Median and related local filters for tensor-valued images

  • Authors:
  • Martin Welk;Joachim Weickert;Florian Becker;Christoph Schnörr;Christian Feddern;Bernhard Burgeth

  • Affiliations:
  • Mathematical Image Analysis Group, Faculty of Mathematics and Computer Science, Bldg. E11, Saarland University, 66041 Saarbrücken, Germany;Mathematical Image Analysis Group, Faculty of Mathematics and Computer Science, Bldg. E11, Saarland University, 66041 Saarbrücken, Germany;Computer Vision, Graphics, and Pattern Recognition Group, Faculty of Mathematics and Computer Science, University of Mannheim, 68131 Mannheim, Germany;Computer Vision, Graphics, and Pattern Recognition Group, Faculty of Mathematics and Computer Science, University of Mannheim, 68131 Mannheim, Germany;Mathematical Image Analysis Group, Faculty of Mathematics and Computer Science, Bldg. E11, Saarland University, 66041 Saarbrücken, Germany;Mathematical Image Analysis Group, Faculty of Mathematics and Computer Science, Bldg. E11, Saarland University, 66041 Saarbrücken, Germany

  • Venue:
  • Signal Processing
  • Year:
  • 2007

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Abstract

We develop a concept for the median filtering of tensor data. The main part of this concept is the definition of median for symmetric matrices. This definition is based on the minimisation of a geometrically motivated objective function which measures the sum of distances of a variable matrix to the given data matrices. This theoretically well-founded concept fits into a context of similarly defined median filters for other multivariate data. Unlike some other approaches, we do not require by definition that the median has to be one of the given data values. Nevertheless, it happens so in many cases, equipping the matrix-valued median even with root signals similar to the scalar-valued situation. Like their scalar-valued counterparts, matrix-valued median filters show excellent capabilities for structure-preserving denoising. Experiments on diffusion tensor imaging, fluid dynamics and orientation estimation data are shown to demonstrate this. The orientation estimation examples give rise to a new variant of a robust adaptive structure tensor which can be compared to existing concepts. For the efficient computation of matrix medians, we present a convex programming framework. By generalising the idea of the matrix median filters, we design a variety of other local matrix filters. These include matrix-valued mid-range filters and, more generally, M-smoothers but also weighted medians and @a-quantiles. Mid-range filters and quantiles allow also interesting cross-links to fundamental concepts of matrix morphology.