Numerical study of the thermally adaptive emissivity of VO2-polymer nanostructured coatings.

The emissivity of an opal photonic crystal loaded with thermochromic VO2 nanoparticles is studied through optical calculations, highlighting the influence of the structure by comparison with a homogenized model. Parameters are first set to maximize the structure influence on material emissivity. Then, a full study of the influence of the VO2 concentration is made to identify, on one hand, cases with the highest structure impact, and on the other hand, interesting cases for applications such as energy-efficient coatings for buildings, satellites, and camouflage applications.

Multi-angle color prediction of glossy anodized titanium samples through the determination of the oxide layer structural parameters.

The purpose of the present study is to predict the whole chromatic path traveled by the colors of glossy anodized titanium samples in every specular geometry. It is based on measurements of the samples' reflectance spectra in a limited number of specular geometries, which allow us to obtain the oxide layer structural parameters (thickness, refractive index), which are then put into an optical model to predict the samples' reflectance spectra in every specular geometry. A good color prediction performance is obtained, with an average ΔE94 color distance over all samples and geometries of 1.9. The oxide layer structural parameters are also in good agreement with refractive index values extracted from the literature and thicknesses measured on electron microscopy images of sample sections.

Modeling the specular spectral reflectance of partially ordered alumina nanopores on an aluminum substrate.

Anodizing of aluminum generates a porous alumina layer comprising cylindrical nanopores (300 nm diameter) extending essentially perpendicular to the substrate. The pore distribution over the surface exhibits a short-distance order close to hexagonal arrangement. On the contrary, long-distance order cannot be defined: the arrangement is not periodic. Visual observation of such nanoporous layers shows a reddish specular reflectance consistent with reflectance spectrum measurements. This work is a parametric study aiming at demonstrating that color effects are caused by the presence of disorder illustrated by the deviations from periodicity in terms of nanopore location and nanopore radius. Using the method of Rigorous Coupled Wave Analysis (RCWA), the reflectance spectrum has been simulated. Although our calculations were done using a simple one-dimensional (1D) model, a fair fit with experimental results is found.

Color calibration of an RGB camera mounted in front of a microscope with strong color distortion.

This paper aims at showing that performing color calibration of an RGB camera can be achieved even in the case where the optical system before the camera introduces strong color distortion. In the present case, the optical system is a microscope containing a halogen lamp, with a nonuniform irradiance on the viewed surface. The calibration method proposed in this work is based on an existing method, but it is preceded by a three-step preprocessing of the RGB images aiming at extracting relevant color information from the strongly distorted images, taking especially into account the nonuniform irradiance map and the perturbing texture due to the surface topology of the standard color calibration charts when observed at micrometric scale. The proposed color calibration process consists first in computing the average color of the color-chart patches viewed under the microscope; then computing white balance, gamma correction, and saturation enhancement; and finally applying a third-order polynomial regression color calibration transform. Despite the nonusual conditions for color calibration, fairly good performance is achieved from a 48 patch Lambertian color chart, since an average CIE-94 color difference on the color-chart colors lower than 2.5 units is obtained.