'''Active shape models (ASMs)''' are [[statistical modelsmodel]]s of the [[shape]] of objects which iteratively deform to fit to an example of the object in a new image. 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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The technique has been widely used to analyse images of faces, mechanical assemblies and medical images (in 2D and 3D).
It is closely related to the [[Activeactive Appearanceappearance Modelmodel]]. It is also known as a 'Smart“Smart Snake'Snakes”<ref>{{citejournal| 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| number=61| pages=38--59| year=1995}} [http://www.cs.ualberta.ca/~nray1/CMPUT615/Snake/cootes_cviu95.pdf]</ref> method, since it is analog to an [[Activeactive contour model]] which would respect explicit shape constraints.
