Table 5.

Performance indicator metrics.

SN	PEM	Expressions in mathematics
1	EN	EN = −;where p(i) is the probability of occurrence of intensity i in the image.
2	SF	SF= ,where RF = CF = where m= rows, n = columns, x(i, j) is the intensity value at ith row and jth column pixel.
3	SSIM	SSIM (x, y) = ; where is the sample mean, is the variance and is the covariance of image x and image, c1 and c2 are two constants.
4	MSE	MSE =; where FO (i, j) is a fused output and S (i, j) is a reference image.
5	MSSIM	MSSIM= |); where FO is a fused output and S is a source image, k is the number of local windows in the image.
6	RMSE	RMSE = ; where m= rows, n = columns, FO (i, j) is a fused output image and S (i, j) is a reference image.
7	PSNR	PSNR = 10*; where MAX is the maximum intensity value of an image.
8	NMI	NMI = , where FO is a fused image and S is a source image, MI is the mutual information \:MI(FO;S) = EN (FO)–EN (FO | S); where EN is an entropy.
9	VIF	VIF = ; where is the covariance of source image and output image in the bth block at the kth sub-band, is the scalar gain field.
10	FSIM	FSIM = ;SL is similarity at location x; PCm is maximum phase congruency.