University of Oulu

A multiscale framework for affine invariant pattern recognition and registration

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Author: Rahtu, Esa
Organizations: University of Oulu, Faculty of Technology, Department of Electrical and Information Engineering
University of Oulu, Infotech Oulu
Format: eBook
Online Access: PDF Full Text (PDF, 1.5 MB)
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Language: English
Published: 2007
Publish Date: 2007-10-23
Thesis type: Doctoral Dissertation
Defence Note: Academic dissertation to be presented, with the assent of the Faculty of Technology of the University of Oulu, for public defence in Auditorium TS101, Linnanmaa, on November 2nd, 2007, at 12 noon
Reviewer: Doctor Joni-Kristian Kämäräinen
Doctor Tomás Suk


This thesis presents a multiscale framework for the construction of affine invariant pattern recognition and registration methods. The idea in the introduced approach is to extend the given pattern to a set of affine covariant versions, each carrying slightly different information, and then to apply known affine invariants to each of them separately. The key part of the framework is the construction of the affine covariant set, and this is done by combining several scaled representations of the original pattern. The advantages compared to previous approaches include the possibility of many variations and the inclusion of spatial information on the patterns in the features.

The application of the multiscale framework is demonstrated by constructing several new affine invariant methods using different preprocessing techniques, combination schemes, and final recognition and registration approaches. The techniques introduced are briefly described from the perspective of the multiscale framework, and further treatment and properties are presented in the corresponding original publications. The theoretical discussion is supported by several experiments where the new methods are compared to existing approaches.

In this thesis the patterns are assumed to be gray scale images, since this is the main application where affine relations arise. Nevertheless, multiscale methods can also be applied to other kinds of patterns where an affine relation is present.

An additional application of one multiscale based technique in convexity measurements is introduced. The method, called multiscale autoconvolution, can be used to build a convexity measure which is a descriptor of object shape. The proposed measure has two special features compared to existing approaches. It can be applied directly to gray scale images approximating binary objects, and it can be easily modified to produce a number of measures. The new measure is shown to be straightforward to evaluate for a given shape, and it performs well in the applications, as demonstrated by the experiments in the original paper.

Series: Acta Universitatis Ouluensis. C, Technica
ISSN-E: 1796-2226
ISBN: 978-951-42-8601-8
ISBN Print: 978-951-42-8600-1
Issue: 282
Copyright information: This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.