On the Alignment of Shapes Represented by Fourier Descriptors

Karl Sjöstrand, Anders Ericsson, Rasmus Larsen

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    Abstract

    The representation of shapes by Fourier descriptors is a time-honored technique that has received relatively little attention lately. Nevertheless, it has many benefits and is applicable for describing a range of medical structures in two dimensions. Delineations in medical applications often consist of continuous outlines of structures, where no information of correspondence between samples exist. In this article, we discuss an alignment method that works directly with the functional representation of Fourier descriptors, and that is optimal in a least-squares sense. With corresponding starting points, the alignment of one shape onto another consists of a single expression. If the starting points are arbitrary, we present a simple iterative scheme to bring a set of shapes into correspondence. Results are given for three different data sets; 62 outlines of the corpus callosum brain structure, 61 outlines of the brain ventricles, and 50 outlines of the right lung. The results show that even though starting points, translations, rotations and scales have been randomized, the alignment succeeds in all cases. As an application of the proposed method, we show how high-quality shape models represented by common landmarks can be constructed in an automatic fashion. If the aligned Fourier descriptors are inverse transformed from the frequency domain to the spatial domain, a set of roughly aligned landmarks are obtained. The positions of these are then adjusted along the contour of the objects using the minimum description length criterion, producing ample correspondences. Results on this are also presented for all three data sets.
    Original languageEnglish
    Title of host publicationInternational Symposium on Medical Imaging 2006, San Diego, CA, USA
    PublisherThe International Society for Optical Engineering (SPIE)
    Publication date2006
    Publication statusPublished - 2006

    Cite this

    Sjöstrand, K., Ericsson, A., & Larsen, R. (2006). On the Alignment of Shapes Represented by Fourier Descriptors. In International Symposium on Medical Imaging 2006, San Diego, CA, USA The International Society for Optical Engineering (SPIE). http://www2.imm.dtu.dk/pubdb/p.php?4045