Elísabet Chorro

Computation and visualization of the MacAdam limits for any lightness, hue angle, and light source

We present a systematic algorithm capable of searching for optimal colors for any lightness L* (between 0 and 100), any illuminant (D65, F2, F7, F11, etc.), and any light source reported by CIE. Color solids are graphed in some color spaces (CIELAB, SVF, DIN99d, and CIECAM02) by horizontal (constant lightness) and transversal (constant hue angle) sections. Color solids plotted in DIN99d and CIECAM02 color spaces look more spherical or homogeneous than the ones plotted in CIELAB and SVF color spaces. Depending on the spectrum of the light source or illuminant, the shape of its color solid and its content (variety of distinguishable colors, with or without color correspondence) change drastically, particularly with sources whose spectrum is discontinuous and/or very peaked, with correlated color temperature lower than 5500 K. This could be used to propose an absolute colorimetric quality index for light sources comparing the volumes of their gamuts, in a uniform color space.

Spectral BRDF-based determination of proper measurement geometries to characterize color shift of special effect coatings

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.

Colorimetric and spectral evaluation of the optical anisotropy of metallic and pearlescent samples

The visual and optical anisotropies of metallic and pearlescent samples have been evaluated using a multi-gonio-spectrophotometer and by adapting a gonio-template over the instrument aperture for measuring the relative spectral reflectance factor when the sample is rotated around an axis normal to its surface. The results show that spectral data greatly vary as the azimuth angle changes, especially in pearlescent samples. Spectral and colorimetric data of the same sample for the interference and aspecular lines seen in complementary angle pairs have been compared, resulting in hue angle being kept constant, but lightness L* and chroma variations are high. In particular, the colour differences ΔEab calculated for pearlescent and metallic samples show that these visual differences can be clearly appreciable, even in metallic samples, but especially in pearlescent ones. Therefore, these types of optical materials do not verify the Helmholtz reciprocity, which is usually applied for digital modelling of material appearance.

Color representation and interpretation of special effect coatings

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.

Analysis of the colorimetric properties of goniochromatic colors using the MacAdam limits under different light sources

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.

Application of the S-CIELAB color model to processed and calibrated images with a colorimetric dithering method

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.

New method for comparing colour gamuts among printing technologies

Abstract The authors have developed a simple method to compare the colour gamuts of different industries (printing, textiles, plastics, etc.) based on representing the reproduced colours in constant lightness L and hue h ab planes. This method allows the analysis of those aspects related to the comparison between the colour gamuts of different industries and the MacAdam and Pointer limits and also of those aspects related to how the colour solid is filled, whether homogeneously or leaving certain unfilled regions for commercial or design reasons. In particular, the authors have compared the colour gamuts of three printing technologies (electrophotography or laser, inkjet and offset) with the same class of paper and characterisation chart, and in this comparison the laser printer has proved to be the best of three printing devices. On the other hand, the authors have checked that gravure technology is better than the other ones due to the substrate nature used at gravure technology.

CIMBNC- Combination and interactions of three kinds of nanoclays structural modifiers, for the colored bio-nanocomposites optimization

P Electrolytic Oxidation (PEO) is a very promising process that can enhance the corrosion and wear resistance by producing a relatively thick, dense and hard oxide ceramic coating on light alloys. The corrosion and wear behaviour of the treated samples strongly depends on some process parameters: current density, voltage, treatment time and electrolyte composition. In particular, the addiction of additives in the electrolyte produces significant changes in the resistance of the obtained coatings. In literature several works can be found concerning the addiction of silicon carbide or graphite particles in PEO coatings, in order to improve the wear resistance on aluminium alloys. However, there is little knowledge regarding the improvement of wear resistance of PEO treated magnesium alloys. In this work, 3g/l of graphite nanoparticles were added to an electrolyte containing sodium phosphates and sodium silicates in order to improve the wear resistance of the coatings produced on AZ91 and AZ80 magnesium alloy. Treatments were conducted at high current densities and short treatment times (two different treatment times were tested). The thickness, the morphology and the composition of the coatings were studied with SEM-EDS and XRD. The wear resistance was analyzed with a tribometer and the corrosion resistance of the samples was studied with potentiodynamic polarization tests and EIS tests. The results showed that the graphite nanoparticles seal the pores that characterize the typical surface of a PEO treated magnesium alloy. This fact produced an improvement both in the corrosion resistance and in the wear resistance.U of treated wastewater can be a sustainable water resource management policy. However, high organic matters and pathogen load along with the array of emerging recalcitrant micro-pollutants, that escape the sewage treatment plant, requires expensive advanced oxidation processes (AOPs) before use. Utilization of treated waste water in managed aquifer recharge (MAR), either in the form of riverbank filtration (RBF), lake bank filtration (LBF) and artificial recharge (AR) are costeffective and have been shown to degrade recalcitrant pharmaceuticals and personal care products (PPCPs). Carbamazepine (CBZ) and diatrizoate (DTZ) are two such persistent pharmaceuticals not degraded in in sewage treatment process. CBZ is an antiepileptic drug prescribed in seizure disorder, bipolar disorder, neuralgia, schizophrenia and depression. DTZ is used as iodinated X-ray contrast agents. Objective of this study was to evaluate removal of CBZ, and DTZ in simulated MAR with functionalized iron oxide nanoparticle and biological treatment. A long cylindrical acrylic column was filled with sand (0.8 ~ 1.2 mm). Hydraulic conductivity, flow rate and retention time were calculated before injecting CBZ and DTZ containing artificial wastewater at estimated load of 7.89 μg/g and 10.62 μg/g, respectively. The effluent concentration at different sampling point on the column during the experimental period was analyzed by SPE-HPLC. When inoculated with a mixed microbial culture, previously known for its metabolic potential, 89.63% of CBZ and 83.66% of DTZ were removed. Because the degradation capacity of pharmaceutical substances was more than 70% in the long-term operation in the soil layer, it will be combined the adsorption and bio-degradation process. This study not only confirmed the ability of MAR to treat the CBZ and DTZ in physicochemical and biological process, but also envisioned the possibility to treat the effluents from sewage plants.P which is a new branch of photonics, is based on the interaction of light with surface plasmon in nanostructured free-electron-rich metallic structures. Surface plasmon is a collective excitation of the electrons within the conduction band of a metal. Localized surface plasmon resonances occurring in metallic nanoparticles generates confined light fields, which enables enhancement of Raman scattering and nonlinear processes. Enhancement of signal amplification by localized surface plasmon was first discovered as surface-enhanced Raman scattering (SERS, in 1974) then made another techniques, tip-enhanced Raman scattering (TERS, in 2000) and surface-enhanced coherent anti-stokes Raman scattering (SE-CARS, in 1994). These three types of plasmon-enhanced vibrational spectroscopies have certain potential for the detection of any types of molecules at single-molecule level along with refinement of metallic nanostructures, however, only few specific molecules were reported as target molecules at single-molecule level. In this talk, the reported experiments which already succeeded plasmon-enhanced single-molecule detections using SERS, TERS and SE-CARS will be introduced and what is needed more will be discussed for universal detection of molecules using plasmon-enhanced single-molecule spectroscopy.T performance of polyamide lattices with electro-deposited metal was evaluated. This was achieved by irreversible compaction of the structures involved in the investigation. The versatility of additive manufacturing was utilized in order to fabricate the lattices. It demonstrated that metal coating of polymer lattices could significantly improve their compression properties. This methodology could provide new opportunities in terms of light weight energy absorbing structures in a wide variety of applications.

Visual and instrumental correlation of sparkle by the magnitude estimation method

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.

MSc degree in Color Technology for the Automotive Sector

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.