Thresholding algorithms in an orthonormal basis are studied to estimate noisy discrete signals degraded by a linear operator whose inverse is not bounded. For signals in a set $\Theta$, sufficient conditions are established on the basis to obtain a maximum risk with minimax rates of convergence. Deconvolutions with kernels
having a Fourier transform which vanishes at high frequencies are examples of unstable inverse problems, where a thresholding in a wavelet basis is a suboptimal estimator. A new "mirror wavelet" basis is constructed to obtain a deconvolution risk which is proved to be asymptotically equivalent to the minimax risk over bounded variation signals. This thresholding estimator is used to restore blurred satellite images.
References
[1] ABRAMOVICH, F. and SILVERMAN, B. W. (1998). Wavelet decomposition approaches to statistical inverse problems. Biometrika 85 115-129.
[2] ALVAREZ, L. and MOREL, J.-M. (1994). Formalization and computational aspects of image analysis. Acta Numer. 3 1-59.
[3] COIFMAN, R. R. and DONOHO, D. (1995). Translation invariant de-noising. Technical Report 475, Dept. Statistics, Stanford Univ.
[4] COIFMAN, R. R., MEy ER, Y. and WICKERHAUSER, M. V. (1992). Wavelet analysis and signal processing. In Wavelets and Their Applications (M. B. Ruskai, G. Bey lkin, R. Coifman et al., eds.) 153-178. Jones and Bartlett, Boston.
[5] DAUBECHIES, I. (1988). Orthonormal bases of compactly supported wavelets. Comm. Pure Appl. Math. 41 909-996.
[6] DEVORE, R. A., JAWERTH, B. and LUCIER, B. J. (1992). Image compression through wavelet transform coding. IEEE Trans. Inform. Theory 38 719-746.
[7] DONOHO, D. (1993). Unconditional bases are optimal bases for data compression and for statistical estimation. Appl. Comput. Harmon. Anal. 1 100-115.
[8] DONOHO, D. (1995). Nonlinear solution of linear inverse problems by wavelet-vaguelette decomposition. Appl. Comput. Harmon. Anal. 2 101-126.
[9] DONOHO, D. and JOHNSTONE, I. (1994). Ideal spatial adaptation via wavelet shrinkage. Biometrika 81 425-455.
[10] DONOHO, D., JOHNSTONE, I., KERKy ACHARIAN, G. and PICARD, D. (1995). Wavelet shrinkage: Asy mptopia? (with discussion). J. Roy. Statist. Soc. Ser. B 57 301-369.
[11] DONOHO, D., LIU, R. C. and MACGIBBON, K. B. (1990). Minimax risk over hy perrectangles, and implications. Ann. Statist. 18 1416-1437.
[12] DONOHO, D., MALLAT, S. and VON SACHS, R. (1996). Estimating covariances of locally stationary processes: Consistency of best basis methods. In Proc. IEEE-SP International Sy mposium on Time-Frequency and Time-Scale Analy sis 337-340. IEEE, New York.
[13] IBRAGIMOV, I. A. and KHAS'MINSKII, R. Z. (1982). Bounds for the quality of nonparametric regression estimates. Theory Probab. Appl. 27 81-94.
[14] JOHNSTONE, I. M. and SILVERMAN, B. W. (1995). Wavelet threshold estimators for data with correlated noise. Technical report, Dept. Statistics, Stanford Univ.
[15] KALIFA, J. (1999). Restauration minimax et déconvolution dans une base d'ondelettes miroirs. Ph. D. thesis, Ecole Poly technique.
[16] KALIFA, J. and MALLAT, S. (1999). Minimax restoration and deconvolution. Bayesian Inference in Wavelet Based Models. Lecture Notes in Statist. 141 115-138. Springer, Berlin.
[17] KALIFA, J., MALLAT, S. and ROUGÉ, B. (2003). Deconvolution by thresholding in mirror wavelet. IEEE Trans. Image Process. To appear.
[18] KOLACZy K, E. (1996). A wavelet shrinkage approach to tomographic image reconstruction. J. Amer. Statist. Assoc. 91 1079-1090.
[19] LEE, N.-Y. and LUCIER, B. J. (2001). Wavelet methods for inverting the Radon transform with noisy data. IEEE Trans. Image Process. 10 79-94.
[20] MALLAT, S. (2000). A Wavelet Tour of Signal Processing, 2nd ed. Academic Press, New York.
[21] MEy ER, Y. (1992). Wavelets and Operators. Cambridge Univ. Press.
[22] O'SULLIVAN, F. (1986). A statistical perspective on ill-posed inverse problems. Statist. Sci. 1 502-527.
[23] PENSKY, M. and VIDAKOVIC, B. (1999). Adaptive wavelet estimator for nonparametric density deconvolution. Ann. Statist. 27 2033-2053.
[24] ROUGÉ, B. (1993). Remarks about space-frequency and space-scale representations to clean and restore noisy images in satellite frameworks. In Progress in Wavelet Analy sis and Applications (Y. Meyer and S. Roques, eds.) 433-442. Frontières, Paris.
[25] ROUGÉ, B. (1997). Théorie de la chaine image optique et restauration. Ph. D. thesis, Univ. Paris-Dauphine.
[26] TSy BAKOV, A. B. and CAVALIER, L. (2001). Sharp adaptation for inverse problems with random noise. Probab. Theory Related Fields 123 323-354.
[27] WANG, Y. (1997). Minimax estimation via wavelets for indirect long-memory data. J. Statist. Plann. Inference 64 45-55.
[28] WICKERHAUSER, M. V. (1994). Adapted Wavelet Analy sis from Theory to Software. Peters, Natick, MA.
[29] ZIEMER, W. P. (1989). Weakly Differentiable Functions: Sobolev Spaces and Functions of Bounded Variation. Springer, Berlin.