Abstract :
It is well-known that curvelets provide optimal approximations for so-called cartoon images which are defined as piecewise C2-functions, separated by a C2 singularity curve. In this paper, we consider the more general case of piecewise Cβ-functions, separated by a Cβ singularity curve for β (1;2]. We first prove a benchmark result for the possibly achievable best N-term approximation rate for this more general signal model. Then we introduce what we call α-curvelets, which are systems that interpolate between wavelet systems on the one hand (α = 1) and curvelet systems on the other hand (α= 1/2). Our main result states that those frames achieve this optimal rate for α = 1/β, up to log-factors.