Image analysis – Pattern recognition – Feature extraction
Patent
1994-08-09
1999-11-02
Boudreau, Leo
Image analysis
Pattern recognition
Feature extraction
382201, 382203, 382206, 382224, G06K 946, G06K 966, G06K 950, G06K 962
Patent
active
059785071
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of forming a template of an image of an object, which template finds particular, but not exclusive, application to the recognition of objects in images for security and surveillance applications and in model-based image coding.
BACKGROUND OF THE INVENTION
A template is a representation of an image of an object which aims to contain the image's salient features so that the template can be subsequently compared to other images, the goodness of fit of the template to another image providing a measure of the likelihood that this image is of or contains a sub-image of the object. For example, a series of templates may be formed from respective images of the faces of a group of people. An image of a person's face captured by a security camera could then be compared to the templates to determine if that person is one of the group.
A known approach to the use of templates is described in an article entitled "Feature Extraction From Faces Using Deformable Templates" by A L Yuille, D S Cohen and P W Hallinan, Harvard Robotics Laboratory Technical Report 33-2, 1988. In this approach a feature or object of interest is described by a geometric representation which is specified by a set of parameters which incorporate knowledge of the shape of the object. The article gives examples of two such templates; one for use in recognising an eye and the other a mouth. In the former case the eye template decided upon by the authors incorporated a circle corresponding to the outer boundary of the iris, boundary coutours corresponding to the top and bottom of the eye comprising two parabolas, regions corresponding to the whites of the eyes, and two points corresponding to the centres of the whites of the eyes.
The template of Yuille et al is deformable in that the components of the template can move subject to notional structural, restraining forces between the components. When the template is matched to a test image, the components of the template are attracted to various valleys, edge and peak components of the image which attractive forces are generally resisted by the structural forces between the components of the template. An energy function is defined in terms of the attraction of the template components to the features of the image and the structural forces resisting deformation of the template, the template being deformed to minimise this energy function. This energy function gives a measure of the goodness of fit of the template to the image and can be used as a measure of whether the template has, in fact, been successfully matched to the image, ie that the image does indeed correspond to the template.
This approach to the forming of templates was devised so that a priori information available about the appearance of the features of the object to which the template was to be matched, in Yuille et al's particular case facial features, could be incorporated into the template so providing a mechanism for detecting edges or other features which comprise local information as global structures.
BRIEF DESCRIPTION OF THE INVENTION
The Applicant has appreciated that there are, however, disadvantages associated with this approach to forming a template. Firstly, because the template design is based on a priori information, it is important that the information incorporated into the template is accurate. For example, a simplification of an edge so that it can be mirrored in the template as a single geometric line may in fact hinder matching of the template to an image. It has been found, for example, that the edge of the lower eyelid can vary considerably between the populations of different countries so that a template designed to recognise a typically "Western" eye fairs badly when it is attempted to fit the template to a typically "Eastern" eye.
It is also a characteristic of such a known template that it will, in some cases, not describe accurately the feature in an image but rather what the human perceives to be the salient features of the object in the image. A f
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Shackleton Mark A
Welsh William J
Boudreau Leo
British Telecommunications public limited company
Shalwala Bipin
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