Image Enhancement
High-frequency emphasis filters may be used to achieve contrast
enhancement or sharpening.
(Note: High-frequency emphasis filter » Highpass filter + a constant.)
Directional "sector" filters may be designed to enhance, extract, or remove features at preferred orientations, by virtue of the rotational property of the Fourier transform.
While space domain operations affect local pixel values and features, frequency domain operations affect the image globally.
While normally we are concerned with the magnitude spectrum t a large extent, the phase spectrum is also important.
Phase has been shown to be associated with edge information to a larger extent than the magnitude of the frequency components.