Double density wavelet transformation for speckle reduction of SAR images

Discrete wavelet transformations (DWTs) based on over-sampled filter banks, proposed in [1], axe used for speckle reduction of SAR images. The oversampled DWT is called double density DWT (DD-DWT) and is based on a single scaling function (lowpass) and two distinct wavelet functions (highpass). The DD-DWT is useful for speckle reduction through its subband images and the speckle reduction is obtained by thresholding the subband-image coefficients of the digitized SAR images. A thresholding method using non-linear functions which are adapted for each selected subband is used in the paper. The non-linear functions are based on sigmoid functions. The denoising method shows great promise for speckle removal and hence can provide good detection performance for SAR based recognition.