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Main | Mathematical Models in Computer Vision: The Handbook, Springer (2005) | ||
Editors Preface Contents Contributors References Sample Chapter Order |
ABSTRACT: Nonlinear diffusion filtering and
wavelet shrinkage are two methods that serve the same purpose, namely
discontinuity-preserving denoising. In this chapter we give a survey on
relations between both paradigms when space-discrete or fully discrete
versions of nonlinear diffusion filters are considered. For the
case of space-discrete diffusion, we show equivalence between soft Haar
wavelet shrinkage and total variation (TV) diffusion for 2-pixel
signals. For the general case of $N$-pixel signals, this leads us to a
numerical scheme for TV diffusion with many favourable properties. Both
considerations are then extended to 2-D images, where an analytical
solution for $2\times 2$ pixel images serves as building block for a
wavelet-inspired numerical scheme for TV diffusion. When replacing
space-discrete diffusion by fully discrete one with an explicit time
discretisation, we obtain a general relation between the shrinkage
function of a shift-invariant Haar wavelet shrinkage on a single scale
and the diffusivity of a nonlinear diffusion filter. This allows to
study novel, diffusion-inspired shrinkage functions with competitive
performance, to suggest new shrinkage rules for 2-D images with better
rotation invariance, and to propose coupled shrinkage rules for colour
images where a desynchronisation of the colour channels is avoided.
Finally we present a new result which shows that one is not restricted
to shrinkage with Haar wavelets: By using wavelets with a higher number
of vanishing moments, equivalences to higher-order diffusion-like PDEs
are discovered.
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Last Update: December20th,
2004, you can mail your comments to: nikos.paragios@computer.org
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