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The evaluation of Shannon\u2032s entropy is based on Parzen windowing method (Mangin, 2000) with the spline\u2010based shading model. This allows us to express the derivatives of the entropy criterion analytically, which enables efficient use of gradient\u2010based optimization algorithms. Seven different gradient\u2010 and nongradient\u2010based optimization algorithms were initially tested on a set of 40 simulated retinal images, generated by a model of the respective image acquisition system. Among the tested optimizers, the gradient\u2010based optimizer with varying step has shown to have the fastest convergence while providing the best precision. The final algorithm proved to be able of suppressing approximately 70% of the artificially introduced non\u2010homogenous illumination. To assess the practical utility of the method, it was qualitatively tested on a set of 336 real retinal images; it proved the ability of eliminating the illumination inhomogeneity substantially in most of cases. The application field of this method is especially in preprocessing of retinal images, as preparation for reliable segmentation or registration.<\/jats:p>","DOI":"10.1155\/2010\/780262","type":"journal-article","created":{"date-parts":[[2010,7,5]],"date-time":"2010-07-05T06:31:41Z","timestamp":1278311501000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":15,"title":["Retrospective Illumination Correction of Retinal Images"],"prefix":"10.1155","volume":"2010","author":[{"given":"Libor","family":"Kubecka","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jiri","family":"Jan","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Radim","family":"Kolar","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2010,7,4]]},"reference":[{"key":"e_1_2_6_1_2","doi-asserted-by":"crossref","unstructured":"KubeckaL.andJanJ. 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