Model of active contour

A model of active contour , often named snake (English snake) in the literature, is a dynamic structure used in Image processing and artificial Vision. They were introduced in a formal way by Kass and Witkin in 1987.

Several approaches are possible and make it possible to solve the problem of the segmentation and the Détection of contour by using a model of deformable curve which marries the shape of the objects.

Principles

A model of active contour is made of a series of points mobile and distributed on a curve in two dimensions. The curve (which can be closed) is placed in the zone of interest of the image or around an object. Several equations describe its evolution: the curve moves and marries slowly contours of the objects according to various parameters like elasticity, the tolerance with the noise, etc

This dynamics is based on the concept of energy intern and external, the goal being to minimize total energy present along the curve. Constraints make it possible to preserve a smooth curve with equidistant points while leaving a certain free field for the deformations. Internal energy corresponds to the morphology and the characteristics of curve (ache, length, etc). External energy comes from the image, the criteria are variable (presence of marked edges, noise, etc).

The evolution is done in an iterative way and the algorithms can be the subject of various optimizations and technical numerical.

Use

Several methods taking again this principle were formulated according to the problems to solve: Medical imagery, Pattern recognition, Segmentation of image, Stéréovision, followed objects moving, etc

A tool based on an active contour is for example available in the graphic applications like The Gimp or Photoshop, it makes it possible automatically to follow a contour in an image. Within the framework of the segmentation, a closed model makes it possible to delimit areas of the image.

Extensions

The process can be wide with other dimensions, in particular in 3D where the curve takes the shape of an envelope which gradually marries the surface of an object. Such methods are used to solve the problems of voluminal Segmentation.

Random links: