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Obtaining Bidirectional Texture Reflectance of Human Skin by means of a Kaleidoscope

Computer Science Honours - Rhodes University 17 March 2004. Obtaining Bidirectional Texture Reflectance of Human Skin by means of a Kaleidoscope. Jude Radloff Supervised by Shaun Bangay and Adele Lobb. Context. Within field of Computer Graphics and Virtual Reality VRSIG

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Obtaining Bidirectional Texture Reflectance of Human Skin by means of a Kaleidoscope

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  1. Computer Science Honours - Rhodes University 17 March 2004 Obtaining Bidirectional Texture Reflectance of Human Skin by means of a Kaleidoscope Jude Radloff Supervised by Shaun Bangay and Adele Lobb

  2. Context • Within field of Computer Graphics and Virtual Reality • VRSIG REALISTIC IMAGE RENDERING

  3. Interaction of light with a surface

  4. Interaction of Light with a Surface Polarisation Sub-surface scattering Fluorescence Phosphorescence Reflection Absorption Transmittance • Bidirectional Texture Function • Sufficient physical accuracy • while being manageable

  5. Bidirectional Texture Function BTFλ ( θi, Φi, θo, Φo, u, v ) • λ = wavelength of light (colour) • θi, Φi = incoming light direction • θo, Φo = outgoing light direction • u, v = surface position co-ordinates Describes how the incoming light is reflected out, relative to its position

  6. Measuring a BTF Standard technique: • Essentially an array of cameras all pointing toward surface sample from different directions • Difficult and cumbersome • Resulting sample for human skin: weak

  7. Alternative Technique Han and Perlin in ACM SIGGRAPH 2003 paper • Use of a kaleidoscope • Reflections off mirrors allow surface sample to be viewed simultaneously from many directions, without the camera changing position • Effect analogous to previous technique • Richer BTF sample

  8. Technique

  9. Table of BTFs x: view angle y: illumination angle

  10. My Process • 1. Simulate kaleidoscope – ray-tracing • 2. Build kaleidoscope, using a sample with known BTF • 3. Optimise configuration to sample human skin • 4. Write a surface shader using the BTF information obtained

  11. Implementation Details Simulation Phase • Radiance package – ray-tracing • Unix operating system Implementation Phase • Front Surface Mirrors • High transmission glass • Hi-resolution camera • Non-polarised projector, eg. DLP

  12. Experimental design • Taper angle • Dimensions • Choice of regular polygon for base

  13. Details of Paper • Han, Jefferson Y. and Perlin, Ken. Measuring Bidirectional Texture Reflectance with a Kaleidoscope. In Proceedings of ACM SIGGRAPH 2003, ACM Press. New York. Computer Graphics Proceedings, Annual Conference Series, ACM. • http://csshaun.ict.ru.ac.za/journals/acm/ SIGGRAPH/2003/paper063.pdf

  14. Questions?

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