ImageBased Rendering

1
Image-Based Rendering

• Part III
• Image/Geometry Hybrid
• for Architecture

2
Introduction

• Slides mostly about Debevec SIGGRAPH 1996 paper
• Similar work done in photogrammetry community.

3
Methodology

• Small number of photographs
• Build blocks model
• Establish edge correspondences
• Reconstruct via minimization of error
• View-dependent texture mapping
• Stereo correspondence for details

4
Example of Façade
Image
Model
Image Model
New View
5
Blocks Model

• Simple polyhedra
• Size shape defined
• by a few parameters
• Relations
• Rotation and Translation
• Can be constrained (ex. one block right on top of
  another, rotation about one axis only).

6
Why Blocks?

• Good for architecture
• High level
• Explicit surfaces
• Few parameters for minimization process
• 33 variables for tower example

7
Reconstruction

• Minimize total error
• Sum of distances between model and image edges (l
  is length of edge)

8
Initial Guess (to avoid local min)

• Estimate camera rotation
• Use vertical horizontal edges of buildings
• Estimate single camera position
• Then run complete optimization
• Run times are short (minutes).

9
Images with edges marked
10
Model
11
Novel View
12
View-Dependent Texture Mapping

• Tries to do better than picture on a box
• Use multiple images
• If there is only one that hits a pixel, use it
• If there are more, blend (based on view angle)
  nearest
• Avoids visible seams by decreasing weights near
  image boundaries
• Bad objects (like cars) painted out hole fill

13
Image Only
14
Model-Based Stereopsis

• Use stereo to measure deviation from model
• Correlation
• Epipolar constraint

15
Similar Products

• Canoma
• http//www.metacreations.com/products/canoma/
• http//www.tilenut.com/canoma/index.html
• Geometra
• http//www.geometra-3d.com/geometra.htm
• Demo available
• PhotoModeler
• http//www.photomodeler.com
• Free Lite version

16
References

• Debevec, Paul E.,Taylor, C.J.,and Malik, J.
  Modeling and rendering architecture from
  photographs A hybrid geometry- and image-based
  approach. SIGGRAPH 96
• Paul Debevecs home page
• http//www.cs.berkeley.edu/debevec/
• Descriptions of several models