Image fusion attempts to combine complementary information from multiple images of the same scene, so that the resultant image is more suitable for human visual pereption and computer-processing tasks such as segmentation, feature extraction and object recongnition. This paper presents an approach that fuses images with diverse focuses by first decomposing the source images into blocks and the combing them by the use of spatial frequency. The algorithm is computataionally simple and can be implemented in real-time applications. Experimental results show that the propsed method is superior to wavelet transform based methods in both objective and visual evaluations.