Image Classification Using Spatial Pyramid Coding and Visual Word Reweighting

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The ignorance on spatial information and semantics of visual words becomes main obstacles in the bag-of-visual-words (BoW) method for image classification. To address the obstacles, we present an improved BoW representation using spatial pyramid coding (SPC) and visual word reweighting. In SPC procedure, we adopt the sparse coding technique to encode visual features with the spatial constraint. Visual features from the same spatial sub-region of images are collected to generate the visual vocabulary. Additionally, a relaxed but simple solution for semantic embedding into visual words is proposed. We relax the semantic embedding from ideal semantic correspondence to naive semantic purity of visual words, and reweight each visual word according to its semantic purity. Higher weights are given to semantically distinctive visual words, and lower weights to semantically general ones. Experiments on a public dataset demonstrate the effectiveness of the proposed method.