Micro-appearance models explicitly model the interaction of light with microgeometry at the fiber scale to produce realistic appearance. To effectively match them to real fabrics, we introduce a new appearance matching framework to determine their parameters. Given a micro-appearance model and photographs of the fabric under many different lighting conditions, we optimize for parameters that best match the photographs using a method based on calculating derivatives during rendering. This highly applicable framework, we believe, is a useful research tool because it simplifies development and testing of new models.Using the framework, we systematically compare several types of micro-appearance models. We acquired computed microtomography (micro CT) scans of several fabrics, photographed the fabrics under many viewing/illumination conditions, and matched several appearance models to this data. We compare a new fiber-based light scattering model to the previously used microflake model. We also compare representing cloth microgeometry using volumes derived directly from the micro CT data to using explicit fibers reconstructed from the volumes. From our comparisons, we make the following conclusions: (1) given a fiber-based scattering model, volume- and fiber-based microgeometry representations are capable of very similar quality, and (2) using a fiber-specific scattering model is crucial to good results as it achieves considerably higher accuracy than prior work.

Matching Real Fabrics with Micro-Appearance Models

Realistic visualization of cloth has many applications in computer graphics. An ongoing research problem is how to best represent and capture cloth models, specifically when considering computer aided design of cloth. Previous methods produce highly realistic images, however, they are either difficult to edit or require the measurement of large databases to capture all variations of a cloth sample. We propose a pipeline to reverse engineer cloth and estimate a parametrized cloth model from a single image. We introduce a geometric yarn model, integrating state-of-the-art textile research. We present an automatic analysis approach to estimate yarn paths, yarn widths, their variation and a weave pattern. Several examples demonstrate that we are able to model the appearance of the original cloth sample. Properties derived from the input image give a physically plausible basis that is fully editable using a few intuitive parameters.

Image-Based Reverse Engineering and Visual Prototyping of Woven Cloth

Efficient physically accurate modeling and rendering of woven cloth at a yarn level is an inherently complicated task due to the underlying geometrical and optical complexity. In this paper, a novel and general approach to physically accurate cloth rendering is presented. By using a statistical volumetric model approximating the distribution of yarn fibers, a prohibitively costly explicit geometrical representation is avoided. As a result, accurate rendering of even large pieces of fabrics containing orders of magnitudes more fibers becomes practical without sacrifying much generality compared to fiber-based techniques. By employing the concept of local visibility and introducing the effective fiber density, limitations of existing volumetric approaches regarding self-shadowing and fiber density estimation are greatly reduced.

A volumetric approach to predictive rendering of fabrics

Friction plays an important role in the processing behaviour of fabrics or prepregs into geometries that require significant inter-ply and intra-ply movements. In previous studies, coefficient of friction is generally assumed to be constant. This paper presents a detailed experimental investigation of the frictional behaviour of carbon fibres at meso-scale. The inter-tow angle was found to have a significant effect on the tow friction when the fibres are parallel; whereas the effect of tow size was marginal. A numerical model was developed to investigate inter-filament friction from tow friction using finite element analysis. The filament-to-pulley friction was found to have a significant effect on the overall load–displacement behaviour, unlike the filament-to-filament friction. A range of intra-tow filament-to-filament friction coefficient was also indicated within which the inter-filament slippage began.

Effects of inter-tow angle and tow size on carbon fibre friction

This course is about recent advances in the challenging field of physically-based appearance modeling of cloth. Apart from geometrical complexity, optical complexity presents complications as highly anisotropic single and multiple scattering effects often dominate the appearance. Many types of fibers are highly translucent and multiple scattering significantly influences the observed color. Since a cloth model may potentially consist of billions of fibers, finding a viable level of geometrical abstraction is difficult. After explaining the general structure of several types of textiles, we give an overview of different approaches that have been proposed to render cloth. As the micro-geometry of cloth can be represented using an explicit representation of a fiber assembly, we continue by explaining optical properties of fibers; these can be derived from first principles of physics such as absorption or index of refraction. Understanding light scattering from fibers is essential, when a physically-based cloth renderer is designed. However, as storing these fibers explicitly is often too costly, more efficient statistical descriptions of cloth have also been proposed that can be used together with volumetric rendering techniques to allow for physically-based image synthesis, while retaining most of the flexibility of explicit methods. A major part of this course will focus on these approaches. We discuss the theory and practice of physically-based rendering of anisotropic media. The discussion begins with a review of linear transport theory, upon which current methods for rendering volumetric cloth are based. Relevant implementation details are discussed at each stage, and the final result will be the pseudocode of a Monte Carlo path tracer for volumetric cloth representations. Although rendering of cloth is a very specialized task, many of the concepts, developed in this field, can be used for rendering other materials with complex micro-geometry as well.

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Recent advances in physically-based appearance modeling of cloth

An algorithm of 3D modeling of fibers assemblies has been developed. The method extends a concept of ‘virtual location’ for simulation of fiber distributions in yarns cross-section from 2D to 3D modeling of yarns structure. The distributions function used in the model demonstrates all of the properties of the ideal and real yarns. A series of further cross-section at equal intervals along the yarn length is given. Each cross-section is rotated by a pre-determined amount relative to previous one, to allow for the yarn twist and parameters of fibers migration. The fiber curve in each interval between two successive cross-sections is approximated by NURBS. Also curve generation based on twist of each fiber is determined by centerline configurations of their constituent fibers and the generative model. Each fiber is created by sweeping a closed curve along a centerline path. The simulated yarns structure using the algorithm described can model wider variety and yield an improved visual representation ...

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Keartisak Sreprateep

Papers

Computer Aided Modeling of Fiber Assemblies