Finding similar trailing edges in large collections of photographs of sperm whales
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Abstract
The North Atlantic and Mediterranean Sperm Whale Catalogue (NAMSC 1.0) contains images collected via the cooperative effort of several individuals studying sperm whales in the North Atlantic and Mediterranean. The collection offers an important opportunity to test matching algorithms as an aid to photo-identification of individual sperm whales. Of the 2,081 photographs in the catalogue, 1,929 were of sufficient quality for photo-identification. The trailing edge of the fluke, an identifying feature, was extracted by an interactive method. Subsequently, the trailing edge was represented in a normalised form by an affine transformation. Left and right halves were processed separately. Using different methods, 489 matching pairs of photographs were found. Based on these confirmed matches, the power of several measures of similarity was compared. The measure of similarity calculated by cross-correlating the continuous wavelet transforms of the extracted contours was found to perform best in practice. No conclusive matches between photographs from different geographic locations were found.
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