Despeckling Images Using a Preprocessing Filter and Discrete Wavelet Transform-Based Noise Reduction Techniques

Synthetic aperture radar (SAR) images are difficult to analyze due to speckle noise, which is a characteristic of multiplicative noise. Over the last few decades, a number of studies have been performed regarding the removal of speckle noise. However, the existing studies exhibit edge information loss when removing speckle noise. In this paper, we propose an algorithm using speckle reducing anisotropic diffusion (SRAD), soft thresholding, and a guided filter to effectively remove speckle noise from SAR images while preserving edge information. The proposed algorithm first obtains a filtered image by applying an SRAD filter to a noise image. To further remove the multiplicative noise remaining in the filtered image, a logarithmic transformation is applied to convert it into additive noise. The filtering image was decomposed into multiresolution images using discrete wavelet transform (DWT). Soft thresholding and a guided filter were used for each of the high-frequency subimages and the low-frequency subimage. Then, an inverse DWT and an exponential transform are applied to the denoised image. The experimental results indicate that the proposed algorithm shows better performance than the conventional filtering method in terms of both objective and subjective performances.