulas in the blue region.

The main objective of this work was to test the performance of major formulas for assessment of small suprathreshold color differences in the blue region. The models examined include CIELAB color space based equations, including CIELAB, CIE94, CIEDE2000, CMC (l:c), BFD (l:c), and formulas based on more uniform color spaces, such as DIN99d, CAM02-SCD, CAM02-UCS, OSA-GP, and OSA-Eu in comparison against data obtained via visual assessments. For this purpose, a dataset around the CIE high-chroma blue color center, hereafter called NCSU-B2, was developed. The NCSU-B2 dataset comprised 65 textile substrates and a standard, with a mean ΔE(ab)* color difference of 2.72, ranging from 0.54-5.72. Samples were visually assessed by 26 subjects against the reference gray scale in three separate trials with at least 24 h between assessments. A total of 5070 assessments were obtained. The standardized residual sum of squares (STRESS) index was used to examine the performance of various formulas for this dataset, as well as a previously developed NCSU-B1 low-chroma blue dataset [Color Res. Appl. 36, 27, 2011], and blue centers from other established visual datasets. Results show that formulas based on more recent uniform color spaces provide better agreement with perceptual data compared with models based on CIELAB space.

Evaluation of small suprathreshold color differences under different background colors

A psychophysical experiment under constant stimuli is conducted on a CRT display to measure the visual suprathreshold color differences for five color centers recommended by CIE under the same five background colors. The performances of four CIELAB-based, three CIECAM02-based, and two OSA-UCS-based formulas are tested. Detailed analysis results indicate the existence of chromatic crispening effect. CIEDE2000 performs best for the gray center and gray background, whereas CAM02-LCD and CAM02-UCS have the best performance for non-neutral backgrounds. CAM02-LCD significantly outperforms all other formulas for all color centers under all background colors.

Analyzing small suprathreshold differences of LCD-generated colors

Small suprathreshold color differences around five CIE color centers were investigated on a typical liquid crystal display (LCD) with fluorescent backlight using the method of constant stimuli. The results were evaluated using probit analysis and compared with surface-color differences of the RIT-DuPont dataset. We focused especially on the relationship between T50 distances obtained from LCD and surface-color stimuli and on the influence of the display's narrowband primaries and its relatively low luminance level on interobserver uncertainty. The low luminance level of the LCD decreases the perceived color differences. However, considering the visual uncertainty of the experimental data, we could not reject the hypothesis that T50 distances from the RIT-DuPont and our experiment agree up to a constant scaling factor. In addition, we found significantly higher interobserver variability in the estimation of small color differences if the colors are viewed on an LCD. There are some indications that color-difference perception might be influenced by individual color-matching functions and, thus, by the spectral power distribution of the stimuli. We provide the experimental data, including all spectral stimuli shown to the observers, on our website.

Investigations of suprathreshold color-difference tolerances with different visual scales and different perceptual correlates using CRT colors

In order to investigate the performance of suprathreshold color-difference tolerances with different visual scales and different perceptual correlates, a psychophysical experiment was carried out by the method of constant stimuli using CRT colors. Five hue circles at three lightness (L*=30, 50, and 70) and chroma (C*ab=10, 20, and 30) levels were selected to ensure that the color-difference tolerances did not exceed the color gamut of the CRT display. Twelve color centers distributed evenly every 30 degrees along each hue circle were assessed by a panel of eight observers, and the corresponding color-difference tolerances were obtained. The hue circle with L*=50 and C*ab=20 was assessed with three different visual scales (DeltaV=3.06, 5.92, and 8.87 CIELAB units), which ranged from small to large visual scales, while the remaining hue circles were observed only with the small visual scale. The lightness tolerances had no significant correlation with the hue angles, while chroma and hue tolerances showed considerable hue angle dependences. The color-difference tolerances were linearly proportional to the visual scales but with different slopes. The lightness tolerances with different lightness levels but the same chroma showed the crispening effect to some extent, while the chroma and hue tolerances decreased with the increment of the lightness. For the color-difference tolerances with different chroma levels but the same lightness, there was no correlation between the lightness tolerances and the chroma levels, while the chroma and hue tolerances were nearly linearly proportional to the chroma levels.

基于阈上小色差的色差公式权重函数研究

基于阈上小色差的色差公式权重函数研究

Visual evaluation at scale of threshold to suprathreshold color difference

Visual evaluation experiments of color discrimination threshold and suprathreshold color-difference comparison were carried out using CRT colors based on the psychophysical methods of interleaved staircase and constant stimuli, respectively. A large set of experimental data was generated ranged from threshold to large suprathreshold color difference at the five CIE color centers. The visual data were analyzed in detail for every observer at each visual scale to show the effect of color-difference magnitude on the observer precision. The chromaticity ellipses from this study were compared with four previous published data, of CRT colors by Cui and Luo, and of surface colors by RIT-DuPont, Cheung and Rigg, and Guan and Luo, to report the reproducibility of this kind of experiment using CRT colors and the variations between CRT and surface data, respectively. The present threshold data were also compared against the different suprathreshold data to show the effect of color-difference scales. The visual results were further used to test the three advance color-difference formulae, CMC, CIE94, and CIEDE2000, together with the basic CIELAB equation. In their original forms or with optimized KL values, the CIEDE2000 outperformed others, followed by CMC, and with the CIELAB and CIE94 the poorest for predicting the combined dataset of all color centers in the present study. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 198–208, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20106

Correlation between visual and colorimetric scales ranging from threshold to large color difference

AbstractPsychophysical experiments of color discrimination threshold and suprathreshold color‐difference comparison were carried out with CRT‐generated stimuli using the interleaved staircase and constant stimuli methods, respectively. The experimental results ranged from small (including threshold) to large color difference at the five CIE color centers, which were satisfactorily described by chromaticity ellipses as equal color‐difference contours in the CIELAB space. The comparisons of visual and colorimetric scales in CIELAB unit and threshold unit indicated that the colorimetric magnitudes typically were linear with the visual ones, though with different proportions in individual directions or color centers. In addition, color difference was generally underestimated by the Euclidean distance in the CIELAB space, whereas colorimetric magnitude was perceptually underestimated for threshold unit, implying the present color system is not a really linear uniform space. Furthermore, visual data were used to test the CIELAB‐based color‐difference formulas. In their original forms CIEDE2000 performed a little better than CMC, followed by CIELAB, and with CIE94 showing the worst performance for the combined data set under the viewing condition in this study. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 349–359, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10081

Threshold color differences compared to supra-threshold color differences

Threshold color difference ellipses, as represented by the MacAdam ellipses have been compared to unit contours implicit in the CIE94 color difference formula, found to represent small supra-threshold color differences well, both in the CIE chromaticity diagram as well as the a*, b* diagram. The results indicate that the two types of contours are significantly different. While threshold differences are well described by incremental changes in cone sensitivity supra-threshold differences are well-described by increments in the opponent color parameters a* and b*. A comparison of the hue angles in the a*, b* diagram of the MacAdam ellipses and the CIE94 contours for the same 25 colors indicates no correlation (correlation coefficient −0.1). The conclusion is that threshold and supra-threshold color difference perception operates at different levels in the color vision system.

Threshold color differences compared to supra-threshold color differences

Threshold color differences compared to supra-threshold color differences