Ultrasonic speckle reduction based on soft thresholding in quaternion wavelet domain

Speckle reduction is a tough task for ultrasound images processing resulting to their low resolution and contrast. Quaternion wavelet (QW) is of some superior properties compared to discrete wavelets, such as nearly shift-invariant wavelet coefficients and phase based texture presentation. So we aim to exploit the excellent performances of speckle reduction in quaternion wavelet domain (QWD) based on the soft thresholding method. The algorithm uses quaternion wavelet transform (QWT) to decompose the ultrasound images, and then apply five typical criterions to set threshold for QW coefficients. Furthermore, we conduct two experiments on a synthetic speckle image and a real ultrasound image. The performance of the proposed speckle reduction algorithm, using QWT with soft thresholding, is demonstrated superior to that using wavelet transform (WT) and classical algorithms.