Appearance Models for Graphics

COMS 6998-3, Lecture 1

Ravi Ramamoorthi

• This course mainly focuses on materials• But appearance depends on geometry, materials, lights

Computer Graphics Rendering

Geometry

Lighting

Materials

Rendering

ViewpointCamera

Image

Photorealistic Rendering

Materials/Lighting(Texture Reflectance[BRDF] Lighting)

Realistic input models required

Arnold Renderer: Marcos Fajardo

Rendering Algorithm

80’s,90’s: Physically based

Geometry

70’s, 80’s: Splines90’s: Range Data

One Motivation: Digital Actors

Final Fantasy

Shrek

Computer Vision Analysis

• Most algorithms assume very simple lighting, materials

Image

Lighting

Materials

Vision alg.

ViewpointCamera

Geometry

Inverse Rendering

Geometry Inverse Rend

ViewpointCamera

Lighting

• Useful for acquiring material models in graphics• Recognizing materials in vision

Materials

Material Recognition

Photographs of 4 spheres in 3 different

lighting conditions

courtesy Dror and Adelson

Complex materials

• Geometry, illumination, reflectance all important• Often scales of geometry: Continuum of geometry/reflectance

Appearance important other areas

• Physics• Materials science• Cosmetics• Building materials• Car paints• Textiles• ArtUsing computer, complex simulations doable

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

Outline

• Why appearance models?

• Examples of recent graphics images

• Approaches: Physical, structural, phenomenological methods

• Overview of course logistics

Outdoor Scenes

Deussen et al. 98

Weathering: Metallic Patinas

Dorsey and Hanrahan 96

Weathering: Flows

Dorsey and Hanrahan 96

3D Texture (CURET database)

Dana et al 97

Diffraction

Stam 99

Subsurface Scattering

Jensen et al. 2001

Hair

Marschner et al.

Approaches

• Physical: Understand basic physics

• Structural: Understand microstructure (patinas, fabrics, layered models)

• Phenomenological: Empirical

Physical example: Fresnel• Dielectrics: Increasing specularities grazing angles

• Metals: reflection changes with wavelength

Copper-colored Cook-Torrance

Fresnel functions

(Micro)Structure

Hair Fiber

CD

Plastic microfabric

Phenomenological Models

• Lambertian:

• Phong:– Really corresponds to extended light source

• Also, gaussian surfaces, splines, wavelets, Zernike polynomials, spherical harmonics, …

• BRDF itself phenomenological model

cos iB L

s s

v LB R L R V

Taxonomy of Materials

Renderman World

Plastic Metal Matte

ShinyPlastic ThinPlastic

RoughMetal

Real World?

Real World

Animal Vegetable Mineral

Skin Hair Leaves Bark Marble

Course Goals, Format

• Goal: Background and current research on appearance models in graphics and vision

Course Goals, Format

• Goal: Background and current research on appearance models in graphics and vision

• Columbia is the best place for this!!

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/

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)

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%)

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

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.

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

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

Questions?