Codebook optimization using word activation forces for scene categorization

Visual codebook based quantization of robust appearance descriptors extracted from local image patches is an effective means of capturing image statistics for texture analysis and natural scene classification. In this paper, based on the newly proposed statistics of word activation forces (WAFs), we optimize the codebook. Currently, codebooks are typically created from a set of training images using a clustering algorithm. However, these codebooks are often functionally limited due to redundancy. We show that WAFs can remove the redundancy efficiently. In the experiment, the proposed method achieved the state-of-the-art performance on the Caltech-101, fifteen natural scene categories and VOC2007 databases. The optimization method also offers insights into the success of several recently proposed images classification approaches, including vector quantization (VQ) coding in the Spatial Pyramid Matching (SPM), sparse coding SPM (ScSPM), and Locality-constrained Linear Coding (LLC).