Influence of the effect pigment size on the sparkle detection distance

5 págs.; 5 figs.In an effort to create more dynamic looking automobiles, there is an ever increasing trend among automobile manufacturers towards the use of gonio-apparent coatings in car bodies. These coatings consist of transparent pigments mixed with metallic or interference flakes. The flakes in the coating cause a change in color and brightness of the finish with viewing and illumination direction. This change in appearance accentuates the 3D shading of a car body, making it visually more attractive. Besides this angular dependence on viewing/illumination direction, the metallic finishes also exhibit a visually complex texture. Depending on the properties of the finish and the viewing and illumination conditions, the flakes exhibit a sparkle like texture, while the glossy clear coat may show a rough or smooth surface. As a result of these complex visual attributes, capturing the appearance and finding a perfect color match for an automotive coating is a non trivial task. The main objective of this work is to evaluate the relationship between the special-effect pigments size, and the maximum distance which is detectable the sparkle texture effect. For this, two different sets of samples with different structural features were evaluated in a lighting booth specifically designed for the visual experiment. The booth allows to vary the lighting conditions, the viewing geometry and the distance at which the sample is perceived. The visual experiment was applied to evaluate the high correlation between a structural parameter (i.e. pigment size) and the visual appearance attribute related with texture (sparkle detection distance). Under some fixed environmental conditions, as light intensity, color temperature and geometry of the light source, the sparkle detection distance was evaluated by applying the adjustment psychophysical method for two panel sets (metallic grays and blues), with known pigment sizes and colorimetry, with a small set of observers. The visual results show that a greater the pigment size, a greater the sparkle detection, but with some considerations. In future, we will extend this method, even reinforced applying the statistical design of experiments (DOE), for understanding the relevance and interplay of structural (size, shape, concentration, orientation, etc.), environmental (illuminance level, color rendering, geometry, etc.) and colorimetric (dark vs. light background, chroma, etc.) factors on the sparkle detection distance. © 2015 Society for Imaging Science and Technology.Authors are grateful to EMRP for funding the project “Multidimensional reflectometry for industry”. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. We would like to thank the Ministry of Economy and Competitiveness for the coordinated project “New developments in visual optics, vision and color technology” (DPI2011-30090-C02). Omar Gómez would also like to thank the Ministry of Economy and Competitiveness for his pre- doctoral fellowship grant (FPI BES-2012-053080).Peer Reviewe

Medida de goniofluorescencia en materiales fotoluminiscentes

1 pág.; 1 fig.; XI Reunión Nacional de Óptica, Salamanca, 1-4 Septiembre de 2015; http://rno11.usal.es/Se ha medido la función de distribución de la luminiscencia bidireccional (BLDF) para seis patrones de fluorescencia bajo diferentes geometrías de observación y detección. Estas medidas se realizaron con el gonioespectrofotómetro GEFE, usando iluminación monocromática y un espectrorradiómetro como detector. Se encontró que, en general, que la forma en que variaba la fluorescencia era la misma para todo patrón y dirección de irradiación: variación simétrica con el ángulo de detección (¿d) respecto a ¿d=0º.Peer Reviewe

Fast and accurate 3d rendering of automotive coatings

CI C23, Darmstadt, Germany, October 19-23, 2015The color of automot ve coat ngs var es w th llum nat on and detect on angles. For 3D render ng of these coat ngs currently two categor es of methods ex st, a m ng at e ther color accuracy or at computat onal speed. Current methods that a m for color accuracy are based on measurement data from BRDF nstruments. Since many hundreds of measurement geometr es are needed to capture the color var at on w th angles, these methods requ re t me-expens ve nterpolat on of large three-d mensional Look-Up Tables. Current methods that aim for computational speed use physically crude approximations, usually taking into account color variations with respect to only one of the four angular dimensions. Here, we derive a new approach for 3D rendering of automotive and other gonio-apparent coatings, which is a dedicated form of microfacet models. It aims at improved color accuracy as compared to the current computationally inexpensive methods, combined with higher computational speed and lower cost as compared to current color-accurate rendering techniques. The new approach utilizes a recently developed physical analysis method, introducing flake-based parameters and isochromatic lines, for the reflection properties of automotive coatings. This makes it more accurate than current fast rendering methods. The new method naturally leads to two- rather than three-dimensional Look-up Tables, which explains the small computation time it needs. We show that when applied to 3D rendering, this method indeed leads to accurate 3D rendering of automotive coatings while requiring reduced computation times. For numerical errors found in some special cases, solutions are found and tested.Peer Reviewe

Visual scale definition for graininess texture by applying multidimensional scaling

CIE 2019, Washington DC, June 14 to 22, 2019. -- http://washington2019.cie.co.atThe visual appearance of a product is a critical parameter implicated in the purchase decision of customers and allows the manufacturer to know about the reproducibility of its production. For these reasons, during the last years different efforts have been carried out by industrial manufacturers to provide attractive visual effects by using, for instance, special-effect pigments. Special-effect pigments provide a change in colour with viewing and illumination direction and a visually complex texture. Depending on the properties of the finish and the viewing and illumination conditions, the flakes exhibit a sparkle or graininess like texture. Under bright direct illumination conditions, such as sunlight, the flakes in a metallic finish glitter create a sparkling effect. Under diffuse illumination such as a cloudy sky, metallic finishes create a salt and pepper appearance or a light/dark irregular pattern. However, there are no standards that propose the mathematical and optical algorithms to measure and calculate the sparkle or graininess effect. Therefore, the objective of this work is to propose a visual scale for graininess texture based on the multidimensional scaling algorithm (MDS) to be compared with instrumental scales

Color characterization of coatings with diffraction pigments

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 AmericaEuropean Metrology Research Programme (EMRP) (EMRP IND52); Comunidad de Madrid (SINFOTON-CM: S2013/MIT-2790); Ministerio de Economía y Competitividad (MINECO) (DIP2015-65814).Peer Reviewe

Optica Applicata

This study describes a novel spectral LED-based tunable light source used for customized lighting solutions, especially for the reconstruction of CIE (Commission Internationale de l’Éclairage) standard illuminants. The light source comprises 31 spectral bands ranging from 400 to 700 nm, an integrating cube and a control board with a 16-bit resolution. A minimization algorithm to calculate the weighting values for each channel was applied to reproduce illuminants with precision. The differences in spectral fitting and colorimetric parameters showed that the reconstructed spectra were comparable to the standard, especially for the D65, D50, A and E illuminants. Accurate results were also obtained for illuminants with narrow peaks such as fluorescents (F2 and F11) and a high-pressure sodium lamp (HP1). In conclusion, the developed spectral LED-based light source and the minimization algorithm are able to reproduce any CIE standard illuminants with a high spectral and colorimetric accuracy able to advance available custom lighting systems useful in the industry and other fields such as museum lighting.Postprint (published version

Global color estimation of special-effect coatings from measurements by commercially available portable multiangle spectrophotometers

11 págs.; 12 figs.; 3 tabs.; OCIS codes: (330.1710) Color, measurement; (330.1720) Color vision; (290.1483) BSDF, BRDF, and BTDF.Colors of special-effect coatings have strong dependence on illumination/viewing geometry and an appealing appearance. An open question is to ask about the minimum number of measurement geometries required to completely characterize their observed color shift. A recently published principal components analysis (PCA)-based procedure to estimate the color of special-effect coatings at any geometry from measurements at a reduced set of geometries was tested in this work by using the measurement geometries of commercial portable multiangle spectrophotometers X-Rite MA98, Datacolor FX10, and BYK-mac as reduced sets. The performance of the proposed PCA procedure for the color-shift estimation for these commercial geometries has been examined for 15 special-effect coatings. Our results suggest that for rendering the color appearance of 3D objects covered with special-effect coatings, the color accuracy obtained with this procedure may be sufficient. This is the case especially if geometries of X-Rite MA98 or Datacolor FX10 are used. © 2014 Optical Society of AmericaThe authors are grateful to EMRP for funding the project “Multidimensional Reflectometry for Industry.” The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. This study was also supported by the Spanish Ministry of Economy and Competitiveness under grant no. DPI2011-30090-C02-02 and the European Union.Peer Reviewe

Visibility of sparkle in metallic paints

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 AmericaEuropean 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.Peer Reviewe

An insight into the present capabilities of national metrology institutes for measuring sparkle

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

Measurement of goniofluorescence in photoluminescent materials

28th Session, Manchester/UK, June 28 - July 4, 2015; http://session2015.cie.co.at/Fluorescent materials absorb light at a certain wavelength interval and then reemit it at other longer wavelengths, after about 10-8 seconds. Their colour appearance depends upon the combined effect of the fluorescent and reflected radiation. This work is focused in the measurement of the fluorescence of photolumiscent materials as a function of the irradiation and detection directions, which may be called as ¿goniofluorescence¿. It was measured the spectral bidirectional luminiscence distribution function (BLDF) of five fluorescent samples at different combinations of irradiation and detection directions. The measurements were performed with the goniospectrophotometer GEFE, using monochromatic irradiation and a spectrorradiometer as detector. A general behaviour was observed for the five samples and the studied excitation wavelengths: the dependence of the excitation spectrum on the detection direction ¿s is almost symmetrical with respect to ¿s = 0o, decreasing towards high angles.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” (IO-CSIC), Agencia Estatal CSIC) are also grateful to the Comunidad de Madrid for funding the project SINFOTON-CM: S2013/MIT-2790.Peer Reviewe