“…Existing pixel-level image fusion methods generally include substitution methods, multi-resolution fusion methods and neural network based methods. The substitution methods such as intensity hue saturation [ 6 , 7 ], principal component analysis [ 8 ] based methods can be implemented with high efficiency but at the expense of reduced contrast and distortion of the spectral characteristics. Image fusion methods based on the multi-resolution decomposition techniques can preserve important image features better than substitution methods via the decomposition of images at a different scale to several components using pyramid (e.g., contrast pyramid [ 9 ] and gradient pyramid [ 10 ]), empirical mode decomposition [ 11 ] or various transforms including wavelet transform [ 12 , 13 , 14 ], curvelet transform [ 15 ], ripplet transform [ 16 ], contourlet transform [ 17 ], non-subsampled contourlet transform (NSCT) [ 18 , 19 , 20 , 21 , 22 ] and shift-invariant shearlet transform [ 23 , 24 ].…”