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Metrics of color-difference formula improvement (i.e., standardized residual sum of squares and Pearson product moment correlation) are shown to convey the same information. Furthermore, each metric has two computational forms that assume different linear data models, specifically, with or without an ordinate intercept. It is essential to choose a computational form that matches the data model. We recommend explicitly declaring whether or not the data have been centered, i.e., by subtracting the mean value from each datum, to match the intercept-free data model. Statistical testing of the metrics assumes independent, normally distributed randomness of residuals from the data model, and homogeneous variance. Procedures consistent with these assumptions include robust statistical tests, homogenizing data transformations, and meta-analysis.

We studied skin color in participants before and after a 100‐m sprint using a Konica Minolta CM‐2600d spectrophotometer. Four body positions (forehead, cheek, neck, and inner forearm) were measured for the approximately 30 students (non‐professional runners) who participated in the experiment. Skin reflectance was measured three times at each position before running and again soon afterward. Analysis of the data showed that average measurement repeatability (mean color difference from the mean [MCDM]) was 0.5, 0.4, 0.3, and 0.2 CIELAB units for forehead, cheek, neck, and inner forearm, respectively. However, average skin color differences produced by running were 1.8, 2.2, 2.0, and 1.7 CIELAB units for forehead, cheek, neck, and inner forearm positions, respectively, which are considerably higher than repeatability before or after running. Furthermore, appearance variation was analyzed in the CIELAB space, and it was found that sprinting for 100 m considerably changes the values of the red‐green a* coordinate, while the lightness L* and yellow‐blue b* coordinates remain almost constant. More specifically, on average, a* decreases after running for the forehead, cheek, and neck positions, while the opposite is true for the inner forearm position. The findings in this article may be useful to test previous physical models, achieve more realistic images of human skin after sprinting, and contribute to work of CIE TC 1‐92 on skin spectra database.

Spectral and color characterizations reveal aspects of artworks which support the criteria for restoration and subsequent processes. Usually, the aim is to characterize the different compounds and ...

We will discuss some of main topics in two recent publications on color from the International Commission on Illumination (CIE): CIE 015:2018 and CIE 248:2022. Regarding CIE 015:2018, it is the 4th edition of the most important CIE general publication on colorimetry, generally known as ‘CIE publication 15’. Among main novelties in CIE 015:2018 with respect to its previous 2004 edition, we can mention the introduction of the next four topics: 1) Cone-fundamental-based colorimetric observers; 2) New CIE illuminants (indoor daylight illuminants, smoothed daylight illuminants, illuminant E, and white LED illuminants); 3) The CIE colour appearance model CIECAM02; 4) The CIE 2017 color fidelity index. As a consequence of the active research on color appearance during the past few years, CIE 248:2022 proposed the CIECAM16 color appearance model for related colors and CIE 1931 standard colorimetric observer. In general, color appearance models provide a viewing-condition-specific method for the transformation of the tristimulus values X, Y, Z, to or from perceptual attribute correlates. CIECAM16 replaces CIECAM02 and may be useful for color management systems and image industries. CIECAM16 is simpler and maintains the predictions of experimental visual data made by CIECAM02. Finally, we will discuss advances in two issues related to color included in the current CIE Research Strategy: 1) A roadmap toward a new CIE colorimetry based on cone fundamentals, currently studied by CIE Technical Committee 1-98; 2) Color differences in tri-dimensional object colors and spatio-chromatic complexity, currently studied by CIE Technical Committees 8-17 and 8-14, respectively. In overall, we can conclude that color science is an active inter- and multi-disciplinary research field where optics continues playing a key role.

The aim of this study was to quantify orange-peel texture with an instrumentally based single-number index highly correlated with equivalent visual assessments. We prepared 3 achromatic (black, grey, and white) and 4 chromatic (red, green, blue, and yellow) scales, each with 8 different levels of orange-peel texture. Each scale had a sample with a minimum degree of orange peel, which was considered to be the standard sample. The visual differences between the standard sample and the remaining ones with progressively increasing degrees of orange peel in each scale were assessed by a panel of 28 observers using a prepared one dimensional lightness scale based on CIELAB. The usual parameters for surface texture provided by the BYK instrument were measured for each of the 56 paint samples and used to develop different models under the assumption of the additivity principle. The coefficients of these models and their performance with respect to visually assessed equivalent differences in orange peel were determined. Ridge regression was used to address multicollinearity between parameters. The validity of the models derived as well as other indices were further tested using the ACT (Advanced Coating Technologies) standard panels. ANOVA analyses indicate that chromatic samples have no adverse significant effects on the orange peel. Predictions of visual orange peel texture results by one of our models are considerably good [R2 = 0.98; STRESS (Standardized Residual Sum of Squares) = 6.3] and therefore, this index is recommended as an index of orange peel.

National Natural Science Foundation of China (61775170); Ministry of Science and Innovation (National Government of Spain) with support of the European Research Development Fund (European Union) (PID2019-107816GB-I00/SRA/10.13039/501100011033)., A psychophysical experiment using 3D printed samples was conducted to investigate the change of perceived color differences caused by two different illuminations and two 3D sample shapes. 150 pairs of 3D printed samples around five CIE color centers [Color Res. Appl. 20, 399–403, 1995], consisting of 75 pairs of spherical samples and 75 pairs of flat samples, with a wide range of color differences covering from small to large magnitude, were printed by an Mcor Iris paper-based 3D color printer. Each pair was assessed twice by a panel of 10 observers using a gray-scale psychophysical method in a spectral tunable LED viewing cabinet with two types of light sources: diffuse lighting with and without an additional overhead spotlight. The experimental results confirmed that the lighting conditions had more effect on the perceived color difference between complex 3D shapes than between 2D objects. The results for 3D and 2D objects were more similar under only diffuse lighting. Current 3D results had good correlations with previous ones [Color Res. Appl. 24, 356-368, 1999; J. Opt. Soc. Am. A 36, 789-799, 2019] using 2D samples with large color differences, meaning that color-difference magnitude had more effect on perceived color differences than sample shape and lighting. Considering ten modern color-difference formulas, the best predictions of the current experimental data were found for CAM02-LCD formula [Color Res. Appl. 31, 320-330, 2006]. For current results, it was also found that predictions of current color-difference formulas were below average inter-observer variability, and remarkable improvements were found by adding power corrections [Opt. Express 23, 597-610, 2015]., National Natural Science Foundation of China (NSFC) 61775170, Ministry of Science and Innovation (National Government of Spain), European Research Development Fund (European Union) PID2019-107816GB-I00/SRA/10.13039/501100011033

Los autores agradecen la colaboración al Ministerio de Ciencia e Innovación del Gobierno de España (PID2019-107816GB-I00 / AEI / 10.13039/501100011033), Se propone una aplicación novedosa de la fórmula SCTV (Spot Color Tone Value) proveniente de la industria de reproducción gráfica, para el control de la calidad del proceso de recubrimiento de tabletas farmacéuticas. Se analizan dos procedimientos: uno mediante la obtención de los espectros de reflectancia, de los cuales se pueden derivar los atributos cromáticos, y otro a partir de la obtención de las coordenadas de color de una imagen fotográfica calibrada. Nuestro objetivo es reducir la necesidad de intervención, extracción y destrucción de tabletas durante el control de calidad, además de facilitar el control y evaluación del proceso de forma remota, generando respuestas en tiempo real para la toma de decisiones., A novel application of the SCTV (Spot Color Tone Value) formula from the graphic reproduction industry is proposed for the quality control of the pharmaceutical tablet coating process. Two procedures are analyzed: one by obtaining reflectance spectra, from which the chromatic attributes can be derived, and the other from obtaining the color coordinates of a calibrated photographic image. Our goal is to reduce the intervention, extraction and destruction of tablets during quality control, as well as simplify the control and evaluation of the process remotely, generating real-time responses for taking decisions., Ministerio de Ciencia e Innovación del Gobierno de España PID2019-107816GB-I00 / AEI / 10.13039/501100011033

10 pags., 9 figs., 3 tabs., 1 app., The dependence of color differences on the illumination and viewing directions for two widely used gray scales for color change (SDCE and AATCC) was evaluated through measuring the spectral bidirectional reflectance distribution function (BRDF) by a gonio-spectrophotometer of metrological quality. Large incidence and viewing angles must be specially avoided using these gray scales because, in these conditions, color differences vary considerably from those established in ISO 105-A02 and ASTMD2616-12. While the visual appearance of the SDCE and AATCC gray scales for color change is similar, our results indicate that their goniochromatic properties are different. Finally, some recommendations regarding observation distance and illumination angle are given to correctly use these gray scales for visual experiments., European Metrology Research Programme (EMRP IND52); Ministerio de Economía y Competitividad (FIS2013-40661-P, FIS2016-80983-P); Comunidad de Madrid (S2013/MIT-2790).

Objective To evaluate color and whiteness changes of natural teeth under nine white LED illuminants recently proposed by CIE. Methods From spectral reflectance factors of 36 caries-free upper central incisors, corresponding colors under illuminant D65 and CIE 1931 standard colorimetric observer were computed for all tested illuminants, using the chromatic adaptation transform CAT16. Color differences (CIELAB and CIEDE2000 units) and whiteness ( W I D and W I O indices) from teeth illuminated by CIE standard illuminants (D65 and A) and white LED illuminants were calculated. The appearance of 630 pairs of teeth under all illuminants was also evaluated. Results Color gamuts from 36 teeth under tested illuminants showed similar volume and shape in CIELAB color space, but their centers of gravity changed in many different directions with respect to colors under D65 or A illuminants: Considering colors under D65/A, color shifts produced by white LED illuminants were in the ranges 2.0–8.6/1.1–7.0 CIELAB units (1.4–8.2/0.6–6.8 CIEDE2000 units). Average W I D and W I O values for the 36 teeth under different illuminants ranged from −5.8 to +19.3 and from −7.7 to +11.1, respectively. Considering 630 pairs of teeth, average color differences (mainly lightness differences) were below 0.5 CIELAB units (0.3 CIEDE2000 units), and average whiteness differences ranged from 8.1 to 10.7 for W I D (23.4–25.1 for W I O ). Significance Using CIE LED illuminants, most changes in color and whiteness for individual teeth were above typical threshold values of perceptibility and acceptability in dentistry. However, considering pairs of teeth, the average color and whiteness differences under all tested illuminants were very similar.

We performed spectrophotometric measurements of skin reflectance at four body locations (forehead, cheek, neck, and back of hand), before and after two weeks of sun exposure, for 103 first-year college students. Skin reflectance was measured twice at each body location, before and after two weeks of sun exposure, obtaining an average repeatability (mean color difference from the mean) in the range of 0.2-0.5 CIELAB units (D65 illuminant, CIE 1931 standard observer). However, the average skin color differences before and after two weeks of sun exposure were in the range of 3.6-3.9 CIELAB units, considerably higher than measured repeatability, as a consequence of suntanning. Skin color appearance variation was analyzed in the CIELAB color space, and it was found that at all body locations two weeks of sun exposure made lightness L

A range of phyllosilicate compositions have been detected spectroscopically on Mars, but the largest fraction by far corresponds to clay minerals rich in Fe and Mg. Given that most of our understanding of Martian clays comes from remote sensing data, it is critically important to explore the details of how compositional variation affects spectral features of phyllosilicates. The greatest efforts have focused so far on near-infrared (NIR) spectroscopy. Recently, ambiguities have been detected in the NIR spectra of 2:1 phyllosilicates with intermediate Fe Mg content that preclude mineral and chemical discrimination. Such ambiguities highlight the relevance of exploring the visible spectral range as a complementary tool to characterize Martian phyllosilicates precisely. This article reports the investigation of laboratory reflectance spectra (330–800 nm) from 34 Earth analogues of Martian phyllosilicates with a wide range of Mg Fe composition, including nontronite, celadonite and saponite end-members, as well as interstratified glauconite-nontronite, talc-nontronite, and talc-saponite. The spectra indicated the presence of Fe(III) by absorption modulations and a decrease in total reflectance, especially in samples with tetrahedral Fe(III). Absorption bands at 370 and 420 nm were diagnostic of octahedrically and tetrahedrally coordinated Fe(III), respectively. Band amplitudes in the second derivative of the Kubelka-Munk function correlated positively with Fe(III) content (R2 > 0.8). Standard color analyses of the visible reflectance spectra under the CIE illuminant D65 indicated that the CIELAB color parameter a*10 was positively correlated with tetrahedral Fe(III), b*10 was positively correlated with octahedral Fe(III), and L*10 was negatively correlated with Fe(III) in both structural sites. Because Fe(II) was in relatively low amount, it did not provide clear spectral evidence. Multiple regression models using the amplitude of the diagnostic absorption bands predicted well absolute Fe content in the phyllosilicates (R2 = 0.89) and the ratio Fe/(Fe + Mg + Al) (R2 = 0.84). CIELAB color parameters improved the prediction of total Fe (R2 = 0.92) and the ratio Fe/(Fe + Mg + Al) (R2 = 0.93). Application of these analyses to Martian data has challenges set by Fe oxide dust coating and spatial and spectral resolution. However, these results mark an avenue to develop testable tools using visible-wavelength spectral data from both satellite and lander probes to help establishing Fe content and mineral identification of Martian phyllosilicates.

The main aim of our current investigation is the colorimetric evaluation of protective treatments (consolidants) applied to traditional Islamic plasterworks, under natural ageing conditions. From a...

This paper addresses the way in which the random selection of different sets of samples influences the values of two colour-rendering indices analogous to the ones proposed by the International Commission on Illumination (CIE Publ. 13.3, 1995), Ra, and the Illuminating Engineering Society (IES Technical Memorandum TM-30-15, 2015), Rf. We report results found for 11 light sources, representative of current indoor and outdoor lighting, using a database with 12 123 spectral reflectance factors from real objects. For these 11 light sources, the differences between official Ra and Rf values and those computed using 100 iterations with 6000 random samples from our database proved to be in the range [−13, 2] and [−15, −1], respectively, the highest differences corresponding to sources with narrow peaks in their spectral power distributions. For 100 random subsets of 10 samples from our database, the average standard deviations of the 11 light sources for indices analogous to Ra and Rf were 8 and 5 (or 2 and 1 using 110 samples) respectively. The standard deviations in computed Ra and Rf values, using subsets with different numbers of samples n, can be modelled as inversely proportional to the square root of n. We propose a method to estimate these standard deviations for n = 6000 using reduced sets of 10 spectral reflectance factors.

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.

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.

Iron electronic transitions produce intense colors in minerals with moderate to high Fe content, which phenomenon allows using color and visible spectroscopy to identify and quantify Fe-bearing minerals. This approach is especially useful for Mars investigation due to the limited analytical instruments available at Mars. The challenges are: (1) overlap between Fe electronic absorption bands of Fe-bearing minerals, (2) band wavelengths are modified by chemical and structural variables, and (3) particle size effects can modify mineral color. The magnitude of these difficulties, however, depends on the mineral mixture investigated. In this study, we further probe the potential of visible-range data for investigation of Fe-minerals. The samples were mineral mixtures from the Riotinto area (SW Spain) that resulted from acidic alteration and contained Fe in oxy-hydroxides, hydroxysulfates and phyllosilicates. Samples were studied using visible/near-infrared spectroscopy, X-ray diffraction and thermogravimetry. The wavelength range 320–1000 nm was investigated using spectral second derivatives and CIELAB color parameters. Hematite was readily detected, below X-ray diffraction detection limits, from the band at 520–560 nm. Jarosite was readily identified by the combined presence of bands at ~390 and ~ 440 nm. Thermogravimetric and CIELAB color analyses indicated goethite as the most common Fe-rich mineral in the samples. Correlations between CIELAB color parameters were controlled by goethite, where jarosite-rich specimens aligned with the correlations but some samples containing hematite plotted outside them. Quantification of goethite was attempted as calibrated against thermogravimetric data. Calibration was not possible below ~10 wt% goethite. Above this value, results from spectral second derivatives allowed quantification up to the maximum goethite content of ~35 wt% (linear correlation with R2 = 0.89). Goethite quantification with CIELAB color parameters was hindered by hematite. In samples with very low or no hematite, goethite quantification was possible with parameters L*10 (R2 = 0.83) and hab,10 (R2 = 0.65), also up to ~35 wt% goethite. Consequently, if accurate calibration is possible and depending on mineral mixture components, spectroscopic and CIELAB color parameters should allow goethite quantification in a wide concentration range.

[EN] Results from different authors showed deviations of radial orientation in the a*-b* plane (tilt) for the major axes of chromaticity-discrimination ellipses centered around the International Commission on Illumination (CIE) red color center [Color Res. Appl. 3, 149 (1978)], which are not considered by most of the current advanced color-difference formulas (e.g., CIEDE2000). We performed a visual experiment using red printed samples in order to test the influence of the separation between samples (gap) on the mentioned tilt. Our results confirm a counterclockwise tilt of fitted a*-b* ellipses with a magnitude of approximately 36 degrees for samples with no separation, which is similar to that detected by other authors, and a reduction of the mentioned tilt owing to the separation of the samples. We detected a tilt of approximately 22 degrees for samples with a black gap of 0.5 mm and a tilt of approximately 25 degrees for samples with a white gap of 3 mm. Notably, the uncertainty of previous values given by the corresponding credibility intervals of 95% posterior probability is approximately +/- 8 degrees of the mean values. Finally, we study the performance of the most widely used color-difference formulas in the graphic arts sector using our current experimental results, and conclude that the performance of the CAM02-SCD and CAM02-UCS color-difference formulas is significantly better than that of the CIEDE2000 formula.

Using a categorical scale of 10 U, we have assessed color harmony in two-piece garments (jackets-trousers) considering a vicenarian and a quinquagenarian style. The experiment was performed by a panel of 59 Chinese observers (26 males and 33 females) with normal color vision and ages ranging 20–78 years, considering 300 color combinations for each of the two styles. For a given color combination, comparing results in the vicenarian/quinquagenarian styles for female/male observers, and observers below/above 45 years old, we found generally higher harmony scores for the vicenarian style, male observers, and observers older than 45 years. We found statistically significant differences (Welch two-sample t test, P

Currently the fixed-point iteration method with initial guess m0=0.5 is officially recommended by the CIE MES2 system [CIE 191:2010] in order to compute the adaptation coefficient m and the mesopic luminance L m e s . However, recently, Gao et al. [Opt. Express25, 18365 (2017)] and Shpak et al. [Lighting Res. Technol.49, 111 (2017)] have numerically found that the fixed-point iteration method could be not convergent for large values of S/P. Shpak et al. suspected that, to achieve convergence, the S/P ratio cannot be greater than 17. In this paper, a theoretical consideration for the CIE MES2 system is given. Namely, it is shown that the ratio S/P be smaller than a constant C2 (≈18.1834) is a sufficient condition for the convergence of the fixed-point iteration method. In addition, a new initial guess strategy, achieving faster convergence, is proposed.

We investigated observer metamerism under a variety of viewing conditions, in a set of color-matching experiments using displays and printed color samples under specific light sources. A selection was made of light sources with different illuminances, spectral power distributions, and correlated color temperatures, as well as displays with different sets of primaries. A panel of 157 observers with normal color vision and ages between 20 and 59 years old performed 5465 visual color matches around 9 different color centers. The results from the simulated and real experiments were quite different. Specifically, the mean color difference from the mean changed with experimental viewing conditions, ranging from 0.73 to 1.64 CIELAB units (average 0.99 CIELAB units) in simulated experiments, and from 3.12 to 4.03 CIELAB units (average 3.55 CIELAB units) in real experiments. In real experiments, observers’ variability reduced for light sources with high illuminance and high correlated color temperature. Spectral power distributions affected observer metamerism, but the role played by the primaries of the two displays employed was unclear., National Natural Science Foundation of China (NNSFC), 61675029. Ministry of Economy and Competitiveness of the Government of Spain, co-financed by the European Regional Development Fund (ERDF) of the European Union, research project FIS2016-80983-P.