A hybrid de-speckling filter driven by a novel homogeneity feature

Speckle reduction in synthetic aperture radar (SAR) images is a key point to facilitate applicative tasks. A filter aimed at de-speckling should energetically smooth homogeneous regions, while preserving point targets, edges, and linear features. A trade-off, however, should be arranged on textured areas. Filtering capabilities depend on local image characteristics, and generally no filter outperforms the others in every situation. In this work, a set of adaptive filters is considered with attention to those oriented towards a multiresolution approach. Images are individually processed by each filter, and the output at each pixel position is obtained by choosing one out of the channels. The selection is based on thresholding a pixel feature based on a novel definition of inhomogeneity for SAR images and capable of describing both textured areas and ideal scatterers. Results on true SAR images show that also an empirical choice of thresholds is non-critical: the proposed scheme outperforms each filter individually, at least according to visual criteria.