Multi-Focus Image Fusion Based on Spatial Frequency in Discrete Cosine Transform Domain Cao, Liu ; Jin, Longxu ; Tao, Hongjiang ; Li, Guoning ; Zhuang, Zhuang ; Zhang, Yanfu Abstract Publication: IEEE Signal Processing Letters Pub Date: February 2015 DOI: 10.1109/LSP.2014.2354534 Bibcode: 2015ISPL...22..220C