A new image fusion algorithm, based on lattice filters and spatial frequency, to merge ERS and multispectral SPOT data is presented. First, ERS and SPOT data are decomposed into their subbands with analysis lattice filter structure. The detail subbands are decomposed into blocks, and these blocks are merged according to a predefined Spatial Frequency based rule. Finally, the fused image is obtained by synthesis lattice filter structure. © 2011 IEEE.