This thesis presents documentation and analysis of the Bidirectional Reflectance Distribution Function (BRDF) of cloth through actual measured data. Although significant cloth appearance modeling research exists, light reflectance has not been a focus. For many graphics applications, replicating the motion and/or texture of cloth coupled with a general reflectance model has been sufficient. For physical accuracy, however, correctly modeling how light interacts with a material is a necessity. Part of the difficulty in developing and verifying physically accurate models is scarcity of data. This thesis presents and examines reflectance data covering a breadth of cloth materials acquired with the UCSD Spherical Gantry. Over 30 different types of cloth were measured in total, made of some of the most common fibers such as cotton, linen, rayon, silk, wool, nylon, and polyester. Included in the analysis is an assessment of several well-known BRDF models that could be easily assumed to work for a material such as cloth. The performance of each model is evaluated with a non-linear constrained SQP algorithm that fits the models to the measured data. Through numerical errors and function plots, the conclusion is that while some models are sufficient for some cloth materials, most textiles exhibit complex reflectance properties that are not accounted for. Furthermore, BRDF data can vary greatly within the family of textiles depending on numerous variables such as fiber class, thread structure, fabrication method, and finishing

This paper introduces a simple shading model for cloth. The model can simulate both the anisotropic highlights on cloth as well as the complex color shifts seen in cloth made of different colored threads. Our model is based on extensive Bidirectional Reflectance Distribution Function (BRDF) measurements of several cloth samples. We have also measured the scattering profile of several different individual cloth threads. Based on these measurements we have derived a simple model capable of predicting the light scattered by different threads. We model cloth as a collection of threads in a weave pattern which provides information about the coverage of the different thread types as well as their tangent directions. Our model also accounts for shadowing and masking by the threads. We validate our model by comparing predicted and measured values and we show how we can use the model to recover parameters for different cloth samples including silk, velvet, linen, and polyester with varying weaving patterns. We can also, model the appearance of novel physically plausible cloth fabrics. Finally, we demonstrate that our model can run in real-time on a GPU.

Pre-2018 CSE ID: CS2012-0975