Fractional wavelets, derivatives, and Besov spaces
Journal
Proceedings of SPIE - The International Society for Optical Engineering
Journal Volume
5207
Journal Issue
1
Date Issued
2003-01-01
Author(s)
Unser, Michael
Abstract
We show that a multi-dimensional scaling function of order γ (possibly fractional) can always be represented as the convolution of a polyharmonic B-spline of order γ and a distribution with a bounded Fourier transform which has neither order nor smoothness. The presence of the B-spline convolution factor explains all key wavelet properties: order of approximation, reproduction of polynomials, vanishing moments, multi-scale differentiation property, and smoothness of the basis functions. The B-spline factorization also gives new insights on the stability of wavelet bases with respect to differentiation. Specifically, we show that there is a direct correspondence between the process of moving a B-spline factor from one side to another in a pair of biorthogonal scaling functions and the exchange of fractional integrals/derivatives on their wavelet counterparts. This result yields two "eigen-relations" for fractional differential operators that map biorthogonal wavelet bases into other stable wavelet bases. This formulation provides a better understanding as to why the Sobolev/Besov norm of a signal can be measured from the lp -norm of its rescaled wavelet coefficients. Indeed, the key condition for a wavelet basis to be an unconditional basis of the Besov space Bqs(L p(Rd)) is that the s-order derivative of the wavelet be in Lp.
Subjects
Besov spaces | Fractional derivatives | Multi-dimensional wavelets | Order of approximation | Polyharmonic splines | Wavelet smoothness
Type
conference paper