Random Fourier approximations for skewed multiplicative histogram kernels

  • Authors:
  • Fuxin Li;Catalin Ionescu;Cristian Sminchisescu

  • Affiliations:
  • Institute für Numerische Simulation, University of Bonn;Institute für Numerische Simulation, University of Bonn;Institute für Numerische Simulation, University of Bonn

  • Venue:
  • Proceedings of the 32nd DAGM conference on Pattern recognition
  • Year:
  • 2010

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Abstract

Approximations based on random Fourier features have recently emerged as an efficient and elegant methodology for designing large-scale kernel machines [4]. By expressing the kernel as a Fourier expansion, features are generated based on a finite set of random basis projections with inner products that are Monte Carlo approximations to the original kernel. However, the original Fourier features are only applicable to translation-invariant kernels and are not suitable for histograms that are always non-negative. This paper extends the concept of translation-invariance and the random Fourier feature methodology to arbitrary, locally compact Abelian groups. Based on empirical observations drawn from the exponentiated χ2 kernel, the state-of-the-art for histogram descriptors, we propose a new group called the skewed-multiplicative group and design translation-invariant kernels on it. Experiments show that the proposed kernels outperform other kernels that can be similarly approximated. In a semantic segmentation experiment on the PASCAL VOC 2009 dataset, the approximation allows us to train large-scale learning machines more than two orders of magnitude faster than previous nonlinear SVMs.