Semi-Automatic Topology Semi-Automatic Topology Independent Contour-Based 2 Independent Contour-Based 2

1/2 D Segmentation Using 1/2 D Segmentation Using Live-Wire Live-Wire

Michael KnappMichael Knapp, Armin Kanitsar and , Armin Kanitsar and Meister Eduard GröllerMeister Eduard Gröller

Computer Graphics GroupComputer Graphics Group

Vienna University of TechnologyVienna University of Technology

2 / 14WSCG 2004 - Michael Knapp: Contour-Based 2 ½ D Segmentation using Live-Wire

OverviewOverview

MotivationMotivation Live-WireLive-Wire Segmentation Segmentation

Process Process Cross-SectionsCross-Sections Surface Surface

ReconstructionReconstruction ResultsResults

3 / 14WSCG 2004 - Michael Knapp: Contour-Based 2 ½ D Segmentation using Live-Wire

MotivationMotivation

Segmententation of Segmententation of objects with ...objects with ...

homogeneous contourhomogeneous contour inhomogeneous internal inhomogeneous internal

structurestructure

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Live-WireLive-Wire

Interactive contourInteractive contour

finding methodfinding method Fixed start pointFixed start point Interactively Interactively

moveable moveable end pointend point

Calculation of Calculation of lowest cost pathlowest cost path

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Segmentation Process Segmentation Process OverviewOverview

1.1. Selection of orthogonal cross Selection of orthogonal cross sectionssections

2.2. Manual contour tracingManual contour tracing

3.3. Automatic reconstruction of the Automatic reconstruction of the object surfaceobject surface

4.4. Visualization Visualization

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Segmentation Process (1/2)Segmentation Process (1/2)

The user defines a set of cross-sections The user defines a set of cross-sections through the object and traces the contours through the object and traces the contours

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Segmentation Process (2/2)Segmentation Process (2/2)

The surface is reconstructed from the The surface is reconstructed from the traced contours traced contours

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Surface Reconstruction (1/4)Surface Reconstruction (1/4)

A

BD

EF

C

2.

Create connectivity graph for each slice ...

1.

A

BC

D

EF

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Surface Reconstruction (2/4)Surface Reconstruction (2/4)

Edges are sorted by Edges are sorted by angle around the angle around the centercenter of each area. Every of each area. Every area is convex.area is convex.

Every secondEvery second outgoing outgoing edgeedge - beginning from - beginning from the the incoming edgeincoming edge – is – is evaluated: The edge evaluated: The edge with the lowest average with the lowest average cost per pixel is cost per pixel is selected as successor.selected as successor.

10 / 14WSCG 2004 - Michael Knapp: Contour-Based 2 ½ D Segmentation using Live-Wire

Surface Reconstruction (3/4)Surface Reconstruction (3/4)

The cThe connectivity graphonnectivity graph is an Eulerian graph: is an Eulerian graph: All vertices have an even number of All vertices have an even number of

adjacent edgesadjacent edges Graph contains a closed path containing Graph contains a closed path containing

each edges exactly onceeach edges exactly once Successor selection heuristics avoids Successor selection heuristics avoids

crossing pathscrossing paths Graph can always be decomposited into Graph can always be decomposited into

non-crossing closed pathscircuits.non-crossing closed pathscircuits.

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Surface Reconstruction (4/4)Surface Reconstruction (4/4)

A

BC

D

EF

FA

BD

E

C

... and reconstruct the outline

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Threshold (1400) Contour-Based

Results (1/2)Results (1/2)

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Results (2/2)Results (2/2)

Threshold

Region growing

Our method

14 / 14WSCG 2004 - Michael Knapp: Contour-Based 2 ½ D Segmentation using Live-Wire

Thank You for Thank You for Your Attention !Your Attention !