491 research outputs found
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
Efektivnà a expresivnà mikrofasetové modely
Název: EfektivnĂ a expresivnĂ mikrofasetovĂ© modely Autor: Asen Atanasov Katedra: Katedra softwaru a vĂ˝uky informatiky VedoucĂ: doc. Dr. Alexander Wilkie, Katedra softwaru a vĂ˝uky informatiky Abstrakt: V realistickĂ©m modelovánĂ vzhledu jsou drsnĂ© povrchy, kterĂ© majĂ mikroskopickĂ© detaily, popsány pomocĂ tzv. mikrofazetovĂ˝ch modelĹŻ. Mezi tyto modely patřà analytickĂ© modely, kterĂ© statisticky definujĂ fyzikálnÄ› zaloĹľenĂ˝ mikropovrch. TakovĂ© modely jsou široce pouĹľĂvány v praxi, protoĹľe jsou nenároÄŤnĂ© na vĂ˝poÄŤet a nabĂzejĂ znaÄŤnou flexibilitu ve vzhledu, kterĂ˝ s nimi lze docĂlit. Tyto modely mohou bĂ˝t rozšĂĹ™enĂ© o viditelnĂ© povrchovĂ© prvky prostĹ™ednictvĂm normálovĂ© mapy. Stále však existujĂ oblasti, ve kterĂ˝ch lze tento obecnĂ˝ typ modelu vylepšit: dĹŻleĹľitĂ© funkce, jako je Ĺ™ĂzenĂ anizotropie, nÄ›kdy postrádajĂ analytická Ĺ™ešenĂ a účinnĂ© vykreslovánĂ normálovĂ˝ch map vyĹľaduje pĹ™esnĂ© a obecnĂ© filtrovacĂ algoritmy. Posunujeme pĹ™edchozĂ práci v následujĂcĂch oblastech: odvodĂme analytickĂ© anizotropnĂ modely, pĹ™eformulujeme problĂ©m filtrovánĂ a navrhneme efektivnĂ filtraÄŤnĂ algoritmus zaloĹľenĂ˝ na novĂ© datovĂ© struktuĹ™e filtraÄŤnĂch dat. KonkrĂ©tnÄ› odvodĂme obecnĂ˝ vĂ˝sledek v mikrofazetovĂ© teorii: na základÄ› libovolnĂ©ho mikropovrchu definovanĂ©ho pomocĂ standardnĂ mikrofazetovĂ© statistiky ukážeme, jak konstruovat statistiku...Title: Efficient and Expressive Microfacet Models Author: Asen Atanasov Department: Department of Software and Computer Science Education Supervisor: doc. Dr. Alexander Wilkie, Department of Software and Computer Science Education Abstract: In realistic appearance modeling, rough surfaces that have micro- scopic details are described using so-called microfacet models. These include analytical models that statistically define a physically-based microsurface. Such models are extensively used in practice because they are inexpensive to compute and offer considerable flexibility in terms of appearance control. Also, small but visible surface features can easily be added to them through the use of a normal map. However, there are still areas in which this general type of model can be improved: important features like anisotropy control sometimes lack analytic solutions, and the efficient rendering of normal maps requires accurate and general filtering algorithms. We advance the state of the art with regard to such models in these areas: we derive analytic anisotropic models, reformulate the filtering problem and propose an efficient filtering algorithm based on a novel filtering data structure. Specifically, we derive a general result in microfacet theory: given an arbitrary microsurface defined via standard...Katedra softwaru a vĂ˝uky informatikyDepartment of Software and Computer Science EducationMatematicko-fyzikálnĂ fakultaFaculty of Mathematics and Physic
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
Under Material Skin Lie the Bones of Identity
This paper explores the automated recognition of objects and materials and their relation to depictions in images of all kinds: photographs, artwork, doodles by children, and any other visual representation. The way artists of all cultures, ages and skill levels depict objects and materials furnishes a gamut of ``depictions'' so wide as to present a severe challenge to current algorithms -- none of them perform satisfactorily across any but a few types of depiction. Indeed, most algorithms exhibit a significant performance loss when the images used are non photographic in nature. This loss can be explained using the tacit assumptions that underlay nearly every algorithm for recognition. Appeal to the Art History literature provides an alternative set of assumptions, that are more robust to variations in depiction and which offer new ways forward for automated image analysis. This is important, not just to advance Computer Vision, but because of the new understanding and applications that it opens
Fatigue of welded high strength steels for automotive chassis and suspension applications
The automotive industry is under expanding legislative pressure to decrease vehicle
weight in order to enhance fuel efficiency; and to improve crash performance as well. For
this purpose, hot rolled FB590 is a high strength steel (HSS) which can be used in
automotive chassis and suspension applications. A major problem affecting mainly car
underbodies is the effect of corrosion, often nucleating at sites where stone chipping has
damaged protective coatings. Therefore, car components are frequently exposed to
aggressive environments as a consequence of aqueous salts from the street coming into
contact with affected and unprotected steel. This circumstance significantly decreases
both the life and the appearance of the influenced parts, and may result in compromised
structural strength leading to catastrophic failure.
The main aim of this research is to further the understanding of the effects of simulated
operational environments. Fatigue tests were initially carried out on mild steel under
tensile loading and two severity-levels of corrosion as preliminary tests. Then a
comprehensive programme of fatigue tests was performed on FB590 and its welds under
bending and tensile loading and covering the range of environmental conditions
experienced in automotive applications. There is no available data for FB590 in terms of
fatigue performance in various environments and under bending and tensile loading as
well. Additional techniques such as surface profilometry, scanning electron microscopy
and so on were added to support the findings. The other aim was to monitor fatigue tests
using a combination of Acoustic Emission (AE) and Digital Image Correlation (DIC) to
identify the damage mechanisms that occur during failure although there had been limited
research in this area. The combination of AE and DIC can provide much useful
information to help to distinguish the different AE signals originating from various
possible failure mechanisms such as plastic deformation, delamination of corrosion
products or DIC paint and crack initiation and propagation. This might be utilized for an
effective and powerful approach to monitoring multiple failure mechanisms; this has
significant applications in automotive chassis testing.
This information can provide a very valuable tool for the purpose of assessing material
for automotive designers, which can then be used to decide on appropriate safety factors
to avoid over-designing products and in order to ensure reliability and robustness of new
products. In addition, the steel industry can also benefit from this research, as these
findings can assist in enhancing the products and diminishing the effects of these
environments on structural integrity
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
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