Simultaneous Speckle Reduction and Contrast Enhancement for Ultrasound Images: Wavelet versus Laplacian Pyramid

Speckle can be described as random multiplicative noise. It hampers the perception and extraction of fine details in the image. Speckle reduction techniques are applied to ultrasound images in order to reduce the noise level and improve the visual quality for better diagnoses. It is also used as preliminary treatment before segmentation and classification. Several methods have been proposed for speckle reduction in ultrasound images. Multiscale contrast enhancement was proven to be very efficient for X-ray images. A recent study by Dippel et al. doing a comparison, contrast enhancement of radiographs (X-ray and mammography), between Laplacian pyramid and wavelet one proves that Laplacian pyramid method gives better result than wavelet one, the filtering aspect was not taken into account. In ultrasound images a strong contrast variation exists which is different from X-ray and mammography. In this paper wavelet pyramid with simultaneous speckle reduction and contrast enhancement was applied for the first time on ultrasound images with area of interest and compared to Laplacian enhancement pyramid. The optimum choice of wavelet bases for ultrasound images is investigated in this study. In order to realize a fair comparison the same non linear modification in both multi-scale schemes is used. The comparison proves that wavelet pyramid gives much better result than Laplacian one for simultaneous speckle reduction and contrast enhancement of ultrasound images