Spherical soft assignment: improving image representation in content-based image retrieval

  • Authors:
  • Liefu Ai;Junqing Yu;Tao Guan

  • Affiliations:
  • School of Computer Science & Technology, Huazhong University of Science and Technology, Wuhan, China;School of Computer Science & Technology, Huazhong University of Science and Technology, Wuhan, China;School of Computer Science & Technology, Huazhong University of Science and Technology, Wuhan, China

  • Venue:
  • PCM'12 Proceedings of the 13th Pacific-Rim conference on Advances in Multimedia Information Processing
  • Year:
  • 2012

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Abstract

Image representation is essential to performance of content-based image retrieval. VLAD has been proved to be superior to BOF. However, hard assignment is utilized in VLAD, which does not consider codeword uncertainty and codeword plausibility. In this paper, each cluster associated to visual word is defined as a hyper-sphere. The radius is denoted as the distance from visual word to the farthest feature point. Spherical soft assignment is proposed to adaptively assign a local feature to close visual words according to corresponding radius. Spherical soft assignment and a descriptor-space soft assignment of state of the art are applied to VLAD. Experiments on multiple datasets demonstrate that the proposed spherical soft assignment can noticeably improve VLAD image representation in image retrieval and be superior to the descriptor-space soft assignment.