Showing papers by "Gemma Piella published in 2001"

An adaptive update lifting scheme with perfect reconstruction

Abstract: The lifting scheme provides a general and flexible tool for the construction of wavelet decompositions and perfect reconstruction filter banks. We propose an adaptive version of this scheme which has the intriguing property that it allows perfect reconstruction without any overhead cost. We restrict ourselves to the update lifting step which affects the approximation signal only. The update lifting filter is assumed to depend pointwise on the norm of the associated gradient vector, in such a way that a large gradient induces a weak update filter. Thus, sharp transitions in a signal (eg, edges in an image) will not be smoothed to the same extent as regions which are more homogeneous.

Adaptive lifting schemes with perfect reconstruction

Abstract: textIn this paper, we propose a framework for constructing adaptive wavelet decompositions using the lifting scheme A major requirement is that perfect reconstruction is possible without any overhead cost In this paper we restrict ourselves to the update lifting stage It is assumed that the update filter utilises local gradient information to adapt itself to the signal in the sense that smaller gradients `evoke' stronger update filters As a result, sharp transitions in a signal will not be smoothed to the same extent as regions which are more homogeneous The approach taken in this paper differs from other adaptive schemes found in the literature in the sense that that no bookkeeping is required in order to have perfect reconstruction