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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]

A color rendition chart, the preferred memory color (PMC) chart, has been produced. It comprises 30 colored patches, divided into three groups: preferred memory colors, reference color‐gamut colors, and a gray scale. The main purpose of the new chart is to enable users to produce satisfactory preferred color reproduction using digital cameras, displays, and printing systems. The methods used to develop the various colors, and the color specification of each color are presented. Finally, several potential applications of the chart for the characterization of imaging devices, for the evaluation of image color quality, and for the calculation of color rendering indices for lighting are suggested. [ABSTRACT FROM AUTHOR]

With the rapid development of mobile imaging devices, there is a strong desire for accurate image reconstruction. However, the conventional colorimetry system is often related to environmental illuminations. Spectral reflectance is the fingerprint of color and is invariant with environmental illuminations. Therefore, the goal of the present study is to verify different algorithms to reconstruct the spectral reflectance from the camera red, green, and blue responses. In this research, the weighted local sample selection method was first combined with pseudo inverse matrix method (PI) and Wiener estimation method (WE) to investigate the optimal sample number on the model accuracy. The optimum local sample numbers of the two combination methods were established. The performance of five methods was evaluated, including PI, WE, smoothing constraint method, weighted pseudo inverse matrix method (WPI) and weighted Wiener estimation method (WWE) under lightings varying a wide range of correlated color temperature (CCT) from 3000 to 10 000 K. The best algorithm (WPI) in different lighting environments was established. The metamerism of different materials was revealed, the impact of materials on training and testing samples was reported. Finally, the methods' performance under different CCTs was revealed in terms of root mean square error and CIEDE2000, and the results from the theoretical simulation and real camera capturing were compared. [ABSTRACT FROM AUTHOR]

The paper describes a comprehensive test to evaluate the performance of current colour‐difference models using available experimental datasets. In total, 28 individual datasets were accumulated to test 17 colour‐difference formulae, 13 of them based on Uniform Colour Spaces (UCSs) in terms of the Standardized Residual Sum of Squares (STRESS) measure. The 28 datasets were divided into three groups: Large Colour‐Difference data (LCD), Small Colour‐Difference data for surface colours (SCDs), and Small Colour Difference data for display colours (SCDd). For each colour model, four versions were tested: the original model, and that including kL‐, Gamma‐ and kL/Gamma, which are the lightness parametric factor, the colour‐difference exponent factor, and the combination of both, respectively, optimized to fit particular dataset(s). The statistical F‐test was applied to test the difference between each pair of models. Furthermore, parametric effects between the large/small colour‐difference magnitudes, and between surface/display colours were investigated. The results showed that CAM16‐UCS significantly outperformed the other models for all groups. It accurately predicted all types of data and should be proposed for colour‐difference evaluation across all industries. [ABSTRACT FROM AUTHOR]

A psychophysical experiment was carried out to specify the preferred and natural memory colours corresponding to 24 familiar objects on mobile displays. These objects were selected to cover a large colour gamut in CIELAB space. One hundred and six observers from five different ethnic groups participated. Forty‐nine colours for each object were rendered three‐dimensionally to cover a large colour range. The results showed inter‐observer variations are small between different ethnic groups, about 1.4 and 1.3 CIEDE2000 colour difference units for naturalness and preference, respectively. Comparing the preference and the naturalness colour centres, the preferred colours are brighter and more colourful than naturalness colours, by 1 and 2 units in L* and C*ab attributes, respectively. Both sets of data show a great hue consistency. The results showed that different ethnic groups agreed well on the objects studied. It was found that the best‐agreed objects are strawberry, green apple, tomato, corn and purple grape, and the worst‐agreed objects are blueberry, broccoli, smurf, green pepper and blue sky. [ABSTRACT FROM AUTHOR]

A psychophysical experiment was carried out to investigate visual comfort when reading on three mobile displays at three luminance levels (100, 250 and 500 cd/m2) at five illuminance levels (0, 10, 100, 500 and 1000 lx). Sixty observers including 20 children, 20 young people and 20 elderly people evaluated visual comfort of 42 text‐background combinations using a six‐category point's method. Various effects of lightness contrast, lightness of background, display luminance, and ambient illuminance on visual comfort for the three age groups were revealed. Most interesting, visual comfort is strongly affected by lightness contrast and different ages. A second‐order polynomial regression model is developed to predict visual comfort based on the display settings and ambient illumination at different ages. It could be a valuable tool to design or evaluate display interfaces. [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]

Experience and experimental results show that the perceived colour appearance of an object varies with the size of that object or the viewing angle. Based on available visual size‐effect data, it is found that the size effect can be compensated in the CAT16 cone‐like space. Furthermore, it is found that, similar to the von Kries chromatic adaptation, size‐effect correction can be operated independently on the different cone channels. Hence, the size effect can be easily built into the CAM16 model to predict the colour appearance for stimuli of varying sizes. [ABSTRACT FROM AUTHOR]

This article describes the results of an experiment to evaluate people's impressions of a live landscape scene, the famous West Lake in Hangzhou, China. We invited seventy students from different academic backgrounds to participate in this project. The goals of this study were to find a method for the evaluation of the perception of a live scene, to reveal differences for subjects from different backgrounds, and to provide a method for teaching students. In the experiment, students sat together and looked at the lake from one similar location. The whole scene was divided into five parts, and the students were asked to give their judgment of those five different subjects. The results were analyzed to find the main components describing the scene. The novel features in the work involved the assessment of the scene using a large number of people, to have observers from various backgrounds, and to provide a new teaching method for colour science and colour design. [ABSTRACT FROM AUTHOR]

Abstract: Color‐appearance models, CIECAM02 and CAM16, usually include two one‐step chromatic adaptation transforms: a forward (one‐step) transform to convert data from a first illuminant to CIE illuminant E, plus a reverse (one‐step) transform to convert the results from CIE illuminant E to a second illuminant. In practice, however, one‐step chromatic adaptation models, that avoid the use of the intermediate CIE illuminant E, are also employed. Tests using the one‐step CAT16 model indicate failures of both the symmetry and transitivity properties, except in the case where the degree of adaptation D is equal to unity. The magnitude of these failures depends on the specific illuminants selected, and increases as the degree of adaptation decreases. From four possible two‐step CAT16 models, we have identified two that obey the symmetry and transitivity properties, one with slightly better predictions of the experimental corresponding‐color datasets available in the literature, and more consistent with the one‐step CAT16 model. The findings of this article confirm that, for incomplete adaptation, the use of the one‐step CAT is incorrect, and we propose that the use of a two‐step CAT16 model be mandatory for future applications. [ABSTRACT FROM AUTHOR]

Abstract: This 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. [ABSTRACT FROM AUTHOR]

This article focuses on human skin colour. Three different colour measuring instruments were used: a tele-spectroradiometer, a de:8° and a 45°:0° spectrophotometers. They were used to measure 47 subjects who were divided into four skin groups: Chinese, Caucasian, South-Asian, and Dark. Eight locations for each subject were measured. The spectral reflectance results were first compared. They all showed the 'W' shape between the 550 nm and 580 nm as found by the other studies. Those from the tele-spectroradiometer had an increase from 600 nm while the others were flatter. The colorimetric data calculated from the spectral measurements revealed similar patterns to describe the colour distribution of each skin group. It was found that two scales: whiteness-depth, and blackness-vividness could well describe these distributions. The results also showed systematic differences between the four ethnic groups, between eight body locations, between two genders, and between the measurements from the three instruments. [ABSTRACT FROM AUTHOR]

The CIECAM02 color-appearance model enjoys popularity in scientific research and industrial applications since it was recommended by the CIE in 2002. However, it has been found that computational failures can occur in certain cases such as during the image processing of cross-media color reproduction applications. Some proposals have been developed to repair the CIECAM02 model. However, all the proposals developed have the same structure as the original CIECAM02 model and solve the problems concerned at the expense of losing accuracy of predicted visual data compared with the original model. In this article, the structure of the CIECAM02 model is changed and the color and luminance adaptations to the illuminant are completed in the same space rather than in two different spaces, as in the original CIECAM02 model. It has been found that the new model (named CAM16) not only overcomes the previous problems, but also the performance in predicting the visual results is as good as if not better than that of the original CIECAM02 model. Furthermore the new CAM16 model is simpler than the original CIECAM02 model. In addition, if considering only chromatic adaptation, a new transformation, CAT16, is proposed to replace the previous CAT02 transformation. Finally, the new CAM16-UCS uniform color space is proposed to replace the previous CAM02-UCS space. A new complete solution for color-appearance prediction and color-difference evaluation can now be offered. [ABSTRACT FROM AUTHOR]

We have used 13 experimental datasets (7420 colour pairs) to study the performance of the weighting function for lightness proposed by the CIEDE2000 colour-difference formula, because it has been suggested that this function can be improved by using the weighting function for lightness SL = 1 adopted by the CIE94 colour-difference formula. Using the standardised residual sum of squares ( STRESS) index, it was found that: (i) replacing the SL in CIEDE2000 with SL = 1 improved the results for 7/13 datasets considered, but the improvement was statistically significant only for 1/13 datasets; (ii) a Whittle-type lightness-difference formula can be used to replace the term ∆ L*/ SL in CIEDE2000, which led to a new colour-difference formula with no statistically significant difference with respect to CIEDE2000 for any of the 13 experimental datasets. A modification of the CIEDE2000 formula using a Whittle-type lightness formula is proposed. [ABSTRACT FROM AUTHOR]

CIE has recommended two previous appearance models, CIECAM97s and CIECAM02. However, these models are unable to predict the appearance of a comprehensive range of colours. The purpose of this study is to describe a new, comprehensive colour appearance model, which can be used to predict the appearance of colours under various viewing conditions that include a range of stimulus sizes, levels of illumination that range from scotopic through to photopic, and related and unrelated stimuli. In addition, the model has a uniform colour space that provides a colour-difference formula in terms of colour appearance parameters. [ABSTRACT FROM AUTHOR]

This article addresses some general practices for the computation of CIE tristimulus values (TSVs), including different methods used for the interpolation, extrapolation, and truncation of data in the visible wavelength range. In each case, a quantitative analysis is presented on the basis of a dataset with 2365 spectral reflectances covering a wide color gamut, assuming six CIE illuminants and the two CIE standard colorimetric observers. For interpolation, it is found that among five tested methods, the (cubic) spline method is the best one when the spectral reflectance factors are uniformly sampled over the visible wavelength range. For extrapolation, it is found that the second-order extrapolation method gives better results than the use of nearest available data points or linear extrapolation methods. With respect to truncation, considering five different usual truncated ranges, it is found that the range from 360 to 780 nm provides more accurate results than the range from 380 to 780 nm currently recommended by CIE for nonfluorescent samples, and the use of the truncated range from 400 to 700 nm in place of the CIE-recommended range of 360 to 830 nm leads to TSVs with considerably high color differences of up to 0.9 CIELAB units. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 10-18, 2017 [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]

This paper aims to successfully reproduce a real lit environment as an image on a self-luminous computer display. The International Commission on Illumination-recommended color appearance model CIECAM02 was used as the core of the whole reproduction system. Two experiments were conducted: to verify the values of the surround parameters specified in CIECAM02 and to produce equal perceived brightness between the room and the computer display by adjusting the illuminance level of the lighting in the room to match that of the displayed image. [ABSTRACT FROM AUTHOR]

This paper aims to successfully reproduce a real lighting environment onto a display. The CIE recommended colour appearance model CIECAM02 was used as the core of the whole system. Two experiments were conducted: to verify the surround parameters in CIECAM02 and to establish the relationship between different illuminances between two viewing fields. [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]

Small displays are widely used; they are small enough to be carried around and are often viewed under extreme surround conditions. Under bright illumination, mobile display users experience 'veiling glare' caused by bright ambient lighting. A refined version of CIECAM02 called 'Refined CIECAM02 and original CIECAM02' were tested to predict visual results in terms of lightness (J), colourfulness (M), and brightness (Q) on a 2-inch sized display (2″) mobile phone under four surround conditions; dark (0 cd/m2), dim (5 cd/m2), average (1000 cd/m2), and bright (10,000 cd/m2). Other than the two versions of CIECAM02 using the original data, a correction to the models' predicted lightness J and a black correction to the original data were developed. Overall, the refined CIECAM02 plus the J correction performed the best for predicting the lightness, brightness and colourfulness under all the viewing conditions, especially for bright surround condition. Furthermore, another experiment was carried out using complex images to verify different versions of CIECAM02. The images were reproduced using JMh (lightness, colourfulness, and hue) spaces from the modified CIECAM02 versions. The experiment was conducted by comparing original images viewed under dim, average, or bright surround conditions and the predicted images were viewed under dark surround condition on two identical mobile displays. The different versions of the CIECAM02 showed similar results to each other for dim and average surround conditions but large differences when predicting the images under bright surround condition. The refined CIECAM02 with the J′ formula performed the best amongst all four CIECAM02 versions. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2013. [ABSTRACT FROM AUTHOR]

A method was explored to optimize the illumination spectrum for surgical lighting. The method simultaneously enhances the color contrast of biological tissue and the color rendering index (CRI) of the light source. Compared to conventional surgical lighting (i.e. based on halogen light sources), the optimized illumination has better color contrast and sufficiently high color rendering, i.e. both CIE Ra and R9 values are above 85. [ABSTRACT FROM AUTHOR]