Boundary Extraction in Natural Images Using Ultrametric Contour Maps Pablo Arbeláez Université Paris Dauphine Presented by Derek Hoiem
What is segmentation?
Segmentation is a result
What is segmentation? Segmentation is a result Segmentation is a process Woman Face
What is segmentation? Segmentation is a result Segmentation is a process Segmentation is a guide
Segmentation as a Guide Multiple Segmentations
Segmentation as a Guide Multiple Segmentations Hierarchy of Segmentations
Key Concepts/Contributions Hierarchical segmentation by iterative merging Ultrametric dissimilarities Thorough evaluation on BSDS
Hierarchical Segmentation λ 3 Region ImageDendrogram Contour Image
Ultrametric Contour Map Ultrametric –Definition: D(x,y) <= max{ D(x,z), D(z,y) } The union R 12 of two regions R 1 and R 2 must have >= distance to adjacent region R 3 than either R 1 or R 2 λ
Ultrametric Contour Map
Region Dissimilarity 1.D c (R 1, R 2 ): mean boundary contrast –contrast(x) = max L*a*b* diff within radius of x 2.D g (R 1, R 2 ): mean boundary gradient –gradient(x) = Pb(x) 3.D a (R 1 ): Area + α 3 Scatter (in color space) D(R 1, R 2 ) = [D c (R 1, R 2 ) + α 1 D g (R 1, R 2 )] · min{ D a (R 1 ), D a (R 2 ) } α2α2 Learned Parameters: x i = 4.5 α 1 = 5 α 2 = 0.2 α 3 = 0
Examples Contrast Contrast + Gradient Contrast + Gradient + Region
Algorithm Summary Create Initial Contours: –Extrema in gray channel form regions –Assign pixels to regions based on above ultrametric Iteratively merge regions –Keep adjacency/distance matrix
Comparison Martin et al. (Pb) Canny edge detector Hierarchical watersheds (using MFM for gradient) [Najman and Schmitt 1996] Variational (global energy minimization)
Pb No Boundary Boundary [Martin Fowlkes Malik 2004] Oriented Edges Brightness Gradient Color Gradient Texture Gradient
Pb
Variational Method [Koepfler Lopez Morel 1994] Originally Wavelet-based Textons
Comparison MFM: Martin et al. (Pb) Canny: Canny edge detector WS: Hierarchical watersheds (using MFM for gradient) [Najman and Schmitt 1996] MS: Variational (global energy minimization) Edge-BasedRegion-Based
Comparison
Results
Best Results
Best Results
Best Results
Best Results
Median Results
Worst Results
Hierarchies vs. Multiple Segmentations
Revising Segmentation