One of the most common digital-signal-processing techniques is the discrete Fourier transform (DFT), which breaks a signal into its component frequencies and can be represented as a matrix.
Each of its pixels is sensitive to specific incident angles and supplies a component of the mathematical operation called the Fourier Transform to produce an image about 20 pixels across.
Fast Fourier transform (FFT) is the main algorithm for harmonic analysis in electric power system, but when there is the decaying DC component in input signal, FFT algorithm will have higher error.