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Samia Bouchafa Bertrand Zavidovique

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  1. THE COST-TIST 283  Symmetry operators and their application in computer vision Vito Di Gesù Cesare Valenti Samia Bouchafa Bertrand Zavidovique IEF University of Orsay France DMA University of Palermo Italy iAstro Workshop Granada 21-22 February 2002

  2. Symmetry is a property that characterizes the invariance of a given system. • It is one of the most prominent spatial relations perceived by human beings. • Psychologists of perception, assign a relevant role to symmetry in attentive mechanism in both visual and auditory systems • Image segmentation • Object-parts representation and description • Detection of points of interest Symmetry and perception iAstro Workshop Granada 21-22 February 2002

  3. iAstro Workshop Granada 21-22 February 2002

  4. Computer vision tasks global symmetry local symmetry Computation paradigm edge gray levels hybrid Computing Symmetry iAstro Workshop Granada 21-22 February 2002

  5. Edge Based Computation Symmetry Axial Transform (SAT)(Blum, Nagel, 1978) Smoothed Local Symmetry (SLS)(Brady, Asada, 1984) Affine transformations and symmetry (Mukhergee, Zisserman, Brady, Chan, Cipolla, 1995) Partial occlusion(Sato, Cipolla, 1997) String oriented approach (Atallah, 1985), (Bruckstein and Shaked, 1995) iAstro Workshop Granada 21-22 February 2002

  6. Gray Levels Approaches Texture analysis and symmetry measures (Cheterikov and Haralick, 1995) Measures based on the Radom’s transform (Kiryati and Gofman, 1996) Context free attentional operators(Reisfeld, Wolfson and Yeshurun 1995) iAstro Workshop Granada 21-22 February 2002

  7. Circular Symmetry Symmetry TransformDi Gesù, Valenti, 1994 iAstro Workshop Granada 21-22 February 2002

  8. Discrete Symmetry Transform iAstro Workshop Granada 21-22 February 2002

  9. Points of interest iAstro Workshop Granada 21-22 February 2002

  10. Pyramid-DST(Di Gesù,Valenti 1996) Discrete Fourier Transform of D0 and then: iAstro Workshop Granada 21-22 February 2002

  11. iAstro Workshop Granada 21-22 February 2002

  12. iAstro Workshop Granada 21-22 February 2002

  13. Tracking problems iAstro Workshop Granada 21-22 February 2002

  14. Face analysis Applications:security systems, criminology. physical access control, man-machine interactions iAstro Workshop Granada 21-22 February 2002

  15. Expression analysis Neutral, Sadness, Disgust, Happiness, Fear, Anger, Surprise iAstro Workshop Granada 21-22 February 2002

  16. Object recognition systemsChella, Di Gesu’, Infantino, Intravaia, Valenti 1997 • Object Recognition Using Multiple Views • 3D shape reconstruction from image sequences iAstro Workshop Granada 21-22 February 2002

  17. Eoperator erosion Iterated Object TransformDi Gesù, Zavidovique, 2002 The IOT computes the symmetry transform, T, on steadilyintensity reduced versions of the input image iAstro Workshop Granada 21-22 February 2002

  18. Contrast change and level lines • Contrast change definition Non-decreasing funtion g • Level set : • Contrast change impact • some level sets disappearance • no geometric deformation • Motion impact (+ noise) • some new level sets appearance • Geometric deformation • level lines crossing iAstro Workshop Granada 21-22 February 2002

  19. Detection criteria • How can we reconstruct the scene S ? • Possibilities for each line : 1. The line is present • no detection 2. The line is not present • Doubt : Is the reference complete ? Is the background uniform ? 3. The line crosses another one • detection Week Detection Strong Detection iAstro Workshop Granada 21-22 February 2002

  20. Image Sequence Reference Updating Level line Extraction tracking of level lines Characterization Comparison - Appearance of new lines - Crossings between lines Local Orientations Detection Motion detection algorithm iAstro Workshop Granada 21-22 February 2002

  21. Local characterization local orientation Level line characterization • Two possibilities : Global characterization surface, other moments of inertia, etc. Associated level line Our choice :local characterization - Point detection - No level lines occlusions management iAstro Workshop Granada 21-22 February 2002

  22. The result of the detection algorithm that is insensible towards contrast changes. The original sequence presents some contrast changes due the automatic gain control of the camera and to natural scene illumination changes. In the sequence, only points affected bymotion are displayed iAstro Workshop Granada 21-22 February 2002

  23. iAstro Workshop Granada 21-22 February 2002

  24. Fast Marching Methods and Level Set Methods are numerical techniques which can follow the evolution of interfaces. These interfaces can develop sharp corners, break apart, and merge together. The techniques have a wide range of applications, including problems in fluid mechanics, combustion, manufacturing of computer chips, computer animation, image processing, structure of snowflakes, and the shape of soap bubbles. These are two fundamentally different approaches to the problem of tracking moving interfaces, yet they share a common theory and numerical methodology. iAstro Workshop Granada 21-22 February 2002

  25. Edge Based Computation Symmetry Axial Transform (SAT)(Blum, Nagel, 1978) iAstro Workshop Granada 21-22 February 2002

  26. Smoothed Local Symmetry (SLS) (Brady, Asada, 1984) iAstro Workshop Granada 21-22 February 2002

  27. Input DST Edge based operator Yeshurun iAstro Workshop Granada 21-22 February 2002

  28. Face analysis and algorithmsCardaci, Di Gesu’, Intravaia, 1998 • The algorithm is based on an attentive architecture. • local and global symmetry operators • Reisfeld, Wolfson,Yeshurun (1995) Di Gesù, Valenti, Strinati, (1997) • graph theoretical algorithms Zhan (1972) • facial anatomy (model driven) Russel, (1994) iAstro Workshop Granada 21-22 February 2002

  29. iAstro Workshop Granada 21-22 February 2002

  30. Gelstat clustering (GC) A relational graph (FG) is then built from the retrieved FC Structural information are represented by a simple Internal Model (IM) based on psycho-visual correlation between components of face Chen, Yachida (1996) iAstro Workshop Granada 21-22 February 2002

  31. Results A sequence with global contrast changes Séquence initiale iAstro Workshop Granada 21-22 February 2002

  32. Results The same crossing junction but different lighting conditions iAstro Workshop Granada 21-22 February 2002

  33. Applications Road environment Vehicle/pedestrian detection and counting Subway environment Stationnary objects/human detection iAstro Workshop Granada 21-22 February 2002

  34. Comparisons Level lines Reference sequence Six months before Gradients orientation Grey levels Laplacian iAstro Workshop Granada 21-22 February 2002

  35. Comparisons Gradient orientations Problems with stability and thresholding ! iAstro Workshop Granada 21-22 February 2002