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CS 563 Advanced Topics in Computer Graphics
by Emmanuel Agu
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Outline
Overview: about me, about class
What is photorealistic rendering?
Raytracing introduction
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Professor Background
Dr. Emmanuel Agu (professor, “Emmanuel”)Research areas
Computer Graphics (photorealistic rendering, etc)Mobile Computing (mobile graphics, cell, iPhone, etc)Wireless networking
This class: creating computer-generated photorealistic images
Ray tracing Humans (face, skin)Nature (water, trees, seashells)Animals (feathers)… etc
Research opportunitiesIndependent Study ProjectMQPMS thesesPhD theses
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Student Background
NameClass (undergrad (seniors), masters, PhD …)Full and Part-time studentProgramming experience (C, C++, java)Systems experience (Unix, windows,…)Helpful background
At least one graphics class takenSolid math skills…. Other (Physics, computer vision, image science, ???)
Students intro themselves!Important: fill in above info, say what you want from this class
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Course Prerequisites
No official prerequisiteHowever, will assume you
Can program in C/C++Have probably taken at least 1 graphics course (OpenGL?), based on raster graphics?You are fearless. can quickly pick up graphics and image processing algorithms and techniques, (lectures will briefly cover them in class as needed)have background in calculus, linear algebraCan read/understand text, research articles, fill in gapsCan program in C, learn rendering package, tools
Still have questions? See me
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Syllabus
http://www.cs.wpi.edu/~emmanuel/courses/cs563/S10/Office hours:
Wednesdays: 4:30 - 5:30Note: Please use office hours or book appointments
Questions of general interest, post on myWPIEmail me if you have specific questionsText Book: Ray tracing from the ground up plusselected papersNote: Most lectures will be based on the text. But student can supplement from papers, web
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Textbook
Ray Tracing from the ground upby Kevin Suffern
Author has experience in ray tracing
Grew out of his classes
Text Condenses lots of state-of-the art theory + code + explanation of code
Working code, more concrete
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Course Structure
GradingNo examsAbout 4 presentations each (40%)Class participation: discussions, answer questions (10%)One final rendering project, chosen by you (50%)Students will score other projects at the end. Part of grade determined by your peers
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Why This Class?
WPI graduate course requirementsMasters, PhD, grad course requirements
WPI research requirementsWant to do research in graphics (MS, PhD theses)
Work in graphicsRendering for movie studio, architectural firm, etcAnimation, etc.
HobbyistWant to build cooler stuffUnderstand more how visual effects, etc happen
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Course Objectives
Understand state-of-the-art techniques for photorealistic renderingBecome conversant with cutting edge graphics literatureHands-on exploration of one (or more) of the techniques encountered (a project). Learning and using raytracing to generate amazing pictures. Possibly extend one of the studied techniques, implement new ones
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Class Time
Two halves with 15 minutes breakEach half
50 minute presentation followed by20 minute discussion of topic(s) and questions
Commons presentation mistakesAvoid: putting too much on a slide (talk!!)Too many slides for alloted time (2-3 mins/slide)50 mins: about 20 – 25 slides
First two student presentations in two weeks time
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Presentations
I will try to guide you on how to present effectively I will be strict with time if you go too longGet right to the point (core), offer motivation & insightsCommunicate basic ideas to fellow studentsOffer a ‘roadmap’ for studying the paperLook over reading list & let me know which topics you want to presentNote: can use additional resources to build your talk. Must give credit. If not.. Cheating!!!Don’t just summarize! Find authors websites, videos, images, supplementary cool stuff
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Final Project
Implement one of the rendering techniques discussed in class, use ray tracer from textMay also use high end package to create models
MayaRendermanBlenderPovRay, etc
Must submit your final project proposal by March 31st, 2010Can get ambitious: Implement new photorealistic technique from a paperIdeas?? See Stanford rendering competitionhttp://graphics.stanford.edu/courses/cs348b-competition/
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Class resources
Where to do the projects:On your home computer, download ray tracerOn campus computer labs
Class textSupplementary books:
Physically-based rendering by Pharr and HumphreysComputer graphics using OpenGL by F.S. Hill and Kelley, 3rd
edition, Chapter 12Other books I place on reserve in CS 563 folder in library
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Outline
Overview: about me, about class
What is photorealistic rendering?
Raytracing introduction
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What is Rendering?
Create a 2D picture of a 3D worldPhotorealistic: Indistinguishable from photo
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Applications
MoviesIndustrial designArchitectureDemo productsVirtual reality (games)
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Photorealistic vs real-time rendering
• Photorealistic rendering(E.g. Ray tracing)
• Can take days to render•Used in: movies, adverts
• Raster graphics:(E.g. OpenGL, DirectX) fast: milliseconds to renderpoor image quality
Used in: games, simulators
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Photorealistic Rendering
Ingredients: Require good models forGeometry (Realistic shapes, meshes)Light source (sky, light bulb, flourescent)Volume through which light travels (smoke, fog, mist, water)Materials: Reflection/refraction at object surfaces (velvet, wood, polished, rough, smooth)Cameras: Lens and film
Old approach: Fudge it! (E.g. Phong’s shading) New approach:
study light physicsderive models, adapt equations from physics papersUse physically-based models for renderingCapture: Place cameras/equipment around real objects/phenomena and collect dataMeasure: phenomena
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Physically-based rendering
uses physics to simulate the interaction between matter and light, realism is primary goal
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Exactly What Can We Capture?1. Appearance1. Appearance
2. Geometry2. Geometry
3. Reflectance & Illumination3. Reflectance & Illumination4. Motion4. Motion
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Scanning 3D geometry
Quest for greater realism: Trend in Computer Graphics towards very large polygonal models
Projects on precise 3D scanning (Stanford, IBM,etc)
Model: David, 2 billion polygons
Courtesy: Stanford Michael Angelo 3D scanning project
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What can we model?
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Physically-based Appearance Models
Why?Sky appears blue?Wet sand appears darker than dry sand?Iridescent surfaces (CD-ROM, butterflies, hummingbird) wings) appear to have different colors when viewed in different directions ?Old and weathered surfaces appear different from new ones?Rusted surfaces appear different from un-rusted ones?
Appearance models in computer graphics and vision try to answer these questions
Using physics-based appearance models to render:Humans (face, skin)Nature (water, trees, seashells)Animals (feathers, butterflies)
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History: Geometric Aspects First
Transformation/clipping and the graphics pipeline
Evans and Sutherland
Hidden line and surface algorithmsSutherland, Sproull, Shumacker
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History: Simple Shading
Simple shading and texturingGouraud ⇒ interpolating colorsPhong ⇒ interpolating normalsBlinn, Catmull, Williams ⇒ texturing
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History: Optical Aspects Second
Reflection and texture models Cook and Torrance ⇒ BRDFPerlin ⇒ Procedural texturesCook, Perlin ⇒ Shading languages
Illumination algorithms Whitted ⇒ Ray tracingCohen, Goral, Wallace, Greenberg, Torrance
Nishita, Nakamae ⇒ RadiosityKajiya ⇒ Rendering equation
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Lighting
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Lighting Simulation
The Rendering EquationGiven a scene consisting of geometric primitives with material properties and a set of light sources, compute the illumination at each point on each surface
ChallengesPrimitives complex: lights, materials, shapesInfinite number of light paths
How to solve it?Radiosity Finite elementRay tracing Monte Carlo
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Lighting Example: Cornell Box
Hard Shadows
Caustics Indirect IlluminationSurface Color
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Lighting Example: Diffuse Reflection
Surface Color Diffuse Shading
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Lighting Example: Shadows
No Shadows Shadows
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Lighting Example: Soft Shadows
Hard ShadowsPoint Light Source
Soft ShadowsArea Light Source
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Radiosity: Indirect Illumination
Simulated
Program of Computer GraphicsCornell University
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Early Radiosity
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Early, Early Radiosity
Parry Moon and Domina Spencer (MIT), Lighting Design, 1948
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Lighting Effects: Glossy Materials
Hard Shadows Soft Shadows
Caustics Indirect Illumination
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Caustics
Jensen 1995
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Complex lighting
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Complex Indirect Illumination
Modeling: Stephen Duck; Rendering: Henrik Wann Jensen
Mies Courtyard House with Curved Elements
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Radiosity: “Turing Test”
Measured Simulated
Program of Computer GraphicsCornell University
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Materials
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Plastic
Classic Computer Graphics Model
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Brushed Copper
Classic Computer Graphics Model
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Material Taxonomy
PlasticShiny Plastic
Rough MetalShiny Metal
Matte
From Apodaca and Gritz, Advanced RenderMan
RenderMan
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Shadows on Rough Surfaces
Without self-shadowing With self-shadowing
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Translucency
Surface Reflection Subsurface Reflection
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Translucent objects
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Water Flows on the Venus
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Patinas
A Sense of TIme
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Final FantasySquareUSA
Virtual Actors: Faces
Jensen,Marschner,Levoy,Hanrahan
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Virtual Actors: Hair
Black Brown
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Refraction/dispersion
Iridescent: Wavelength-dependent phenomena
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Coupling Modeling & Rendering
Fedkiw, Stam, Jensen 2001
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Clouds and Atmospheric Phenomena
7am
9am
6:30pm
Hogum MountainSunrise and sunset
Modeling: Simon PremozeWilliam Thompson
Rendering: Henrik Wann Jensen
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Vegetation
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Texture and complex materials
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Outline
Overview: about me, about class
What is photorealistic rendering?
Introduction to Raytracing
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Introduction to ray tracing
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Ray Casting (Appel, 1968)
View point (eye)
Virtual Screen
Light source
Objects to Ray trace
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Ray Casting (Appel, 1968)
Case A Case B
1. Build ray2. Cast ray into scene through pixel
tdireyetrtdirectionoriginray
rc+=+=
)()(
Case A: Hits no objects (background)Case B: Hits at least one object
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Ray Casting (Appel, 1968)
( ) ( )( )∑=
⋅+⋅+nls
i
nisidiaa VRkNLkIIk
1
1. Ray hits object, build secondary ray to light source2. Evaluate shading at hit point
Question: What if secondary ray hits another object before light source?
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Secondary Ray hits object
First Intersection point in the shadow of the second object
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Ray Casting (Appel, 1968)
direct illumination
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Recursive ray tracing (Whitted, 1980)
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Reflected Ray
When a ray hits an object, a reflected ray is generated which istested against all of the objects in the scene.
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Reflection: Contribution from reflected ray
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Transparency
If intersected object is transparent, transmitted ray is generated and tested against all the objects in the scene.
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Transparency: Contribution from transmitted ray
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Reflected rays can generate other reflected rays that can generate other reflected rays, etc.
Case A: Scene with no reflection rays
Reflected Ray: Recursion
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Case B: Scene with one layer of reflection
Reflected Ray: Recursion
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Case C: Scene with two layers of reflection
Reflected Ray: Recursion
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Recursive ray tracing creates tree of rays
Reflective and/or transmitted rays are continually generated until ray leaves the scene without hitting any object or a preset recursion level has been reached.
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Ray tracer components
CamerasFilmsLightsRay-object intersectionVisibilitySurface scatteringRecursive ray tracing
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Why Ray Tracing Looks Fake/Effects
Jagged edgesHard shadowsEverything in focusObjects completely stillSurfaces perfectly shinyGlass perfectly clear
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Why Ray Tracing Looks Fake
Distributed Ray TracingRob Cook, SIGGRAPH 84Replace single ray with distribution of raysNot just fat ray through pixel, but fat rays everywhereCast Multiple
Eye raysShadow rays
Reflection raysRefraction rays
SupersamplingCast multiple rays from eye through different parts of same pixel
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Why Ray Tracing Looks Fake
Motion blurCast multiple rays from eye through same point in each pixelEach of these rays intersects the scene at a different timeReconstruction filter controls shutter speed, length
Depth of FieldBetter simulation of camera model
f-stopfocus
Others (soft shadow, glossy, etc)
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Photon Mapping
Jensen EGRW 95, 96Simulates the transport of individual photonsTwo parts. First
Photons emitted from sourcePhotons deposited on surfaces
Secondly:Photons reflected from surfaces to other surfacesPhotons collected by rendering
Good for:Light through waterCloud illuminationMarble
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Rendering Techniques
Photon mapping examples
Images: courtesy of Stanford rendering contest
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Final words: To do
Before next classRead chapters 1 – 4 of textMany concepts familiar to CS 543 studentsIf you did not take CS 543 with me, skim
Ray tracing chapter: F.S Hill, “Computer Graphics Using OpenGL”, 2nd edition, Prentice Hall, 2000
Homework 0Download and install class ray tracerRun several examples
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References/Shamelessly stolen
Pat Hanrahan, CS 348B, Spring 2005 class slidesYung-Yu Chuang, Image Synthesis, class slides, National Taiwan University, Fall 2005Kutulakos K, CSC 2530H: Visual Modeling, course slidesUIUC CS 319, Advanced Computer Graphics Course slideshttp://www.siggraph.org/education/materials/HyperGraph/raytrace/rtrace0.htm