Active shape model: Difference between revisions

Revision as of 09:58, 25 January 2012

Revision as of 22:31, 20 March 2012

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'''Active shape models (ASMs)''' are [[statistical model]]s of the [[shape]] of objects which iteratively deform to fit to an example of the object in a new image, developed by Tim Cootes and Chris Taylor in 1995 .<ref name=Cootes>{{cite journal| author=T.F. Cootes and C.J. Taylor and D.H. Cooper and J. Graham| title=Active shape models - their training and application| journal=Computer Vision and Image Understanding| pages=38–59| year=1995| issue=61}} [http://www.cs.ualberta.ca/~nray1/CMPUT615/Snake/cootes_cviu95.pdf]</ref>. The shapes are constrained by the PDM ([[point distribution model]]) [[Statistical Shape Model]] to vary only in ways seen in a training set of labelled examples.

The shape of an object is represented by a set of points (controlled by the shape model). The ASM algorithm aims to match the model to a new image. It works by alternating the following steps:

* Look in the image around each point for a better position for that point

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To locate a better position for each point one can look for strong edges, or a match to a statistical model of what is expected at the

point. The original methodology suggests using the [[Mahalanobis distance]] to detect a better position for each landmark point .<ref name=Cootes/>.

The technique has been widely used to analyse images of faces, mechanical assemblies and medical images (in 2D and 3D).