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The aim of this study is to measure color changes caused by two regenerative protocols over 3 months, and the effectiveness of internal bleaching. Twenty extracted human maxillary anterior teeth were used. The apex and canal were prepared to reproduce immature teeth. Teeth were divided: group 1: Triple-antibiotic-paste was applied for 3 weeks and then changed for blood until 3 months. Group 2: Blood was inoculated and sealed at cemento-enamel junction level with Biodentine for 3 months. Both groups were subjected to three sessions of internal bleaching. Color assessments were taken at baseline and at 2 and 3 weeks, 2 and 3 months, and 1, 2, and 3 weeks from the beginning the bleaching phase. Statistical significance was considered at P = .05. Both techniques produce color changes above the acceptability limit at 2 weeks. Chromatic variation caused by Triple-antibiotic-paste was intense and progressive over time. Replacement of the Triple-antibiotic-paste with blood made the color change more intense and progressive, with significant statistical differences at 2 and 3 months (T4 > T3; P = .028). The internal bleaching technique was statistically more effective in the Triple-antibiotic-paste group at 1 week (P = .002). Both techniques cause unacceptable color changes, causing Triple-antibiotic-paste more staining than Biodentine. Two sessions of internal bleaching recovered clinically perceptible color in both regenerative endodontic procedures without returning the original color.

In this work, we built a multi‐primary display model based on the new quantum dots (QD) technology to enlarge the display color gamut. In this way, first the emission spectral radiance curves of the three RGB channels of a commercial QD display were fitted to a four‐parameter function. From this modeling, it is possible to gain new theoretical color primaries by selecting new spectral peaks (cyan, yellow, magenta, and/or additional RGB primaries) and imposing some colorimetric conditions for the resulting white of this proposed theoretical multi‐primary display. Proper characterization to assess the performance of the display was conducted to know if the basic “gain‐offset‐gamma” (GOG) model can be used for direct and inverse color reproduction (from RGB to CIE‐XYZ, and vice versa). The GOG model was found to well characterize this display. The spatial uniformity of the display was also evaluated in luminance and color chromaticity terms. Finally, with the primaries modeling and color characterization based on the GOG model, a 5‐primary model (RGBYC) was tested. The evaluation of this theoretical RGBYC display model confirms the gamut enlargement, which can also improve goniochromatic color reproduction. We would like to thank the Spanish Ministry of Economy and Competitiveness for Project DPI2015-65814-R. Khalil Huraibat would also like to thank the Ministry of Economy and Competitiveness for his pre-doctoral fellowship grant (FPI BES-2016-077325).

12 pags., 4 figs., Large effect pigments, widely used in various fields of industrial applications, produce characteristic visual textures known as sparkle and graininess, which need to be quantified by objective or subjective methods. The development of preliminary measurement scales for sparkle and graininess, whose recommendation is now under discussion in the International Commission on Illumination (CIE), is described in this article. These scales are absolute, linear and traceable to standards of optical radiation metrology. The main purpose of this article is to justify the convenience of adopting these preliminary measurements scales, showing clear evidence that they correlate well with subjective evaluations. Before standardization, these scales need to be validated with more experimental data, including different specimens and experimental systems from other research groups., Ministerio de Ciencia, Innovación y Universidades (RTI2018-096000-B-I00); EURAMET and the European Union (16NRM08).

Sparkle and graininess are textural effects that appear as intrinsic spatial features of coatings containing goniochromatic pigments, whereas others such as mottling are undesired outcomes. In this study, we present new methods for the evaluation of sparkle, graininess and mottling of automotive coatings through images acquired with a novel gonio-hyperspectral imaging system based on light-emitting diodes with extended spectral sensitivity beyond the visible range (368&ndash, 1309 nm). A novel analysis of sparkle that considered the amount of sparkling spots was used. Graininess was quantified through a novel statistical descriptor based on the energy descriptor computed from the histogram. A new index was proposed for an enhanced detection of mottling based on the analysis of striping, which was better observed and quantified in the infrared range. Spectral assessments showed a strong relationship with color and spectral reflectance for graininess and mottling. In conclusion, the results showed that these new spatial and spectral methods are a suitable, alternative and potential approach for the assessment of these textural features.

[EN] Several different instruments have been introduced into the market to obtain good color characterization for different measurement configurations. These commercial instruments have different optical and working configurations, however, the measurement data provided by each instrument should be similar to have good consistency when comparing them to each other measuring the same sample material. Therefore, the purpose of this work was to apply an inter-model agreement study of spectral and colorimetric data of three instruments (CM-M6, BYK-mac-I, and MA98). Two different statistical tests were applied following ASTM recommendations. In general, the measurement geometries close to the specular direction and the flop direction showed greater deviations. In addition, the partial color differences calculated for the comparison of MA98 versus CM-M6 were larger than the BYK-mac-i versus CM-M6 comparison. Finally, it can be concluded that most of the measurement geometries were statistically significantly different from each other which means that these differences were due to systematic or bias errors and not exclusively to random errors., EMRP, Grant/Award Numbers: Bidirectional reflectance definitions (16NRM08), 16NRM08; Spanish Ministry of Economy and Competitiveness, Grant/Award Number: DPI2015-65814-R; Ministry of Economy and Competitiveness, Grant/Award Number: DPI2015-65814-R; European Union; EURAMET

Color tolerances of curved gonio‐apparent panels have been studied in this work. To achieve that, an experimental set‐up of the illumination and tilt variation of two identical coated panels was designed for simulation of curved panels with both concave and convex borders and with and without effect pigments (perceived as solid and gonio‐apparent colors, respectively). Finally, visual and instrumental measures were collected with both curvatures. The results show that the relationship of the instrumental color difference with the tilt angle can be modeled by a second‐order and the vertex did not depend on illumination, but on coating type. The critical angles (the angle marked when the color discrepancy between two identical samples is merely perceived) assessed by the observers showed that they were not equal according to border, nor according to coating type. The color tolerances at these angles were clearly higher than the conventional chromatic thresholds of industrial color comparisons. This work was funded by the Spanish Ministry of Economy and Competitiveness for Coordinated Project “New developments in visual optics, vision and color technology” under Grant (DPI2011–30090-C02). ‘This report was compiled within the EMRP IND52 Project xD-Reflect “Multidimensional reflectometry for industry.” The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.’

11 pags., 11 figs., 3 tabs., app. -- OCIS codes: (290.1483) BSDF, BRDF, and BTDF; (120.1840) Densitometers, reflectometers; (120.5700) Reflection., The field of spectral radiance factor (SRF) measurements has seen growing interest in recent years. Scale conformity has so far only been established between the national metrology institutes (NMIs) of Germany and the USA. This study aims at a bigger, multilateral scale comparison. For this purpose, a total of six NMIs participated in a scale comparison of goniospectrophotometers based on neutral and colored diffusely reflecting ceramics samples. In addition, two universities, providing a home-built gonioreflectometer and two widely used commercially available color measurement instruments, respectively, were involved. The wavelength range of the scale comparison covers the visible wavelength range from 380 nm to 780 nm. Results indicate systematic issues and that the uncertainty evaluation of the NMIs requires further work; although for the greatest part of the covered spectral range the agreement is good., This work has been realized within the European Metrology Research Program (EMRP) project JRPIND52. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. We thank the European Commission and EURAMET e.V. for financial support.

Evaluation is an educational tool to promote effective learning that can involve students with more guarantees of achieving successfully the objectives. In this way, our objective is the development of strategies to improve teaching quality through the use of self-evaluation rubrics. To use rubrics as evaluation tool offers advantages regarding other resources. By means of the rubric, the students know before the evaluation the criteria with which they will be evaluated, which allows them a global understanding of the subject and to know the relationship of the different abilities. In addition, this tool is very useful to promote the responsibility of the students and, in short, to encourage a much more autonomous learning and for the student to feel part of the educational process. This educational research has been developed within the subject of Environmental and Occupational Optometry of the Degree in Optics and Optometry of the University of Alicante. The educational experience proposed in this project has a double objective: to promote the collaborative work of the student and to promote self-evaluation as an instrument of learning and motivation. The collaborative work to be evaluated consisted of the design of an oral presentation on aspects addressed in the subject. On the other hand, the teachers involved designed and elaborated an evaluation rubric through Corubrics tool. It contains fundamental aspects to be taken into account by the students. Thus, they could think about what they are doing, how they are doing it and identify what they have learnt in the classroom. The rubric is divided into 8 items that evaluate both aspects of the content and aspects related to their attitude. Each category was described with four levels, from 4 (very correct) to 1 (very weak). 43 students participated in this study who were divided into two groups (A and B). In each group, the students worked in subgroups of a maximum of 3 people, with 6 oral presentations in group A and 9 in group B. The evaluation of the oral exposition was carried out in a group way. In this way, the rubric was completed individually by the rest of the students without differentiating between the members of the group. Furthermore, the same rubric was used by the teaching staff. Regarding the results, it is necessary to look at different aspects. On one hand, with respect to academic results, 73% of the students obtained a grade of B, and the remaining 27% obtained the grade of D, which is a good indicator of the degree of involvement of the students. It should be noted that there were maximum deviations of 84% and minimum deviations of 10% between the grades given by the teaching staff and the students. In this sense, it is important to mention that many of the items were systematically evaluated with the maximum score by most students. For this reason, it was thought appropriate to modulate the final grade by means of different percentages between teacher (60%) and student (40%). Finally, the evaluation of educational innovation itself was carried out using a scale designed for this purpose. After the analysis of the results, it can be said that the proposed objective has been achieved. The degree of student participation has been high, as reflected in the academic results. On the other hand, this experience has been valued positively by the students. Therefore, self-evaluation can be considered as a very useful tool for learning and motivation.

[EN] In order to consider 3D objects from suitable Fused Deposition Modelling (FDM) printers as prototypes for the automotive sector, this sample must be able to reproduce textural effects (sparkle or graininess) or metallic or gonio-appearance to reinforce the attractive appeal of these materials. This study worked with two different commercial filaments: grey metallic PLA (poly(lactic acid)) and ABS (acrylonitrile-butadiene-styrene copolymer) with diffractive pigments. For both materials, a statistical design of experiments (DoE) was carried out to find the printing parameters effect on the final 3D-objects gonio-appearance. The selected printing parameters were printing speed (2 levels), layer height (2 levels) and sample thickness (3 levels). Twelve smooth square objects were printed from each material. The ABS-diffractive filaments achieved the most significant flop and higher sparkle values than metallic PLA. Graininess was high when working with PLA filaments instead of ABS. Layer height was the most significant parameter to maximize PLA objects' flop or sparkle effects. The best result was found when printing at 0.1 mm. For the ABS samples, the stronger flop and sparkle effects were achieved with the 50 mm/s printing speed, the 0.1 mm layer height and the lowest thickness level. This study shows the methodology to study the printing parameters effects and interactions to maximize the FDM-3D-objects gonio-appearance., This research was funded by the Spanish Agencia Estatal de Investigacion (AEI), the European Union (FEDER funds) (Contract MAT2016-77742-C2-1-P) and the Spanish Ministry of Economy and Competitiveness (project DPI2015-65814-R).

A validation of the graininess attribute was made by means of a psychophysical experiment and the multidimensional scaling algorithm. A visual experiment was designed to obtain graininess differences to be used like the dissimilarity matrix in the MDS algorithm. The results revealed that two dimensions are needed to characterize the graininess effect. The BYK-mac-i instrument and a gonio-hyperspectral imaging system were employed to evaluate the statistical dimensions. On one hand, the first dimension correlated well with the graininess value provided by the BYK-mac-i (r2 = 0.9566). However, we were unable to find a relationship with dimension 2 and any parameter measured by this instrument. Furthermore, the images captured by the gonio-hyperspectral imaging system were processed. A good relationship with the correlation parameter was observed (r2 = 0.8958). However, no relationship was established with dimension 2. Based on these conclusions, further research is necessary that focuses on the new imaging processes and a new visual experiment. The authors are grateful to the EMRP for funding Project ‘Multidimensional Reflectometry for Industry’ (JRPI21) and Project ‘Bidirectional reflectance definitions’ (16NRM08). The EMRP is jointly funded by EMRP participating countries within EURAMET and the European Union. We thank the Spanish Ministry of Economy and Competitiveness for Project DPI2015-65814-R.

Our purpose was to improve the thermal, mechanical and optimal properties of an epoxy bioresin using optimum hybrid natural pigments previously synthesised in our lab. Next, we searched for the best combinations of factors in the synthesis of natural hybrid nanopigments and then incorporated them into the bioresin. We combined three structural modifiers in the nanopigment synthesis, surfactant, coupling agent (silane) and a mordant salt (alum), selected to replicate mordant textile dyeing with natural dyes. We used Taguchi s design L8 to seek final performance optimisation. We selected three natural dyes, chlorophyll, beta-carotene and beetroot extract, and used two laminar nanoclay types, montmorillonite and hydrotalcite. The thermal, mechanical and colorimetric characterisation of the composite obtained by mixing natural hybrid nanopigments (bionanocomposite) was made. The natural dye interactions with both nanoclays improved the thermal stabilities, colour performance and UV VIS light exposure stability of natural dyes and bioresins. The best bionanocomposite materials were found in an acidic pH [3, 4] environment and by modifying nanoclays with mordant and surfactant during the nanopigment synthesis process, We thank the Spanish Ministry of Economy and Competitiveness for funding Projects DPI2011-30090-C02-02 and DPI2015-68514-R.

8 págs.; 7 figs., The spectral bidirectional reflectance distribution function (BRDF) is the key quantity to specify the spectral reflectance of materials for any condition of irradiation and detection, and its characterization is quite important for surfaces with a high dependence on these conditions, such as iridescent coatings. In order to evaluate the calibration and measurement capabilities (CMC) of National Metrology Institutes with the ability to measure the spectral BRDF, a case study interlaboratory comparison is in progress. Spectral BRDF has both spectral and geometric dependence, and this multidimensionality must be treated in the comparison to provide useful information to the participants about their CMCs. A data analysis method for the comparison is presented in this work, which was tested by simulations for different scenarios. The proposed method assesses whether the experimental data from each participant are consistent with those from the others. Finally, one-dimensional and multidimensional degrees of equivalence are defined, which should allow systematic deviations of spectral and geometric nature to be identified., This report was compiled within the EMRP IND52 Project xD-Reflect ‘Multidimensional reflectometry for industry’. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. Part of the authors (Instituto de Óptica ‘Daza de Valdés’, Agencia Estatal CSIC) are also grateful to Comunidad de Madrid for funding the project SINFOTON-CM: S2013/MIT-2790.

18 pags., 15 figs., 1 tab., Large-effect pigments, due to their strongly specular reflectance, produce a special visual texture known as sparkle. The use of these pigments in many industries (automotive, cosmetic, paper, architecture...) makes the control of this visual texture necessary. Sparkle measurands have been defined in this article, so that traceability of sparkle measurements can be provided by national metrology institutes or designated institutes. Some of them (Physikalisch-Technische Bundesanstalt, Eidgenössisches Institut für Metrologie, Cesky Metrologicky Institut and Consejo Superior de Investigaciones Científicas) have tested their existing measurement capabilities for the defined sparkle measurands, and their results are presented and thoroughly compared. Two possible sources of systematic error have been identified: inadequate illumination and collection solid angles, and an inadequate size of the virtual aperture used to assess the luminous flux reflected by the effect pigments. Finally, it has been shown that the measures correlate excellently with the sparkle visual data. The results shown in this research support the sparkle measurands defined here as adequate quantities for defining the standard measurement scale of sparkle claimed by industry., This article was written within the EMPIR 16NRM08 Project ‘Bidirectional reflectance definition’ (BiRD). The EMPIR is jointly funded by the participating countries within EURAMET and the European Union. Some of the authors (Instituto de Optica ‘Daza de Valdes’) are also grateful to Comunidad de Madrid for funding the project S2018/NMT4326-SINFOTON2-C.

[EN] Alumosilicate materials of different morphologies, such as platy and tubule nanoclays, may serve as an efficient, protective encasing for colored organic substances and nanoparticles. The adsorption of dyes onto the nanoclays increases their stability against thermal, oxidative, and acid¿base-induced decomposition. Natural organic dyes form stable composites with clays, thus allowing for ¿green¿ technology in production of industrial nanopigments. In the presence of high-surface-area alumosilicate materials, semiconductor nanoparticles known as quantum dots are stabilized against agglomeration during their colloid synthesis, resulting in safe colors. The highly dispersed nanoclays such as tubule halloysite can be employed as biocompatible carriers of quantum dots for the dual labeling of living human cells¿both for dark-field and fluorescence imaging. Therefore, complexation of dyes with nanoclays allows for new, stable, and inexpensive color formulations., Y.L., V.V., A.S., and A.N. thank the Ministry of Education and Science of the Russian Federation (grant 14.Z50.31.0035) for funding this work. Authors are grateful to Mikhail S. Kotelev (Gubkin University) for the TEM micrographs. The human cell labeling work was performed by RF and ER according to the Russian Government Program of Competitive Growth of Kazan Federal University. The authors also thank the Spanish Ministry of Economy and Competitiveness for funding Projects DPI2011-30090-C02-02 and DPI2015-68514-R

For improving color reproduction accuracy of mobile displays, we recently developed a generic model for device-specific display characterization model that also accounts for the influence of illuminance from ambient light. In the present article, this MDCIM model (Mobile Display Characterization and Illumination Model) is applied to a Samsung Galaxy S4 display, representing OLED displays. The performance of the model was tested by determining the values of all model parameters using publicly available technical data only. We organized visual tests under various ambient illuminance levels from 600 to 3000 lux. Seven observers compared the color of displayed images with the color of physical samples. With the MDCIM method, the quality of the color match was shown to improve considerably as compared to using only device-independent encoding color space. On a five-point scale to quantify color reproduction accuracy, the MDCIM resulted in more than 1 unit improvement at 1000 lux illuminance. At lower and higher illuminance, the improvement was even larger. Color reproduction accuracy was found to be at least reasonable, according to the subjective assessment of visual observers, for more than 75% of the samples when using the MDCIM method, but only 20% or less when using the common device-independent encoding color space.

[EN] Solar thermal coatings are designed to achieve the highest incident solar flux into the receiver of a tower solar plant. These materials are subjected to extreme working conditions of temperature and solar concentrated radiation. Much effort is being made to develop a durable and high absorptive coating that can provide an excellent solar to heat conversion efficiency. Complex deposition techniques (PVD, CVD, electrodeposition, etc.) are developed and tested to achieve solar selectivity. High solar absorptance paints are an alternative technique, that is, easy to apply and implement in the field. In paint, pigments are the compound that provides high absorptance values, whose stability impacts the durability of optical properties. The search for new selective solar pigments for solar receivers is a promising route to improve the efficiency of this technology. In this work, novel nanocomposites were synthesized from low-cost organic materials such as table sugar. Promising results were obtained when intercalated and calcined in the laminar structure of montmorillonite, a type of smectite clay. The pigments were tested in a paint format on metallic coupons at different temperatures to obtain absorptivities above 96% of absorptance after 24 h at 700 degrees C. Further experiments are still needed to obtain optimum conditions to maximize the coating's absorptivity and durability at high temperature., The authors like to thank Abengoa Solar S. A. for providing the necessary resources to conduct this research.

[EN] A general procedure for developing stable solar absorptive coatings at both high temperature and a high solar radiation concentration is presented. In order to generally improve thermal efficiency, a coating with high solar absorptance is applied all over the surface of receiver tubes that is subjected to extreme working conditions. Consequently, a durable coating with high absorptivity for sunlight is needed. An alternative paint formulation research and development line to Pyromark-2500, the paint currently used in many commercial solar thermal power plants (CSP) is proposed. Pigment synthesis is developed by intercalating metallic salts into laminar or tubular clay structures. Metallic pxides, which provide paint with its color properties, are obtained by a calcination process. Addition of silane or surfactants during the pigment synthesis is also optimized. Once dried and ground to a precise size, pigments are mixed with a commercial binder and applied to a metallic substrate to study their properties. Thermal stability to high temperature is studied with different tests. The results showed that laminar structure was preferred to intercalate larger amounts of metallic salt into the clay structure, and no significant differences were found when using silane or surfactant modifiers. Although the highest absorptivity value was 85% after 24 h at 600 degrees C, samples presented very good adherence to the metallic substrate. Addition of a small quantity of commercial black pigment to the paint composition could improve the absorptivity and maintain the excellent adhesion shown. Furthermore, montmorillonite clay, modified with a surfactant before adding metallic salt, and without silane, resulted in a black pigment in a powder form. This pillared clay could be used in future paint formulations. (C) 2017 Elsevier Ltd. All rights reserved., The research that has led to these results was funded by Abengoa Solar New Technologies S.A. by a private contract with the Colour and Vision Group of the University of Alicante.

The default method for color representation on displays involves sRGB as device-independent encoding color space. For improving color reproduction accuracy, we develop a device-specific display characterization model for the Apple iPad Air 2. In separate articles, we will evaluate the same method for other devices and for other display technologies. This model is combined with an easy-to-implement new method to account for the influence of illuminance from ambient light. The combination is called the mobile display characterization and illumination model (MDCIM) for the iPad Air 2, representing modern liquid crystal displays. Seven observers performed psychophysical tests at ambient illuminance levels from 600 to 3000 lx. They visually compared colors of calculated images with those of physical samples. The MDCIM model achieves similar color reproduction accuracy as when using the default method involving sRGB encoding at 1000 lx, while considerably improving color accuracy at other illuminance levels. At 600 lx, 98% of the observers prefer images directly generated with the MDCIM model over those created using the default method. The average color reproduction accuracy improves by two categories on a five-point scale. At 3000 lx, the percentage of colors that is represented at least reasonably well, according to the subjective assessment of visual observers, increased from 0% to 60%.

The interest in gonioapparent pigments (metallic, pearlescent, interference, or diffractive) has increased in the last few years, especially for applications in the automotive industry. To assure a proper characterization of colors with gonioapparent pigments, commercial devices have appeared to characterize the color in different geometries, which are called multiangle spectrophotometers. As the gonioapparent pigments and multiangle instruments are relatively new, no studies exist regarding the instrumental-based procedure followed in the industry, and if the results provided are in agreement with the observer perception. Consequently, the main objective of this study was to examine the correlation of the instrumental color differences with visual assessments. The instrumental color difference was calculated with the color difference formula AUDI2000 (specific for this sector) between the pairs of similar samples of three types of coated panels (solid, metallic, and pearlescent). The values measured by a telespectroradiometer in a directional lighting booth and the colorimetric values obtained by means of a multiangle spectrophotometer BYK-mac were considered for this purpose. Additionally, a visual experiment was conducted to quantify the color difference by using the gray-scale method. The results revealed that an acceptable instrumental correlation existed despite the visual and the instrumental correlation being worse. In particular, it was checked that observers accepted a larger number of color pairs, that is, the visual color difference was smaller than the tolerance demanded by the industry (derived from AUDI2000). The authors thank the Ministry of Economy and Competitiveness for the coordinated project “New developments in visual optics, vision and color technology” (DPI2011-30090-C02). Francisco Javier Burgos also thanks the Autonomous Government of Catalonia for his predoctoral fellowship grant and Omar Gómez to the Ministry of Economy and Competitiveness for his predoctoral fellowship (FPI BES-2012-053080).

PurposeThis research deals with a new kind of nanopigment, obtained from the combination of organic dyes and layered nanoclays, that the authors call nanoclay‐colorant pigment (NCP). Whilst they have already been employed in inks and coatings, to date these nanopigments have not been used as pigments for polymers. The existing lack of knowledge surrounding them must be redressed in order to bridge the gap between current academic studies and commercial exploitation. Therefore, the main purpose of this paper is to examine the hitherto unknown aspects of the NCP, which relate specifically to their applicability as a new type of colorant for polymers.Design/methodology/approachA blue NCP has been prepared at the laboratory according to the patented method of synthesis (patent WO0104216), using methylene blue and montmorillonite nanoclay. It has then been applied to a thermoplastic polymer (linear low‐density polyethylene – LLDPE) to obtain a coloured sample. Furthermore, samples with the same polymer but using conventional blue colorants have been prepared under the same processing conditions. The mechanical, thermal and colorimetric properties of these materials have been compared.FindingsThe thermal stability of the sample coloured with NCP is reduced to some extent, while the mechanical strength is slightly increased. Moreover, this sample has better colour performance than the conventionally pigmented samples.Originality/valueIn this paper, a blue NCP has been synthesised and successfully employed with polyethylene and the obtained sample shows better colour performance than polyethylene with conventional pigments.

We propose a luminance adaptation model (LAM) to increase the dynamic range of an imaging system when scenes containing areas of low and high illumination are imaged. The LAM that we developed is based on capturing images at different exposure times to obtain digital levels within the linear response zone for all the pixels in the image. The levels are subsequently transformed to a reference exposure time that is common to all pixels. We use a linear transformation whose coefficients are determined by the digital levels obtained for a set of flat-spectrum samples. In this study, the LAM is applied to a multispectral imaging system that is based on a CCD camera used for color measurements and spectral reconstructions. It is shown to be a very useful method for increasing the dynamic range of the system, whilst maintaining its accuracy.

6 pags., 3 figs. -- IS&T International Symposium on Electronic Imaging 2019 Color Imaging XXIV: Displaying, Processing, Hardcopy, and Applications, The digital representation of three dimensional objects with different materials has become common not only in the games and movie industry, but also in designer software, e-commerce and other applications. Although the rendered images often seem to be realistic, a closer look reveals that their color accuracy is often insufficient for critical applications. Storage of the angledependent color properties of metallic coatings and other gonioapparent materials demands large amounts of data. Apart from that, also rendering sparkle, gloss and other visual texture phenomena is still a subject of active research. Current approaches are computationally very demanding, and require manual ad-hoc setting of many model parameters. In this paper, we describe a new approach to solve these problems. We combine a multi-spectral physics-based approach to make BRDF representation more efficient. We also account for the common loss in color accuracy due to the varying technical specifications of displays, and we correct for the influence from ambient lighting. The rendering framework presented here is shown to be capable of rendering sparkle and gloss as well, based on objective measurement of these properties. This takes out the subjective phase of manual fine-tuning of model parameters that is characteristic for many current rendering approaches. A feasibility test with the new spectral rendering pipeline shows that is indeed able to produce realistic rendering of color, sparkle, gloss and other texture aspects. The computation time is small enough to make the rendering real-time on an iPad 2017, i.e. with low memory footprint and without high demands on graphic card or data storage., This study was also supported by the Spanish Ministry of Economy and Competitiveness under grant no. DPI2011-30090-C02-02 and the European Union. Khalil Huraibat would also like to thank the Ministry of Economy and Competitiveness for his pre-doctoral fellowship grant (FPI BES- 2016- 077325). The authors are also grateful to EMRP for funding the project “Bidirectional Reflectance Definitions”. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union

Interest in applications of natural dye applications has increased because of their antibacterial properties and the possibility of extracting them from nature and residues. Using nanoclays as hosts to reinforce natural dye properties has been successfully demonstrated. However, no one has attempted to optimize the polymer matrix and hybrid pigment properties at the same time to ensure the best final properties for bio-composite applications. Using a statistical design for experiments, we propose the best combination of modifiers with the best nanoclay as the host of three natural dyes: chlorophyll, &beta, carotene, and betanine. Using the L9 Taguchi designs, we learned both the influence of the nanoclay structure, and the addition moment of surfactant, mordant salt, and silane modifiers. FTIR, XRD, DTG, integration sphere spectrophotometer, and UV-aging tests were used to characterize the hybrid pigments and epoxy bioresin composites. The degradation temperatures of the three natural dyes rose and the reinforcement of the stability of three natural dyes to UV&ndash, Vis radiation exposure was demonstrated, which avoided the migration of these dyes from bioresin to wet ribbing. Optimal results were obtained with hydrotalcite clay (calcined or not) by using surfactant and mordant before the natural dye, and before or after silane.

espanolEn el siguiente trabajo se realiza la impregnacion de diferentes sustratos polimericos con agentes biocidas y con un colorante textil, comunmente empleados en los procesos de acabados textiles. En este estudio se realiza la seleccion del colorante Disperse Red 167 (DR167), mediante la comparacion de solubilidad en CO2 supercritico (scCO2) entre varios colorantes dispersos. Los agentes biocidas seleccionados han sido; esencia de clavo (eugenol) y aceite esencial de oregano. Se ha realizado la impregnacion de diferentes sustratos polimericos; poliester (PES), polipropileno (PP), y algodon (CO), en diferentes condiciones. En total se realizaron impregnaciones utilizando diez concentraciones relativas del DR167. El objetivo principal es determinar las condiciones optimas de procesado para cada sustrato. Para determinar el rendimiento de la tintura en scCO2 se han representado los diagramas cromaticos de las muestras tintadas en diferentes condiciones. Las muestras de PES son las que presentan mayor rendimiento de color, sabiendo que esta es la unica fibra que presenta afinidad con el DR167. Para determinar el efecto de inhibicion de las bacterias se han realizado ensayos de actividad antimicrobiana y actividad fungicida. Puede indicarse que si se observo cierta actividad inhibitoria frente algunos microorganismos, como Staphylococcus aureus, mientras que no se observo una actividad inhibitoria importante frente a otros como Pseudomonas aeruginosa EnglishIn this paper has done an impregnation with biocides agents, and a textile dye, commonly used in textile finishing processes, for different polymeric substrates. In this study has selected the Disperse Red 167 dye (DR167), by comparing solubility in supercritical CO2 (scCO2). Biocide agents have been selected, oil of cloves (eugenol) and essential oil of oregano. Impregnation has been made of different polymeric substrates; polyester (PES), polypropylene (PP), and cotton (CO), under different conditions. Finally impregnations were performed using relative concentrations of DR167. The main objective is to determine an optimum process condition for each substrate. To determine the yield of DR167 are shown scCO2 color diagrams of the samples, dyed under different conditions. PES samples shows the best color results, knowing than this is the only fiber that had affinity for the DR167. To analyze the inhibition bacterial effect, have been done antimicrobial activity test, and fungicidal activity test. It's shows that, if there was some inhibitory activity against some microorganism such as Staphylococcus aureus, while there was no significant inhibitoy activity against Pseudomonas aereuginosa.

In spite of color being one of the physicochemical parameters most commonly used to characterize ornamental stone, there is yet no standardized protocol for measuring this parameter. Such a protocol is of particular importance for characterizing the color of heterogeneous surfaces, as in the case of granite. The aim of the present study was to determine the minimum area and the number of measurements required to characterize the color of granite rocks. A spectrophotometer and a tristimulus colorimeter, were used to measure the color of granite samples, and the measurements were expressed in CIE L*a*b* color system units. Three parameters were considered as variable factors: the type of rock (Labrador Claro, Grissal, Rosa Porrino, and Blanco Cristal), surface finish (polished, honed, sawn, and flamed), and target area (circular apertures of diameter 5, 8, 10, and 50 mm). The results of the application of multivariate analysis of variance and of the classical CIELAB formula and CIE L*a*b*-based color-difference formulae (i.e., CIE94 and CIEDE2000) to the data revealed that, although all considered factors affected the minimal area and the number of measurements required, the different circular apertures of both the instruments can be disregarded if the number of measurements and area recommended in this study are used. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010

Along past second semester of course 2007-08, at first time a new optional subject, Visual Ergonomics, was taught by blearning methodology in Graduate of Optics and Optometry at the University of Alicante. In this word the some issues most outstanding , both positive and negative, are described in this first implementation with a reduced group of students. The theoretical section was mainly developed by b-learning methodology interchanging on-class training, the most of them as feed-back, with virtual sessions supported by some web 2.0 digital tools as a blog, multimedia and interactive sessions, and team work (where teacher participates as one additional member, inside a strategy pre-conceived of situational leadership applied to classroom). The informal opinion polls, collected in course final, show that, in spite of the fact the students were conscious they had clearly approved this subject, the vast of them did not friendly accept so educational innovations in this short period. Then, as epilogue to this experience in education, this subject could not teach in course 2008-09 because any student is enrolled. Although this discipline is highly recommended from national guidelines for future Graduate in Optics and Optometry, it is not sure it continues at the University of Alicante. However, I hope the positive issues of this experience in education can be extrapolated with success in other pre and university degrees.

11 págs.; 18 figs.; 1 tab. OCIS codes: (290.1483) BSDF, BRDF, and BTDF; (050.1940) Diffraction; (030.5630) Radiometry; (120.5820) Scattering measurements., Coatings with diffraction pigments present high iridescence, which needs to be characterized in order to describe their appearance. The spectral bidirectional reflectance distribution functions (BRDFs) of six coatings with SpectraFlair diffraction pigments were measured using the robot-arm-based goniospectrophotometer GEFE, designed and developed at CSIC. Principal component analysis has been applied to study the coatings of BRDF data. From data evaluation and based on theoretical considerations, we propose a relevant geometric factor to study the spectral reflectance and color gamut variation of coatings with diffraction pigments. At fixed values of this geometric factor, the spectral BRDF component due to diffraction is almost constant. Commercially available portable goniospectrophotometers, extensively used in several industries (automotive and others), should be provided with more aspecular measurement angles to characterize the complex reflectance of goniochromatic coatings based on diffraction pigments, but they would not require either more than one irradiation angle or additional out-of-plane geometries. © 2016 Optical Society of America, European Metrology Research Programme (EMRP) (EMRP IND52); Comunidad de Madrid (SINFOTON-CM: S2013/MIT-2790); Ministerio de Economía y Competitividad (MINECO) (DIP2015-65814).

Most real surfaces and objects show variations in appearance with viewing and illumination directions. Besides angular dependency, they also show spatial variation in color, i.e., they exhibit some sort of texture. Of the surfaces we see, surfaces colored by special-effect pigments produce several complex visual effects, like change in color and lightness with viewing and illumination angles, and effects like sparkle and gloss on other textures. In the last two decades, different commercial devices have appeared to help ensure the proper characterization of materials with special-effect pigments. However, the instrumental characterization of sparkle is currently available only by a commercial device integrated into a multi-angle spectrophotometer. As it is difficult to find complete open original studies about the sparkle effect for designing and calibrating this commercial instrument, the main objective of this work was to check whether a good visual and instrumental correlation exists between the sparkle that the observer perceives and the sparkle value provided by the device using some subsets of goniochromatic samples with different types of special-effect pigments and colors. Visual assessments were made by a conventional magnitude estimation method in a directional lighting booth, which belonged to the same company owner of the sparkle instrument, in different geometries and at distinct illuminance levels. The results revealed that there was a good visual correlation of the sparkle grade value. By separately analyzing the factors used in its instrument algorithm, such as sparkle intensity and sparkle area values, it was clearly shown that the correlation was not good or simply did not exist. Consequently, and perhaps in regards to the choice of new special-effect pigments, such as synthetic mica and other future ones, we generated herein even more questions about current mathematical algorithms, and only recognized calculating this texture effect at the industrial level. The authors are grateful to the EMRP for funding the project “Multidimensional Reflectometry for Industry”. The EMRP is jointly funded by EMRP participating countries within EURAMET and the European Union. We thank the Spanish Ministry of Economy and Competitiveness for the coordinated project DPI2011-30090-C02 and project DPI-2015-68514 and University of Alicante for project GRE13-28. Omar Gómez Lozano would also like to thank the above-cited ministry for his pre-doctoral fellowship (FPI BES-2012-053080).

7 págs.; 3 figs.; OCIS codes: (330.1710) Color, measurement; (330.1070) Vision - acuity; (330.1720) Color vision; (330.1800) Vision - contrast sensitivity; (330.6180) Spectral discrimination; (350.1260) Astronomical optics., For suitable illumination and observation conditions, sparkles may be observed in metallic coatings. The visibility of these sparkles depends critically on their intensity, and on the paint medium surrounding the metallic flakes. Based on previous perception studies from other disciplines, we derive equations for the threshold for sparkles to be visible. The resulting equations show how the visibility of sparkles varies with the luminosity and distance of the light source, the diameter of the metallic flakes, and the reflection properties of the paint medium. The predictions are confirmed by common observations on metallic sparkle. For example, under appropriate conditions even metallic flakes as small as 1 ¿m diameter may be visible as sparkle, whereas under intense spot light the finer grades of metallic coatings do not show sparkle. We show that in direct sunlight, dark coarse metallic coatings show sparkles that are brighter than the brightest stars and planets in the night sky. Finally, we give equations to predict the number of visually distinguishable flake intensities, depending on local conditions. These equations are confirmed by previous results. Several practical examples for applying the equations derived in this article are provided. © 2015 Optical Society of America, European Metrology Research Programme (EMRP) Spanish Ministry of Economy and Competitiveness(DPI2011-30090-C02) Comunidad de Madrid (CM: S2013/MIT-2790). The EMRP is jointly funded by the EMRP participating countries within the European Association of National Meteorlogy (EURAMET) and the European Union.

Several methods to determine the color gamut of any digital camera are shown. Since an input device is additive, its color triangle was obtained from their spectral sensitivities and it was compared with the theoretical sensors of Ives-Abney-Yule and MacAdam. On the other hand, the RGB digital data of the optimal or MacAdam colors were simulated to transform them into XYZ data according to the colorimetric profile of the digital camera. From this, the MacAdam limits associated to the digital camera are compared with the corresponding ones of the CIE-1931 XYZ standard observer, resulting that our color device has much smaller MacAdam loci than those of the colorimetric standard observer. Taking this into account, we have estimated the reduction of discernible colors by the digital camera applying a chromatic discrimination model and a packing algorithm to obtain color discrimination ellipses. Calculating the relative decrement of distinguishable colors by the digital camera in comparison with the colorimetric standard observer at different luminance factors of the optimal colors, we have found that the camera distinguishes considerably fewer very dark than very light ones, but relatively much more colors with middle lightness (Y between 40 and 70, or L* between 69.5 and 87.0). This behavior is due to the short dynamic range of the digital camera response. Contract grant sponsor: Ministerio de Educación y Ciencia (Spain), contract grant number: DPI2002-00118, DPI2005-08999-C02.

In this study, a novel gonio-hyperspectral imaging system based on light-emitting diodes for the analysis of automotive coatings was validated colorimetrically and spectrally from 368 to 1309 nm. A total of 30 pearlescent, 30 metallic, and 30 solid real automotive coatings were evaluated with this system, the BYK-mac and X-Rite MA98 gonio-spectrophotometers, and also with the SPECTRO 320 spectrometer for further comparison. The results showed very precise correlations, especially in the visible range. In conclusion, this new system provides a deeper assessment of goniochromatic pigments than current approaches due to the expansion of the spectral range to the infrared. Ministerio de Ciencia e Innovación (MICINN) (DPI2011-30090-C02-01); European Union. Francisco J. Burgos-Fernández thanks the Government of Catalonia for his Ph.D. grant.

Nowadays, the measurement and management of color quality of the gonio-apparent materials is complex, but highly demanded in many industrial sectors, as automotive, cosmetics, plastics for consumer electronics, printing inks, architectural coatings, etc. It is necessary to control complex instrumentation and to do visual assessments of texture and color differences to get, for instance, a visual harmony in car bodies; and a profound knowledge of physics and chemistry of special-effect pigments for their optical formulation to obtain attractive visual effects in coatings, plastics, etc, combining among them and with solid pigments. From University of Alicante, for the academic year 2013-14, we are organizing the first MSc degree in Color Technology for the Automotive Sector, with a design of contents embracing CIE colorimetry and visual perception, included the AUDI2000 color difference formula, instrumentation and color management software, fundamentals of coatings and plastics in the automotive sector, and, optical formulation of pigments. The MSc syllabus, with 60 ECTS, is designed to be taught in two semesters: from September to February with on classroom theoretical and practical activities, and, from March to June at virtual level, with internships of training in some companies. Therefore, the MSc Thesis would be the performance report during the internship in companies or research institutions. Some multinational companies, both as car makers and coatings and plastics providers, from European and non-European countries have already shown their support and interest in welcoming students for specific training, even some job offers when the first MSc edition finishes.

From a set of gonioapparent automotive samples from different manufacturers we selected 28 low-chroma color pairs with relatively small color differences predominantly in lightness. These color pairs were visually assessed with a gray scale at six different viewing angles by a panel of 10 observers. Using the Standardized Residual Sum of Squares (STRESS) index, the results of our visual experiment were tested against predictions made by 12 modern color-difference formulas. From a weighted STRESS index accounting for the uncertainty in visual assessments, the best prediction of our whole experiment was achieved using AUDI2000, CAM02-SCD, CAM02-UCS and OSA-GP-Euclidean color-difference formulas, which were no statistically significant different among them. A two-step optimization of the original AUDI2000 color-difference formula resulted in a modified AUDI2000 formula which performed both, significantly better than the original formula and below the experimental inter-observer variability. Nevertheless the proposal of a new revised AUDI2000 color-difference formula requires additional experimental data. This research was supported by the Ministry of Economy and Competitiveness (Spain), research projects DPI2011-30090-C02 and FIS2010-19839, with European Regional Development Fund.

The technological fields where solid-state lighting can be applied are constantly growing. In relation to this topic, we built a spectral LED-based tuneable light source for the reconstruction of CIE standard illuminants. This light source consists of 31 spectral channels from 400nm to 700nm, an integrating cube and a control board with 16 bit resolution. Moreover, a minimization routine was developed to calculate the weighting values per channel for reproducing standard illuminants. The differences in colorimetric and fitting parameters between standard spectra and the theoretical and experimental ones, showed that the reconstructed spectra were very similar to the standard ones, specially for the D65 and A illuminants. However, there was a certain mismatching from 500nm to 600nm due to the lack of LEDs in this region. In conclusion, the developed LED-based light source and minimization routine are able to reproduce CIE standard illuminants with high accuracy.

12 pags.; 11 figs.; 3 tabs.; OCIS codes: (330.1710) Color, measurement; (330.1720) Color vision; (290.1483) BSDF, BRDF, and BTDF., A representation of the color gamut of special effect coatings is proposed and shown for six different samples, whose colors were calculated from spectral bidirectional reflectance distribution function (BRDF) measurements at different geometries. The most important characteristic of the proposed representation is that it allows a straightforward understanding of the color shift to be done both in terms of conventional irradiation and viewing angles and in terms of flake-based parameters. A different line was proposed to assess the color shift of special effect coatings on a*,b*-diagrams: the absorption line. Similar to interference and aspecular lines (constant aspecular and irradiation angles, respectively), an absorption line is the locus of calculated color coordinates from measurement geometries with a fixed bistatic angle. The advantages of using the absorption lines to characterize the contributions to the spectral BRDF of the scattering at the absorption pigments and the reflection at interference pigments for different geometries are shown. © 2014 Optical Society of America., “Plan Nacional de Física”, funding FIS2010-19756-E, to CSIC’s JAE Program, and the “European Social Fund” for awarding us a research grant. This study was also supported by the Spanish Ministry of Economy and Competitiveness under Grant No. DPI2011-30090-C02-02 and the European Union.

In this study, a digital CMOS camera was calibrated for use as a non-contact colorimeter for measuring the color of granite artworks. The low chroma values of the granite, which yield similar stimulation of the three color channels of the camera, proved to be the most challenging aspect of the task. The appropriate parameters for converting the device-dependent RGB color space into a device-independent color space were established. For this purpose, the color of a large number of Munsell samples (corresponding to the previously defined color gamut of granite) was measured with a digital camera and with a spectrophotometer (reference instrument). The color data were then compared using the CIELAB color formulae. The best correlations between measurements were obtained when the camera works to 10-bits and the spectrophotometric measures in SCI mode. Finally, the calibrated instrument was used successfully to measure the color of six commercial varieties of Spanish granite. The present study was financially supported by the Xunta de Galicia (09TMT014203PR) and the European Union and Spanish Ministry of Economy and Competitiveness under grants DPI2008-06455-C02-02 and DPI2011-30090-C02-02. Dr. Patricia Sanmartín acknowledges a scholarship for postgraduate studies abroad (2012 Call) from Barrié de la Maza Foundation. She is currently supported by a postdoctoral contract within the framework of the 2011–2015 Galician Plan for Research, Innovation and Growth (Plan I2C) for the year 2012.

In this study, a new type of nanopigment, obtained from a nanoclay (NC) and a dye, was synthesized in the laboratory, and these nanopigments were used to color an ethylene vinyl acetate (EVA) copolymer. Several of these nanoclay-based pigments (NCPs) were obtained through variations in the cation exchange capacity (CEC) percentage of the NC exchanged with the dye and also including an ammonium salt. Composites of EVA and different amounts of the as-synthesized nanopigments were prepared in a melt-intercalation process. Then, the morphological, mechanical, thermal, rheological, and colorimetric properties of the samples were assessed. The EVA/NCP composites developed much better color properties than the samples containing only the dye, especially when both the dye and the ammonium salt were exchanged with NC. Their other properties were similar to those of more conventional EVA/NC composites. One of the authors (V.M.R.) thanks the Conselleria d’Empresa, Universitat i Ciència, for a Ph.D. grant (contract grant number BFPI/2007/038) that she received.

In this study, a novel kind of hybrid pigment based on nanoclays and dyes was synthesized and characterized. These nanoclay-based pigments (NCPs) were prepared at the laboratory with sodium montmorillonite nanoclay (NC) and methylene blue (MB). The cation-exchange capacity of NC exchanged with MB was varied to obtain a wide color gamut. The synthesized nanopigments were thoroughly characterized. The NCPs were melt-mixed with linear low-density polyethylene (PE) with an internal mixer. Furthermore, samples with conventional colorants were prepared in the same way. Then, the properties (mechanical, thermal, and colorimetric) of the mixtures were assessed. The PE–NCP samples developed better color properties than those containing conventional colorants and used as references, and their other properties were maintained or improved, even at lower contents of dye compared to that with the conventional colorants. This research was supported by the Spanish Ministry for Education and Science (contract grant number DPI2005-08999-C02-02) and, the Spanish Ministry of Science and Innovation (contract grant numbers DPI2008-06455-C02-02 and DPI2011-30090-C02-02). One of the authors (V.M.) thanks the Conselleria d’Empresa, Universitat i Ciència, for a Ph.D. grant (contract grant number BFPI/2007/038).

Light sources with three spectral bands in specific spectral positions are known to have high-color-discrimination capability. W. A. Thornton hypothesized that they may also enhance color discrimination for color-deficient observers. This hypothesis was tested here by comparing the Rösch-MacAdam color volume for color-deficient observers rendered by three of these singular spectra, two reported previously and one derived in this paper by maximization of the Rösch-MacAdam color solid. It was found that all illuminants tested enhance discriminability for deuteranomalous observers, but their impact on other congenital deficiencies was variable. The best illuminant was the one derived here, as it was clearly advantageous for the two red-green anomalies and for tritanopes and almost neutral for red-green dichromats. We conclude that three-band spectra with high-colordiscrimination capability for normal observers do not necessarily produce comparable enhancements for color-deficient observers, but suitable spectral optimization clearly enhances the vision of the color deficient., This work was supported by the European Regional Development Fund through Program COMPETE (FCOMP-01-0124-FEDER-009858), by National Portuguese funds through Fundacao para a Ciencia e a Tecnologia (grant PTDC/EEA-EEL/098572/2008), and by the European Union and Spanish Ministry of Economy and Competitiveness under grant DPI2011-30090-C02-02., info:eu-repo/semantics/publishedVersion

New color-measuring instruments known as multiangle spectrophotometers have been recently created to measure and characterize the goniochromism of special-effect pigments in many materials with a particular visual appearance (metallic, interference, pearlescent, sparkle, or glitter). These devices measure the gonioapparent color from the spectral relative reflectance factor and the L*a*b* values of the sample with different illumination and observation angles. These angles usually coincide with requirements marked in American Society for Testing and Materials (ASTM) and Deutsches Institut Für Normung standards relating to the gonioapparent color, but the results of comparisons between these instruments are still inconclusive. Therefore, the main purpose of this study is to compare several multiangle spectrophotometers at a reproducibility level according to ASTM E2214-08 guidelines. In particular, we compared two X-Rite multi-gonio spectrophotometers (MA98 and MA68II), a Datacolor multi-gonio spectrophotometer (FX10), and a BYK multi-gonio spectrophotometer (BYK-mac). These instruments share only five common measurement geometries: 45° × −30° (as 15°), 45° × −20° (as 25°), 45° × 0° (as 45°), 45° × 30° (as 75°), 45° × 65° (as 110°). Specific statistical studies were used for the reproducibility comparison, including a Hotelling test and a statistical intercomparison test to determine the confidence interval of the partial color differences ΔL*, Δa*, Δb*, and the total color difference ΔE*ab. This was conducted using a database collection of 88 metallic and pearlescent samples that were measured 20 times without the replacement of all the instruments. The final findings show that in most measurement geometries, the reproducibility differences between pairs of instruments are statistically significant, although in general, there is a better reproducibility level at certain common geometries for newer instruments (MA98 and BYK-mac). This means that these differences are due to systematic or bias errors (angle tolerances for each geometry, photometric scales, white standards, etc.), but not exclusively to random errors. However, neither of the statistical tests used is valid to discriminate and quantify the detected bias errors in this comparison between instruments. Spanish Ministry of Science and Innovation; contract grant number: DPI2008-06455-C02-02.

A reduced set of measurement geometries allows the spectral reflectance of special effect coatings to be predicted for any other geometry. A physical model based on flake-related parameters has been used to determine nonredundant measurement geometries for the complete description of the spectral bidirectional reflectance distribution function (BRDF). The analysis of experimental spectral BRDF was carried out by means of principal component analysis. From this analysis, a set of nine measurement geometries was proposed to characterize special effect coatings. It was shown that, for two different special effect coatings, these geometries provide a good prediction of their complete color shift. ©2013 Optical Society of America., The authors are grateful to “Plan Nacional de Física”for funding this work (FIS2010-19756-E), to CSIC’s JAE Program, and the “European Social Fund” for awarding us a research trainee. This study was also supported by the Spanish Ministry of Economy and Competitiveness under the grant DPI2011-30090-C02-02 and the European Union.

Technological innovation in all areas has led to the appearance in recent years of new metallic and pearlescent materials, yet no exhaustive studies have been conducted to assess their colorimetric capabilities. The chromatic variability of these special-effect pigments may largely be due to the three-dimensional effect of their curved shapes and orientations when they are directionally or diffusely illuminated. Our study examines goniochromatic colors using the optimal colors (MacAdam limits) associated with normal colors (photometric scale of relative spectral reflectance from 0 to 1) under certain conventional illuminants and other light sources. From a database of 91 metallic and interference samples and using a multi-gonio-spectrophotometer, we analyzed samples with lightness values of more than 100 and others with lightness values of less than 100, but with higher chromaticities than optimal colors, which places them beyond the MacAdam limits. Our study thus demonstrates the existence of chromatic perceptions beyond the normal solid color associated with these materials and independent of the light source. The challenge for future research, therefore, is to replicate and render these color appearances in current and future color reproduction technologies for computer graphics. This research was supported by means of the grant number DPI2008-06455-C02-02 of the Spanish Ministry of Science and Innovation.

It has been reported that for certain colour samples, the chromatic adaptation transform CAT02 imbedded in the CIECAM02 colour appearance model predicts corresponding colours with negative tristimulus values (TSVs), which can cause problems in certain applications. To overcome this problem, a mathematical approach is proposed for modifying CAT02. This approach combines a non-negativity constraint for the TSVs of corresponding colours with the minimization of the colour differences between those values for the corresponding colours obtained by visual observations and the TSVs of the corresponding colours predicted by the model, which is a constrained non-linear optimization problem. By solving the non-linear optimization problem, a new matrix is found. The performance of the CAT02 transform with various matrices including the original CAT02 matrix, and the new matrix are tested using visual datasets and the optimum colours. Test results show that the CAT02 with the new matrix predicted corresponding colours without negative TSVs for all optimum colours and the colour matching functions of the two CIE standard observers under the test illuminants considered. However, the accuracy with the new matrix for predicting the visual data is approximately 1 CIELAB colour difference unit worse compared with the original CAT02. This indicates that accuracy has to be sacrificed to achieve the non-negativity constraint for the TSVs of the corresponding colours. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011

Preprint, We estimated the number of colors perceived by color normal and color-deficient observers when looking at the theoretic limits of object-color stimuli. These limits, the optimal color stimuli, were computed for a color normal observer and CIE standard illuminant D65, and the resultant colors were expressed in the CIELAB and DIN99d color spaces. The corresponding color volumes for abnormal color vision were computed using models simulating for normal trichromatic observers the appearance for dichromats and anomalous trichomats. The number of colors perceived in each case was then computed from the color volumes enclosed by the optimal colors also known as MacAdam limits. It was estimated that dichromats perceive less than 1% of the colors perceived by normal trichromats and that anomalous trichromats perceive 50%-60% for anomalies in the medium-wavelength-sensitive and 60%-70% for anomalies in the long-wavelength-sensitive cones. Complementary estimates obtained similarly for the spectral locus of monochromatic stimuli suggest less impairment for color-deficient observers, a fact that is explained by the two-dimensional nature of the locus. © 2010 Optical Society of America., This work was supported by the Spanish Ministry for Education and Science (DPI2005-08999-C02-02); the Spanish Ministry of Science and Innovation (DPI2008-06455-C02-02); the Centro de Fisica at Minho University, Braga, Portugal and the Portuguese Fundacao para a Ciencia e a Tecnologia (PTDC/EEA-EEL/098572/2008). Esther Perales was supported by the Spanish Ministry for Education and Science with the BES-2006-13518 grant, and Joao M. M. Linhares was supported by the Portuguese Fundacao para a Ciencia e a Tecnologia with the SFRH/BD/35874/ grant. We are grateful to David H. Foster for helpful discussions and to two reviewers and the editor for valuable advice., info:eu-repo/semantics/publishedVersion

For several decades, imaging sensors (CCD and CMOS) have been extensively used in many types of imaging capture devices (cameras and scanners). This first stage in any digital imaging workflow is very important in order to control the exact colour reproduction of images in subsequent applications (astronomy, television, cinema, printing, machine vision, mobiles, 3 etc). However, there are many parameters (spectral sensitivities, white balance, dynamic range, etc) which can negatively influence accurate control of the colour reproduction of digital imaging devices. Nevertheless, if all these parameters are controlled, it is possible to transform a conventional digital imaging capture device into a versatile tele-colorimeter or even tele-spectrocolorimeter. In this chapter, the fundamentals and challenges of camera-based colour measurement will be explained, including several aspects of specialinterest, such as the control of raw RGB colour space, and the similarities and differences between spectral and colorimetric characterization and calibration. Finally, future trends with clear industrial applications will be described, including case studies focused on the spatial-chromatic dithering of texture images (textiles, ceramic tiles, natural stones, etc), and the pseudo-visualization of non-visible images from multi-spectral imaging capture.

This work uses the S-CIELAB color model to compare images that have been calibrated and processed using a colorimetric dithering method which simulates increments in viewing distance. Firstly, we obtain XYZ calibrated images by applying the appropriate color transformations to the original images. These transformations depend on whether the image is viewed on a display device or encoded by a capture device, for example. Secondly, we use a colorimetric dithering method consisting of a partitive additive mixing of XYZ tristimulus values. The number of dithered pixels depends on simulated viewing distance. The dithered tristimulus values are transformed to digital data to observe the dithering effects in the image. Finally, we predict color differences using the S-CIELAB model as color appearance model for images. Moreover, this paper proposes some applications of this method to artistic and industrial problems where one must compare two images that appear different at close viewing distance, but match when they are seen from afar.