How do I actually apply the convolution theorem? I have my fourier transformed image matrix, and a Fourier transformed kernel, but how do I actually multiply these together to achieve the intended effect of the kernel? Is it through matrix multiplication or some other method? The dimensions are different though.


1 Answer 1


You have many great code examples at our community:

The last 2 have a specific code to do image filtering in frequency domain.

  • $\begingroup$ Thank you. From reading those posts, I understand that you have to pad the two matrices with 0s, and then element multiplying them. I am doing this manually instead of with code, as I do not have any coding knowledge, so am I understanding it right? $\endgroup$
    – botman
    Commented Sep 10, 2021 at 13:24
  • $\begingroup$ Indeed. You need to pad them both to the same size according to your needs. $\endgroup$
    – Royi
    Commented Sep 10, 2021 at 17:05
  • $\begingroup$ @botman, Anything missing in my answer? Could you tell me what's missing in order to accept it? $\endgroup$
    – Royi
    Commented Mar 25, 2023 at 12:04

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