Pattern matching based on a generalized Fourier transform
Dinesh Nair*, Ram Rajagopal, and Lothar Wenzel
National Instruments
1 1500 N. Mopac Expwy, Austin, TX 78759, USA
ABSTRACT
In a two-dimensional pattern matching problem, a known template image has be located in another image, irrespective of the
template's position, orientation and size in the image. One way to accomplish invariance to the changes in the template is by
forming a set of feature vectors that encompass all the variations in the template. Matching is then performed by finding the
best similarity between the feature vector extracted from the image to the feature vectors in the template set. In this paper we
introduce a new concept of a generalized Fourier transform. The generalized Fourier transform offers a relatively robust and
extremely fast solution to the described matching problem. The application of the generalized Fourier transform to scale
invariant pattern matching is shown here.
Keywords: pattern matching, generalized Fourier transform, Walsh transform, machine vision
1. INTRODUCTION
Pattern matching is the technique used in machine vision to quickly locate known reference or fiducial patterns in an image.
With pattern matching you create a model or template that represents the object you are searching for. Then in your machine
vision application the model is searched for in each acquired image. A score is calculated for each match. The score relates
how close the model matches the matched pattern. Pattern matching is the key to many applications. Pattern matching can
provide your application with information about the presence or absence, number, and location of the model within an image
[1][2][3]. Figure 1 shows an example of typical pattern matching application.
(a)
Figure 1: A pattern matching example. (a) Image of the template (pattern) to be located. (b) Matches found in an
inspection image.
Advanced Signal Processing Algorithms, Architectures, and Implementations X, Franklin T. Luk,
Editor, Proceedings of SPIE Vol. 4116 (2000) © 2000 SPIE · 0277-786X/00/$15.00 472