A modified sigma filter for noise reduction in images

Noise reduction is a very important processing step in digital imaging and several different techniques were proposed in the open literature. Among them, sigma filter has been shown to be a good solution both in terms of filtering accuracy and computational complexity. However, the sigma filter does not preserve well small edges especially for high level of additive noise. In this paper, we introduce a new sigma filter for noise reduction in images. We propose here a new method that first decomposes the input image in four components that are independently processed using a standard sigma filter. The output image is reconstructed from the filtered components. Comparative results between our approach and the sigma filter, on synthetic images and also on real images obtained with a camera phone are shown.