Computing rank-convolutions with a mask

  • Authors:
  • László Babai;Pedro F. Felzenszwalb

  • Affiliations:
  • University of Chicago, Chicago, IL;University of Chicago, Chicago, IL

  • Venue:
  • ACM Transactions on Algorithms (TALG)
  • Year:
  • 2009

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Abstract

Rank-convolutions have important applications in a variety of areas such as signal processing and computer vision. We define a mask as a function taking only values zero and infinity. Rank-convolutions with masks are of special interest to image processing. We show how to compute the rank-k convolution of a function over an interval of length n with an arbitrary mask of length m in O(n&sqrt;m log m) time. The result generalizes to the d-dimensional case. Previously no algorithm performing significantly better than the brute-force O(nm) bound was known. Our algorithm seems to perform well in practice. We describe an implementation, illustrating its application to a problem in image processing. Already on relatively small images, our experiments show a signficant speedup compared to brute force.