In this paper we propose a new contour\ud
descriptor for reconstructing fish otolith contours that\ud
uses half the number of coefficients needed by the\ud
classical elliptical Fourier descriptors (EFDs) for the\ud
same accuracy. The efficiency of the proposed shape\ud
descriptor has been tested with two different species,\ud
Liza aurata and Liza ramada, belonging to the family\ud
Mugilidae (http://aforo.cmima.csic.es), and two populations\ud
(from the USA and Canada) of the family\ud
Merlucciidae. These groups are characterized by high\ud
similarity between species; therefore, accurate, detailed\ud
shape analyses of their otoliths can help to identify and\ud
discriminate morphologically close species or different\ud
populations. For comparative purposes the descriptor\ud
was also tested with specimens of Mullus barbatus\ud
(Family Mullidae). For a certain number of coefficients\ud
(<50) the new descriptor clearly outperforms the\ud
reconstruction accuracy of the EFD.Peer ReviewedPostprint (published version
In this work, a comparative study between Elliptic\ud
Fourier and B-spline descriptors is carried out for comparing\ud
their efficiency in characterizing the contour shape of image\ud
objects. In both cases, the goal is to obtain the least\ud
representation error using the fewest possible number of\ud
coefficients. With Fourier descriptors, different number of\ud
harmonics are used while the remaining ones are set to zero. In\ud
the B-spline case, coefficients are obtained iteratively using a\ud
least-square filter, followed by a decimation procedure. Linear\ud
and cubic B-splines are considered. In general, data will be more\ud
compressed when the lower number of coefficients is used, but\ud
the representation error also increases considerably. We use a\ud
signal/error ratio, expressed in dBs, to measure the similarity of\ud
each approximation. The signal value is obtained from the\ud
‘modulo’ addition of all coordinate points, whereas the error\ud
value is computed accumulating the ‘modulo’ distance between\ud
original and reconstructed shape. It can be shown that for a\ud
lower compression rate, the results do not vary significantly in all\ud
three methods. For higher compression rates, Elliptic Fourier\ud
Descriptors are more efficient than linear and cubic B-splines,\ud
especially in soft contours, but B-splines have lower\ud
computational cost.Peer ReviewedPostprint (published version
The shape analysis of otoliths, which are calcified\ud
structures in the inner ear of teleostean fishes, is known to be\ud
particularly relevant to address species identification and stock\ud
discrimination. Generally, scientists use classical methodologies\ud
of statistical analysis and shape recognition such as Fourier\ud
shape descriptors and Principal Component Analysis (PCA).\ud
These methods are subject to several limitations mainly to their\ud
incapacity to locate irregularities because they are based on global\ud
characterization of shape. Recently, more advanced techniques\ud
are proposed in this context in order to improve classification\ud
accuracies. The first recent method exploits the potential of shape\ud
geodesics which rely on local shape features for classification\ud
issues. The second one addresses the Best-Basis paradigm which\ud
combines the Wavelet Transform, and the potential of statistical\ud
analysis in order to fully automate the selection process of efficient\ud
features for classification. These methods have been shown to\ud
significantly outperform the standard approaches but they are not\ud
compared together yet. This study compare these two methods on\ud
a real dataset. The comparison is performed on\ud
600\ud
striped red\ud
mullet calcified structures collected for the NESPMAN European\ud
project. For each method, performances are reported for the\ud
classification of samples coming from three geographical zones\ud
in the Northwest European seas: the Bay of Biscay, a mixing zone\ud
composed of the Celtic Sea and the Western English Channel and\ud
a northern zone composed of the Eastern English Channel and\ud
the North Sea. Comparison shows that both methods lead to same\ud
conclusions.Peer ReviewedPostprint (published version
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