Theoretical CMB power spectrum along with the reconstructed power spectra, using the DCT and WT dictionaries. The panels show the reconstructions for different fractions of the coefficients. The inner plots show the differences between the actual and the reconstructed power spectra. Both dictionaries suffer from boundary effects, but this is more severe for DCT because the corresponding atoms are not compactly supported. The power spectrum that is decomposed onto the two dictionaries is in the form ℓ(ℓ + 1)C[ℓ] /2π.