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OpenCV simplified for beginners by the use of examples. Learn OpenCV with basic implementation of different algorithms. Please visit The Fourier Transform will decompose an image into its sinus and cosines components. It will transform an image from its spatial domain to its frequency domain. Mathematically a two dimensional images Fourier transform is: Here f is the image value in its spatial domain and F in its frequency domain. The result of the transformation is complex numbers. dft Performs a forward or inverse Discrete Fourier transform of a 1D or 2D floating-point array. void DFT(InputArray src, OutputArray dst, int flags=0, int nonzeroRows=0) multiple vectors simultaneously and can be used to decrease the overhead (which is sometimes several times larger than the processing itself) to perform 3D and higher-dimensional transformations and so forth. same size as input, which is the fastest option and which is what the function does by default; however, you may wish to get a full complex array (for simpler spectrum an*lysis, and so on) - pas* the flag to enable the function to produce a full-size complex output array. size, however, if the input array has conjugate-complex symmetry (for example, it is a result of forward transformation with not, you can pas* the flag and then the function will as*ume the symmetry and produce the real output array (note that when the input is packed into a real array and inverse transformation is executed, the function treats the input as a packed complex-conjugate symmetrical array, and the output will also be a real array). handle the rest of the rows more efficiently and save some time; this technique is very useful for calculating array cross-correlation or void IDFT(InputArray src, OutputArray dst, int flags=0, int nonzeroRows=0) We know that we can represent image as a matrix, and matrix can not be elliptical. So when you want to crop a elliptical area from an image, then you have to extract the elliptical region and remove rest of the information outside the ellipse. This can be done by AND