“…The reason is that multiscale method incorporates image details at different resolutions, and contrast is relevant to the viewing distance. The contrast combined with multiscale representation were widely used in the literature of image enhancement [32][33][34]38,39] and image fusion [35][36][37], where the multiscale representation was implemented by pyramid decomposition [34], [36], wavelet decompositions [32,34,36], scale-space approach [33] and homomorphic transform [39]. In view of efficiency, the multiscale representation in the proposed model, however, was operated by iteratively applying a low-pass filter and downsampling the filtered image by a factor of 2, as did in MS-SSIM [4].…”