Mining Multilevel Image Semantics via Hierarchical Classification

In this paper, we have proposed a novel framework for mining multilevel image semantics via hierarchical classification. To bridge the semantic gap more successfully, salient objects are used to characterize the intermediate image semantics effectively. The salient objects are defined as the connected image regions that capture the dominant visual properties linked to the corresponding physical objects in an image. To achieve a more reliable and tractable concept learning in high-dimensional feature space, a novel algorithm called <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">product of mixture-experts</i> (PoM) is proposed to reduce the size of training images and speed up concept learning. A novel hierarchical concept learning algorithm is proposed by incorporating concept ontology and multitask learning to enhance the discrimination power of the concept models and reduce the computational complexity for learning the concept models for large amount of image concepts, which may have huge intra-concept variations and inter-concept similarities on their visual properties. A hyperbolic image visualization algorithm has been developed for allowing users to specify their queries easily and assess the query results interactively. Our experiments on large-scale image collections have also obtained very positive results.