Time-Varying BRDFs |
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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] [©]
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Image
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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.
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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).
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Slides
EGWNP 2006 presentation With videos (zip file)
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Database
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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.
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Time Varying Surface Appearance
Oren-Nayar Reflectance Model
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