Multiscale Representations for Manifold-Valued Data

We describe multiscale representations for data observed on equispaced grids and taking values in manifolds such as the sphere $S^2$, the special orthogonal group $SO(3)$, the positive definite matrices $SPD(n)$, and the Grassmann manifolds $G(n,k)$. The representations are based on the deployment of Deslauriers--Dubuc and average-interpolating pyramids "in the tangent plane" of such manifolds, using the $Exp$ and $Log$ maps of those manifolds. The representations provide "wavelet coefficients" which can be thresholded, quantized, and scaled in much the same way as traditional wavelet coefficients. Tasks such as compression, noise removal, contrast enhancement, and stochastic simulation are facilitated by this representation. The approach applies to general manifolds but is particularly suited to the manifolds we consider, i.e., Riemannian symmetric spaces, such as $S^{n-1}$, $SO(n)$, $G(n,k)$, where the $Exp$ and $Log$ maps are effectively computable. Applications to manifold-valued data sources of a geometric nature (motion, orientation, diffusion) seem particularly immediate. A software toolbox, SymmLab, can reproduce the results discussed in this paper

Refinable functions for dilation families

We consider a family of d × d matrices W e indexed by e ∈ E where (E, μ) is a probability space and some natural conditions for the family (W e ) e ∈ E are satisfied. The aim of this paper is to develop a theory of continuous, compactly supported functions $\varphi: {{\mathbb R}}^d \to {\mathbb{C}}$ which satisfy a refinement equation of the form $$\varphi (x) = \int_E \sum\limits_{\alpha \in {{\mathbb Z}}^d} a_e(\alpha)\varphi\left(W_e x - \alpha\right) d\mu(e)$$ for a family of filters $a_e : {{\mathbb Z}}^d \to {\mathbb{C}}$ also indexed by e ∈ E. One of the main results is an explicit construction of such functions for any reasonable family (W e ) e ∈ E . We apply these facts to construct scaling functions for a number of affine systems with composite dilation, most notably for shearlet system

Hermite Subdivision Schemes and Taylor Polynomials

International audienceWe propose a general study of the convergence of a Hermite subdivision scheme $\mathcal H$ of degree $d>0$ in dimension 1. This is done by linking Hermite subdivision schemes and Taylor polynomials and by associating a so-called Taylor subdivision (vector) scheme $\cal S$. The main point of investigation is a spectral condition. If the subdivision scheme of the finite differences of $\mathcal S$ is contractive, then $\mathcal S$ is $C^0$ and $\mathcal H$ is $C^d$. We apply this result to two families of Hermite subdivision schemes, the first one is interpolatory, the second one is a kind of corner cutting, both of them use Obreshkov interpolation polynomial