Approach to Cloth Synthesis and Visualization

Vladimir L. Volevich, Edward A. Kopylov,

Andrei B. Khodulev, Olga A. Karpenko

Contents Introduction Cloth Structure Explicit Cloth Model Ray Tracing Results and Images Conclusions and Future Work Acknowledgements References

INTRODUCTION

A realistic visualization of fabrics in computer graphics is important for human animation, fashion and interior design, and other fields of science and technology. Some techniques for visualization and modeling of woven materials and knitted fabrics were already proposed in computer graphics literature. Researches were mainly done in two directions:

investigation of physical and mechanical phenomena of woven textiles (such as deformation, wrinkling and crumpling) [2, 4]
investigation of optical properties of the cloth [1, 3, 5].

From the optical point of view the realism of an image is the result of a good correspondence of the local light scattering model applied. Some classes of objects are satisfactory described by computationally simple non-physically-based local illumination models widely used in computer graphics. As for materials with more complex optical properties, such as cloth, anisotropic paint, dusty surfaces, skin, leaves etc., the standard methods seem to be inappropriate for the realistic appearance visualization. To find a suitable physically-based model for woven textiles we concentrate on the cloth structure.

First of all we investigated the cloth patterns with a scanning electronic microscope. Considering the cloth structure in details we come to explicit model where straight fiber segments are represented by geometrical primitives that belong to some repetitive cloth element called micro-element (rapport). It differs from the other approaches, for example one proposed in [1], because parameters of real cloth structure are considered during the modeling. The optical characteristics of a micro-element describe average properties of the cloth in a point. Observing the cloth from distance we see the true picture.

For qualitative rendering it is sufficient to compute BSDF (Bi-directional Scattering Distribution Function):

for cloth micro-element, where :
- is the unit semi-sphere, - is the unit sphere;
- the elevation and azimuth angles of incidence;
- the elevation and azimuth angles of reflection / transmission.

This BSDF determines optical properties of a cloth point in full. It is natural to subdivide the process of cloth rendering into two steps. At first is computed for a cloth micro-element. Virtual goniometric spectrophotometer based on Forward Monte Carlo Ray Tracing was developed for it. Then any object with assigned BSDF can be rendered by means of appropriate computer graphics software. For this purpose we used Specter 5.10 system distributed by Integra, Inc. (http://www.integra.co.jp).

In the next section we give a brief introduction with a cloth object structure and some basic terms which are necessary for its specification. Explicit Cloth Model describes the explicit model for representation of woven fabrics at micro level. The BSDF calculation by means of virtual goniometric spectrophotometer is explained in Ray Tracing . The results of applying the explicit model to the silk samples are presented in Results and Images .

Contents Introduction Cloth Structure Explicit Cloth Model Ray Tracing Results and Images Conlcusions and Future Work Acknowledgements References


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