Advanced material appearance modeling (original) (raw)
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Digital modeling of the appearance of materials
2005
We present an introduction to the digital modeling of materials for realistic image synthesis. We present a visual tour of images of real materials, and consider how they are classified by the effects that need to be modeled to realistically render them. Essential appearance concepts such as diffuse, specular, subsurface scattering and wave effects will be defined and illustrated. We will then discuss popularly used numerical models such as Ward, Lafortune and Cook-Torrance. We will discuss these in terms of the effects they capture and the visual impact of the parameters of each model, and will not cover their mathematical derivations. We will conclude with the consideration of models that simulate the processing or aging of materials to predict their variation with time. The goal of the course is to provide an introduction to translating observation of materials in the real world into model parameters and/or code for synthesizing realistic images.
Reflectance and texture of real-world surfaces
ACM Transactions on Graphics, 1999
In this work, we investigate the visual appearance of real-world surfaces and the dependence of appearance on the geometry of imaging conditions. We discuss a new texture representation called the BTF (bidirectional texture function) which captures the variation in texture with illumination and viewing direction. We present a BTF database with image textures from over 60 different samples, each observed with over 200 different combinations of viewing and illumination directions. We describe the methods involved in collecting the database as well as the importqance and uniqueness of this database for computer graphics. A related quantity to the BTF is the familiar BRDF (bidirectional reflectance distribution function). The measurement methods involved in the BTF database are conducive to simultaneous measurement of the BRDF. Accordingly, we also present a BRDF database with reflectance measurements for over 60 different samples, each observed with over 200 different combinations of v...
Physically-Accurate Fur Reflectance: Modeling, Measurement and Rendering
: A rendering of the Wolf scene under environment lighting using (left) our physically-based double cylinder fur reflectance model with parameters from our database of animal fur samples, and (right) energy conserving Marschner model ] with best-fit parameters. Insets showing detailed comparisons from top to bottom using our model, Marschner model and Kajiya-Kay model. Since the Marschner model consists of only specular lobes, it often produces dark regions (limbs and tail). Furthermore, since the T T lobe is extremely strong in the Marschner model, especially for light colored fur fibers, it completely fails in heterogeneous regions (head) where dark colored fur is covered by light colored fur. The Kajiya-Kay model produces empirically plausible but hard-and-solid appearance, and it doesn't fit the measured reflectance data in Sec. 6.
Advanced Material Rendering in Blender
International Journal of Virtual Reality
Physically correct and realistic visual appearance rendering or analysis of material surface visual properties require complex descriptive models capable of modelling material dependence on variable illumination and viewing conditions. The recent most advanced representation of visual properties of surface materials is a Bidirectional texture function (BTF). BTF is 7D function of planar coordinates, spectral coordinate, and viewing and illumination angles, respectively. Unlike smooth textures, it specifies their altering appearance due to varying illumination and viewing conditions. This BTF visual appearance dependency on viewing and illumination conditions significantly complicates not only its acquisition, representation, and modelling but also makes its rendering noticeably more demanding. BTF textures are acquired by costly measurements of real materials and their subsequent nontrivial processing. While several techniques for measurement or processing of BTF textures have been ...
Grand Challenges: Material Appearance Modelling in the Automotive Industry
Material reflectance definitions are core to high fidelity visual simulation of objects within a compelling 3D scene. In the automotive industry these are used across the entire business process: from conceptualisation of a new product range, through to the final sale. However, current state-of-the-art of material representations leave much to be desired for fast and practical deployment in the industry. Even after decades of research and development, there are no interoperable standards for material models to facilitate exchange between applications. A large discrepancy also exists between the quality of material models used (and indeed the quality at which they can be displayed) across the spectrum of use-cases within the industry. Focussing on the needs of the Automotive Industry, in this position paper, we summarise the main issues that limit the effective use of material models. Furthermore, we outline specific solutions we believe could be investigated in order to address this...
2015
Characterizing the appearance of real-world surfaces is a fundamental problem in multidimensional , computer vision and computer graphics. In this paper, we outline a unified perception-based approach to modeling of the appearance of materials for computer graphics and reflectometry. We discuss the differences and the common points of data analysis and modeling for BRDFs in both physical and in virtual application domains. We outline a mathematical framework that captures important problems in both types of application domains, and allows for application and performance comparisons of statistical and machine learning methods. For comparisons between methods, we use criteria that are relevant to both statistics and machine learning, as well as to both virtual and physical application domains. Additionally, we propose a class of multiple testing procedures to test a hypothesis that a material has diffuse reflection in a generalized sense. We treat a general case where the number of hy...
Modelling the Appearance of Heritage Metallic Surfaces
2016
Polished metallic surfaces exhibit a high degree of specularity, which makes them difficult to reproduce accurately. We have applied two different techniques for modelling a heritage object known as the Islamic handbag. Photogrammetric multi-view stereo enabled a dense point cloud to be extracted from a set of photographs with calibration targets, and a geometrically accurate 3D model produced. A new method based on photometric stereo from a set of images taken in an illumination dome enabled surface normals to be generated for each face of the object and its appearance to be rendered, to a high degree of visual realism, when illuminated by one or more light sources from any angles. The specularity of the reflection from the metal surface was modelled by a modified Lorentzian function.
An Appearance Model for Textile Fibers
Computer Graphics Forum, 2017
Figure 1: Volumetric rendering of three fabric samples using our highly-detailed physically-based BCSDFs models. Our model is based on the optical and structural parameters particular of each cloth fiber. From left to right, a 2-ply knitted garter (7 twist/cm, 120 fibers/yarn) of cotton fibers, a single-ply woven satin made of silk (1 twist/cm, 30 fibers/yarn) and a 2-ply knitted garter (4 twist/cm, 160 fibers/yarn) made of polyester fibers. Silk and cotton pieces are colored with reactive dyes, and a disperse dye is used for polyester.
Modelling and Visualisation of the Optical Properties of Cloth
Computer Simulation
Cloth and garment visualisations are widely used in fashion and interior design, entertaining, automotive and nautical industry and are indispensable elements of visual communication. Modern appearance models attempt to offer a complete solution for the visualisation of complex cloth properties. In the review part of the chapter, advanced methods that enable visualisation at micron resolution, methods used in three-dimensional (3D) visualisation workflow and methods used for research purposes are presented. Within the review, those methods offering a comprehensive approach and experiments on explicit clothes attributes that present specific optical phenomenon are analysed. The review of appearance models includes surface and image-based models, volumetric and explicit models. Each group is presented with the representative authors' research group and the application and limitations of the methods. In the final part of the chapter, the visualisation of cloth specularity and porosity with an uneven surface is studied. The study and visualisation was performed using image data obtained with photography. The acquisition of structure information on a large scale namely enables the recording of structure irregularities that are very common on historical textiles, laces and also on artistic and experimental pieces of cloth. The contribution ends with the presentation of cloth visualised with the use of specular and alpha maps, which is the result of the image processing workflow.