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Measuring color matching differences between observers is an important means of investigating individual differences in human color vision. In this article, we introduce a new LED‐based visual trichromator with which we have estimated color matching functions and cone spectral sensitivities in a group of five normal observers. The trichromator has side‐by‐side semi‐circular matching fields that are illuminated by two spectrally tunable LED light sources, each comprised of 18 LEDs with center wavelengths ranging from 400 to 700 nm. We used Maxwell's method to derive a set color match. A fixed triplet of red‐green‐blue (RGB) primaries produced the white standard field of 120 cd/m2 in one field. The other field, the mixture field, was illuminated by one of 11 different triplets of lights with various center wavelengths. Observers adjusted the intensities of the triplets in the mixture field to match the white standard field. All matches were made for field diameters of 2° and 10° of visual angle to allow comparisons with colorimetric standards and were repeated five times. Calibrations and tests showed that the trichromator and the measurements were stable and repeatable. Grassmann's laws predict that at the 11 color matches the excitations in the three cone types should be the same. Consequently, we can use those matches and a model of how cone spectral sensitivities vary between individuals to estimate the three underlying corneal cone spectral sensitivities for each observer (and thus how they vary from the standard (or mean) observer). We find good agreement with the CIE 2006 standards, but our observers show small but consistent differences. [ABSTRACT FROM AUTHOR]

Image naturalness is a potent attribute to enhance image quality, and it is related to people's perception of memory colors. Many previous experiments aimed to locate the memory colors on different media. Their findings indicate that the memory colors obtained vary between color patches and images and between experimental techniques. However, there were no satisfying models with appropriate memory color centers to scale the image naturalness. This study generated an image database including three prototypical memory colors images (sky, grass, and skin) and their local processed images. First, visual naturalness and preference data were collected from a psychophysical experiment. Then, the distribution of naturalness followed by memory color positions was analyzed. Based on the distribution pattern, the ellipsoid models for each prototypical memory color were established. The results from the present memory color centers were compared with those from the other studies. Results show that the present color centers always give better prediction accuracy in image naturalness models. Finally, an image preference model was developed based on the image naturalness and colorfulness. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the perception of neutral white and chromatic adaptation on a display under ambient lighting conditions with different chromaticities and illuminance levels. The desktop display was arranged to simulate a mobile phone. The neutral white was the whitest point that excluded chromatic color. Only one original image was used and it comprised black text against a white background under CIE illuminant D65 and the CIE 1964 standard colorimetric observer. Forty‐two rendered images were made to cover a representative area of chromaticity space that might be considered white. Eleven ambient lighting conditions were applied with five values of correlated color temperature (3000, 4000, 5000, 6000, and 8000 K) each at two illuminance levels (500 and 1000 lx) plus a dark condition. A psychophysical experiment was conducted where observers were asked to judge each image in terms of "neutrality" under each ambient lighting condition. The results showed that there were significant differences between different ambient lighting conditions. All the available data including the present were used to develop an incomplete chromatic adaptation function with different scaling factors for the incomplete adaptation factor (D) in CAT02. The function suggests that the illuminance and chromaticity of the illuminant had a clear trend on chromatic adaptation. However, the degree of adaptation is affected by the viewing conditions in each experiment. [ABSTRACT FROM AUTHOR]

The study aims to propose an approach of white LED spectral optimization based on mesopic luminance and color gamut volume for dim lighting conditions. Three optimal white LED spectra with relatively higher mesopic luminance and color gamut volume, the highest mesopic luminance, and the largest gamut volume are recommended for reducing energy consumption and enhancing color perception and recognition of human eyes. The theoretical simulation shows that the spectra with higher correlated color temperatures (CCT) and S/P-ratio increase the mesopic luminance and also extend the range of color gamut with the decreasing of lighting level. An evaluation model is developed to faster predict mesopic luminance, color gamut volume, and S/P ratio for lighting applications. [ABSTRACT FROM AUTHOR]

Displays such as mobile phones are viewed under surround conditions that vary from dark night to bright sunlight. The overall goal of this study is to test the appropriateness of CIECAM02 for mobile displays, and modify it according to any insufficiency found. Firstly, the testing of CIECAM02 is described using the visual data from 2-inch display of three achromatic backgrounds (gray, black, and white), and three surround conditions (dark, dim, and average). Secondly, CIECAM02 was tested under four surround conditions (dark, dim, average, and bright), and three displays (2-, 4-, and 7-inch), with only the gray background used, to focus more on the surround conditions. Those twelve experimental phases were used to refine CIECAM02, considering the surround factors. The surround parameters ( c, F, and NC) were optimized, and Ncb was modified from the CIECAM02; the modified model is named MobileCAM-v1. Colourfulness prediction by MobileCAM-v1 has been improved, especially for a black background under average surround condition. A further refined version of CIECAM02, MobileCAM-v2, was developed, for mobile displays viewed under different surround conditions. A set of equations based on surrounding conditions was first derived, to be able to accurately define surround parameters. The MobileCAM-v2 model gave the largest improvement in brightness, followed by lightness, and with colourfulness the smallest. The improvement is significant for bright surround conditions, improving the performance of CIECAM02 in predicting the visual results. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 114-124, 2015 [ABSTRACT FROM AUTHOR]

A set of 10 color pairs was proposed and produced in 2002 to show the advantages of the CIEDE2000 color-difference formula with respect to CIELAB. These 10 color pairs illustrated each of the five corrections to CIELAB proposed by CIEDE2000. The 10 color pairs were visually assessed, under reference conditions close to those proposed by CIEDE2000, by two groups of 31 and 21 inexperienced observers, using two different gray scales. Average visual results in these experiments fitted CIEDE2000 predictions much better than CIELAB, as shown by a decrease of Standardized Residual Sum of Squares values of about 20 units. Current visual results showed only the improvement of CIEDE2000 upon CIELAB in predictions of perceived color differences, but they are not recommended for testing new advanced color-difference formulas. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 429-436, 2013. [ABSTRACT FROM AUTHOR]