Active Appearance Model
Encyclopedia
An active appearance model (AAM) is a computer vision
algorithm for matching a statistical model
of object shape and appearance to a new image. They are built during a training phase. A set of images, together with coordinates of landmarks that appear in all of the images, is provided to the training supervisor.
The approach is widely used for matching and tracking faces and for medical image interpretation
.
The algorithm uses the difference between the current estimate of appearance and the target image to drive an optimization
process.
By taking advantage of the least squares
techniques, it can match to new images very swiftly.
It is related to the active shape model
(ASM). One disadvantage of ASM is that it only uses shape constraints (together with some information about the image structure near the landmarks
), and does not take advantage of all the available information – the texture across the target object. This can be modelled using an AAM.
Computer vision
Computer vision is a field that includes methods for acquiring, processing, analysing, and understanding images and, in general, high-dimensional data from the real world in order to produce numerical or symbolic information, e.g., in the forms of decisions...
algorithm for matching a statistical model
Statistical model
A statistical model is a formalization of relationships between variables in the form of mathematical equations. A statistical model describes how one or more random variables are related to one or more random variables. The model is statistical as the variables are not deterministically but...
of object shape and appearance to a new image. They are built during a training phase. A set of images, together with coordinates of landmarks that appear in all of the images, is provided to the training supervisor.
The approach is widely used for matching and tracking faces and for medical image interpretation
Medical imaging
Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
.
The algorithm uses the difference between the current estimate of appearance and the target image to drive an optimization
Optimization (mathematics)
In mathematics, computational science, or management science, mathematical optimization refers to the selection of a best element from some set of available alternatives....
process.
By taking advantage of the least squares
Least squares
The method of least squares is a standard approach to the approximate solution of overdetermined systems, i.e., sets of equations in which there are more equations than unknowns. "Least squares" means that the overall solution minimizes the sum of the squares of the errors made in solving every...
techniques, it can match to new images very swiftly.
It is related to the active shape model
Active shape model
Active shape models are statistical models 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...
(ASM). One disadvantage of ASM is that it only uses shape constraints (together with some information about the image structure near the landmarks
Landmark point
In morphometrics, landmark point or shortly landmark is a point in a shape object in which correspondences between and within the populations of the object are preserved. In other disciplines, landmarks may be known as vertices, anchor points, control points, sites, profile points, 'sampling'...
), and does not take advantage of all the available information – the texture across the target object. This can be modelled using an AAM.
External links
- Free Tools for experimenting with AAMs from Manchester University.
- Description of AAMs from Manchester University.
- Tim Cootes' home page (one of the original co-inventors of AAMs).
- Mikkel B. Stegmann's home page of AAM-API, open source C++ AAM implementation.
- Original Active Appearance Model Open-source Matlab implementation
- http://cvsp.cs.ntua.gr/software/AAMtools/ AAMtools: An Active Appearance Modeling Toolbox
- http://web.mac.com/jsaragih/FaceTracker/FaceTracker.html FaceTracker, free for research purposes only.
- http://www.opentl.org Open Tracking Library.
Some reading
- Edwards G, Taylor C, Cootes T. Interpreting face images using active appearance models Proceeding of the International Conference on Face And Gesture Recognition 1998, pages 300-305 (first publication of AAM algorithm)
- T. F. Cootes, G. J. Edwards, and C. J. Taylor. Active appearance models. IEEE TPAMI, 23(6):681–685, 2001
- T. F. Cootes, C. J. Taylor, D. H. Cooper, and J. Graham. Training models of shape from sets of examples. In Proceedings of BMVC’92, pages 266–275, 1992
- S. C. Mitchell, J. G. Bosch, B. P. F. Lelieveldt, R. J. van der Geest, J. H. C. Reiber, and M. Sonka. 3-d active appearance models: Segmentation of cardiac MR and ultrasound images. IEEE Trans. Med. Imaging, 21(9):1167–1178, 2002
- T.F. Cootes, G. J. Edwards, and C. J. Taylor. Active appearance models. ECCV, 2:484–498, 1998[pdf
]