Two-Dimensional Pattern Matching with Combined Scaling and Rotation

  • Authors:
  • Christian Hundt;Maciej Liśkiewicz

  • Affiliations:
  • Institut für Informatik, Universität Rostock, Germany;Institut für Theoretische Informatik, Universität zu Lübeck, Germany

  • Venue:
  • CPM '08 Proceedings of the 19th annual symposium on Combinatorial Pattern Matching
  • Year:
  • 2008

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Abstract

The problem of two-dimensional pattern matching invariant under a given class of admissible transformations $\mathcal{F}$ is to find in text Tmatches of transformed versions f(P) of the pattern P, for all fin $\mathcal{F}$. In this paper, pattern matching invariant under compositions of real scaling and rotation are investigated. We give a new discretization technique for this class of transformations and prove sharp lower and upper bounds on the number of different possibilities to transform a pattern in this way. Subsequently, we present the first efficient pattern matching algorithm invariant under compositions of scaling and rotation. The algorithm works in time O(m2n6) for patterns of size m2and texts of size n2. Our method can also be applied to the image matching problem, the well known issue in the image processing research.