In this paper, we propose a pixel level image fusion algorithm for merging Landsat thematic mapper (TM) images and SPOT panchromatic images. The two source images are first decomposed using the discrete wavelet frame transform (DWFT), which is both aliasing free and translation invariant. Wavelet coefficients from TM’s approximation subband and SPOT’s detail subbands are then combined together, and the fused image is reconstructed by performing the inverse DWFT. Experimental results show that the proposed approach outperforms methods based on the intensity-hue-saturation transform, principal component analysis and discrete wavelet transform in preserving spectral and spatial information, especially in situations where the source images are not perfectly registered.