Samia Bouchafa Bertrand Zavidovique

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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. - PowerPoint PPT Presentation

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  • Samia BouchafaBertrand ZavidoviqueIEF University of Orsay FranceVito Di GesCesare ValentiDMA University of Palermo Italy

    iAstro Workshop Granada 21-22 February 2002

  • Symmetry and perception

    iAstro Workshop Granada 21-22 February 2002

  • iAstro Workshop Granada 21-22 February 2002

  • Computing Symmetry

    iAstro Workshop Granada 21-22 February 2002

  • Edge Based ComputationSymmetry 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

  • Gray Levels ApproachesTexture analysis and symmetry measures (Cheterikov and Haralick, 1995)Measures based on the Radoms transform (Kiryati and Gofman, 1996)Context free attentional operators (Reisfeld, Wolfson and Yeshurun 1995)

    iAstro Workshop Granada 21-22 February 2002

  • Symmetry TransformDi Ges, Valenti, 1994

    iAstro Workshop Granada 21-22 February 2002

  • Discrete Symmetry Transform

    iAstro Workshop Granada 21-22 February 2002

  • Points of interest

    iAstro Workshop Granada 21-22 February 2002

  • Pyramid-DST(Di Ges,Valenti 1996)Discrete Fourier Transform of D0 andthen:

    iAstro Workshop Granada 21-22 February 2002

  • iAstro Workshop Granada 21-22 February 2002

  • iAstro Workshop Granada 21-22 February 2002

  • Tracking problems

    iAstro Workshop Granada 21-22 February 2002

  • Face analysisApplications:security systems, criminology. physical access control, man-machine interactions

    iAstro Workshop Granada 21-22 February 2002

  • Expression analysisNeutral, Sadness, Disgust, Happiness, Fear, Anger, Surprise

    iAstro Workshop Granada 21-22 February 2002

    Neutral

    Smiling

    Neutral

    92%

    8%

    Smiling

    20%

    80%

  • Object recognition systems Chella, Di Gesu, Infantino, Intravaia, Valenti 1997Object Recognition Using Multiple Views3D shape reconstruction from image sequences

    iAstro Workshop Granada 21-22 February 2002

  • Iterated Object TransformDi Ges, Zavidovique, 2002The IOT computes the symmetry transform, T, on steadily intensity reduced versions of the input image

    iAstro Workshop Granada 21-22 February 2002

  • Contrast change and level linesContrast change definitionNon-decreasing funtion gLevel set :Contrast change impactsome level sets disappearanceno geometric deformation

    Motion impact (+ noise)some new level sets appearance Geometric deformation level lines crossing

    iAstro Workshop Granada 21-22 February 2002

  • Detection criteria

    How can we reconstruct the scene S ?

    Possibilities for each line :1. The line is present no detection2. The line is not present Doubt :Is the reference complete ?Is the background uniform ?3. The line crosses another one detectionWeek Detection Strong Detection

    iAstro Workshop Granada 21-22 February 2002

  • Motion detection algorithm

    iAstro Workshop Granada 21-22 February 2002

  • Level line characterizationTwo possibilities :Global characterization surface, other moments of inertia, etc.Associated level lineOur choice : local characterization- Point detection- No level lines occlusions management

    iAstro Workshop Granada 21-22 February 2002

  • 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 by motion are displayedThe result of the detection algorithm that is insensible towards contrast changes.

    iAstro Workshop Granada 21-22 February 2002

  • iAstro Workshop Granada 21-22 February 2002

  • 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

  • Edge Based ComputationSymmetry Axial Transform (SAT) (Blum, Nagel, 1978)

    iAstro Workshop Granada 21-22 February 2002

  • Smoothed Local Symmetry (SLS) (Brady, Asada, 1984)

    iAstro Workshop Granada 21-22 February 2002

  • DSTEdge based operatorYeshurunInput

    iAstro Workshop Granada 21-22 February 2002

  • Face analysis and algorithmsCardaci, Di Gesu, Intravaia, 1998The algorithm is based on an attentive architecture.

    local and global symmetry operators Reisfeld, Wolfson,Yeshurun (1995) Di Ges, Valenti, Strinati, (1997)

    graph theoretical algorithms Zhan (1972)

    facial anatomy (model driven) Russel, (1994)

    iAstro Workshop Granada 21-22 February 2002

  • iAstro Workshop Granada 21-22 February 2002

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

    iAstro Workshop Granada 21-22 February 2002

    Neutral

    Smiling

    Neutral

    92%

    8%

    Smiling

    20%

    80%

  • ResultsSquence initialeA sequence with global contrast changes

    iAstro Workshop Granada 21-22 February 2002

  • ResultsThe same crossing junction but different lighting conditions

    iAstro Workshop Granada 21-22 February 2002

  • ApplicationsRoad environment Vehicle/pedestrian detection and countingSubway environment Stationnary objects/human detection

    iAstro Workshop Granada 21-22 February 2002

  • ComparisonsReference sequenceSix months beforeLevel linesGrey levelsLaplacianGradients orientation

    iAstro Workshop Granada 21-22 February 2002

  • ComparisonsGradient orientationsProblems with stability and thresholding !

    iAstro Workshop Granada 21-22 February 2002