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

Computational Light Transport for Forward and Inverse Problems.

El transporte de luz computacional comprende todas las técnicas usadas para calcular el flujo de luz en una escena virtual. Su uso es ubicuo en distintas aplicaciones, desde entretenimiento y publicidad, hasta diseño de producto, ingeniería y arquitectura, incluyendo el generar datos validados para técnicas basadas en imagen por ordenador. Sin embargo, simular el transporte de luz de manera precisa es un proceso costoso. Como consecuencia, hay que establecer un balance entre la fidelidad de la simulación física y su coste computacional. Por ejemplo, es común asumir óptica geométrica o una velocidad de propagación de la luz infinita, o simplificar los modelos de reflectancia ignorando ciertos fenómenos. En esta tesis introducimos varias contribuciones a la simulación del transporte de luz, dirigidas tanto a mejorar la eficiencia del cálculo de la misma, como a expandir el rango de sus aplicaciones prácticas. Prestamos especial atención a remover la asunción de una velocidad de propagación infinita, generalizando el transporte de luz a su estado transitorio. Respecto a la mejora de eficiencia, presentamos un método para calcular el flujo de luz que incide directamente desde luminarias en un sistema de generación de imágenes por Monte Carlo, reduciendo significativamente la variancia de las imágenes resultantes usando el mismo tiempo de ejecución. Asimismo, introducimos una técnica basada en estimación de densidad en el estado transitorio, que permite reusar mejor las muestras temporales en un medio parcipativo. En el dominio de las aplicaciones, también introducimos dos nuevos usos del transporte de luz: Un modelo para simular un tipo especial de pigmentos gonicromáticos que exhiben apariencia perlescente, con el objetivo de proveer una forma de edición intuitiva para manufactura, y una técnica de imagen sin línea de visión directa usando información del tiempo de vuelo de la luz, construida sobre un modelo de propagación de la luz basado en ondas.<br /

The Appearance of Platelet-Polymer Composite Coatings: Microstructural Characterization, Hybrid Modeling, and Predictive Design.

The appearance of a platelet-containing polymer composite coating is governed by the microstructure and optical properties included scattering particles and platelets. Many models attempt to predict the coating's appearance, but do not utilize the complete 3D-microstructure, reducing their predictive utility. In this thesis, laser scanning confocal microscopy was used to measure the effect of platelet orientation on angle-dependent lightness, and quantify the spacing between platelets, from which a new microstructural property, the gap factor, was determined. The gap factor is a measure of the average gap size between platelets per unit material surface length. It ranged from 0 to 2 for the systems studied in this thesis. An increase in gap factor of about 0.1, keeping the orientation similar, reduced the near-specular lightness of the physical samples by more than 20%. A 3D hybrid-simulation was created using wave-optics to simulate the bidirectional-reflection-distribution-function (BRDF) for individual platelets. This was combined with ray-tracing to quantify the scattering behavior of a platelet array. This model more accurately predicted the lightness of a silver paint sample than an orientation-based microfacet-model, and was used to study how the surface roughness of the platelets influences lightness. The lightness at 15 degrees off-specular was about 130 when the root-mean square of the amplitude of the roughness, sigma(RMS), was much less than the wavelength of light. Lightness reduced to about 80 when sigma(RMS) was about equal to the wavelength of light. This effect of sigma(RMS) on lightness was found to be more significant with decreases in the roughness correlation length. The hybrid model was also used to study how width, thickness, and volume concentration of the platelets change the near-specular and backscattered lightness. The observed reduction in near-specular lightness with gap factor was verified. However, the resultant 2nd-order exponential decay was weaker than observed. This was attributed wave-scattering by faces and edges, behavior not included in the current model, but may be added in the future. This hybrid model can be used in the future to design unique microstructures to produce new and novel visual or functional effects using manufacturing techniques such as 3D-printing.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133404/1/cseubert_1.pd

BRDF representation and acquisition

Photorealistic rendering of real world environments is important in a range of different areas; including Visual Special effects, Interior/Exterior Modelling, Architectural Modelling, Cultural Heritage, Computer Games and Automotive Design. Currently, rendering systems are able to produce photorealistic simulations of the appearance of many real-world materials. In the real world, viewer perception of objects depends on the lighting and object/material/surface characteristics, the way a surface interacts with the light and on how the light is reflected, scattered, absorbed by the surface and the impact these characteristics have on material appearance. In order to re-produce this, it is necessary to understand how materials interact with light. Thus the representation and acquisition of material models has become such an active research area. This survey of the state-of-the-art of BRDF Representation and Acquisition presents an overview of BRDF (Bidirectional Reflectance Distribution Function) models used to represent surface/material reflection characteristics, and describes current acquisition methods for the capture and rendering of photorealistic materials

BRDF Representation and Acquisition

Photorealistic rendering of real world environments is important in a range of different areas; including Visual Special effects, Interior/Exterior Modelling, Architectural Modelling, Cultural Heritage, Computer Games and Automotive Design. Currently, rendering systems are able to produce photorealistic simulations of the appearance of many real-world materials. In the real world, viewer perception of objects depends on the lighting and object/material/surface characteristics, the way a surface interacts with the light and on how the light is reflected, scattered, absorbed by the surface and the impact these characteristics have on material appearance. In order to re-produce this, it is necessary to understand how materials interact with light. Thus the representation and acquisition of material models has become such an active research area. This survey of the state-of-the-art of BRDF Representation and Acquisition presents an overview of BRDF (Bidirectional Reflectance Distribution Function) models used to represent surface/material reflection characteristics, and describes current acquisition methods for the capture and rendering of photorealistic materials

Image based surface reflectance remapping for consistent and tool independent material appearence

Physically-based rendering in Computer Graphics requires the knowledge of material properties other than 3D shapes, textures and colors, in order to solve the rendering equation. A number of material models have been developed, since no model is currently able to reproduce the full range of available materials. Although only few material models have been widely adopted in current rendering systems, the lack of standardisation causes several issues in the 3D modelling workflow, leading to a heavy tool dependency of material appearance. In industry, final decisions about products are often based on a virtual prototype, a crucial step for the production pipeline, usually developed by a collaborations among several departments, which exchange data. Unfortunately, exchanged data often tends to differ from the original, when imported into a different application. As a result, delivering consistent visual results requires time, labour and computational cost. This thesis begins with an examination of the current state of the art in material appearance representation and capture, in order to identify a suitable strategy to tackle material appearance consistency. Automatic solutions to this problem are suggested in this work, accounting for the constraints of real-world scenarios, where the only available information is a reference rendering and the renderer used to obtain it, with no access to the implementation of the shaders. In particular, two image-based frameworks are proposed, working under these constraints. The first one, validated by means of perceptual studies, is aimed to the remapping of BRDF parameters and useful when the parameters used for the reference rendering are available. The second one provides consistent material appearance across different renderers, even when the parameters used for the reference are unknown. It allows the selection of an arbitrary reference rendering tool, and manipulates the output of other renderers in order to be consistent with the reference

Painting light, touching space : investigating how luminosity and the materiality of the surface of paintings create spatial illusions and contribute to the poetics of space

[v.1]. Dissertation -- [v.2]. Exegesi

Modelling the total appearance of gonio-apparent surfaces using stereo vision

Over recent decades, the textured coating provided by metallic surfaces has been an important factor in attracting customers of the automobile industry. This has meant that quantifying the appearance of coating products is essential for product development and quality control. The appearance of these coated products strongly depends on the viewing geometry, giving rise to a variety of properties of perceptual attributes such as texture, colour and gloss. Due to the visually-complex nature of such coatings, there remains an unsatisfied demand to develop techniques to measure the total appearance of metallic coatings. This study describes which aims to define the total appearance of metallic coatings and then objectively characterise it. Total appearance here refers to the combination of three properties of perceptual attributes of the surface: glint, coarseness and brightness. A number of metallic panels were visually scaled and a computational model capable for predicting three perceptual attributes was developed. A computational model was developed to relate the results from this psychophysical experiment to data obtained from a stereo image capture system. This is a new alternative technique aimed at solving one of the most challenging problems in computer vision: stereo matching. In the system, two images are captured by a same camera under two different lighting conditions to mimic stereoscopic vision. This not only addresses the problem of stereo matching (i.e. to find the corresponding pixels between two images) but also enhances the effect of perceptual attributes. After linearisation of camera response, spatial uniformity correction was performed to minimise the effect of uneven illumination. A characterisation method was then used to transfer the RGB to device-independent values. Two images captured under different lighting conditions were merged to obtain stereo data. In glint feature extraction, the pixels in the final image were segmented into two regions: bright spots and dark background. Next, statistical analyses were applied to extract features. Finally a model was created to predict the glint attribute of the metallic coating panels based on an image captured by the stereo capture system. In coarseness feature extraction, the merged image transformed to frequency domain using a discrete Fourier Transform. An octave bandpass filter was then applied to the Fourier Spectra image and data analysis was carried out to achieve the “image variance value” for each band. In similar to final step of glint, a model was created to predict the coarseness attribute