Image regularization by nonnegatively constrained Conjugate Gradient

In the image reconstruction context the nonnegativity of the computed solution is often required. Conjugate Gradient (CG), used as a reliable regularization tool, may give solutions with negative entries, particularly when large nearly zero plateaus are present. The active constraints set, detected...

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Bibliographic Details
Published in:Applied mathematics and computation 2018-06, Vol.327, p.35-45
Main Authors: Favati, P., Lotti, G., Menchi, O., Romani, F.
Format: Article
Language:English
Subjects:
Conjugate Gradient
Image reconstruction
Nonnegativity constraints
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Summary:In the image reconstruction context the nonnegativity of the computed solution is often required. Conjugate Gradient (CG), used as a reliable regularization tool, may give solutions with negative entries, particularly when large nearly zero plateaus are present. The active constraints set, detected by projection onto the nonnegative orthant, turns out to be largely incomplete leading to poor effects on the accuracy of the reconstructed image. In this paper an inner-outer method based on CG is proposed to compute nonnegative reconstructed images with a strategy which enlarges subsequently the active constraints set. This method appears to be especially suitable for the reconstruction of images having large nearly zero backgrounds. The numerical experimentation validates the effectiveness of the proposed method when compared to other strategies for nonnegative reconstruction.
ISSN:0096-3003
1873-5649
DOI:10.1016/j.amc.2018.01.011