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  • Lionel Simonot
Lionel Simonot

Lionel Simonot
Université de Poitiers | UP · Institut de recherche de Poitiers : Recherche ingénierie en matériaux, mécanique et énergétique pour les transports, l'énergie et l'environnement (Institut Pprime)

Maitre de conférences

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94
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Publications

Publications (94)
Article
Full-text available
The definition of BRDF as a ratio of radiance to irradiance assumes that the geometrical optics framework applies, implicitly meaning that spatial coherence and diffraction of light have no significant effect in the reflection process. However, recent applications of BRDF push at increasing the angular resolution and thus at reducing the solid angl...
Conference Paper
In this presentation, we discuss the implications of increasing requirements on angular resolution in measuring the BRDF, the Bidirectional Reflection Diffusion Function, in particular for the control of manufactured artefacts. To account for fast angular variations with respect to the direction of illumination or to the direction of observation, c...
Book
Full-text available
Comment mesurer une quantité de lumière ? Le tout, avec des bougies ou des flambeaux, des réglets, et l’œil de l’observateur ? Dans cet essai de 1729, Pierre Bouguer présente la première méthode pour mesurer la « force de la lumière », ce que l’on appellerait aujourd’hui l’intensité lumineuse. D’abord, il la met en application pour quantifier la pr...
Article
Full-text available
In lighting simulations, a luminaire is usually modeled using a luminous intensity distribution emitted by a single-point source. This so-called far-field approach is valid as long as the dimensions of the luminaire are much smaller than the distance to the calculation surface. This assumption is generally not met in standard indoor lighting and ma...
Article
Metal nanostructures supported on a dielectric substrate possess unique plasmonic properties that are highly dependent on their morphologies. We show that such nanostructures can be modified upon exposure to an ultra-low-energy ion-beam bombardment (< 100 eV) near the sputtering threshold of the metal. This plasma treatment can be easily implemente...
Conference Paper
Full-text available
In the CIE1931 xy chromaticity diagram, the set of visible colors is delimited by the spectrum locus representing the monochromatic radiations and by the purple line, set of non-spectral colors obtained by binary mixing between monochromatic radiations at the two extremities of the visible range. In contrast with the spectrum locus, which represent...
Article
Full-text available
Les concepteurs lumière au théâtre ont à leur disposition une grande gamme de projecteurs permettant de façonner les faisceaux lumineux. Ces projecteurs sont des dispositifs optiques constitués notamment de réflecteurs et de lentilles. À ce titre, ils peuvent être utilisés pour illustrer un cours d’optique géométrique. Leur manipulation permet de v...
Conference Paper
Full-text available
It can be easily observed that a white support printed with halftone ink layers changes color when coated with a clear layer. The color change can be explained by purely optical phenomena, for example the perception of a different amount of light scattered by the ink-matter interface if the observer is not too far from the specular direction. But c...
Conference Paper
Full-text available
Goniospectrophotometer ConDOR designed by CNAM, France, measures BRDF at very high angular resolution (0.014°), comparable to that of human vision. This is achieved using a very collimated light beam and a dedicated Fourier lens. Interestingly, the BRDF of glossy surfaces measured at this resolution exhibits a granular aspect around the specular di...
Chapter
Feux de bois, lampes à l’huile, bougies, éclairage au gaz… Avant l’électricité, l’histoire de l’éclairage est une histoire de combustion. La maitrise de l’électricité au XIXe siècle va radicalement transformer la physico-chimie de l’éclairage. Au cours du XXe siècle, trois grandes technologies vont co-exister en segmentant le marché : - la célèbre...
Article
Full-text available
The bidirectional reflectance distribution function (BRDF) and the bidirectional scattering - surface reflectance distribution function (BSSRDF), which relate radiance at the surface to irradiance and radiant flux, respectively, are regarded as the most fundamental scattering quantities used to determine the reflectance of objects. However, for mat...
Article
Full-text available
Comment mesurer une quantité de lumière ? Cette question fondamentale pour toute expérience optique n’allait pas de soi jusqu’au XVIII e siècle. Il fallait inventer un instrument et un protocole de mesure utilisant le seul photodétecteur alors disponible : l’œil humain. Plusieurs savants et quelques grands peintres contribuèrent sur plus de deux si...
Article
Full-text available
In many commercial instruments for measuring reflectance, the area illuminated on the measured object is identical to the area from which light is collected. This configuration is suitable for strongly scattering materials such as paper, but issues arise with translucent materials, because a portion of the incident light spreads around the illumina...
Article
On the request of the Louvre Museum, Mona Lisa's portrait was digitised with Lumiere Technology's high-resolution multispectral camera. The data from this digitisation revealed for the first time the spolvero (a drawing transfer technique) of the portrait. These discoveries change the history of this iconic symbol of Western painting because they a...
Article
Microfacet-based material appearance models are commonly considered as a physical plausible representation of matter-light interaction. With such models, the microgeometry of a surface element is defined by a statistical distribution of microfacets. The mathematical formulation ensures physical plausibility, such as energy conservation and reciproc...
Article
Full-text available
The scattering of light by a surface is described by the bidirectional reflectance distribution function (BRDF). Unfortunately, this function cannot be straightforwardly acquired or modeled. French researchers have proposed interesting contributions to the field, with several models and accurate experimental systems. For instance, the National Metr...
Article
Full-text available
The color of a surface structured at the mesoscopic scale differs from the one of a flat surface of the same material because of the light inter-reflections taking place in the concavities of the surface, as well as shadowing effects. The color variation arises not only in scattering materials, but also in the absence of scattering, e.g., in metals...
Article
Full-text available
Avec l’invention de la peinture à l’huile au XV e siècle, la couleur prend une autre dimension : elle se construit dans l’épaisseur de la matière picturale. En effet, le nombre de couches déposées module la clarté et la saturation de la couleur, tandis qu’un fond blanc diffusant donne l’impression d’une lumière provenant de l’arrière du tableau tel...
Chapter
L'observation d'un objet et l'analyse que nous pouvons en faire repose non seulement sur sa forme, mais également sur la manière dont il réfléchit la lumière. Nous savons dire très naturellement s'il est mat ou brillant, rugueux ou lisse, transparent, translucide, iridescent, brossé, ou parfois même poreux. L'objectif de ce chapitre est de parcouri...
Chapter
Les modèles de réflectance à base distributions de microfacettes sont souvent employés à la fois pour des aspects pratiques de mesure ou d'analyse et pour des besoins de production de contenus graphiques utilisant les méthodes de simulation d'éclairage. Leur utilisation est particulièrement intéressante pour des conducteurs (métaux) rugueux car les...
Chapter
Bien que les modèles de microfacettes soient souvent utilisés, la démonstration permettant d’obtenir leur expression assez compacte est rarement donnée. Nous faisons ici la démonstration selon une approche radiométrique d’abord à l’échelle de la microfacette puis à l’échelle macroscopique. L’expression générique intégrale obtenue ne présente pas de...
Book
Full-text available
L’apparence d’un objet (mat, satiné ou brillant ; transparent, translucide ou opaque ; de couleur variant avec la direction d’incidence et/ou d’observation) dépend de sa capacité à diffuser la lumière. Acquérir, reconstruire, compresser, modéliser et simuler cette propriété radiométrique multidimensionnelle (aux composantes spectrale, spatiale, an...
Chapter
La BRDF a souvent une allure continue et lisse, quand on la mesure en lumière blanche et avec des ouvertures angulaires assez larges pour les faisceaux incident et mesuré – ce faisant, on procède à un moyennage des luminances, lesquelles sont elles-mêmes le résultat moyen en puissance d'ondes réfléchies et diffractées par la surface. Mais si on dev...
Chapter
Ce chapitre constitue une introduction didactique à la physique de l'apparence visuelle. L'aspect mat, les reflets sur des surfaces polies, la brillance, la rétroréflexion, l'anisotropie, les réflexions en couches minces, l'iridescence, la fluorescence et la phosphorescence sont d'abord présentés de manière visuelle. Dans un second temps, plus théo...
Chapter
Les différentes aires d'un objet concave s'éclairent entre elles à travers un processus comprenant plusieurs réflexions de la lumière, appelé phénomène d'interréflexion, et qui dépend des géométries de l'objet et de l'éclairage. Pour une prédiction correcte de la luminance perçue en chaque point par un observateur ou un capteur, un modèle d'interré...
Chapter
La transparence et l'opacité sont des concepts physiques et visuels assez bien définis pour les matériaux, le premier étant lié à la capacité du matériau à laisser passer la lumière sans la diffuser, le second à ne pas laisser passer la lumière du tout. En revanche, le concept de translucidité est plus flou. Il est courant de placer les matériaux t...
Article
Microfacet distributions are considered nowadays as a reference for physically plausible BSDF representations. Many authors have focused on their physical and mathematical correctness, while introducing means to enlarge the range of possible appearances. This article is dedicated to Normal Distribution Functions (NDFs) and the influence of their sh...
Conference Paper
Full-text available
The color of a surface structured at the mesoscopic scale differs from the one of a flat surface of the same material because of the light interreflections taking place in the concavities of the surface, as well as the shadowing effect. The color variation depends not only on the surface topology but also on the spectral reflectance of the material...
Conference Paper
Full-text available
Translucency is a visual property attributed to objects that light may cross without transmitting a clear image of the scene which is behind. In absence of a more precise definition, this perceptual attribute is often considered as an intermediate between transparency, which is the property of objects that light may cross by transmitting a clear im...
Article
Full-text available
On a tous vu la tranche d'une table, d'une porte ou d'une vitrine en verre et noté son aspect vert sombre, parfois opaque, qui semble en contradiction avec l'idée de transparence associée au matériau. C'est une histoire de réflexions internes totales qui permettent de guider la lumière d'un bord au bord parallèle opposé. C'est aussi une histoire d'...
Article
Full-text available
The effect of Ge alloying on the growth morphology and intrinsic stress evolution during deposition of Cu thin films is investigated using in situ and real time diagnostics, complemented by ex situ microstructural characterizations. Cu1-xGex alloys with x up to 0.15 were sputter-deposited at room temperature on Si substrates, while measuring simult...
Article
Full-text available
Strongly scattering supports coated with thick transparent medium display a bright halo with a characteristic ring shape when illuminated in one point by a thin pencil of light. The halo, whose size is related to the coating thickness, is due to the Fresnel internal reflections of the light scattered by the diffusing support at the coating–air inte...
Conference Paper
Full-text available
Interactive RGB Transparency is an open source tool dedicated to the visualization of transparency effects in digital color images. Transparency effect can be rendered as a binary color mixing between foreground and background layers, which can be uniformly colored layers or downloaded images, while the transparency rate can be modified interactive...
Conference Paper
Full-text available
The different areas of a concave object illuminate each other by a multiple light reflection process, called interreflections, depending on the geometries of the object and the lighting. For an accurate prediction of the radiance perceived from each point of the object by an observer or a camera, an interreflection model is necessary, taking into a...
Article
Photochromic reaction dynamics in silver nanoparticles embedded in mesoporous titanium dioxide thin films is investigated by combining real-time grazing incidence small-angle x-ray scattering (GISAXS) and optical transmission measurements during UV–visible laser exposure cycles. While GISAXS probes changes in the particle size distribution, transmi...
Article
This paper focuses on microfacet reflectance models, and more precisely on the definition of a new and more general distribution function, which includes both Beckmann's and GGX distributions widely used in the computer graphics community. Therefore, our model makes use of an additional parameter γ, which controls the distribution function slope an...
Article
Full-text available
Specular microfacet distributions have been successfully employed by many authors for representing glossiness of materials. They are generally combined with a Lambertian term to account for the colored aspect. These representations make use of the Fresnel reflectance factor at the interface, but the transmission factor at the interface should also...
Article
Full-text available
Giving paper and polymer photochromic properties under laser irradiation is challenging due to the low resistance of these materials to heat, their flexibility, and their possibly irregular structure. However, we could successfully deposit TiO2/Ag/TiO2 layers stacking on flexible white glossy paper and transparent polyethylene terephalate (PET) sub...
Article
Full-text available
A classical way of coloring a surface in order to create a still image is the application of a colored coating. The more recent digital printing systems enable depositing thick coatings or successive ink layers. The color rendering of the surface depends on the optical properties of the coated materials (optical index, spectral scattering and absor...
Article
Full-text available
The four-flux model is a method to solve light radiative-transfer problems in planar, possibly multilayer structures. The light fluxes are modeled as two collimated and two diffuse beams propagating forward and backward perpendicularly to the layer stack. In the present contribution, we develop a four-flux model relying on a matrix formalism to det...
Article
Full-text available
The influence of TiO2 nano-particles (nano-TiO2) was studied relative to the mechanical and optical properties of CMYK printed paperboard after coating with a UV-curable varnish. Commercial duplex paperboard (glazed grayback paperboard, 230 g/m 2) was printed with a CMYK offset printing process. Board samples were coated with a nano-TiO2 modified U...
Article
Full-text available
To assess the accuracy of virtual cleaning of Old Master paintings (i.e. digital removal of discolored varnishes), a physical model was developed and experimentally tested using reflectance imaging spectroscopy on three paintings undergoing conservation treatment. The model predicts the reflectance spectra of the painting without varnish or after a...
Article
Full-text available
The Volmer-Weber growth of high-mobility metal films is associated with the development of a complex compressive-tensile-compressive stress behavior as the film deposition proceeds through nucleation of islands, coalescence, and formation of a continuous layer. The tensile force maximum has been attributed to the end of the islands coalescence stag...
Article
It is reported on a reactive magnetron sputtering-based deposition method to synthesize, at room temperature, photochromic nanocomposite thin films consisting of Ag nanoparticles sandwiched between nanoporous TiO2 layers. The fabrication process is compatible with large-scale production and functional flexible substrates. It is shown that when TiO2...
Conference Paper
Full-text available
Specific objective of the study Imaging detectors are ubiquitous in radiometry and more recently, also gained traction in photometry. The initial challenge was to conciliate the quantum efficiency of silicon-based array sensors with the perceptual photopic sensitivity. Some imaging luminance meter devices (ILMDs) are now able to achieve f1' mismatc...
Article
Full-text available
The most convenient way to assess the color rendering of a coated, painted, or printed surface in various illumination and observation configurations is predict its spectral, angular reflectance using an optical model. Most of the time, such a surface is a stack of layers having different scattering properties and different refractive indices. A ge...
Article
Full-text available
We introduce a model allowing convenient calculation of the spectral reflectance and transmittance of duplex prints. It is based on flux transfer matrices and enables retrieving classical Kubelka–Munk formulas, as well as extended formulas for nonsymmetric layers. By making different assumptions on the flux transfers, we obtain two predictive model...
Technical Report
Full-text available
La modélisation de la diffusion multiple de la lumière doit prendre en compte la localisation spatiale des éléments diffusants, et la répartition angulaire des flux donnée par la diffusion simple. Le problème général étant complexe, de nombreuses méthodes de résolution ont été proposées selon des hypothèses simplificatrices. Nous présentons une mét...
Article
Leaf reflectance of monocotyledons generally displays a strong azimuthal anisotropy due to the longitudinal orientation of the veins. The Cook and Torrance (CT) bidirectional reflectance distribution function model was adapted to account for this distinctive feature. The resulting ACT (Anisotropic Cook and Torrance) model is based on the decomposit...
Article
Full-text available
The color rendering of superposed coloring components is often an issue either to predict or to simulate the appearance of colored surfaces. In graphical software, for example, transparence options are available to display different layouts on top of each other. With two colored layers, tuning the transparency of the top layer enables transitioning...
Article
Full-text available
Structural and optical modifications induced by low-energy (≤80 eV) bias-plasma annealing of silver nanoclusters (2–25 nm) grown by magnetron sputtering deposition are reported. By combining postmortem structural characterizations and real-time optical measurements, we show that etching effects associated with enhanced Ag mobility result in progres...
Article
Full-text available
Radiometric and photometric quantities rely on a geometric description of the beam subtended by a source and a receptor. In this paper, a generalization of this description is proposed as the product of the apparent size of the source times the receptor angular extent, whatever the natures of these elements: point, line, surface, or volume. The obt...
Article
Full-text available
Real-time surface differential reflectance spectroscopy in the visible range is used to study the optical response of silver nanoclusters, prepared by magnetron sputtering deposition, during cyclic treatments in different oxygen atmospheres and low-energy bias argon plasma. Changes in the reflectance show that the exposure to non-ionized (or partia...
Article
Full-text available
Refractory metal alloy WTi films were elaborated by magnetron sputtering from an alloyed target (W:Ti ∼ 70:30 at%). Film continuity threshold has been determined at 4.5 ± 0.2 nm using in situ surface differential reflectance (SDR) technique. Prior to film continuity, deposition of a continuous interfacial layer is suggested by both in situ and real...
Article
Full-text available
We calculate, in the quasistatic coupled dipole approximation, the analytical expressions of the effective dielectric tensor of a single layer of polydisperse ellipsoidal nanoparticles with two of their principal axes in the layer's plane and embedded in a homogeneous dielectric medium. The organization (isotropic or anisotropic) and orientation (w...
Article
Full-text available
Surface differential reflectance spectroscopy (SDRS) is sensitive enough to observe the minute changes in the surface plasmon resonance (SPR) of noble metal nanoparticles (NPs), which is extremely dependent on the morphology and organization of the NPs as well as on the chemical atmosphere surrounding them. Taking this SPR as a signature, we have s...
Conference Paper
Full-text available
Surface differential reflectance spectroscopy (SDRS), an optical characterization technique, is sensitive enough to observe the minute changes in the surface plasmon resonance (SPR) of noble metal nanoparticles (NPs). This SPR, which causes a sharp absorption of light in the visible range, is extremely sensitive not only to the morphology and organ...