obtaining bidirectional texture reflectance of human skin by means of a kaleidoscope jude radloff...
TRANSCRIPT
Obtaining Bidirectional Obtaining Bidirectional Texture Reflectance of Texture Reflectance of
Human Skin by means of a Human Skin by means of a Kaleidoscope Kaleidoscope
Jude RadloffJude Radloff
Supervised by Shaun Bangay and Adele LobbSupervised by Shaun Bangay and Adele Lobb
Computer Science Honours - Rhodes University17 March 2004
ContextContext
Within field of Computer Graphics Within field of Computer Graphics and Virtual Realityand Virtual Reality
VRSIGVRSIG
REALISTIC IMAGE REALISTIC IMAGE RENDERINGRENDERING
Interaction of light with a Interaction of light with a surfacesurface
Interaction of Light with a SurfaceInteraction of Light with a Surface
PolarisationPolarisationSub-surface scatteringSub-surface scattering
FluorescenceFluorescencePhosphorescencePhosphorescence
ReflectionReflectionAbsorptionAbsorption
TransmittanceTransmittance
Bidirectional Texture Function- Sufficient physical accuracy
while being manageable
Bidirectional Texture FunctionBidirectional Texture Function
BTFλ ( θi, Φi, θo, Φo, u, v )
λ = wavelength of light (colour)θi, Φi = incoming light directionθo, Φo = outgoing light directionu, v = surface position co-ordinates
Describes how the incoming light is reflected
out, relative to its position
Measuring a BTFMeasuring a BTF
Standard technique:Standard technique:
Essentially an array of cameras all Essentially an array of cameras all pointing toward surface sample from pointing toward surface sample from different directionsdifferent directions
Difficult and cumbersomeDifficult and cumbersome Resulting sample for human skin: weakResulting sample for human skin: weak
Alternative TechniqueAlternative TechniqueHan and Perlin in ACM SIGGRAPH 2003 paperHan and Perlin in ACM SIGGRAPH 2003 paper
Use of a kaleidoscopeUse of a kaleidoscope Reflections off mirrors allow surface sample to Reflections off mirrors allow surface sample to
be viewed simultaneously from many directions, be viewed simultaneously from many directions, without the camera changing positionwithout the camera changing position Effect analogous to previous techniqueEffect analogous to previous technique
Richer BTF sampleRicher BTF sample
TechniqueTechnique
Table of BTFsTable of BTFs
x: view angle
y: illumination angle
My ProcessMy Process
1. Simulate kaleidoscope – ray-tracing1. Simulate kaleidoscope – ray-tracing 2. Build kaleidoscope, using a sample 2. Build kaleidoscope, using a sample
with known BTFwith known BTF 3. Optimise configuration to3. Optimise configuration to
sample human skinsample human skin 4. Write a surface shader using the BTF 4. Write a surface shader using the BTF
information obtainedinformation obtained
Implementation DetailsImplementation Details
Simulation PhaseSimulation Phase Radiance package – ray-tracingRadiance package – ray-tracing Unix operating systemUnix operating system
Implementation PhaseImplementation Phase Front Surface MirrorsFront Surface Mirrors High transmission glassHigh transmission glass Hi-resolution cameraHi-resolution camera Non-polarised projector, eg. DLPNon-polarised projector, eg. DLP
Experimental designExperimental design
Taper angleTaper angle DimensionsDimensions Choice of regular polygon for baseChoice of regular polygon for base
Details of PaperDetails of Paper
Han, Jefferson Y. and Perlin, Ken. Han, Jefferson Y. and Perlin, Ken. Measuring Bidirectional Texture Measuring Bidirectional Texture Reflectance with a KaleidoscopeReflectance with a Kaleidoscope. In . In Proceedings of ACM SIGGRAPH 2003, Proceedings of ACM SIGGRAPH 2003, ACM Press. New York. Computer ACM Press. New York. Computer Graphics Proceedings, Annual Conference Graphics Proceedings, Annual Conference Series, ACM.Series, ACM.
http://csshaun.ict.ru.ac.za/journals/acm/http://csshaun.ict.ru.ac.za/journals/acm/SIGGRAPH/2003/paper063.pdfSIGGRAPH/2003/paper063.pdf
Questions?Questions?