C1, C2, and C3 avoid singularities when the denominators would other wise be small,where K1 and K2 are arbitrarily taken as 0.01 and 0.03,respectively,and L is the dynamic range of the image [9]. Regardless of the choice of constants, MSSIM=1 occurs only if the images are identical. Following Wang et al. [9], a Gaussian-weighted convolution window was chosen.
Eq.(4) implies that every part of the 2D field is equally important for analyzing the structure,which is a poor assumption for acoustic signals.In light of this,a weighted SSIM(WSSIM) was used