Lace Curtain: Rendering and Animating Woven Cloth
Based on an Impression-Evaluation Model
Atsushi Ishida
Sosuke Kaji
Lisa ParkKensuke Tobitani
Kwansei Gakuin University
Kwansei Gakuin University
Kwansei Gakuin University
Kwansei Gakuin University
Aya Shiraiwa
Eriko Aiba
Noriko Nagata∗
Kwansei Gakuin University
Kwansei Gakuin University
Kwansei Gakuin University
JAIST

1Introduction

Woven fabric is frequently used in computer graphics. To express therealistic appearance of a woven fabric, it is important to represent itsluster, transparency, and motion. In our previous study, we proposeda physically based BTDF model of woven cloth [Nomura et al. 2011]
and a method of estimating the motion properties of woven cloth fromsubjective impression [Ishida et al. 2012]. However, for the further
enhancement of the texture of materials in animations, it is necessary
to construct a comprehensive impression model for the evaluation ofwoven cloth that includes the relationship between optics and motions,impressions and emotions that are evoked by the impressions. In thisstudy, we propose an impression-evaluation model for the renderingof woven fabrics.

2Impression-evaluation model for woven
clothIn order to clarify the relationship between impressions and physicalcharacteristics, we measured optical and motion properties and performed experiments to evaluate subjective impressions.

rendering of animations with different subjective impressions using
global illumination as see in Figure1.

(a)Stiff and rough impression.
The curtain motion is rigid and little influence of transmitted light.

Measurements of woven cloth To evaluate the six woven fabric samples, we measured BRDF/BTDF by using a BRDF instrument,
the OGM-3 (Optical Gyro Measuring Machine), and we measured
motion properties such as bend, shear, compression, and stretch byusing a handle instrument, the KES (Kawabata Evaluation System).
Then, we applied PCA (principal component analysis) to the measured
BRDF/BTDF data to derive the major physical properties.
Experiments for impression evaluation We performed experiments to evaluate impressions using actual woven fabrics whose states
are stationary or moving. We used adjective word-pairs related to theoptical and motion properties. As a result of a factor analysis of thedata obtained, we found out that the factors ”softness” and ”smoothness” for the optics and the factors ”flexibility” and ”weight” for themotions influence the emotions evoked by the texture of woven fabrics. Furthermore, the relationship between the measured data and thesubjective impressions to weave structure were obtained using a multiple regression analysis.

3

Estimation of optical/motion properties
using the impression-evaluation model

We estimated the physical parameters for rendering using the relationships between the optical and motion properties in the impressionevaluation model. For example, from the thickness of warp/weft, theoptical/motion properties, such as the value of bend and the directionaltransmittance, were estimated.

4Rendering with BTDF based photon sampling for global illumination

We used photon mapping for to determine global illumination. In order to represent realistic transmitted light, we introduced a photon
sampling based on a woven cloth BTDF model similar to arbitrary
BRDF based importance sampling[Montes et al. 2009]. Thus, it waspossible to precisely express the BTDF properties of woven cloth, suchas direct transmittance and scattering by the thread. We performed the∗ e-mail:nagata@kwansei.ac.jp

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SIGGRAPH 2013, July 21 – 25, 2013, Anaheim, California.
2013 Copyright held by the Owner/Author.
ACM 978-1-4503-2261-4/13/07(b)Pliable and smooth impression.
The curtain motion is wavy and influence of the transmitted light wasconfirmed in the direction of direct transmission.

Figure 1: Scenes of curtain animations with different impression (inthe same flame time).

5 Conclusion

We clarified the structure of the impression-evaluation of woven fabrics and proposed a method to render such fabrics on the basis of theimpression-evaluation model. By estimating the physical characteristics from impressions, the expression of texture of woven fabrics wasimproved. We are planning to apply our approach to various materials.

References
I SHIDA , A., I SHIGO , E., A IBA , E., AND NAGATA , N. 2012.
Lace Curtain: Rendering Animation of Woven Cloth using
BRDF/BTDF- Estimating physical characteristic from subjective
impression. In ACM SIGGRAPH 2012 posters.
M ONTES , R., U RENA , C., G ARCIA , R., AND L ASTRA , M. 2009. An
Importance Sampling Method for Arbitrary BRDFs. In Computer
Vision and Computer Graphics. Theory and Applications, Springer
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N OMURA , S., I SHIDA , A., I SHIGO , E., O KAMOTO , T.,
M IZUSHIMA , Y., AND NAGATA , N. 2011. Lace Curtain: Modelingand Rendering Woven Cloth using Microfacet BSDF-Production ofa catalog of curtain animations-. In ACM SIGGRAPH 2011 posters.