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Local regularization for n-dimensional integral equations with applications to image processing

Changjun Cui1, Patricia K Lamm2 and Thomas L Scofield3

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We examine the method of local regularization for the solution of linear first-kind integral equations on {\bb R}^n . We provide a theoretical analysis of the method and prove that the regularized solutions converge to the true solution as the level of error in perturbed data goes to zero. We also develop an iterative numerical algorithm based on this theory and describe its implementation. Our testing with a number of examples shows that local regularization tends to perform better than a classical method we call Tik-CG (a method based on a conjugate gradient algorithm with stopping criteria applied to standard Tikhonov regularization) when performance is measured in terms of relative error in solutions and/or in perceived sharpness of images. Unfortunately, this improvement can come at a cost as testing shows that the local regularization algorithm tends to be slower than the Tik-CG approach when applied to 2D images. As we illustrate with our numerical results, however, a compromise can be found by using the converged Tik-CG image as the starting value for the iterative local regularization method.


PACS

02.30.Zz Inverse problems

02.60.Gf Algorithms for functional approximation

42.30.Wb Image reconstruction; tomography

02.60.Nm Integral and integrodifferential equations

MSC

94A08 Image processing (compression, reconstruction, etc.) (See also 68U10)

45D05 Volterra integral equations (See also 34A12)

47A52 Ill-posed problems, regularization

65F22 Ill-posedness, regularization

65R32 Inverse problems

Subjects

Mathematical physics

Computational physics

Optics, quantum optics and lasers

Dates

Issue 4 (August 2007)

Received 27 February 2007, in final form 31 May 2007

Published 6 July 2007



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