Snakes : Active Contour Models MICHAEL KASS International journal of computer vision

Abstract A snake:an energy-minimizing spline guided by external constraint forces and influenced by image forces A unified account of a number of visual problems: detection of edges,lines and subjective contours;motion tracking;and stereo matching Interactive interpretation

Introduction image information ->The surface evolution ->lock onto nearby edges segmentation problems ->Optimization problems energy minimization->energy functions Design principles: advantageous properties ->Energy reduction Internal forces&Image forces&external constraint forces

Methodology The traditional method of contour extraction:gradient->edge points->contour Snake:continuous and smooth closed contour- >near the features of interest->gradient- >ultimate location uniqueness

mathematical model V(s):represent the position of a snake

V’(s),v’’(s) E int :the internal energy of the spline due to bending α(s) :makes the snake act like a membrane “ 应 力 ” β(s):makes it act like a thin plate “ 刚度 ” noise Contour convergence performance Proper location

E ext :external energy function ->moving direction E img :image forces ->edge->minimization- >accuration E constraint :external constraint forces,specific problems ext

principle of operation Snake: parameterized curve Internal forces: Shape characteristics of contour curve External forces: behavior Energy function ->minimize