Enhancing image retrieval for complex queries using external knowledge sources

Annotation-based image retrieval associates textual descriptions to images based on human perception. A user query, composed of keywords of choice and for retrieval, are usually matched lexically with the textual descriptions associated for stored images to extract the best matches. This paradigm will not produce appropriate desired results for complex queries if a semantic approach is not considered. This paper proposes an image retrieval framework which integrates external knowledge sources for obtaining a higher-level inference that can both handle complex queries and increase the number of relevant retrievals. The framework includes a parser where a semantic representation graph is initially generated from both image captions and query. The semantic representation of image captions is stored in the form of Resource Description Framework (RDF) triples, while the user query is translated into a SPARQL language query. For better query understanding, the external knowledge sources (ConceptNet, WordNet), are next fused together with the parser's output in a significant process named query expansion to infer combined and expanded knowledge about the terms used in the query. Also, the expansion process generates a set of expansion rules to semantically expand the user query to adapt the inferred knowledge. The expanded query is matched against the stored RDF triplets to indicate the best matched image retrievals. Retrievals are eventually ranked using a relation similarity metric to obtain a ranked list of relevant images. Experimental studies carried on two Flickr datasets show that the proposed framework outperforms related work with 40% increase in the number of relevant retrievals at almost full accuracy. The framework achieves additionally an average increase for the accuracy at givenkin the range of 50-72% for up to the tenth retrieval.