Time-Varying BRDFs

The properties of virtually all real-world materials change with time, causing their BRDFs to be time-varying. However, none of the existing BRDF models and databases take time variation into consideration; they represent the appearance of a material at a single time instance. In this work, we address the acquisition, analysis, modeling and rendering of a wide range of time-varying BRDFs. We have developed an acquisition system that is capable of sampling a material's BRDF at multiple time instances, with each time sample acquired within 36 seconds. We have used this acquisition system to measure the BRDFs of a wide range of time-varying phenomena which include the drying of various types of paints (watercolor, spray, and oil), the drying of wet rough surfaces (cement, plaster, and fabrics), the accumulation of dusts (household and joint compound) on surfaces, and the melting of materials (chocolate). Analytic BRDF functions are fit to these measurements and the model parameters variations with time are analyzed. Each category exhibits interesting and sometimes non-intuitive parameter trends. These parameter trends are then used to develop analytic time-varying BRDF (TVBRDF) models. The analytic TVBRDF models enable us to apply effects such as paint drying and dust accumulation to arbitrary surfaces and novel materials.

Publications

"Time-Varying BRDFs,"
Bo Sun, Kalyan Sunkavalli, Ravi Ramamoorthi, Peter Belhumeur and Shree Nayar,
IEEE Transactions on Visualization and Computer Graphics,
Mar, 2007.
[PDF] [bib] [©]

"Time-Varying BRDFs,"
Bo Sun, Kalyan Sunkavalli, Ravi Ramamoorthi, Peter Belhumeur and Shree Nayar,
Eurographics 2006 Workshop on Natural Phenomena,
Sep, 2006.
[PDF] [bib] [©]

Image

  Drying Watercolors:

Objects painted with watercolors dry over time. The dragon is rendered with our acquired blue watercolor on white paper. The bunny is rendered with a synthesized green watercolor on white paper. The bird is rendered with the blue watercolor on synthesized pink paper. The white sphere suspended in the corner represents a heat source.

     

Video

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  Time-Varying BRDF Video:

This video clip shows the acquisition, analysis, modeling and rendering of a wide range of time-varying BRDFs. It demonstrates a simple acquisition robotic rig that is capable of sampling a material's BRDF at multiple time instances, with each time sample acquired within 36 seconds. We also show the developed analytic Time-Varying BRDF functions for a number of interesting natural phenomena including the drying of various paints (watercolor, spray, and oil), the drying of wet rough surfaces (cement, plaster, and fabric), and the accumulation of dusts (household and joint compound).

     

Slides

EGWNP 2006 presentation     With videos (zip file)

Database

  Time-Varying BRDF (TVBRDF) Database:

We have acquired a variety of samples including watercolors, spray paints, oil paints, fabrics, cement, clay, plaster, joint compound dust, household dust and chocolate. A complete list of our 41 samples and the models used to fit their data can be found on the project page.

Our goal is to use this database to first identify temporal trends in the estimated parameter values that are associated with each type of time-varying phenomenon (drying paint, drying wet surface, dust accumulation). Next, we propose analytic functions that model these temporal trends in parameter values. These models enable us to apply several of the above physical processes to novel materials.

     

Time Varying Surface Appearance

Oren-Nayar Reflectance Model