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The Free-form Light Stage is a method for capturing and relighting real objects by taking pictures and manipulating a hand-held light source. It allows for easy and cheap data acquisition, is portable and scalable. Future work includes testing on large objects, alternative filters, and improving accuracy in illuminant direction estimation.
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The Free-form Light Stage Vincent Masselus Philip Dutré Frederik Anrys Department of Computer Science
The Free-form Light Stage • Capture appearance of an object • With hand–held light source • Relight real objects The Free-form Light Stage
Related work • Image-based relighting • Combination of Basis Images [Nimeroff et al.1994] • Light Stage [Debevec et al. 2000] The Free-form Light Stage
Illuminant direction estimation Take pictures and move hand-held light source Basis images · W1 + · W2 + · Wn + … Create weighted sum Relit object Incident light map The Free-form Light Stage
Taking the pictures The Free-form Light Stage
· W2 + · Wn · W1 + + · Wn-1 + … = Relighting The Free-form Light Stage
Illuminant direction estimation Basis images Take pictures and move hand-held light source The Free-form Light Stage
Illuminant direction estimation Diffuse white spheres The Free-form Light Stage
Lamberts Law Ii = ρ IL ( Ni · L) L N3 I3 L N1 L I1 I2 N2 Illuminant direction estimation The Free-form Light Stage
Illuminant direction estimation The Free-form Light Stage
Illuminant direction estimation The Free-form Light Stage
… A direction per basis image The Free-form Light Stage
Accuracy of estimation The Free-form Light Stage
Illuminant direction estimation Basis images · W1 + · W2 + · Wn + … Incident light map Create weighted sum Take pictures and move hand-held light source The Free-form Light Stage
use an angular Voronoi diagram Weight computation • Weight is based on incident light in neighborhood of light source direction • Non-uniform sampling of light source directions The Free-form Light Stage
… Plot directions on a hemisphere The Free-form Light Stage
Plot directions on hemisphere 30 light directions The Free-form Light Stage
Create an angular Voronoi Diagram 30 light directions The Free-form Light Stage
Choose a parameterization The Free-form Light Stage
Filter each Voronoi cell Filter the incident light map Overlay incident light map with angular Voronoi diagram The Free-form Light Stage
400 light directions Using all illuminant directions 30 light directions The Free-form Light Stage
· W1 + · W2 + · W3 + · Wn Relighting … The Free-form Light Stage
Relighting · W1 + · W2 + = · W3 + … · Wn The Free-form Light Stage
· W1 + · W2 + · Wn + … Create weighted sum Relit object Illuminant direction estimation Take pictures and move hand-held light source Basis images Incident light map The Free-form Light Stage
Results 400 basis images The Free-form Light Stage
Results 400 basis images The Free-form Light Stage
Results 500 basis images The Free-form Light Stage
Results 500 basis images The Free-form Light Stage
Results 500 basis images The Free-form Light Stage
Results The Free-form Light Stage
Results The Free-form Light Stage
Augmented virtuality The Free-form Light Stage
Conclusion • Relighting real objects • Easy and cheap data acquisition • Portable • Scalable • Future work • Test BIG objects • Alternative filters • Sampling density accuracy in illuminant direction estimation • For more info: see the EGWR ’02 paper The Free-form Light Stage
Acknowledgements • Frank Suykens and Pieter Peers • Environment maps from: • http://www.debevec.org/Probes • http://www.cs.kuleuven.ac.be/~graphics • FWO Grant #G.0354.00 The Free-form Light Stage