Automatic Nacre Thickness Measurement of Tahitian Pearls

International audienceIn this paper a methodology for an automatized measurement of the nacre thickness of Tahitian pearls is presented. An adapted snake approach as well as our own developed circle detection algorithm are implemented to extract the nacre boundaries out of X-ray images. The results are validated by experts currently performing manually the obligatory nacre thickness control for millions of Tahitian pearls that are exported each year. Equivalent articles propose methods suitable for round pearls, whereas this paper contains methods to evaluate the nacre profile of pearls independently of their shape. As the algorithms are not specifically parametrized for Tahitian pearls, the methods can be adapted for quality assessment of other pearls as well

Food science sourcebook

2 v. : ill. ; 26 cm2nd edition.Rev. ed. of: Source book for food scientists. c1978"An AVI book."Pt. 1. Terms and descriptions -- pt. 2. Food composition,properties, and general data

Maritime expressions:a corpus based exploration of maritime metaphors

This study uses a purpose-built corpus to explore the linguistic legacy of Britain’s maritime history found in the form of hundreds of specialised ‘Maritime Expressions’ (MEs), such as TAKEN ABACK, ANCHOR and ALOOF, that permeate modern English. Selecting just those expressions commencing with ’A’, it analyses 61 MEs in detail and describes the processes by which these technical expressions, from a highly specialised occupational discourse community, have made their way into modern English. The Maritime Text Corpus (MTC) comprises 8.8 million words, encompassing a range of text types and registers, selected to provide a cross-section of ‘maritime’ writing. It is analysed using WordSmith analytical software (Scott, 2010), with the 100 million-word British National Corpus (BNC) as a reference corpus. Using the MTC, a list of keywords of specific salience within the maritime discourse has been compiled and, using frequency data, concordances and collocations, these MEs are described in detail and their use and form in the MTC and the BNC is compared. The study examines the transformation from ME to figurative use in the general discourse, in terms of form and metaphoricity. MEs are classified according to their metaphorical strength and their transference from maritime usage into new registers and domains such as those of business, politics, sports and reportage etc. A revised model of metaphoricity is developed and a new category of figurative expression, the ‘resonator’, is proposed. Additionally, developing the work of Lakov and Johnson, Kovesces and others on Conceptual Metaphor Theory (CMT), a number of Maritime Conceptual Metaphors are identified and their cultural significance is discussed

TOWARDS A COMPUTER VISION BASED QUALITY ASSESSMENT OF TAHITIAN PEARLS : Automatic Nacre Thickness Measurement and Color Classification

The nacre thickness measurement of Tahitian pearls is part of an obligatory quality control for pearls deemed for exportation. It is currently done manually by government experts for over 7 million pearls annually with an export volume of over 61 million €. In Part I of this thesis our algorithm to automatize this procedure under consideration of the unique features of Tahitian pearls is presented. The developed algorithm was tested on X-ray images of 298 Tahitian pearls that were classified manually by government experts. The detection accuracy of our algorithm reaches 98% in its basic form and 100% with a proposed optimized version. A prototype was developed and is currently implemented at the governmental institution in charge of the obligatory control. In Part II of this thesis, our work on normalized rgb color space theory and the classification of Tahitian pearls based on their perceived color is presented. A quintessence of the presented work is the formalization of chromatic index calculation in the context of normalized rgb histogram binning. It is shown that every chromatic index based on a linear combination of normalized rgb channels can be expressed by a single variable; an angle that corresponds to the human perceptual parameter Hue. Experimental classifications based on Artificial Neural Networks and chromatic indices over the whole possible range of the normalized rgb color space were conducted by classifying 150 Tahitian pearls that were labeled by 7 experts. The results show that the choice of chromatic indices affects significantly the classification performance of an ANN with a given topology. The global performance varies within a range of up to 20% over the tested feature vectors. Furthermore does the classification accuracy of each class depend on the chosen index, with variations up to 100% between different feature vectors. These findings are of great importance for computer vision applied to color object classification, as currently only a handful of chromatic indices are used in the literature, which is a drastic limitation of possible classification results. Additionally, a new binning strategy is proposed that takes into account the topology of the normalized rgb color space. The application of the proposed topological binning has in tendency a positive effect on the global classification rate when compared to standard equidistant binning. For certain human classifications, the accuracy difference is significant with variations of up to 18%. Furthermore, it is shown that it is generally feasible to classify Tahitian pearls based on their perceived color. Classification rates of over 84% for training and over 79% for test data are reached for all 8 used human classifications.La mesure de l'épaisseur de la nacre des perles de Tahiti s'inscrit dans un processus de contrôle obligatoire de la qualité des perles destinées à l'exportation. Ce contrôle est actuellement opéré manuellement par des experts du Pays et porte sur plus de 7 millions de perles par an, pour un montant à l'exportation supérieur à 58 millions d'euros. Dans la première partie de cette thèse, nous présentons l'algorithme que nous avons développé afin d'automatiser ce contrôle. L'algorithme a été soumis à un banc d'essai de 298 perles classées par des experts du Pays et présentées sous forme d'images prises aux rayons X. La version standard de notre algorithme permet d'obtenir une précision de détection de 98%. Une version optimisée est proposée, qui atteint une précision de détection de 100%. Un prototype a été développé et est actuellement implémenté par les autorités chargées du contrôle. Dans la seconde partie, nous présentons notre travail sur la théorie de l’espace colorimétrique normalisée rgb ainsi que sur la classification des perles de Tahiti d'après leurs couleurs perçues. L'apport central de ce travail est la formalisation du calcul des indices chromatiques dans le contexte du calcul d’histogramme rgb. On montre notamment que tous les indices chromatiques basés sur une combinaison linéaire des canaux rgb peuvent être exprimés au moyen d'une variable unique : l'angle correspondant au paramètre perceptuel ‘Teinte’. Des classifications expérimentales par réseau de neurones artificiels avec des indices chromatiques balayant tout l'espace rgb ont été conduites sur 150 perles étiquetées par 7 experts. Les résultats montrent que le choix de l'indice chromatique affecte grandement les performances d'un réseau de neurones pour une topologie de connections donnée, avec une variation de la performance globale dépassant 20%. De plus, la précision de classification de chaque classe dépend aussi de l'indice choisi, avec une variation allant jusqu'à 100% entre différents indices. Ces constatations sont d'une grande importance en matière de vision par ordinateur appliquée à la classification de la couleur des objets. En effet, seuls quelques indices chromatiques sont actuellement utilisés dans la littérature, ce qui constitue une limitation forte du potentiel de classification en termes de résultats. En outre, une nouvelle stratégie de répartition des classes des histogrammes rgb est proposée, qui prend en compte la topologie de l'espace rgb normalisé. Son application a un effet positif potentiel sur le taux global de classification comparativement à la classification avec une répartition équidistante standard. Pour certaines classifications humaines, la différence de précision est significative, avec des variations allant jusqu'à 18%. De plus, on montre qu'il est généralement possible de classifier les perles de Tahiti selon leurs couleurs perçues. Pour chacune des 8 classifications humaines utilisées, le taux de classification est supérieur à 84% sur l'ensemble d'apprentissage et 79% sur l'ensemble de test