Speckle Noise Analysis

Abstract: speckle noise reduction is one of the most important processes to enhance the quality of Ultrasound images. Image variance is a granular speckle or noise that exists inherently in and degrades image quality . Before using the images of the Ultrasound for diagnosis, the first step is to reduce the effect of speckle noise. Most speckle reduction techniques have been studied by researchers; but there is no comprehensive method that takes into account all the constraints. Filtering is one of the standard methods used to reduce speckle noise. This paper compares different speckle reduction filters and presents the performance analysis to reduce speckle noise in ultrasound images in terms of the evaluation parameters of MSE, PSNR.

Index

This process is sometimes known as the wavelet shrinkage, as the detail coefficients shrunk towards zero. Three schemes to reduce the size of the wavelet coefficients, namely the keep-or-kill hard thresholding, soft thresholding shrinkage or kill introduced by [26] and the recent semi soft or firm threshold. The wavelet coefficient is reduced more efficiently if the coefficients are limited, that is, most of the coefficients are zero and a minority of coefficients with magnitude greater than can render the image [27]. The criteria for each scheme is described as follows. Since λ denotes the threshold limit, Xw denotes the input wavelet coefficients and wavelet coefficients denote Yt-out threshold, we define the following threshold

Bayes rule contraction
Based on Bayes' rule this is another technique to determine the threshold for image de-noising in the wavelet domain. Bays Rule allows us to write the expression in terms of the estimated probability density of the noise and the signal image. The threshold equation is given as:

The Bayesian threshold described above provides a natural extension to incorporate higher order
3. Conclusion

The results obtained for the various thresholding schemes are given in Table 2 [27]. From Table 2, it is observed that there is a significant improvement approach subband threshold in terms of parameters for assessing the quality of the image on the global threshold approach. This is because the threshold approach employs a subband adaptive threshold approach to respond to changes in the noise content of the different subbands. In contrast, the global threshold is based on a threshold of threshold Visu all subbands. The label (written in the parentheses) in Table 2 indicates the global (I) and sub-band threshold (II), Bayes (1) or Visu (2) rule of contraction and the disc (i), soft (ii) or soft (iii) semi threshold function used to generate the image. Optimal threshold scheme article of contraction and contraction function is determined by the criteria, namely increased SNR and PSNR values, minimum variance, MSE values and correlation coefficient is nearly equal to one. From Table 2, it is observed that the subband decomposition (II) with soft threshold (ii)