Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài:Research Article Smooth Adaptation by Sigmoid Shrinkage | Hindawi Publishing Corporation EURASIP Journal on Image and Video Processing Volume 2009 Article ID 532312 16 pages doi 2009 532312 Research Article Smooth Adaptation by Sigmoid Shrinkage Abdourrahmane M. Atto EURASIP Member Dominique Pastor EURASIP Member and Gregoire Mercier Lab-STICC CNRS UMR3192 TELECOM Bretagne Technopôle Brest-Iroise CS 83818 29238 Brest Cedex 3 France Correspondence should be addressed to Abdourrahmane M. Atto Received 27 March 2009 Accepted 6 August 2009 Recommended by James Fowler This paper addresses the properties of a subclass of sigmoid-based shrinkage functions the non zeroforcing smooth sigmoid-based shrinkage functions or SigShrink functions. It provides a SURE optimization for the parameters of the SigShrink functions. The optimization is performed on an unbiased estimation risk obtained by using the functions of this subclass. The SURE SigShrink performance measurements are compared to those of the SURELET SURE linear expansion of thresholds parameterization. It is shown that the SURE SigShrink performs well in comparison to the SURELET parameterization. The relevance of SigShrink is the physical meaning and the flexibility of its parameters. The SigShrink functions performweak attenuation of data with large amplitudes and stronger attenuation of data with small amplitudes the shrinkage process introducing little variability among data with close amplitudes. In the wavelet domain SigShrink is particularly suitable for reducing noise without impacting significantly the signal to recover. A remarkable property for this class of sigmoid-based functions is the invertibility of its elements. This propertymakes it possible to smoothly tune contrast enhancement reduction . Copyright 2009 Abdourrahmane M. Atto et al. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and reproduction in any medium provided the original .