The image of a cat:













The spectra of the image obtained by DFT, DCT and WHT, respectively:



















The low-pass filtered images (by DFT and DCT, respectively). Note the ringing effect caused by the ideal filter.

















The low-pass filtered images (by DFT, DCT and WHT, respectively). The ringing effect no longer exists due to the Butterworth filter.

















These are high-pass filtered images.