Theoretical Foundations for Discrete Forward-and-Backward Diffusion Filtering

  • Authors:
  • Martin Welk;Guy Gilboa;Joachim Weickert

  • Affiliations:
  • Mathematical Image Analysis Group Faculty of Mathematics and Computer Science, Saarland University, Saarbrücken, Germany 66041;3DV Systems, Yokneam, Israel 20692;Mathematical Image Analysis Group Faculty of Mathematics and Computer Science, Saarland University, Saarbrücken, Germany 66041

  • Venue:
  • SSVM '09 Proceedings of the Second International Conference on Scale Space and Variational Methods in Computer Vision
  • Year:
  • 2009

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Abstract

Forward-and-backward (FAB) diffusion is a method for sharpening blurry images (Gilboa et al. 2002). It combines forward diffusion with a positive diffusivity and backward diffusion where negative diffusivities are used. The well-posedness properties of FAB diffusion are unknown, and it has been observed that standard discretisations can violate a maximum-minimum principle. We show that for a novel nonstandard space discretisation which pays specific attention to image extrema, one can apply a modification of the space-discrete well-posedness and scale-space framework of Weickert (1998). This allows to establish well-posedness and a maximum-minimum principle for the resulting dynamical system. In the fully discrete 1-D case with an explicit time discretisation, a maximum-minimum principle and total variation reduction are proven in spite of the fact that negative diffusivities may appear. This provides a theoretical justification for applying FAB diffusion to digital images.