I hope that you:I hope that you:•Looked at book & website•Checked Pre-requisites (change before Friday!)•Participate! Ask Questions! Get Inspired …

CS395: Advanced Computer CS395: Advanced Computer GraphicsGraphics

week 1:week 1: ‘5 Minute Madness’ ‘5 Minute Madness’Ben Watson watsonb@cs.northwestern.edu

Jack Tumblin jet@cs.northwestern.edu

Image-Space TechniquesImage-Space Techniques• ‘‘Image’Image’==A 2D map of light intensities from a lens==A 2D map of light intensities from a lens• ‘‘Digital Image’Digital Image’==a 2D grid of numbers (pixels)==a 2D grid of numbers (pixels)

• PROBLEMS: PROBLEMS: – What is What is betweenbetween all those points? all those points?

– WhyWhy go digital? Why is it go digital? Why is it betterbetter than film? than film?

– How can I combine the best of many pictures? Edit easily?How can I combine the best of many pictures? Edit easily?

GOAL:GOAL:– More Flexibility; let me do more than just display!

Image-Space TechniquesImage-Space TechniquesGOAL: More flexibility!GOAL: More flexibility!

• Compositing /Matte: cut-and-paste, Compositing /Matte: cut-and-paste, transparency , the ‘digital optical bench’ transparency , the ‘digital optical bench’ (Pixar`84)…(Pixar`84)…

• Warp: image as a ‘rubber sheet’, you can cut, Warp: image as a ‘rubber sheet’, you can cut, stretch, and change at willstretch, and change at will

• Environment Matte (Salesin99…)Environment Matte (Salesin99…)

• Video Textures(Schodl 2000)Video Textures(Schodl 2000)

• Polynomial Texture Map (Malzburg2001)Polynomial Texture Map (Malzburg2001)

http://grail.cs.washington.edu/projects/envmatte/

Global IlluminationGlobal IlluminationOr ‘Physically Accurate Rendering’Or ‘Physically Accurate Rendering’

• PROBLEMS: PROBLEMS: – ‘CG looks a bit weird, & needs lots of tweaking…– No Predictive Ability: can’t compute light meter #s

• GOALS:GOALS:– ‘Pixel Drawing’ Rendering from 1st principles;– ScienceScience: fundamental optical principles, invariants

Global IlluminationGlobal Illumination??Basic Physics!? ??Basic Physics!? Why isn’t this solved already?Why isn’t this solved already?

– Endlessly Bouncing Light: • Radiance Field is 5-D• The Rendering Equation (+ the math makes it look more scary than it is)

– REAL Materials are Interesting, largely unmeasured• BRDF alone is 4D, ‘spiky’, interesting

• But Light scatters WITHIN materials too!

– Computational Complexity—cleverness wanted… (naïve solutions are exponential time: O(eN))

Global IlluminationGlobal Illumination

But real surfaces are more complicated!Specular efx., etc.

Global IlluminationGlobal Illumination• Seminal Papers:Seminal Papers:

Kajiya, Goral, Hanrahan, Cohen, Rushmeier, …

• Excellent Freeware Solution: Excellent Freeware Solution: Greg Wards’ RADIANCE

• (1(1stst sub-area to struggle for relevance sub-area to struggle for relevance – (Why bother when light maps/ multitexturing on my $200

video card looks great in real time?)

• Opinion: soon other areas will hit this scrutiny)Opinion: soon other areas will hit this scrutiny)

Light Fields & Light Fields & ApproximationsApproximations

An Inspired Observation:An Inspired Observation: (at an informal ‘bull session’ at (at an informal ‘bull session’ at SIGGRAPH`94: Levoy, Hanrahan, Rushmeier, Cohen, others…)SIGGRAPH`94: Levoy, Hanrahan, Rushmeier, Cohen, others…)

• Idealized ‘Bubble of Cameras’ records all raysIdealized ‘Bubble of Cameras’ records all rays

• Any image outside bubble == subset of rays Any image outside bubble == subset of rays

…

…

Light Fields & Light Fields &

ApproximatioApproximationsns

.http://graphics.stanford.edu/projects/lightfield/.http://graphics.stanford.edu/projects/lightfield/

http://www.intel.com/research/mrl/research/lfm/http://www.intel.com/research/mrl/research/lfm/

PROBLEM:PROBLEM: – Prompt rendering dull, inaccurate result.– Poor tradeoff of interaction vs. rendering realism.

Can’t we do more than movies?

GOAL:GOAL:– Capture ALL the light leaving an object– Fast sort, re-display allows interaction.

Light Fields & Light Fields & ApproximationsApproximations

• ‘‘Lumigraph’ or ‘Light Field’ Lumigraph’ or ‘Light Field’ – Limited, practical subset of this 5-D ray set– 2-plane camera: easy way to organize the rays.– Light Field cameras possible (but tough/expensive)

– Storage efficiency is low—compression needed!– ‘Output only’; can’t change lighting effects– Tangles together light & surface efx.

Light Fields & Light Fields & ApproximationsApproximations

Light Fields & Light Fields & ApproximationsApproximations

Recent:Recent:Try to separate illumination from surface properties in the Try to separate illumination from surface properties in the

light-field data. light-field data. Univ. of Washington SIGGRAPH 2000Univ. of Washington SIGGRAPH 2000

Image-Based Modeling Image-Based Modeling & Rendering& Rendering

PROBLEM:PROBLEM:• Geometric modeling is tedious, slow, expensive• Most modeled objects exist already; • 3D laser scanning, etc. is expensive, finicky, difficult• Geom. Models almost never look as good as photos

Meanwhile: prices fall, speed & capacity rise for Digital Cameras, Displays, Memory, Desktop PCs…

!Lets use cameras to eliminate the tedium!!Lets use cameras to eliminate the tedium!

Image-Based Modeling Image-Based Modeling & Rendering& Rendering

• GOAL 1: Generalize Photography: GOAL 1: Generalize Photography: – Get MORE than light; – Estimate shape, texture, reflectance, lighting, …– A Re-thinking of pointwise 3-D scanning…

• GOAL 2: Generalize Image Viewing:GOAL 2: Generalize Image Viewing: – Interactive, movable viewpoint– ‘Reprojection: re-use already-rendered image parts

Image-Based Modeling Image-Based Modeling & Rendering& Rendering

• Seminal Papers:Seminal Papers:– McMillan`95: Plenoptic Function…– Kanade– View-based Reconstruction…– LDI Trees– Image-Based Visual Hulls (Gortler,McMillan…)

http://graphics.lcs.mit.edu/~wojciech/vh/results.html