Fourier theory is pretty complicated mathematically. But there are some beautifully simple holistic concepts behind Fourier theory which are relatively easy to explain intuitively. There are other sites on the web that can give you the mathematical formulation of the Fourier transform. I will present only the basic intuitive insights here, as applied to spatial imagery.
M. Porter. (2022)cite arxiv:2201.07794Comment: working paper (associated with my data-ethics lecture at the 2021 AMS Short Course on Mathematical and Computational Methods for Complex Social Systems); not yet refereed; private comments and suggestions are appreciated.
J. Berner, P. Grohs, G. Kutyniok, und P. Petersen. (2021)cite arxiv:2105.04026Comment: This review paper will appear as a book chapter in the book "Theory of Deep Learning" by Cambridge University Press.