In multi-modality image fusion, source image decomposition, such as multi-scale transform (MST), is a necessary step and also widely used. However, when MST is directly used to decompose source images into high-and low-frequency components, the corresponding decomposed components are not precise enough for the following infrared-visible fusion operations. This paper proposes a non-subsampled contourlet transform (NSCT) based decomposition method for image fusion, by which source images are decomposed to obtain corresponding high-and low-frequency sub-bands. Unlike MST, the obtained high-frequency sub-bands have different decomposition layers, and each layer contains different information. In order to obtain a more informative fused high-frequency component, maximum absolute value and pulse coupled neural network (PCNN) fusion rules are applied to different sub-bands of high-frequency components. Activity measures, such as phase congruency (PC), local measure of sharpness change (LSCM), and local signal strength (LSS), are designed to enhance the detailed features of fused low-frequency components. The fused high-and low-frequency components are integrated to form a fused image. The experiment results show that the fused images obtained by the proposed method achieve good performance in clarity, contrast, and image information entropy.Entropy 2019, 21, 1135 2 of 16 for infrared-visible image fusion, have been widely applied to the target recognition in different environments, such as smart city, battlefield, remote sensing, and so on [2,3].In recent years, transform domain based methods have become the mainstream in infrared-visible image fusion, which include pyramid, wavelet transform, multi-scale geometric transform, sparse representation [4,5], and so on. Pyramid, wavelet transform, and multi-scale geometric transform can be categorized as MST-based methods. MST-based methods have three main steps. First, MST is employed to decompose each source image into high-frequency sub-bands at different scales and directions as well as one low-frequency sub-band. Then, the obtained high-and low-frequency sub-bands are fused separately following different fusion rules. Finally, the fused image is obtained by performing the inverse MST on both fused high-and low-frequency sub-bands. Double-tree complex wavelet transform as a kind of wavelet transform can only capture a limited amount of edge information, but cannot correctly and effectively represent the discontinuity of lines and curves [6]. As a true two-dimensional (2D) multi-scale geometric analysis method, contourlet transform (CT) possesses localization, multi-resolution, multi-scale, multi-direction, and anisotropy.As a shift-invariant version of CT, NSCT performs well in transform domain, and has been widely used in image fusion. NSCT has multi-scale and multi-direction features, which can solve the limitations of traditional wavelet methods in the representation of image curves and edges [7]. Compared with traditional MST-based image fusion methods, NSCT has shif...