This work compares two general and formal solutions to the problem of fusion of multispectral images with high-resolution panchromatic observations. The former exploits the generalized Laplacian pyramid, which is an oversampled structure obtained by subtracting from an image its lowpass version. The latter relies on an undecimated wavelet decomposition, which is another bandpass representation achieved from a conventional octave wavelet transform by omitting all decimators and upsampling the filterbank. Both the methods selectively perform spatial-frequencies spectrum substitution from an image to another. The major novelty is that both the decompositions are not critically-sampled, thus avoiding possible impairments in the fused images, due to missing cancellation of aliasing terms. Quantitative results are presented and discussed on SPOT data (XS+P).