Matrix rounding under the Lp-discrepancy measure and its application to digital halftoning

  • Authors:
  • Tetsuo Asano;Naoki Katoh;Koji Obokata;Takeshi Tokuyama

  • Affiliations:
  • Japan Advanced Institute of Science and Technology, Tatsunokuchi, Japan;Kyoto University, Kyoto, Japan;Japan Advanced Institute of Science and Technology, Tatsunokuchi, Japan;Tohoku University, Sendai, Japan

  • Venue:
  • SODA '02 Proceedings of the thirteenth annual ACM-SIAM symposium on Discrete algorithms
  • Year:
  • 2002

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Abstract

In this paper we study the problem of rounding a real-valued matrix into an integer-valued matrix to minimize an Lp-discrepancy measure between them. To define the Lp-discrepancy measure, we introduce a family F of regions (rigid submatrices) of the matrix, and consider a hypergraph defined by the family. The difficulty of the problem depends on the choice of the region family F. We first investigate the rounding problem by using integer programming problems with convex piecewise-linear objective functions, and give some nontrivial upper bounds for the Lp-discrepancy. Then, we propose "laminar family" for constructing a practical and well-solvable class of F. Indeed, we show that the problem is solvable in polynomial time if F is a union of two laminar families. Finally, we show that the matrix rounding using L1-discrepancy for a union of two laminar families is suitable for developing a high-quality digital-halftoning software.