shy shalom bar ilan u niversity
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1
Lior Shapira Tel Aviv University
Shy Shalom Bar Ilan University
Ariel Shamir The Interdisciplinary CenterDaniel Cohen Or Tel Aviv University
Contextual Part Analogies in 3D
Objects
H.Zhang
Presented by Dana Silverbush
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Overview Motivation
Why part analogies The whole shape method (in a glimpse) The Contextual Part Analogies Process
Partition Measure Determine distance
Results Local vs. contextual Robustness
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Motivation Why find part analogies
Analogies in a set of objects Partial match queries Instrument to carry information from one to
many (semantic information, tags, deformation, operations).
Dial dial dial dialdial dial dial dial
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Whole Shape Analogy Given q find similar s in set S Common technique:
define f() and calculate for q and S
f(q)
Sf(s)
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Whole Shape Analogy Given q find similar s in set S Common technique:
define f() and calculate for q and S Similarity: Two shape Sa, Sb, are similar if
f(Sa) is close to f(Sb) in some sense, i.e. Dist(Sa,Sb) is small.
- = ?
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Part Analogy Process Instead of using Dist(f(Sa),f(Sb) for the
whole shapes, use it on sub parts! Three main issues:
What sub-parts (segmentation)? What descriptor f()? What distance Dist(f(Sa), f(Sb))?
The process:Partition
• Test• Cluster• Smooth
Measure
• Define f()
Distance
• Dist()• Contextual distance
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Measure Through Volume The Shape Diameter Function (SDF)
Connects volume to surface Ray Shooting & Averaging
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextual
distance
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Volume Normalization
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextual
distance
for different scales
Move to log-space: enhance delicate parts
Notice the horn and the
nose separate
better
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Segmentation
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextual
distance
Fit Gaussian Mixture Model (GMM) of k Gaussians to the histogram of SDF.
Each face has a vector of length k signifying its probability to be in each cluster
Normalized SDF
faces
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Optimize Segmentation
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextual
distance
Employ an alpha expansion graph-cut algorithm to solve the k-way graph-cut
Get start segmentation
find min-cut to optimize energy
functionSwap alpha tags
GMM Smoothing
Incorporates edge length + angleProbability (face f belongs to cluster Xf)
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Compare relative size
of part
Local SDF Signature
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextual
distance
• Normalized histogram of SDF values within the part
• The size of the part as a percentage of the whole model
Compare volumetric measure
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Compare relative size
of part
Local SDF Signature
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextual
distance
• Normalized histogram of SDF values within the part
• The size of the part as a percentage of the whole model
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Not Good Enough…
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextua
l distance
• The part is not a separate shape• We want to think of it in its context.• A finger is closer to another finger than it is to a
cylinder!
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Create Hierarchy
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextua
l distance
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Create Hierarchy
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextua
l distance
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Parts Contextual Distance
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextua
l distance
Context of a part -> the path between the node representing the part, and the root of the object tree
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Parts Contextual Distance
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextua
l distance
Context of a part -> the path between the node representing the part, and the root of the object tree
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Parts Contextual Distance
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextua
l distance
Context of a part -> the path between the node representing the part, and the root of the object tree
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Parts Contextual Distance
Partition • Test• Cluster• Smooth
Measure • Define f() Distance • Dist()• Contextua
l distance
Context of a part -> the path between the node representing the part, and the root of the object tree
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RESULTS
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Advantage to context-awareness
Comparing local signature to a context-aware distance measure
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Advantage to context-awareness
Preforming part queries in several categories (human leg, armadillo leg and airplane wing)
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Robustness to K-Partitioning Five distinct partitioning were inserted,
making part hierarchy different for each model
Query the dinopet hand returns matching hand from all dinopet variants
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Robustness to K-Partitioning Five distinct partitioning were inserted,
making part hierarchy different for each model
Query the dinopet hand returns matching hand from all dinopet variants
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Analogies Between Parts
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Automatic Tagging
All results marked with a yellow diamond have already been tagged ‘head’.
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Conclusion Analogies based on parts Utilizes Shape Diameter Function (SDF) Segmentation + Distance New Contextual Distance based on
segmentation hierarchy
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Thank You!
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