CS 563 Advanced Topics in Computer Graphics Introduction To IBR

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CS 563 Advanced Topics in Computer
GraphicsIntroduction To IBR

• By Cliff Lindsay

Slide Show 99 Siggraph6
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What Is IBR?

• IBR
• Multidisciplinary field that includes computer
  vision and graphics
• Techniques that replace and/or augment polygon
  models
• Primary data pre-rendered images and photographs
  as input

The Rendering Spectrum 3
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Where Did IBR Come From?

• Photo-realism
• Modeling ability has been stifled by rendering
  advancements
• Availability of inexpensive digital image
  acquisition hardware
• Recent graphics accelerators trends
• Necessity to render object that cant be rendered
  using polygons

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Tenants and Common Techniques of IBR

• Rendering time is decoupled from scene complexity
• Images are used as input
• Exploits coherence
• Pre-calculation of scene data/images

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Computer Vision ? Computer Graphics IBR.

• Combining CG and Computer Vision
• Vision Technology Lacks robust Algorithms
• The Graphics Industry Needs better modelling

Siggraph 99 Course on Image-based Rendering6
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How Does IBR Compare to Traditional Rendering?

• Image Warping Vs. Matrix Transformations
• Perspective Division Vs. Projective Normalization
• What the !_at_ Is A Splat Kernel?

1 Image from Leonard McMillan
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Approaches

• 2D Approaches
• Texture Mapping
• Sprite, Billboards, and Impostors
• Image Layering
• 3D approaches
• LDI (2.5D)
• View Interpolation Morphing
• Mosaics
• 4D approaches
• The Lumigraph
• Light Fields

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Texturing Mapping

• Texture Space (u,v) ? 3D Object Space (x0, y0,
  z0) ? Screen Space (x, y) 5
• Texture mapping has close ties to Image Warping
• Wide Industry Support (hardware and Software)
• Filtering

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Sprites, Billboards, and Impostors (Oh my!)

• Sprites
• Pure 2D image
• No warping, or projection (like mouse cursor)
• Billboards
• Sprite applied to a polygon
• Alpha channel usually employed
• Uses texture mapping for acceleration
• Impostors
• Billboards created on the fly.
• Can represent complex models
• Error metric associated w/ changed views

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Billboards

• Billboards
• Oriented toward viewer
• Matrix transformations (classical pipeline)
• Special effects (lens flares, laser/light bursts,
  etc)
• Hard to render objects (clouds, fire, smoke)

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Impostors

• Impostor Techniques
• Error Angle
• Off Screen Rendering
• Polygon Texturing
• Texture resolution need not exceed screen
  resolution
• texres screenres objsize/(2 distance
  tan(fov/2))

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Billboard Example
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Billboard Example
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Lumigraph/Light Fields 0

• Plenoptic function
• An image is a collection of radiance values a
  long a ray.
• Radiance value for all possible rays Plenoptic
  function
• 4D (for our purpose)

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Lumigraph/Light Fields 1

• Represent an object by its extents
• Each point on a cube has multiple rays eminating.
• Each wall has 2 planes (12 planes make a cube)

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Lumigraph/Light Fields 2

• You parameterize a ray using the 2 planes
• L(s, t, u, v) radiance for a ray
• Ray plane intersection make it easy and fast

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Lumigraph/Light Fields 3

• Sample of the objects on the plane are not
  continuos
• Gaps are Created

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Lumigraph/Light Fields 4

• Continuos luminance is a linear sum
• B basis function for which we can calculate at
  grid points
• If we use a constant value, the coefficient take
  on the values of the grid points

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Lumigraph/Light Fields 5
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Lumigraph/Light Fields 6

• Example Rendering

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View Interpolation
View Morphing - more to come next presentation!
Reference Image 1
Reference Image 2
Corresponding Pixels
Morph maps
Based on diagrams from Watt8
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View Morphing
View Morphing - more to come next presentation!
View Morphing9
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View Morphing
View Morphing - more to come next presentation!
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View Morphing9
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Recent Developments The Future of IBR

• Surface Light fields
• High Dynamic Range Radiance Maps
• View-dependent texture-mapping (VDTM)
• IBO (Image Based Objects)

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Conclusion

• Rendering time is decoupled from scene complexity
• Images are used as input
• Pre-calculation of scene data/images

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Additional Resources

• http//citeseer.nj.nec.com/cs - NEC Digital
  Library
• http//www.siggraph.org
• http//www.debevec.org/ (View Morphing, High
  Dynamic Range Radiance Maps, Projective
  Texture-Mapping)
• http//www-2.cs.cmu.edu/7Eph/869/www/misc.html
  (a cool site with a bunch of IBR links)
• http//www.peter-oel.de/ibmr-focus/ (Another cool
  site)

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References

• 1 McMillan, Leonard, An Image-Based Approach
  to Three-Dimensional Computer Graphics , ,
  http//graphics.laces.mitt.edu/mcmillan/IBRwork/d
  efense23.html, date unknown, Cited slide 6.
• 2 McMillan, Leonard, Gortler, Steven,
  Applications of Computer Vision to Computer
  Graphics, ACM Siggraph, Vol. 33 no. 4, Nov. 99
• 3 Akenine-Moller, Tomas, Haines, Eric,
  Real-Time Rendering, 2nd Edition, A K Peters,
  2002
• 4 Watt, Alan, 3D Computer Games,
  Addison-Wesley Pub Co, Volume 1, 2nd edition,
  1999
• 5 Heckbert, Paul S., Survey of Texture
  Mapping, IEEE Computer Graphics Applications,
  Cited slide 10, November 1986,
• 6 Cohen, Michael, Course on Image-based,
  Modeling, Rendering, and Lighting, Siggraph 99
• 7 Mcmillian, Leonard, Bishop, Gary, Plenoptic
  Modeling An Image-Based Rendering System,
  Proceedings of SIGGRAPH 95, (Los Angeles, CA
  August 6-11, 1995), pp. 39-46
• 8 Watt, Alan, 3D Computer Graphics,
  Addison-Wesley Pub Co, 3nd edition (),
• 2000
• 9 Chen, S.E., Williams L., View Interpolation
  for Image Synthesis, ACM Siggraph 95
• 10Gortler, S, Cohen, M, Girzesczuk, R,
  Szeliski, R, The Lumigraph, ACM Siggraph, 1996