Noise reduction in ultrasound images using wavelet and spatial filtering techniques

Image de-noising is very crucial task before proceeding with image processing task like segmentation, texture analysis and feature extraction. The de-noising of ultrasound images is important because in order to get good result of diagnosis, the area of interest in digital medical images must be sharp, clear and free from noise. An ultrasound image can be corrupted with noise during acquisition, transmission, storage and the retrieval process. Noise which occurs in ultrasound images can be classified as, salt and pepper noise, additive white Gaussian noise (AWGN), speckle noise. The filter is used to remove noise so that the area of region needed is clearer. This paper will categorise the linear and non-linear filters based on spatial domain and wavelet domain. The filtering procedure in spatial filtering includes direct manipulation of pixels. Wavelet domain comes under non-data adaptive transform of transform domain. The future trends in the area of de-noising will also be discussed.