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Statistical and numerical techniques for photorealistic image synthesis

Statistical and numerical techniques for photorealistic image synthesis. Kartic Subr. Who am I?. Born in India Bangalore University (Bachelor of Engineering) 2001 Hewlett Packard, India/Singapore 6 years in USA PhD , University of California Irvine, 2008

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Statistical and numerical techniques for photorealistic image synthesis

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  1. Statistical and numerical techniquesfor photorealistic image synthesis Kartic Subr

  2. Who am I? • Born in India • Bangalore University (Bachelor of Engineering) 2001 • Hewlett Packard, India/Singapore • 6 years in USA • PhD, University of California Irvine, 2008 • Advisor: Jim Arvo (PhD Yale University), pioneered methods in light transport • 2 years in France • Post doctoral researcher, ARTIS, INRIA-Grenoble (2008-2010)

  3. My goal: Generating realistic visuals Gustave Courbet, Stone-Breakers, 1849. Realism in art Wilhelm Oswald Gustav Achenbach, Abendstimmung in der Campagna, 1850.

  4. My goal: Generating realistic visuals Photograph: Nicéphore Niépce, 1826 Gustave Courbet, Stone-Breakers, 1849. Realism in art Wilhelm Oswald Gustav Achenbach, Abendstimmung in der Campagna, 1850.

  5. Notion of “realism” depends on technology Pedro Campos Gerhard Richter, 1983 Hyperrealism

  6. Realistic image synthesis

  7. Image ? Image synthesis involves light transport Light sources Digital models of scene (geometry + materials) Virtual camera

  8. Image synthesis adds visual impact Digital model Captured video + digital model Avatar

  9. Applications of image synthesis Entertainment Advertising Virtual prototyping Defense Biomedical imaging

  10. Multidisciplinary nature of the problem • Physically based optical simulations • Mathematical tools for analysis • Numerical techniques for light transport solution • Understanding biological processes eg. Perception et cognition

  11. Reflection of light is an integration

  12. Light transport: multi-domain integration • Combinatorial explosion from sampling each domain Exposure time Image space Aperture Visible spectrum Reflectance Direct illumination Indirect illumination [Efficient sampling strategies for Monte Carlo integration (my PhD thesis)]

  13. Talk outline • Recent contributions • Simulating defocus • Rendering translucent materials • Research plan • Core problems in image synthesis • Model representation and abstraction

  14. My contributions: Fourier depth of field

  15. Defocus blur is important in photography

  16. Defocus is due to aperture integraion Lens Aperture Image Pixel p

  17. Defocus Pixel p Lens Aperture Scene Image Pixel p

  18. Monte Carlo estimation of aperture integral NA primary rays per pixel Aperture Image Integrate at p

  19. Aperture integration is very costly NP x NA Primary rays Image Aperture NP pixels NA Aperture samples

  20. Paradox: Blurry image is costlier to compute! 64 x #primary rays of the pinhole image

  21. Observation 1: Image Blurry regions should not require dense sampling of the image

  22. Observation 2: Lens Regions in focus should notrequire profuse sampling of the lens for diffuse objects

  23. Fourier depth of field • Fourier domain analysis of finite aperture cameras • Adaptive sampling • Speedup of around 20 over existing algorithms [ACM Transactions on Graphics 2009. Presented at ACM SIGGRAPH 09] Collaborators: MIT

  24. My contributions: Translucent materials

  25. Translucency: Sub-surface scattering Opaque Translucent • Brute force Monte Carlo: prohibitively expensive • Diffusion approximations: severe constraints on geometry

  26. Finite difference method on new domain • Approximation: diffusion equation • Domain: Dual graph of tetrahedralization Diffuse flux

  27. Rendering translucent materials • Arbitrary geometry • Heterogenous materials • Dynamically deforming shapes • In real-time! [Computer Graphics Forum 2010. To be presented at Eurographics 2010] [Collaborators: Microsoft Research, Tsinghua University]

  28. Research program Model representation and abstraction Realistic image synthesis

  29. 1. Realistic image synthesis • Bandwidth driven sampling • Transport of local light field spectrum • Derive spatial / angular sampling rates • co-advising PhD student Laurent Belcour (ARTIS) • Importance vs radiance • Tracing from eye vs tracing from light • Monte Carlo matrix chain multiplication Short-term Long-term

  30. Importance vs radiance Radiance

  31. Importance vs radiance Importance

  32. Importance vs radiance

  33. MC matrix-chain product estimator

  34. MC matrix-chain product estimator Related to optimal matrix chain multiplication using dynamic programming?

  35. 2. Model representation and abstraction • Abstracting detail in geometry • First step: images (published at SIGGRAPH Asia 09) • Alternate representation • Voxel data to represent geometry and materials Short-term Long-term

  36. Detail = oscillations between extrema Local maxima Input Local minima

  37. Image multiscale decomposition 1D Intensity Input Fine + Medium + Coarse Pixels

  38. Allows smoothing high-contrast detail Input Smoothed

  39. Thank you! • Collaborators • Established • MIT, USA • Microsoft Research • Tsinghua University, China • University of California, Irvine • Current • Cornell University, USA • University of California, Berkeley • Potential • Indian Institute of Information Technology • International journal publications • Computer Graphics Forum 2010: Translucent materials. 4th author of 6 • TOG 2009: Multiscale image decomposition. 1st author of 3 • TOG 2009: Fourier Depth of Field. 2nd author out of 5 • Refereed international conference papers • Pacific Graphics 2007: Statistical hypotheses. 1st author of 2 • Interactive raytracing 2007: Steerable importance sampling. 1st author of 2 • ICIAP 2005: Contrast enhancement. 1st author of 3

  40. Merci ! • Collaborators • Established • MIT, USA • Microsoft Research • Tsinghua University, China • University of California, Irvine • LJK Grenoble • Current • Cornell University, USA • University of California, Berkeley • Potential • Indian Institute of Information Technology • International journal publications • Computer Graphics Forum 2010: Translucent materials. 4th author of 6 • TOG 2009: Multiscale image decomposition. 1st author of 3 • TOG 2009: Fourier Depth of Field. 2nd author out of 5 • Refereed international conference papers • Pacific Graphics 2007: Statistical hypotheses. 1st author of 2 • Interactive raytracing 2007: Steerable importance sampling. 1st author of 2 • ICIAP 2005: Contrast enhancement. 1st author of 3 • Teaching • Columbia University, USA (120 h) • University of California, Irvine (360 h) • Industry • Rhythm and Hues Studios • NVIDIA Corporation • Hewlett Packard

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