Based on the multi-resolution wavelet analysis, three thresholding methods: soft-thresholding, hard thresholding, and the high-pass thresholding are studied in this paper. The proposed high-pass thresholding method is a new effective algorithm for suppressing speckle in synthetic aperture radar (SAR) images. The method suppresses speckle by applying a high-pass function to process the amplitude of each detail image of the wavelet subspaces. The threshold of the function is novel and is computed by the maximal amplitude, the decomposition level p-th of the detail image. Application to SAR images has shown that the wavelet domain filtering methods promise a good tradeoff between speckle removal and edge protection. And the new high-pass thresholding method is more satisfactory in both speckle suppression and detail information preservation, and hence may provide better detection performance for SAR based recognition.
"Wavelet-domain suppression of speckle in single-look SAR images", Proc. SPIE 4552, Image Matching and Analysis, (20 September 2001); doi: 10.1117/12.441515; https://doi.org/10.1117/12.441515