  The application of wavelet transforms to Synthetic Aperture Radar (SAR)
imagery has improved despeckling performance. To deduce the problem of
filtering the multiplicative noise to the case of an additive noise, the
wavelet decomposition is performed on the logarithm of the image gray levels.
The detail coefficients produced by the bidimensional discrete wavelet
transform (DWT-2D) needs to be thresholded to extract out the speckle in
highest subbands. An initial threshold value is estimated according to the
noise variance. In this paper, an additional fuzzy thresholding approach for
automatic determination of the rate threshold level around the traditional
wavelet noise thresholding (initial threshold) is applied, and used for the
soft or hard-threshold performed on all the high frequency subimages. The
filtered logarithmic image is then obtained by reconstruction from the
thresholded coefficients. This process is applied a single time, and
exclusively to the first level of decomposition. The exponential function of
this reconstructed image gives the final filtered image. Experimental results
on test images have demonstrated the effectiveness of this method compared to
the most of methods in use at the moment.
