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Snakes!

Snakes!. Nilanjan Ray. Inside Active Contours/Snakes. Cost function (Kass,Witkin,Terzopoulos,1987 ):. A snake point / snaxel: ( X ( s ), Y ( s )). I : Image,  ,  : non-negative parameters. Internal force. Minimization. External force. A circle and a snake. Gradient descent equations

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Snakes!

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  1. Snakes! Nilanjan Ray

  2. Inside Active Contours/Snakes Cost function (Kass,Witkin,Terzopoulos,1987): A snake point / snaxel: (X(s),Y(s)) I: Image, , : non-negative parameters Internal force Minimization External force A circle and a snake Gradient descent equations solved iteratively from initial snake

  3. Failure of Traditional Snake Success of edge-force Failure of edge-force KWT snake is quite sensitiveto initial snake position

  4. Gradient Vector Flow: A Breakthrough Gradient Vector Flow (Xu and Prince, 1998): GVF for the circle GVF in snake A circle and GVF snake evolution

  5. Can GVF Help With Minimal User Interaction? What if we want to minimize user interaction to a single mouse click? What if the user wants a single mouse click to delineate an object boundary? Failure of GVF snake Unfortunately, GVF snake fails here

  6. DirichletBoundary Condition As Remedy Enhanced GVF-PDE (Ray, Acton, ICIP 2002, IEEE TMI 2003):  D  C Dirichlet boundary condition D : Rectangular image domain  D : Boundary of D  C : Initial snake (red contour) C : Region bounded by  C n : Boundary condition at  C Matlab demonstration

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