Appearance Models for Graphics

1. Appearance Models for Graphics COMS 6998-3, Lecture 1 Ravi Ramamoorthi

2. This course mainly focuses on materials • But appearance depends on geometry, materials, lights Computer Graphics Rendering Geometry Lighting Rendering Image Materials Viewpoint Camera

3. Geometry 70’s, 80’s: Splines 90’s: Range Data Rendering Algorithm 80’s,90’s: Physically based Materials/Lighting (Texture Reflectance[BRDF] Lighting) Realistic input models required Arnold Renderer: Marcos Fajardo Photorealistic Rendering

4. One Motivation: Digital Actors Final Fantasy Shrek

5. Computer Vision Analysis Image Lighting Vision alg. Geometry Materials Viewpoint Camera • Most algorithms assume very simple lighting, materials

6. Materials Inverse Rendering Lighting Geometry Inverse Rend Viewpoint Camera • Useful for acquiring material models in graphics • Recognizing materials in vision

7. Material Recognition Photographs of 4 spheres in 3 different lighting conditions courtesy Dror and Adelson

8. Complex materials • Geometry, illumination, reflectance all important • Often scales of geometry: Continuum of geometry/reflectance

9. Appearance important other areas • Physics • Materials science • Cosmetics • Building materials • Car paints • Textiles • Art Using computer, complex simulations doable

10. Topics • Modeling how light interacts with matter • Measurement/acquisition of materials • Image-based modeling and rendering • Analytic methods • Real-time rendering • Focus mainly on computational methods

11. Outline • Why appearance models? • Examples of recent graphics images • Approaches: Physical, structural, phenomenological methods • Overview of course logistics

12. Outdoor Scenes Deussen et al. 98

13. Weathering: Metallic Patinas Dorsey and Hanrahan 96

14. Weathering: Flows Dorsey and Hanrahan 96

15. 3D Texture (CURET database) Dana et al 97

16. Diffraction Stam 99

17. Subsurface Scattering Jensen et al. 2001

18. Hair Marschner et al.

19. Approaches • Physical: Understand basic physics • Structural: Understand microstructure (patinas, fabrics, layered models) • Phenomenological: Empirical

20. Physical example: Fresnel • Dielectrics: Increasing specularities grazing angles • Metals: reflection changes with wavelength Copper-colored Cook-Torrance

21. Fresnel functions

22. (Micro)Structure CD Hair Fiber Plastic microfabric

23. Phenomenological Models • Lambertian: • Phong: • Really corresponds to extended light source • Also, gaussian surfaces, splines, wavelets, Zernike polynomials, spherical harmonics, … • BRDF itself phenomenological model

24. Taxonomy of Materials Renderman World Plastic Metal Matte ShinyPlastic ThinPlastic RoughMetal

25. Real World? Real World Animal Vegetable Mineral Skin Hair Leaves Bark Marble

26. Course Goals, Format • Goal: Background and current research on appearance models in graphics and vision

27. Course Goals, Format • Goal: Background and current research on appearance models in graphics and vision • Columbia is the best place for this!!

28. Course Goals, Format • Goal: Background and current research on appearance models in graphics and vision • Columbia is the best place for this!! • Format: Alternate lectures, student presentations of papers • http://www.cs.columbia.edu/~ravir/6998/

29. Course Logistics • No textbooks. Required readings are papers available online (except 3 handouts today) • Office hours: before class. My contact info is on my webpage: http://www.cs.columbia.edu/~ravir • Will (almost certainly) count for PhD elective breadth in graphics/HCI (if taken on grades)

30. Requirements • Pass-Fail • Show up to class regularly • Present 1 (maybe 2) paper(s) • Prefer you do this rather than just sit in • Grades • Attend class, participate in discussions (10%) • Present 2 (maybe 3) papers (30%) • Project (60%)

31. Project • Wide flexibility if related to course (some ideas off main course webpage). Can be done in groups of 2-3 • Implementation/extension of one of the papers • Modeling of challenging natural object • Theoretical analysis/extension/verification • Best projects will go beyond simple implementation (try something new, some extensions) • Alternative (less desirable): Summary of 3 or more papers in an area • Best projects will explore links/framework not discussed by authors, and suggest future research directions

32. Prerequisites • Strong interest in graphics (and vision) • Computer graphics experience (4160) • What if lacking prerequisites? Next slide • Course will move quickly • Covering recent and current active research • Some material quite technical • Assume some basic knowledge • Many topics. Needn’t fully follow each one, but doing so will be most rewarding.

33. If in doubt/Lack prerequisites • Material is deep, not broad • May be able to pick up background quickly • Course requirements need you to really fully understand only one/two areas (topics) • But if completely lost, won’t be much fun • If in doubt, see if you can more or less follow some of papers after background reading • Ultimately, your call

34. Assignment this week • E-mail me (ravir@cs) • Name, e-mail, status (Senior, PhD etc.) • Will you be taking course grades or P/F • Background in graphics/any special comments • Optional: Papers you’d like to present FCFS • Paper presenters for next week [You (may) get a one-paper reduction in load] • Oren-Nayar, Torrance-Sparrow, Koenderink-van Doorn

35. Questions?