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Object Retrieval From Multimedia Databases

In comparison with traditional types of databases, dealing with large multimedia databases brings many new challenges, like semantics assignment, the choice of an adequate similarity measure and data indexing. In this paper, we will discuss several approaches to the solution of these problems. In this respect, we will focus in particular on content-based image retrieval methods and their merits in comparison with the more traditional text-based approach. The main challenges include an improved extraction of image features from the data and efficient indexing of the extracted high-dimensional features. Introduction Storing large amounts of multimedia data, such as images, video or sound recordings is nowadays well feasible, as available storage capacity increases. Many multimedia databases exist currently, for example Flickr [Yahoo] or Wikimedia commons [Wikimedia Foundation] can be considered as large databases of images. This poses many new challenges, as it is important to be able to search for the interesting data amongst all the available data in database. Currently most commonly used way is searching using only metadata (Text-based image retrieval) – every piece of multimedia data in the database has associated metadata, like name, description or annotation, often added manually, when adding the data to the database. The information is then used to search the database and the multimedia data themselves are only referenced by the metadata. For example, if you want to obtain an image of Prague Castle using text-based search, you enter "Prague Castle" in the search box and then browse through results. Figure 1. Panorama of Northern part of Blansko, Czech Republic [Wikimedia commons, 2006] This approach has several disadvantages. First, the metadata are added by humans, usually by many people that have created the original data. This is prone to errors and omissions. More importantly, different people may find different parts of the data interesting. For example in Figure 1, most people will find the city as an interesting part of the picture. Others may find the clouds, a small village in the 171 WDS'08 Proceedings of Contributed Papers, Part I, 171–176, 2008. ISBN 978-80-7378-065-4 © MATFYZPRESS