24 IBLighting

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Image-Based Lighting

15-463: Computational PhotographyAlexei Efros, CMU, Fall 2005

Eirik Holmyvik

with a lot of slides

donated by Paul Debevec


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Inserting Synthetic Objects

Why does this look so bad?

Wrong camera orientation

Wrong lighting No shadows


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Solutions

Wrong Camera Orientation Estimate correct camera orientation and renender object

Use corresponding points to warp the object/scene

Only works for small warps and/or mostly planar objects

Lighting & Shadows

Estimate (eyeball) all the light sources in the scene andsimulate it in your virtual rendering

But what happens if lighting is complex?

Extended light sources, mutual illumination, etc.


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Environment Maps

Simple solution for shiny objects

Models complex lighting as a panoramic image

i.e. amount of radiance coming in from each direction

A plenoptic function!!!


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reflective surface

v r

viewer

environmenttexture image

n

projector function convertsreflection vector (x, y, z) totexture image (u, v)

Environment Mapping

Reflected ray: r=2(nv)n-v

Texture is transferred in the direction of the reflected rayfrom the environment map onto the objectWhat is in the map?


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What approximations are made?

The map should contain a view of the world with thepoint of interest on the object as the eye

We cant store a separate map for each point, so one map isused with the eye at the center of the object

Introduces distortions in the reflection, but we usually dontnotice

Distortions are minimized for a small object in a large room

The object will not reflect itself!


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Environment Maps

The environment map may take one of several forms: Cubic mapping

Spherical mapping

other

Describes the shape of the surface on which the mapresides

Determines how the map is generated and how it isindexed


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Cubic Mapping

The map resides on the surfaces of a cube around theobject

Typically, align the faces of the cube with the coordinate axes

To generate the map:

For each face of the cube, render the world from the center ofthe object with the cube face as the image plane

Rendering can be arbitrarily complex (its off-line)

To use the map:

Index the R ray into the correct cube face

Compute texture coordinates


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Cubic Map Example


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Sphere Mapping

Map lives on a sphereTo generate the map:

Render a spherical panorama from the designed center point

To use the map: Use the orientation of the R ray to index directly into the

sphere


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Example


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What about real scenes?

from Terminator 2


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Real environment maps

We can use photographs to capture environment maps The first use of panoramic mosaics

How do we deal with light sources? Sun, lights, etc? They are much much brighter than the rest of the

enviarnment

User High Dynamic Range photography, of course!

Several ways to acquire environment maps: Stitching mosaics

Fisheye lens

Mirrored Balls


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Stitching HDR mosaicsStitching HDR mosaics

http://www.gregdowning.com/HDRI/stitched/http://www.gregdowning.com/HDRI/stitched/


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Scanning Panoramic

Cameras

Scanning Panoramic

CamerasPros:

veryhigh res (10K x 7K+)Full sphere in one scan no stitching

Good dynamic range, some are HDR

Issues:

More expensive

Scans take a whileCompanies: Panoscan, Sphereon

Pros:

veryhigh res (10K x 7K+)Full sphere in one scan no stitching

Good dynamic range, some are HDR

Issues:

More expensive

Scans take a whileCompanies: Panoscan, Sphereon


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See also www.kaidan.comSee also www.kaidan.com


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Fisheye ImagesFisheye Images


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Mirrored SphereMirrored Sphere


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Sources of Mirrored BallsSources of Mirrored Balls

2-inch chrome balls ~ $20 ea.

McMaster-Carr Supply Company

www.mcmaster.com

6-12 inch large gazing balls

Bakers Lawn Ornamentswww.bakerslawnorn.com

Hollow Spheres, 2in 4in Dube Juggling Equipment

www.dube.com

FAQ on www.debevec.org/HDRShop/

2-inch chrome balls ~ $20 ea.

McMaster-Carr Supply Company

www.mcmaster.com

6-12 inch large gazing balls

Bakers Lawn Ornamentswww.bakerslawnorn.com

Hollow Spheres, 2in 4in Dube Juggling Equipment

www.dube.com

FAQ on www.debevec.org/HDRShop/


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0.340.34

0.580.58

=> 59%

Reflective

=> 59%

Reflective

Calibrating

Mirrored Sphere

Reflectivity

Calibrating

Mirrored Sphere

Reflectivity

Real World HDR Lighting Environments


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Real-World HDR Lighting Environments

Lighting Environments from the Light Probe Image Gallery:http://www.debevec.org/Probes/

Lighting Environments from the Light Probe Image Gallery:http://www.debevec.org/Probes/

FunstonBeach

UffiziGallery

EucalyptusGrove

GraceCathedral

A i i th Li ht P bAcquiring the Light Probe


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Acquiring the Light ProbeAcquiring the Light Probe

Assembling the Light ProbeAssembling the Light Probe


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Assembling the Light ProbeAssembling the Light Probe


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Not just shinyNot just shiny

We have captured a true radiancemap

We can treat it as an extended (e.g

spherical) light sourceCan use Global Illumination to

simulate light transport in the scene

So, all objects (not just shiny) canbe lighted

Whats the limitation?

We have captured a true radiancemap

We can treat it as an extended (e.g

spherical) light sourceCan use Global Illumination to

simulate light transport in the scene

So, all objects (not just shiny) canbe lighted

Whats the limitation?

Illumination ResultsIllumination Results


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Illumination ResultsIllumination Results


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Comparison: Radiance

map versus single image

Comparison: Radiance

map versus single image


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Putting it all togetherPutting it all together

Synthetic Objects+

Real light!

Synthetic Objects+

Real light!


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CG Objects Illuminated by a Traditional CGLight SourceCG Objects Illuminated by a Traditional CGLight Source


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Illuminating Objects using

Measurements of Real Light

Illuminating Objects using

Measurements of Real Light

ObjectObject

LightLight

http://radsite.lbl.gov/radiance/http://radsite.lbl.gov/radiance/

Environmentassigned glowmaterial

property inGreg WardsRADIANCE

system.

Environmentassigned glow

material

property inGreg WardsRADIANCE

system.


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Paul Debevec. A Tutorial on Image-Based Lighting. IEEEComputer Graphics and Applications, Jan/Feb 2002.Paul Debevec. A Tutorial on Image-Based Lighting. IEEEComputer Graphics and Applications, Jan/Feb 2002.


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Rendering with Natural LightRendering with Natural Light

SIGGRAPH 98 Electronic Theater


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RNL Environmentmapped onto

interior of largecube


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MOVIE!MOVIE!

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