Whereas manually drawn contours could contain artifacts related to hand tremor, automatically detected contours could contain noise and inaccuracies due to limitations or errors in the procedures for the detection and segmentation of the related regions. To improve the further step of description, modeling procedures are desired to eliminate the artifacts in a given contour, while preserving the important and significant details present in the contour. In this work, are presented a couple of polygonal modeling methods, first a method applied direct on the original contour and other derived from the turning angle function. Both methods use the following parametrization Smin e µmax to infer about removing or maintain a given segment. By the using of the mentioned parameters the proposed methods could be configured according to the application problem. Both methods have been shown eficient to reduce the influence of noise and artifacts while preserving relevant characteristic for further analysis. Systems to support the diagnosis by images (CAD) and retrieval of images by content (CBIR) use shape descriptor methods to make possible to infer about factors existing in a given contour or as base to classify groups with dierent patterns. Shape factors methods should represent a value that is aected by the shape of an object, thus it is possible to characterize the presence of a factor in the contour or identify similarity among contours. Shape factors should be invariant to rotation, translation or scale. In the present work there are proposed the following shape features: index of the presence of convex region (XRTAF ), index of the presence of concave regions (V RTAF ), index of convexity (CXTAF ), two measures of fractal dimension (DFTAF e DF1 TAF ) and the index of spiculation (ISTAF ). All derived from the smoothed turning angle function. The smoothed turning angle function represent the contour in terms of their concave and convex regions. The polygonal modeling and the shape descriptors methods were applied on the breast masses classification issue to evaluate their performance. The polygonal modeling procedure proposed in this work provided higher compression and better polygonal fitness. The best classification accuracies, on discriminating between benign masses and malignant tumors, obtain for XRTAF , V RTAF , CXTAF , DFTAF , DF1 TAF and ISTAF , in terms of area under the receiver operating characteristics curve, were 0:92, 0:92, 0:93, 0:93, 0:92 e 0:94, respectively. / Contornos obtidos manualmente podem conter ruídos e artefatos oriundos de tremores da mão bem como contornos obtidos automaticamente podem os conter dado a problemas na etapa de segmentação. Para melhorar os resultados da etapa de representação e descrição, são necessários métodos capazes de reduzir a influência dos ruídos e artefatos enquanto mantém características relevantes da forma. Métodos de aproximação poligonal têm como objetivo a remoção de ruídos e artefatos presentes nos contornos e a melhor representação da forma com o menor número possível de segmentos de retas. Nesta disserta ção são propostos dois métodos de aproximação poligonal, um aplicado diretamente no contorno e outro que é obtido a partir da função tangencial do contorno original. Ambos os métodos fazem uso dos parâmetros Smin e µmax para inferirem sobre a permanência ou remoção de um dado segmento. Com a utilização destes parâmetros os métodos podem ser configurados para serem utilizados em vários tipos de aplicações. Ambos os métodos mostram-se eficientes na remoção de ruídos e artefatos, enquanto que características relevantes para etapas de pós-processamento são mantidas. Sistemas de apoio ao diagnóstico por imagens e de recuperação de imagens por conte údo fazem uso de métodos descritores de forma para que seja possível inferir sobre características presentes em um dado contorno ou ainda como base para medir a dissimilaridade entre contornos. Métodos descritores de características são capazes de representar um contorno por um número, assim é possível estabelecer a presença de uma característica no contorno ou ainda identificar uma possível similaridade entre os contornos. Métodos para extração de características devem ser invariantes a rotação, translação e escala. Nesta dissertação são propostos os seguintes métodos descritores de características: índice de presença de regiões convexas (XRTAF ), índice da presença de regiões côncavas (V RTAF ), índice de convexidade (CXTAF ), duas medidas de dimensão fractal (DFTAF e DF1 TAF ) e o índice de espículos (ISTAF ). Todos aplicados sobre a função tangencial suavizada. A função tangencial suavizada representa o contorno em termos de suas regiões côncavas e regiões convexas. Os métodos de aproximação poligonal e descritores de características foram aplicados para o problema de classificação de lesões de mama. Os resultados obtidos, mostraram que os métodos de aproximação poligonal propostos neste trabalho resultam em polígonos mais compactos e com melhor representação do contorno original. Os melhores resultados de classificação, na discriminação entre lesões benignas e tumores malignos, obtidos por XRTAF , V RTAF , CXTAF , DFTAF , DF1 TAF e ISTAF , em termos da área sob a curva ROC, foram 0:92, 0:92, 0:93, 0:93, 0:92 e 0:94, respectivamente. / Mestre em Ciência da Computação

Les objets numériques 3D sont utilisés dans de nombreux domaines, les films d'animations, la visualisation scientifique, l'imagerie médicale, la vision par ordinateur.... Ces objets sont généralement représentés par des maillages à faces triangulaires avec un nombre énorme de triangles. La simplification de ces objets, avec préservation de la géométrie originale, a fait l'objet de nombreux travaux durant ces dernières années. Dans cette thèse, nous proposons un algorithme de simplification qui permet l'obtention d'objets simplifiés de grande précision. Nous utilisons des fusions de couples de sommets avec une relocalisation du sommet résultant qui minimise une métrique d'erreur. Nous utilisons deux types de mesures quadratiques de l'erreur : l'une uniquement entre l'objet simplifié et l'objet original (Accurate Measure of Quadratic Error (AMQE) ) et l'autre prend aussi en compte l'erreur entre l'objet original et l'objet simplifié ((Symmetric Measure of Quadratic Error (SMQE)) . Le coût calculatoire est plus important pour la seconde mesure mais elle permet une préservation des arêtes vives et des régions isolées de l'objet original par l'algorithme de simplification. Les deux mesures conduisent à des objets simplifiés plus fidèles aux originaux que les méthodes actuelles de la littérature. / Complex 3D digital objects are used in many domains such as animation films, scientific visualization, medical imaging and computer vision. These objects are usually represented by triangular meshes with many triangles. The simplification of those objects in order to keep them as close as possible to the original has received a lot of attention in the recent years. In this context, we propose a simplification algorithm which is focused on the accuracy of the simplifications. The mesh simplification uses edges collapses with vertex relocation by minimizing an error metric. Accuracy is obtained with the two error metrics we use: the Accurate Measure of Quadratic Error (AMQE) and the Symmetric Measure of Quadratic Error (SMQE). AMQE is computed as the weighted sum of squared distances between the simplified mesh and the original one. Accuracy of the measure of the geometric deviation introduced in the mesh by an edge collapse is given by the distances between surfaces. The distances are computed in between sample points of the simplified mesh and the faces of the original one. SMQE is similar to the AMQE method but computed in the both, direct and reverse directions, i.e. simplified to original and original to simplified meshes. The SMQE approach is computationnaly more expensive than the AMQE but the advantage of computing the AMQE in a reverse fashion results in the preservation of boundaries, sharp features and isolated regions of the mesh. For both measures we obtain better results than methods proposed in the literature.

Modeling the "thick description" of photographs began at the intersection of personal and institutional descriptions. Comparing institutional descriptions of particular photos that were also used in personal online conversations was the initial phase. Analyzing conversations that started with a photographic image from the collection of the Library of Congress (LC) or the collection of the Manchester Historic Association (MHA) provided insights into how cultural heritage institutions could enrich the description of photographs by using informal descriptions such as those applied by Facebook users. Taking photos of family members, friends, places, and interesting objects is something people do often in their daily lives. Some photographic images are stored, and some are shared with others in gatherings, occasions, and holidays. Face-to-face conversations about remembering some of the details of photographs and the event they record are themselves rarely recorded. Digital cameras make it easy to share personal photos in Web conversations and to duplicate old photos and share them on the Internet. The World Wide Web even makes it simple to insert images from cultural heritage institutions in order to enhance conversations. Images have been used as tokens within conversations along with the sharing of information and background knowledge about them. The recorded knowledge from conversations using photographic images on Social Media (SM) has resulted in a repository of rich descriptions of photographs that often include information of a type that does not result from standard archival practices. Closed group conversations on Facebook among members of a community of interest/practice often involve the use of photographs to start conversations, convey details, and initiate story-telling about objets, events, and people. Modeling of the conversational use of photographic images on SM developed from the exploratory analyses of the historical photographic images of the Manchester, NH group on Facebook. The model was influenced by the typical model of Representation by Agency from O'Connor in O'Connor, Kearns, and Anderson Doing Things with Information: Beyond Indexing and Abstracting, by considerations of how people make and use photographs, and by the notion of functionality from Patrick Wilson's Public Knowledge, Private Ignorance: Toward a Library and Information Policy. The model offers paths for thickening the descriptions of photographs in archives and for enriching the use of photographs on social media.