Announcements
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Project 3 grades out today,
write-ups online asap |
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Project 4 extension: Thurs, 11:59pm |
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Multiview stereo
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Readings |
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S. M. Seitz and C. R. Dyer, Photorealistic
Scene Reconstruction by Voxel Coloring, International Journal of Computer
Vision, 35(2), 1999, pp. 151-173. |
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http://www.cs.washington.edu/homes/seitz/papers/ijcv99.pdf |
Choosing the stereo
baseline
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What’s the optimal baseline? |
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Too small: large depth error |
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Too large: difficult search problem |
The Effect of Baseline on
Depth Estimation
Slide 5
Slide 6
Multibaseline Stereo
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Basic Approach |
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Choose a reference view |
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Use your favorite stereo
algorithm BUT |
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replace two-view SSD with SSD
over all baselines |
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Limitations |
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Must choose a reference view
(bad) |
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Visibility! |
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CMU’s 3D Room Video |
The visibility problem
Volumetric stereo
Discrete
formulation: Voxel Coloring
Complexity and
computability
Issues
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Theoretical Questions |
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Identify class of all
photo-consistent scenes |
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Practical Questions |
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How do we compute
photo-consistent models? |
Slide 13
Reconstruction from
Silhouettes (C = 2)
Volume intersection
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Reconstruction Contains the
True Scene |
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But is generally not the same |
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In the limit (all views) get visual
hull |
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Complement of all lines that
don’t intersect S |
Voxel algorithm for
volume intersection
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Color voxel black if on
silhouette in every image |
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for M images, N3 voxels |
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Don’t have to search 2N3
possible scenes! |
Properties of Volume
Intersection
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Pros |
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Easy to implement, fast |
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Accelerated via octrees
[Szeliski 1993] or interval techniques [Matusik 2000] |
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Cons |
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No concavities |
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Reconstruction is not
photo-consistent |
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Requires identification of
silhouettes |
Slide 18
Voxel Coloring Approach
Depth Ordering: visit occluders first!
Panoramic Depth Ordering
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Cameras oriented in many
different directions |
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Planar depth ordering does not
apply |
Panoramic Depth Ordering
Panoramic Layering
Panoramic Layering
Compatible Camera
Configurations
Calibrated Image
Acquisition
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Calibrated Turntable |
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360° rotation (21 images) |
Voxel Coloring Results
(Video)
Limitations of Depth
Ordering
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A view-independent depth order
may not exist |
Slide 29
Space Carving Algorithm
Which shape do you get?
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The Photo Hull is the UNION of
all photo-consistent scenes in V |
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It is a photo-consistent scene
reconstruction |
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Tightest possible bound on the
true scene |
Space Carving Algorithm
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The Basic Algorithm is Unwieldy |
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Complex update procedure |
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Alternative: Multi-Pass Plane Sweep |
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Efficient, can use
texture-mapping hardware |
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Converges quickly in practice |
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Easy to implement |
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Multi-Pass Plane Sweep
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Sweep plane in each of 6
principle directions |
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Consider cameras on only one
side of plane |
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Repeat until convergence |
Multi-Pass Plane Sweep
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Sweep plane in each of 6
principle directions |
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Consider cameras on only one
side of plane |
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Repeat until convergence |
Multi-Pass Plane Sweep
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Sweep plane in each of 6
principle directions |
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Consider cameras on only one
side of plane |
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Repeat until convergence |
Multi-Pass Plane Sweep
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Sweep plane in each of 6
principle directions |
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Consider cameras on only one
side of plane |
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Repeat until convergence |
Multi-Pass Plane Sweep
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Sweep plane in each of 6
principle directions |
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Consider cameras on only one
side of plane |
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Repeat until convergence |
Multi-Pass Plane Sweep
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Sweep plane in each of 6
principle directions |
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Consider cameras on only one
side of plane |
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Repeat until convergence |
Space Carving
Results: African Violet
Space Carving
Results: Hand
Other Approaches