Combining Global and Local Information for Knowledge-Assisted Image Analysis and Classification
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Research Article Combining Global and Local Information for Knowledge-Assisted Image Analysis and Classification G. Th. Papadopoulos,1, 2 V. Mezaris,2 I. Kompatsiaris,2 and M. G. Strintzis1, 2 1 Department 2 Centre
of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Thessaloniki 54006, Greece for Research and Technology Hellas (CERTH), Informatics and Telematics Institute, Thermi 57001, Greece
Received 8 September 2006; Revised 23 February 2007; Accepted 2 April 2007 Recommended by Ebroul Izquierdo A learning approach to knowledge-assisted image analysis and classification is proposed that combines global and local information with explicitly defined knowledge in the form of an ontology. The ontology specifies the domain of interest, its subdomains, the concepts related to each subdomain as well as contextual information. Support vector machines (SVMs) are employed in order to provide image classification to the ontology subdomains based on global image descriptions. In parallel, a segmentation algorithm is applied to segment the image into regions and SVMs are again employed, this time for performing an initial mapping between region low-level visual features and the concepts in the ontology. Then, a decision function, that receives as input the computed region-concept associations together with contextual information in the form of concept frequency of appearance, realizes image classification based on local information. A fusion mechanism subsequently combines the intermediate classification results, provided by the local- and global-level information processing, to decide on the final image classification. Once the image subdomain is selected, final region-concept association is performed using again SVMs and a genetic algorithm (GA) for optimizing the mapping between the image regions and the selected subdomain concepts taking into account contextual information in the form of spatial relations. Application of the proposed approach to images of the selected domain results in their classification (i.e., their assignment to one of the defined subdomains) and the generation of a fine granularity semantic representation of them (i.e., a segmentation map with semantic concepts attached to each segment). Experiments with images from the personal collection domain, as well as comparative evaluation with other approaches of the literature, demonstrate the performance of the proposed approach. Copyright © 2007 G. Th. Papadopoulos et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
Recent advances in both hardware and software technologies have resulted in an enormous increase of the number of images that are available in multimedia databases or over the internet. As a consequence, the need for techniques and tools supporting their effective and efficient manipulation has emerged. To this end, several approach
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