A lapped transform domain enhanced lee filter with edge detection for speckle noise reduction in SAR images

Abstract

This paper describes a method which uses Lapped orthogonal transform (LOT) domain adaptive enhanced Lee filter for despeckling SAR images. Since LOT is block transform, the transform coefficients are first remapped into octave type form and then the enhanced Lee filtering is applied to subband LOT coefficients. The motivation of using Lapped transform lies in its ability to preserve oscillatory type of features present in the images like textures. For more edge preservation during despeckling process, the modified ratio of averages (MROA) edge detector is applied to the approximation subband to obtain edge information which is then employed in the proposed framework to obtain edge information in other subbands. Based on this edge information we classify the edge and non edge coefficients in all oriented subbands at various decomposition levels. Experiments using true SAR images show that the LOT domain enhanced Lee filter in proposed edge preserving framework smoothes the speckle very well in homogeneous regions while preserving more edges and texture information. The proposed despeckling filter shows significant improvement over enhanced Lee filtering in spatial and wavelet domain and also outperforms one recent undecimated wavelet domain method.