To find the visually salient subregions of an image, we need to look at its frequency spectrum. So far we have treated all our images and video frames in the spatial domain, that is, by analyzing the pixels or studying how the image intensity changes in different subregions of the image. However, the images can also be represented in the frequency domain, that is, by analyzing the pixel frequencies or studying how often and with what periodicity the pixels show up in the image.
An image can be transformed from the space domain into the frequency domain by applying the Fourier transform. In the frequency domain, we no longer think in terms of image coordinates (x,y). Instead, we aim to find the spectrum of an ...
